全文获取类型
收费全文 | 4223篇 |
免费 | 717篇 |
国内免费 | 622篇 |
专业分类
化学 | 3158篇 |
晶体学 | 70篇 |
力学 | 182篇 |
综合类 | 33篇 |
数学 | 668篇 |
物理学 | 1451篇 |
出版年
2024年 | 11篇 |
2023年 | 115篇 |
2022年 | 152篇 |
2021年 | 173篇 |
2020年 | 222篇 |
2019年 | 227篇 |
2018年 | 191篇 |
2017年 | 156篇 |
2016年 | 223篇 |
2015年 | 225篇 |
2014年 | 249篇 |
2013年 | 338篇 |
2012年 | 375篇 |
2011年 | 346篇 |
2010年 | 241篇 |
2009年 | 268篇 |
2008年 | 283篇 |
2007年 | 243篇 |
2006年 | 199篇 |
2005年 | 175篇 |
2004年 | 124篇 |
2003年 | 108篇 |
2002年 | 112篇 |
2001年 | 96篇 |
2000年 | 94篇 |
1999年 | 62篇 |
1998年 | 43篇 |
1997年 | 36篇 |
1996年 | 56篇 |
1995年 | 46篇 |
1994年 | 41篇 |
1993年 | 39篇 |
1992年 | 34篇 |
1991年 | 40篇 |
1990年 | 32篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有5562条查询结果,搜索用时 15 毫秒
1.
2.
Bao Nguyen Xuan Duy Khanh Phan Quoc Tung Nguyen Minh 《Set-Valued and Variational Analysis》2022,30(2):465-486
Set-Valued and Variational Analysis - We aim to establish Karush-Kuhn-Tucker multiplier rules involving higher-order complementarity slackness under Hölder metric subregularity. These rules... 相似文献
3.
Dr. Takeshi Nanjo Natsuki Kato Xuan Zhang Prof. Yoshiji Takemoto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(68):15504-15507
Strategies for the formation of amide bonds, that is, one of the most basic and important transformations in organic synthesis, have so far focused predominantly on dehydration reactions. Herein, we report and demonstrate the practical utility of a novel decarboxylative amidation of α-ketoacids by using inexpensive tert-butyl hydroperoxide (TBHP), which is characterized by high yields, a broad substrate scope, mild reaction conditions, and a unique chemoselectivity. These features enable the synthesis of peptides from amino acid derived α-ketoacids under preservation of the stereochemical information. 相似文献
4.
5.
6.
7.
5-Perfluorophenyl 4,5-dihydro-1H-pyrazoles were synthesized from 1,3-dipolar cycloaddition reaction of perfluorobenyl 2,4,6-triisopropylbenzenesulfonylhydrazone and α,β-unsaturated carbonyl compounds or acrylonitrile in THF or water. It was worthy to note that better results were obtained when water was employed as the solvent, which was considered as an effective, economic and environmentally friendly method to synthesize these pyrazole derivatives. 相似文献
8.
研究了γ-辐照前后纯Y2SiO5和Eu3+掺杂的Y2SiO5晶体吸收光谱的变化,辐照后,未退火和氢气退火的纯Y2SiO5晶体在260~270 nm和320 nm波段产生了附加吸收峰,分别是由F心和O-心的吸收引起的;经过空气退火的纯YSO晶体中,由于消除了氧空位,因此辐照后没有出现色心吸收峰。在Eu3+∶Y2SiO5晶体中,不但有相同的F心和O-心吸收峰,而且还有Eu2+离子在300 nm和390 nm的吸收峰。随着辐照剂量的增加,色心附加吸收峰增强。空气退火能减少Eu3+∶Y2SiO5晶体中的色心,而氢气退火能增加色心。 相似文献
9.
Liang Liao Yi Pang Liming Ding Frank E. Karasz 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3149-3158
A soluble cyano‐substituted poly[(1,3‐phenylene vinylene)‐alt‐(1,4‐phenylene vinylene)] derivative ( 9 ) was synthesized and characterized. Comparison between 9 and its model compound ( 10 ) showed that the chromophore in 9 remained to be well defined as a result of a π‐conjugation interruption at adjacent m‐phenylene units. The attachment of a cyano substituent only at the β position of the vinylene allowed the maximum electronic impact of the cyano group on the optical properties of the poly(p‐phenylene vinylene) material. At a low temperature (?108 or ?198 °C), the vibronic structures of 9 and 10 were partially resolved. The absorption and emission spectra of a film of 9 were less temperature‐dependent than those of a film of 10 , indicating that the former had a lower tendency to aggregate. A light‐emitting diode (LED) based on 9 emitted yellow light (λmax ≈ 578 nm) with an external quantum efficiency of 0.03%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3149–3158, 2003 相似文献
10.
Richard Kotek Kyeong Pang Ben Schmidt Alan Tonelli 《Journal of Polymer Science.Polymer Physics》2004,42(23):4247-4254
Poly(ethylene isophthalate) (PEI) was synthesized for this research with essentially a condensation polymerization of isophthalic acid and ethylene glycol catalyzed by zinc acetate and antimony trioxide. Several samples were obtained, and their characteristics were observed and compared with poly(ethylene terephthalate) (PET). The synthesized PEI samples were chemically identified by 1H NMR. Thermal analysis with differential scanning calorimetry (DSC) yielded results that indicate the samples were primarily amorphous, with a glass‐transition temperature of 55–60 °C. Molecular weights of these PEI samples were also obtained through intrinsic viscosity measurements (Mark–Houwink equation). Molecular weights varied with conditions of the polymerization, and the highest molecular weight achieved was 21,000 g/mol. Finally, the diffusion coefficient, solubility, and permeability of CO2 gas in PEI were measured and found to be substantially lower than in PET, as anticipated from their isomeric chemical structures. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta‐substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4247–4254, 2004 相似文献