全文获取类型
收费全文 | 128029篇 |
免费 | 1929篇 |
国内免费 | 285篇 |
专业分类
教育 | 89380篇 |
科学研究 | 13683篇 |
各国文化 | 2059篇 |
体育 | 9756篇 |
综合类 | 212篇 |
文化理论 | 1160篇 |
信息传播 | 13993篇 |
出版年
2021年 | 1007篇 |
2020年 | 1728篇 |
2019年 | 2674篇 |
2018年 | 3239篇 |
2017年 | 3523篇 |
2016年 | 3546篇 |
2015年 | 2442篇 |
2014年 | 3326篇 |
2013年 | 28109篇 |
2012年 | 2564篇 |
2011年 | 2957篇 |
2010年 | 2541篇 |
2009年 | 2792篇 |
2008年 | 2610篇 |
2007年 | 2326篇 |
2006年 | 2610篇 |
2005年 | 2565篇 |
2004年 | 3130篇 |
2003年 | 2476篇 |
2002年 | 2256篇 |
2001年 | 2160篇 |
2000年 | 1745篇 |
1999年 | 1634篇 |
1998年 | 1514篇 |
1997年 | 1567篇 |
1996年 | 1753篇 |
1995年 | 1529篇 |
1994年 | 1521篇 |
1993年 | 1515篇 |
1992年 | 1550篇 |
1991年 | 1472篇 |
1990年 | 1487篇 |
1989年 | 1374篇 |
1988年 | 1233篇 |
1987年 | 1160篇 |
1986年 | 1198篇 |
1985年 | 1447篇 |
1984年 | 1319篇 |
1983年 | 1307篇 |
1982年 | 1285篇 |
1981年 | 1208篇 |
1980年 | 1186篇 |
1979年 | 1272篇 |
1978年 | 1236篇 |
1977年 | 1132篇 |
1976年 | 1020篇 |
1975年 | 830篇 |
1974年 | 820篇 |
1973年 | 793篇 |
1971年 | 653篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
This paper is concerned with the analysis of the problem of dynamic perforation of visco-plastic plates by a cylindrical projectile, leading to a failure of the plate by a plug formation. Assuming the behavior of the plate material is nonlocal visco-plastic, the classical theory of visco-plasticity for Bingham solids is generalized to take the non-local effects into consideration. The target plate being thin, it is assumed that only the contributions of vertical shearing stress need be taken into account. The effect of the impact is represented by a uniform velocity distribution over a circular region of the plate surface. The expressions of velocity, strain rate and shear stress are obtained and some particular cases are discussed. Some numerical results concerning stress distributions are also included. 相似文献
952.
953.
It is often desirable to represent carrier distribution systems by networks so that analysis can be made to predict the behavior of these systems. Modeling of two canonical carrier distribution systems, the star-shaped system and the parallel-wire system by networks was carried out in this paper. The representation is given in terms of lumped parameters when the lengths of the carrier lines are short and it is given in terms of lumped and distributed parameters when the lengths of the carrier lines are long. 相似文献
954.
Raimond A. Struble 《Journal of The Franklin Institute》1978,306(1):63-76
It has been tacitly understood that Fourier's representation theorem applies only to a very restricted class of functions. On the contrary, by adopting an appropriate algebraic viewpoint, it is explained in this article how the theorem can be readily extended to include all (non-pathological) functions. 相似文献
955.
956.
957.
958.
David Aston 《Endeavour》1978,2(3):142-148
Although the principle of separation by centrifugation has been known for nearly a century, the technical difficulties of using it in practice are very great. Only in comparatively recent years has there been sufficient understanding of the underlying theory, and availability of suitable materials of construction, for the high-speed centrifuge to be used as a powerful aid to medical research and, very recently, as a means of separating isotopes on an industrial scale. 相似文献
959.
L S Hewitt 《Child development》1975,46(2):540-544
Dutch boys 8 and 12 years old read brief stories about a harm doer whose intentions were either good or bad and whose actions resulted in either minor or serious injury to a victim. The harm doer had previously been either strongly provoked or not provoked by the victim. The older boys differentiated their evaluations of the harm doer's naughtiness on the basis of provocation and intentions, while the younger boys failed to differentiate their evaluations of the provoked harm doer on the basis of intentions. Both age groups strongly differentiated their judgments of the victim's naughtiness on the basis of his role as provoker, except when the victim was seriously injured by a bad-intentioned aggressor. 相似文献
960.