全文获取类型
收费全文 | 133870篇 |
免费 | 17079篇 |
国内免费 | 12577篇 |
专业分类
化学 | 84110篇 |
晶体学 | 1423篇 |
力学 | 7366篇 |
综合类 | 692篇 |
数学 | 21702篇 |
物理学 | 48233篇 |
出版年
2024年 | 366篇 |
2023年 | 2102篇 |
2022年 | 3747篇 |
2021年 | 3965篇 |
2020年 | 4285篇 |
2019年 | 4064篇 |
2018年 | 4894篇 |
2017年 | 4771篇 |
2016年 | 5778篇 |
2015年 | 5565篇 |
2014年 | 6585篇 |
2013年 | 8552篇 |
2012年 | 12481篇 |
2011年 | 11892篇 |
2010年 | 8539篇 |
2009年 | 8038篇 |
2008年 | 7373篇 |
2007年 | 6715篇 |
2006年 | 6290篇 |
2005年 | 9065篇 |
2004年 | 7536篇 |
2003年 | 5227篇 |
2002年 | 3237篇 |
2001年 | 2608篇 |
2000年 | 2084篇 |
1999年 | 2272篇 |
1998年 | 1870篇 |
1997年 | 1635篇 |
1996年 | 1619篇 |
1995年 | 1425篇 |
1994年 | 1298篇 |
1993年 | 1046篇 |
1992年 | 1088篇 |
1991年 | 951篇 |
1990年 | 801篇 |
1989年 | 619篇 |
1988年 | 479篇 |
1987年 | 402篇 |
1986年 | 379篇 |
1985年 | 304篇 |
1984年 | 216篇 |
1983年 | 179篇 |
1982年 | 144篇 |
1981年 | 96篇 |
1980年 | 71篇 |
1979年 | 58篇 |
1976年 | 101篇 |
1975年 | 59篇 |
1974年 | 49篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
22.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
23.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献
24.
本文主要研究的是相函数为齐次椭圆多项式的自由高阶Schrodinger方程.通过相函数等值面的几何性质,得到了解算子的Strichartz加权估计和极大算子加权估计. 相似文献
25.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献
26.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
27.
By further generalizing the skew-symmetric triangular splitting iteration method studied by Krukier, Chikina and Belokon (Applied Numerical Mathematics, 41 (2002), pp. 89–105), in this paper, we present a new iteration scheme, called the modified skew-Hermitian triangular splitting iteration method, for solving the strongly non-Hermitian systems of linear equations with positive definite coefficient matrices. We discuss the convergence property and the optimal parameters of this new method in depth. Moreover, when it is applied to precondition the Krylov subspace methods like GMRES, the preconditioning property of the modified skew-Hermitian triangular splitting iteration is analyzed in detail. Numerical results show that, as both solver and preconditioner, the modified skew-Hermitian triangular splitting iteration method is very effective for solving large sparse positive definite systems of linear equations of strong skew-Hermitian parts. 相似文献
28.
X Y Liu C J Li 《Science in China. Series B, Chemistry, life sciences & earth sciences》1989,32(10):1215-1223
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP. 相似文献
29.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献
30.
Q. B. Li 《Optics and Lasers in Engineering》1989,11(2)
The smoothing spline function has been used for differentiation of photomechanical data in experimental stress analysis. However, since the available software packages use the algorithm with the so-called natural boundary conditions which are not necessarily suitable in many circumstances, errors tend to occur in both the first and second derivatives. In this paper we have modified the algorithm so that the user can have more freedom in selecting boundary conditions which suit the problem best and therefore, as a result, improve the accuracy of the analysis. Two examples are given to show the improvement achievable using the new scheme. 相似文献