全文获取类型
收费全文 | 23956篇 |
免费 | 2735篇 |
国内免费 | 3318篇 |
专业分类
化学 | 5271篇 |
晶体学 | 156篇 |
力学 | 2996篇 |
综合类 | 567篇 |
数学 | 14044篇 |
物理学 | 6975篇 |
出版年
2024年 | 25篇 |
2023年 | 221篇 |
2022年 | 356篇 |
2021年 | 497篇 |
2020年 | 604篇 |
2019年 | 586篇 |
2018年 | 593篇 |
2017年 | 805篇 |
2016年 | 881篇 |
2015年 | 660篇 |
2014年 | 1243篇 |
2013年 | 1694篇 |
2012年 | 1279篇 |
2011年 | 1559篇 |
2010年 | 1332篇 |
2009年 | 1600篇 |
2008年 | 1637篇 |
2007年 | 1722篇 |
2006年 | 1575篇 |
2005年 | 1524篇 |
2004年 | 1250篇 |
2003年 | 1134篇 |
2002年 | 932篇 |
2001年 | 889篇 |
2000年 | 799篇 |
1999年 | 687篇 |
1998年 | 609篇 |
1997年 | 574篇 |
1996年 | 419篇 |
1995年 | 355篇 |
1994年 | 300篇 |
1993年 | 230篇 |
1992年 | 181篇 |
1991年 | 152篇 |
1990年 | 157篇 |
1989年 | 105篇 |
1988年 | 95篇 |
1987年 | 89篇 |
1986年 | 79篇 |
1985年 | 87篇 |
1984年 | 74篇 |
1983年 | 46篇 |
1982年 | 65篇 |
1981年 | 60篇 |
1980年 | 38篇 |
1979年 | 38篇 |
1978年 | 31篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Numerical simulation aspects, related to low Reynolds number free boundary viscous flows at micro and mesolevel during the resin impregnation stage of the liquid composite moulding process (LCM), are presented in this article. A free boundary program (FBP), developed by the authors, is used to track the movement of the resin front accurately by accounting for the surface tension effects at the boundary. Issues related to the global and local mass conservation (GMC and LMC) are identified and discussed. Unsuitable conditions for LMC and consequently GMC are uncovered at low capillary numbers, and hence a strategy for the numerical simulation of such flows is suggested. FBP encompasses a set of subroutines that are linked to modules in ANSYS. FBP can capture the void formation dynamics based on the analysis developed. We present resin impregnation dynamics in two dimensions. Extension to three dimensions is a subject for further research. Several examples are shown and efficiency of different stabilization techniques are compared. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
82.
The paper presents a new formulation of the integral boundary element method (BEM) using subdomain technique. A continuous approximation of the function and the function derivative in the direction normal to the boundary element (further ‘normal flux’) is introduced for solving the general form of a parabolic diffusion‐convective equation. Double nodes for normal flux approximation are used. The gradient continuity is required at the interior subdomain corners where compatibility and equilibrium interface conditions are prescribed. The obtained system matrix with more equations than unknowns is solved using the fast iterative linear least squares based solver. The robustness and stability of the developed formulation is shown on the cases of a backward‐facing step flow and a square‐driven cavity flow up to the Reynolds number value 50 000. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
83.
Dong Il Han Hoe Jin Hah Hong-Woo Park Sang Man Koo 《Journal of Sol-Gel Science and Technology》2004,32(1-3):47-51
Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of RaSi(OR)3/RbSi(OR)3 or RaSi(OR)3/TEOS (Ra: phenyl; Rb: vinyl, methyl). 相似文献
84.
85.
自组装量子点材料作为一种新型的光电材料无论在理论和实际应用都成为当今物理学界的研 究热点.由GaAs包围的InAs小岛,由于较大的晶格失配(≈-0.067),应变效应在量子点 的 形成过程中起主导作用.大部分计算量子点结构应变分布的方法都是基于数值解法,需要大 量的计算工作.给出用格林函数法推导各种常见形状量子点应变分布的解析表达式详细过程,讨论了弹性各向异性和形状各向异性对量子点应变分布的影响程度.结果表明对于不 同形状量子点结构中主要部分的应变分布都是相似的,流体静压变部分的特征值随量子点形状的变化不
关键词:
自组装量子点
格林函数
应变分布 相似文献
86.
87.
Two-Layered Poly-o-phenylenediamine/Polyaniline Composite: Electrosynthesis and Spectroelectrochemical Properties 总被引:1,自引:0,他引:1
E. Yu. Pisarevskaya E. V. Ovsyannikova N. M. Alpatova 《Russian Journal of Electrochemistry》2004,40(9):969-976
Spectroelectrochemical properties of poly-o-phenylenediamine (PPD) and the synthesized composite of PPD and polyaniline—two chemically related polymers containing an amino-substituted benzene ring but having different conduction nature—are studied. The polyaniline synthesis on PPD-modified electrodes involves stages of the reaction initiation, the copolymer formation, and the formation of a polyaniline layer at the copolymer/solution interface. 相似文献
88.
By extracting combinatorial structures in well-solved nonlinear combinatorial optimization problems, Murota (1996,1998) introduced the concepts of M-convexity and L-convexity to functions defined over the integer lattice. Recently, Murota–Shioura (2000, 2001) extended these concepts to polyhedral convex functions and quadratic functions in continuous variables. In this paper, we consider a further extension to more general convex functions defined over the real space, and provide a proof for the conjugacy relationship between general M-convex and L-convex functions.Mathematics Subject Classification (1991): 90C10, 90C25, 90C27, 90C35This work is supported by Grant-in-Aid of the Ministry of Education, Culture, Sports, Science and Technology of Japan 相似文献
89.
Periodica Mathematica Hungarica - In our paper we study the usage of partially defined Boolean functions (PDBFs) for generating cryptographically strong Boolean functions. A PDBF can be considered... 相似文献
90.
We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen–Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non‐linear. We employ two‐scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献