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   821790篇
  免费   182433篇
  国内免费   30072篇
  2018年   8886篇
  2017年   8388篇
  2016年   11352篇
  2015年   15327篇
  2014年   17218篇
  2013年   23770篇
  2012年   26923篇
  2011年   27511篇
  2010年   20523篇
  2009年   23461篇
  2008年   25401篇
  2007年   25900篇
  2006年   23185篇
  2005年   22500篇
  2004年   22165篇
  2003年   21028篇
  2002年   21082篇
  2001年   38392篇
  2000年   36898篇
  1999年   33512篇
  1998年   16898篇
  1997年   16495篇
  1996年   15686篇
  1995年   15210篇
  1994年   14837篇
  1993年   14346篇
  1992年   28313篇
  1991年   27222篇
  1990年   27359篇
  1989年   26760篇
  1988年   24187篇
  1987年   22914篇
  1986年   21193篇
  1985年   20829篇
  1984年   17123篇
  1983年   14769篇
  1982年   12186篇
  1981年   10937篇
  1980年   10468篇
  1979年   16052篇
  1978年   12722篇
  1977年   11716篇
  1976年   11114篇
  1975年   11556篇
  1974年   12515篇
  1973年   12315篇
  1972年   11482篇
  1971年   10495篇
  1970年   9135篇
  1969年   8800篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
182.
The selective action of the antibiotics chloramphenicol and cycloheximide on the synthesis of ferredoxin in liquid cultures of Chlamydomonas reinhardii was studied. Highly specific antibodies raised against Chlamydomonas ferredoxin were used to determine the in vivo synthesis of apoferredoxin and conversion into native protein. The results indicate that 80S ribosomes are involved in the synthesis. Chlamydomonas cells growing in the absence of iron did not synthesize immunologically detectable amounts of ferredoxin. We suggest that this is based upon feed-back inhibition of apoferredoxin synthesis at the translational level.Abbreviations CAP chloramphenicol - CHI cycloheximide - IgG Immunoglobulin G - PBS 140.4 mM NaCl. 9 mM Na2HPO4, 1.3 mM NaH2PO4 (pH 74) - SDS sodium dodecvl sulphate - Fd Ferredoxin - apoFd Apoferredoxin - CM-Fd Scarboxymethylated Fd - TCA-Fd Fd treated with trichloroacetic acid  相似文献   
183.
Chromatophores from Rhodopseudomonas capsulata cells grown semiaerobically in the dark oxidize NADH, succinate, and dichlorophenolindophenol. In the presence of N3? these activities are inhibited, but light induces oxidation of dichlorophenolindophenol with O2 as a terminal electron acceptor. Cyanide also inhibits electron transport but much higher concentrations are required to inhibit the photooxidation than the dark oxidation. The photooxidation was studied in a mutant strain of Rhodopseudomonas capsulata (YIV) which cannot grow anaerobically in the light, but similarly to the wild type, grows in the presence of oxygen. Chromatophores from YIV mutant catalyze photophosphorylation and dark oxidation activities with the same properties as those of the wild type. However, the rate of photooxidation in the mutant is only one-third that of the wild type. Based on the differential inhibitor sensitivity and on the mutation it is suggested that the photooxidase is different from the two respiratory oxidases and that this photooxidation activity might be essential for growth of the cells under anaerobic conditions in the light.  相似文献   
184.
185.
An apparatus for polyacrylamide slab gel electrophoresis is decribed which combines all parts into one integral unit. It eliminates several steps in the process of sealing, pouring, and setting the gels. Construction is easy with modest workshop facilities and the design easily adapted to suit most requirements. The apparatus provides a high degree of versatility and is suitable for use with many slab gel electrophoretic techniques.  相似文献   
186.
187.
188.
Conditions for breaking various medically important yeasts using glass beads, 30 ml Corex centrifuge tubes, and a Vortex mixer were determined. From 75–95% ofCandida hyphal cells and all species of yeasts exceptSporothrix schenckii were broken when 10 g of 0.45–0.50 mm glass beads, 50–300 mg of wet cells in 5 ml of buffer, and 90 s of vortexing were employed. Yeasts ofSporothrix schenckii broke more efficiently when 0.25–0.30 mm beads were used.  相似文献   
189.
190.
A random sample of schoolchildren, 119 boys and 153 girls, was tested in the fall of 1983. The data presented here are anthropometric data (height, weight, fat % and vital capacity) and oxygen uptake directly measured on a bicycle ergometer. The mean height and weight for boys were 179.1 cm and 67.7 kg, and those for girls were 168.0 cm and 59.6 kg. The mean fat content was 9.1% for boys and 19.1% for girls, and their mean vital capacities were 4.91 and 3.61 respectively. The boys had a high maximal oxygen uptake (51.7 ml X kg-1 X min-1) showing no reduction over the age span studied. The girls' maximal oxygen uptake was lower (overall mean 40.0 ml X kg-1 X min-1) with a small reduction from 16 to 19 years of age. When comparing maximal oxygen uptake per kg lean body mass in the two sexes, the boys had 18.4% higher values than the girls, indicating that girls of this age have the lower fitness level. The results of maximal aerobic power measurement in the boys compare well with findings from other investigations using direct measurements, indicating that the fitness of teenage boys is kept at a high level. Comparable data from various countries for girls show different pictures, but it appears that in general they have a low fitness level.  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