全文获取类型
收费全文 | 17299篇 |
免费 | 709篇 |
国内免费 | 9篇 |
专业分类
化学 | 12460篇 |
晶体学 | 102篇 |
力学 | 327篇 |
数学 | 2321篇 |
物理学 | 2807篇 |
出版年
2023年 | 138篇 |
2022年 | 135篇 |
2021年 | 215篇 |
2020年 | 273篇 |
2019年 | 295篇 |
2018年 | 263篇 |
2017年 | 277篇 |
2016年 | 619篇 |
2015年 | 543篇 |
2014年 | 603篇 |
2013年 | 1117篇 |
2012年 | 1324篇 |
2011年 | 1427篇 |
2010年 | 820篇 |
2009年 | 670篇 |
2008年 | 1241篇 |
2007年 | 1196篇 |
2006年 | 1059篇 |
2005年 | 986篇 |
2004年 | 836篇 |
2003年 | 670篇 |
2002年 | 578篇 |
2001年 | 235篇 |
2000年 | 213篇 |
1999年 | 139篇 |
1998年 | 106篇 |
1997年 | 112篇 |
1996年 | 157篇 |
1995年 | 101篇 |
1994年 | 103篇 |
1993年 | 96篇 |
1992年 | 97篇 |
1991年 | 70篇 |
1990年 | 59篇 |
1989年 | 48篇 |
1988年 | 53篇 |
1987年 | 47篇 |
1986年 | 70篇 |
1985年 | 95篇 |
1984年 | 78篇 |
1983年 | 55篇 |
1982年 | 78篇 |
1981年 | 78篇 |
1980年 | 75篇 |
1979年 | 63篇 |
1978年 | 59篇 |
1977年 | 48篇 |
1976年 | 61篇 |
1975年 | 32篇 |
1974年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
21.
A.F. Mesquita A.O. Porto G.M. de Lima J.M. Delgado F.S. Lameiras 《Solid State Communications》2005,136(3):133-137
Hexagonal and cubic cadmium selenide were prepared from a chemical route by using cadmium chloride and potassium selenium hydride obtained from reaction of selenium powder and potassium boron hydride. The product obtained was thermally treated under argon flux at 300, 500 and 600 °C for 2 h and characterized by X-ray photoelectron spectroscopy and X-ray diffraction. The X-ray diffraction data were refined by Rietveld method and the structural parameters were determined for the phases of each annealed samples. At 300 °C five phases were identified: Cubic and hexagonal cadmium selenides and the contaminants: Potassium chloride, boron oxide and cadmium boron oxide. At 500 and 600 °C only the hexagonal cadmium selenide phase was identified besides the other above mentioned contaminant. 相似文献
22.
Affine Arithmetic: Concepts and Applications 总被引:2,自引:0,他引:2
Affine arithmetic is a model for self-validated numerical computation that keeps track of first-order correlations between computed and input quantities. We explain the main concepts in affine arithmetic and how it handles the dependency problem in standard interval arithmetic. We also describe some of its applications. 相似文献
23.
C. M. Silva R. S. Amaral A. Amaral J. A. Santos Júnior D. C. Santos L. E. Lima S. V. Silveira 《Journal of Radioanalytical and Nuclear Chemistry》2006,270(1):237-241
Summary Studies performed by the Brazilian Nuclear Corporation (NUCLEBRAS), in collaboration with the Geological Survey Company of
Brazil (CPRM), identified high levels of natural uranium in the districts of Pedra and Venturosa, in the rural region of the
state of Pernambuco (PE) - Brazil, where the maximum value found in rocks was 22,000 mg. 相似文献
24.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
25.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
26.
André Markoff 《Mathematische Annalen》1886,27(2):177-182
Sans résumé 相似文献
27.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献
28.
Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations. 相似文献
29.
Recent mass measurements of proton-rich nuclei close to the N=Z line were used for the calculation of the interaction strength δV pn between valence protons and neutrons. When compared with δV pn values calculated from mass values of the AME’95 mass tables, the breaking down of the SU(4) symmetry is verified at Z=32,33,34. 相似文献
30.
Biosorption of Chromium(III) by Biomass of Seaweed Sargassum sp. in a Fixed-Bed Column 总被引:2,自引:0,他引:2
Eneida Sala Cossich Edson Antonio da Silva Célia Regina Granhen Tavares Lúcio Cardozo Filho Teresa Massako Kakuta Ravagnani 《Adsorption》2004,10(2):129-138
This work aimed at modeling chromium biosorption using the biomass of seaweed Sargassum sp. in a fixed-bed column. The mathematical model used was obtained from the mass balance of the component in the liquid phase and in the biosorbent material. The effects of both axial dispersion in the column and the resistance to mass transfer in the solid were considered for the solution of the partial differential equations of the model, using the Galerkin method on finite elements. To represent the equilibrium data of the batch system the Langmuir isotherm were used. The chromium ion adsorption capacity of the seaweed Sargassum sp., at a temperature of 30°C and pH 3.5, was 2.61 mmol/g. The model performance was evaluated from experimental data obtained at 30°C for flow rates of 2, 6 and 8 mL/min. The parameters of the model, mass transfer and axial dispersion coefficients, were adjusted from these experimental data. The model proved adequate to describe chromium biosorption dynamics in fixed-bed columns. 相似文献