全文获取类型
收费全文 | 47323篇 |
免费 | 244篇 |
国内免费 | 544篇 |
专业分类
系统科学 | 1216篇 |
丛书文集 | 131篇 |
教育与普及 | 277篇 |
理论与方法论 | 516篇 |
现状及发展 | 29992篇 |
研究方法 | 266篇 |
综合类 | 13524篇 |
自然研究 | 2189篇 |
出版年
2013年 | 802篇 |
2012年 | 448篇 |
2011年 | 2468篇 |
2009年 | 594篇 |
2008年 | 666篇 |
2007年 | 728篇 |
2006年 | 822篇 |
2005年 | 990篇 |
2004年 | 2108篇 |
2003年 | 1725篇 |
2002年 | 1402篇 |
2001年 | 1035篇 |
2000年 | 571篇 |
1999年 | 753篇 |
1998年 | 643篇 |
1997年 | 770篇 |
1996年 | 530篇 |
1995年 | 394篇 |
1994年 | 680篇 |
1993年 | 687篇 |
1992年 | 709篇 |
1991年 | 632篇 |
1990年 | 685篇 |
1989年 | 516篇 |
1988年 | 487篇 |
1987年 | 492篇 |
1986年 | 587篇 |
1985年 | 718篇 |
1984年 | 648篇 |
1983年 | 560篇 |
1982年 | 723篇 |
1981年 | 772篇 |
1980年 | 836篇 |
1979年 | 1125篇 |
1978年 | 1062篇 |
1977年 | 1067篇 |
1976年 | 976篇 |
1975年 | 948篇 |
1974年 | 701篇 |
1973年 | 996篇 |
1972年 | 1066篇 |
1971年 | 1036篇 |
1970年 | 1069篇 |
1969年 | 992篇 |
1968年 | 955篇 |
1967年 | 837篇 |
1966年 | 670篇 |
1965年 | 560篇 |
1964年 | 474篇 |
1963年 | 414篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
A. Farina A. ProtopapaRadar Dpt Selenia S. p. A. Via Tiburtina Km. - Rome Italy 《系统工程与电子技术(英文版)》1992,(3)
After a brief recall of the Sidelobe Canceler (SLC) working principle, including the derivation of a general formula for the Cancellation Ratio (CR), the effects of channel mismatching are investigated. In particular, curves providing CRvalues as a function of amplitude and phase channel mismatching, radar bandwidth, and jammer direction of arrival (JDOA) are provided for the cases of one and two auxiliary antennas. Subsequently, a time -space processor for performance restoration is analyzed in detail. In addition to the above mentioned quantities, the attainable CR value is expressed as a function of the space-time processor parameters. The contribution of the paper is related to the derivation of a number of mathematical equations of CR for several cases of practical interest for the radar engineer. In addition, several curves are presented to assist design of SLC systems. 相似文献
112.
等截面垂直管道中气粉流的临界管长 总被引:2,自引:1,他引:1
彭一川 《东北大学学报(自然科学版)》1995,16(6):573-578
考虑重力和摩擦力的影响,建立了描述垂直管道中气粉流行为的数学模型,采用马赫数检验法,确定了产生摩擦壅塞时的临界管长,计算表明,当气粉流以不同方式喷入相同的冶金熔池时,底吹垂直管道比顶吹垂直管道需要更大的临界管长。 相似文献
113.
114.
115.
116.
117.
118.
M. Harada S. Yenbutra K. Tsuchiya S. Takada 《Cellular and molecular life sciences : CMLS》1985,41(12):1610-1611
Summary Karyotypes ofMyotis siligorensis, Myotis mystacinus, Pipistrellus pulveratus, Tylonycteris robustula, Miniopterus schreibersi fuliginosus, Hipposideros fulvus andAselliscus stoliczkanus from Thailand are investigated.Acknowledgment. The authors are very grateful to Dr N. Ratanawarabhan, Mrs S. Sittilert, P. Noonpakdee and S. Kuanchalern of Thailand Institute of Scientific and Technological Research for their valuable advice and assistance during our field survey in Thailand. 相似文献
119.
120.
Descartes is always concerned about knowledge. However, the Galileo affair in 1633, the reactions to his Discourse on method, and later his need to reply to objections to his Meditations provoked crises in Descartes’s intellectual development the import of which has not been sufficiently recognized. These events are the major reasons why Descartes’s philosophical position concerning how we know and what we may know is radically different at the end of his life from what it was when he began. We call this later position Descartes’s epistemic stance and contrast it with his earlier methodological, metaphysical realism. Yet Descartes’s epistemic views cannot be separated from other aspects of his work, for example, his views concerning God, causality, metaphysics, and the nature of science. A further meta-implication is that serious errors await any scholar who cites early Cartesian texts in support of late Cartesian positions, or who uses later texts in conjunction with early ones to support a reading of Descartes’s philosophy. 相似文献