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   40639篇
  免费   117篇
  国内免费   201篇
系统科学   407篇
丛书文集   875篇
教育与普及   76篇
理论与方法论   143篇
现状及发展   19154篇
研究方法   1576篇
综合类   18206篇
自然研究   520篇
  2013年   294篇
  2012年   512篇
  2011年   1085篇
  2010年   234篇
  2008年   676篇
  2007年   799篇
  2006年   734篇
  2005年   722篇
  2004年   714篇
  2003年   716篇
  2002年   656篇
  2001年   1280篇
  2000年   1214篇
  1999年   782篇
  1992年   781篇
  1991年   563篇
  1990年   667篇
  1989年   656篇
  1988年   619篇
  1987年   686篇
  1986年   663篇
  1985年   803篇
  1984年   630篇
  1983年   508篇
  1982年   478篇
  1981年   531篇
  1980年   627篇
  1979年   1272篇
  1978年   1059篇
  1977年   1061篇
  1976年   856篇
  1975年   885篇
  1974年   1264篇
  1973年   1073篇
  1972年   1069篇
  1971年   1205篇
  1970年   1579篇
  1969年   1260篇
  1968年   1200篇
  1967年   1216篇
  1966年   1033篇
  1965年   732篇
  1964年   218篇
  1959年   406篇
  1958年   682篇
  1957年   451篇
  1956年   411篇
  1955年   389篇
  1954年   365篇
  1948年   229篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
We investigated occupied squirrel middens and squirrel sightings and vocalizations as indicators of red squirrel ( Tamiasciurus hudsonicus ) abundance in high-elevation whitebark pine ( Pinus albicaulis ) zone. Data were collected 1984-1989 from line transects located on 2 study sites in the Yellowstone ecosystem. We evaluated the performance of each measure on the basis of precision and biological considerations. We concluded that, of the 3 measures, active middens were the best indicator of red squirrel abundance. We also observed that the density of active middens dropped by 48%-66% between 1987 and 1989, following a severe drought and extensive wildfires that burned one of the study sites during 1988.  相似文献   
72.
Gene polymorphism in Netherton and common atopic disease.   总被引:13,自引:0,他引:13  
Atopic dermatitis (AD) and asthma are characterized by IgE-mediated atopic (allergic) responses to common proteins (allergens), many of which are proteinases. Loci influencing atopy have been localized to a number of chromosomal regions, including the chromosome 5q31 cytokine cluster. Netherton disease is a rare recessive skin disorder in which atopy is a universal accompaniment. The gene underlying Netherton disease (SPINK5) encodes a 15-domain serine proteinase inhibitor (LEKTI) which is expressed in epithelial and mucosal surfaces and in the thymus. We have identified six coding polymorphisms in SPINK5 (Table 1) and found that a Glu420-->Lys variant shows significant association with atopy and AD in two independent panels of families. Our results implicate a previously unrecognized pathway for the development of common allergic illnesses.  相似文献   
73.
74.
High-affinity, Na+-independent binding of beta-alanine to a synaptosomal fraction of rat brain was potently inhibited by glycine and by some other alpha-amino acids, but not by taurine or GABA. This binding mechanism, which was also sensitive to both bicuculline and strychnine, might involve synaptic receptors for both beta-alanine and glycine.  相似文献   
75.
M N Islam 《Experientia》1978,34(2):254-255
Antibodies against nucleotide-peptides of beef heart do crossreact with nucleotide-peptides of other beef organs, but with nucleotide-peptides of Ehrlich tumor cells. Antibodies against the latter do not crossreact with nucleotide-peptides of normal organs, but do so with nucleotide-peptides of a rat hepatoma.  相似文献   
76.
Stimulation of the nucleus accumbens evokes a potent inhibition in neurons of the ventral tegmental area. GABA is likely to act as a transmitter in this descending inhibitory system.  相似文献   
77.
M A Khan 《Experientia》1978,34(6):784-785
Red fibres of the pigeon pectoralis muscle showed high ATPase reaction at pH 9.4. Veronal-acetate pretreatment completely inhibited the ATPase reaction in these red fibres but not in type I fibres of the gastrocnemius. The former are type II red muscle fibres and hence are unlike type I red, the so-called slow-twitch muscle fibres.  相似文献   
78.
The effect of gamma-rays on iron-free conalbumin was studied by isoelectric focusing technique. The results obtained can be interpreted on the basis of radiation-induced conformational changes of the macromolecules through a cleavage of disulphide bridges. Treatments with reagents acting on disulphide bridges lead to isoelectric focusing patterns that confirm this hypothesis.  相似文献   
79.
T Kambara  M Hirata  T Hiraoka 《Experientia》1978,34(4):526-528
Partial purification of neutral proteolytic enzymes in guinea-pig lymphocytes yielded 2 enzymes. Both enzymes were heat-labile and inhibited by thiol reagents. The molecular weights were more than 200,000 and 150,000-200,000, and optimal pH around 9 and 8, respectively.  相似文献   
80.
The presence of hydrocortisone in virus-infected cell cultures leads to enhancement of the syncytia forming ability of Newcastle disease virus and to production of vescicular stomatitis virus particles which loose their infectivity upon storage below 0 degrees C.  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