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   48299篇
  免费   17306篇
  国内免费   645篇
  2023年   137篇
  2022年   298篇
  2021年   924篇
  2020年   2469篇
  2019年   4061篇
  2018年   4247篇
  2017年   4375篇
  2016年   4623篇
  2015年   5019篇
  2014年   4784篇
  2013年   5429篇
  2012年   3452篇
  2011年   3145篇
  2010年   4007篇
  2009年   2598篇
  2008年   1860篇
  2007年   1391篇
  2006年   1338篇
  2005年   1309篇
  2004年   1219篇
  2003年   1119篇
  2002年   1029篇
  2001年   917篇
  2000年   785篇
  1999年   690篇
  1998年   282篇
  1997年   247篇
  1996年   224篇
  1995年   202篇
  1994年   186篇
  1993年   150篇
  1992年   334篇
  1991年   306篇
  1990年   258篇
  1989年   278篇
  1988年   236篇
  1987年   192篇
  1986年   190篇
  1985年   210篇
  1984年   151篇
  1983年   138篇
  1982年   113篇
  1981年   116篇
  1979年   139篇
  1978年   107篇
  1977年   94篇
  1976年   84篇
  1975年   106篇
  1974年   108篇
  1973年   93篇
排序方式: 共有10000条查询结果,搜索用时 611 毫秒
61.
Five polymorphic microsatellite loci were characterized for Penaeus (Litopenaeus) vannamei. Loci were isolated using a partial Sau3A1 genomic library by the sequencing of randomly selected clones and by a biotinylated (CT)10 and (GT)10 probes screening procedure. The last strategy resulted in the most useful data. About 40% of the clones showed a previously reported satellite/microsatellite (PVS1), reducing the chance of finding new microsatellite regions. Whereas two of the microsatellite loci with more than 10 alleles will be useful for mating analysis in a breeding program, the others might prove useful for population genetic studies.  相似文献   
62.
63.
64.
65.
An enzymatic activity present in high-speed supernatant fluids of rat skeletal muscle was found that catalyzes the release of ADP-ribose from ADP-ribosylated-modified lysozyme. The nature of the product was proved by chromatographic studies and proton nuclear magnetic resonance spectroscopy. The enzyme activity is stimulated by Mg2+, dithioerythritol, and flouride. These results and those published earlier (Soman, G., Mickelson, J.R., Louis, C.F., and Graves, D.J. (1984) Biochem. Biophys. Res. Commun. 120, 973-980) show that ADP-ribosylation is a reversible process in skeletal muscle.  相似文献   
66.
  1. Shifts in dominance and species reordering can occur in response to global change. However, it is not clear how altered precipitation and disturbance regimes interact to affect species composition and dominance.
  2. We explored community‐level diversity and compositional similarity responses, both across and within years, to a manipulated precipitation gradient and annual clipping in a mixed‐grass prairie in Oklahoma, USA. We imposed seven precipitation treatments (five water exclusion levels [?20%, ?40%, ?60%, ?80%, and ?100%], water addition [+50%], and control [0% change in precipitation]) year‐round from 2016 to 2018 using fixed interception shelters. These treatments were crossed with annual clipping to mimic hay harvest.
  3. We found that community‐level responses were influenced by precipitation across time. For instance, plant evenness was enhanced by extreme drought treatments, while plant richness was marginally promoted under increased precipitation.
  4. Clipping promoted species gain resulting in greater richness within each experimental year. Across years, clipping effects further reduced the precipitation effects on community‐level responses (richness and evenness) at both extreme drought and added precipitation treatments.
  5. Synthesis: Our results highlight the importance of studying interactive drivers of change both within versus across time. For instance, clipping attenuated community‐level responses to a gradient in precipitation, suggesting that management could buffer community‐level responses to drought. However, precipitation effects were mild and likely to accentuate over time to produce further community change.
  相似文献   
67.
68.
69.
70.
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