全文获取类型
收费全文 | 103264篇 |
免费 | 10276篇 |
国内免费 | 7919篇 |
专业分类
化学 | 47988篇 |
晶体学 | 642篇 |
力学 | 9031篇 |
综合类 | 1460篇 |
数学 | 35980篇 |
物理学 | 26358篇 |
出版年
2023年 | 968篇 |
2022年 | 1392篇 |
2021年 | 2932篇 |
2020年 | 2837篇 |
2019年 | 2849篇 |
2018年 | 2453篇 |
2017年 | 2881篇 |
2016年 | 3374篇 |
2015年 | 3104篇 |
2014年 | 4383篇 |
2013年 | 7402篇 |
2012年 | 4913篇 |
2011年 | 5736篇 |
2010年 | 5174篇 |
2009年 | 6311篇 |
2008年 | 6414篇 |
2007年 | 6536篇 |
2006年 | 5503篇 |
2005年 | 4600篇 |
2004年 | 4300篇 |
2003年 | 4020篇 |
2002年 | 6083篇 |
2001年 | 3206篇 |
2000年 | 2683篇 |
1999年 | 2329篇 |
1998年 | 2147篇 |
1997年 | 1728篇 |
1996年 | 1589篇 |
1995年 | 1432篇 |
1994年 | 1314篇 |
1993年 | 1091篇 |
1992年 | 1054篇 |
1991年 | 828篇 |
1990年 | 672篇 |
1989年 | 507篇 |
1988年 | 552篇 |
1987年 | 457篇 |
1986年 | 431篇 |
1985年 | 551篇 |
1984年 | 423篇 |
1983年 | 238篇 |
1982年 | 461篇 |
1981年 | 628篇 |
1980年 | 573篇 |
1979年 | 597篇 |
1978年 | 463篇 |
1977年 | 354篇 |
1976年 | 318篇 |
1974年 | 109篇 |
1973年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
991.
采用精密声级计和双通道声学分析仪,对林杏琴会堂的声场分布、噪声本底和混响时间作了分区测试,应用建筑声学理论对会堂的音质状况进行了分析,并提出改善会堂音质的若干建议. 相似文献
992.
Michelle J. S. Spencer Andrew Hung Ian K. Snook Irene Yarovsky 《Surface science》2003,540(2-3):420-430
The adsorption of atomic S on the Fe(1 1 0) surface is examined using density functional theory (DFT). Three different adsorption sites are considered, including the atop, hollow and bridge sites and the S is adsorbed at a quarter monolayer coverage in a p(2 × 2) arrangement. The hollow site is found to be the most stable, followed by the bridge and atop sites. At all three sites, S adsorption results in relatively minor surface reconstruction, with the most significant being that for the hollow site, with lateral displacements of 0.09 Å. Comparisons between S-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the S. At the hollow site, the presence of S causes an increase in the surface Fe d-orbital density of states between 4 and 5 eV. However, S adsorption has no significant effect on the structure and magnetic properties of the lower substrate layers. 相似文献
993.
994.
The sorption, diffusion, and pervaporation (PV) properties of benzene/cyclohexane (Bz/Cx) mixtures on cation-exchange membranes containing copper ions (Cu(II)) were investigated. The equilibrium sorption isotherms of pure vapors in the membranes and the partial solubility of binary solutions in the membranes were described using the UNIQUAC model. The τiM and τMi values were 0.978 and 0.591 for Bz, and 0.922 and 0.475 for Cx. The transient regimes of vapor sorption were employed to calculate the concentration-dependent diffusion coefficients. Long’s model sufficiently explained the diffusivity of Bz and Cx in the membranes. The pre-exponential factors were 3×10−13 m2/s and the plasticization factors were 3.0 and 3.6 for Bz and Cx, respectively. Excellent agreement was found with the experimental results applying the solubility and diffusivity data to simulate the pervaporation performance (flux and selectivity) using the modified Maxwell–Stefan equation. The membrane containing Cu(II) demonstrates better facilitating capability for Bz transport than that with Na(I), mainly due to its preferential sorption property toward Bz. Replacing Na(I) with Cu(II) into a Neosepta membrane resulted in better separation efficiency and higher Bz flux throughout the entire Bz concentration range. 相似文献
995.
Simone Calogero 《Journal of Differential Equations》2004,204(2):323-338
The Nordström-Vlasov system is a Lorentz invariant model for a self-gravitating collisionless gas. We establish suitable a priori bounds on the solutions of this system, which together with energy estimates and the smoothing effect of “momentum averaging” yield the existence of global weak solutions to the corresponding initial value problem. In the process we improve the continuation criterion for classical solutions which was derived recently. The weak solutions are shown to preserve mass. 相似文献
996.
定常的热传导-对流问题的Galerkin/Petrov最小二乘混合元方法 总被引:1,自引:0,他引:1
1.引言 热传导-对流问题是大气动力学中的一个重要的方程,这个方程组也称为强迫耗散的非线性系统方程组,其较Navier-Stokes方程多了一个未知函数温度场,且温度与速度和压力之间存在着复杂的非线性关系.从热动力学可知,任何运动都会产生热量即有温度,而且温度与速度和压力之间必定互相转化,因此对该非线性系统的研究更具有实际意义.[1]先对 相似文献
997.
998.
振动系统的模态分析实验设计 总被引:8,自引:0,他引:8
利用模态分析原理和简单试验仪器,得到了直观的悬臂梁和圆盘前4阶模态振型,使学生熟悉了模态分析原理和测试方法,有利于学生对振动规律的理解. 相似文献
999.
Under suitable assumptions, a functional central limit theorem is obtained for a three-dimensional model of Maxwellian molecules. This model is related to a nonlinear Boltzmann-type equation. It will be proved that the family of the distributions induced by fluctuation processes converges weakly. 相似文献
1000.
In this paper, existence criteria are established for the existence of periodic solutions of a second order sublinear differential equation with delay and forcing function. Our method is based on careful a priori estimation and continuation theorems, and our sublinear condition is an improvement of the boundedness condition in some recent results. 相似文献