全文获取类型
收费全文 | 2087篇 |
免费 | 298篇 |
国内免费 | 244篇 |
专业分类
化学 | 654篇 |
晶体学 | 21篇 |
力学 | 850篇 |
综合类 | 9篇 |
数学 | 419篇 |
物理学 | 676篇 |
出版年
2024年 | 2篇 |
2023年 | 38篇 |
2022年 | 45篇 |
2021年 | 49篇 |
2020年 | 53篇 |
2019年 | 41篇 |
2018年 | 64篇 |
2017年 | 83篇 |
2016年 | 83篇 |
2015年 | 105篇 |
2014年 | 113篇 |
2013年 | 190篇 |
2012年 | 112篇 |
2011年 | 133篇 |
2010年 | 103篇 |
2009年 | 103篇 |
2008年 | 123篇 |
2007年 | 122篇 |
2006年 | 134篇 |
2005年 | 113篇 |
2004年 | 112篇 |
2003年 | 88篇 |
2002年 | 85篇 |
2001年 | 68篇 |
2000年 | 84篇 |
1999年 | 65篇 |
1998年 | 52篇 |
1997年 | 41篇 |
1996年 | 41篇 |
1995年 | 41篇 |
1994年 | 24篇 |
1993年 | 19篇 |
1992年 | 16篇 |
1991年 | 20篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1971年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有2629条查询结果,搜索用时 15 毫秒
11.
活动标形法的论述首推苏步青译,佐佐木重夫著《微分几何学》,还有的著作从外微分形式引入活动标形,本文论证取曲面的正交曲率网为参数网时,曲面论的基本公式就是活动标形的微分形式,并用其分析了点啮合齿轮传动误差. 相似文献
12.
The properties of pulsed laser vapor doping on p-Si(1 0 0) with a KrF (248 nm) excimer pulsed laser (248 nm) and BCl3 gas are reported in this paper. The doped samples are characterized by the resistance measured using a four-probe method, since the sheet resistance changes with the carrier concentration of the sample. The doping effects with the variation of laser energy density, pulse number, and the pressure of BCl3 were investigated in terms of the sheet resistance. In this way, the optimized parameters were obtained and used for the positive heavy doping on p-Si(1 0 0) and p-Si(1 1 1). Then, using a square mesh under the above conditions, an image doping was completed. Finally, the metal–semiconductor Ohmic contacts were realized by plating Ag and Cu films on the doped surface. 相似文献
13.
Asymptotic methods for contact problems are expounded. Some typical integral equations are considered 相似文献
14.
A combined programming and iteration algorithm for finite element analysis of three-dimensional contact problems 总被引:3,自引:0,他引:3
Comparing with two-dimensional contact problems, three-dimensional frictional contact problems are more difficult to deal
with, because of the unknown slip direction of the tangential force and enormous computing time. In order to overcome these
difficulties, a combined PQP (Parametric Quadratic Programming) and iteration method is derived in this paper. The iteration
algorithm, which alleviates the difficulty of unknown slip direction, is used along with the PQP method to cut down computing
costs. Numerical example is given to demonstrate the validity of the present algorithm.
The project supported by the Machinary and Electronics Ministry of China 相似文献
15.
To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA, incorporating a dynamic model of the human body with a finite element model of the seat structure was used. Modifications were performed in the program for reconstruction of an occupant's head impact with the interior walls or bulkhead. A viscoelastic-type contact force model was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft. 相似文献
16.
Existence of a solution for a Signorini contact problem for Maxwell-Norton materials 总被引:1,自引:0,他引:1
The aim of this article is to study the quasistatic evolutionof a MaxwellNorton three-dimensional viscoelastic solidwith contact constraints. After introducing the appropiate functionalframework, we will discretize the problem in time using an implicitscheme whose resultant variational inequality is well posed.By using monotonicity arguments together with compensated compactnesstechniques, we will prove that the corresponding discrete solutionconverges to a solution of the continuous problem. 相似文献
17.
In this paper the effects of surface roughness and annealing temperature (T) of latex coating films on adhesion are discussed for the different stages of the film formation process. The surface free energy of latex films was assessed in terms of practical work of adhesion (W) (or adherence) using a custom-built adhesion-testing device (ATD), atomic force microscopy (AFM), and contact angle measurements. For preannealed latex films surface roughness averages (Ra) were determined from AFM height images and were related to the values of W obtained from ATD measurements at room temperature. The results obtained using these tests exhibiting surface behavior on different length scales indicate a dependence of the measured adhesion on surface roughness and temperature, as well as on the length scale of the measurements.First preannealed samples were studied, which were obtained by heat treatment above the respective glass transition temperatures (Tg). Increasing the temperature of preannealing resulted in a decrease of the adherence observed in ATD experiments at room temperature. However, on the nanoscale, using AFM, no significant variation of the adherence was observed. This observation can be explained by roughness arguments. Preannealing decreases roughness which results in lower adherence values measured by ATD while for essentially single asperity AFM experiments roughness has an insignificant effect. Specimens were also annealed over a constant period of time (90 min) at different temperatures. At the end of the heat treatment, adhesion was measured at the treatment temperature by ATD. The amplified effect of temperature observed in this case on adherence is attributed to the combination of roughness decrease and increasing test temperature. In a third set of experiments completely annealed samples were studied by ATD as well as by AFM as a function of temperature. With increasing T values ATD showed a decrease in adherence, which is attributed to a decreasing surface free energy of the annealed films at elevated T values. AFM, on the other hand, showed an opposite trend which is assigned to increasing penetration of the tip into the tip/wetting polymer samples versus increasing temperature. Finally, annealing isotherms as a function of time were investigated by ATD in situ at different temperatures. This last set of experiments allowed us to optimize annealing time and temperature to achieve complete curing. 相似文献
18.
文中以强化低温固体界面间的接触导热为出发点 ,实验测定了低温环境下两种金属界面在过度加载前后的接触热导值 ,指出过度加载是一种经济有效的强化导热方法 ,对卸载过程接触热导率大于同次加载过程接触热导的“hysteresis”现象产生机理进行了分析 相似文献
19.
20.
The Newton filtration and d-determination of bifurcation problems related to C~0 contact equivalence
SU Dan & ZHANG Dunmu School of Mathematics Statistics Wuhan University Wuhan China 《中国科学A辑(英文版)》2006,49(5)
In this paper, from the Newton filtration's point of view, we construct the singular Riemannian metric and use the method in singular theory to study the bifurcation problems, and give the sufficient condition of d-determination of bifurcation problems with respect to C0 contact equivalence. The special cases of the main result in this paper are the results of Sun Weizhi and Zou Jiancheng. 相似文献