全文获取类型
收费全文 | 19959篇 |
免费 | 1755篇 |
国内免费 | 1篇 |
专业分类
21715篇 |
出版年
2023年 | 98篇 |
2022年 | 81篇 |
2021年 | 225篇 |
2020年 | 135篇 |
2019年 | 181篇 |
2018年 | 403篇 |
2017年 | 423篇 |
2016年 | 452篇 |
2015年 | 407篇 |
2014年 | 499篇 |
2013年 | 788篇 |
2012年 | 1431篇 |
2011年 | 1547篇 |
2010年 | 811篇 |
2009年 | 569篇 |
2008年 | 1311篇 |
2007年 | 1285篇 |
2006年 | 1217篇 |
2005年 | 1072篇 |
2004年 | 995篇 |
2003年 | 958篇 |
2002年 | 917篇 |
2001年 | 758篇 |
2000年 | 878篇 |
1999年 | 388篇 |
1998年 | 181篇 |
1997年 | 137篇 |
1996年 | 176篇 |
1995年 | 164篇 |
1994年 | 137篇 |
1993年 | 146篇 |
1992年 | 128篇 |
1991年 | 121篇 |
1990年 | 125篇 |
1989年 | 113篇 |
1988年 | 113篇 |
1987年 | 110篇 |
1986年 | 106篇 |
1985年 | 144篇 |
1984年 | 143篇 |
1983年 | 123篇 |
1982年 | 162篇 |
1981年 | 149篇 |
1980年 | 107篇 |
1979年 | 121篇 |
1978年 | 92篇 |
1977年 | 86篇 |
1976年 | 78篇 |
1975年 | 77篇 |
1974年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
Development and validation of a bioreactor for physical stimulation of engineered cartilage 总被引:1,自引:0,他引:1
A bioreactor has been developed to apply different regimes of physical stimulation to tissue specimens under highly controlled conditions. The computer-controlled device exposes specimens to compressive deformation at various strains and frequencies, measures the load applied to each sample and allows simultaneous medium stirring at different velocities. Validation tests confirmed the accuracy of the system in (i) its displacement (errors averaged 0.072+/-0.051 microm), and in (ii) setting the contact with the samples utilizing micrometer screws coupled to plungers (errors averaged 1.74+/-0.36% for samples of 1.60-3.18 mm thickness), thus ensuring accurate compressive deformation. The developed bioreactor, which represents an advance in the technology for physical stimulation of tissue specimens, is currently used to apply compressive deformation and hydrodynamic forces to human chondrocytes cultured in biodegradable polymer scaffolds, with the goals of (i) engineering functional grafts for the repair of cartilage defects (ii). 相似文献
202.
203.
204.
Primarily, 50 characters taken from herbarium specimens, cultivated plants, and whole populations ofPrimula veris L. were critically evaluated. Only 24 characters were found to be suitable for taxonomic use. The geographical and multivariate analysis of about 1000 herbarium specimens from the whole area lead to a reduction of the number of subspecies. Only a less restricted subsp.veris (incl. subsp.canescens, subsp.inflata and probably including subsp.macrocalyx) and subsp.columnae (incl. subsp.suaveolens) can be distinguished considering the variability of characters within an individuum, under different culture conditions, and during the growth period. The status of the taxon macrocalyx cannot be cleared presently. 相似文献
205.
For malaria transmission to occur, Plasmodium sporozoites must infect the salivary glands of their mosquito vectors. This study reports that Anopheles gambiae SRPN6 participates in a local salivary gland epithelial response against the rodent malaria parasite, Plasmodium berghei . We showed previously that SRPN6, an immune inducible midgut invasion marker, influences ookinete development. Here we report that SRPN6 is also specifically induced in salivary glands with the onset of sporozoite invasion. The protein is located in the basal region of epithelial cells in proximity to invading sporozoites. Knockdown of SRPN6 during the late phase of sporogony by RNAi has no effect on oocyst rupture but significantly increases the number of sporozoites present in salivary glands. Despite several differences between the passage of Plasmodium through the midgut and the salivary glands, this study identifies a striking overlap in the molecular responses of these two epithelia to parasite invasion. 相似文献
206.
Schwab U Seppänen-Laakso T Yetukuri L Agren J Kolehmainen M Laaksonen DE Ruskeepää AL Gylling H Uusitupa M Oresic M;GENOBIN Study Group 《PloS one》2008,3(7):e2630
Background
The effect of weight loss on different plasma lipid subclasses at the molecular level is unknown. The aim of this study was to examine whether a diet-induced weight reduction result in changes in the extended plasma lipid profiles (lipidome) in subjects with features of metabolic syndrome in a 33-week intervention.Methodology/Principal Findings
Plasma samples of 9 subjects in the weight reduction group and 10 subjects in the control group were analyzed using mass spectrometry based lipidomic and fatty acid analyses. Body weight decreased in the weight reduction group by 7.8±2.9% (p<0.01). Most of the serum triacylglycerols and phosphatidylcholines were reduced. The decrease in triacylglycerols affected predominantly the saturated short chain fatty acids. This decrease of saturated short chain fatty acid containing triacylglycerols correlated with the increase of insulin sensitivity. However, levels of several longer chain fatty acids, including arachidonic and docosahexanoic acid, were not affected by weight loss. Levels of other lipids known to be associated with obesity such as sphingolipids and lysophosphatidylcholines were not altered by weight reduction.Conclusions/Significance
Diet-induced weight loss caused significant changes in global lipid profiles in subjects with abnormal glucose metabolism. The observed changes may affect insulin sensitivity and glucose metabolism in these subjects.Trial Registration
ClinicalTrials.gov NCT00621205相似文献207.
