全文获取类型
收费全文 | 7397篇 |
免费 | 727篇 |
国内免费 | 540篇 |
专业分类
化学 | 1616篇 |
晶体学 | 59篇 |
力学 | 3653篇 |
综合类 | 123篇 |
数学 | 1283篇 |
物理学 | 1930篇 |
出版年
2024年 | 11篇 |
2023年 | 57篇 |
2022年 | 163篇 |
2021年 | 293篇 |
2020年 | 218篇 |
2019年 | 149篇 |
2018年 | 166篇 |
2017年 | 237篇 |
2016年 | 308篇 |
2015年 | 228篇 |
2014年 | 290篇 |
2013年 | 501篇 |
2012年 | 307篇 |
2011年 | 367篇 |
2010年 | 303篇 |
2009年 | 386篇 |
2008年 | 396篇 |
2007年 | 417篇 |
2006年 | 415篇 |
2005年 | 359篇 |
2004年 | 354篇 |
2003年 | 312篇 |
2002年 | 264篇 |
2001年 | 256篇 |
2000年 | 266篇 |
1999年 | 224篇 |
1998年 | 188篇 |
1997年 | 167篇 |
1996年 | 164篇 |
1995年 | 136篇 |
1994年 | 112篇 |
1993年 | 105篇 |
1992年 | 90篇 |
1991年 | 85篇 |
1990年 | 57篇 |
1989年 | 51篇 |
1988年 | 53篇 |
1987年 | 50篇 |
1986年 | 36篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 2篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有8664条查询结果,搜索用时 109 毫秒
31.
32.
33.
The stress tensor of a massless scalar field satisfying a mixed boundary condition in a (1 + 1)-dimensional Reissner- Nordstrom black hole background is calculated by using Wald's axiom. We find that Dirichlet stress tensor and Neumann stress tensor can be deduced by changing the coefficients of the stress tensor calculated under a mixed boundary condition. The stress tensors satisfying Dirichlet and Neumann boundary conditions are discussed. In addition, we also find that the stress tensor in conformal flat spacetime background differs from that in flat spacetime only by a constant. 相似文献
34.
35.
主成分分析方法是在经济管理中经常使用的多元统计分析方法,在变量降维方面扮演着很重要的角色,是进行多变量综合评价的有力工具。但传统的主成分分析对于异常值十分敏感,计算结果很容易受到异常值影响,而实际数据常包含异常情况,通常分析很少考虑它们的作用。本文基于MCD估计提出一种稳健的主成分分析方法,模拟和实证分析结果表明,该方法对于抵抗异常值有很好的效果。 相似文献
36.
Some effective methods for unconstrained optimization based on the solution of systems of ordinary differential equations 总被引:5,自引:0,他引:5
A. A. Brown M. C. Bartholomew-Biggs 《Journal of Optimization Theory and Applications》1989,62(2):211-224
In this paper, we review briefly some methods for minimizing a functionF(x), which proceed by follwoing the solution curve of a system of ordinary differential equations. Such methods have often been thought to be unacceptably expensive; but we show, by means of extensive numerical tests, using a variety of algorithms, that the ODE approach can in fact be implemented in such a way as to be more than competitive with currently available conventional techniques.This work was supported by a SERC research studentship for the first author. Both authors are indebted to Dr. J. J. McKeown and Dr. K. D. Patel of SCICON Ltd, the collaborating establishment, for their advice and encouragement. 相似文献
37.
For the methylsilsesquioxane film whose optical birefringence is almost zero, it was recently reported that its vertical thermal expansion coefficient (CTE) was approximately one order of magnitude larger than the lateral CTE. Though the birefringence is not an absolute predictor of anisotropic behavior, the discrepancy in both the CTEs was so remarkable that it was essential to investigate whether the anisotropy was intrinsic property or not. If the effect of Poisson's ratio is considered in the calculation of the vertical CTE and when elastic modulus measured by surface acoustic wave spectroscopy is used in the assessment of the lateral CTE, both the CTEs are coincident with each other. Therefore, it can be concluded that the discrepancy in the CTEs can be attributed to a higher in‐plane polymer chain orientation but it can also arise from the misleadingly assumed modulus and Poisson's ratio. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3109–3120, 2006 相似文献
38.
It is thought that the extensive industrial use of arsenic, gallium and indium, which have applications as the materials for III–V semiconductors, will increase human exposure to these compounds in the near future. We have undertaken the development of new biological indicators for assessing exposure to these elements. Element-specific alterations in protein synthesis patterns were expected to occur following exposure to arsenic compounds. We examined alterations in protein synthesis in primary cultures of rat kidney proximal tubule epithelial cells by sodium arsenite, gallium chloride and indium chloride, utilizing two-dimensional gel electrophoresis. After incubation with the chemicals for 20 h, newly synthesized proteins were labeled with [35S]methionine. A protein with a molecular weight (Mr) of 30 000 was markedly induced on exposure to 10 μM arsenite or 300 μM gallium chloride, and synthesis of proteins with Mr values of 85 000, 71 000, 65 000, 51 000, 38 000 and 28 000 were also increased by exposure to arsenite and gallium chloride. No significant changes were observed upon exposure to indium. Some of these increased proteins could be heat-shock proteins. 相似文献
39.
The growth of Ge and SiGe alloy films on Si substrates has attracted considerable interest in the last years because of their importance for optoelectronic devices as well as Si-based high speed transistors. Here we give a short overview on our recent real time stress measurements of Ge and SiGe alloy films on Si(0 0 1) performed with a sensitive cantilever beam technique and accompanied by structural investigations with atomic force microscopy. Characteristic features in the stress curves provide detailed insight into the development and relief of the misfit strain. For the Stranski–Krastanow system Ge/Si(0 0 1) as well as for SiGe films with Si contents below 20%, the strain relaxation proceeds mainly into two steps: (i) by the formation of 3D islands on top of the Ge wetting layer; (ii) via misfit dislocations in larger 3D islands and upon their percolation. 相似文献
40.
各向异性材料中共线刚性线夹杂的纵向剪切问题 总被引:8,自引:2,他引:6
本文研究各向异性材料中共线刚性线夹杂,(有时称作“硬裂纹”或“反裂纹”问题)的纵向剪切问题。利用复变函数方法,提出了一般问题的公式和某些实际重要问题的封闭形式解,考察了刚性线端点附近的应力分布.从本文解答的特殊情形,可以直接导出各向同性材料相应问题的公式和结果,包括某些已有的结果 ̄[7]. 相似文献