全文获取类型
收费全文 | 24418篇 |
免费 | 652篇 |
国内免费 | 141篇 |
专业分类
化学 | 16731篇 |
晶体学 | 123篇 |
力学 | 577篇 |
数学 | 4339篇 |
物理学 | 3441篇 |
出版年
2022年 | 177篇 |
2021年 | 260篇 |
2020年 | 301篇 |
2019年 | 317篇 |
2018年 | 233篇 |
2017年 | 194篇 |
2016年 | 481篇 |
2015年 | 453篇 |
2014年 | 492篇 |
2013年 | 1308篇 |
2012年 | 1138篇 |
2011年 | 1431篇 |
2010年 | 726篇 |
2009年 | 708篇 |
2008年 | 1259篇 |
2007年 | 1280篇 |
2006年 | 1251篇 |
2005年 | 1212篇 |
2004年 | 1054篇 |
2003年 | 911篇 |
2002年 | 816篇 |
2001年 | 348篇 |
2000年 | 278篇 |
1999年 | 249篇 |
1998年 | 276篇 |
1997年 | 309篇 |
1996年 | 358篇 |
1995年 | 240篇 |
1994年 | 279篇 |
1993年 | 262篇 |
1992年 | 239篇 |
1991年 | 240篇 |
1990年 | 192篇 |
1989年 | 232篇 |
1988年 | 240篇 |
1987年 | 201篇 |
1986年 | 196篇 |
1985年 | 291篇 |
1984年 | 336篇 |
1983年 | 218篇 |
1982年 | 366篇 |
1981年 | 337篇 |
1980年 | 316篇 |
1979年 | 317篇 |
1978年 | 322篇 |
1977年 | 292篇 |
1976年 | 281篇 |
1975年 | 251篇 |
1974年 | 249篇 |
1973年 | 236篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
The ‘normal’ reaction of α-lactams (aziridinones) is mcleophilic ring ening,1 which can occur with fission of either one of the three bonds (a-b-c), depending on the reagent, to yield and acyclic addition prodnct (I,II,III).2 相似文献
982.
A brief overview is presented on recent advances in the application of nickel coordination complexes as mediators of olefin polymerisation; in some cases involving stereo-regular polymer formation where appropriate. Emphasis is also given on recent findings concerning di- and tri-nuclear Ni clusters with details on ethylene, methyl methacrylate or styrene-based monomer polymerisations. 相似文献
983.
984.
985.
Robert L. Lowe Sheng-Tao John YuLixiang Yang Stephen E. Bechtel 《Journal of sound and vibration》2014
In this paper, we present a characteristics-based approach for solving elastic wave problems with time-dependent traction boundary conditions. A generalized mathematical model for this important class of problems is expressed as a set of first-order, linear, hyperbolic partial differential equations. We analyze the mathematical structure of this first-order linear system, verify its hyperbolicity, derive its characteristic form, and deduce its eigenvalues, eigenvectors, and Riemann invariants. The eigenvalues correspond to the wave speeds, while the Riemann invariants are used to construct a solution by the method of characteristics. 相似文献
986.
The paper provides an analytical review of some fundamental problems of solid mechanics in high technologies. The review relies partly on the invited report presented by the authors at the 10th All-Russian Congress on Theoretical and Applied Mechanics held in Nizhny Novgorod in 2011. Attention is focused on the problems involved in technologies of materials with a bulk fine-grained (nano) structure and in technologies used to control mechanical properties of surfaces and interfaces. 相似文献
987.
988.
989.
Oleg G. Salnikov Kirill V. Kovtunov Danila A. Barskiy Valery I. Bukhtiyarov Robert Kaptein Igor V. Koptyug 《Applied magnetic resonance》2013,44(1-2):279-288
Parahydrogen-induced polarization has been successfully used for a kinetic study of propylene hydrogenation over a Pt/Al2O3 catalyst. It was shown that the reaction orders with respect to hydrogen are different for the pairwise and the non-pairwise hydrogen addition and are equal to 0.7 and 0.1, respectively. This observation of different reaction orders confirms the coexistence of different types of active sites which are responsible for the overall and the pairwise hydrogen addition to the propylene C=C double bond. Moreover, 0.7 reaction order with respect to H2 for pairwise hydrogen addition indicates that the contribution of pairwise addition depends on the concentration of molecular hydrogen. Therefore, this observation can be developed into a practical tool for producing fluids with highly polarized nuclear spins by changing the hydrogen concentration. 相似文献
990.