全文获取类型
收费全文 | 223916篇 |
免费 | 1756篇 |
国内免费 | 676篇 |
专业分类
化学 | 123427篇 |
晶体学 | 3349篇 |
力学 | 8599篇 |
综合类 | 7篇 |
数学 | 24669篇 |
物理学 | 66297篇 |
出版年
2020年 | 2111篇 |
2019年 | 2371篇 |
2018年 | 3289篇 |
2017年 | 3203篇 |
2016年 | 4439篇 |
2015年 | 2525篇 |
2014年 | 4005篇 |
2013年 | 9654篇 |
2012年 | 7325篇 |
2011年 | 8971篇 |
2010年 | 6355篇 |
2009年 | 6144篇 |
2008年 | 8609篇 |
2007年 | 8647篇 |
2006年 | 8039篇 |
2005年 | 7363篇 |
2004年 | 6574篇 |
2003年 | 5917篇 |
2002年 | 5797篇 |
2001年 | 6030篇 |
2000年 | 4771篇 |
1999年 | 3535篇 |
1998年 | 3084篇 |
1997年 | 3132篇 |
1996年 | 2956篇 |
1995年 | 2406篇 |
1994年 | 2494篇 |
1993年 | 2554篇 |
1992年 | 2672篇 |
1991年 | 2738篇 |
1990年 | 2639篇 |
1989年 | 2590篇 |
1988年 | 2533篇 |
1987年 | 2498篇 |
1986年 | 2419篇 |
1985年 | 3155篇 |
1984年 | 3324篇 |
1983年 | 2654篇 |
1982年 | 2936篇 |
1981年 | 2811篇 |
1980年 | 2599篇 |
1979年 | 2807篇 |
1978年 | 2948篇 |
1977年 | 2960篇 |
1976年 | 2917篇 |
1975年 | 2764篇 |
1974年 | 2732篇 |
1973年 | 2872篇 |
1972年 | 1907篇 |
1967年 | 1854篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
A. V. Ivanov M. Yu. Tsentalovich E. G. Kogan L. G. Tomilova N. S. Zefirov 《Russian Chemical Bulletin》2008,57(8):1676-1679
The chlorination of benzene, toluene, and o-xylene with molecular chlorine in the presence of the phthalocyanine complexes of different structures was studied. The transformations
of the catalysts during the reaction were investigated.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1644–1647, August, 2008. 相似文献
22.
The kinetics of unhindered sedimentation of a titanium dioxide suspension (as model dispersed system) was studied, and the effect of the concentration and mode of addition of various formulations based on anionic and cationic acrylamide copolymers on their flocculation properties in aqueous salt (NaCl) solutions was evaluated. 相似文献
23.
S. A. Bulgakova A. I. Mashin I. A. Kazantseva D. E. Kashtanov M. M. Jones G. S. Tsepkov A. V. Korobkov A. V. Nezhdanov 《Russian Journal of Applied Chemistry》2008,81(8):1446-1451
Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined. 相似文献
24.
W M Niessen M A de Kraa E R Verheij P J Bergers G F La Vos U R Tjaden J van der Greef 《Rapid communications in mass spectrometry : RCM》1989,3(1):1-4
On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL. 相似文献
25.
Martin E. Schimpf J. Calvin Giddings 《Journal of Polymer Science.Polymer Physics》1989,27(6):1317-1332
The thermal diffusion coefficient DT has been obtained for 17 polymer-solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field-flow fractionation. The polymers examined include polystyrene, poly(alpha-methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent. 相似文献
26.
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
27.
In basin modelling the thermodynamics of a multicomponent multiphase fluid flux are computationally too expensive when derived from an equation of state and the Gibbs equality constraints. In this article we present a novel implicit molar mass formulation technique using binary mixture thermodynamics. The two proposed solution methods, with and without cross derivative terms between components, are based on a preconditioned Newton‐GMRES scheme for each time‐step with analytical computation of the derivatives. These new algorithms reduce significantly the numerical effort for the computation of the molar masses, and we illustrate the behavior of these methods with numerical computations. Copyright © 2004 John Wiley & Sons Ltd. 相似文献
28.
A method for computing low Mach number flows using high‐resolution interpolation and difference formulas, within the framework of the Marker and Cell (MAC) scheme, is presented. This increases the range of wavenumbers that are properly resolved on a given grid so that a sufficiently accurate solution can be obtained without extensive grid refinement. Results using this scheme are presented for three problems. The first is the two‐dimensional Taylor–Green flow which has a closed form solution. The second is the evolution of perturbations to constant‐density, plane channel flow for which linear stability solutions are known. The third is the oscillatory instability of a variable density plane jet. In this case, unless the sharp density gradients are resolved, the calculations would breakdown. Under‐resolved calculations gave solutions containing vortices which grew in place rather than being convected out. With the present scheme, regular oscillations of this instability were obtained and vortices were convected out regularly. Stable computations were possible over a wider range of sensitive parameters such as density ratio and co‐flow velocity ratio. Copyright © 2004 John Wiley Sons, Ltd. 相似文献
29.
30.