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 31 毫秒
971.
972.
973.
Formulae are derived for the deflection surface of a symmetrically loaded circular plate having several points supports which are situated at equal distances apart on a single concentric circle. There is no restriction on the diameter of the support circle, which may be as large as the diameter of the plate itself. The results of this paper compare favorably with published experimental results. Numerical deflection coefficients for a uniformly loaded plate are provided, and these could be utilized for optimizing the positions and the number of concentrated supports. 相似文献
974.
The difficulties in solving Fredholm integral equations of the first kind are well known. A classical method has been to convert the equation into a set of m linear algebraic equations in n unknowns (m?n). For computational convenience, it is customary to force m = n and solve the resulting ill-conditioned system using one technique or other. In the general case, a feasible solution, if it exists, can be found by determining the generalized inverse of the coefficient matrix. One method of finding the generalized inverse is to reformulate the problem and observe the steady state response of a system of ordinary differential equations with prescribed initial conditions. Results obtained from this reformulation are found to be comparable in quality to those obtained earlier by other methods. Analog and digital computer implementations are discussed. 相似文献
975.
In this paper, the stability equation method is applied to the analysis of nonlinear systems with characteristics equations having complex coefficients. Three types of systems are studied: those with unstable open-loop poles, unstable characteristics roots or an equal number of open-loop poles and zeros. 相似文献
976.
977.
Ioannis M. Besieris 《Journal of The Franklin Institute》1974,297(4):243-258
The electromagnetic radiation arising from a longitudinally and a transversely oriented magnetic dipole in a dissipative uniaxially anisotropic medium is determined by writing separate equations for the electromagnetic field intensities, and utilizing a spectral representation in the space-time Fourier domain. It is established that explicit, time- dependent, analytical solutions are possible in the case where the permitivity, permeability and conductivity tensors are simultaneously diagonalizable by means of a collineatory transformation, and the permittivity and conductivity tensors are directly proportional to each other. 相似文献
978.
Georges D. Szakasits 《Research Policy》1974,3(1):18-28
The article deals with the results achieved by the adoption of the SAPPHO method (developed by the Science Policy Research Unit of Sussex University) to the conditions of the Hungarian electronics industry. The results coincide to a great extent with those established in the course of the survey made in England, although there are some significant differences. 相似文献
979.
980.