全文获取类型
收费全文 | 2126篇 |
免费 | 118篇 |
国内免费 | 190篇 |
专业分类
化学 | 1723篇 |
晶体学 | 50篇 |
力学 | 72篇 |
综合类 | 30篇 |
数学 | 135篇 |
物理学 | 424篇 |
出版年
2023年 | 14篇 |
2022年 | 36篇 |
2021年 | 39篇 |
2020年 | 34篇 |
2019年 | 45篇 |
2018年 | 42篇 |
2017年 | 44篇 |
2016年 | 64篇 |
2015年 | 35篇 |
2014年 | 53篇 |
2013年 | 174篇 |
2012年 | 140篇 |
2011年 | 64篇 |
2010年 | 56篇 |
2009年 | 78篇 |
2008年 | 89篇 |
2007年 | 96篇 |
2006年 | 103篇 |
2005年 | 103篇 |
2004年 | 91篇 |
2003年 | 79篇 |
2002年 | 63篇 |
2001年 | 61篇 |
2000年 | 75篇 |
1999年 | 59篇 |
1998年 | 49篇 |
1997年 | 65篇 |
1996年 | 67篇 |
1995年 | 67篇 |
1994年 | 47篇 |
1993年 | 44篇 |
1992年 | 64篇 |
1991年 | 28篇 |
1990年 | 33篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1974年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有2434条查询结果,搜索用时 0 毫秒
1.
We examine two criteria for balance of a gain graph, one based on binary cycles and one on circles. The graphs for which each criterion is valid depend on the set of allowed gain groups. The binary cycle test is invalid, except for forests, if any possible gain group has an element of odd order. Assuming all groups are allowed, or all abelian groups, or merely the cyclic group of order 3, we characterize, both constructively and by forbidden minors, the graphs for which the circle test is valid. It turns out that these three classes of groups have the same set of forbidden minors. The exact reason for the importance of the ternary cyclic group is not clear. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
2.
A. Zubeldia M. Larraaga P. Remiro I. Mondragon 《Journal of Polymer Science.Polymer Physics》2004,42(21):3920-3933
The microstructure and fracture behavior of epoxy mixtures containing two monomers of different molecular weights were studied. The variation of the fracture toughness by the addition of other modifiers was also investigated. Several amounts of high‐molecular‐weight diglycidyl ether of bisphenol A (DGEBA) oligomer were added to a nearly pure DGEBA monomer. The mixtures were cured with an aromatic amine, showing phase separation after curing. The curing behavior of the epoxy mixtures was investigated with thermal measurements. A significant enhancement of the fracture toughness was accompanied by slight increases in both the rigidity and strength of the mixtures that corresponded to the content of the high‐molecular‐weight epoxy resin. Dynamic mechanical and atomic force microscopy measurements indicated that the generated two‐phase morphology was a function of the content of the epoxy resin added. The influence of the addition of an oligomer or a thermoplastic on the morphologies and mechanical properties of both epoxy‐containing mixtures was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3920–3933, 2004 相似文献
3.
Tsonka Stefanova Baicheva 《Designs, Codes and Cryptography》1998,13(3):223-227
The covering radius of all ternary cyclic codes of length up to 25 is given. Some of the results were obtained by computer
and for others mathematical reasonings were applied. The minimal distances of all codes were recalculated. 相似文献
4.
The aim of this paper is to introduce a new functional in thestudy of swelling porous elastic soils saturated by a fluid.This new functional is a useful tool; it allows us to provethe existence of solutions in the case of a compressible fluid.We also prove the stability of solutions and the exponentialdecay in the case of an incompressible fluid. We study as wellthe continuous dependence with respect to the initial time. 相似文献
5.
Thiw work is concerned with the formulation of constituent interactions and corresponding balance relations in classical mixture theory as based on a model for the (classical) constituent structure of such a mixture. 相似文献
6.
Aït Hmaïdouch L. Mançour Billah S. El Hadek M. 《Journal of Thermal Analysis and Calorimetry》2002,69(2):659-667
The solid—liquid equilibria of the ternary system H2O—Al(NO3)3—Mg(NO3)2 were studied at –30, –20, –10 and 0°C by using a synthetic method which allows to detemine all the characteristic points of isothermal sections. The stable solid phases which appear are respectively: ice, Al(NO3)3·9H2O, Mg(NO3)2·9H2O and Mg(NO3)2·6H2O. Neither double salts nor mixed crystals are observed in the temperature and composition field studied. Polytherm diagram layout show two invariant transformations correspond with an eutectic point and a peritectic point.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
7.
8.
Dielectric relaxation study of the binary mixtures of poly(vinyl pyrrolidone) (PVP) (Mw=24000, 40000 and 360000 g mol−1) with ethyl alcohol (EA) and poly(ethylene glycol)s (PEGs) (Mw=200 and 400 g mol−1) in dilute solutions of dioxane were carried out at 10.1 GHz and 35°C. The relaxation time of PVP-EA mixtures was interpreted
by the consideration of a wait-and-switch model in the local structure of self-associated ethyl alcohol molecules and also
the PVP chain length as a geometric constraint for the reorientational motion of ethyl alcohol molecules. The formation of
complexes and effect of PVP chain length on the molecular dynamics, chain flexibility and stretching of PEG molecules in PVP-PEG
mixtures were explored from the comparative values of dielectric relaxation time. Further, relaxation time values in dioxane
and benzene solvent confirm the viscosity independent molecular dynamics in PVP-EA mixtures but the values vary significantly
with the non-polar solvent environment. 相似文献
9.
O. E. Aleksandrov 《Fluid Dynamics》2006,41(6):976-983
It is shown that the convective transport in a binary mixture in the presence of vortex convection can be described in terms of Fick’s law with an effective diffusion coefficient independent of the concentration. The form of the effective diffusion coefficient is found for arbitrary convection in the mixture. A generalization of the Stefan-Maxwell diffusion equation is proposed to include an arbitrary rotational mixture velocity field. The characteristics of convective transport are considered with reference to a three-component mixture. A solution of the equation of three-component mixture transport through a long capillary in the presence of convection homogeneous along the capillary axis is presented. It is established that for sharply different component diffusion coefficients a mixture density extremum may appear inside the capillary and then change or disappear depending on the convective flow intensity. 相似文献
10.
Summary Six commercial hydrogen standards containing helium, oxygen, nitrogen, methane and carbon dioxide at trace levels were analyzed
by gas chromatography, for periods up to 105 days. The concentrations, in the range of 0–120 μmol mol−1, were stable (with the exception of oxygen) but often significantly different from the certified values provided by the suppliers,
especially for helium, oxygen and nitrogen. Concurrently, some experiments were carried out to verify the stability of gas
mixtures based on hydrogen stored in cylinders submitted to different chemical and physical treatments. The causes that led
to the deviations observed, as well as the decreases in oxygen, are discussed.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996. 相似文献