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   1164399篇
  免费   127014篇
  国内免费   817篇
  2018年   10959篇
  2017年   10357篇
  2016年   14939篇
  2015年   20145篇
  2014年   23740篇
  2013年   34117篇
  2012年   38009篇
  2011年   38552篇
  2010年   26179篇
  2009年   24086篇
  2008年   33980篇
  2007年   35021篇
  2006年   32977篇
  2005年   31826篇
  2004年   31489篇
  2003年   30187篇
  2002年   29274篇
  2001年   53843篇
  2000年   54041篇
  1999年   42880篇
  1998年   15144篇
  1997年   15795篇
  1996年   14741篇
  1995年   13765篇
  1994年   13334篇
  1993年   13242篇
  1992年   35095篇
  1991年   33995篇
  1990年   33092篇
  1989年   32133篇
  1988年   29850篇
  1987年   28060篇
  1986年   26077篇
  1985年   25872篇
  1984年   21556篇
  1983年   18095篇
  1982年   13785篇
  1981年   12385篇
  1980年   11646篇
  1979年   19846篇
  1978年   15447篇
  1977年   14042篇
  1976年   12780篇
  1975年   14131篇
  1974年   15191篇
  1973年   14969篇
  1972年   13536篇
  1971年   12314篇
  1970年   10599篇
  1969年   10169篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
Murina  M. A.  Roshchupkin  D. I.  Sergienko  V. I. 《Biophysics》2021,66(4):535-540
Biophysics - A technology has been developed for the preparation of novel chloramine compounds related to adenosine derivatives. The optical absorption characteristics of...  相似文献   
982.
Glushakova  A. M.  Lysak  L. V.  Kachalkin  A. V.  Ivanova  A. E.  Umarova  A. B.  Abramyan  I. A.  Ezhelev  Z. S.  Maksimova  I. A. 《Microbiology》2021,90(2):176-186
Microbiology - In a model experiment, the transformation of microbial complexes of cultivated saprotrophic bacteria and yeasts during freezing-thawing was studied in various natural substrates that...  相似文献   
983.
Microbiology - The surface of the MA8 magnesium alloy, modified by laser treatment, was found to acquire superhydrophilic properties and high bactericidal activity against Escherichia coli K12...  相似文献   
984.
Islam  M.D. Dhin  Price  Adam H.  Hallett  Paul D. 《Plant and Soil》2021,467(1-2):515-530
Plant and Soil - Cracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research...  相似文献   
985.
Journal of Evolutionary Biochemistry and Physiology - A study of the effect of a seasonal decrease in ambient temperature on the composition of free amino acids and ninhydrin-positive secondary...  相似文献   
986.
Journal of Evolutionary Biochemistry and Physiology - Due to a high occurrence of diabetes mellitus (DM) and its complications, insulin-positive cells detected in different organs are of great...  相似文献   
987.
Journal of Evolutionary Biochemistry and Physiology - Changes in bioelectrical impedance of the myocardium and liver were revealed in male Wistar rats chronically exposed to doxorubicin....  相似文献   
988.
989.
Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a key enzyme in the protection of biomembranes exposed to oxidative stress. We investigated the role of mitochondrial PHGPx in apoptosis using RBL2H3 cells that overexpressed mitochondrial PHGPx (M15 cells), cells that overexpressed non-mitochondrial PHGPx (L9 cells), and control cells (S1 cells). The morphological changes and fragmentation of DNA associated with apoptosis occurred within 15 h in S1 and L9 cells upon exposure of cells to 2-deoxyglucose (2DG). The release of cytochrome c from mitochondria was observed in S1 cells after 4 h and was followed by the activation of caspase-3 within 6 h. Overexpression of mitochondrial PHGPx prevented the release of cytochrome c, the activation of caspase-3, and apoptosis, but non-mitochondrial PHGPx lacked the ability to prevent the induction of apoptosis by 2DG. An ability to protect cells from 2DG-induced apoptosis was abolished when the PHGPx activity of M15 cells was inhibited by diethylmalate, indicating that the resistance of M15 cells to apoptosis was indeed due to the overexpression of PHGPx in the mitochondria. The expression of members of the Bcl-2 family of proteins, such as Bcl-2, Bcl-xL, Bax, and Bad, was unchanged by the overexpression of PHGPx in cells. The levels of hydroperoxides, including hydrogen and lipid peroxide, in mitochondria isolated from S1 and L9 cells were significantly increased after the exposure to 2DG for 2 h, while the level of hydroperoxide in mitochondria isolated from M15 cells was lower than that in S1 and L9 cells. M15 cells were also resistant to apoptosis induced by etoposide, staurosporine, UV irradiation, cycloheximide, and actinomycin D, but not to apoptosis induced by Fas-specific antibodies, which induces apoptosis via a pathway distinct from the pathway initiated by 2DG. Our results suggest that hydroperoxide, produced in mitochondria, is a major factor in apoptosis and that mitochondrial PHGPx might play a critical role as an anti-apoptotic agent in mitochondrial death pathways.  相似文献   
990.
Improving our knowledge of the links between ecology and evolution is especially critical in the actual context of global rapid environmental changes. A critical step in that direction is to quantify how variation in ecological factors linked to habitat modifications might shape observed levels of genetic variability in wild populations. Still, little is known on the factors affecting levels and distribution of genetic diversity at the individual level, despite its vital underlying role in evolutionary processes. In this study, we assessed the effects of habitat quality on population structure and individual genetic diversity of tree swallows (Tachycineta bicolor) breeding along a gradient of agricultural intensification in southern Québec, Canada. Using a landscape genetics approach, we found that individual genetic diversity was greater in poorer quality habitats. This counter-intuitive result was partly explained by the settlement patterns of tree swallows across the landscape. Individuals of higher genetic diversity arrived earlier on their breeding grounds and settled in the first available habitats, which correspond to intensive cultures. Our results highlight the importance of investigating the effects of environmental variability on individual genetic diversity, and of integrating information on landscape structure when conducting such 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