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   8046篇
  免费   747篇
  国内免费   3篇
  2023年   30篇
  2022年   57篇
  2021年   176篇
  2020年   102篇
  2019年   130篇
  2018年   146篇
  2017年   136篇
  2016年   254篇
  2015年   412篇
  2014年   424篇
  2013年   532篇
  2012年   652篇
  2011年   674篇
  2010年   394篇
  2009年   371篇
  2008年   537篇
  2007年   514篇
  2006年   475篇
  2005年   434篇
  2004年   404篇
  2003年   373篇
  2002年   354篇
  2001年   58篇
  2000年   47篇
  1999年   73篇
  1998年   82篇
  1997年   73篇
  1996年   74篇
  1995年   51篇
  1994年   32篇
  1993年   41篇
  1992年   33篇
  1991年   73篇
  1990年   50篇
  1989年   30篇
  1988年   30篇
  1987年   25篇
  1986年   22篇
  1985年   40篇
  1984年   33篇
  1983年   27篇
  1982年   30篇
  1981年   27篇
  1980年   34篇
  1979年   13篇
  1977年   19篇
  1976年   16篇
  1975年   16篇
  1974年   16篇
  1973年   15篇
排序方式: 共有8796条查询结果,搜索用时 0 毫秒
51.
Summary Earlier studies found that cotton (Gossypium hirsutum L.) cotyledons contain several mRNAs which are more abundant during late embryogenesis than in mid-embryogenesis or early germination. They are here termed Late embryogenesis-abundant mRNAs, encoded by Lea loci. Complementary DNA clones for 18 such mRNA sequences, defined at a hybridization criterion of Tm-15°C, were identified in a mature embryo cDNA library by differential cDNA hybridization. At a lower hybridization criterion, some sequence homology was found within several of these cloned Lea mRNA sequences. Each Lea mRNA sequence comprises 0.04–1.3% of mature embryo poly(A)+ mRNA, a level ten-fold to several hundred-fold higher than in young embryo or 24 h seedling poly(A)+ mRNA. Of 18 Lea mRNA sequences examined in cultured young embryos, the level of at least 13 are specifically increased by exogenous abscisic acid (ABA), several to a level near that in normal mature embryos. However, the abundance of several of the sequences does not appear to be significantly modulated by ABA. The LEA polypeptides encoded by 10 Lea mRNA sequences were identified by hybrid-arrested translation. They include most of the late embryogenesis-abundant, ABA-inducible, polypeptides previously identified. Preliminary results suggest that many of the individual Lea mRNA sequences are transcribed from 1–3 genes in each of cotton's two subgenomes.  相似文献   
52.
Thirty-nine isolates of Cryptococcus neoformans, nineteen serotype AD and twenty serotype BC, were assayed for susceptibility to eight antifungal agents using an in vitro agar dilution assay. Media employed were Kimmig agar and yeast nitrogen base supplemented with 10% glucose. The antifungal agents used were ketoconazole, amphotericin B, 5-fluorocytosine, nystatin, miconazole, BAY N 7133, ICI 153,066, and itraconazole. No clinically significant differences in in vitro minimum inhibitory concentrations were detected between serotypes AD and BC against any of the compounds tested. An adverse medium effect was observed in two of the assays, but the outcome of the AD/BC comparison was not affected. This is the first report in which the in vitro antifungal susceptibilities of Cryptococcus neoformans serotypes are analyzed.  相似文献   
53.
The polymeric dyes Poly B-411, Poly R-481, and Poly Y-606 were examined as possible alternatives to the radiolabeled lignin previously used as a substrate in lignin biodegradation assays. Like lignin degradation, the decolorization of these dyes by the white rot basidiomycete Phanerochaete chrysosporium occurred during secondary metabolism, was suppressed in cultures grown in the presence of high levels of nitrogen, and was strongly dependent on the oxygen concentration in the cultures. A variety of inhibitors of lignin degradation, including thiourea, azide, and 4′-O-methylisoeugenol, also inhibited dye decolorization. A pleiotropic mutant of P. chrysosporium, 104-2, lacking phenol oxidase and ligninolytic activity was also not able to decolorize the polymeric dyes, whereas a phenotypic revertant strain, 424-2, regained this capacity. All of these results suggest that the ligninolytic degradation activity of the fungus was responsible for the decolorization of these dyes.  相似文献   
54.
Plant Molecular Biology - DNAs complementary to the mRNAs coding for the major cotton 48 kD and 52 kD storage proteins have been cloned and used to characterize the principal cotton storage protein...  相似文献   
55.
56.
Streptomycin resistance in Rhizobium japonicum   总被引:1,自引:0,他引:1  
Mutants resistant to varying concentrations of streptomycin were recovered from two streptomycin-sensitive, effective nitrogen-fixing strains of Rhizobium japonicum. To determine if there were an upper limit of resistible antibiotic concentration, 3 mutants which were resistant to 10000 μg/ml were challenged by higher concentrations of streptomycin. Only one grew well at 25000 μg/ml, and none grew at 50000 μg/ml. All mutants maintained a smooth colonial morphology, and none exhibited streptomycin-dependence. Streptomycin-resistant mutants of both strains were examined for properties of infectivity and effectiveness. All mutants tested retained the symbiotic properties of the parental strains. The retention of these parental properties by the streptomycin-resistant mutants of R. japonicum is different from the properties described for phenotypically similar mutants in certain other rhizobial species.  相似文献   
57.
Bacterial extracts prepared by ultrasonic disruption were reacted with both narrow- and broad-spectrum reference (homologous) and cross-reacting (heterologous) precipitins produced in rabbits. Quantitation of the reaction was obtained by densitometry of the antigen-antibody interface. Comparisons were made of sonic extracts from various starting populations all equated to the same nitrogen concentrations, and of various nitrogen levels derived from five bacterial population levels prepared separately. Sources of error are probed to show under what circumstances cross-reactions would be of greater magnitude than reference ones. The feasibility was shown of using quantitative densitometry of the interface combined with broadly reacting precipitins to identify bacteria on an intergeneric and interspecies scale. Problems associated with the use of absorbed or monospecific precipitins are explained.  相似文献   
58.
59.
60.
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