全文获取类型
收费全文 | 74505篇 |
免费 | 8962篇 |
国内免费 | 5405篇 |
专业分类
化学 | 34888篇 |
晶体学 | 385篇 |
力学 | 4614篇 |
综合类 | 1292篇 |
数学 | 25324篇 |
物理学 | 22369篇 |
出版年
2023年 | 671篇 |
2022年 | 970篇 |
2021年 | 2219篇 |
2020年 | 2040篇 |
2019年 | 2106篇 |
2018年 | 1718篇 |
2017年 | 2070篇 |
2016年 | 2667篇 |
2015年 | 2383篇 |
2014年 | 3373篇 |
2013年 | 5665篇 |
2012年 | 3643篇 |
2011年 | 4272篇 |
2010年 | 3821篇 |
2009年 | 4437篇 |
2008年 | 4692篇 |
2007年 | 4832篇 |
2006年 | 3962篇 |
2005年 | 3266篇 |
2004年 | 2769篇 |
2003年 | 2823篇 |
2002年 | 4995篇 |
2001年 | 2427篇 |
2000年 | 1782篇 |
1999年 | 1442篇 |
1998年 | 1320篇 |
1997年 | 1103篇 |
1996年 | 1017篇 |
1995年 | 927篇 |
1994年 | 872篇 |
1993年 | 789篇 |
1992年 | 755篇 |
1991年 | 548篇 |
1990年 | 458篇 |
1989年 | 398篇 |
1988年 | 392篇 |
1987年 | 336篇 |
1986年 | 356篇 |
1985年 | 477篇 |
1984年 | 360篇 |
1983年 | 195篇 |
1982年 | 396篇 |
1981年 | 555篇 |
1980年 | 481篇 |
1979年 | 518篇 |
1978年 | 420篇 |
1977年 | 327篇 |
1976年 | 273篇 |
1974年 | 98篇 |
1973年 | 174篇 |
排序方式: 共有10000条查询结果,搜索用时 90 毫秒
21.
Petr P. Sharin Sofia P. Yakovleva Susanna N. Makharova Maria I. Vasilieva Vasilii I. Popov 《Composite Interfaces》2019,26(1):53-65
The structural-phase state of the contact zone and the factors that influence on the strength of diamond retention in the diamond carbide composites were determined. Composites were obtained by the new hybrid technology that eliminates the reheating of the metalized coating. The elaborated technology combines the thermal diffusion metallization of a diamond and the sintering by the scheme of self-dosed impregnation in a one-stage technological cycle. By the methods of electron microscopy, X-ray diffraction analysis, and Raman spectroscopy the structural and phase characteristics of the interphase boundary were investigated. The improvement of chemical and mechanical adhesion between the diamond and carbide matrix was obtained. It was shown that the specific productivity of the samples with a metalized diamond component is 39% higher than those without metallization. 相似文献
22.
23.
Yasuhito Tanaka 《Operations Research Letters》2019,47(5):406-409
We study a dynamic free-entry oligopoly with sluggish entry and exit of firms under general demand and cost functions. We show that the number of firms in a steady-state open-loop solution for a dynamic free-entry oligopoly is smaller than that at static equilibrium and that the number of firms in a steady-state memoryless closed-loop solution is larger than that in an open-loop solution. 相似文献
24.
Bilender P. Allahverdiev 《Mathematical Methods in the Applied Sciences》2019,42(1):229-236
In this study, maximal dissipative second‐order dynamic operators on semi‐infinite time scale are studied in the Hilbert space , that the extensions of a minimal symmetric operator in limit‐point case. We construct a self‐adjoint dilation of the dissipative operator together with its incoming and outgoing spectral representations so that we can determine the scattering function of the dilation as stated in the scheme of Lax‐Phillips. Moreover, we construct a functional model of the dissipative operator and identify its characteristic function in terms of the Weyl‐Titchmarsh function of a self‐adjoint second‐order dynamic operator. Finally, we prove the theorems on completeness of the system of root functions of the dissipative and accumulative dynamic operators. 相似文献
25.
Awatif Alqahtani Mohamed Jleli Bessem Samet 《Mathematical Methods in the Applied Sciences》2019,42(3):861-870
In this paper, some nonlocal in time differential inequalities of Sobolev type are considered. Using the nonlinear capacity method, sufficient conditions for the nonexistence of nontrivial global classical solutions are provided. 相似文献
26.
ABSTRACTA class of semilinear parabolic reaction diffusion equations with multiple time delays is considered. These time delays and corresponding weights are to be optimized such that the associated solution of the delay equation is the best approximation of a desired state function. The differentiability of the mapping is proved that associates the solution of the delay equation to the vector of weights and delays. Based on an adjoint calculus, first-order necessary optimality conditions are derived. Numerical test examples show the applicability of the concept of optimizing time delays. 相似文献
27.
本文针对求矩阵方程AXB+CXD=F唯一解的参数迭代法,分析当矩阵A,B,C,D均是Hermite正(负)定矩阵时,迭代矩阵的特征值表达式,给出了最优参数的确定方法,并提出了相应的加速算法. 相似文献
28.
This paper develops a framework to deal with the unconditional superclose analysis of
nonlinear parabolic equation. Taking the finite element pair $Q_{11}/Q_{01} × Q_{10}$ as an example,
a new mixed finite element method (FEM) is established and the $τ$ -independent superclose
results of the original variable $u$ in $H^1$-norm and the flux variable $\mathop{q} \limits ^{\rightarrow}= −a(u)∇u$ in $L^2$-norm are deduced ($τ$ is the temporal partition parameter). A key to our analysis is an
error splitting technique, with which the time-discrete and the spatial-discrete systems are
constructed, respectively. For the first system, the boundedness of the temporal errors is obtained. For the second system, the spatial superclose results are presented unconditionally, while the previous literature always only obtain the convergent estimates or require
certain time step conditions. Finally, some numerical results are provided to confirm the
theoretical analysis, and show the efficiency of the proposed method. 相似文献
29.
30.
The electrochemical behavior of austenitic stainless steel (Type 304) in 3 M sulfuric acid with 3.5% recrystallized sodium chloride at specific concentrations of butan-1-ol was investigated with the aid of potentiodynamic polarization, open circuit measurement and weight loss technique. Butan-1-ol effectively inhibited the steel corrosion with a maximum inhibition efficiency of 78.7% from weight-loss analysis and 80.9% from potentiodynamic polarization test at highest concentration studied. Adsorption of the compound obeyed the Freundlich isotherm. Thermodynamic calculations reveal physiochemical interactions and spontaneous adsorption mechanism. Surface characterizations showed the absence of corrosion products and topographic modifications of the steel. Statistical analysis depicts the overwhelming influence and statistical significance of inhibitor concentration on the inhibition performance. 相似文献