全文获取类型
收费全文 | 72992篇 |
免费 | 5513篇 |
国内免费 | 6711篇 |
专业分类
化学 | 27385篇 |
晶体学 | 289篇 |
力学 | 6525篇 |
综合类 | 1317篇 |
数学 | 27708篇 |
物理学 | 21992篇 |
出版年
2023年 | 614篇 |
2022年 | 1240篇 |
2021年 | 1384篇 |
2020年 | 1464篇 |
2019年 | 1736篇 |
2018年 | 1372篇 |
2017年 | 1639篇 |
2016年 | 1879篇 |
2015年 | 1758篇 |
2014年 | 2531篇 |
2013年 | 4609篇 |
2012年 | 2843篇 |
2011年 | 3398篇 |
2010年 | 2967篇 |
2009年 | 4178篇 |
2008年 | 4554篇 |
2007年 | 4745篇 |
2006年 | 4372篇 |
2005年 | 3626篇 |
2004年 | 3318篇 |
2003年 | 3353篇 |
2002年 | 3049篇 |
2001年 | 2579篇 |
2000年 | 2518篇 |
1999年 | 2248篇 |
1998年 | 2106篇 |
1997年 | 1727篇 |
1996年 | 1546篇 |
1995年 | 1393篇 |
1994年 | 1295篇 |
1993年 | 1105篇 |
1992年 | 1077篇 |
1991年 | 830篇 |
1990年 | 694篇 |
1989年 | 593篇 |
1988年 | 557篇 |
1987年 | 431篇 |
1986年 | 375篇 |
1985年 | 436篇 |
1984年 | 427篇 |
1983年 | 209篇 |
1982年 | 340篇 |
1981年 | 400篇 |
1980年 | 302篇 |
1979年 | 293篇 |
1978年 | 220篇 |
1977年 | 207篇 |
1976年 | 155篇 |
1974年 | 110篇 |
1973年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
该文讨论一类带有奇异系数的双重调和方程{△^2u-μu/|x|^s=f(x,u),x∈Ω,u=δu/δv=0,x∈δΩ,这里Ω包含R^N是包含0的有界光滑区域,u∈H0^2(Ω),μ∈R是参数,0≤s≤2,△^2=△△表示双重拉普拉斯算子,当f(x,u)=u^p,p=2N/N-4时,上述问题就是一个临界双重调和问题,该文运用Sobolev-Hardy不等式和变分方法,得到它的解的存在性的一些结果。 相似文献
143.
基于相对论平均场理论,研究了各种相互作用参数组(NL1、NL3、NLSH、TM1和GL-97)对中子星物质的性质和中子星整体结构的影响.发现参数组NL1、NL3和NLSH所给出的中子星内部的介子场强度、物质的组成比例、物态方程和中子星的整体特点基本相同,但与TM1和GL-97之间有较大的差别.相对于其他参数组,GL-97给出的介子场强度最弱,中子星的相对数密度最大,物态方程也最软,同时采用GL-97参数组计算的中子星的最大质量也最小. 相似文献
144.
The concept of super hamiltonian semigroup is introduced. As a result, the structure theorems obtained by A. Cherubini and A. Varisco on quasi commutative semi-groups and quasi hamiltonian semigroups respectively are extended to super hamiltonian semigroups. 相似文献
145.
Results of two urgent and practically important directions of research on the indirect oxidation of organic compounds by highly reactive intermediates generated electrochemically from oxygen (HO2
–, HO2
·, HO·) are considered and orderly arranged. The studies in question are the indirect synthesis and mineralization of organic toxicants in waste water. 相似文献
146.
车前子中多糖含量的测定 总被引:12,自引:1,他引:11
采用蒽酮-硫酸法比色测定,用精制车前子多糖测得车前子多糖对葡萄糖的换算因子,对我国同属不同品种的车前子不同采集时间及炮制前后其多糖含量进行了比较研究。结果表明:此测定方法简便可行。供试液在8h内显色稳定,重现性较好,平均回收率为97.8%,RSD=1.41%(n=5)。江西吉安产大粒车前子生品多糖含量在9.15%~9.83%之间,炮制后其多糖含量在6.29%~6.81%之间;南昌新祺周车前GAP标准基地的大粒车前子生品多糖含量为7.85%~8.38%,炮制后其多糖含量为6.01%~6.64%;东北产的小粒车前子生品多糖含量为6.61%,炮制后其多糖含量为6.45%。 相似文献
147.
We treat here of the question of absorbing boundary conditionsfor nonlinear diffusion equations. We use the conditions designedfor the linear equation, we prove them to be well posed forthe nonlinear problem, and through numerical experiments thatthey are well suited for reactiondiffusion equations. 相似文献
148.
149.
A group representation of radiation propagation in an anisotropic medium is developed. The system of wave equations for electromagnetic potentials, obtained from the Maxwell equations with account for the constitutive equations, has been factorized. It is shown that the linear differential operator of the factorized system is orthogonal in transparent crystals and unitary in gyrotropic ones and is represented through the momentum operator. On the basis of the commutation relations for the components of this operator, the eigenvalue problem has been solved and the expression for the change in the radiant energy in the crystal in the form of spherical waves has been obtained. The dependences of the ray and phase velocities and the polarization vectors of waves on the birefringence anisotropy and gyrotropy as well as on the angular momentum, displacement current, and bound charge determining them have been analyzed. It has been established that in the general case of gyrotropic crystals where the nonreciprocity phenomenon takes place and in magnetoelectrics Maxwell equations are represented in a form similar to the Dirac equations and the electromagnetic radiation is correctly described by means of bispinors and is quantized as fermions. 相似文献
150.
Andrey Pereverzev 《Foundations of Physics Letters》2003,16(5):411-428
We argue that it may be possible to consistently explain the quantum measurement by assuming that the wave function is in one-to-one correspondence with objective physical reality and has no probabilistic interpretation. In the context of such approach we consider the model of a harmonic oscillator linearly coupled to a heat bath and treat the oscillator as the system being measured. Three classes of initial pure states for the bath are considered. Exact expressions for the average values and variances of the oscillator coordinate and momentum as functions of time are considered for each class of pure states. It is shown that these quantities exhibit different asymptotic behavior for different classes of initial states of the bath. In particular, if each mode of the bath is initially in a coherent state, then for an arbitrary initial state of the oscillator the variances of the oscillator coordinate and momentum asymptotically approach the same values as for a coherent state of the free oscillator, while the averages of coordinate and momentum show a Brownian-like behavior. We argue that such behavior shows several features of the quantum measurement and supports our interpretation of the wave function. 相似文献