全文获取类型
收费全文 | 8971篇 |
免费 | 771篇 |
国内免费 | 1篇 |
专业分类
9743篇 |
出版年
2024年 | 12篇 |
2023年 | 39篇 |
2022年 | 110篇 |
2021年 | 228篇 |
2020年 | 113篇 |
2019年 | 152篇 |
2018年 | 188篇 |
2017年 | 161篇 |
2016年 | 291篇 |
2015年 | 469篇 |
2014年 | 508篇 |
2013年 | 545篇 |
2012年 | 775篇 |
2011年 | 736篇 |
2010年 | 459篇 |
2009年 | 424篇 |
2008年 | 569篇 |
2007年 | 570篇 |
2006年 | 531篇 |
2005年 | 536篇 |
2004年 | 491篇 |
2003年 | 457篇 |
2002年 | 433篇 |
2001年 | 74篇 |
2000年 | 51篇 |
1999年 | 104篇 |
1998年 | 111篇 |
1997年 | 71篇 |
1996年 | 56篇 |
1995年 | 58篇 |
1994年 | 50篇 |
1993年 | 52篇 |
1992年 | 40篇 |
1991年 | 32篇 |
1990年 | 39篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1971年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有9743条查询结果,搜索用时 15 毫秒
101.
Jessica Royles Jérôme Ogée Lisa Wingate Dominic A. Hodgson Peter Convey Howard Griffiths 《Global Change Biology》2012,18(10):3112-3124
Signy Island, maritime Antarctic, lies within the region of the Southern Hemisphere that is currently experiencing the most rapid rates of environmental change. In this study, peat cores up to 2 m in depth from four moss banks on Signy Island were used to reconstruct changes in moss growth and climatic characteristics over the late Holocene. Measurements included radiocarbon dating (to determine peat accumulation rates) and stable carbon isotope composition of moss cellulose (to estimate photosynthetic limitation by CO 2 supply and model CO 2 assimilation rate). For at least one intensively 14C‐dated Chorisodontium aciphyllum moss peat bank, the vertical accumulation rate of peat was 3.9 mm yr?1 over the last 30 years. Before the industrial revolution, rates of peat accumulation in all cores were much lower, at around 0.6–1 mm yr?1. Carbon‐13 discrimination (Δ), corrected for background and anthropogenic source inputs, was used to develop a predictive model for CO 2 assimilation. Between 1680 and 1900, there had been a gradual increase in Δ, and hence assimilation rate. Since 1800, assimilation has also been stimulated by the changes in atmospheric CO 2 concentration, but a recent decline in Δ (over the past 50–100 years) can perhaps be attributed to documented changes in temperature and/or precipitation. The overall increase in CO 2 assimilation rate (13C proxy) and enhanced C accumulation (14C proxy) are consistent with warmer and wetter conditions currently generating higher growth rates than at any time in the past three millennia, with the decline in Δ perhaps compensated by a longer growing season. 相似文献
102.
p38 mitogen-activated protein kinase is the central regulator of cyclic AMP-dependent transcription of the brown fat uncoupling protein 1 gene 总被引:5,自引:0,他引:5 下载免费PDF全文
103.
Lisa Borkner Andrew Kaiser Willeke van de Kasteele Reinhard Andreesen Andreas Mackensen John B. Haanen Ton N. Schumacher Christian Blank 《Cancer immunology, immunotherapy : CII》2010,59(8):1173-1183
Adoptive cell transfer (ACT), either using rapidly expanded tumor infiltrating lymphocytes or T-cell receptor transduced peripheral
blood lymphocytes, can be considered one of the most promising approaches in cancer immunotherapy. ACT results in the repopulation
of the host with high frequencies of tumor-specific T cells; however, optimal function of these cells within the tumor micro-environment
is required to reach long-term tumor clearance. We and others have shown that ongoing anti-tumor immune responses can be impaired
by the expression of ligands, such as PD-L1 (B7-H1) on tumor cells. Such inhibitory molecules can affect T cells at the effector
phase via their receptor PD-1. PD-L1/PD-1 interaction has indeed been shown crucial in inducing T-cell anergy and maintaining
peripheral tolerance. In order to maximize anti-tumor responses, antibodies that target the PD-1/PD-L1 axis are currently
in phase I/II trials. Alternatively, a more refined approach could be the selective targeting of PD-1 in tumor-specific T
cells to obtain long-term resistance against PD-1-mediated inhibition. We addressed whether this goal could be achieved by
means of retroviral siRNA delivery. Effective siRNA sequences resulting in the reduction of surface PD-1 expression led to
improved murine as well as human T-cell immune functions in response to PD-L1 expressing melanoma cells. These data suggest
that blockade of PD-1-mediated T-cell inhibition through siRNA forms a promising approach to achieve long-lasting enhancement
of tumor-specific T-cell function in adoptive T-cell therapy protocols. 相似文献
104.
