全文获取类型
收费全文 | 763629篇 |
免费 | 40139篇 |
国内免费 | 30732篇 |
专业分类
化学 | 344147篇 |
晶体学 | 10110篇 |
力学 | 34750篇 |
综合类 | 357篇 |
数学 | 82323篇 |
物理学 | 238753篇 |
无线电 | 124060篇 |
出版年
2022年 | 6073篇 |
2021年 | 8312篇 |
2020年 | 9166篇 |
2019年 | 10982篇 |
2018年 | 12864篇 |
2017年 | 13446篇 |
2016年 | 18171篇 |
2015年 | 13480篇 |
2014年 | 18738篇 |
2013年 | 36892篇 |
2012年 | 30555篇 |
2011年 | 35159篇 |
2010年 | 28975篇 |
2009年 | 29944篇 |
2008年 | 31489篇 |
2007年 | 31406篇 |
2006年 | 29504篇 |
2005年 | 26632篇 |
2004年 | 25731篇 |
2003年 | 22737篇 |
2002年 | 22486篇 |
2001年 | 24960篇 |
2000年 | 19803篇 |
1999年 | 16403篇 |
1998年 | 14200篇 |
1997年 | 13545篇 |
1996年 | 13179篇 |
1995年 | 12225篇 |
1994年 | 12192篇 |
1993年 | 12015篇 |
1992年 | 12257篇 |
1991年 | 12116篇 |
1990年 | 11258篇 |
1989年 | 10705篇 |
1988年 | 10139篇 |
1987年 | 8950篇 |
1986年 | 8454篇 |
1985年 | 10297篇 |
1984年 | 10512篇 |
1983年 | 8292篇 |
1982年 | 8710篇 |
1981年 | 8292篇 |
1980年 | 7968篇 |
1979年 | 8196篇 |
1978年 | 8219篇 |
1977年 | 8213篇 |
1976年 | 8439篇 |
1975年 | 7392篇 |
1974年 | 7405篇 |
1973年 | 7544篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
991.
Compositions of generalized fractional integral operators involving Gauss hy-pergeometric function with power weights are studied. Composition formulas for such integrals which are the operators of the same type are obtained. In parti-cular, compositions of two identical operators are given. 相似文献
992.
993.
It is proved that biorthogonal polynomials obey two different kinds of Christoffel-Darboux-type formulae, one linking polynomials with a different parameter and one combining polynomials with different degrees. This is used to produce a mixed recurrence relation, which is valid for all biorthogonal polynomials. This recurrence relation establishes several results on interlacing property of zeros of successive biorthogonal polynomials and leads to a new result on the interlace of zeros of orthogonal polynomials (of equal degrees) with respect to two distributionsdψ(x) andx p dψ(x), 0<p≤1, with support in either [0, 1] or [1, ∞). 相似文献
994.
995.
S. P. Mukherjee A. K. Chattopadhyay 《The Journal of the Operational Research Society》1989,40(5):489-494
Consider an organization with several categories of staff, each having a specified number of members. The age of entry into service and the age of retirement are both specified. Withdrawals occur at time-independent rates. Under this set-up, the authors have computed the maximum ages at which promotions should take place, assuming that the staff members continuing at various ages are random. Some illustrative calculations have been carried out. 相似文献
996.
Birational equivalence in the symplectic category 总被引:7,自引:0,他引:7
997.
The diffraction of plane surface gravitational waves by the edge of an ice cover lying on the surface of an incompressible fluid of infinitely great depth is considered. The ice cover is simulated by a thin elastic plate. The wave reflection and transmission coefficients are determined when it interacts with the ice cover. A wave field is constructed in the fluid under the conditions that a periodic lumped force and a lumped moment act on the edge of the ice cover. It is shown that as the incident wavelength increases the reflection coefficient tends to zero and the transmission coefficient tends to unity. 相似文献
998.
The annealing algorithm (Ref. 1) is modified to allow for noisy or imprecise measurements of the energy cost function. This is important when the energy cannot be measured exactly or when it is computationally expensive to do so. Under suitable conditions on the noise/imprecision, it is shown that the modified algorithm exhibits the same convergence in probability to the globally minimum energy states as the annealing algorithm (Ref. 2). Since the annealing algorithm will typically enter and exit the minimum energy states infinitely often with probability one, the minimum energy state visited by the annealing algorithm is usually tracked. The effect of using noisy or imprecise energy measurements on tracking the minimum energy state visited by the modified algorithms is examined.The research reported here has been supported under Contracts AFOSR-85-0227, DAAG-29-84-K-0005, and DAAL-03-86-K-0171 and a Purdue Research Initiation Grant. 相似文献
999.
1000.
A criterion for the local taper angle of a low-loss single-mode fibre coupler is established by considering the dominant mode coupling in the coupler taper. Effects due to structure parameters, such as cladding/core thickness ratio, corecladding index difference and core separation, are investigated. It is found that the criterion for the coupler taper can be well approximated by that for the single-mode fibre taper with the same structure parameters. 相似文献