全文获取类型
收费全文 | 29266篇 |
免费 | 2165篇 |
国内免费 | 1671篇 |
专业分类
化学 | 1854篇 |
晶体学 | 66篇 |
力学 | 4274篇 |
综合类 | 343篇 |
数学 | 22550篇 |
物理学 | 4015篇 |
出版年
2024年 | 41篇 |
2023年 | 302篇 |
2022年 | 381篇 |
2021年 | 466篇 |
2020年 | 641篇 |
2019年 | 696篇 |
2018年 | 693篇 |
2017年 | 775篇 |
2016年 | 834篇 |
2015年 | 643篇 |
2014年 | 1240篇 |
2013年 | 2358篇 |
2012年 | 1328篇 |
2011年 | 1573篇 |
2010年 | 1379篇 |
2009年 | 1872篇 |
2008年 | 1964篇 |
2007年 | 1963篇 |
2006年 | 1665篇 |
2005年 | 1358篇 |
2004年 | 1275篇 |
2003年 | 1201篇 |
2002年 | 1120篇 |
2001年 | 873篇 |
2000年 | 853篇 |
1999年 | 731篇 |
1998年 | 736篇 |
1997年 | 636篇 |
1996年 | 536篇 |
1995年 | 406篇 |
1994年 | 364篇 |
1993年 | 298篇 |
1992年 | 278篇 |
1991年 | 236篇 |
1990年 | 197篇 |
1989年 | 115篇 |
1988年 | 102篇 |
1987年 | 89篇 |
1986年 | 99篇 |
1985年 | 129篇 |
1984年 | 135篇 |
1983年 | 75篇 |
1982年 | 113篇 |
1981年 | 70篇 |
1980年 | 63篇 |
1979年 | 61篇 |
1978年 | 46篇 |
1977年 | 29篇 |
1976年 | 20篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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
72.
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
73.
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.
74.
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.
75.
差分吸收光谱法测量大气痕量气体浓度误差分析及改善方法 总被引:8,自引:2,他引:6
差分吸收光谱技术(DOAS)中采用线性最小二乘拟合方法,用痕量气体标准差分吸收截面对测量得到的差分吸收光谱进行拟合,得出大气中痕量气体的浓度.计算结果的准确性不仅取决于光谱的测量精度,而且受标准差分吸收截面以及仪器函数和温度等诸多因素的影响.详细地分析了计算误差的产生原因,提出了用高浓度样品池得到标准吸收截面的方法,针对光谱固有结构,以及温度对标准吸收截面的影响,改进了浓度反演算法.大量的实验表明,综合运用上述方法,即便对低浓度的样气,相对测量误差也能降低到10%以下. 相似文献
76.
77.
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
78.
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
79.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
80.
凹整数规划的分枝定界解法 总被引:3,自引:0,他引:3
凹整数规划是一类重要的非线性整数规划问题,也是在经济和管理中有着广泛应用的最优化问题.本文主要研究用分枝定界方法求解凹整数规划问题,这一方法的基本思想是对目标函数进行线性下逼近,然后用乘子搜索法求解连续松弛问题.数值结果表明,用这种分枝定界方法求解凹整数规划是有效的. 相似文献