全文获取类型
收费全文 | 78082篇 |
免费 | 340篇 |
国内免费 | 376篇 |
专业分类
化学 | 24176篇 |
晶体学 | 801篇 |
力学 | 6745篇 |
数学 | 31991篇 |
物理学 | 15085篇 |
出版年
2020年 | 27篇 |
2018年 | 10443篇 |
2017年 | 10267篇 |
2016年 | 6069篇 |
2015年 | 850篇 |
2014年 | 305篇 |
2013年 | 328篇 |
2012年 | 3792篇 |
2011年 | 10518篇 |
2010年 | 5634篇 |
2009年 | 6037篇 |
2008年 | 6580篇 |
2007年 | 8741篇 |
2006年 | 205篇 |
2005年 | 1291篇 |
2004年 | 1516篇 |
2003年 | 1956篇 |
2002年 | 1002篇 |
2001年 | 242篇 |
2000年 | 296篇 |
1999年 | 149篇 |
1998年 | 191篇 |
1997年 | 146篇 |
1996年 | 198篇 |
1995年 | 123篇 |
1994年 | 83篇 |
1993年 | 96篇 |
1992年 | 60篇 |
1991年 | 64篇 |
1990年 | 50篇 |
1989年 | 63篇 |
1988年 | 64篇 |
1987年 | 63篇 |
1986年 | 58篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 37篇 |
1982年 | 44篇 |
1981年 | 39篇 |
1980年 | 49篇 |
1979年 | 45篇 |
1978年 | 36篇 |
1973年 | 26篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
We give an overview of some remarkable connections between symmetric informationally complete measurements (SIC-POVMs, or SICs) and algebraic number theory, in particular, a connection with Hilbert’s 12th problem. The paper is meant to be intelligible to a physicist who has no prior knowledge of either Galois theory or algebraic number theory. 相似文献
993.
994.
Ni@CeO2 core–shell catalysts were synthesized via a facile surfactant-assisted hydrothermal method and their catalytic performance in the dry reforming of methane (DRM) reaction was evaluated. A variety of techniques including XRD, N2 adsorption–desorption, SEM, TEM, TPO, TGA were employed to characterize the prepared or spent catalysts. The encapsulation by the CeO2 shell, on one side, can restrict the sintering and growth of Ni nanoparticles under harsh reaction conditions. On the other side, compared to the conventional shell material of SiO2, CeO2 can provide more lattice oxygens and vacancies, which is helpful to suppress coke deposition. Consequently, the Ni@CeO2 core–shell catalysts exhibited better catalytic activity and stability in the DRM reaction with respect to the referenced Ni@SiO2 core–shell catalysts and Ni/CeO2 supported catalysts. 相似文献
995.
996.
Cristiana Cesari Iacopo Ciabatti Cristina Femoni Maria Carmela Iapalucci Stefano Zacchini 《Journal of Cluster Science》2017,28(4):1963-1979
The reactions of [Ni16(C2)2(CO)23]4? and [Ni38C6(CO)42]6? with CuCl afforded mixtures of the previously reported [HNi42C8(CO)44(CuCl)]7? bimetallic octa-carbide cluster and the new [HNi43C8(CO)45]7? and [HNi44C8(CO)46]7? homo-metallic octa-carbides. The three species have very similar properties resulting always in co-crystals such as [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1?x]·6.5MeCN (x = 0.14) (86% [HNi42C8(CO)44(CuCl)]7?, 14%[HNi43C8(CO)45]7?/[HNi44C8(CO)46]7?) and [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1?x]·5.5MeCN (x = 0.30) (70% [HNi42C8(CO)44(CuCl)]7?, 30% [HNi43C8(CO)45]7?/[HNi44C8(CO)46]7?). The new homo-metallic octa-carbides can be obtained free from the Ni–Cu octa-carbido cluster by reacting [Ni10(C2)(CO)16]2? in thf with a stoichiometric amount of CuCl, and crystals of [NMe4]6[H2Ni43+xC8(CO)45+x]·6MeCN (x = 0.72), which contain [H2Ni44C8(CO)46]6? (72%) and [H2Ni43C8(CO)45]6? (28%), have been obtained. Despite the different charges and compositions, these anions display almost identical structures, which are also closely related to those previously reported for the bimetallic Ni–Cd octa-carbido clusters [Ni42+xC8(CO)44+x(CdCl)]7? and [HNi42+xC8(CO)44+x(CdBr)]6?. Indeed, all these clusters are based on the same Ni42C8 cage decorated by miscellaneous [CdX]+ (X = Cl, Br), [CuCl] and [Ni(CO)] fragments. 相似文献
997.
998.
999.
1000.
A polyacrylonitrile (PAN) homopolymer and a copolymer with methyl acrylate were analyzed by differential scanning calorimetry (DSC) in order to establish a method for the kinetic analysis of the stabilization reaction steps during heat treatment. The application of a program rarely used for the study of the chemical transformation of PAN and its copolymers resulted in five separate steps, which can be assigned with large probability to various cyclization and oxidation reactions. A more exact identification of the reactions needs further measurements and considerations. Overlapping peaks appearing in the DSC traces were deconvoluted and then quantitatively analyzed to obtain kinetic parameters. The kinetics of the processes were described by the Kissinger model. The model could be fitted well to four of the five processes that may indicate that these belong to individual reactions of the first order. The parameters obtained agree well with the few values of similar investigations published in the literature up to now. The results have large practical relevance, since the kinetic parameters obtained can be used in the preparation of intermediates and for the optimization of the stabilization process. 相似文献