全文获取类型
收费全文 | 2506篇 |
免费 | 352篇 |
国内免费 | 4篇 |
出版年
2021年 | 36篇 |
2019年 | 24篇 |
2018年 | 27篇 |
2016年 | 54篇 |
2015年 | 83篇 |
2014年 | 98篇 |
2013年 | 98篇 |
2012年 | 123篇 |
2011年 | 111篇 |
2010年 | 70篇 |
2009年 | 67篇 |
2008年 | 89篇 |
2007年 | 103篇 |
2006年 | 82篇 |
2005年 | 98篇 |
2004年 | 90篇 |
2003年 | 85篇 |
2002年 | 71篇 |
2001年 | 81篇 |
2000年 | 61篇 |
1999年 | 73篇 |
1998年 | 32篇 |
1997年 | 26篇 |
1996年 | 30篇 |
1995年 | 26篇 |
1994年 | 28篇 |
1993年 | 27篇 |
1992年 | 54篇 |
1991年 | 49篇 |
1990年 | 52篇 |
1989年 | 47篇 |
1988年 | 42篇 |
1987年 | 38篇 |
1986年 | 39篇 |
1985年 | 45篇 |
1984年 | 35篇 |
1983年 | 37篇 |
1982年 | 25篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 39篇 |
1978年 | 29篇 |
1977年 | 30篇 |
1976年 | 31篇 |
1975年 | 22篇 |
1974年 | 33篇 |
1973年 | 33篇 |
1972年 | 29篇 |
1971年 | 35篇 |
1966年 | 32篇 |
排序方式: 共有2862条查询结果,搜索用时 21 毫秒
961.
Roxanne S. Beltran Nissa Kreidler Dirk H. Van Vuren Scott A. Morrison Erika S. Zavaleta Kelly Newton Bernie R. Tershy Donald A. Croll 《Restoration Ecology》2014,22(6):790-797
Understanding how insular ecosystems recover or are restructured after the eradication of an invasive species is crucial in evaluating conservation success and prioritizing island conservation efforts. Globally, herbivores have been removed from 762 islands, most with limited active restoration actions following eradication. Few studies have documented the effects of invasive herbivore removal after multiple decades of passive recovery. Here we evaluate recovery of vegetation on Santa Cruz Island, California, after the removal of feral sheep (Ovis aries) in 1984. We repeat a study conducted in 1980, and examine vegetation changes 28 years after the eradication. Before eradication, grazed areas were characterized by reduced plant cover, high exposure of bare ground, and erosion. After 28 years of passive recovery, transect data showed a 23% increase in woody overstory, whereas analysis of photographs from landscapes photographed pre‐ and post‐eradication showed a 26% increase in woody vegetation. Whole island vegetation maps similarly showed a transition from grass/bare ground (74.3% of cover) to woody plants (77.2% of cover), indicating the transition away from predominantly exotic annual grassland toward a community similar to the overstory of coastal scrubland but with an understory dominated by non‐native annual grasses. We estimate that replacement of grasses/bare ground by native woody vegetation has led to 70 and 17% increases in the stored carbon and nitrogen pools on the island, respectively. Our results demonstrate that these island ecosystems can experience significant recovery of native floral communities without intensive post‐eradication restoration, and results of recovery may take decades to be realized. 相似文献
962.
Bareket Dassa Ilya Borovok Vered Ruimy-Israeli Raphael Lamed Harry J. Flint Sylvia H. Duncan Bernard Henrissat Pedro Coutinho Mark Morrison Pascale Mosoni Carl J. Yeoman Bryan A. White Edward A. Bayer 《PloS one》2014,9(7)
Background
A complex community of microorganisms is responsible for efficient plant cell wall digestion by many herbivores, notably the ruminants. Understanding the different fibrolytic mechanisms utilized by these bacteria has been of great interest in agricultural and technological fields, reinforced more recently by current efforts to convert cellulosic biomass to biofuels.Methodology/Principal Findings
Here, we have used a bioinformatics-based approach to explore the cellulosome-related components of six genomes from two of the primary fiber-degrading bacteria in the rumen: Ruminococcus flavefaciens (strains FD-1, 007c and 17) and Ruminococcus albus (strains 7, 8 and SY3). The genomes of two of these strains are reported for the first time herein. The data reveal that the three R. flavefaciens strains encode for an elaborate reservoir of cohesin- and dockerin-containing proteins, whereas the three R. albus strains are cohesin-deficient and encode mainly dockerins and a unique family of cell-anchoring carbohydrate-binding modules (family 37).Conclusions/Significance
Our comparative genome-wide analysis pinpoints rare and novel strain-specific protein architectures and provides an exhaustive profile of their numerous lignocellulose-degrading enzymes. This work provides blueprints of the divergent cellulolytic systems in these two prominent fibrolytic rumen bacterial species, each of which reflects a distinct mechanistic model for efficient degradation of cellulosic biomass. 相似文献963.