Atwal GS Rabadán R Lozano G Strong LC Ruijs MW Schmidt MK van't Veer LJ Nevanlinna H Tommiska J Aittomäki K Bougeard G Frebourg T Levine AJ Bond GL 《PloS one》2008,3(4):e1951
Germline genetics, gender and hormonal-signaling pathways are all well described modifiers of cancer risk and progression. Although an improved understanding of how germline genetic variants interact with other cancer risk factors may allow better prevention and treatment of human cancer, measuring and quantifying these interactions is challenging. In other areas of research, Information Theory has been used to quantitatively describe similar multivariate interactions. We implemented a novel information-theoretic analysis to measure the joint effect of a high frequency germline genetic variant of the p53 tumor suppressor pathway (MDM2 SNP309 T/G) and gender on clinical cancer phenotypes. This analysis quantitatively describes synergistic interactions among gender, the MDM2 SNP309 locus, and the age of onset of tumorigenesis in p53 mutation carriers. These results offer a molecular and genetic basis for the observed sexual dimorphism of cancer risk in p53 mutation carriers and a model is proposed that suggests a novel cancer prevention strategy for p53 mutation carriers. 相似文献
208.
Levels and determinants of inflammatory biomarkers in a Swiss population-based sample (CoLaus study)
Marques-Vidal P Bochud M Bastardot F Lüscher T Ferrero F Gaspoz JM Paccaud F Urwyler A von Känel R Hock C Waeber G Preisig M Vollenweider P 《PloS one》2011,6(6):e21002
Objective
to assess the levels and determinants of interleukin (IL)-1β, IL-6, tumour necrosis factor (TNF)-α and C-reactive protein (CRP) in a healthy Caucasian population.Methods
population sample of 2884 men and 3201 women aged 35 to 75. IL-1β, IL-6 and TNF-α were assessed by a multiplexed particle-based flow cytometric assay and CRP by an immunometric assay.Results
Spearman rank correlations between duplicate cytokine measurements (N = 80) ranged between 0.89 and 0.96; intra-class correlation coefficients ranged between 0.94 and 0.97, indicating good reproducibility. Among the 6085 participants, 2289 (37.6%), 451 (7.4%) and 43 (0.7%) had IL-1β, IL-6 and TNF-α levels below detection limits, respectively. Median (interquartile range) for participants with detectable values were 1.17 (0.48–3.90) pg/ml for IL-1β; 1.47 (0.71–3.53) pg/ml for IL-6; 2.89 (1.82–4.53) pg/ml for TNF-α and 1.3 (0.6–2.7) ng/ml for CRP. On multivariate analysis, greater age was the only factor inversely associated with IL-1β levels. Male sex, increased BMI and smoking were associated with greater IL-6 levels, while no relationship was found for age and leisure-time PA. Male sex, greater age, increased BMI and current smoking were associated with greater TNF-α levels, while no relationship was found with leisure-time PA. CRP levels were positively related to age, BMI and smoking, and inversely to male sex and physical activity.Conclusion
Population-based levels of several cytokines were established. Increased age and BMI, and to a lesser degree sex and smoking, significantly and differentially impact cytokine levels, while leisure-time physical activity has little effect. 相似文献209.
Influence of drought on plant performance through changes in belowground tritrophic interactions 下载免费PDF全文
Anouk Guyer Bruce E. Hibbard Annelie Holzkämper Matthias Erb Christelle A. M. Robert 《Ecology and evolution》2018,8(13):6756-6765
Climate change is predicted to increase the risk of drought in many temperate agroecosystems. While the impact of drought on aboveground plant‐herbivore‐natural enemy interactions has been studied, little is known about its effects on belowground tritrophic interactions and root defense chemistry. We investigated the effects of low soil moisture on the interaction between maize, the western corn rootworm (WCR, Diabrotica virgifera), and soil‐borne natural enemies of WCR. In a manipulative field experiment, reduced soil moisture and WCR attack reduced plant performance and increased benzoxazinoid levels. The negative effects of WCR on cob dry weight and silk emergence were strongest at low moisture levels. Inoculation with entomopathogenic nematodes (EPNs, Heterorhabditis bacteriophora) was ineffective in controlling WCR, and the EPNs died rapidly in the warm and dry soil. However, ants of the species Solenopsis molesta invaded the experiment, were more abundant in WCR‐infested pots and predated WCR independently of soil moisture. Ant presence increased root and shoot biomass and was associated with attenuated moisture‐dependent effects of WCR on maize cob weight. Our study suggests that apart from directly reducing plant performance, drought can also increase the negative effects of root herbivores such as WCR. It furthermore identifies S. molesta as a natural enemy of WCR that can protect maize plants from the negative impact of herbivory under drought stress. Robust herbivore natural enemies may play an important role in buffering the impact of climate change on plant‐herbivore interactions. 相似文献
210.