全文获取类型
收费全文 | 194972篇 |
免费 | 2122篇 |
国内免费 | 615篇 |
专业分类
化学 | 107973篇 |
晶体学 | 3297篇 |
力学 | 7815篇 |
综合类 | 4篇 |
数学 | 18348篇 |
物理学 | 60272篇 |
出版年
2016年 | 2268篇 |
2015年 | 1689篇 |
2014年 | 2401篇 |
2013年 | 7833篇 |
2012年 | 5258篇 |
2011年 | 6620篇 |
2010年 | 4431篇 |
2009年 | 4374篇 |
2008年 | 5999篇 |
2007年 | 6161篇 |
2006年 | 5919篇 |
2005年 | 5413篇 |
2004年 | 4956篇 |
2003年 | 4440篇 |
2002年 | 4304篇 |
2001年 | 5779篇 |
2000年 | 4391篇 |
1999年 | 3515篇 |
1998年 | 2742篇 |
1997年 | 2781篇 |
1996年 | 2735篇 |
1995年 | 2519篇 |
1994年 | 2396篇 |
1993年 | 2293篇 |
1992年 | 2781篇 |
1991年 | 2669篇 |
1990年 | 2613篇 |
1989年 | 2642篇 |
1988年 | 2581篇 |
1987年 | 2589篇 |
1986年 | 2410篇 |
1985年 | 3279篇 |
1984年 | 3290篇 |
1983年 | 2720篇 |
1982年 | 2915篇 |
1981年 | 2858篇 |
1980年 | 2766篇 |
1979年 | 2900篇 |
1978年 | 3143篇 |
1977年 | 2963篇 |
1976年 | 2898篇 |
1975年 | 2757篇 |
1974年 | 2707篇 |
1973年 | 2720篇 |
1972年 | 1761篇 |
1971年 | 1467篇 |
1968年 | 1932篇 |
1967年 | 2129篇 |
1966年 | 1921篇 |
1965年 | 1497篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
801.
802.
803.
804.
A new technique has been developed to compute mean and fluctuating concentrations in complex turbulent flows (tidal current near a coast and deep ocean). An initial distribution of material is discretized into any small clouds which are advected by a combination of the mean flow and large scale turbulence. The turbulence can be simulated either by kinematic simulation (KS) or direct numerical simulation. The clouds also diffuse relative to their centroids; the statistics for this are obtained from a separate calculation of the growth of individual clouds in small scale turbulence, generated by KS. The ensemble of discrete clouds is periodically re-discretized, to limit the size of the small clouds and prevent overlapping. The model is illustrated with simulations of dispersion in uniform flow, and the results are compared with analytic, steady state solutions. The aim of this study is to understand how pollutants disperses in a turbulent flow through a numerical simulation of fluid particle motion in a random flow field generated by Fourier modes. Although this homogeneous turbulent is rather a “simple” flow, it represents a building block toward understanding pollutant dispersion in more complex flow. The results presented here are preliminary in nature, but we expect that similar qualitative results should be observed in a genuine turbulent flow. 相似文献
805.
Our research group has been interested in synthesis of proton transfer compounds as new supramolecular synthons for the onepot preparation of self-assembled transition metal complex-organo-networks since 2000. We have focused on the proton delivery from acids, which are considered as suitable proton donors, to amines as proton acceptors. The results were production of several proton transfer ion pairs possessing some remaining donor sites applied for coordination to metallic centers in preparation of metal-organic structures. Some of the complexes showed contributions of both cationic and anionic fragments of the starting ion pair, while some others contained only one of these species as ligand. Much of the investigations on reviewed compounds focused on the concept of supramolecular systems, co-crystallization, stereochemically active lone pairs, coordination polyhedron and mainly on various interactions involve including van der Waals, ion pairing, hydrogen bondings, face to face π-π stackings and edge to face C-H...π, C-O...π, N-H...π, S-O...π, Ti...π and Hg-Cl...π interactions. The mentioned interactions are the most commonly used strategies in the extension of supramolecular structures. 相似文献
806.
