全文获取类型
收费全文 | 26391篇 |
免费 | 685篇 |
国内免费 | 195篇 |
专业分类
化学 | 18377篇 |
晶体学 | 228篇 |
力学 | 782篇 |
综合类 | 1篇 |
数学 | 3757篇 |
物理学 | 4126篇 |
出版年
2022年 | 224篇 |
2021年 | 322篇 |
2020年 | 368篇 |
2019年 | 337篇 |
2018年 | 295篇 |
2017年 | 244篇 |
2016年 | 544篇 |
2015年 | 477篇 |
2014年 | 562篇 |
2013年 | 1261篇 |
2012年 | 1375篇 |
2011年 | 1716篇 |
2010年 | 843篇 |
2009年 | 723篇 |
2008年 | 1423篇 |
2007年 | 1485篇 |
2006年 | 1538篇 |
2005年 | 1445篇 |
2004年 | 1304篇 |
2003年 | 1148篇 |
2002年 | 1054篇 |
2001年 | 408篇 |
2000年 | 345篇 |
1999年 | 265篇 |
1998年 | 286篇 |
1997年 | 309篇 |
1996年 | 390篇 |
1995年 | 288篇 |
1994年 | 291篇 |
1993年 | 254篇 |
1992年 | 234篇 |
1991年 | 232篇 |
1990年 | 204篇 |
1989年 | 160篇 |
1988年 | 215篇 |
1987年 | 189篇 |
1986年 | 160篇 |
1985年 | 313篇 |
1984年 | 322篇 |
1983年 | 219篇 |
1982年 | 320篇 |
1981年 | 285篇 |
1980年 | 283篇 |
1979年 | 265篇 |
1978年 | 273篇 |
1977年 | 251篇 |
1976年 | 236篇 |
1975年 | 199篇 |
1974年 | 208篇 |
1973年 | 217篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Marilyn M. Olmstead James C. Fettinger Soya Gamsey Jacob W. Clary Bakthan Singaram 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(6):o333-o335
The structures of three chiral vinyldioxazaborocanes are reported, namely (2E)‐ and (2Z)‐6‐benzyl‐2‐buten‐2‐yl‐1,3,6,2‐dioxazaborocane, C27H30BNO2, (II) and (III), respectively, and (2Z)‐2‐buten‐2‐yl‐6‐isobutyl‐1,3,6,2‐dioxazaborocane, C24H32BNO2, (IV). These compounds may be useful in asymmetric reactions. In the structures reported here, the N—B donor–acceptor bond is longer than in any previously reported analogous compounds. 相似文献
63.
E. A. Davis A. Singh S. F. J. Cox S. R. Kreitzman T. L. Estle B. Hitti R. L. Lichti R. DuVarney 《Hyperfine Interactions》1994,86(1):705-710
Studies of the muonium fractions in the amorphous oxide a-SiO have been carried out by RF resonance at TRIUMF, Canada and LF repolarization techniques at RAL, U.K. The resonance measurements confirm the presence of the interstitial Mu centre in this intermediate oxide of silicon. Analysis of the data gathered at RAL, using a recently-developed fitting technique, reveals that the Mu* state is present here as well, but with lower relative fractions than in a-Si. However, as in the latter material, but in contrast to c-Si, this bond-centre species appears to be stable up to room temperature. 相似文献
64.
Dave J Adams Eric G Hope Peter J Pogorzelec 《Journal of organometallic chemistry》2004,689(8):1413-1417
The hydroformylation of long chain alkenes under fluorous biphase conditions and in neat perfluorocarbon solvents is reviewed. Special emphasis is placed upon the authors' evaluation of the steric and electronic influence of perfluoroalkylation on catalyst activity, regioselectivity and retention in the fluorocarbon phase. 相似文献
65.
During the last 55 years there have been many results concerning conditions that force a ring to be commutative. These results were stimulated by Jacobson's famous result and were extensively developed by Herstein. This paper will survey the area by organizing the results according to whether they come from variations on Herstein's conditions, depend on general polynomial conditions, depend on the presence of a derivation, or whether a ring has special properties that make commutativity more easily accessible. Finally, the most recent conditions concern product sets and lead to results in a new area of inquiry. 相似文献
66.
Nathalie Charton Achim Feldermann Alexander Theis Martina H. Stenzel Thomas P. Davis Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5559-5559
The original article to which this Erratum refers was published in J Polym Sci Part A: Polym Chem (2004) 42(20) 5170–5179. No abstract. 相似文献
67.
68.
Benjamin Falk Santiago M. Vallinas James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2003,41(4):579-596
This article describes the development of optical pyrometry (OP) as a new analytical technique for the continuous monitoring of the progress of both free‐radical and cationic photopolymerizations. The method is rapid, reproducible, and very easy to implement. A temperature profile of a photopolymerization can be obtained. Preliminary studies have shown that the temperatures of some polymerizing monomers can easily reach temperatures in excess of 250 °C. The effects of the mass and reactivity of the monomer, light intensity, structures, and concentrations of the photoinitiators and monomers as well as the presence or absence of oxygen on various free‐radical and cationic photopolymerizations were examined with this method. Coupling of real‐time infrared spectroscopy with OP provides a convenient method for simultaneously monitoring both the chemical conversion and the temperature of a photopolymerization. This combined technique affords new insights into the effects of temperature‐induced autoacceleration on the course of photopolymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 579–596, 2003 相似文献
69.
Hydrogenated amorphous GaP films have been prepared by reactive rf sputtering. Infrared spectroscopy, optical transmission and reflection, photothermal deflection spectroscopy and dc conductivity have been studied to investigate the local bonding configurations, the optical absorption edges and the temperature dependence of the conductivity as a function of hydrogen content. The results are discussed and compared with the effects of hydrogenation on amorphous Si. 相似文献
70.