全文获取类型
收费全文 | 24764篇 |
免费 | 660篇 |
国内免费 | 138篇 |
专业分类
化学 | 16961篇 |
晶体学 | 130篇 |
力学 | 577篇 |
数学 | 4342篇 |
物理学 | 3552篇 |
出版年
2022年 | 143篇 |
2021年 | 264篇 |
2020年 | 303篇 |
2019年 | 320篇 |
2018年 | 234篇 |
2017年 | 197篇 |
2016年 | 486篇 |
2015年 | 460篇 |
2014年 | 495篇 |
2013年 | 1309篇 |
2012年 | 1152篇 |
2011年 | 1452篇 |
2010年 | 735篇 |
2009年 | 715篇 |
2008年 | 1271篇 |
2007年 | 1295篇 |
2006年 | 1269篇 |
2005年 | 1231篇 |
2004年 | 1082篇 |
2003年 | 930篇 |
2002年 | 836篇 |
2001年 | 361篇 |
2000年 | 288篇 |
1999年 | 258篇 |
1998年 | 283篇 |
1997年 | 310篇 |
1996年 | 363篇 |
1995年 | 244篇 |
1994年 | 283篇 |
1993年 | 268篇 |
1992年 | 240篇 |
1991年 | 241篇 |
1990年 | 195篇 |
1989年 | 232篇 |
1988年 | 240篇 |
1987年 | 201篇 |
1986年 | 196篇 |
1985年 | 293篇 |
1984年 | 339篇 |
1983年 | 219篇 |
1982年 | 370篇 |
1981年 | 341篇 |
1980年 | 316篇 |
1979年 | 321篇 |
1978年 | 328篇 |
1977年 | 293篇 |
1976年 | 280篇 |
1975年 | 253篇 |
1974年 | 249篇 |
1973年 | 239篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
Robert Pendrill Ole W. Sørensen Göran Widmalm 《Magnetic resonance in chemistry : MRC》2014,52(3):82-86
Site‐specific 13C isotope labeling is a useful approach that allows for the measurement of homonuclear 13C,13C coupling constants. For three site‐specifically labeled oligosaccharides, it is demonstrated that using the J‐HMBC experiment for measuring heteronuclear long‐range coupling constants is problematical for the carbons adjacent to the spin label. By incorporating either a selective inversion pulse or a constant‐time element in the pulse sequence, the interference from one‐bond 13C,13C scalar couplings is suppressed, allowing the coupling constants of interest to be measured without complications. Experimental spectra are compared with spectra of a nonlabeled compound as well as with simulated spectra. The work extends the use of the J‐HMBC experiments to site‐specifically labeled molecules, thereby increasing the number of coupling constants that can be obtained from a single preparation of a molecule. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
993.
994.
995.
996.
Peter E.J. Vos Claes Eskilsson Alessandro Bolis Sehun Chun Robert M. Kirby 《International Journal of Computational Fluid Dynamics》2013,27(3):107-125
Time-stepping algorithms and their implementations are a critical component within the solution of time-dependent partial differential equations (PDEs). In this article, we present a generic framework – both in terms of algorithms and implementations – that allows an almost seamless switch between various explicit, implicit and implicit–explicit (IMEX) time-stepping methods. We put particular emphasis on how to incorporate time-dependent boundary conditions, an issue that goes beyond classical ODE theory but which plays an important role in the time-stepping of the PDEs arising in computational fluid dynamics. Our algorithm is based upon J.C. Butcher's unifying concept of general linear methods that we have extended to accommodate the family of IMEX schemes that are often used in engineering practice. In the article, we discuss design considerations and present an object-oriented implementation. Finally, we illustrate the use of the framework by applications to a model problem as well as to more complex fluid problems. 相似文献
997.
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
998.
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
999.
1000.