全文获取类型
收费全文 | 7438篇 |
免费 | 790篇 |
国内免费 | 952篇 |
专业分类
化学 | 3020篇 |
晶体学 | 73篇 |
力学 | 642篇 |
综合类 | 118篇 |
数学 | 2476篇 |
物理学 | 2851篇 |
出版年
2024年 | 12篇 |
2023年 | 66篇 |
2022年 | 124篇 |
2021年 | 145篇 |
2020年 | 192篇 |
2019年 | 198篇 |
2018年 | 170篇 |
2017年 | 202篇 |
2016年 | 252篇 |
2015年 | 180篇 |
2014年 | 296篇 |
2013年 | 545篇 |
2012年 | 400篇 |
2011年 | 481篇 |
2010年 | 349篇 |
2009年 | 452篇 |
2008年 | 453篇 |
2007年 | 508篇 |
2006年 | 439篇 |
2005年 | 410篇 |
2004年 | 357篇 |
2003年 | 341篇 |
2002年 | 286篇 |
2001年 | 271篇 |
2000年 | 250篇 |
1999年 | 218篇 |
1998年 | 190篇 |
1997年 | 169篇 |
1996年 | 163篇 |
1995年 | 135篇 |
1994年 | 126篇 |
1993年 | 76篇 |
1992年 | 105篇 |
1991年 | 94篇 |
1990年 | 68篇 |
1989年 | 67篇 |
1988年 | 53篇 |
1987年 | 48篇 |
1986年 | 44篇 |
1985年 | 31篇 |
1984年 | 35篇 |
1983年 | 19篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 21篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1973年 | 10篇 |
排序方式: 共有9180条查询结果,搜索用时 15 毫秒
91.
Vincenzo Recupero 《Journal of Mathematical Analysis and Applications》2004,300(2):387-407
In this paper we study a model of phase relaxation for the Stefan problem with the Cattaneo–Maxwell heat flux law. We prove an existence and uniqueness result for the resulting problem and we show that its solution converges to the solution of the Stefan problem as the two relaxation parameters go to zero, provided a relation between these parameters holds. 相似文献
92.
93.
94.
B. Y. Myung J. S. Kim J. J. Kim T. H. Yoon 《Journal of polymer science. Part A, Polymer chemistry》2003,41(21):3361-3374
2,2‐Bis[4(4‐aminophenoxy)phenyl]phthalein‐3′,5′‐bis(trifluoromethyl)anilide (6FADAP), containing fluorine and phthalimide moieties, was synthesized via the Williamson ether condensation reaction from 1‐chloro‐4‐nitrobenzene and phenolphthalein‐3′,5′‐bis(trifluoromethyl)anilide, which was followed by hydrogenation. Monomers such as 2,2‐bis[4(4‐aminophenoxy)phenyl]phthalein‐anilide containing phthalimide groups and 2,2‐bis[4(4‐aminophenoxy)phenyl]phthalein containing only phthalein moieties were also synthesized for comparison. The monomers were first characterized by Fourier transform infrared (FTIR), 1H NMR, 19F NMR, elemental analysis, and titration and were then used to prepare polyimides with 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride. The polyimides were designed to have molecular weights of 20,000 g/mol via off‐stoichiometry and were characterized by FTIR, NMR, gel permeation chromatography (GPC), differential scanning calorimetry, and thermogravimetric analysis. Their solubility, water absorption, dielectric constant, and refractive index were also evaluated. The polyimides prepared with 6FADAP, containing fluorine and phthalimide moieties, had excellent solubility in N‐methylpyrrolidinone, N,N‐dimethylacetamide, tetrahydrofuran, CHCl3, tetrachloroethane, and acetone, and GPC analysis showed a molecular weight of 18,700 g/mol. The polyimides also exhibited a high glass‐transition temperature (290 °C), good thermal stability (~500 °C in air), low water absorption (1.9 wt %), a low dielectric constant (2.81), a low refractive index, and low birefringence (0.0041). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3361–3374, 2003 相似文献
95.
Periodica Mathematica Hungarica - Let X 1,X 2,... be a sequence of independent and identically distributed random variables, and put % MATHTYPE!MTEF!2!1!+-%... 相似文献
96.
Xuming Xie 《Journal of Differential Equations》2004,197(2):349-426
This paper concerns the existence of solutions to a steady needle crystal growth problem in a one-sided model. We rigorously prove that for small nonzero anisotropy γ, analytic symmetric needle crystal solutions exist in the limit of surface tension ε2 if only if the stokes constant S for a relatively simple nonlinear differential equation is zero. This Stokes constant S depends on the parameter β=29/7γε−8/7 and earlier numerical calculations by a number of investigators have shown this to be zero for a discrete set of values of β. It is also proven that for γ=0, there can be no symmetric needle crystal solution in the considered space.The methodology consists of two steps. First, the original problem is reduced to a weak half-strip problem for any γ in a compact set of [0,1) by relaxation of the symmetry condition. The weak problem is shown to have a unique solution in the function space considered for any γ∈[0,γm] for some γm>0. When a symmetry is invoked, the weak problem is shown equivalent to the original needle crystal problem. Next, by considering the behavior of the solution in neighborhood of an appropriate complex turning point for γ∈(0,γm], we extract an exponentially small term in ε as ε→0+ that generally violates the symmetric condition. We prove that the symmetry condition is satisfied for small ε when the parameter β is constrained appropriately. 相似文献
97.
98.
The propagation of solitons through optical couplers is studied here in this paper. Both the twin-core couplers as well as the multiple-core couplers are considered here in this paper. The parameter dynamics of the solitons that are governed by the coupled generalized nonlinear Schrodinger's equation, due to non-Kerr law nonlinearity, has been obtained for such couplers. 相似文献
99.
Frank N. Proske Madan L. Puri 《Proceedings of the American Mathematical Society》2003,131(9):2937-2944
In this article we prove a strong law of large numbers for Borel measurable nonseparably valued random elements in the case of generalized random sets.
100.
由于含时波包方法具有经典的直观又不乏量子力学的准确 ,选择含时波包方法来处理F +CH2 D2 →CH2 D/CHD2 +DF/HF反应 .把半刚性振转子 (SVRT)模型应用到该反应体系中 ,研究了两个通道中该反应从基态反应物开始在修正过的J1(MJ1)势能面上计算出来了反应几率、积分截面、速率常数 .反应几率随能量变化的图的数值结果给出了振荡结构 ,这些振荡结构是可以和动力学振荡联系起来的 .而这些振荡结构在积分截面随着能量变化的图中就被反应几率求和后的平均结果所掩盖了 .速率常数和实验结果的比较也得到了较好的结果 . 相似文献