全文获取类型
收费全文 | 319977篇 |
免费 | 4571篇 |
国内免费 | 1113篇 |
专业分类
化学 | 174707篇 |
晶体学 | 4490篇 |
力学 | 13173篇 |
综合类 | 7篇 |
数学 | 37509篇 |
物理学 | 95775篇 |
出版年
2020年 | 2112篇 |
2019年 | 2100篇 |
2018年 | 2117篇 |
2017年 | 2015篇 |
2016年 | 4122篇 |
2015年 | 3458篇 |
2014年 | 4662篇 |
2013年 | 14398篇 |
2012年 | 11212篇 |
2011年 | 13867篇 |
2010年 | 8555篇 |
2009年 | 8535篇 |
2008年 | 12736篇 |
2007年 | 12945篇 |
2006年 | 12549篇 |
2005年 | 11469篇 |
2004年 | 10291篇 |
2003年 | 9045篇 |
2002年 | 8893篇 |
2001年 | 10187篇 |
2000年 | 7789篇 |
1999年 | 6162篇 |
1998年 | 4943篇 |
1997年 | 4774篇 |
1996年 | 4839篇 |
1995年 | 4397篇 |
1994年 | 4154篇 |
1993年 | 3978篇 |
1992年 | 4477篇 |
1991年 | 4316篇 |
1990年 | 4045篇 |
1989年 | 3846篇 |
1988年 | 4134篇 |
1987年 | 3796篇 |
1986年 | 3693篇 |
1985年 | 5344篇 |
1984年 | 5418篇 |
1983年 | 4393篇 |
1982年 | 4769篇 |
1981年 | 4812篇 |
1980年 | 4560篇 |
1979年 | 4675篇 |
1978年 | 4674篇 |
1977年 | 4650篇 |
1976年 | 4603篇 |
1975年 | 4516篇 |
1974年 | 4364篇 |
1973年 | 4532篇 |
1972年 | 2574篇 |
1971年 | 1887篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
321.
This work consists of two parts. In Part I, we shall give a systematic study of Lorentz conformal structure from structural viewpoints. We study manifolds with split-complex structure. We apply general results on split-complex structure for the study of Lorentz surfaces.In Part II, we study the conformal realization of Lorentz surfaces in the Minkowski 3-space via conformal minimal immersions. We apply loop group theoretic Weierstrass-type representation of timelike constant mean curvature for timelike minimal surfaces. Classical integral representation formula for timelike minimal surfaces will be recovered from loop group theoretic viewpoint. 相似文献
322.
The six‐step synthesis of the new podand‐type ligand 6,6′,6″‐[methylidenetri(1H‐pyrazole‐1,3‐diyl)]tris[pyridine‐2‐carboxylic acid] (LH3) is described. Reaction of LH3 with LnCl3 ?6 H2O (Ln=Eu, Gd, Tb) in MeOH resulted in the isolation of [LnL]?HCl complexes characterized by elemental analysis, mass and IR spectroscopy. Photophysical studies of the Eu and Tb complexes in aqueous solutions revealed the characteristic luminescence features of the metal atoms, indicative of an efficient ligand‐to‐metal energy‐transfer process. Determination of the luminescence quantum yields in H2O showed the Tb complex to be highly luminescent (?=15%), while, for the Eu complex, the quantum efficiency was only 2%. Excited‐state‐lifetime measurements in H2O and D2O evidenced the presence of ca. three H2O molecules in the first coordination sphere of the complexes. Investigation of the Gd complex allowed the determination of the ligand‐centered triplet state and showed the ligand to be well suited for energy transfer to the metal. The luminescence properties of the complexes are described, and the properties of the ligand as a suitable complexation pocket is questioned. 相似文献
323.
Several 2- and 4-alkylcyclohexadienones were prepared and shown to accept electrons to produce ketyl radical anions that dissociated rapidly at room temperature to release carbon-centered radicals and an aromatic phenoxide type anion. In the PET process with benzyl-substituted cyclohexadienones, initiated with triethylamine, the benzyl radicals dimerised or abstracted an H-atom from solvent. In electrochemical reductions, and in reductions with alkali metals in liquid ammonia, the benzyl radicals were further reduced to anions. 相似文献
324.
Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods. 相似文献
325.
In this paper, we prove convergence rates for spherical spline Hermite interpolation on the sphere Sd−1 via an error estimate given in a technical report by Luo and Levesley. The functionals in the Hermite interpolation are either point evaluations of pseudodifferential operators or rotational differential operators, the desirable feature of these operators being that they map polynomials to polynomials. Convergence rates for certain derivatives are given in terms of maximum point separation. 相似文献
326.
In this paper, a generalized anti–maximum principle for the second order differential operator with potentials is proved. As an application, we will give a monotone iterative scheme for periodic solutions of nonlinear second order equations. Such a scheme involves the Lp norms of the growth, 1 ≤ p ≤ ∞, while the usual one is just the case p = ∞. 相似文献
327.
328.
329.
S. P. Savin L. M. Zelenyi E. Amata J. Buechner J. Blecki S. I. Klimov B. Nikutowski J. L. Rauch S. A. Romanov A. A. Skalsky V. N. Smirnov P. Song K. Stasiewicz 《JETP Letters》2004,79(8):368-371
The study of the interaction between collisionless plasma flow and stagnant plasma revealed the presence of an outer boundary layer at the border of a geomagnetic trap, where the super-Alfvén subsonic laminar flow changes over to the dynamic regime characterized by the formation of accelerated magnetosonic jets and decelerated Alfvén flows with characteristic relaxation times of 10–20 min. The nonlinear interaction of fluctuations in the initial flow with the waves reflected from an obstacle explains the observed flow chaotization. The Cherenkov resonance of the magnetosonic jet with the fluctuation beats between the boundary layer and the incoming flow is the possible mechanism of its formation. In the flow reference system, the incoming particles are accelerated by the electric fields at the border of boundary layer that arise self-consistently as a result of the preceding wave-particle interactions; the inertial drift of the incoming ions in a transverse electric field increasing toward the border explains quantitatively the observed ion acceleration. The magnetosonic jets may carry away downstream up to a half of the unperturbed flow momentum, and their dynamic pressure is an order of magnitude higher than the magnetic pressure at the obstacle border. The appearance of nonequilibrium jets and the boundary-layer fluctuations are synchronized by the magnetosonic oscillations of the incoming flow at frequencies of 1–2 mHz. 相似文献
330.
A power mode method for the estimation of the power transmitted to a flexible receiver by an array of point force excitations is described. The vibrational power transmitted by N discrete point forces is regarded as the power transmitted by N independent power modes following eigendecomposition of the mobility matrix of the receiving structure. Approximate expressions for the upper and lower bounds and the mean value of the transmitted power are then developed in terms of these power modes. The approach is extended to more general cases, including that where both force and moment excitations are applied to the structure and where there are velocity source excitations. Numerical examples are presented. 相似文献