全文获取类型
收费全文 | 25057篇 |
免费 | 2026篇 |
国内免费 | 1469篇 |
专业分类
化学 | 1100篇 |
晶体学 | 64篇 |
力学 | 4045篇 |
综合类 | 333篇 |
数学 | 19709篇 |
物理学 | 3301篇 |
出版年
2024年 | 33篇 |
2023年 | 251篇 |
2022年 | 286篇 |
2021年 | 398篇 |
2020年 | 581篇 |
2019年 | 607篇 |
2018年 | 626篇 |
2017年 | 694篇 |
2016年 | 765篇 |
2015年 | 562篇 |
2014年 | 1092篇 |
2013年 | 2015篇 |
2012年 | 1125篇 |
2011年 | 1339篇 |
2010年 | 1156篇 |
2009年 | 1565篇 |
2008年 | 1639篇 |
2007年 | 1655篇 |
2006年 | 1461篇 |
2005年 | 1211篇 |
2004年 | 1115篇 |
2003年 | 1080篇 |
2002年 | 1002篇 |
2001年 | 800篇 |
2000年 | 783篇 |
1999年 | 674篇 |
1998年 | 660篇 |
1997年 | 570篇 |
1996年 | 421篇 |
1995年 | 343篇 |
1994年 | 280篇 |
1993年 | 248篇 |
1992年 | 228篇 |
1991年 | 209篇 |
1990年 | 168篇 |
1989年 | 93篇 |
1988年 | 83篇 |
1987年 | 76篇 |
1986年 | 74篇 |
1985年 | 98篇 |
1984年 | 107篇 |
1983年 | 65篇 |
1982年 | 74篇 |
1981年 | 53篇 |
1980年 | 44篇 |
1979年 | 39篇 |
1978年 | 31篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Zhao Hanzhong 《Acta Mechanica Solida Sinica》2002,15(2):156-162
A finite difference/boundary integral procedure to determine the acoustic reflected pressure from a fluid-loaded bi-laminated
plate is described. The bi-laminate is composed of a piezoelectric layer and an elastic layer in contact with the fluid, and
is held by an acoustically hard baffle. In the numerical model, the fluid pressure at fluid/solid interface is replaced by
a continuum of point sources weighted by the normal acceleration of the elastic plate, and the governing equation system is
solved in the solid domain. With the normal acceleration found, the reflected pressure in the fluid is determined by an integral
expression involving the Green's function. It is demonstrated that an appropriate applied voltage potential across the piezoelectric
layer has the effect of cancelling either the reflected or scattered pressure of the plate at any chosen field points in the
fluid.
Project supported by the National Natural Science Foundation of China (No. 10172039). 相似文献
72.
We analyze the effect of co-segregation on the mobility of grain boundaries within the framework of the impurity drag theory originally proposed by Cahn and Lücke and Stüwe for an ideal solution. The new derivation extends this model to the case where there are two types of impurities (or three components in the alloy). Since the resultant expression for the boundary mobility is complicated, numerical solutions were obtained for several cases to show how co-segregation affects the boundary mobility. Depending on the relative diffusivities of the two impurities which are both attracted to the boundary, the mobility may either increase or decrease with increasing concentration of one of the impurities. When one of the impurities is attracted to the boundary and the other repelled from the boundary, increasing the concentration of the attractive impurity can lead to a sharp decrease in the boundary mobility. 相似文献
73.
Patrick Dehornoy 《Algebra Universalis》2002,48(2):223-248
We solve the word problem of the identity x(yz) = (xy)(yz) by investigating a certain group describing the geometry of that identity. We also construct a concrete realization of the
one-generated free algebra relative to the above identity.
Received March 23, 2001; accepted in final form July 6, 2002. 相似文献
74.
Existence and Uniqueness of Endemic States for the Age-structured MSEIR Epidemic Model 总被引:1,自引:0,他引:1
Geni Gupur 《应用数学学报(英文版)》2002,18(3):441-454
The existence and uniqueness of positive steady states for the age-structured MSEIR epidemic model with age-dependent transmission coefficient is considered. Threshold results for the existence of endemic states are established; under certain conditions, uniqueness is also shown. 相似文献
75.
We establish the existence and stability of multidimensional transonic shocks for the Euler equations for steady potential compressible fluids. The Euler equations, consisting of the conservation law of mass and the Bernoulli law for the velocity, can be written as a second-order, nonlinear equation of mixed elliptic-hyperbolic type for the velocity potential. The transonic shock problem can be formulated into the following free boundary problem: The free boundary is the location of the transonic shock which divides the two regions of smooth flow, and the equation is hyperbolic in the upstream region where the smooth perturbed flow is supersonic. We develop a nonlinear approach to deal with such a free boundary problem in order to solve the transonic shock problem. Our results indicate that there exists a unique solution of the free boundary problem such that the equation is always elliptic in the downstream region and the free boundary is smooth, provided that the hyperbolic phase is close to a uniform flow. We prove that the free boundary is stable under the steady perturbation of the hyperbolic phase. We also establish the existence and stability of multidimensional transonic shocks near spherical or circular transonic shocks.
76.
利用变分法证明平面调和函数的外问题的确切形式;在此基础上,建立外问题的具有间接变量的等价边界积分方程;传统的外问题及边界积分方程不具有普遍适用性,本文对此进行了详细的讨论. 相似文献
77.
Richard Moeckel 《Transactions of the American Mathematical Society》2005,357(8):3105-3117
The five relative equilibria of the three-body problem give rise to solutions where the bodies rotate rigidly around their center of mass. For these solutions, the moment of inertia of the bodies with respect to the center of mass is clearly constant. Saari conjectured that these rigid motions are the only solutions with constant moment of inertia. This result will be proved here for the planar problem with three nonzero masses with the help of some computational algebra and geometry.
78.
79.
An analytical solution of a linearized problem of the emission of periodic internal waves by part of a plane which oscillates with a small amplitude in an arbitrary direction in a viscous exponentially stratified fluid is constructed. Solutions of the dispersion equation are given for all positions of the emitting surface (arbitrary, vertical, horizontal, and critical when one of the beam propagation directions is collinear with the emitting surface). The possibility of transition to the case of a uniform fluid, which is important for applications, is analyzed. 相似文献
80.
We discuss the problem of transmitting polarized pulses along optical fibers with variable dispersion. The dissipation and mean dispersion are assumed to be zero, which allows using the model of the vector nonlinear Schrödinger equation. We consider an optical fiber consisting of arms of equal length, which is assumed to be large. We propose an asymptotic recursive procedure for calculating the amplitude and the phase of an optical pulse propagating along the optical cable with variable dispersion. 相似文献