全文获取类型
收费全文 | 17501篇 |
免费 | 552篇 |
国内免费 | 369篇 |
专业分类
化学 | 7062篇 |
晶体学 | 390篇 |
力学 | 1142篇 |
综合类 | 21篇 |
数学 | 1688篇 |
物理学 | 8119篇 |
出版年
2023年 | 100篇 |
2022年 | 249篇 |
2021年 | 234篇 |
2020年 | 171篇 |
2019年 | 201篇 |
2018年 | 260篇 |
2017年 | 219篇 |
2016年 | 376篇 |
2015年 | 319篇 |
2014年 | 441篇 |
2013年 | 834篇 |
2012年 | 1006篇 |
2011年 | 1257篇 |
2010年 | 933篇 |
2009年 | 921篇 |
2008年 | 1044篇 |
2007年 | 1035篇 |
2006年 | 1026篇 |
2005年 | 827篇 |
2004年 | 728篇 |
2003年 | 569篇 |
2002年 | 531篇 |
2001年 | 954篇 |
2000年 | 658篇 |
1999年 | 530篇 |
1998年 | 351篇 |
1997年 | 361篇 |
1996年 | 278篇 |
1995年 | 230篇 |
1994年 | 218篇 |
1993年 | 174篇 |
1992年 | 179篇 |
1991年 | 166篇 |
1990年 | 156篇 |
1989年 | 134篇 |
1988年 | 102篇 |
1987年 | 90篇 |
1986年 | 76篇 |
1985年 | 83篇 |
1984年 | 58篇 |
1983年 | 39篇 |
1982年 | 29篇 |
1981年 | 30篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 19篇 |
1976年 | 27篇 |
1975年 | 28篇 |
1974年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
161.
Least-squares finite difference (LSFD) method, one of mesh-free methods, is used to solve slider air bearings problem through discritizing the generalized Reynolds equation into nonlinear systems of algebraic equations. Two approximation schemes for the linearization of these equations are presented and compared. And, some new techniques to search supporting points for the reference node in the mesh-free method were proposed and explored. Therefore, these improvements eliminate some potential limitation of the LSFD method previously published and further facilitate its employment in complex slider models. Advanced step slider as an example of negative pressure sliders is simulated and verified using the improved LSFD mesh-free method in head disk systems. 相似文献
162.
Using the Ward-Takahashi identity, on-shell condition, bound Dirac equation and off-shell expansion, a reduced version of half off-shell virtual photon nucleon vertex has been suggested. The vertex are decomposed into several different order terms: the on-shell terms, first and second off-shell terms. The off-shell behaviour of the form factors is discussed in the one meson loop model. Using the reduced vertex and parametrized off-shell form factors the quasielastic response functions are calculated for several nuclei at ¦q¦–kf and for56Fe at large ¦q¦ up to 1.14 GeV/c and at ?q2=0.9 (GeV/c)2. The Coulomb sums are evaluated and a comparison of the theoretical prediction with data is given. The off-shell electron nucleon cross section is calculated and compared with the “cc1” off-shell extrapolation. 相似文献
163.
本文利用^1HNMR,UV-Vis方法,研究了t-BuNO二聚体在有机溶剂及水溶液中的裂解反应产物,分析了其反应的动力学,提出了在非极性的有机相中t-BuNO二聚体为均裂反应,而在极性的水相中为均裂和异裂同时进行的竞争反应。 相似文献
164.
A molecular dynamics method has been used to simulate the argon ion-assisted deposition of Cu/Co/Cu multilayers and to explore ion beam assistance strategies that can be used during or after the growth of each layer to control interfacial structures. A low-argon ion energy of 5–10 eV was found to minimize a combination of interfacial roughness and interlayer mixing (alloying) during the ion-assisted deposition of multilayers. However, complete flattening with simultaneous ion assistance could not be achieved without some mixing between the layers when a constant ion energy approach was used. It was found that multilayers with lower interfacial roughness and intermixing could be grown either by modulating the ion energy during the growth of each metal layer or by utilizing ion assistance only after the completion of each layers deposition. In these latter approaches, relatively high-energy ions could be used since the interface is buried and less susceptible to intermixing. The interlayer mixing dependence upon the thickness of the over layer has been determined as a function of ion energy. 相似文献
165.