Lisa N. Barrow Sabrina M. McNew Nora Mitchell Spencer C. Galen Holly L. Lutz Heather Skeen Thomas Valqui Jason D. Weckstein Christopher C. Witt 《Ecology letters》2019,22(6):987-998
Variation in susceptibility is ubiquitous in multi‐host, multi‐parasite assemblages, and can have profound implications for ecology and evolution in these systems. The extent to which susceptibility to parasites is phylogenetically conserved among hosts can be revealed by analysing diverse regional communities. We screened for haemosporidian parasites in 3983 birds representing 40 families and 523 species, spanning ~ 4500 m elevation in the tropical Andes. To quantify the influence of host phylogeny on infection status, we applied Bayesian phylogenetic multilevel models that included a suite of environmental, spatial, temporal, life history and ecological predictors. We found evidence of deeply conserved susceptibility across the avian tree; host phylogeny explained substantial variation in infection status, and results were robust to phylogenetic uncertainty. Our study suggests that susceptibility is governed, in part, by conserved, latent aspects of anti‐parasite defence. This demonstrates the importance of deep phylogeny for understanding present‐day ecological interactions. 相似文献
105.
Thomas Walker Lisa Klasson Mohammed Sebaihia Mandy J Sanders Nicholas R Thomson Julian Parkhill Steven P Sinkins 《BMC biology》2007,5(1):39-9
Background
Wolbachia are obligate endosymbiotic bacteria maternally transmitted through the egg cytoplasm that are responsible for several reproductive disorders in their insect hosts, such as cytoplasmic incompatibility (CI) in infected mosquitoes. Species in the Culex pipiens complex display an unusually high number of Wolbachia-induced crossing types, and based on present data, only the wPip strain is present. 相似文献106.
107.
KLOTHO allele status and the risk of early-onset occult coronary artery disease 总被引:10,自引:0,他引:10 下载免费PDF全文
Arking DE Becker DM Yanek LR Fallin D Judge DP Moy TF Becker LC Dietz HC 《American journal of human genetics》2003,72(5):1154-1161
We previously identified a functional variant of KLOTHO (termed "KL-VS"), which harbors two amino acid substitutions in complete linkage disequilibrium and is associated with reduced human longevity when in homozygosity. Klotho-deficient mice display extensive arteriosclerosis when fed a normal diet, suggesting a potent genetic predisposition. To determine whether klotho influences atherosclerotic risk in humans, we performed cross-sectional studies to assess the association between the KL-VS allele and occult coronary artery disease (CAD) in two independent samples of apparently healthy siblings of individuals with early-onset (age <60 years) CAD (SIBS-I [N=520] and SIBS-II [N=436]). Occult CAD was defined as the occurrence of a reversible perfusion defect during exercise thallium scintigraphy and/or as an abnormal result of an exercise electrocardiogram (SIBS-I, n=97; SIBS-II, n=56). In SIBS-I, the KL-VS allele conferred a relative odds of 1.90 (95% confidence interval 1.21-2.98) for occult CAD, after adjusting for familial intraclass correlations (P<.005). Logistic regression modeling, incorporating known CAD risk factors, demonstrated that the KL-VS allele is an independent risk factor (P<.019) and that the imposed risk of KL-VS allele status is influenced by modifiable risk factors. Hypertension (P<.022) and increasing high-density lipoprotein cholesterol (HDL-C) levels (P<.022) mask or reduce the risk conferred by the KL-VS allele, respectively, whereas current smoking (P<.004) increases the risk. Remarkably concordant effects of the KL-VS allele and modifying factors on the risk of occult CAD were seen in SIBS-II. These results demonstrate that the KL-VS allele is an independent risk factor for occult CAD in two independent high-risk samples. Modifiable risk factors, including hypertension, smoking status, and HDL-C level, appear to influence the risk imposed by this allele. 相似文献
108.
