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   490388篇
  免费   51981篇
  国内免费   366篇
  542735篇
  2018年   4893篇
  2017年   4580篇
  2016年   6490篇
  2015年   9720篇
  2014年   10646篇
  2013年   14881篇
  2012年   17145篇
  2011年   16771篇
  2010年   10978篇
  2009年   9518篇
  2008年   14488篇
  2007年   14912篇
  2006年   13956篇
  2005年   13444篇
  2004年   13076篇
  2003年   12338篇
  2002年   11978篇
  2001年   20024篇
  2000年   20547篇
  1999年   16426篇
  1998年   5571篇
  1997年   5677篇
  1996年   5269篇
  1995年   5083篇
  1994年   5023篇
  1993年   4913篇
  1992年   13090篇
  1991年   12604篇
  1990年   12164篇
  1989年   11760篇
  1988年   11082篇
  1987年   10503篇
  1986年   9962篇
  1985年   10106篇
  1984年   8395篇
  1983年   7204篇
  1982年   5721篇
  1981年   5339篇
  1980年   4837篇
  1979年   8106篇
  1978年   6527篇
  1977年   5995篇
  1976年   5678篇
  1975年   6364篇
  1974年   7003篇
  1973年   6965篇
  1972年   6364篇
  1971年   5799篇
  1970年   5021篇
  1969年   4972篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Current literature related to the impact of probiotics on the incidence of gastrointestinal tract infections (GITIs) has shown mixed results and no systematic review available with pooled analysis exists. Thus, the aim of this systematic review was to provide contemporary evidence regarding the overall and strain-specific influence of probiotics in preventing GITIs among infants and children attending childcare centres. The review shortlisted 18 RCTs after screening through the initial search results of 779 articles. However, only 15 trials were deemed eligible, addressing at least one outcome in the pooled analysis. It is concluded that the supplementation of probiotics (overall effect) may reduce the risk of GITI episode by 26%, with Lacticaseibacillus paracasei, Limosilactobacillus reuteri and Lacticaseibacillus rhamnosus GG being specifically potent probiotic strains in reducing GITI episode, duration of infection and absence from childcare respectively. There is insufficient evidence to determine the effect of Bifidobacterium animalis subsp. lactis BB-12 based on the findings of the trials included in this review.  相似文献   
972.
BioControl - Blackberry (Rubus glaucus Benth.) is affected by several diseases, such as grey mould (Botrytis cinerea Pers.), downy mildew (Peronospora sp.) and anthracnose (Colletotrichum sp.),...  相似文献   
973.
Russian Journal of Bioorganic Chemistry - The full-length cDNA sequences of suppressor of cytokine signaling 5 (SOCS5) from Andrias davidianus gene, named as adSOCS5, was cloned and characterized...  相似文献   
974.
An unsuspected biomineralization process, which produces intracellular inclusions of amorphous calcium carbonate (ACC), was recently discovered in unicellular eukaryotes. These mineral inclusions, called micropearls, can be highly enriched with other alkaline-earth metals (AEM) such as Sr and Ba. Similar intracellular inclusions of ACC have also been observed in prokaryotic organisms. These comparable biomineralization processes involving phylogenetically distant microorganisms are not entirely understood yet. This review gives a broad vision of the topic in order to establish a basis for discussion on the possible molecular processes behind the formation of the inclusions, their physiological role, the impact of these microorganisms on the geochemical cycles of AEM and their evolutionary relationship. Finally, some insights are provided to guide future research.  相似文献   
975.
The Vfm quorum sensing (QS) system is preponderant for the virulence of different species of the bacterial genus Dickeya. The vfm gene cluster encodes 26 genes involved in the production, sensing or transduction of the QS signal. To date, the Vfm QS signal has escaped detection by analytical chemistry methods. However, we report here a strain-specific polymorphism in the biosynthesis genes vfmO and vfmP, which is predicted to be related to the production of different analogues of the QS signal. Consequently, the Vfm communication could be impossible between strains possessing different variants of the genes vfmO/P. We constructed three Vfm QS biosensor strains possessing different vfmO/P variants and compared these biosensors for their responses to samples prepared from 34 Dickeya strains possessing different vfmO/P variants. A pattern of specificity was demonstrated, providing evidence that the polymorphism in the genes vfmO/P determines the biosynthesis of different analogues of the QS signal. Unexpectedly, this vfmO/P-dependent pattern of specificity is linked to a polymorphism in the ABC transporter gene vfmG, suggesting an adaptation of the putative permease VfmG to specifically bind different analogues of the QS signal. Accordingly, we discuss the possible involvement of VfmG as co-sensor of the Vfm two-component regulatory system.  相似文献   
976.
Sturkenboom  H. N.  van Hattem  V. A. E.  Nieuwland  W.  Paris  F. M. A.  Magro  M.  Anthonio  R. L.  Algin  A.  Lipsic  E.  Bruwiere  E.  Van den Branden  B. J. L.  Polad  J.  Tonino  P.  Tio  R. A. 《Netherlands heart journal》2022,30(2):96-105
Netherlands Heart Journal - The current study aimed to evaluate changes in treatment delay and outcome for ST-segment elevation myocardial infarction (STEMI) in the Netherlands during the first...  相似文献   
977.
Netherlands Heart Journal - To compare early clinical outcomes after transcatheter aortic valve implantation (TAVI) with three consecutive generations of self-expanding valves (SEVs). Clinical...  相似文献   
978.
Neurochemical Research - Parkinson’s disease (PD) is one of the most common forms of neurodegenerative diseases and research on potential therapeutic agents for PD continues. Rotenone is a...  相似文献   
979.
acta ethologica - The Brazilian ruby, Heliodoxa rubricauda, is a forest species of hummingbird endemic to the Atlantic Forest. It belongs to an Andean clade of birds with robust and strong legs and...  相似文献   
980.
Journal of Applied Phycology - Microalgal biotechnology still needs to alleviate the productivity bottleneck before achieving the full extent of its promises. With this goal in mind, many studies...  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