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   2881篇
  免费   190篇
  国内免费   5篇
  2022年   6篇
  2021年   36篇
  2020年   13篇
  2019年   20篇
  2018年   28篇
  2017年   23篇
  2016年   50篇
  2015年   64篇
  2014年   81篇
  2013年   228篇
  2012年   157篇
  2011年   173篇
  2010年   112篇
  2009年   103篇
  2008年   163篇
  2007年   177篇
  2006年   167篇
  2005年   171篇
  2004年   159篇
  2003年   137篇
  2002年   147篇
  2001年   63篇
  2000年   75篇
  1999年   72篇
  1998年   32篇
  1997年   45篇
  1996年   22篇
  1995年   31篇
  1994年   33篇
  1993年   23篇
  1992年   41篇
  1991年   35篇
  1990年   37篇
  1989年   33篇
  1988年   27篇
  1987年   27篇
  1986年   35篇
  1985年   29篇
  1984年   17篇
  1983年   11篇
  1982年   27篇
  1981年   20篇
  1980年   17篇
  1979年   17篇
  1978年   18篇
  1977年   15篇
  1976年   11篇
  1975年   10篇
  1974年   6篇
  1972年   10篇
排序方式: 共有3076条查询结果,搜索用时 125 毫秒
101.
The optimal condition for the rat DNA polymerase beta activity with (rA)n . (dT)12-18 as a template-primer was determined. The activity was remarkably affected by the concentration of the primer, (dT)12-18' and the mixing ratio of (dT)12-18 to (rA)n. DNA polymerase beta requires higher primer concentration (Km = 11.1 microM with respect to 3'-OH of the primer) than DNA polymerase gamma (Km = 0.04 microM) or oncornaviral DNA polymerase (Km = 0.08 microM) and the enzyme represented the maximum activity in the base ratio of 2:1 with (dT)12-18 and (rA)n suggesting the difference in reaction mechanisms of these enzymes. Under the optimized conditions, the specific activity of the near homogeneous preparation of DNA polymerase beta was 1,000,000 units per mg protein.  相似文献   
102.
Aphidicolin, a tetracyclic diterpenoid, is known to be antiviral and to inhibit the incorporation of thymidine into DNA of cultured human embryonic lung cells. We examined effects of the compound on the activity of several DNA polymerases obtained from subcellular fractions of rat liver. Aphidicolin at a concentration of 15 μg/ml caused a 85% reduction in level of the activity of crude and partially purified DNA polymerases from the cytosol. However, aphidicolin even at a concentration of 75 μg/ml failed to affect the activity of crude and partially purified DNA polymerases from nuclear and mitochondrial fractions.  相似文献   
103.
Carbon dioxide enhanced chloroplast regeneration in glucose-bleachedcells of Chlorella protothecoides in the presence of CMU inthe light. Both the formation of chlorophyll and the synthesesof RNA and protein were considerably enhanced. The CO2 metabolism of algal cells during greening was investigatedusing 14C-bicarbonate as the tracer. Radiocarbon was largelyincorporated into purine and pyrimidine bases in nucleic acidand the arginine in protein, specifically at the crabon atomsderived from carbamylphosphate. 1Part of this investigation was reported at the conference onthe "Autonomy and biogenesis of mitochondria and chloroplasts"held at Canberra in 1969 (4). (Received August 19, 1975; )  相似文献   
104.
This work is concerned with the optimization study of the semibatch fermentation by which an amino acid is produced. The particular fermentation studied is the synthesis of lysine by the auxotrophic mutant. Applying Green's theorem to the maximization problem was proposed, and it succeeded in determining the feed rate of the substrate that maximized the production rate of the desired product.  相似文献   
105.
An enzyme activity specific for UV-DNA1 was found in the extract of Bacillus subtilis(Marburg 168). The enzyme preparation obtained from the extract by ammonium sulfate precipitation acts on UV-DNA endonucleolytically and induces single strand breaks. The number of single strand breaks introduced in DNA is proportional to UV dose.  相似文献   
106.
