全文获取类型
收费全文 | 3426篇 |
免费 | 272篇 |
出版年
2024年 | 4篇 |
2023年 | 46篇 |
2022年 | 99篇 |
2021年 | 152篇 |
2020年 | 115篇 |
2019年 | 112篇 |
2018年 | 98篇 |
2017年 | 87篇 |
2016年 | 149篇 |
2015年 | 305篇 |
2014年 | 288篇 |
2013年 | 267篇 |
2012年 | 344篇 |
2011年 | 350篇 |
2010年 | 181篇 |
2009年 | 111篇 |
2008年 | 157篇 |
2007年 | 138篇 |
2006年 | 134篇 |
2005年 | 120篇 |
2004年 | 73篇 |
2003年 | 60篇 |
2002年 | 69篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 23篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有3698条查询结果,搜索用时 46 毫秒
91.
Sreenath R. Palle LeAnne M. Campbell Devendra Pandeya Lorraine Puckhaber Lauren K. Tollack Sylvain Marcel Sabarinath Sundaram Robert D. Stipanovic Thomas C. Wedegaertner Lori Hinze Keerti S. Rathore 《Plant biotechnology journal》2013,11(3):296-304
Cottonseed remains a low‐value by‐product of lint production mainly due to the presence of toxic gossypol that makes it unfit for monogastrics. Ultra‐low gossypol cottonseed (ULGCS) lines were developed using RNAi knockdown of δ‐cadinene synthase gene(s) in Gossypium hirsutum. The purpose of the current study was to assess the stability and specificity of the ULGCS trait and evaluate the agronomic performance of the transgenic lines. Trials conducted over a period of 3 years show that the ULGCS trait was stable under field conditions and the foliage/floral organs of transgenic lines contained wild‐type levels of gossypol and related terpenoids. Although it was a relatively small‐scale study, we did not observe any negative effects on either the yield or quality of the fibre and seed in the transgenic lines compared with the nontransgenic parental plants. Compositional analysis was performed on the seeds obtained from plants grown in the field during 2009. As expected, the major difference between the ULGCS and wild‐type cottonseeds was in terms of their gossypol levels. With the exception of oil content, the composition of ULGCS was similar to that of nontransgenic cottonseeds. Interestingly, the ULGCS had significantly higher (4%–8%) oil content compared with the seeds from the nontransgenic parent. Field trial results confirmed the stability and specificity of the ULGCS trait suggesting that this RNAi‐based product has the potential to be commercially viable. Thus, it may be possible to enhance and expand the nutritional utility of the annual cottonseed output to fulfil the ever‐increasing needs of humanity. 相似文献
92.
Nury M. Steuerwald David M. Foureau H. James Norton Jie Zhou Judith C. Parsons Naga Chalasani Robert J. Fontana Paul B. Watkins William M. Lee K. Rajender Reddy Andrew Stolz Jayant Talwalkar Timothy Davern Dhanonjoy Saha Lauren N. Bell Huiman Barnhart Jiezhun Gu Jose Serrano Herbert L. Bonkovsky 《PloS one》2013,8(12)
Drug-induced liver injury (DILI) is the most common cause of acute liver failure in the United-States. The aim of the study was to describe serum immune profiles associated with acute DILI, to investigate whether there are profiles associated with clinical features or types of DILI and/or with prognosis, and to assess temporal changes in levels. Twenty-seven immune analytes were measured in the sera of 78 DILI subjects in the Drug-Induced Liver Injury Network (DILIN) and compared with 40 healthy controls. Immune analytes (14 cytokines, 7 chemokines and 6 growth factors) were measured by BioPlex multiplex ELISA at DILI onset and after 6 months. A modeling process utilizing immune principles was used to select a final set of variables among 27 immune analytes and several additional clinical lab values for prediction of early death (within 6 months of DILI onset). Nineteen of the 27 immune analytes were differentially expressed among healthy control, DILI onset and 6-month cohorts. Disparate patterns of immune responses, especially innate and adaptive cellular (mostly TH17) immunity were evident. Low values of four immune analytes (IL-9, IL-17, PDGF-bb and RANTES) and serum albumin are predictive of early death [PPV = 88% (95% CI, 65%-100%), NPV = 97% (95% CI, 93%-100%), accuracy = 96% (95% CI, 92%-100%)].
