全文获取类型
收费全文 | 123652篇 |
免费 | 1869篇 |
国内免费 | 279篇 |
专业分类
教育 | 86254篇 |
科学研究 | 13413篇 |
各国文化 | 1982篇 |
体育 | 9385篇 |
综合类 | 205篇 |
文化理论 | 1062篇 |
信息传播 | 13499篇 |
出版年
2021年 | 969篇 |
2020年 | 1653篇 |
2019年 | 2557篇 |
2018年 | 3066篇 |
2017年 | 3342篇 |
2016年 | 3382篇 |
2015年 | 2323篇 |
2014年 | 3206篇 |
2013年 | 27295篇 |
2012年 | 2433篇 |
2011年 | 2796篇 |
2010年 | 2415篇 |
2009年 | 2687篇 |
2008年 | 2452篇 |
2007年 | 2188篇 |
2006年 | 2484篇 |
2005年 | 2453篇 |
2004年 | 3038篇 |
2003年 | 2349篇 |
2002年 | 2157篇 |
2001年 | 2079篇 |
2000年 | 1677篇 |
1999年 | 1570篇 |
1998年 | 1468篇 |
1997年 | 1516篇 |
1996年 | 1689篇 |
1995年 | 1463篇 |
1994年 | 1464篇 |
1993年 | 1469篇 |
1992年 | 1504篇 |
1991年 | 1416篇 |
1990年 | 1438篇 |
1989年 | 1329篇 |
1988年 | 1194篇 |
1987年 | 1128篇 |
1986年 | 1159篇 |
1985年 | 1418篇 |
1984年 | 1293篇 |
1983年 | 1274篇 |
1982年 | 1256篇 |
1981年 | 1182篇 |
1980年 | 1158篇 |
1979年 | 1248篇 |
1978年 | 1214篇 |
1977年 | 1119篇 |
1976年 | 1000篇 |
1975年 | 810篇 |
1974年 | 811篇 |
1973年 | 782篇 |
1971年 | 637篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
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
922.
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
923.
924.
925.
926.
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
927.
928.
929.
William N. Anderson Richard J. Duffin George E. Trapp 《Journal of The Franklin Institute》1974,298(1):9-27
A mathematical theory is developed for an imagined device termed a “junctor”. A junctor could be used to interconnect two n-terminal networks giving rise to another n-terminal network. Actually a junctor is itself a simple network with three banks of n-terminals internally connected in some fashion by perfectly conducting wires. Adjacency matrices are formulated to analyze various junctors and their current flows. The main problem treated concerns conditions which would ensure that the junctor operation is associative. 相似文献
930.
The functional integral representation for the space-time Hopf characteristic functional associated with boundary-free incompressible fluid turbulence is evaluated accurately to order R-2, where R is the dimensionless Reynolds number in the theory. This work extends the results obtained previously for C-dominant turbulence to the regime of experimentally accessible large Reynolds numbers. We obtain a characteristic functional of non-Gaussian form as an asymptotically exact solution to the theory for large values of R. Two-point and three-point velocity correlation tensors of physical interest are derived from the characteristic functional. 相似文献