全文获取类型
收费全文 | 12730篇 |
免费 | 1123篇 |
国内免费 | 696篇 |
专业分类
化学 | 1177篇 |
晶体学 | 56篇 |
力学 | 2971篇 |
综合类 | 132篇 |
数学 | 8186篇 |
物理学 | 2027篇 |
出版年
2024年 | 22篇 |
2023年 | 165篇 |
2022年 | 137篇 |
2021年 | 187篇 |
2020年 | 323篇 |
2019年 | 342篇 |
2018年 | 357篇 |
2017年 | 350篇 |
2016年 | 407篇 |
2015年 | 344篇 |
2014年 | 523篇 |
2013年 | 1221篇 |
2012年 | 560篇 |
2011年 | 643篇 |
2010年 | 533篇 |
2009年 | 739篇 |
2008年 | 755篇 |
2007年 | 760篇 |
2006年 | 676篇 |
2005年 | 619篇 |
2004年 | 553篇 |
2003年 | 512篇 |
2002年 | 451篇 |
2001年 | 383篇 |
2000年 | 394篇 |
1999年 | 331篇 |
1998年 | 333篇 |
1997年 | 289篇 |
1996年 | 228篇 |
1995年 | 160篇 |
1994年 | 160篇 |
1993年 | 126篇 |
1992年 | 151篇 |
1991年 | 116篇 |
1990年 | 95篇 |
1989年 | 69篇 |
1988年 | 46篇 |
1987年 | 47篇 |
1986年 | 47篇 |
1985年 | 47篇 |
1984年 | 65篇 |
1983年 | 40篇 |
1982年 | 50篇 |
1981年 | 42篇 |
1980年 | 35篇 |
1979年 | 31篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 281 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.
本文用B-网方法确定了△_(nm)~((2))剖分上二次双周期样条函数空间的维数,给出了插值条件的几种提法,证明了解的存在唯一性. 相似文献
23.
Addition of aqueous hydrogen peroxide significantly accelerates the substitution reactions of hydroxide salts with haloarenes bearing electron withdrawing substituents. A similar effect is observed in the reactions of hydroxide salts with halogenated heteroarenes. Reactions are carried out in water or water-THF at ambient temperature or at 50-60 °C. 相似文献
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.
A graph is called supereulerian if it has a spanning closed trail. Let G be a 2-edge-connected graph of order n such that each minimal edge cut SE(G) with |S|3 satisfies the property that each component of G−S has order at least (n−2)/5. We prove that either G is supereulerian or G belongs to one of two classes of exceptional graphs. Our results slightly improve earlier results of Catlin and Li. Furthermore, our main result implies the following strengthening of a theorem of Lai within the class of graphs with minimum degree δ4: If G is a 2-edge-connected graph of order n with δ(G)4 such that for every edge xyE(G) , we have max{d(x),d(y)}(n−2)/5−1, then either G is supereulerian or G belongs to one of two classes of exceptional graphs. We show that the condition δ(G)4 cannot be relaxed. 相似文献
28.
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
29.
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
30.
非光滑非凸多目标规划解的充分条件 总被引:4,自引:0,他引:4
Kuhn-Tucker型条件的充分性一直是最优化理论中引人注意的一个问题.本文对非光滑函数提出了几个非凸概念,然后,讨论了非光滑非凸多目标规划中Kuhn-Tucker型条件和Fritz John型条件的充分性,在很弱的条件下,建立了一系列充分条件. 相似文献