Chloroplast-nucleus interactions were examined in cells of Euglenagracilis Z synchronized under photoautotrophic conditions. Thechloroplasts were localized near the cell periphery. At an earlystage of the cell cycle, however, some chloroplasts were transientlylocated in the inner space close to the nucleus. Electron microscopyusing serial cell sections revealed that the chloroplast formedprotrusions at several sites, which became associated with thenucleus. The outer membrane of the chloroplast envelope wasin contact, or at least continuous in part, with the outer membraneof the nuclear envelope at the sites of association, and densematerial was present in the chloroplast membrane. A chromosomewas close to each site of the association between these twoorganelles. Most of the chloroplasts including those in associationwith the nucleus were connected by fine bridges. The 4',6-diamidino-2-phenylindole-stainednucleoids in the chloroplast associated with the nucleus appearedto have a thread-like shape. There was another type of chloroplast-nucleusconnection, in which an intervening membranous body was in contactwith the outer part of the nuclear envelope on one side andwith the chloroplast envelope on the other side. 1 This work was reported at the 48th Annual Meeting of the BotanicalSociety of Japan, Kyoto, October, 1983. (Received June 5, 1984; Accepted November 20, 1984)  相似文献   
107.
Diamine oxidase (DAO) (EC 1.4.3.6) was purified from pea epicotyls to homogeneity by the criterion of polyacrylamide gel electrophoresis (PAGE). The pu  相似文献   
108.
Phosphofructokinase (ATP:D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) was purified to homogeneity from pig livers. Polyclonal antibody against the enzyme was induced in a rabbit, and the IgG fraction was obtained by chromatography on a Protein A-Sepharose CL-4B column. The specific antibody was purified further by immunoaffinity chromatography on a phosphofructokinase-conjugated affinity column. Intermediate catabolic products of phosphofructokinase were extracted from fresh pig livers under conditions of inhibition of proteinases, concentrated by chromatography on an anti-phosphofructokinase IgG-conjugated affinity column, and purified by two-dimensional polyacrylamide gel electrophoresis. Their cross-reactivities to the purified phosphofructokinase were assessed by an immunoelectrotransfer blot method. The intact form of phosphofructokinase in pig liver was demonstrated as the major spot of 84 kDa on the blot. Polypeptides of 68, 64, 56, and 51 kDa showed apparent cross-reactivities to phosphofructokinase. The structural homology among them was confirmed by proteinase V8 digestion followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The possibility of artifacts in preparation was ruled out by an internal tracer method. Thus, it is concluded that the predominant isozyme of phosphofructokinase in pig liver (84 kDa) is in vivo degraded via intermediate catabolic products of 68, 64, 56, and 51 kDa.  相似文献   
109.
New work situations designed at the stage when new machine systems are introduced are realized on the assumption that the new systems can maintain their designed functions consistently, generally eliminating previous work habits and without sufficient knowledge about real working processes and skills. This may produce differences between designed and real working situations. Some examples are presented from observations on influence of modern design of cargo ships on their crews. It was difficult for crews to maintain stable working conditions, especially when machine systems deviated from their designed functions. Often the crew had to work in off-duty hours giving up private freetime activities. Among various factors contributing to the discrepancies between designed and real work, lack of availability of the new systems is the most important factor. Also important is lack of back-up systems which would function either when the machine systems are out of order or when previous working skills and habits must be applied. A need for developing methods of evaluation of these two factors from ergonomic points of view is pointed out.  相似文献   
110.
Phrymarolin II, a unique naturally-occurring lignan having a 1,2-dioxygenated 3,7-dioxabicyclo[3.3.0]octane skeleton, was synthesized by the reaction of sesamol, in the presence of cadmium carbonate, with 1-acetoxy-2-chloro-6-(2′-methoxy-4′,5′-methylenedioxyphenyl)-3,7-dioxabicyclo[3.3.0]octane. The latter was prepared through 13 steps starting from an aldol condensation of β-vinyl-γ-butyrolactone with 2-methoxy-4,5-methylenedioxybenzaldehyde. Three diastereomers of phrymarolin II were also obtained.  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