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   28873篇
  免费   97篇
  国内免费   158篇
系统科学   149篇
丛书文集   499篇
教育与普及   42篇
理论与方法论   100篇
现状及发展   13451篇
研究方法   1278篇
综合类   13213篇
自然研究   396篇
  2013年   269篇
  2012年   412篇
  2011年   809篇
  2010年   168篇
  2008年   523篇
  2007年   576篇
  2006年   576篇
  2005年   535篇
  2004年   538篇
  2003年   498篇
  2002年   499篇
  2001年   937篇
  2000年   865篇
  1999年   615篇
  1992年   595篇
  1991年   414篇
  1990年   486篇
  1989年   494篇
  1988年   460篇
  1987年   546篇
  1986年   474篇
  1985年   596篇
  1984年   484篇
  1983年   364篇
  1982年   340篇
  1981年   367篇
  1980年   462篇
  1979年   889篇
  1978年   757篇
  1977年   740篇
  1976年   611篇
  1975年   632篇
  1974年   845篇
  1973年   756篇
  1972年   779篇
  1971年   840篇
  1970年   1073篇
  1969年   813篇
  1968年   820篇
  1967年   795篇
  1966年   681篇
  1965年   472篇
  1964年   156篇
  1959年   249篇
  1958年   440篇
  1957年   292篇
  1956年   259篇
  1955年   246篇
  1954年   239篇
  1948年   162篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Sister chromatid exchange was studied in lymphocyte and fibroblast cultures. Alcohol caused no disturbance under normal conditions but an acetaldehyde level above 40 muM inhibited cell multiplication and elevated SCE considerably. A high acetaldehyde level is thought to elicit the fetal alcohol syndrome, a view supported by clinical and experimental observations.  相似文献   
72.
73.
M K Feldman 《Experientia》1978,34(1):97-98
Monolayer cultures of normal, preneoplastic and neoplastic murine mammary epithelial cells were exposed to various types of mammalian serum. A progressive decline in levels of thymidine incorporation together with a change in the ordering of sera which stimulates optimal incorporation was observed in the transformed cells.  相似文献   
74.
Our results indicate that pig lymphocytes in culture complete their 1st division at 24 h. At 36 h there are 9% of cells in 2nd division. 3rd mitosis appears at 48 h; and at 72 h there are cells engaged in the 4th division.  相似文献   
75.
The ability of cells to adhere to a substratum was altered by treatment with trypsin but was restored after a 1.5-h culture. A concomitant incorporation of [3H] leucine and [14C] glucosamine in the trypsin-sensitive cell surface glycoproteins was observed and almost reached a plateau within 1.50 h following the treatment with trypsin.  相似文献   
76.
A M Comunetti 《Experientia》1978,34(7):889-893
Many persons react to a kind of external agent by unconscious muscular reactions if they move across a place where this agent is supposed to be particularly active. Such places normally coincide with geological discontinuities, such as water veins, mineral ores. Practitioners of this art of detecting claim that the reaction patterns on different levels above ground are identical as vertical projections of the source pattern, this without perceptible attenuation. In some cases the supposed source was believed to have been found up to several hundred meters below ground surface. The statement of perpendicular propagation, which is the subject of this paper, is of prime importance for an approach towards understanding and all kinds of prospecting.  相似文献   
77.
K Kawazu  S Nakajima  M Ariwa 《Experientia》1979,35(10):1294-1295
Two insect development inhibitors against Drosophila melanogaster have been isolated from the leaves of X. canadense and identified as xanthumin and 8-epi-xanthatin.  相似文献   
78.
P Alm  M Elmér 《Experientia》1979,35(10):1387-1388
In rats undergoing unilateral extirpation of the pelvic ganglion, the adrenergic innervation disappeared on the ipsilateral side of the urinary bladder. It had reappeared after 6--9 weeks.  相似文献   
79.
In a survey of the intracellular bile salt oxidoreductase activity in fecal bacteria, 16 strains of nuclear dehydrogenating clostridia and 2 strains of non-nuclear dehydrogenating C. paraputrificum were demonstrated unable to oxidize cholate at any of the 3 OH groups. Since nuclear dehydrogenation at the delta-1 and delta-4 position requires a 3-oxo precursor steroid, it appears that these organisms require the presence of a 3 alpha-hydroxysteroid dehydrogenating organism for nuclear dehydrogenation.  相似文献   
80.
S M Yeh  C F Meares 《Experientia》1979,35(6):715-716
The synthesis and initial applications are reported for 1-[p-(palmitamido)-phenyl]ethylenedinitrilotetraacetic acid. The results demonstrate the versatility of this spectroscopic probe molecule, which allows choice of a particular technique for a particular system as well as use of multiple spectroscopic techniques for complementary information about hydrophobic regions in biological systems.  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