全文获取类型
收费全文 | 31378篇 |
免费 | 73篇 |
国内免费 | 142篇 |
专业分类
系统科学 | 196篇 |
丛书文集 | 396篇 |
教育与普及 | 82篇 |
理论与方法论 | 103篇 |
现状及发展 | 13670篇 |
研究方法 | 1398篇 |
综合类 | 15312篇 |
自然研究 | 436篇 |
出版年
2013年 | 226篇 |
2012年 | 475篇 |
2011年 | 890篇 |
2010年 | 194篇 |
2008年 | 566篇 |
2007年 | 649篇 |
2006年 | 641篇 |
2005年 | 647篇 |
2004年 | 640篇 |
2003年 | 598篇 |
2002年 | 552篇 |
2001年 | 1066篇 |
2000年 | 1010篇 |
1999年 | 653篇 |
1994年 | 343篇 |
1992年 | 607篇 |
1991年 | 473篇 |
1990年 | 539篇 |
1989年 | 484篇 |
1988年 | 442篇 |
1987年 | 522篇 |
1986年 | 518篇 |
1985年 | 626篇 |
1984年 | 490篇 |
1983年 | 434篇 |
1982年 | 391篇 |
1981年 | 393篇 |
1980年 | 423篇 |
1979年 | 1041篇 |
1978年 | 804篇 |
1977年 | 754篇 |
1976年 | 597篇 |
1975年 | 652篇 |
1974年 | 878篇 |
1973年 | 763篇 |
1972年 | 738篇 |
1971年 | 878篇 |
1970年 | 1172篇 |
1969年 | 856篇 |
1968年 | 780篇 |
1967年 | 843篇 |
1966年 | 741篇 |
1965年 | 529篇 |
1959年 | 292篇 |
1958年 | 481篇 |
1957年 | 345篇 |
1956年 | 323篇 |
1955年 | 269篇 |
1954年 | 267篇 |
1948年 | 235篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A. E. Yassen H. A. Hassan L. S. Kawashti 《Cellular and molecular life sciences : CMLS》1994,50(11-12):1111-1114
A detailed karyotypic analysis of two Egyptian species of bats,Taphozous perforatus andTaphozous nudiventris, was made on the basis of conventional data and G-band patterns. No detectable karyotypic difference was found between the two species (2n=42, F.N. 64). By comparison of G-band patterns, some differences between the two species were seen in the corresponding autosomal pairs. These results are reported for the first time in Egypt. 相似文献
42.
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
43.
C. Ambrogi Lorenzini C. Bucherelli A. Giachetti G. Tassoni 《Cellular and molecular life sciences : CMLS》1991,47(10):1019-1026
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
44.
A latent class probit model for analyzing pick any/N data 总被引:3,自引:3,他引:0
A latent class probit model is developed in which it is assumed that the binary data of a particular subject follow a finite
mixture of multivariate Bermoulli distributions. An EM algorithm for fitting the model is described and a Monte Carlo procedure
for testing the number of latent classes that is required for adequately describing the data is discussed. In the final section,
an application of the latent class probit model to some intended purchase data for residential telecommunication devices is
reported.
Geert De Soete is supported as “Bevoegdverklaard Navorser” of the Belgian “Nationaal Fonds voor Wetenschappelijk Onderzoek.” 相似文献
45.
提出了一个关于氧化物半导瓷晶界势垒起源的新观点,认为晶界势垒起源于烧结过程中外界氧在晶界中的扩散,与材料的结构、化学缺陷、掺杂、外界气氛、烧结工艺、组成状态等有密切关系,并用此理论解释了许多实验现象。 相似文献
46.
论述了交织编码的工作原理,给出了一种交织扩展Golay码的改进型软件设计方案,用TMS320C25实现了其编译码器并给出了模拟实验结果。实验结果表明,它能准确地纠正不大于72比特位的差错;处理128×128×8比特位的一幅图像数据的运行时间为0.412s. 相似文献
47.
Aspirin-like drugs may block pain independently of prostaglandin synthesis inhibition 总被引:2,自引:0,他引:2
K. Brune W. S. Beck G. Geisslinger S. Menzel-Soglowek B. M. Peskar B. A. Peskar 《Cellular and molecular life sciences : CMLS》1991,47(3):257-261
Summary Using flurbiprofen, a chiral anti-inflammatory and analgesic 2-arylpropionic acid derivative, the enantiomers of which are not converted to each other (less than 5%) in rats or man, we obtained evidence that prostaglandin synthesis inhibition is primarily mediating the anti-inflammatory activity but prostaglandin synthesis independent mechanisms contribute to the analgesic effects. Thus, the S-form inhibited prostaglandin synthesis, inflammation and nociception in rats. The R-form had much less effect on prostaglandin synthesis and did not affect inflammation. It did, however, block nociception in rats almost as potently as the S-form. S-flurbiprofen, in contrast to the R-form, was clearly ulcerogenic in the gastrointestinal mucosa. These results indicate additional molecular mechanisms of analgesia and suggest the use of R-arylpropionic acids as analgesics. 相似文献
48.
The genetic engineering of production traits in domestic animals 总被引:1,自引:0,他引:1
49.
史济群 《华中科技大学学报(自然科学版)》1994,(3)
报道一种新颖的激光开槽、埋槽电极硅太阳电池的结构、工艺流程及其研制结果。在AM1.5,25℃,100mW/cm2的条件下,以面积为45cm3的36片硅片研制的硅太阳电池的输出参数的平均值为JSC=36.1mA/cm2,V∞=633mV,F.F.=0.798,η=18.23%,最后分析了种高性能硅太阳电池的设计特点。 相似文献
50.
Low-molecular-weight GTP-binding proteins are strong candidates for regulators of membrane traffic. In yeast, mutations in the sec4 or ypt1 genes encoding small GTP-binding proteins inhibit constitutive membrane flow at the plasma membrane or Golgi complex, respectively. It has been suggested that membrane fusion-fission events are regulated by cycling of small GTP-binding proteins between a membrane-bound and free state, but although most of these small proteins are found in both soluble and tightly membrane-bound forms, there is no direct evidence to support such cycling. In rat brain a small GTP-binding protein, rab3A, is exclusively associated with synaptic vesicles, the secretory organelles of nerve terminals. Here we use isolated nerve terminals to study the fate of rab3A during synaptic vesicle exocytosis. We find that rab3A dissociates quantitatively from the vesicle membrane after Ca2(+)-dependent exocytosis and that this dissociation is partially reversible during recovery after stimulation. These results are direct evidence for an association-dissociation cycle of a small GTP-binding protein during traffic of its host membrane. 相似文献