全文获取类型
收费全文 | 13160篇 |
免费 | 1642篇 |
国内免费 | 1047篇 |
专业分类
化学 | 2343篇 |
晶体学 | 133篇 |
力学 | 3384篇 |
综合类 | 130篇 |
数学 | 6441篇 |
物理学 | 3418篇 |
出版年
2024年 | 17篇 |
2023年 | 144篇 |
2022年 | 189篇 |
2021年 | 239篇 |
2020年 | 385篇 |
2019年 | 356篇 |
2018年 | 346篇 |
2017年 | 388篇 |
2016年 | 480篇 |
2015年 | 415篇 |
2014年 | 603篇 |
2013年 | 1128篇 |
2012年 | 659篇 |
2011年 | 795篇 |
2010年 | 640篇 |
2009年 | 828篇 |
2008年 | 810篇 |
2007年 | 858篇 |
2006年 | 740篇 |
2005年 | 646篇 |
2004年 | 628篇 |
2003年 | 564篇 |
2002年 | 483篇 |
2001年 | 433篇 |
2000年 | 427篇 |
1999年 | 349篇 |
1998年 | 353篇 |
1997年 | 299篇 |
1996年 | 255篇 |
1995年 | 172篇 |
1994年 | 157篇 |
1993年 | 148篇 |
1992年 | 149篇 |
1991年 | 121篇 |
1990年 | 103篇 |
1989年 | 63篇 |
1988年 | 48篇 |
1987年 | 46篇 |
1986年 | 44篇 |
1985年 | 50篇 |
1984年 | 63篇 |
1983年 | 41篇 |
1982年 | 50篇 |
1981年 | 38篇 |
1980年 | 25篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1976年 | 6篇 |
1973年 | 10篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
21.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
22.
23.
24.
25.
Cai Xiaochun 《Annals of Differential Equations》2006,22(1):1-6
In this paper, we apply a critical point theorem and obtain the condition for the existence of three solutions to two-point boundary value problem of a second order nonlinear difference equation. 相似文献
26.
We propose a framework, based on classical mixture theory, to describe the isothermal flow of an incompressible fluid through a deformable inelastic porous solid. The modeling of the behavior of the inelastic solid takes into account changes in the elastic response due to evolution in the microstructure of the material. We apply the model to a compression layer problem. The mathematical problem generated by the model is a free boundary problem. 相似文献
27.
方程w"-w+f(t,w)=O的Dirichlet边值问题的正解存在性与多解性 总被引:1,自引:0,他引:1
姚庆六 《应用泛函分析学报》2002,4(1):4-9
考察了下列常微分方程的Dirichlet边值问题的正解[w″(t)-w(t) f(t,w(t))=0,0≤t≤1 w(0)=w(1)=0建立了n正解的存在性,其中n是一个任意的自然数。 相似文献
28.
F. S. de Aguiar L. B. Bernardes S. Goulart Rosa Jr. 《Journal of statistical physics》1991,64(3-4):673-682
Metastability in the ferromagneticp-state Potts model defined on the Cayley tree is discussed. It is shown that the sign of the boundary fieldH
s
determines the order of the transition as well as the stability of the low-temperature phase. Lowering the temperature withH
s
>0, a system withp<2 (p>2) will display a second (first)-order transition to a metastable (stable) phase. ForH
s
>0 a second (first)-order transition to a metastable (stable) phase occurs ifp>2 (p<2). In this case the system also has a residual entropy which is negative forp<2. 相似文献
29.
This paper reports that the m-plane GaN layer is grown on (200)-plane LiAlO2 substrate by metal-organic chemical wpour deposition (MOCVD) method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer's thickness. The high transmittance (80%), sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate. 相似文献
30.
Rossella Bartolo Anna Germinario Miguel Sánchez 《Annals of Global Analysis and Geometry》2002,21(1):63-84
In this paper the problem of the geodesic connectedness and convexity ofincomplete Riemannian manifolds is analyzed. To this aim, a detailedstudy of the notion of convexity for the associated Cauchy boundary iscarried out. In particular, under widely discussed hypotheses,we prove the convexity of open domains (whose boundaries may benondifferentiable) of a complete Riemannian manifold. Variationalmethods are mainly used. Examples and applications are provided,including a result for dynamical systems on the existence oftrajectories with fixed energy. 相似文献