全文获取类型
收费全文 | 3545篇 |
免费 | 108篇 |
国内免费 | 12篇 |
专业分类
化学 | 2281篇 |
晶体学 | 76篇 |
力学 | 80篇 |
数学 | 285篇 |
物理学 | 943篇 |
出版年
2023年 | 39篇 |
2022年 | 72篇 |
2021年 | 72篇 |
2020年 | 85篇 |
2019年 | 79篇 |
2018年 | 60篇 |
2017年 | 67篇 |
2016年 | 103篇 |
2015年 | 84篇 |
2014年 | 121篇 |
2013年 | 304篇 |
2012年 | 214篇 |
2011年 | 253篇 |
2010年 | 147篇 |
2009年 | 148篇 |
2008年 | 201篇 |
2007年 | 185篇 |
2006年 | 114篇 |
2005年 | 118篇 |
2004年 | 99篇 |
2003年 | 60篇 |
2002年 | 67篇 |
2001年 | 54篇 |
2000年 | 40篇 |
1999年 | 27篇 |
1998年 | 20篇 |
1997年 | 25篇 |
1996年 | 34篇 |
1995年 | 39篇 |
1994年 | 37篇 |
1993年 | 46篇 |
1992年 | 27篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1988年 | 33篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 34篇 |
1984年 | 37篇 |
1983年 | 40篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 34篇 |
1979年 | 33篇 |
1978年 | 36篇 |
1977年 | 31篇 |
1976年 | 24篇 |
1974年 | 22篇 |
1973年 | 21篇 |
排序方式: 共有3665条查询结果,搜索用时 15 毫秒
131.
Vicinal proton couplings in cyclopropane have been calculated using Dirac-Van Vleck and variational methods in valence bond formalism. The couplings may be considered as taking place along a path comprising either three or four intervening bonds. Inclusion of all exchange integrals in the appropriate fragment models leads to a satisfactory ratio of Jcis/Jtrans . In this respect valence bond results appear to be superior to those obtained using a molecular orbital approach. The present valence bond results on couplings in cyclopropane are not affected by the choice of models for bonding in cyclopropane, namely the Coulson-Moffitt model or the Walsh model. 相似文献
132.
Someshwarnath Pandey Balakrishna Kolli Sarada P. Mishra Asit B. Samui 《Journal of polymer science. Part A, Polymer chemistry》2012,50(6):1205-1215
Three new types of siloxane‐based photoactive liquid crystalline polymers containing azo side groups were synthesized through the click chemistry route. The polymers having molecular weight range of 14,000–34,000 g mol?1 were soluble in most of the polar solvents like chloroform, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, and dichloromethane. The photoresponsive trans–cis photoisomerization under UV radiation and cis–trans relaxation process in dark for the polymers were studied. The isomerization rate constants were found to be 0.01–0.04 sec?1 and 1.16*10?4–4.67*10?4 sec?1, respectively. It has been noted that the polymers showed high intensity absorption for n‐π* in chloroform. Both trans and cis forms of azide monomers having azo moiety exhibited molar extinction coefficient ( ? max) in the range of 22,000–33,000 L mol?1 cm?1. The thermotropic behavior of the polymers was studied by polarizing optical microscope (POM) and differential scanning calorimetry (DSC) experiments. Polymer P1 showed liquid crystalline textures of nematic droplets, whereas P2 showed smectic focal conic texture and nematic droplets. Polymer P1 was also studied for photomechanical bending on exposure to UV radiation. The polymers showed initial degradation temperature in the range of 210–275°C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
133.
134.
135.
136.
The wavelengths of the vibronic peaks of the low temperature photoluminescence of anthracene, phenanthrene, benzophenone and phthalic acid crystals do not change considerably, but their relative intensity changes significantly with grinding. The dislocations may change both the absorption coefficient and absorption spectra of the crystals, hence the photoluminescence emission may be affected by the grinding. 相似文献
137.
Condensation of uracil derivatives (1,3,4) with acetone in the presence of triethylamine gave pyranopyrimidines (2,5,6). 相似文献
138.
Apurva Pandey Dr. Eszter Boros 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(26):7340-7350
Drug discovery aimed at the efficient eradication of life-threatening bacterial infections, especially in light of the emergence of multi-drug resistance of pathogenic bacteria, has remained a challenge for medicinal chemists over the past several decades. As nutrient acquisition and metabolism at the host-pathogen interface become better elucidated, new drug targets continue to emerge. Metal homeostasis is among these processes, and thus provides opportunities for medicinal inorganic chemists to alter or disrupt these processes selectively to impart bacteriostatic or bacteriotoxic effects. In this minireview, we showcase some of the recent work from the field of metal-based antibacterial agents and highlight divergent strategies and mechanisms of action. 相似文献
139.
B. H. Doreswamy Chandra K. Mantelingu M. A. Sridhar M. Mahendra 《Research on Chemical Intermediates》2014,40(8):2659-2665
The isolation of stable carbenes of the Arduengo and Wanzlick type has prompted us to look for stable nitrenium ions of the related structural type 1-Hydroxy-3-methyl benzotriazolium trifluromethane sulfonate. Nitrenium ions are azocations with structure and survive long enough under in vitro conditions to bind with biological nucleophiles, i.e. DNA bases, and play an important role in carcinogenic processes involving the metabolism of aromatic amines. The title compound (C15H16F3N6O5S) was isolated and crystallized in the monoclinic space group Cc with cell parameters a = 19.866(1) Å, b = 13.128(9) Å, c = 7.673(5) Å, and Z = 4. The structure has both intra- and intermolecular hydrogen bonds. 相似文献
140.
Pradumn Kumar Pandey Bibhas Adhikari Jayanta Chakraborty 《Journal of mathematical chemistry》2018,56(5):1467-1480
In this paper we interpret nucleation as a network formation process. Inspired by this interpretation we propose a social network model which produces networks with communities. 相似文献