Conclusions
Acute DILI is associated with robust and varying immune responses. High levels of expression of cytokines associated with innate immunity are associated with a poor prognosis, whereas high levels of expression of adaptive cytokines are associated with good long-term prognosis and eventual recovery. Serum immune analyte profiles at DILI onset appear to be of prognostic, and perhaps, diagnostic significance. 相似文献93.
Michael S. Stalvey Katrina L. Clines Viktoria Havasi Christopher R. McKibbin Lauren K. Dunn W. Joon Chung Gregory A. Clines 《PloS one》2013,8(11)
Low bone mass and increased fracture risk are recognized complications of cystic fibrosis (CF). CF-related bone disease (CFBD) is characterized by uncoupled bone turnover—impaired osteoblastic bone formation and enhanced osteoclastic bone resorption. Intestinal malabsorption, vitamin D deficiency and inflammatory cytokines contribute to CFBD. However, epidemiological investigations and animal models also support a direct causal link between inactivation of skeletal cystic fibrosis transmembrane regulator (CFTR), the gene that when mutated causes CF, and CFBD. The objective of this study was to examine the direct actions of CFTR on bone. Expression analyses revealed that CFTR mRNA and protein were expressed in murine osteoblasts, but not in osteoclasts. Functional studies were then performed to investigate the direct actions of CFTR on osteoblasts using a CFTR knockout (Cftr−/−) mouse model. In the murine calvarial organ culture assay, Cftr−/− calvariae displayed significantly less bone formation and osteoblast numbers than calvariae harvested from wildtype (Cftr+/+) littermates. CFTR inactivation also reduced alkaline phosphatase expression in cultured murine calvarial osteoblasts. Although CFTR was not expressed in murine osteoclasts, significantly more osteoclasts formed in Cftr−/− compared to Cftr+/+ bone marrow cultures. Indirect regulation of osteoclastogenesis by the osteoblast through RANK/RANKL/OPG signaling was next examined. Although no difference in receptor activator of NF-κB ligand (Rankl) mRNA was detected, significantly less osteoprotegerin (Opg) was expressed in Cftr−/− compared to Cftr+/+ osteoblasts. Together, the Rankl:Opg ratio was significantly higher in Cftr−/− murine calvarial osteoblasts contributing to a higher osteoclastogenesis potential. The combined findings of reduced osteoblast differentiation and lower Opg expression suggested a possible defect in canonical Wnt signaling. In fact, Wnt3a and PTH-stimulated canonical Wnt signaling was defective in Cftr−/− murine calvarial osteoblasts. These results support that genetic inactivation of CFTR in osteoblasts contributes to low bone mass and that targeting osteoblasts may represent an effective strategy to treat CFBD. 相似文献
94.
Narisara Chantratita Sarunporn Tandhavanant Nicolle D. Myers Sudeshna Seal Arkhom Arayawichanont Aroonsri Kliangsa-ad Lauren E. Hittle Robert K. Ernst Mary J. Emond Mark M. Wurfel Nicholas P. J. Day Sharon J. Peacock T. Eoin West 《PloS one》2013,8(11)
B. pseudomallei is a gram-negative bacterium that causes the tropical infection melioidosis. In northeast Thailand, mortality from melioidosis approaches 40%. As exemplified by the lipopolysaccharide-Toll-like receptor 4 interaction, innate immune responses to invading bacteria are precipitated by activation of host pathogen recognition receptors by pathogen associated molecular patterns. Human melioidosis is characterized by up-regulation of pathogen recognition receptors and pro-inflammatory cytokine release. In contrast to many gram-negative pathogens, however, the lipopolysaccharide of B. pseudomallei is considered only weakly inflammatory. We conducted a study in 300 healthy Thai subjects to investigate the ex vivo human blood response to various bacterial pathogen associated molecular patterns, including lipopolysaccharide from several bacteria, and to two heat-killed B. pseudomallei isolates. We measured cytokine levels after stimulation of fresh whole blood with a panel of stimuli. We found that age, sex, and white blood cell count modulate the innate immune response to B. pseudomallei. We further observed that, in comparison to other stimuli, the innate immune response to B. pseudomallei is most highly correlated with the response to lipopolysaccharide. The magnitude of cytokine responses induced by B. pseudomallei lipopolysaccharide was significantly greater than those induced by lipopolysaccharide from Escherichia coli and comparable to many responses induced by lipopolysaccharide from Salmonella minnesota despite lower amounts of lipid A in the B. pseudomallei lipopolysaccharide preparation. In human monocytes stimulated with B. pseudomallei, addition of polymyxin B or a TLR4/MD-2 neutralizing antibody inhibited the majority of TNF-α production. Challenging existing views, our data indicate that the innate immune response to B. pseudomallei in human blood is largely driven by lipopolysaccharide, and that the response to B. pseudomallei lipopolysaccharide in blood is greater than the response to other lipopolysaccharide expressing isolates. Our findings suggest that B. pseudomallei lipopolysaccharide may play a central role in stimulating the host response in melioidosis. 相似文献
95.