Background
Small trials with short term follow up suggest pharmacists’ interventions targeted at healthcare professionals can improve prescribing. In comparison with clinical guidance, contemporary statin prescribing is sub-optimal and achievement of cholesterol targets falls short of accepted standards, for patients with atherosclerotic vascular disease who are at highest absolute risk and who stand to obtain greatest benefit. We hypothesised that a pharmacist-led complex intervention delivered to doctors and nurses in primary care, would improve statin prescribing and achievement of cholesterol targets for incident and prevalent patients with vascular disease, beyond one year.Methods
We allocated general practices to a 12-month Statin Outreach Support (SOS) intervention or usual care. SOS was delivered by one of 11 pharmacists who had received additional training. SOS comprised academic detailing and practical support to identify patients with vascular disease who were not prescribed a statin at optimal dose or did not have cholesterol at target, followed by individualised recommendations for changes to management. The primary outcome was the proportion of patients achieving cholesterol targets. Secondary outcomes were: the proportion of patients prescribed simvastatin 40 mg with target cholesterol achieved; cholesterol levels; prescribing of simvastatin 40 mg; prescribing of any statin and the proportion of patients with cholesterol tested. Outcomes were assessed after an average of 1.7 years (range 1.4–2.2 years), and practice level simvastatin 40 mg prescribing was assessed after 10 years.Findings
We randomised 31 practices (72 General Practitioners (GPs), 40 nurses). Prior to randomisation a subset of eligible patients were identified to characterise practices; 40% had cholesterol levels below the target threshold. Improvements in data collection procedures allowed identification of all eligible patients (n = 7586) at follow up. Patients in practices allocated to SOS were significantly more likely to have cholesterol at target (69.5% vs 63.5%; OR 1.11, CI 1.00–1.23; p = 0.043) as a result of improved simvastatin prescribing. Subgroup analysis showed the primary outcome was achieved by prevalent but not incident patients. Statistically significant improvements occurred in all secondary outcomes for prevalent patients and all but one secondary outcome (the proportion of patients with cholesterol tested) for incident patients. SOS practices prescribed more simvastatin 40 mg than usual care practices, up to 10 years later.Interpretation
Through a combination of educational and organisational support, a general practice based pharmacist led collaborative intervention can improve statin prescribing and achievement of cholesterol targets in a high-risk primary care based population.Trial Registration
International Standard Randomised Controlled Trials Register ISRCTN61233866 相似文献964.
Sayeema Daudi Kevin H. Eng Paulette Mhawech-Fauceglia Carl Morrison Anthony Miliotto Amy Beck Junko Matsuzaki Takemasa Tsuji Adrienne Groman Sacha Gnjatic Guillo Spagnoli Shashikant Lele Kunle Odunsi 《PloS one》2014,9(8)
The MAGE cancer-testis antigens (CTA) are attractive candidates for immunotherapy. The aim of this study was to determine the frequency of expression, humoral immunity and prognostic significance of MAGE CTA in human epithelial ovarian cancer (EOC). mRNA or protein expression frequencies were determined for MAGE-A1, -A3, -A4, -A10 and -C1 (CT7) in tissue samples obtained from 400 patients with EOC. The presence of autologous antibodies against the MAGE antigens was determined from 285 serum samples. The relationships between MAGE expression, humoral immunity to MAGE antigens, and clinico-pathologic characteristics were studied. The individual frequencies of expression were as follows: A1: 15% (42/281), A3: 36% (131/390), A4: 47% (186/399), A10: 52% (204/395), C1: 16% (42/267). Strong concordant expression was noted with MAGE-A1:–A4, MAGE-A1:–C1 and MAGE-A4:–A10 (p<0.0005). Expression of MAGE-A1 or -A10 antigens resulted in poor progression free survival (PFS) (OR 1.44, CI 1.01–2.04, p = 0.044 and OR 1.3, CI 1.03–1.64, p = 0.03, respectively); whereas, MAGE-C1 expression was associated with improved PFS (OR 0.62, CI 0.42–0.92, p = 0.016). The improved PFS observed for MAGE-C1 expression, was diminished by co-expression of MAGE-A1 or -A10. Spontaneous humoral immunity to the MAGE antigens was present in 9% (27/285) of patients, and this predicted poor overall survival (log-rank test p = 0.0137). These findings indicate that MAGE-A1, MAGE-A4, MAGE-A3, and MAGE-A10 are priority attractive targets for polyvalent immunotherapy in ovarian cancer patients. 相似文献
965.
