全文获取类型
收费全文 | 21764篇 |
免费 | 3101篇 |
国内免费 | 3694篇 |
专业分类
化学 | 12106篇 |
晶体学 | 177篇 |
力学 | 1710篇 |
综合类 | 1588篇 |
数学 | 5655篇 |
物理学 | 7323篇 |
出版年
2024年 | 58篇 |
2023年 | 661篇 |
2022年 | 711篇 |
2021年 | 847篇 |
2020年 | 847篇 |
2019年 | 634篇 |
2018年 | 696篇 |
2017年 | 885篇 |
2016年 | 919篇 |
2015年 | 1051篇 |
2014年 | 1500篇 |
2013年 | 1912篇 |
2012年 | 2049篇 |
2011年 | 1963篇 |
2010年 | 1640篇 |
2009年 | 1741篇 |
2008年 | 1439篇 |
2007年 | 1614篇 |
2006年 | 1538篇 |
2005年 | 1039篇 |
2004年 | 712篇 |
2003年 | 564篇 |
2002年 | 528篇 |
2001年 | 526篇 |
2000年 | 441篇 |
1999年 | 437篇 |
1998年 | 285篇 |
1997年 | 188篇 |
1996年 | 139篇 |
1995年 | 134篇 |
1994年 | 125篇 |
1993年 | 131篇 |
1992年 | 113篇 |
1991年 | 100篇 |
1990年 | 79篇 |
1989年 | 46篇 |
1988年 | 38篇 |
1987年 | 46篇 |
1986年 | 32篇 |
1985年 | 36篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1976年 | 2篇 |
1971年 | 1篇 |
1959年 | 30篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
本文报道了用吸附溶出伏安法测定毗喳酮.以悬汞电极为工作电极,在Na}B,O,-NaOH介质(pH=10)中,毗喳酮产生一尖锐的吸附还原峰,E,二一1. 29V (vs. SCE ),峰电流与毗喳酮浓度在2. 0 X 10-'-8. 0 X 10-smol " L-’范围内呈良好的线性关系.检测限为2. 0 X 10-0mol " L-'(富集90s).本文对毗喳酮在悬汞电极上的电化学行为进行了探讨,对测定毗喳酮的最佳条件进行了详细的选择,利用本法测定了片剂中毗喳酮含量,结果满意. 相似文献
112.
ZHANGZHAOJI 《高校应用数学学报(英文版)》1995,10(3):357-359
This paper solves an open problem of Vaserstein. The main result is: the equation x^m y^m=z^m has a solution in SL2z if and only if m is not divisible by 4 or 6 and m is not congruent to 3 modulo 6. 相似文献
113.
The activity coefficients of NaBr in the NaBr–NaPropionate–H2O and NaBr–NaButyrate–H2O systems were determined from EMF measurements at constant total ionic strength of 0.1 0.5 1.0 1.5 2.0 and 2.5 mol-kg–1 and at 25° C. The activity coefficients were fitted using Scatchard, Pitzer and Lim equations. Finally the excess Gibbs free energy of these mixtures were also calculated. 相似文献
114.
Cai Kairen 《数学年刊B辑(英文版)》1991,12(3):267-271
The author gives an optimum estimate of the first eigenvalue of a compact Riemannian manifold. It is shown that let M be a compact Riemannian manifold, then the first eigenvalue λ_1 of the Laplace operator of M satisfies α_1+max{0,-(n-1)K}≥π~2/d~2 where d is the diameter of M and (n-1)K is the negative lower bound of the Ricci curvature of M. 相似文献
115.
X. H. Sun 《Acta Mathematica Hungarica》1994,65(3):229-236
116.
The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and 13C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (Tg) for the in situ blends, contrary to an increase of Tg with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007 相似文献
117.
This paper presents two differential systems, involving first and second order derivatives of problem functions, respectively, for solving equality-constrained optimization problems. Local minimizers to the optimization problems are proved to be asymptotically stable equilibrium points of the two differential systems. First, the Euler discrete schemes with constant stepsizes for the two differential systems are presented and their convergence theorems are demonstrated. Second, we construct algorithms in which directions are computed by these two systems and the stepsizes are generated by Armijo line search to solve the original equality-constrained optimization problem. The constructed algorithms and the Runge–Kutta method are employed to solve the Euler discrete schemes and the differential equation systems, respectively. We prove that the discrete scheme based on the differential equation system with the second order information has the locally quadratic convergence rate under the local Lipschitz condition. The numerical results given here show that Runge–Kutta method has better stability and higher precision and the numerical method based on the differential equation system with the second information is faster than the other one. 相似文献
118.
《Communications in Nonlinear Science & Numerical Simulation》2007,12(5):784-793
We consider the dynamical behavior of the strongly damped wave equations under homogeneous Neumann boundary condition. By the property of limit set of asymptotic autonomous differential equations, we prove that in certain parameter region, the system has a one-dimensional global attractor, which is a periodic horizontal curve. 相似文献
119.
激光标线的原理和实验 总被引:1,自引:1,他引:0
根据几何光学知识分析了激光标线原理.理论和实验表明:激光标线长度与激光光束形状、光学元件形状及材料折射率有关.并讨论了激光标线向两侧扩展的原因. 相似文献
120.
徐宪民 《数学年刊A辑(中文版)》2003,(3)
Riemann曲面M上的平方可测1-形式全体和解析1-形式全体均可构成Hilbert空间。本文讨论Riemann曲面上的解析映射导出的这类Hilbert空间上的复合算子,研究复合算子的正常性、拟正常性的诱导映射特征。特别地,当M有有限三角剖分时,证明了正常复合算子、拟正常复合算子、酉复合算子、等距复合算子和可逆复合算子等价。 相似文献