全文获取类型
收费全文 | 2766篇 |
免费 | 99篇 |
国内免费 | 5篇 |
专业分类
化学 | 2138篇 |
晶体学 | 36篇 |
力学 | 58篇 |
数学 | 76篇 |
物理学 | 562篇 |
出版年
2022年 | 14篇 |
2021年 | 25篇 |
2020年 | 47篇 |
2019年 | 47篇 |
2018年 | 34篇 |
2017年 | 14篇 |
2016年 | 55篇 |
2015年 | 44篇 |
2014年 | 43篇 |
2013年 | 115篇 |
2012年 | 147篇 |
2011年 | 141篇 |
2010年 | 57篇 |
2009年 | 89篇 |
2008年 | 150篇 |
2007年 | 136篇 |
2006年 | 172篇 |
2005年 | 125篇 |
2004年 | 119篇 |
2003年 | 107篇 |
2002年 | 98篇 |
2001年 | 64篇 |
2000年 | 62篇 |
1999年 | 38篇 |
1998年 | 21篇 |
1997年 | 22篇 |
1996年 | 34篇 |
1995年 | 36篇 |
1994年 | 32篇 |
1993年 | 26篇 |
1992年 | 46篇 |
1991年 | 32篇 |
1990年 | 44篇 |
1989年 | 49篇 |
1988年 | 40篇 |
1987年 | 33篇 |
1986年 | 29篇 |
1985年 | 62篇 |
1984年 | 56篇 |
1983年 | 22篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 32篇 |
1979年 | 41篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 35篇 |
1975年 | 24篇 |
1974年 | 18篇 |
1973年 | 19篇 |
排序方式: 共有2870条查询结果,搜索用时 31 毫秒
31.
32.
33.
A simple and sensitive spectrophotometric determination of bismuth(III) is based on the reaction between bismuth(III) and o-hydroxyhydroquinonephthalein in the presence of Brij 58 in acidic media. The calibration graph is linear over the range 0-3.5 mug/ml bismuth(III) in the final solution, and the apparent molar absorptivity at 520 nm is 9.03 x 10(4) l. mole(-1). cm(-1). The proposed method is 2-10 times more sensitive than other methods, and simpler. It has been applied to the assay of bismuth(III) in pharmaceutical preparations, such as dermatol and bismuth subnitrate, with good results. 相似文献
34.
35.
36.
37.
Simulation of aerated lagoon using artificial neural networks and multivariate regression techniques
Karla Patricia Oliveira-Esquerre Aline C. da Costa Roy Edward Bruns Milton Mori 《Applied biochemistry and biotechnology》2003,106(1-3):437-449
The aim of this study was to develop an empirical model that provides accurate predictions of the biochemical oxygen demand
of the output stream from the aerated lagoon at International Paper of Brazil, one of the major pulp and paper plants in Brazil.
Predictive models were calculated from functional link neural networks (FLNNs), multiple linear regression, principal components
regression, and partial least-squares regression (PLSR). Improvement in FLNN modeling capability was observed when the data
were preprocessed using the PLSR technique. PLSR also proved to be a powerful linear regression technique for this problem,
which presents operational data limitations. 相似文献
38.
39.
Takehiko Yamato Masashi Yasumatsu Yoshiyuki Saruwatari Louis Korbla Doamekpor 《Journal of inclusion phenomena and macrocyclic chemistry》1994,19(1-4):315-331
Novel macrocyclic compounds, hexahydroxy[1.0.1.0.1.0]- (2b) and octahydroxy[1.0.1.0.1.0.1.0]metacyclophane (2c) have been prepared in 50–70% yield by base-catalyzed condensation of 5,5-di-tert-butyl-2,2-dihydroxybiphenyl (1) with formaldehyde in refluxing xylene. An attempted alkylation of the flexible macrocycles2b and2c with ethyl bromoacetate in the presence of Cs2CO3 under acetonitrile reflux gave only one pure stereoisomer3 and4, respectively, while other possible isomers were not observed. The structural characterization of these products is also discussed. The two-phase solvent extraction data indicated that hexaethyl ester3 and octaethyl ester4 show strong metal affinity, comparable with that of the corresponding calix[n]arenes, and a high K+ selectivity was observed for octaethyl ester4.1H-NMR titration of hexaethyl ester3 and octaethyl ester4 with KSCN clearly demonstrate that a 11 complex is formed which is stable on the NMR time scale.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes. 相似文献
40.
Shindo M Yoshikawa T Itou Y Mori S Nishii T Shishido K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(2):524-536
Ynolates were found to react with alpha-alkoxy-, alpha-siloxy-, and alpha-aryloxyketones at room temperature to afford tetrasubstituted olefins with high Z selectivity. Since the geometrical selectivity was determined in the ring opening of the beta-lactone enolate intermediates, the torquoselectivity was controlled by the ethereal oxygen atoms. From experimental and theoretical studies, the high Z selectivity is induced by orbital and steric interactions rather than by chelation. In a similar manner, alpha-dialkylamino ketones provided olefins with excellent Z selectivity. These products can be easily converted into multisubstituted butenolides and gamma-butyrolactams in good yield. 相似文献