首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   21378篇
  免费   1634篇
  国内免费   1546篇
  24558篇
  2024年   56篇
  2023年   250篇
  2022年   657篇
  2021年   1161篇
  2020年   764篇
  2019年   932篇
  2018年   906篇
  2017年   672篇
  2016年   946篇
  2015年   1296篇
  2014年   1564篇
  2013年   1713篇
  2012年   1886篇
  2011年   1753篇
  2010年   1079篇
  2009年   984篇
  2008年   1129篇
  2007年   1001篇
  2006年   856篇
  2005年   739篇
  2004年   566篇
  2003年   546篇
  2002年   446篇
  2001年   322篇
  2000年   325篇
  1999年   325篇
  1998年   189篇
  1997年   170篇
  1996年   181篇
  1995年   175篇
  1994年   158篇
  1993年   116篇
  1992年   158篇
  1991年   113篇
  1990年   110篇
  1989年   77篇
  1988年   54篇
  1987年   46篇
  1986年   35篇
  1985年   35篇
  1984年   17篇
  1983年   15篇
  1982年   17篇
  1981年   7篇
  1980年   4篇
  1979年   2篇
  1978年   1篇
  1975年   2篇
  1966年   1篇
  1950年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
104.
Yang  Z. T.  Lu  D. X.  Hong  E.-K.  Zhang  B. Y.  Jiang  M. C.  Yang  Y. J.  Zhang  D. J. 《Molecular Biology》2020,54(6):911-918
Molecular Biology - Brassica campestris L. is the important oil-bearing crop in China. Rapeseed cake is the main byproduct of rapeseed oil extraction. As the main active ingredient in rapeseed...  相似文献   
105.
106.
Cobalt-rich crusts are important metallic mineral resources with great economic potential, usually distributed on seamounts located in the Pacific Ocean. Microorganisms are believed to play a role in the formation of crusts as well as in metal cycling. To explore the microbial diversity related to cobalt-rich crusts, 16S ribosomal RNA gene clone libraries were constructed from three consecutive sediment layers. In total, 417 bacterial clones were obtained from three bacterial clone libraries, representing 17 distinct phylogenetic groups. Proteobacteria dominated in the bacterial communities, followed by Acidobacteria and Planctomycetes. Compared with high bacterial diversity, archaea showed a remarkably low diversity, with all 137 clones belonging to marine archaeal group I except one novel euryarchaeotal clone. The microbial communities were potentially involved in sulfur, nitrogen and metal cycling in the area of cobalt-rich crusts. Sulfur oxidation and metal oxidation were potentially major sources of energy for this ecosystem. This is the first reported investigation of microbial diversity in sediments associated with cobalt-rich crusts, and it casts fresh light on the microbial ecology of these important ecosystems.  相似文献   
107.
Sexual plant reproduction is a critical developmental step in the life cycle of higher plants, to allow maternal and paternal genes to be transmitted in a highly regulated manner to the next generation. During evolution, a whole set of signal transduction machinery is developed by plants to ensure an error-free recognition between male and female gametes and initiation of zygotic program. In the past few years, the molecular machineries underlying this biological process have been elucidated, particularly on the importance of synergid cells in pollen tube guidance, the Ca++ spike as the immediate response of fertilization and the epigenetic regulation of parental gene expressions in early zygotic embryogenesis. This review outlines the most recent development in this area.  相似文献   
108.
An inhibitor-tolerance strain, Bacillus coagulans GKN316, was developed through atmospheric and room temperature plasma (ARTP) mutation and evolution experiment in condensed dilute-acid hydrolysate (CDH) of corn stover. The fermentabilities of other hydrolysates with B. coagulans GKN316 and the parental strain B. coagulans NL01 were assessed. When using condensed acid-catalyzed steam-exploded hydrolysate (CASEH), condensed acid-catalyzed liquid hot water hydrolysate (CALH) and condensed acid-catalyzed sulfite hydrolysate (CASH) as substrates, the concentration of lactic acid reached 45.39, 16.83, and 18.71 g/L by B. coagulans GKN316, respectively. But for B. coagulans NL01, only CASEH could be directly fermented to produce 15.47 g/L lactic acid. The individual inhibitory effect of furfural, 5-hydroxymethylfurfural (HMF), vanillin, syringaldehyde and p-hydroxybenzaldehyde (pHBal) on xylose utilization by B. coagulans GKN316 was also studied. The strain B. coagulans GKN316 could effectively convert these toxic inhibitors to the less toxic corresponding alcohols in situ. These results suggested that B. coagulans GKN316 was well suited to production of lactic acid from undetoxified lignocellulosic hydrolysates.  相似文献   
109.
The TALE homeodomain-containing PBC and MEIS proteins play multiple roles during metazoan development. Mutations in these proteins can cause various disorders, including cancer. In this study, we examined the roles of MEIS proteins in mesoderm development in C. elegans using the postembryonic mesodermal M lineage as a model system. We found that the MEIS protein UNC-62 plays essential roles in regulating cell fate specification and differentiation in the M lineage. Furthermore, UNC-62 appears to function together with the PBC protein CEH-20 in regulating these processes. Both unc-62 and ceh-20 have overlapping expression patterns within and outside of the M lineage, and they share physical and regulatory interactions. In particular, we found that ceh-20 is genetically required for the promoter activity of unc-62, providing evidence for another layer of regulatory interactions between MEIS and PBC proteins.  相似文献   
110.

Background and Purpose

Growing evidence has emerged and controversial results reported on possible relationship between aspirin use and lung cancer risk. We, therefore, conducted this updated and comprehensive meta-analysis to evaluate this issue, with focus on dose-risk and duration-risk relationships.

Methods

We searched electronic databases including PUBMED, EMBASE and Cochrane library to identify eligible studies. Relative risk (RR) and its 95% confidence interval (CI) were used for cohort studies, while odds ratio (OR) were employed for case-control studies. The random effects and fixed effects models were used for analyses.

Results

18 studies were identified including 19835 lung cancer cases, which were eligible for inclusion in the present meta-analysis. Pooled data from case-control studies showed a significant inverse association between regular aspirin use and lung cancer risk. But for cohort studies, insignificant association was detected with little evidence of heterogeneity (RR: 1.05, 95%CI: 0.95 – 1.16; I2: 10.3%, p value: 0.351). In case-control studies, standard aspirin use (>325mg) was related to lower lung cancer incidence, compared with low-dose aspirin use (75–100mg). A similar trend was observed in cohort studies. Besides, when analysis was restricted to long time regular aspirin use (>5 years), insignificant results were reported in both cohort and case-control studies. Finally, regular aspirin use might result in higher reduction of non-small cell lung cancer incidence among men.

Conclusions

Our findings do not support the protective effect of regular aspirin use on lung cancer risk. Long time aspirin use, sex, dose and type of lung cancer might alter the effect of aspirin use on lung cancer risk. More well-designed studies are needed to further clarify these associations.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号