全文获取类型
收费全文 | 1181篇 |
免费 | 71篇 |
国内免费 | 33篇 |
专业分类
化学 | 880篇 |
晶体学 | 13篇 |
力学 | 18篇 |
数学 | 65篇 |
物理学 | 309篇 |
出版年
2023年 | 10篇 |
2022年 | 11篇 |
2021年 | 37篇 |
2020年 | 23篇 |
2019年 | 30篇 |
2018年 | 44篇 |
2017年 | 29篇 |
2016年 | 39篇 |
2015年 | 40篇 |
2014年 | 53篇 |
2013年 | 85篇 |
2012年 | 101篇 |
2011年 | 117篇 |
2010年 | 66篇 |
2009年 | 66篇 |
2008年 | 67篇 |
2007年 | 62篇 |
2006年 | 50篇 |
2005年 | 40篇 |
2004年 | 60篇 |
2003年 | 29篇 |
2002年 | 30篇 |
2001年 | 20篇 |
2000年 | 21篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 18篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1967年 | 5篇 |
排序方式: 共有1285条查询结果,搜索用时 93 毫秒
91.
An additive measure in o-minimal expansions of fields 总被引:1,自引:0,他引:1
92.
Herrera-Alonso M McCarthy TJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(21):9184-9189
Electrophilic aromatic substitution reactions were studied at poly(p-xylylene) (PPX) film surface-reaction medium interfaces. The extent of the reactions (depth of penetration and degree of substitution) was determined by the interaction of the polymer with the reaction solution. Reaction with chlorosulfonic acid to produce sulfonyl chloride and sulfone functionalities occurred readily in the bulk of PPX, and yields were sensitive to time and temperature. Confinement of this reaction to the PPX surface was achieved by controlling the concentration of the acid. Functionalization of PPX with N-methylol-2-chloroacetamide in sulfuric acid to produce the chloroamidomethylated derivative occurred in high yield and was confined to the surface region of PPX. Hydrolysis of the amide to generate aminomethylated PPX was assessed by XPS and a derivatization reaction. Friedel-Crafts type chemistry (acylation and alkylation reactions) also produced functionalized surfaces, but with lower degrees of substitution than the other two reactions and was strictly surface-confined. 相似文献
93.
A. Yu. Men’shikova Yu. O. Skurkis T. G. Evseeva Z. P. Shkarubskaya T. B. Tennikova S. S. Ivanchev 《Russian Journal of Applied Chemistry》2004,77(12):2011-2016
Adsorption and chemisorption of bovine serum albumin on polystyrene particles obtained by dispersion polymerization and containing graft polystyrene/polyvinylpyrrolidone copolymers and carboxy groups of the initiator in the surface layer were studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 12, 2004, pp. 2036–2041.Original Russian Text Copyright © 2004 by Menshikova, Skurkis, Evseeva, Shkarubskaya, Tennikova, Ivanchev. 相似文献
94.
A prototype calix[4]arene-based receptor for carbohydrate recognition containing peptide and phosphate binding groups 总被引:2,自引:0,他引:2
Segura M Bricoli B Casnati A Muñoz EM Sansone F Ungaro R Vicent C 《The Journal of organic chemistry》2003,68(16):6296-6303
A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calix[4]arenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaG degrees = 19.6 kJ mol(-)(1)) compared to the corresponding alpha anomer 13b (DeltaG degrees = 17.0 kJ mol(-)(1)) and to the beta-galactoside 13c (DeltaG degrees = 17.7 kJ mol(-)(1)) in CDCl(3). A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the (1)H NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed. 相似文献
95.
Ortiz-Marciales M González E De Jesús M Espinosa S Correa W Martínez J Figueroa R 《Organic letters》2003,5(19):3447-3449
[reaction: see text] Representative B-butyl- and B-methyl-1,3,2-oxazaborolidines derived from ephedrine and norephedrine were prepared in good yield and excellent purity by one-pot treatment of B-H oxazaborolidines with the corresponding organolithium reagent and subsequent hydrolysis of the cyclic borohydride intermediate with anhydrous ammonium chloride. 相似文献
96.
Gianni Bosi Juan Carlos Candeal Esteban Induráin Esteban Oloriz Margarita Zudaire 《Order》2001,18(2):171-190
In the framework of the analysis of orderings whose associated indifference relation is not necessarily transitive, we study the structure of an interval order and its representability through a pair of real-valued functions. We obtain a list of characterizations of the existence of a representation, showing that the three main techniques that have been used in the literature to achieve numerical representations of interval orders are indeed equivalent. 相似文献
97.
Margarita A. Deneva Pepa I. Uzunova Marin N. Nenchev 《Optical and Quantum Electronics》2007,39(3):193-212
We report (theory, experimental check) an improved approach for generation of a tunable, subnanosecond pulse (0.1–0.4 ns),
based on a single pulsation (“spike”) separation from the transient oscillations in a dye laser with active mirror (AMIR).
A pumping by 20–50 ns pulses from Q-switched Nd:YAG laser is considered. The separation is in original, two-spectral selective
channels cavity, where the forced by AMIR quenched generation at one of the wavelength stops initially started spiking generation
at the other wavelength after the first spike development. The AMIR quickly starts the quenching generation at a precisely
controlled moment and with necessary intensity thus assuring the desired separation. An advantage is a high reproducibility
of the separation for high (~250%) pump power fluctuations combined with tuning in large range (~20 nm). To obtain such an
operation we form ~1 ns leading front pump pulse by electrooptical temporal cutting of the input pump pulse and use an optical
delay line. This increases also a few times the power in the separated spike (to be ~100 kW). Our approach widens the combinations
of lasers for effective applications of spike separation technique (dye lasers excited by Q-switched solid-state or Cu-vapor
lasers). 相似文献
98.
N. Yu. Svechnikov V. G. Stankevich A. M. Lebedev K. A. Men’shikov B. N. Kolbasov V. V. Kriventsov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2007,1(1):13-17
Homogeneous deuterated hydrocarbon films redeposited from a deuterium plasma discharge inside the T-10 tokamak vacuum chamber are studied using photoluminescence methods; EXAFS, EPR, and IR spectroscopies; and temperature measurements. The photoluminescence excitation spectra of sp 3-sp 2 nanostructures of tokamak films are compared with those of sp 2 nanostructures of C60 fullerite films. The effect of defect states on photoluminescence and its temperature quenching is discussed. It is concluded that the model of temperature luminescence quenching for homogeneous deuterated tokamak films is similar to that for amorphous a-C:H films. 相似文献
99.
The possibility of cyclotron maser cooling of the transverse motion of electrons in a beam with the oblate velocity distribution characteristic of the setups with electron cooling has been analyzed. 相似文献
100.