全文获取类型
收费全文 | 149870篇 |
免费 | 26240篇 |
国内免费 | 29065篇 |
专业分类
化学 | 105252篇 |
晶体学 | 3357篇 |
力学 | 9726篇 |
综合类 | 2631篇 |
数学 | 20371篇 |
物理学 | 63838篇 |
出版年
2024年 | 480篇 |
2023年 | 2538篇 |
2022年 | 5467篇 |
2021年 | 5654篇 |
2020年 | 5800篇 |
2019年 | 5554篇 |
2018年 | 5161篇 |
2017年 | 5649篇 |
2016年 | 6565篇 |
2015年 | 7327篇 |
2014年 | 8943篇 |
2013年 | 11633篇 |
2012年 | 12995篇 |
2011年 | 13370篇 |
2010年 | 10746篇 |
2009年 | 10642篇 |
2008年 | 11529篇 |
2007年 | 10200篇 |
2006年 | 9796篇 |
2005年 | 8314篇 |
2004年 | 6419篇 |
2003年 | 4929篇 |
2002年 | 4614篇 |
2001年 | 4231篇 |
2000年 | 4093篇 |
1999年 | 3266篇 |
1998年 | 2387篇 |
1997年 | 2081篇 |
1996年 | 2041篇 |
1995年 | 1799篇 |
1994年 | 1754篇 |
1993年 | 1474篇 |
1992年 | 1294篇 |
1991年 | 1060篇 |
1990年 | 935篇 |
1989年 | 822篇 |
1988年 | 634篇 |
1987年 | 543篇 |
1986年 | 493篇 |
1985年 | 389篇 |
1984年 | 309篇 |
1983年 | 287篇 |
1982年 | 241篇 |
1981年 | 175篇 |
1980年 | 131篇 |
1979年 | 89篇 |
1978年 | 46篇 |
1977年 | 33篇 |
1976年 | 37篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
多目标半定规划的互补弱鞍点和G-鞍点最优性条件 总被引:1,自引:0,他引:1
对于含矩阵函数半定约束和多个目标函数的多目标半定规划问题,给出Lagrange函数在弱有效意义下的互补弱鞍点和Geofrrion恰当有效意义下的G-鞍点的定义及其等价定义.然后,在较弱的凸性条件下,利用含矩阵和向量约束的择一性定理,建立多目标半定规划的互补弱鞍点和G-鞍点充分必要条件. 相似文献
143.
The effects of partial substitution of Mn for Co on the thermoelectric properties of Ca3MnxCo4−xO9 (x=0, 0.03, 0.9), prepared by sol-gel process, were investigated at the temperatures from 380 K down to 5 K. The results indicate that the substitution of Mn for Co results in increase in thermopower at temperatures >∼80 K, and substantial (23-31% at 300 K) decrease in lattice thermal conductivity in the whole temperature range investigated. The temperature behavior of ZT suggests that Ca3MnxCo4−xO9 with light Mn substitution would be a promising candidate for high-temperature thermoelectric applications. 相似文献
144.
In this paper we consider the dual problems for multiobjective programming with generalized convex functions. We obtain the weak duality and the strong duality. At last, we give an equivalent relationship between saddle point and efficient solution in multiobjective programming. 相似文献
145.
Spontaneous emission behavior from atoms (or molecules) in one-dimensional photonic crystal with a defect is investigated. Taken all the TE and TM modes into account, the normalized spontaneous emission rate of the atom is calculated as a function of the position of the atom in the crystal. Results for both nonabsorbing dielectric structure and absorbing dielectric structure are presented. With the increase of the thickness of the defect in which the atoms are embedded, the oscillations of the spontaneous emission rate versus the position of the atom become dense and the lifetime distribution becomes narrow and sharp. The PC effect may lead to the coexistence of both accelerated and inhibited decay processes. 相似文献
146.
Huimin Xie Biao Li Robert Geer Bai Xu James Castracane 《Optics and Lasers in Engineering》2003,40(3):163-177
A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method. 相似文献
147.
Under dielectric continuum approximation, interface optical (IO) phonon modes and the Frohlich electron-IO phonon interaction Hamiltonian in a multi-shell spherical nanoheterosystem were derived and studied. Numericalcalculations on three-layer and four-layer CdS/HgS spherical nanoheterosystems have been performed. Results revealthat there are four IO phonon modes for the three-layer system and six IO phonon modes for the four-layer system.On each interface, there are two IO phonon modes, the frequency of one is between WTO,CdS and WLO,CdS, and that ofthe other is between WTO,HgS and WLO,HgS. With the increasing of quantum number l, the frequency of each IO modeapproaches one of the two frequency values of the single CdS/HgS heterostructure, and the potential for each IO modeis more and more localized at a certain interface, furthermore, the coupling between the electron-lO phonons becomes weaker. 相似文献
148.
Comment on “A Hierarchy of Integrable Nonlinear Lattice Equations and New Integrable Symplectic Map“
Comment on a recent paper on Commun. Theor. Phys. (Beijing, China) 38 (2002) pp. 523-528. 相似文献
149.
溃坝问题的间断有限元方法 总被引:2,自引:0,他引:2
本文研究90年代初提出的Runge-Kutta间断Galerkin有限元方法,给出该方法的精度分析,通过经典算例验证该方法处理间断问题、捕捉锐利波形的能力,并将其推广到求解浅水问题.针对坝底无摩擦,无坡度的理想情形进行讨论,给出方溃坝和圆溃坝问题的数值模拟结果. 相似文献
150.