S. V. Trukhanov V. V. Fedotova A. V. Trukhanov S. G. Stepin H. Szymczak 《Crystallography Reports》2008,53(7):1177-1180
Nanocrystalline manganite La0.50Ba0.50MnO3 was synthesized by the soft-chemical method. For this purpose, the sol-gel method was modified and improved. A trihydric saturated alcohol, e.g., glycerol, was suggested as a new organic matrix. The crystal structure of the composite was studied by X-ray powder diffraction at room temperature. A La0.50Ba0.50MnO3 powder annealed in air at T = 500°C is characterized by a perovskite-like cubic structure with the unit-cell parameter a = 3.869 Å. The chemical composition of the sample was studied by electron-probe X-ray microanalysis. The La: Ba: Mn cation ratio in the material was 1: 1: 2. The surface topography was examined with a scanning electron microscope. The crystallite size was ~30 nm. The dependence of the crystal structure and the surface topology on the annealing temperature was studied. The high-temperature treatment in air resulted in the growth of larger, micrometer-size, crystallites. 相似文献
807.
Transverse displacement at total reflection near the grazing angle: a way to discriminate between theories 总被引:1,自引:0,他引:1
F. Pillon H. Gilles S. Girard M. Laroche O. Emile 《Applied physics. B, Lasers and optics》2005,80(3):355-357
The transverse shift is observed and precisely measured at total internal reflection on a dielectric interface for a circularly polarized light beam when the incident angle is scanned from the critical angle up to the grazing angle close to 90°. The experimental results show with no doubt that the transverse displacement exists far away from the critical angle and only vanishes at grazing angle. A comparison with theories also allows a discrimination between the most different theoretical models traditionally used to interpret physically this effect. 相似文献
808.
Nuclear spin manipulation using an interface of diluted magnetic semiconductors (DMSs) is proposed. On the basis of the first-principles electronic structure calculation, we show that the hyperfine fields at an impurity site in the interface between a DMS and a base substance is dramatically changed by an external electric field. The electric field dependence of the hyperfine fields at the impurity nucleus in the interface of (InMn)As and (GaMn)As is examined. 相似文献
809.
Summary The stability constants of Eu3+ and Am3+ with the site specific humic acid (YKHA) have been determined. The humic acid has been extracted from the soil of Yongkwang
area belonging geologically to the Okchon Basin of the Korean Peninsula, where the nuclear power plant is located. The total
carboxylate capacity, the acidity constant (pKa), and the binding constants with Eu3+ and Am3+ have been determined for humic acid. 相似文献
810.
Y. A. Abdu T. Ericsson H. Annersten 《Journal of magnetism and magnetic materials》2004,280(2-3):395-403
Fe–Ni alloys below the Invar region with compositions Fe100−xNix (x=21, 24, and 27 at%) were prepared by high-energy ball milling technique (mechanical alloying). The as-milled samples, characterized by X-ray diffraction and Mössbauer spectroscopy, contain a mixture of (BCC) and γ (FCC) phases, whereas the samples annealed at 650°C for 0.5 h show a single γ (FCC) phase displaying a single line Mössbauer spectrum at room temperature (RT). At low temperature, the Mössbauer spectra of annealed Fe76Ni24 and Fe73Ni27 alloys show the existence of a magnetically split pattern together with a broad singlet, which are ascribed to a high-moment ferromagnetic Ni-rich phase and a low-moment Fe-rich phase, respectively. The Fe-rich phase in annealed Fe76Ni24 alloy, which is paramagnetic at RT, undergoes antiferromagnetic ordering at 40 K, estimated from the dramatic line broadening of its spectrum, giving rise to a small hyperfine field (e.g. 2 T at 6 K). The coexistence of these phases is attributed to phase segregation occurring in these alloys as a result of enhanced atomic diffusion. The stability of these alloys towards martensitic (FCC→BCC) transformation at low temperatures is discussed in connection with the Fe–Ni phase diagram below 400°C. 相似文献