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   1408651篇
  免费   124805篇
  国内免费   1413篇
  2021年   18473篇
  2020年   13103篇
  2019年   16721篇
  2018年   18998篇
  2017年   17687篇
  2016年   29468篇
  2015年   43994篇
  2014年   51956篇
  2013年   78796篇
  2012年   40819篇
  2011年   29420篇
  2010年   45462篇
  2009年   46462篇
  2008年   27270篇
  2007年   25015篇
  2006年   30019篇
  2005年   30530篇
  2004年   29714篇
  2003年   27105篇
  2002年   25184篇
  2001年   36120篇
  2000年   33532篇
  1999年   33254篇
  1998年   25967篇
  1997年   25678篇
  1996年   25166篇
  1995年   23294篇
  1994年   23091篇
  1993年   22234篇
  1992年   28719篇
  1991年   26870篇
  1990年   25760篇
  1989年   26634篇
  1988年   24310篇
  1987年   23136篇
  1986年   21941篇
  1985年   23755篇
  1984年   23380篇
  1983年   20613篇
  1982年   20907篇
  1981年   20008篇
  1980年   18857篇
  1979年   19472篇
  1978年   18263篇
  1977年   17345篇
  1976年   16579篇
  1975年   16158篇
  1974年   16479篇
  1973年   16825篇
  1972年   14223篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
992.
993.
A computer simulation model was developed to investigate nitrogenfluxes associated with microbial interactions in plankton communities.A short time scale was used, appropriate to the build-up anddecline of phytoplankton blooms in temperate shelf waters aftera mixing or upwelling event. The model depicts a continuum ofevents, many of which have been observed in coastal, upwellingand oceanic systems, including two phytoplankton peaks correspondingto ‘new production’ and ‘regenerated production’.It predicts that nitrogen loss through sedimentation of phytoplanktonand faeces may result in a smaller bloom with a delayed onsetand prolonged duration. Microbial regeneration of nitrogen wasfound to be important in sustaining the middle stages of a phytoplanktonbloom, whereas micro- and meso-zooplankton regeneration occurredtowards the end of the bloom.  相似文献   
994.
Volatiles from the epicuticular wax of watercress were collected by ether washing and examined using gas chromatographic and mass spectrometric analysi  相似文献   
995.
Ciliated tracheal epithelia cell cultures were investigated immunocytochemically with anti-tubulin and colloidal gold. When rabbit tracheal cultures were fixed in paraformaldehyde, treated with acetone, anti-tubulin and a second antibody coupled to FITC, fluorescence was associated with cytoskeletal and axonemal microtubules. Cilia covering the apical surface of the ciliated tracheal cells fluoresced very brightly thus facilitating identification of this cell type. Electron microscopy of tracheal cultures fixed as above, treated with Triton-X 100 and incubated in anti-tubulin and protein A coupled to colloidal gold resulted in the highly specific localization of tubulin in ciliary axonemes and basal bodies. Omission of primary or secondary antibody resulted in extremely low levels of fluorescence while no colloidal gold particles could be detected in cultures at the electron microscopy level when rabbit anti-tubulin was omitted.  相似文献   
996.
997.
The distribution of regular secondary structures, viz. α-helices and β-strands, along the length of over 70 properties whose secondary structural details have been reported, has been analysed. The occurrence of these regular structures tends to be a maximum at the N- and C-termini. Our analysis suggests that both these free ends could possibly serve as nucleating centers for secondary structures and could play an important role in the folding of proteins.  相似文献   
998.
The flavonoids of five Geranium, fourteen Erodium and four Monsonia species were studied. Quercetin was the most common aglycone with lesse  相似文献   
999.
The 5'-terminal 597 base-pairs (bp) of the Sprague-Dawley rat 18S ribosomal RNA gee and 10 bp of the adjoining transcribed spacer have been sequenced. Previously sequenced 10 large oligonucleotides of rat 18S RNA were located in this region. This mammalian sequence has been compared with the known sequences of yeast and frog 18S rDNA's. The analysis indicates that 534 bp of the 597 bp (89%) are conserved between rat and frog sequences but only 75% of the nucleotides are conserved between rat and yeast in this region. Two large and two small sections have been identified where insertions have been introduced during evolution. Of these 58 bp long inserted sections of the rat rDNA sequence, 50 bp (86%) were G-C base-pairs.  相似文献   
1000.
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