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   1377629篇
  免费   123841篇
  国内免费   1420篇
  2021年   17923篇
  2019年   16218篇
  2018年   17926篇
  2017年   16726篇
  2016年   28294篇
  2015年   42645篇
  2014年   50599篇
  2013年   76962篇
  2012年   38049篇
  2011年   26601篇
  2010年   43908篇
  2009年   45249篇
  2008年   25279篇
  2007年   23233篇
  2006年   28417篇
  2005年   29464篇
  2004年   28619篇
  2003年   26120篇
  2002年   24319篇
  2001年   35300篇
  2000年   32796篇
  1999年   32725篇
  1998年   25805篇
  1997年   25584篇
  1996年   25068篇
  1995年   23197篇
  1994年   23049篇
  1993年   22181篇
  1992年   28526篇
  1991年   26697篇
  1990年   25602篇
  1989年   26469篇
  1988年   24168篇
  1987年   23001篇
  1986年   21797篇
  1985年   23661篇
  1984年   23228篇
  1983年   20550篇
  1982年   20879篇
  1981年   19997篇
  1980年   18841篇
  1979年   19433篇
  1978年   18220篇
  1977年   17325篇
  1976年   16596篇
  1975年   16107篇
  1974年   16407篇
  1973年   16758篇
  1972年   14152篇
  1971年   12856篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
991.
992.
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   
993.
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   
994.
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   
995.
996.
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   
997.
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   
998.
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   
999.
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