全文获取类型
收费全文 | 8252篇 |
免费 | 391篇 |
国内免费 | 40篇 |
专业分类
化学 | 5705篇 |
晶体学 | 58篇 |
力学 | 151篇 |
综合类 | 1篇 |
数学 | 1249篇 |
物理学 | 1519篇 |
出版年
2023年 | 66篇 |
2022年 | 77篇 |
2021年 | 146篇 |
2020年 | 204篇 |
2019年 | 205篇 |
2018年 | 133篇 |
2017年 | 125篇 |
2016年 | 314篇 |
2015年 | 247篇 |
2014年 | 267篇 |
2013年 | 459篇 |
2012年 | 525篇 |
2011年 | 674篇 |
2010年 | 309篇 |
2009年 | 233篇 |
2008年 | 487篇 |
2007年 | 467篇 |
2006年 | 432篇 |
2005年 | 446篇 |
2004年 | 329篇 |
2003年 | 243篇 |
2002年 | 223篇 |
2001年 | 103篇 |
2000年 | 77篇 |
1999年 | 63篇 |
1998年 | 78篇 |
1997年 | 64篇 |
1996年 | 107篇 |
1995年 | 87篇 |
1994年 | 94篇 |
1993年 | 87篇 |
1992年 | 77篇 |
1991年 | 44篇 |
1990年 | 48篇 |
1989年 | 49篇 |
1988年 | 50篇 |
1987年 | 42篇 |
1986年 | 43篇 |
1985年 | 50篇 |
1984年 | 50篇 |
1983年 | 40篇 |
1982年 | 46篇 |
1981年 | 62篇 |
1980年 | 48篇 |
1979年 | 52篇 |
1978年 | 38篇 |
1977年 | 49篇 |
1976年 | 43篇 |
1974年 | 41篇 |
1973年 | 68篇 |
排序方式: 共有8683条查询结果,搜索用时 15 毫秒
1.
Pengjin Qin Li-An Wang Prof. Joseph M. O'Connor Prof. Kim K. Baldridge Yifan Li Burak Tufekci Jiyue Chen Prof. Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18114-18121
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. 相似文献
2.
Timm Bergholz Dr. Benjamin Oelkers Dr. Benedikt Huber Prof. Bernhard Roling Prof. Dr. Jörg Sundermeyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2613-2620
New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C2N5]? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C2N5]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries. 相似文献
3.
Archiv der Mathematik - Motivated by recent results on the minimal base of a permutation group, we introduce a new local invariant attached to arbitrary finite groups. More precisely, a subset... 相似文献
4.
5.
6.
Benjamin J. K. Evans Susan M. Scott Antony C. Searle 《General Relativity and Gravitation》2002,34(10):1675-1684
We have developed a new tool for numerical work in General Relativity: GRworkbench. We discuss how GRworkbench's implementation of a numerically-amenable analogue to Differential Geometry facilitates the development of robust and chart-independent numerical algorithms. We consider, as an example, geodesic tracing on two charts covering the exterior Schwarzschild space-time. 相似文献
7.
8.
Benjamin E. Blass Anil Srivastava Amy L. Faulkner James M. Ridgeway 《Tetrahedron letters》2004,45(6):1275-1277
The solid-phase synthesis of a series of imidazo[1,2-b]pyrazol-2-ones, an interesting 5,5-fused ring system, based on diverse set of hydrazine acids and malanonitriles is described. The method involves formation of 5-aminopyrazoles on solid support and subsequent cyclizative cleavage off the resin. Compounds were obtained in acceptable to excellent yields and are suitable for biological evaluation without further purification. 相似文献
9.
We define admissible quasi-Hopf quantized universal enveloping (QHQUE) algebras by ?-adic valuation conditions. We show that any QHQUE algebra is twist-equivalent to an admissible one. We prove a related statement: any associator is twist-equivalent to a Lie associator. We attach a quantized formal series algebra to each admissible QHQUE algebra and study the resulting Poisson algebras. 相似文献
10.
Feel like writing a review for The Mathematical Intelligencer? You are welcome to submit an unsolicited review of a book of your choice; or, if you would welcome being assigned a book to review, please write us, telling us your expertise and your predilections. 相似文献