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   1858篇
  免费   84篇
  2021年   14篇
  2020年   7篇
  2019年   10篇
  2018年   11篇
  2017年   19篇
  2016年   25篇
  2015年   37篇
  2014年   29篇
  2013年   153篇
  2012年   87篇
  2011年   86篇
  2010年   51篇
  2009年   60篇
  2008年   96篇
  2007年   98篇
  2006年   102篇
  2005年   97篇
  2004年   108篇
  2003年   88篇
  2002年   81篇
  2001年   40篇
  2000年   45篇
  1999年   42篇
  1998年   28篇
  1997年   29篇
  1996年   27篇
  1995年   23篇
  1994年   20篇
  1993年   20篇
  1992年   11篇
  1991年   25篇
  1990年   25篇
  1989年   26篇
  1988年   30篇
  1987年   23篇
  1986年   21篇
  1985年   26篇
  1984年   32篇
  1983年   18篇
  1982年   20篇
  1981年   16篇
  1980年   18篇
  1979年   19篇
  1978年   11篇
  1977年   12篇
  1976年   7篇
  1975年   9篇
  1974年   8篇
  1973年   9篇
  1968年   10篇
排序方式: 共有1942条查询结果,搜索用时 81 毫秒
981.
982.
Effects of hydrofluorene and hydrophenanthrene compounds derived from dehydroabietic acid on the second leaf sheath growth of rice seedlings were examined in the presence and absence of gibberellin A3(GA3). In the absence of GA3, nineteen compounds at 100 ppm inhibited more than 20% the growth of normal rice seedlings. In the presence of GA3 (1.5 ppm) with dwarf rice seedlings, nine compounds at 500 ppm suppressed the elongation caused by the hormone, and a compound was slightly promotive. Then, three compounds were selected and subjected to the bioassay under various conditions.  相似文献   
983.
In the previous paper the author reported that 5(4)-amino-4(5) -imidazolecarboxamide (AICA) was accumulated in peptone medium by Escherichia coli strain B grown as a shaking culture in the absence of sulfonamide inhibitor and glucose. It appeared from the further investigations that l-tryptophan would not replace peptone for the accumulation. However, it was found that indole produced from l-tryptophan by E. coli gave pink color by the Bratton nad Marshall method. In order to eliminate the effect of indole, the procedure by petroleum-ether treatment was applied and it was ascertained that E. coli had an ability to accumulate AICA and AICA-riboside in the peptone or L-tryptophan medium without glucose and sulfonamide inhibitor. But the concentrations of AICA and AICA-riboside measured by the above procedure were smaller than those determined by the Bratton and Marshall method which measured indole produced by the bacteria at the same time.  相似文献   
984.
Hydrocarbon-assimilating yeasts and bacteria were isolated from soil and sewage. The optimal conditions of cell yield from liquid paraffine by a Torulopsis yeast and a Pseudomonas strain were studied. A Torulopsis yeast gave, in optimal condition, 70 percent cell yield on a weight conversion basis from light oil fraction. In a strain of Pseudomonas the additions of amino acids, Fe+ +, Mg+ + and Ca+ + ions were effective for cell production. This strain showed, in optimal condition, 80 percent cell yield (wt%) from kerosene.  相似文献   
985.
The gene lamAI, which encodes a novel laminarinase AI of Trichoderma viride U-1, was cloned using RT-PCR in conjunction with the rapid amplification of cDNA ends (RACE) technique. The open reading frame consisted of 2,277 bp encoding a protein of 759 amino acid residues, including a 32-residue signal prepropeptide. The protein showed 91% sequence similarity to the putative Trichoderma virens β-1,3-glucanase BGN1, but no significant similarity to fungal β-1,6-glucanases or β-1,3-glucanases from other organisms. On 40 h incubation with a solo carbon source, northern analysis revealed that the gene was induced by 0.5% laminaran from Eisenia bicyclis but was not by the same concentration of glucose. The lamAI cDNA was functionally expressed in the methylotrophic yeast Pichia pastoris, resulting in a recombinant enzyme with as high activity against laminaran as native LAMAI. Based on these data, the probable existence of endo-β-1,3:1,6-glucan hydrolases as a subclass of endo-β-1,3-glucanases in some mycoparasitic fungi is suggested.  相似文献   
986.
Adenine-auxotrophic mutant of Bacillus licheniformis formed considerable amount of guanosine from guanine. The guanosine formation was stimulated by the addition of penicillin to the growing cells and by the presence of uridine in the crude extract. The crude extract preserved for long time showed the changes of the enzyme actions for added guanine.  相似文献   
987.
Cultures of Aspergillus flavus and Botrytis cinerea have been found to rapidly convert the fungitoxic isoflavone licoisoflavone A [5,7,2′,4′-tetrahydroxy-3′-(3,3-dimethylallyl)isoflavone] into products with reduced antifungal activity, as judged from TLC plate bioassays against the growth of Cladosporium herbarum. Both fungi produced the same five metabolites, but often in greatly differing quantities. Using physico-chemical procedures, the metabolites were characterized as a glycol (2″,3″-dihydrodihydroxylicoisoflavone A), two dihydrofurano-isoflavones (one of which was identical with lupinisoflavone D found in Lupinus albus roots) and two hydroxydihydropyrano-isoflavones.  相似文献   
988.
Penicillin-resistant mutants were derived from Corynebacterium hydrocarboclastus R-7. One of them produced 84 g/liter of l-glutamic acid from hydrocarbon, though its parent strain produced 26 g/liter.

The penicillin-resistant mutant had stronger activities of substrate consumption and oxygen absorption than the parent strain, and this was one of the reasons for the accumulation of a larger quantity of l-glutamic acid.

The interacellular content of phosphatidyl inositol mannoside (P.I.M) was related to the glutamate productivity, and the higher glutamate productivity of the penicillin-resistant mutant was supposed to be related to the remarkable diminution in the content of P.I.M.  相似文献   
989.
Ren-1 renin is synthesized in the kidney of every mouse. Ren-2 renin has been observed in the submandibular gland (SMG) of male mice carrying two renin genes. However, it is not known if Ren-2 renin is in the kidney and blood of the two-renin gene mice. In this study, a direct ELISA for Ren-2 renin (SMG renin) was established by a sandwich method. This ELISA could measure the Ren-2 active renin in the range from 1 to 100ng and distinguish Ren-2 active renin from not only Ren-1 renin but also Ren-2 prorenin. By a combination of this assay system and conventional methods, the pro-form as well as the active form of Ren-2 renin was found in the kidney and plasma of male AKR mice carrying two-renin genes.  相似文献   
990.
Washed cells of facultative methylotrophs which have the serine pathway showed high activities for l-methionine formation from dl-homocysteine, in the presence of methanol as methyl donor. Strain FM 518, isolated from soil and identified as a bacterium belonging to the genus Pseudomonas, showed the highest activity for l-methionine formation and was used as the parental strain for breeding the l-methionine-producing mutants. An ethionine-resistant mutant, FE 244, derived from strain FM 518, accumulated 0.8 mg/ml l-methionine in a methanol-medium under optimum conditions.  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