全文获取类型
收费全文 | 81833篇 |
免费 | 7235篇 |
国内免费 | 8585篇 |
专业分类
化学 | 36154篇 |
晶体学 | 479篇 |
力学 | 6918篇 |
综合类 | 1364篇 |
数学 | 25982篇 |
物理学 | 26756篇 |
出版年
2023年 | 657篇 |
2022年 | 1332篇 |
2021年 | 1584篇 |
2020年 | 1759篇 |
2019年 | 1979篇 |
2018年 | 1699篇 |
2017年 | 2010篇 |
2016年 | 2401篇 |
2015年 | 2156篇 |
2014年 | 2989篇 |
2013年 | 5658篇 |
2012年 | 3601篇 |
2011年 | 3888篇 |
2010年 | 3280篇 |
2009年 | 4579篇 |
2008年 | 4984篇 |
2007年 | 5216篇 |
2006年 | 4929篇 |
2005年 | 4184篇 |
2004年 | 3882篇 |
2003年 | 3853篇 |
2002年 | 3528篇 |
2001年 | 2915篇 |
2000年 | 2863篇 |
1999年 | 2555篇 |
1998年 | 2346篇 |
1997年 | 1954篇 |
1996年 | 1750篇 |
1995年 | 1587篇 |
1994年 | 1459篇 |
1993年 | 1261篇 |
1992年 | 1223篇 |
1991年 | 916篇 |
1990年 | 769篇 |
1989年 | 665篇 |
1988年 | 620篇 |
1987年 | 484篇 |
1986年 | 410篇 |
1985年 | 466篇 |
1984年 | 449篇 |
1983年 | 227篇 |
1982年 | 364篇 |
1981年 | 414篇 |
1980年 | 318篇 |
1979年 | 312篇 |
1978年 | 240篇 |
1977年 | 219篇 |
1976年 | 170篇 |
1974年 | 116篇 |
1973年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
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
152.
Various antimonate compounds are well known as important inorganic ion exchangers, since they resist radiation and chemical degradation and also exhibit selectivities towards different cations. Ceric, silicon, titanium and ferric antimonates were prepared as inorganic ion exchangers. Characterization of these materials has been described using different techniques, including thermal analysis, surface area measurements, X-ray diffraction and IR-spectroscopy. In batch distribution experiments the influence of HNO3 molarity and Mo concentration for Mo sorption on different matrices is described in terms of their retention capacities and distribution coefficients.The selectivities of these exchangers towards molybdenum are in the order: CeSb > SiSb > FeSb > TiSb. 相似文献
153.
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
154.
The transport of monodisperse as well as polydisperse colloid suspensions in a two-dimensional, water saturated fracture with spatially variable and anisotropic aperture is investigated with a particle tracking model. Both neutrally buoyant and dense colloid suspensions are considered. Although flow and transport in fractured subsurface formations have been studied extensively by numerous investigators, the transport of dense, polydisperse colloid suspensions in a fracture with spatially variable and anisotropic aperture has not been previously explored. Simulated snapshots and breakthrough curves of ensemble averages of several realizations of a log-normally distributed aperture field show that polydisperse colloids exhibit greater spreading than monodisperse colloids, and dense colloids show greater retardation than neutrally buoyant colloids. Moreover, it is demonstrated that aperture anisotropy oriented along the flow direction substantially increases colloid spreading; whereas, aperture anisotropy oriented transverse to the flow direction retards colloid movement. 相似文献
155.
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
156.
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
157.
The binding energy of excitonium negative ion for ground 1S-state in bulk conductors: Ge, Si, CdSe and for green and yellow lines of Cu2O in hyperspherical coordinate method are found. Angular and radial correlations between electrons are taken into account by the channel functions, which are the eigen-functions of operator on the surface of sphere in six-dimensional sphere. The calculation of energies have been done using the adiabatic and Born-Oppenheimer approximations. In Born-Oppenheimer approximation is enough to give a binding energy with only 1.2% error, in adiabatic approximation this error drops to 0.7 %. 相似文献
158.
159.
160.
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