全文获取类型
收费全文 | 2112篇 |
免费 | 45篇 |
国内免费 | 87篇 |
专业分类
化学 | 471篇 |
晶体学 | 4篇 |
力学 | 371篇 |
综合类 | 10篇 |
数学 | 729篇 |
物理学 | 659篇 |
出版年
2023年 | 36篇 |
2022年 | 20篇 |
2021年 | 24篇 |
2020年 | 22篇 |
2019年 | 40篇 |
2018年 | 30篇 |
2017年 | 37篇 |
2016年 | 48篇 |
2015年 | 44篇 |
2014年 | 90篇 |
2013年 | 183篇 |
2012年 | 152篇 |
2011年 | 155篇 |
2010年 | 111篇 |
2009年 | 129篇 |
2008年 | 84篇 |
2007年 | 87篇 |
2006年 | 87篇 |
2005年 | 91篇 |
2004年 | 67篇 |
2003年 | 65篇 |
2002年 | 48篇 |
2001年 | 44篇 |
2000年 | 36篇 |
1999年 | 41篇 |
1998年 | 40篇 |
1997年 | 61篇 |
1996年 | 45篇 |
1995年 | 22篇 |
1994年 | 39篇 |
1993年 | 30篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 19篇 |
1987年 | 23篇 |
1986年 | 10篇 |
1985年 | 28篇 |
1984年 | 29篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2244条查询结果,搜索用时 31 毫秒
31.
32.
本文研究了两斜交圆柱壳的边界元法。提出了用板的基本解叠加级数形式的修正项构成圆柱壳的基本解,提高了计算精度,缩短了计算时间。对区域积分进行特殊处理,从而避免了内部网格的划分,大大减少了数据准备工作量和占机内存。并编制了FORTRAN计算程序,进行了数值计算。 相似文献
33.
本文用样条边界元法分析轴对称圆形基础板的非线性非光滑接触。除事先给出外力与地基表面位移的对应关系外,地基的模型、板的厚薄(Reissner/Kirchhoff型)和外荷载沿径向的分布均可是任意的。文中将地基反力看作板的外载,对变量沿径向采用不等距祥条插值,并用无地基效应的板基本解。算例表明本文方法只要用少量自由度,便可得到令人满意的结果。 相似文献
34.
It is observed that the harmonic balance (HB) method of parametric identification of nonlinear system may not give right identification
results for a single test data. A multiple-trial HB scheme is suggested to obtain improved results in the identification,
compared with a single sample test. Several independent tests are conducted by subjecting the system to a range of harmonic
excitations. The individual data sets are combined to obtain the matrix for inversion. This leads to the mean square error
minimization of the entire set of periodic orbits. It is shown that the combination of independent test data gives correct
results even in the case where the individual data sets give wrong results. 相似文献
35.
36.
This study focuses on the development of a methodology for the determination of some in situ parameters for off-road vehicle mobility on sandy soils. The stress field in the vicinity of and at the interface between a wedge and soil was determined by solving the stress equations using the method of characteristics. The governing equations were solved numerically by using backward finite difference method. The proposed method allows the prediction of any two of the in situ soil parameters δ, φ, and γ (respectively, the interfacial friction angle between the material of a wedge penetrometer and the soil, the internal friction angle, and the unit weight of the soil), given the value of any one of them and the results of penetration tests of two different apex angle wedges. The predictions and the measured values are in agreement. 相似文献
37.
沿垂等温平板的自然对流问题的近似解析解 总被引:1,自引:0,他引:1
本文用加权残值得到了沿垂等温平板的自然对流问题的近似解析解。和已有准确解的比较表明,在平板表面附近,近似解有很好的精度,而且速度场的精度比温度场更好一些。文末还对配域法的准收敛问题作了说明。 相似文献
38.
S. Nima Mahmoodi 《International Journal of Non》2007,42(4):577-587
Microcantilevers have recently received widespread attentions due to their extreme applicability and versatility in both biological and non-biological applications. Along this line, this paper undertakes the non-linear vibrations of a piezoelectrically driven microcantilever beam as a common configuration in many scanning probe microscopy and nanomechanical cantilever biosensor systems. A part of the microcantilever beam surface is covered by a piezoelectric layer (typically ZnO), which acts both as an actuator and sensor. The bending vibrations of the microcantilever beam are studied considering the inextensibility condition and the coupling between electrical and mechanical properties in the piezoelectric materials. The non-linear terms appear in the form of quadratic expression due to presence of piezoelectric layer, and cubic form due to geometrical non-linearities. The Galerkin approximation is then utilized to discretize the equations of motion. In addition, the method of multiple scales is applied to arrive at the closed form solution for the fundamental natural frequency of the system. An experimental setup consisting of a commercial piezoelectric microcantilever attached on the stand of a state-of-the-art microsystem analyzer for non-contact vibration measurement is utilized to verify the theoretical developments. It is found that the experimental results and theoretical findings are in good agreement, which demonstrates that the non-linear modeling framework could provide a better dynamic representation of the microcantilever than the previous linear models. Due to microscale nature of the system, excitation amplitude plays an important role since even a small change in the amplitude of excitation can lead to significant vibrations and frequency shift. 相似文献
39.
Evangelos Tentis Dionissios Margaris Dimitrios Papanikas 《Comptes Rendus Mecanique》2003,331(7):481-487
Designing natural gas pipelines to safely and efficiently handle unsteady flows, requires knowledge of pressure drop, flowrate and temperature distribution throughout the system. The accurate prediction of these parameters is essential in order to achieve optimum cumulative deliverability, and safe and reliable operation. An Adaptive Method of Lines algorithm is formulated for the solution of Euler system of equations, which fully simulates slow and fast transients. Two test cases present the improvement of the numerical solution from grid adaptation. Good results are obtained both for slow and fast transients simulations proving that the suggested numerical procedure is appropriate for such predictions. To cite this article: E. Tentis et al., C. R. Mecanique 331 (2003). 相似文献
40.
On averaged and normal form equations 总被引:2,自引:0,他引:2
P. R. Sethna 《Nonlinear dynamics》1995,7(1):1-10
The method of ayeraging has long been an important method for the analysis of nonlinear systems. One method using normal forms has more recently become a tool in applied mathematics. Both methods convert systems of ordinary differential equations to simpler equations by using a sequence of change of variables. This study can be interpreted as a local analysis in that it treats equations that are nonlinear perturbations of linear equations. We show that the two methods are essentially equivalent.This work has been supported by the National Science Foundation, Grant No. NSF/MEA 8310966. Deceased. 相似文献