全文获取类型
收费全文 | 2418篇 |
免费 | 76篇 |
国内免费 | 13篇 |
专业分类
化学 | 1939篇 |
晶体学 | 26篇 |
力学 | 22篇 |
数学 | 331篇 |
物理学 | 189篇 |
出版年
2023年 | 8篇 |
2022年 | 48篇 |
2021年 | 47篇 |
2020年 | 35篇 |
2019年 | 36篇 |
2018年 | 29篇 |
2017年 | 20篇 |
2016年 | 69篇 |
2015年 | 72篇 |
2014年 | 71篇 |
2013年 | 142篇 |
2012年 | 193篇 |
2011年 | 213篇 |
2010年 | 123篇 |
2009年 | 104篇 |
2008年 | 166篇 |
2007年 | 178篇 |
2006年 | 163篇 |
2005年 | 139篇 |
2004年 | 105篇 |
2003年 | 89篇 |
2002年 | 90篇 |
2001年 | 35篇 |
2000年 | 28篇 |
1999年 | 29篇 |
1998年 | 11篇 |
1997年 | 18篇 |
1996年 | 30篇 |
1995年 | 18篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1973年 | 6篇 |
1972年 | 3篇 |
排序方式: 共有2507条查询结果,搜索用时 15 毫秒
101.
Luis Alvarez‐Thon Carlos Bustos Katherina Espinoza‐Santibaez Maria Teresa Garland Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(10):1200-1204
The title compound, C17H11F5N4O, is described and compared with two closely related analogues in the literature. There are two independent molecules in the asymmetric unit, linked by N—H...O hydrogen bonds and π–π interactions into dimeric entities, presenting a noticeable noncrystallographic C2 symmetry. These dimers are in turn linked by a medium‐strength type‐I C—F...F—C interaction into elongated tetramers. Much weaker C—H...F contacts link the tetramers into broad two‐dimensional substructures parallel to (101). 相似文献
102.
103.
Luis Alvarez Thon Carlos Bustos Fernando Diaz‐Marín Maria Teresa Garland Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(1):101-104
The title compound, C17H10F5N5O2, is described and compared with its 4‐nitrophenyl isomer [Bustos, Sánchez, Schott, Alvarez‐Thon & Fuentealba (2007). Acta Cryst. E 63 , o1138–o1139]. The title molecule presents its nitro group split into two rotationally disordered components, which in conjunction with the rotation of the `unclamped' rings constitute the main molecular differences. Packing is directed by a head‐to‐tail type `I' C—F...F—C interaction, generating double‐chain strips running along [100]. These substructures are interlinked by a variety of weak F...F, O...F, F...π and O...π interactions. 相似文献
104.
Teresa Kowalska 《Monatshefte für Chemie / Chemical Monthly》1985,116(10):1129-1132
An explanation is given for the two possible ways of determination of the activity coefficients of solutes, when applying a new thermodynamic model of adsorption and partition chromatography, i. e. the binary solutions model. 相似文献
105.
Raman Tandon Teresa Unzner Dr. Tobias A. Nigst Dr. Nicolas De Rycke Dr. Peter Mayer Dr. Bernd Wendt Dr. Olivier R. P. David Prof. Dr. Hendrik Zipse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6435-6442
New heterocyclic derivatives of 9‐azajulolidine have been synthesized and characterized with respect to their nucleophilicity and Lewis basicity. The Lewis basicity of these bases as quantified through their theoretically calculated methyl‐cation affinities correlate well with the experimentally measured reaction rates for addition to benzhydryl cations. All newly synthesized pyridines show exceptional catalytic activities in benchmark acylation reactions, which correlate only poorly with Lewis basicity or nucleophilicity parameters. A combination of Lewis basicity with charge and geometric parameters in the framework of a three‐component quantitative structure–activity relationship (QSAR) model is, however, highly predictive. 相似文献
106.
Antonio Doménech‐Carbó María Teresa Doménech‐Carbó Francisco López‐López Francisco Manuel Valle‐Algarra Laura Osete‐Cortina Estrella Arcos‐Von Haartman 《Electroanalysis》2013,25(12):2621-2630
The solid state voltammetric response of Egypt blue, Han blue and ploss blue pigments upon attachment to graphite electrodes in contact with aqueous phosphate buffer at pH 7.0 is studied by voltammetry of microparticles and scanning electrochemical microscopy. Such voltammetric responses, combined with those for synthetic specimens consisting of binary mixtures of the pigment and SiO2 or CaCO3 as well as ternary ones of CaCO3 and SiO2 mixtures allow for the identification of the pigment and the support in samples from wall paintings using different electrochemical parameters, in particular upon performing the Tafel and modified Tafel analysis of voltammetric peaks. Identification of Egypt blue in microsamples of murals from a Roman archaeological site in Castulo (Jaén, Spain) is discussed. 相似文献
107.
108.
The solid phase extraction as a solvent-free method for the analysis of oil and grease in waters was studied. The use of
a PTFE surface as a solid phase allows the retention of the volatile fraction of oil and grease, and further analysis of carbon–hydrogen
bonds using infrared spectroscopy can be done on the surface.
Various oils and grease samples were tested: n-hexadecane, n-tetradecane, n-nonadecane, n-docosane, isooctane, diesel oil
and gasoline. Temperatures from 25° to 90 °C and a range of heating times were checked for extraction.
Precision tests showed relative standard deviation values of around 10% in several samples of the same concentration. Calibration
lines of n-hexadecane showed high correlation coefficients from 0.9 to 30 mg/l. Recoveries for the various oils using different
calibration lines showed values from 90 to 110%.
The method described here is fast and clean, and allows reproducible measurements of oil and grease in water that do not require
the use of a solvent.
Received March 1, 2001; accepted August 15, 2001; published online July 15, 2002 相似文献
109.
Susana Junco Teresa Casimiro Nuno Ribeiro Manuel Nunes Da Ponte Helena Cabral Marques 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):117-121
Naproxen is a poorly soluble anti-inflammatorydrug, the solubility of which canbe enhanced by complexation withbeta-cyclodextrin. Besides that, the inclusioncomplex reduces the incidence of gastrointestinal side effects of the drug. The aim of this work was to compare the physicochemical characteristics of the solid complexes prepared by traditional methods (kneading, freeze-drying and spray-drying) and using a supercritical fluid technology. The unusual solvent properties of carbon dioxide above their critical temperature and pressure were exploited in order to prepare inclusion compounds. Complexes prepared using supercritical fluid technology showed similar properties to those of freeze-drying andspray-drying complexes as proved by DSC, FT-IRand UV. 相似文献
110.
Oliveira SC Paiva TC Visconti AE Giudici R 《Applied biochemistry and biotechnology》1998,74(3):161-172
Discrimination between different rival models for describing the inhibitory effect of ethanol both on yeast growth and on
fermentation was studied for a continuous process of alcoholic fermentation in a tower reactor with recycling of flocculating
cells. Models tested include linear, parabolic, hyperbolic, exponential, and generalized nonlinear power-law types. The best
expressions were identified under the criteria that all the kinetic parameters should assume acceptable values in a feasible
range and should result in the best fit of the experimental data. The kinetic parameters were estimated from steady-state
data of several sugar concentrations in feeding stream (S0 = 160, 170, 180, 190, 200 g/L), constant dilution rate (D = 0.2 h-1), recycle ratio (α = 13.6), and temperature (T = 30°C). The best model for the yeast growth was of power-law type, whereas
for the product formation the best model was of linear type. These models were able to reproduce the trends of the process
variables satisfactorily. 相似文献