全文获取类型
收费全文 | 30759篇 |
免费 | 71篇 |
国内免费 | 85篇 |
专业分类
系统科学 | 319篇 |
丛书文集 | 661篇 |
教育与普及 | 64篇 |
理论与方法论 | 117篇 |
现状及发展 | 14607篇 |
研究方法 | 1150篇 |
综合类 | 13686篇 |
自然研究 | 311篇 |
出版年
2012年 | 348篇 |
2011年 | 711篇 |
2010年 | 154篇 |
2009年 | 152篇 |
2008年 | 430篇 |
2007年 | 515篇 |
2006年 | 498篇 |
2005年 | 509篇 |
2004年 | 579篇 |
2003年 | 520篇 |
2002年 | 459篇 |
2001年 | 897篇 |
2000年 | 905篇 |
1999年 | 558篇 |
1992年 | 527篇 |
1991年 | 420篇 |
1990年 | 485篇 |
1989年 | 462篇 |
1988年 | 409篇 |
1987年 | 446篇 |
1986年 | 481篇 |
1985年 | 596篇 |
1984年 | 426篇 |
1983年 | 387篇 |
1982年 | 361篇 |
1981年 | 409篇 |
1980年 | 432篇 |
1979年 | 1030篇 |
1978年 | 840篇 |
1977年 | 823篇 |
1976年 | 625篇 |
1975年 | 702篇 |
1974年 | 1044篇 |
1973年 | 827篇 |
1972年 | 807篇 |
1971年 | 985篇 |
1970年 | 1232篇 |
1969年 | 1032篇 |
1968年 | 960篇 |
1967年 | 977篇 |
1966年 | 816篇 |
1965年 | 647篇 |
1964年 | 196篇 |
1959年 | 369篇 |
1958年 | 575篇 |
1957年 | 411篇 |
1956年 | 347篇 |
1955年 | 341篇 |
1954年 | 334篇 |
1948年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 2 毫秒
31.
We discuss a generalization of the standard notion of probability space and show that the emerging framework, to be called operational probability theory, can be considered as underlying quantal theories. The proposed framework makes special reference to the convex structure of states and to a family of observables which is wider than the familiar set of random variables: it appears as an alternative to the known algebraic approach to quantum probability. 相似文献
32.
33.
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
34.
35.
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
36.
We investigated the sound communication associated with mating inNezara viridula (L.) to clarify conflicting reports on the medium through which acoustic signals are borne. Recordings made from virgin pairs ofN. viridula during precopulatory and compulatory behaviour have revealed that signals transmitted as vibrations through the substrate are a more likely means of communication than signals transmitted by a radiation of sound pressure waves through the air (at least in Australian populations). We present evidence (additional to that already in the literature) that air-borne acoustics are an unlikely mechanism of sexual communication in this species. Specifically, the recorded pulse train patterns showed no consistency or repeatability in relation to different stages of mating behaviour. In contrast, frequency spectrograms of substrate-borne signals reveal repeatable patterns that do correspond with the stage of mating behaviour. 相似文献
37.
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
38.
39.
Non-Minimum Phase Nonlinear System Predictive Control Based on Local Recurrent Neural Networks 总被引:3,自引:0,他引:3
Abstract: After a recursive multi-step-ahead predictor for nonlinear systems based on local recurrent neural networks isintroduced, an intelligent PID controller is adopted to correct the errors including identified model errors and accumulatederrors produced in the recursive process. Characterized by predictive control, this method can achieve a good controlaccuracy and has good robustness. A simulation study shows that this control algorithm is very effective. 相似文献
40.
Dynamic Characteristics of Inter-Satellite Links in LEO Networks 总被引:1,自引:0,他引:1
To establish an efficient inter-satellite link (ISL) in an LEO network, the effect of geometric characteristics of ISL on the ISLs and the devices on the LEO satellite should be examined. Because of the continuous movement of the LEO satellite, the time-varying behaviours of the ISL's geometric charactersistics continuously change with the changes of the satellite's position on the orbit. These dynamic geometric characteristics of the ISLs are important for ISL's performance analyzing and the design of the devices on the LEO satellite. This paper describes dynamic geometric characteristics of ISL, analyzes the impact of these regulations on the tracking system of the satellite's antenna and the power adjusting system of the satellite's transmitter, with the Iridium system as an example. 相似文献