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   18380篇
  免费   366篇
  国内免费   2篇
  2023年   143篇
  2015年   213篇
  2014年   249篇
  2013年   824篇
  2012年   371篇
  2011年   376篇
  2010年   301篇
  2009年   415篇
  2008年   349篇
  2007年   349篇
  2006年   273篇
  2005年   274篇
  2004年   217篇
  2003年   190篇
  2002年   223篇
  1999年   114篇
  1996年   156篇
  1995年   146篇
  1994年   115篇
  1993年   236篇
  1992年   206篇
  1991年   209篇
  1990年   225篇
  1989年   394篇
  1988年   344篇
  1987年   453篇
  1986年   391篇
  1985年   391篇
  1984年   323篇
  1983年   256篇
  1982年   307篇
  1981年   326篇
  1980年   317篇
  1979年   311篇
  1978年   362篇
  1977年   406篇
  1976年   425篇
  1975年   450篇
  1974年   306篇
  1973年   171篇
  1972年   174篇
  1971年   167篇
  1970年   170篇
  1969年   137篇
  1968年   139篇
  1967年   130篇
  1964年   164篇
  1960年   115篇
  1958年   131篇
  1957年   164篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
An approach to episodic associative memory is presented, which has several desirable properties as a human memory model. The design is based on topological feature map representation of data. An ordinary feature map is a classifier, mapping an input vector onto a topologically meaningful location on the map. A trace feature map, in addition, creates a memory trace on that location. The traces can be stored episodically in a single presentation, and retrieved with a partial cue. Nearby traces overlap, which results in plausible memory interference behavior. Performance degrades gracefully as the memory is overloaded. More recent traces are easier to recall as are traces that are unique in the memory.This research was supported in part by an ITA Foundation grant and by fellowships from the Academy of Finland, the Emil Aaltonen Foundation and the Foundation for the Advancement of Technology (Finland) when the author was at UCLA  相似文献   
72.
73.
A high percentage of plantlets, in which PVX, PVM, and PVS were no longer detectable by precipitin tests was obtained from 100% virus-infected stocks of the potato varieties Rosa and Priobskij rannija by combining meristem (tip) culture with antiphytoviral chemotherapy. When 2,4 - dioxohexahydro 1,3,5-triazinc (DHT) was added to the nutrient media, no virus was detectable serologically in 72% of the corresponding explants of the variety Rosa and in 66% of that of the variety Priobskij rannija, respectively. Contrary to this, all untreated control explants proved virusinfected. Treatment with 2-thiouracil resulted in 46.6%, with cyanoguanidine in 28.6% of plantlets, in which no virus was detectable serologically.  相似文献   
74.
Monoclonal antibodies were produced to electrophoretically pure hydrogenase fromThiocapsa roseopersicina. Protein immunoelectroblotting was used to identify the hydrogenase-specific antibodies. Among the 18 monoclonal antibodies selected by enzyme immunoassay, three were found to react with highly immunogenic trace contaminating proteins. One cell line produced antibody that inhibitied hydrogenase activity. This was the first specific inhibitor of the hydrogenase function. The results suggest that monoclonal antibodies could provide valuable new informations about the enzyme structure as well.  相似文献   
75.
76.
77.
Das Problem der Sekretzellen   总被引:2,自引:0,他引:2  
Dr. Albert Leemann 《Planta》1928,6(2):216-233
Ohne ZusammenfassungMit 17 Textabbildungen.  相似文献   
78.
79.
Summary Consecutive sections of certain neurons in the central ganglia of the pond snail Lymnaea stagnalis appear to be immunoreactive to anti-dopamine and anti-serotonin. The Cerebral Giant Neurons stain in addition with antivasotocin. The observations indicate the presence of two biogenic amines within the same neuron and in addition their co-existence with a biologically active peptide.  相似文献   
80.
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