全文获取类型
收费全文 | 25731篇 |
免费 | 1715篇 |
国内免费 | 1137篇 |
专业分类
化学 | 9575篇 |
晶体学 | 89篇 |
力学 | 176篇 |
综合类 | 56篇 |
数学 | 16891篇 |
物理学 | 1796篇 |
出版年
2023年 | 298篇 |
2022年 | 208篇 |
2021年 | 240篇 |
2020年 | 475篇 |
2019年 | 689篇 |
2018年 | 730篇 |
2017年 | 437篇 |
2016年 | 614篇 |
2015年 | 714篇 |
2014年 | 1105篇 |
2013年 | 1987篇 |
2012年 | 1120篇 |
2011年 | 1638篇 |
2010年 | 1349篇 |
2009年 | 1631篇 |
2008年 | 1847篇 |
2007年 | 1792篇 |
2006年 | 1345篇 |
2005年 | 987篇 |
2004年 | 858篇 |
2003年 | 782篇 |
2002年 | 643篇 |
2001年 | 511篇 |
2000年 | 490篇 |
1999年 | 586篇 |
1998年 | 518篇 |
1997年 | 391篇 |
1996年 | 452篇 |
1995年 | 504篇 |
1994年 | 451篇 |
1993年 | 372篇 |
1992年 | 350篇 |
1991年 | 227篇 |
1990年 | 205篇 |
1989年 | 206篇 |
1988年 | 145篇 |
1987年 | 144篇 |
1986年 | 133篇 |
1985年 | 208篇 |
1984年 | 187篇 |
1983年 | 96篇 |
1982年 | 183篇 |
1981年 | 168篇 |
1980年 | 104篇 |
1979年 | 89篇 |
1978年 | 111篇 |
1977年 | 82篇 |
1976年 | 72篇 |
1975年 | 29篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
L’ubica Holá 《Quaestiones Mathematicae》2018,41(6):829-838
Some boundedness properties of function spaces (considered as topo- logical groups) are studied. 相似文献
992.
《应用有机金属化学》2017,31(12)
This review article provides an overview of the most recent and exciting developments in palladium‐catalyzed C–H activation and mechanistic aspects of these catalytic reactions as the fast‐growing field for the synthesis of phenanthridine derivatives. 相似文献
993.
Fayou Zhao 《Mathematische Nachrichten》2012,285(10):1294-1298
Fu and Lu et al. 7 showed that the commutator $\mathcal {H}_{\beta ,b}$ generated by the fractional Hardy operator and a locally integrable function b is bounded on the homogenous Herz spaces if and only if b is a central bounded mean oscillation function. We show that their result is optimal by giving a counterexample. 相似文献
994.
《应用有机金属化学》2017,31(2)
Synthesis of bis(4‐pyridylamino)triazine stabilized on silica‐coated nano‐Fe3O4 particles, and their feasibility as a reusable heterogeneous basic catalyst are reported. The catalytic performance of this novel material was studied for the green synthesis of highly functionalized 4H ‐pyran, 4H ‐thiopyran and 1,4‐dihydropyridine derivatives via one‐pot multicomponent reactions. Eco‐friendly method, high yield and purity of desired products, short reaction time along with ease of workup procedure outline the advantages of these new methodologies over earlier ones. Surface and magnetic properties of the core–shell hybrid nanoparticles were characterized via transmission and scanning electron microscopies, X‐ray diffraction, energy‐dispersive X‐ray and Fourier transform infrared spectroscopies and vibrating sample magnetometry. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
995.
Preparation,characterization and heterogeneous catalytic applications of GO/Fe3O4/HPW nanocomposite in chemoselective and green oxidation of alcohols with aqueous H2O2
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Graphene oxide ‐ Fe3O4 ‐ NH3+H2PW12O40 ‐ magnetic nanocomposite (GO/Fe3O4/HPW) was prepared by linking amino ‐ functionalized Fe3O4 nanoparticles (Fe3O4 ‐ NH2) on the graphene oxide (GO), and then grafting 12 ‐ tungstophosphoric acid (H3PW12O40) on the graphene oxide ‐ magnetite hybrid (GO ‐ Fe3O4 ‐ NH2). The obtained GO/Fe3O4/HPW nanocomposite was well characterized with different techniques such as FT ‐ IR, TEM, SEM, XRD, EDX, TGA ‐ DTA, AGFM, ICP and BET measurements. The used techniques showed that the graphene oxide layers were well prepared and the various stages of preparation of the GO/Fe3O4/HPW nanocomposites successfully completed. This new nanocomposite displayed excellent performance as a heterogeneous catalyst in the oxidation of alcohols with H2O2. The as ‐ prepared GO/Fe3O4/HPW catalyst was more stable and recyclable at least five times without significantly reducing its catalytic activity. 相似文献
996.
《复变函数与椭圆型方程》2012,57(1):23-25
Here we give a few n-dimensional extensions of a recent result of M. Abe concerning a Cousin I characterization of two-dimensional Stein manifolds. 相似文献
997.
In this paper we analyze the Cauchy problem for the Einstein equation in the case of a non-characteristic initial hypersurface. To find the correct notions for the characteristic and Cauchy data we introduce a complex, which we call the Einstein complex. Then the Cauchy problem acquires correctness in terms of the associated spectral sequence. We define the Cauchy data in such way that they allow us to reconstruct a cohomologously unique formal solution. 相似文献
998.
999.
The paper deals with second order nonlinear evolution inclusions and their applications. We study evolution inclusions involving a Volterra-type integral operator, which are considered within the framework of an evolution triple of spaces. First, we deliver a result on the unique solvability of the Cauchy problem for the inclusion by combining a surjectivity result for multivalued pseudomonotone operators and the Banach contraction principle. Next, we provide a theorem on the continuous dependence of the solution to the inclusion with respect to the operators involved in the problem. Finally, we consider a dynamic frictional contact problem of viscoelasticity for materials with long memory and indicate how the result on evolution inclusion is applicable to the model of the contact problem. 相似文献
1000.
《Optimization》2012,61(4-5):495-505
This paper investigates properties of the optimality equation and optimal policies in discrete time Markov decision processes with expected discounted total rewards under weak conditions that the model is well defined and the optimality equation is true. The optimal value function is characterized as a solution of the optimality equation and the structure of optimal policies is also given. 相似文献