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   36971篇
  免费   3480篇
  国内免费   9篇
  40460篇
  2023年   158篇
  2022年   331篇
  2021年   721篇
  2020年   381篇
  2019年   503篇
  2018年   652篇
  2017年   596篇
  2016年   925篇
  2015年   1595篇
  2014年   1741篇
  2013年   2095篇
  2012年   2937篇
  2011年   2893篇
  2010年   1796篇
  2009年   1674篇
  2008年   2346篇
  2007年   2328篇
  2006年   2081篇
  2005年   2113篇
  2004年   2000篇
  2003年   1831篇
  2002年   1783篇
  2001年   431篇
  2000年   329篇
  1999年   412篇
  1998年   488篇
  1997年   323篇
  1996年   290篇
  1995年   279篇
  1994年   246篇
  1993年   235篇
  1992年   229篇
  1991年   221篇
  1990年   214篇
  1989年   226篇
  1988年   182篇
  1987年   146篇
  1986年   164篇
  1985年   174篇
  1984年   202篇
  1983年   176篇
  1982年   170篇
  1981年   182篇
  1980年   168篇
  1979年   118篇
  1978年   135篇
  1977年   124篇
  1976年   85篇
  1974年   107篇
  1973年   80篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
Via Oswalt’s system of classification, I compare the tool-kits of wild and captive capuchins with those of Tanzanian chimpanzees and Tasmanian aborigines. The results indicate that capuchins have tool-kits that are smaller, and have lower ratios of artifacts to naturefacts, than those of Tanzanian chimpanzees and Tasmanian aborigines. Accordingly, Oswalt’s system can be used productively to assess the relative technological skills of monkeys versus those of apes and humans.  相似文献   
44.
High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180°C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2, 4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed.  相似文献   
45.
46.
Strategies for signal amplification in nucleic acid detection   总被引:3,自引:0,他引:3  
Many aspects of molecular genetics necessitate the detection of nucleic acid sequences. Current approaches involving target amplification (in situ PCR, Primed in situ Labeling, Self-Sustained Sequence Replication, Strand Displacement Amplification), probe amplification (Ligase Chain Reaction, Padlock Probes, Rolling Circle Amplification) and signal amplification (Tyramide Signal Amplification, Branched DNA Amplification) are summarized in the present review, together with their advantages and limitations.  相似文献   
47.
Using two-dimensional polyacrylamide gel electrophoresis, the GroEL homologue ofBacillus subtilis was shown to be induced upon infection with Ø105clz, a clear plaque mutant of the temperate bacteriophage Ø105. Western blotting of one dimensional polyacrylamide gels also showed the induction of the GroEL homologue when cells were infected with Ø105clz.  相似文献   
48.
49.
50.
Summary Microorganisms were able to remove hydrocarbons (pentane and isobutane) from air by biological action in a columnar bioreactor with ceramic packing. The reactor was operated in a liquid continuous mode with gas recirculation and a slow addition of the organic-containing air. After a period of acclimation, the reactor has operated for 12 months with only pentane and isobutane as carbon sources. The gaseous hydrocarbons have been degraded throughout this period. The hydrocarbon removal rates measured between 1 and 2 g h–1 m–3. The microbes were shown to be able to degrade these gaseous hydrocarbons completely in a closed bioreactor without any additional nutrients.Research supported by the Advanced Industrial Concepts Division-Biological and Chemical Technologies Research. U.S. Department of Energy, under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems. Inc.  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