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   8100篇
  免费   537篇
  国内免费   103篇
  2023年   76篇
  2022年   101篇
  2021年   210篇
  2020年   155篇
  2019年   176篇
  2018年   371篇
  2017年   318篇
  2016年   388篇
  2015年   366篇
  2014年   432篇
  2013年   652篇
  2012年   736篇
  2011年   715篇
  2010年   440篇
  2009年   316篇
  2008年   304篇
  2007年   229篇
  2006年   265篇
  2005年   140篇
  2004年   138篇
  2003年   105篇
  2002年   97篇
  2001年   74篇
  2000年   83篇
  1999年   108篇
  1998年   83篇
  1997年   70篇
  1996年   70篇
  1995年   86篇
  1994年   63篇
  1993年   50篇
  1992年   58篇
  1991年   53篇
  1990年   35篇
  1989年   54篇
  1988年   35篇
  1987年   52篇
  1986年   38篇
  1985年   54篇
  1984年   47篇
  1983年   54篇
  1982年   52篇
  1981年   59篇
  1980年   48篇
  1979年   55篇
  1978年   43篇
  1977年   54篇
  1974年   36篇
  1973年   40篇
  1969年   40篇
排序方式: 共有8740条查询结果,搜索用时 31 毫秒
71.
The meadow plant communities,Arrhenatheretum elatioris alopecuretosum pratensis R. Tx. 1937 andMesobrometum erecti stipetosum Vicherek 1960, were chosen for investigations of the underground plant parts. Apparent differences in underground dry weight and its seasonal changes in both the communities were observed. Differences in the soil environment in different periods of the year are reflected in the character of time changes in underground dry weight. The soil environment affects not only the total underground biomass and their changes in time, but also the activity of soil microflora and, consequently, the decomposition rate of dead underground plant parts.  相似文献   
72.
Synthesis of two hydroxy-derivatives of nalidixic acid as a result of microbial transformation was demonstrated in certain species of the genusAspergillus. Aspergillus alliaceus produced 7-hydroxy-nalidixic acid andAspergillus niger 6-hydroxy-nalidixic acid. It was demonstrated that the antibacterial activity of both hydroxy-derivatives (tested inEscherichia coli) was lower than that of the initial nalidixis acid.  相似文献   
73.
Lymphoid cells prepared from rabbit popliteal lymph nodes were cultivated in medium in which the high molecular weight component was replaced by Carbowax 20 M. This substance, in 0.2% concentration, proved to be a substitute for the high molecular weight component in short-term cultivation, and the viability results were similar to those in medium containing normal rabbit serum or 0.5% human serum albumin. In addition, mitoses and the formation of large basophilic cells resembling the blastoid cells induced during cultivation with phytohaemagglutinin were observed in this medium. The results are discussed.  相似文献   
74.
In a model secondary reactionin vitro, a correlation was demonstrated between the size of the antigen dose used for the prestimulation of spleen tissue donors and the type of antibodies formed in the anamnestic reaction. After a small dose of antigen ΦX 174, the antibody response three days after prestimulation was of the 19 S (IgM) type, but later secondary contactin vitro (after four months) did not produce a 19 S anamnestic reaction. After large primary doses of antigen, a short interval between primary and secondary contact led to the formation of 19 and 7 S type antibodies, while after a long interval only 7 S (IgG) type antibodies were formed. The results are discussed in relation to differences in the size of the antigen dose needed to induce short-term 19 S and long-term 7 S immunological memory.  相似文献   
75.
V této práci byly aplikovány na rostlinných objektech reakce s β-oxynaftyl-merkurichloridem a p-nitrobromacetofenonem, popsané k pr?kazu bílkovinných SH na materiálu ?ivo?i?ném. V rostlinných meristematických buňkách obě tyto techniky stejně jako DDD1 a RSR1 jeví vět?inou intensivněj?í zbarvení jader ne? cytoplasmy. Rovně? po aplikaci reakcí na bílkovinné karboxyly a tyrosin je jádro intensivněji zbarveno ne? cytoplasma. Z toho lze soudit, ?e rozdíly v intensitě zbarvení jádra a cytoplasmy v meristematických buňkách rostlinných technikami k pr?kazu bílkovinných SH jsou zp?sobeny spí? rozdílem v celkové koncentraci bílkovin ne? zv??ením podílu cysteinu v jaderných bílkovinách.  相似文献   
76.
77.
78.
The relation of the M1 root length and the frequency of M1 chlorophyll chimeras to the sterility grade and to the frequency of M2 mutants ofArabidopsis thaliana is demonstrated.  相似文献   
79.
Various possibilities of usingSörensen's coefficient of floristic similarity in plant sociology are summarized. A new formula (11), derived from that bySörensen and based on constancy values, is suggested in order to calculate the mean floristic similarity within a set of relevés.  相似文献   
80.
Various possibilities of usingSörensen’s coefficient of floristic similarity in plant sociology are summarized. A new formula (11). derived from that bySörensen and based on constancy values, is suggested in order to calculate the mean floristic similarity within a set of relevés.  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