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   5816篇
  免费   389篇
  国内免费   3篇
  2023年   30篇
  2022年   54篇
  2021年   131篇
  2020年   91篇
  2019年   104篇
  2018年   179篇
  2017年   161篇
  2016年   225篇
  2015年   299篇
  2014年   290篇
  2013年   448篇
  2012年   476篇
  2011年   528篇
  2010年   343篇
  2009年   260篇
  2008年   300篇
  2007年   288篇
  2006年   271篇
  2005年   222篇
  2004年   191篇
  2003年   191篇
  2002年   166篇
  2001年   55篇
  2000年   54篇
  1999年   35篇
  1998年   47篇
  1997年   47篇
  1996年   49篇
  1995年   40篇
  1994年   38篇
  1993年   47篇
  1992年   37篇
  1991年   18篇
  1990年   23篇
  1989年   22篇
  1988年   20篇
  1987年   24篇
  1986年   21篇
  1985年   25篇
  1984年   25篇
  1983年   24篇
  1982年   28篇
  1981年   20篇
  1980年   24篇
  1979年   17篇
  1978年   17篇
  1977年   15篇
  1976年   15篇
  1975年   13篇
  1974年   21篇
排序方式: 共有6208条查询结果,搜索用时 281 毫秒
21.
A cDNA probe for the low density lipoprotein (LDL) receptor gene was used to screen DNA samples from 52 unrelated Finnish patients with the heterozygous form of familial hypercholesterolemia (FH) and 51 healthy controls. Southern blot analysis using the restriction enzyme PvuII revealed an abnormal 11 kb (kilo base-pair) restriction fragment in 16 (31%) of the patients but none of the controls. A more detailed restriction enzyme analysis of the DNA from patients revealed a mutation which apparently is due to an 8 kb deletion extending from intron 15 to exon 18 of the LDL receptor gene. Co-segregation of FH with the mutated gene was demonstrated in three families. These data are consistent with a ‘founder gene effect’ and support the assumption that recombinant DNA methods may have great impact on the diagnostics of FH in genetically homogeneous populations.  相似文献   
22.
Sterol composition was examined during batch growth on complex media containing ethanol, molasses or glucose as the carbon source. The molasses-grown cells exhibited a balanced sterol composition throughout growth, maintaining the proportion of ergosterol to 24:28-dehydroergosterol equal to 1.4. The negative effect of glucose on sterol synthesis manifested itself by decreasing the accumulation of 24:28-dehydroergosterol and total sterols but not of ergosterol. Using ethanol as the sole carbon source, a large amount of 24:28-dehydroergosterol accumulated, partly at the expense of other sterols. The gradual addition of nitrogen source during growth significantly decreased the accumulation of ergosterol, 24:28-dehydroergosterol and of total sterols. A general scheme of regulation of sterol synthesis in baker's yeast is presented.  相似文献   
23.
24.
25.
In submerged Claviceps cultures the activity of hydroxymethylglutaryl-CoA reductase preceded the increase of alkaloid production and of sterol content. During the first alkaloid phase, cell mevalonate was involved in the biosynthesis of both alkaloids and steroids. In the second production phase, it was predominantly used for alkaloid synthesis. Hydroxymethylglutaryl-CoA reductase appears to be a suitable target for physiological manipulation to increase clavine alkaloid yields.  相似文献   
26.
Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia).  相似文献   
27.
Summary Protoplast formation in Curvularia inaequalis was achieved using non-commercial and commercial snail gut enzymes or Trichoderma harzianum enzymes. The cells were grown for enzyme treatment on cellophane sheets or in liquid cultures for varying periods of time. The production of T. harzianum enzymes is discussed. The highest protoplast yields were 2.6x107 protoplasts/ml enzyme solution. Protoplasts were shown to have zero to four nuclei. Protoplast regeneration was succesfully carried out in semisolid agar.  相似文献   
28.
29.
    
Summary The possibility of cloning filamentous fungal genes by expression in the yeast Saccharomyces cerevisiae has been studied. A genome bank of Aspergillus niger was made in E. coli using a yeast cosmid shuttle vector and over 10,000 different cosmid clones were individually isolated. Yeast transformants carrying Aspergillus DNA were screened for the expression of the genes for fungal secreted glycoproteins, -galactosidase, -glucosidase, and amyloglucosidase, and for the expression of fungal genes complementing yeast ura3 and leu2 mutations.Of the five Aspergillus genes studied, only one, -glucosidase, was found to be expressed in yeast, and this at a low level. This suggests that there are essential differences between the genes of yeast and filamentous fungi.  相似文献   
30.
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