The spinal cord of rats contains the sexually dimorphic, steroid‐sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB). In males, SNB dendrite growth is dependent on gonadal steroids: dendrite growth is inhibited after castration, but supported in androgen‐ or estrogen‐treated castrated males. Furthermore, estrogenic support of SNB dendrite growth is mediated by estrogen action at the target musculature, inhibited by estrogen receptor (ER) blockade at the muscle and supported by local estradiol treatment. However, this estrogenic support is restricted to the early postnatal period, after which the morphology of SNB dendrites is insensitive to estrogens. To test if the developmentally restricted effects of estrogens on SNB dendrite growth coincide with the transient expression of ER in the target musculature, ERα expression was assessed during development and in adulthood. ERα expression in extra‐Muscle fiber cells was greatest from postnatal day 7 (P7) to P14 and declined after P21. Because this pattern of ERα expression coincided with the period of estrogen‐dependent dendrite growth, we tested if limiting hormone exposure to the period of maximal ERα expression in extra‐muscle fiber cells could fully support estrogen‐dependent SNB dendrite growth. We restricted estradiol treatment in castrated males from P7 to P21 and assessed SNB dendritic morphology at P28. Treating castrates with estradiol implants at the muscle from P7 to P21 supported dendrite growth to normal levels through P28. These data suggest that the transient ERα expression in target muscle could potentially define the critical period for estrogen‐dependent dendrite growth in SNB motoneurons. © 2011 Wiley Periodicals, Inc. Develop Neurobiol, 2013 相似文献
96.
Matthew J. Cooper Nathan J. Cox Eric I. Zimmerman Brian J. Dewar James S. Duncan Martin C. Whittle Thien A. Nguyen Lauren S. Jones Sreerupa Ghose Roy David M. Smalley Pei Fen Kuan Kristy L. Richards Richard I. Christopherson Jian Jin Stephen V. Frye Gary L. Johnson Albert S. Baldwin Lee M. Graves 《PloS one》2013,8(6)
Protein kinases play key roles in oncogenic signaling and are a major focus in the development of targeted cancer therapies. Imatinib, a BCR-Abl tyrosine kinase inhibitor, is a successful front-line treatment for chronic myelogenous leukemia (CML). However, resistance to imatinib may be acquired by BCR-Abl mutations or hyperactivation of Src family kinases such as Lyn. We have used multiplexed kinase inhibitor beads (MIBs) and quantitative mass spectrometry (MS) to compare kinase expression and activity in an imatinib-resistant (MYL-R) and -sensitive (MYL) cell model of CML. Using MIB/MS, expression and activity changes of over 150 kinases were quantitatively measured from various protein kinase families. Statistical analysis of experimental replicates assigned significance to 35 of these kinases, referred to as the MYL-R kinome profile. MIB/MS and immunoblotting confirmed the over-expression and activation of Lyn in MYL-R cells and identified additional kinases with increased (MEK, ERK, IKKα, PKCβ, NEK9) or decreased (Abl, Kit, JNK, ATM, Yes) abundance or activity. Inhibiting Lyn with dasatinib or by shRNA-mediated knockdown reduced the phosphorylation of MEK and IKKα. Because MYL-R cells showed elevated NF-κB signaling relative to MYL cells, as demonstrated by increased IκBα and IL-6 mRNA expression, we tested the effects of an IKK inhibitor (BAY 65-1942). MIB/MS and immunoblotting revealed that BAY 65-1942 increased MEK/ERK signaling and that this increase was prevented by co-treatment with a MEK inhibitor (AZD6244). Furthermore, the combined inhibition of MEK and IKKα resulted in reduced IL-6 mRNA expression, synergistic loss of cell viability and increased apoptosis. Thus, MIB/MS analysis identified MEK and IKKα as important downstream targets of Lyn, suggesting that co-targeting these kinases may provide a unique strategy to inhibit Lyn-dependent imatinib-resistant CML. These results demonstrate the utility of MIB/MS as a tool to identify dysregulated kinases and to interrogate kinome dynamics as cells respond to targeted kinase inhibition. 相似文献
97.