T. González-Lezana G. Delgado-Barrio P. Villarreal F.X. Gadéa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):227-232
The stabilization method is applied to the case of interacting resonances in the photo-dissociation of van der Waals clusters
composed by a rare gas atom bound to a dihalogen molecule. The study of an illustrative two-dimensional model consisting in
a T-shaped NeI2 molecule shows the adequacy of the method whenever the projection of the stabilization wave functions on the assumed prepared
initial state is accounted for. The agreement of the fragmentation cross-sections with some previous results using the effective
resolvent method and accurate close-coupling calculations is excellent. The method reveals its utility as a complementary
tool since allows, through the analysis of the stabilization wave function in terms of zero-order levels, a precise characterization
of the resonant states involved.
Received 5 April 2002 / Received in final form 24 May 2002 Published online 19 July 2002 相似文献
166.
N.P. Somasiri W.K. Toh X. Chen I.D. Robertson A.A. Rezazadeh 《International Journal of Infrared and Millimeter Waves》2002,23(12):1777-1785
This paper describes numerical modelling of a dual band multi-layered microstrip patch antenna operating at 35GHz on an in-house semi-insulating GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies will be compared to check the accuracy of the different numerical modelling techniques. 相似文献
167.
Buckling and free vibration analyses of stiffened plates using the FSDT mesh-free method 总被引:1,自引:0,他引:1
This paper presents a mesh-free Galerkin method for the free vibration and stability analyses of stiffened plates via the first-order shear deformable theory (FSDT). The model of a stiffened plate is formed by (1) regarding the plate and the stiffener separately, (2) imposing displacement compatible conditions between the plate and the stiffener so that displacement fields of the stiffener can be expressed in terms of the mid-surface displacement of the plate, and (3) superimposing the strain energy of plate and stiffener. Because there are no meshes used in this method, the stiffeners can be placed anywhere on the plate and need not be placed along the mesh lines. Several numerical examples are computed by this method to show its accuracy and convergence. The present results demonstrate good agreement with the existing solutions given by other researchers and the ANSYS. Influences of support size and order of the complete basis functions on the numerical accuracy are also investigated. 相似文献
168.
A novel method of obtaining shearing interferogram by slightly moving the crystal in a photorefractive interferometer is proposed. This method can measure the phase of an object itself instead of its diffraction field, and it is easy to realize continuously changeable shearing distance in any lateral direction and introduce carrier fringes at the same time. Both the theoretical analysis and experimental verification are given. 相似文献
169.
Let (X, X
;
d} be a field of independent identically distributed real random variables, 0 < p < 2, and {a
,
; (
,
)
d ×
d,
≤
} a triangular array of real numbers, where
d is the d-dimensional lattice. Under the minimal condition that sup
,
|a
,
| < ∞, we show that |
|− 1/p ∑
≤
a
,
X
→ 0 a.s. as |
| → ∞ if and only if E(|X|p(L|X|)d − 1) < ∞ provided d ≥ 2. In the above, if 1 ≤ p < 2, the random variables are needed to be centered at the mean. By establishing a certain law of the logarithm, we show that the Law of the Iterated Logarithm fails for the weighted sums ∑
≤
a
,
X
under the conditions that EX = 0, EX2 < ∞, and E(X2(L|X|)d − 1/L2|X|) < ∞ for almost all bounded families {a
,
; (
,
)
d ×
d,
≤
of numbers. 相似文献
170.
Y.X. Yin 《Applied Surface Science》2006,253(3):1584-1589
Wear resistant Cu-based solid solution (Cuss) toughened Cr5Si3 metal silicide composite coatings were fabricated on austenitic stainless steel AISI321 by laser cladding process. Due to the rapidly solidified microstructural characteristics and the excellent toughening effect of Cuss on Cr5Si3, the Cuss/Cr5Si3 coatings have outstanding wear resistance and low coefficient of friction under room temperature dry sliding wear test conditions coupling with hardened 0.45% C steel. 相似文献