Alexander Schulz Christian Walther Helen Morrison Reinhard Bauer 《Journal of visualized experiments : JoVE》2014,(86)
Electrophysiological studies allow a rational classification of various neuromuscular diseases and are of help, together with neuropathological techniques, in the understanding of the underlying pathophysiology1. Here we describe a method to perform electrophysiological studies on mouse sciatic nerves in vivo.The animals are anesthetized with isoflurane in order to ensure analgesia for the tested mice and undisturbed working environment during the measurements that take about 30 min/animal. A constant body temperature of 37 °C is maintained by a heating plate and continuously measured by a rectal thermo probe2. Additionally, an electrocardiogram (ECG) is routinely recorded during the measurements in order to continuously monitor the physiological state of the investigated animals.Electrophysiological recordings are performed on the sciatic nerve, the largest nerve of the peripheral nervous system (PNS), supplying the mouse hind limb with both motoric and sensory fiber tracts. In our protocol, sciatic nerves remain in situ and therefore do not have to be extracted or exposed, allowing measurements without any adverse nerve irritations along with actual recordings. Using appropriate needle electrodes3 we perform both proximal and distal nerve stimulations, registering the transmitted potentials with sensing electrodes at gastrocnemius muscles. After data processing, reliable and highly consistent values for the nerve conduction velocity (NCV) and the compound motor action potential (CMAP), the key parameters for quantification of gross peripheral nerve functioning, can be achieved. 相似文献
966.
Cooper LC Chicchi GG Dinnell K Elliott JM Hollingworth GJ Kurtz MM Locker KL Morrison D Shaw DE Tsao KL Watt AP Williams AR Swain CJ 《Bioorganic & medicinal chemistry letters》2001,11(9):1233-1236
The synthesis and biological evaluation of a series of 2-aryl indoles with high affinity for the human neurokinin-1 (hNK1) receptor are reported, concentrating on optimisation of the indole substitution. 相似文献
967.
Protein L-isoaspartyl methyltransferase (PIMT) repairs abnormal isoaspartyl peptide bonds in age-damaged proteins. It has been reported that synuclein, a protein implicated in neurodegenerative diseases, is a major target of PIMT in mouse brain. To extend this finding and explore its possible relevance to neurodegenerative diseases, we attempted to determine the stoichiometry of isoaspartate accumulation in synuclein in vivo and in vitro. Brain proteins from PIMT knockout mice were separated by 2D electrophoresis followed by on-blot [(3)H]-methylation to label isoaspartyl proteins, and by immunoblotting to confirm the coincident presence of synuclein. On-blot (3)H-methylation revealed numerous isoaspartyl proteins, but no signal in the position of synuclein. This finding was corroborated by immunoprecipitation of synuclein followed by on-blot (3)H-methylation. To assess the propensity of synuclein to form isoaspartyl sites in vitro, samples of recombinant mouse and human α-synucleins were aged for two weeks by incubation at pH 7.5 and 37°C. The stoichiometries of isoaspartate accumulation were extremely low at 0.02 and 0.07 mol of isoaspartate per mol of protein respectively. Using a simple mathematical model based on the first order kinetics of isoaspartyl protein methyl ester hydrolysis, we ascribe the discrepancy between our results and the previous report to methodological limitations of the latter stemming from an inherent, and somewhat counterintuitive, relationship between the propensity of proteins to form isoaspartyl sites and the instability of the (3)H-methyl esters used to tag them. The results presented here indicate that synuclein is not a major target of PIMT in vivo, and emphasize the need to minimize methyl ester hydrolysis when using methylation to assess the abundance of isoaspartyl sites in proteins. 相似文献
968.