98.
R. D. Robarts T. Zohary F. Ojeda C. C.E. Lovengreen R. D. Walmsley 《African Journal of Aquatic Science》2013,38(2):78-81
SUMMARY The spectral composition of the underwater light field was examined in two hypertrophic South African Impoundments (Hartbeespoort and Roodeplaat Dams) under a range of inorganic turbidities and chlorophyll α concentrations. The data indicated that inorganic turbidity and gilvin were dominant to chlorophyll in regulating underwater light attenuation during the present study. Under all conditions the wavelengths between 405 and 510 nm were attenuated more rapidly than near UV and the wavelengths above 510 nm and the 623 nm component penetrated deepest. Under low turbidities the 546 nm wavelength was the next most penetrating component, but its attenuation increased with increasing turbidity. This characteristic of the underwater light field may be important to the cyanobacteria which dominate in these hypertrophic lakes. 相似文献
99.
Jenny Hill Jenna Hoyt Anna Maria van Eijk Lauren D'Mello-Guyett Feiko O. ter Kuile Rick Steketee Helen Smith Jayne Webster 《PLoS medicine》2013,10(7)
Background
Malaria in pregnancy has important consequences for mother and baby. Coverage with the World Health Organization–recommended prevention strategy for pregnant women in sub-Saharan Africa of intermittent preventive treatment in pregnancy (IPTp) and insecticide-treated nets (ITNs) is low. We conducted a systematic review to explore factors affecting delivery, access, and use of IPTp and ITNs among healthcare providers and women.Methods and Results
We searched the Malaria in Pregnancy Library and Global Health Database from 1 January 1990 to 23 April 2013, without language restriction. Data extraction was performed by two investigators independently, and data was appraised for quality and content. Data on barriers and facilitators, and the effect of interventions, were explored using content analysis and narrative synthesis. We conducted a meta-analysis of determinants of IPTp and ITN uptake using random effects models, and performed subgroup analysis to evaluate consistency across interventions and study populations, countries, and enrolment sites. We did not perform a meta-ethnography of qualitative data.Ninety-eight articles were included, of which 20 were intervention studies. Key barriers to the provision of IPTp and ITNs were unclear policy and guidance on IPTp; general healthcare system issues, such as stockouts and user fees; health facility issues stemming from poor organisation, leading to poor quality of care; poor healthcare provider performance, including confusion over the timing of each IPTp dose; and women''s poor antenatal attendance, affecting IPTp uptake. Key determinants of IPTp coverage were education, knowledge about malaria/IPTp, socio-economic status, parity, and number and timing of antenatal clinic visits. Key determinants of ITN coverage were employment status, education, knowledge about malaria/ITNs, age, and marital status. Predictors showed regional variations.Conclusions
Delivery of ITNs through antenatal clinics presents fewer problems than delivery of IPTp. Many obstacles to IPTp delivery are relatively simple barriers that could be resolved in the short term. Other barriers are more entrenched within the overall healthcare system or socio-economic/cultural contexts, and will require medium- to long-term strategies. Please see later in the article for the Editors'' Summary 相似文献100.