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   35092篇
  免费   75篇
  国内免费   119篇
系统科学   345篇
丛书文集   720篇
教育与普及   87篇
理论与方法论   116篇
现状及发展   15312篇
研究方法   1398篇
综合类   16714篇
自然研究   594篇
  2013年   202篇
  2012年   487篇
  2011年   1075篇
  2010年   182篇
  2008年   554篇
  2007年   637篇
  2006年   671篇
  2005年   662篇
  2004年   633篇
  2003年   626篇
  2002年   555篇
  2001年   1068篇
  2000年   1035篇
  1999年   655篇
  1992年   633篇
  1991年   546篇
  1990年   578篇
  1989年   502篇
  1988年   521篇
  1987年   558篇
  1986年   538篇
  1985年   691篇
  1984年   559篇
  1983年   451篇
  1982年   372篇
  1981年   394篇
  1980年   521篇
  1979年   1120篇
  1978年   916篇
  1977年   882篇
  1976年   701篇
  1975年   782篇
  1974年   1050篇
  1973年   927篇
  1972年   913篇
  1971年   1113篇
  1970年   1462篇
  1969年   1098篇
  1968年   914篇
  1967年   1014篇
  1966年   916篇
  1965年   648篇
  1964年   165篇
  1959年   386篇
  1958年   612篇
  1957年   466篇
  1956年   419篇
  1955年   351篇
  1954年   382篇
  1948年   282篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
就近几年图书馆界关于新世纪馆员意识转换及社会角色转换等方面的研究进行了综述,指出新时期的馆员要实现自我社会角色的转换,首先是要明确转换的必要性,然后采取有效的策略逐步地、系统地推进转换,才能取得较好的效果。  相似文献   
22.
Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals.In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation.  相似文献   
23.
1.0MeV208Pb离子在非晶Si中的投影射程RP和射程偏差ΔRP作为注量和温度二者的函数用背散射法进行测定.注量的变化范围为5×1013~7×1014cm-2.注入是在室温和t=-120℃下完成的.由由实验所确定的投影射程,射程偏差与注量或温度无关,并且分别等于295和72.2nm.与TRIM86的计算结果相比较,发现RP的偏离为18%,而ΔRP的偏离为36%.RP和ΔRP二者与注量及温度的无关性,排除了所观察到的与TRIM的矛盾是由于注入期间辐射增强扩散或离子束混合效应而引起的解释。  相似文献   
24.
The genetic engineering of production traits in domestic animals   总被引:1,自引:0,他引:1  
  相似文献   
25.
Analysis of 78 Huntington's disease (HD) chromosomes with multi-allele markers revealed 26 different haplotypes, suggesting a variety of independent HD mutations. The most frequent haplotype, accounting for about one third of disease chromosomes, suggests that the disease gene is between D4S182 and D4S180. However, the paucity of an expected class of chromosomes that can be related to this major haplotype by assuming single crossovers may reflect the operation of other mechanisms in creating haplotype diversity. Some of these mechanisms sustain alternative scenarios that do not require a multiple mutational origin for HD and/or its positioning between D4S182 and D4S180.  相似文献   
26.
D C Gautam  L Kapoor 《Experientia》1991,47(3):280-282
Genotoxic effects of dithane M-45 were studied on the bone marrow cells of male albino mice (Lacca strain) in vivo. Different doses (30 mg, 40 mg and 300 mg/kg b.wt) of dithane M-45 were injected intraperitoneally and their effects were investigated after time intervals of 1, 2, 5 and 10 days. The chromosomal aberrations observed in the bone marrow cells of male mice after treatment with dithane M-45 were fragments, rings, dicentric chromosomes, terminal chromatid deletions, chromatid gaps and breaks. In addition to these chromosomal aberrations, physiological effects such as uneven stretching of chromatin material, end-to-end chromosomal associations, exchange configurations, clumping, stickiness and centromeric associations were also observed.  相似文献   
27.
28.
29.
30.
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