全文获取类型
收费全文 | 24036篇 |
免费 | 543篇 |
国内免费 | 171篇 |
专业分类
化学 | 15580篇 |
晶体学 | 200篇 |
力学 | 754篇 |
数学 | 3427篇 |
物理学 | 4789篇 |
出版年
2022年 | 211篇 |
2021年 | 244篇 |
2020年 | 326篇 |
2019年 | 298篇 |
2018年 | 288篇 |
2017年 | 238篇 |
2016年 | 457篇 |
2015年 | 392篇 |
2014年 | 457篇 |
2013年 | 1169篇 |
2012年 | 1093篇 |
2011年 | 1421篇 |
2010年 | 708篇 |
2009年 | 663篇 |
2008年 | 1185篇 |
2007年 | 1221篇 |
2006年 | 1294篇 |
2005年 | 1165篇 |
2004年 | 1026篇 |
2003年 | 949篇 |
2002年 | 887篇 |
2001年 | 401篇 |
2000年 | 370篇 |
1999年 | 276篇 |
1998年 | 276篇 |
1997年 | 282篇 |
1996年 | 333篇 |
1995年 | 293篇 |
1994年 | 287篇 |
1993年 | 265篇 |
1992年 | 259篇 |
1991年 | 237篇 |
1990年 | 231篇 |
1989年 | 209篇 |
1988年 | 243篇 |
1987年 | 225篇 |
1986年 | 174篇 |
1985年 | 316篇 |
1984年 | 321篇 |
1983年 | 257篇 |
1982年 | 342篇 |
1981年 | 303篇 |
1980年 | 315篇 |
1979年 | 278篇 |
1978年 | 281篇 |
1977年 | 249篇 |
1976年 | 266篇 |
1975年 | 242篇 |
1974年 | 234篇 |
1973年 | 236篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields. 相似文献
12.
13.
Jilly James Chidambaram Ramalechume Asit Baran Mandal 《Journal of Polymer Science.Polymer Physics》2007,45(17):2410-2420
The shape, size, aggregation, hydration, and correlation times of water insoluble PEO‐PPO‐PEO triblock copolymer micelles with sodium dodecylsulfate (SDS) micelles were investigated using transport studies and dynamic light scattering technique. From the conductance of micellar solutions of the polymer in 25 mM SDS and 5 mM NaCl, the hydration of polymer micelles were determined using the principle of obstruction of electrolyte migration by the polymer. The asymmetry of the micellar particles of polymer and polymer‐SDS mixed micellar systems in 5 mM NaCl and their average axial ratios were calculated using intrinsic viscosity and hydration data obeying Simha–Einstein equation. Hydration number and micellar sizes were variable with temperature. The shape of the polymer micelles has been ellipsoidal rather than spherical. The micellar volume, hydrodynamic radius, radius of gyration, diffusional coefficients as well as translational, rotational and effective correlation times have been calculated from the absolute values of the axes. The partial molal volume of polymer micelles has also been determined and its comparison with the molar volume of pure polymer suggested a volume contraction due to immobilization of the water phase by the hydrophilic head groups of the polymer. The thermodynamic activation parameters for viscous flow favor a more ordered water structure around polymer micelles at higher temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2410–2420, 2007 相似文献
14.
In this paper we study a widely used zero equation model of turbulence. The governing equations are derived by applying to the incompressible Navier-Stokes equations the Reynolds time averaging procedure. We achieve closure by employing the eddy viscosity concept. Using the Implicit Function Theorem we obtain an existence and uniquencess result. We also discuss the existence of nonsingular solutions. Finally, we present an algorithm for solving the modeled equations. 相似文献
15.
P. C. Roy 《等离子体物理论文集》1992,32(2):101-107
By using the two-point space correlation function an equation for the power spectral density for a random Langmuir field has been derived. The dispersion relation for a monochromatic wave is regained for a delta spectrum. For a Gaussian spectrum, the maximum growth rate is less than that for a monochromatic wave. For a “meander spectrum”, the growth rate is increased with the width of the spectrum in the first stage then decreased for further increase of the width. 相似文献
16.
Five different analytical schemes for examining isothermal and nonisothermal degradation of polymers were reviewed and found inadequate for describing multistage decomposition. The different schemes were experimentally tested using thermogravimetric analysis data for an ethylene-vinyl acetate (EVA) copolymer, which exhibited a well-behaved two-step decomposition process in a nitrogen environment. Based on these experimental and analytical findings, a generalized methodology was developed capable of describing the exhibited complex decomposition behavior of polymers by combining two or more kinetic mechanisms in a series or parallel arrangement. This composite of combinational methodology thus extends established analytical schemes for describing complex decomposition of polymers in a rational manner, incorporating both experimental and theoretical considerations. 相似文献
17.
James Tanton 《Mathematical Intelligencer》2007,29(3):55-59
This column is a place for those bits of contagious mathematics that travel from person to person in the community, because
they are so elegant, suprising, or appealing that one has an urge to pass them on.
Contributions are most welcome. 相似文献
18.
Benjamin Falk Santiago M. Vallinas James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2003,41(4):579-596
This article describes the development of optical pyrometry (OP) as a new analytical technique for the continuous monitoring of the progress of both free‐radical and cationic photopolymerizations. The method is rapid, reproducible, and very easy to implement. A temperature profile of a photopolymerization can be obtained. Preliminary studies have shown that the temperatures of some polymerizing monomers can easily reach temperatures in excess of 250 °C. The effects of the mass and reactivity of the monomer, light intensity, structures, and concentrations of the photoinitiators and monomers as well as the presence or absence of oxygen on various free‐radical and cationic photopolymerizations were examined with this method. Coupling of real‐time infrared spectroscopy with OP provides a convenient method for simultaneously monitoring both the chemical conversion and the temperature of a photopolymerization. This combined technique affords new insights into the effects of temperature‐induced autoacceleration on the course of photopolymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 579–596, 2003 相似文献
19.
Microscopic petrified grains were collected from a mafic–ultramafic pipe, NE of Dreikeesh, NW Syria. The grains were identified as anthers/gynoecia in herb/grass flowers. Three of the grains showed evidence of magnetism, two slowly dissolved in concentrated HCl, and three microprobed grains showed a montmorillonitic composition. Iron originating from pyroxene was oxidized to magnetite. Released silica formed the mineral suite agate–chalcedony–opal. Warm/cold paleoclimatic fluctuations, occurring during late Pliocene–Holocene, depended on water vapor, CO2 production, and cinders in the atmosphere. Most of these were associated with changing volcanic/tectonic events. Fluctuations were controlled by heat reflected from the Earth's surface being absorbed by water vapor and CO2, which both re-reflected the heat back to the surface, thus, raising the temperature. This cycle was repeated several times during late Pliocene–Holocene. 相似文献
20.