Brian J. Morrison Marcus L. Hastie Yadveer S. Grewal Zara C. Bruce Chris Schmidt Brent A. Reynolds Jeffrey J. Gorman J. Alejandro Lopez 《PloS one》2012,7(12)
Breast cancer is a heterogenous disease, composed of tumour cells with differing gene expressions and phenotypes. Very few antigens have been identified and a better understanding of tumour initiating-cells as targets for therapy is critically needed. Recently, a rare subpopulation of cells within tumours has been described with the ability to: (i) initiate and sustain tumour growth; (ii) resist traditional therapies and allow for secondary tumour dissemination; and (iii) display some of the characteristics of stem cells such as self-renewal. These cells are termed tumour-initiating cells or cancer stem cells, or alternatively, in the case of breast cancer, breast cancer stem cells. Previous studies have demonstrated that breast cancer stem cells can be enriched for in “tumoursphere” culture. Proteomics represents a novel way to investigate protein expression between cells. We hypothesise that characterisation of the proteome of the breast cancer line MCF-7 tumourspheres compared to adherent/differentiated cells identifies proteins of novel interest for further isolating or targeting breast cancer stem cells. We present evidence that: (i) the proteome of adherent cells is different to the proteome of cells grown in sphere medium from either early passage (passage 2) or late passage (passage 5) spheres; (ii) that spheres are enriched in expression of a variety of tumour-relevant proteins (including MUC1 and Galectin-3); and (iii) that targeting of one of these identified proteins (galectin-3) using an inhibitor (N-acetyllactosamine) decreases sphere formation/self-renewal of MCF-7 cancer stem cells in vitro and tumourigenicity in vivo. Hence, proteomic analysis of tumourspheres may find use in identifying novel targets for future therapy. The therapeutic targeting of breast cancer stem cells, a highly clinically relevant sub-population of tumour cells, has the potential to eliminate residual disease and may become an important component of a multi-modality treatment of cancer. 相似文献
969.
Most prevalent among the approaches to address the ever increasing demands for port capacity are the construction of new berths, installation of faster cranes and optimization of existing resources. A less common approach is to employ offshore port service concepts. Here, we endeavor to provide a complete survey of such nontraditional offshore service concepts and demonstrate that all, except a few very unusual concepts, can be well classified into one of thirty two structures or their combinations. Advantages, disadvantages and the container handling chain are discussed. We identify which of these structures can provide any of six possible operational modes. We next focus on a subset of the thirty two structures called the mobile harbor. This concept has recently been proposed and shares some similarities with midstream operation in Hong Kong. We endeavor to address the fundamental question: “Should such a concept be implemented?” We develop an estimate of the cost per unit threshold below which this concept will be viable. The per unit cost estimate of current MH designs is within about 6% of the economic viability threshold for traditional operation in Hong Kong. Other operational modes are not as favorable. As our focus is on the feasibility of the operational paradigm, we do not here address technology issues except to note ongoing efforts to resolve technology hurdles. 相似文献
970.
Engineered Repressible Lethality for Controlling the Pink Bollworm, a Lepidopteran Pest of Cotton 总被引:1,自引:0,他引:1
Neil I. Morrison Gregory S. Simmons Guoliang Fu Sinead O��Connell Adam S. Walker Tarig Dafa��alla Michelle Walters John Claus Guolei Tang Li Jin Thea Marubbi Matthew J. Epton Claire L. Harris Robert T. Staten Ernest Miller Thomas A. Miller Luke Alphey 《PloS one》2012,7(12)
The sterile insect technique (SIT) is an environmentally friendly method of pest control in which insects are mass-produced, irradiated and released to mate with wild counterparts. SIT has been used to control major pest insects including the pink bollworm (Pectinophora gossypiella Saunders), a global pest of cotton. Transgenic technology has the potential to overcome disadvantages associated with the SIT, such as the damaging effects of radiation on released insects. A method called RIDL (Release of Insects carrying a Dominant Lethal) is designed to circumvent the need to irradiate insects before release. Premature death of insects’ progeny can be engineered to provide an equivalent to sterilisation. Moreover, this trait can be suppressed by the provision of a dietary antidote. In the pink bollworm, we generated transformed strains using different DNA constructs, which showed moderate-to-100% engineered mortality. In permissive conditions, this effect was largely suppressed. Survival data on cotton in field cages indicated that field conditions increase the lethal effect. One strain, called OX3402C, showed highly penetrant and highly repressible lethality, and was tested on host plants where its larvae caused minimal damage before death. These results highlight a potentially valuable insecticide-free tool against pink bollworm, and indicate its potential for development in other lepidopteran pests. 相似文献