Lisa M. Stout Ruth E. Blake James P. Greenwood Anna M. Martini & Eben C. Rose 《FEMS microbiology ecology》2009,70(3):70-80
The volcanic Sulphur Springs, St. Lucia, present an extreme environment due to high temperatures, low pH values, and high concentrations of sulfate and boron. St. Lucia offers some unique geochemical characteristics that may shape the microbial communities within the Sulphur Springs area. We chose six pools representing a range of geochemical characteristics for detailed microbial community analyses. Chemical concentrations varied greatly between sites. Microbial diversity was analyzed using 16S rRNA gene clone library analyses. With the exception of one pool with relatively low concentrations of dissolved ions, microbial diversity was very low, with Aquificales sequences dominating bacterial communities at most pools. The archaeal component of all pools was almost exclusively Acidianus spp. and did not vary between sites with different chemical characteristics. In the pool with the highest boron and sulfate concentrations, only archaeal sequences were detected. Compared with other sulfur springs such as those at Yellowstone, the microbial diversity at St. Lucia is very different, but it is similar to that at the nearby Lesser Antilles island of Montserrat. While high elemental concentrations seem to be related to differences in bacterial diversity here, similarities with other Lesser Antilles sites suggest that there may be a biogeographical component as well. 相似文献
109.
Plants are becoming commercially acceptable for recombinant protein production for human therapeutics, vaccine antigens, industrial enzymes, and nutraceuticals. Recently, significant advances in expression, protein glycosylation, and gene-to-product development time have been achieved. Safety and regulatory concerns for open-field production systems have also been addressed by using contained systems to grow transgenic plants. However, using contained systems eliminates several advantages of open-field production, such as inexpensive upstream production and scale-up costs. Upstream technological achievements have not been matched by downstream processing advancements. In the past 10 years, the most research progress was achieved in the areas of extraction and pretreatment. Extraction conditions have been optimized for numerous proteins on a case-by-case basis leading to the development of platform-dependent approaches. Pretreatment advances were made after realizing that plant extracts and homogenates have unique compositions that require distinct conditioning prior to purification. However, scientists have relied on purification methods developed for other protein production hosts with modest investments in developing novel plant purification tools. Recently, non-chromatographic purification methods, such as aqueous two-phase partitioning and membrane filtration, have been evaluated as low-cost purification alternatives to packed-bed adsorption. This paper reviews seed, leafy, and bioreactor-based platforms, highlights strategies for the primary recovery and purification of recombinant proteins, and compares process economics between systems. Lastly, the future direction and research needs for developing economically competitive recombinant proteins with commercial potential are discussed. 相似文献
110.
Sarah?E.?TurnerEmail author Lisa?Gould David?A.?Duffus 《International journal of primatology》2005,26(6):1435-1457
We studied the relationship between maternal behavior and infant disability in 12 mother-infant dyads for the first 5 weeks
of infant life in the free-ranging Japanese macaque (Macaca fuscata) group on Awaji Island, Japan, from May to September 2001. Congenital limb malformations are prevalent in this population,
and as such carry implications for behavior and conservation. We did not detect any differences in maternal activity budgets,
mother-infant physical contact, infant holding, and overall nursing and infant transport time between mothers of non-disabled
infants, disabled infants that were able to cling to their mothers, and disabled infants whose limb structure prevented clinging.
Mothers of infants with limb malformations severe enough to prevent normal clinging behavior manually supported their infants
during nursing and locomotion significantly more than other mothers did theirs. Increased support-carrying and support-nursing,
and higher frequencies of holding the infant to one's ventrum, suggest that mothers of extensively malformed infants may be
investing more to facilitate the survival of their offspring and that infant disability appears to be influencing maternal
behaviors in this population. 相似文献