全文获取类型
收费全文 | 17711篇 |
免费 | 528篇 |
国内免费 | 139篇 |
专业分类
化学 | 11312篇 |
晶体学 | 134篇 |
力学 | 510篇 |
数学 | 2509篇 |
物理学 | 2487篇 |
无线电 | 1426篇 |
出版年
2022年 | 137篇 |
2021年 | 170篇 |
2020年 | 236篇 |
2019年 | 218篇 |
2018年 | 209篇 |
2017年 | 173篇 |
2016年 | 345篇 |
2015年 | 297篇 |
2014年 | 357篇 |
2013年 | 839篇 |
2012年 | 816篇 |
2011年 | 1090篇 |
2010年 | 526篇 |
2009年 | 473篇 |
2008年 | 891篇 |
2007年 | 951篇 |
2006年 | 977篇 |
2005年 | 925篇 |
2004年 | 835篇 |
2003年 | 753篇 |
2002年 | 725篇 |
2001年 | 249篇 |
2000年 | 215篇 |
1999年 | 176篇 |
1998年 | 209篇 |
1997年 | 216篇 |
1996年 | 249篇 |
1995年 | 191篇 |
1994年 | 199篇 |
1993年 | 168篇 |
1992年 | 166篇 |
1991年 | 167篇 |
1990年 | 143篇 |
1989年 | 124篇 |
1988年 | 156篇 |
1987年 | 157篇 |
1986年 | 135篇 |
1985年 | 227篇 |
1984年 | 250篇 |
1983年 | 195篇 |
1982年 | 259篇 |
1981年 | 246篇 |
1980年 | 241篇 |
1979年 | 219篇 |
1978年 | 219篇 |
1977年 | 194篇 |
1976年 | 198篇 |
1975年 | 173篇 |
1974年 | 174篇 |
1973年 | 172篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Simon G. Bott Alan P. Marchand Dongxia Xing Rajesh Shukla Stephen James Obrey K. Venkatesan J. Narasimha Moorthy 《Journal of chemical crystallography》1997,27(11):661-665
NaBH4 reduction of a cage dione proceeds in a stereospecific fashion to give theendo,endo-diol. This reactivity is related to the crystal structure. 相似文献
33.
34.
Emily S. Tepe Ellen S. Deutsch MD Quiana Sampson Stephen Lawless James S. Reilly Robert Thayer Sataloff 《Journal of voice》2002,16(2):244-250
The objective of this study was to determine the incidence of vocal problems in young choir singers and to correlate vocal problems with demographic and behavioral information. A questionnaire addressing vocal habits and hygiene was offered to 571 young choir singers, up to 25 years of age, who sing at least weekly; 129 (22.6%) responded. More than one-half of the respondents had experienced vocal difficulty, particularly older adolescents. Detrimental behaviors and circumstances surveyed were not reflective of the incidence of vocal difficulty, except for morning hoarseness, chronic fatigue, insomnia, and female gender after puberty. Voice care professionals should be aware that self-reported voice difficulties are common among young choral singers, especially postpubescent girls, and children with symptoms consistent with reflux (morning hoarseness) and emotional stress (insomnia). Laryngologists should communicate with choral conductors and singing teachers to enhance early identification and treatment of children with voice complaints, and to develop choral educational strategies that help decrease their incidence. 相似文献
35.
Maria Marques Zhengtian Yu Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1995,33(16):2787-2793
4-Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis (1-η5-indenyl) zir-conium dichloride ( 1 ) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh-exane and cyclohexene were compared. The parameter Kπκp, which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two-fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc. 相似文献
36.
James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2007,45(18):4331-4340
The irradiation of hybrid photopolymer systems consisting of a free radically polymerizable multifunctional acrylate monomer and a cationically polymerizable epoxide or oxetane monomer was conducted under conditions where only the free radical polymerization takes place. This results in the formation of a free‐standing polyacrylate network film containing quiescent oxonium ions along with the unreacted cyclic ether monomer. The subsequent application of a point source of heat to the film ignites a cationic ring‐opening frontal polymerization that emanates from that site and propagates to all portions of the irradiated sample. This article examines the impact of various molecular structural and experimental parameters on these novel hybrid frontal polymerizations that produce interpenetrating network polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4331–4340, 2007 相似文献
37.
James V. Crivello Umut Bulut 《Journal of polymer science. Part A, Polymer chemistry》2005,43(21):5217-5231
Curcumin, a naturally occurring, intensely yellow dye extracted from the spice turmeric, is an efficient photosensitizer for diaryliodonium salt photoinitiators at wavelengths ranging from 340 to 535 nm. With curcumin as a photosensitizer, it is possible to carry out the cationic photopolymerization of a wide variety of epoxide, oxetane, and vinyl monomers with long‐wavelength UV and visible light. An example of the photopolymerization of an epoxide monomer with ambient solar irradiation is provided. Several other curcumin analogues were synthesized, and their use as photosensitizers is examined. With such photosensitizers, the range of spectral sensitivity can be extended well into the visible region of the electromagnetic spectrum. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5217–5231, 2005 相似文献
38.
39.
A solution to Einstein's field equations is presented that represents a Petrov type II electromagnetic null field with one Killing vector. This solution generalizes a vacuum solution previously discovered by Hoenselaers. The solution was found by the peculiar method of generalizing a member of this class inadvertently discovered by making a typing error when checking the vacuum solution with the computer algebra system SHEEP. 相似文献
40.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields. 相似文献