全文获取类型
收费全文 | 58351篇 |
免费 | 5812篇 |
国内免费 | 3486篇 |
专业分类
化学 | 31433篇 |
晶体学 | 604篇 |
力学 | 3169篇 |
综合类 | 176篇 |
数学 | 11939篇 |
物理学 | 20328篇 |
出版年
2024年 | 47篇 |
2023年 | 674篇 |
2022年 | 764篇 |
2021年 | 1101篇 |
2020年 | 1410篇 |
2019年 | 1376篇 |
2018年 | 2306篇 |
2017年 | 2445篇 |
2016年 | 2249篇 |
2015年 | 2006篇 |
2014年 | 2369篇 |
2013年 | 2978篇 |
2012年 | 5959篇 |
2011年 | 5187篇 |
2010年 | 3699篇 |
2009年 | 3343篇 |
2008年 | 2571篇 |
2007年 | 2361篇 |
2006年 | 2222篇 |
2005年 | 5696篇 |
2004年 | 4854篇 |
2003年 | 3005篇 |
2002年 | 1186篇 |
2001年 | 851篇 |
2000年 | 540篇 |
1999年 | 747篇 |
1998年 | 610篇 |
1997年 | 553篇 |
1996年 | 523篇 |
1995年 | 460篇 |
1994年 | 384篇 |
1993年 | 295篇 |
1992年 | 444篇 |
1991年 | 375篇 |
1990年 | 334篇 |
1989年 | 257篇 |
1988年 | 191篇 |
1987年 | 136篇 |
1986年 | 144篇 |
1985年 | 109篇 |
1984年 | 65篇 |
1983年 | 69篇 |
1982年 | 44篇 |
1981年 | 40篇 |
1976年 | 80篇 |
1975年 | 38篇 |
1974年 | 40篇 |
1973年 | 48篇 |
1972年 | 39篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
润滑油的压粘系数和固化压力是弹流理论应用于摩擦学工程设计的关键试验数据。本文报道了20种国产润滑油的压粘系数和其中16种润滑油的最小固化压力的测定结果,并对不同油田的基础润滑油、不同化学结构的合成润滑油和不同用途的工业润滑油的压粘系数和固化压力进行了分析比较。 相似文献
992.
车辆与轨道的动态相互作用,是铁路轮轨接触式运输系统中最基本的问题之一,它直接制约着铁路运营速度的提高和运载重量的增加,也影响着铁路安全运行。本文采用有限元方法,对我国C61型运煤货车,按照车辆/轨道系统的实际几何形状、材料性质和边界条件建立了包括车辆和轨道系统的有限元模型,应用大型非线性动力分析程序LS-DYNA3D来模拟车辆通过轨道错牙接头时的轮/轨动态响应过程。计算结果表明车轮和轨道之间的竖向动态接触力大约是静轮载的2倍,与已有的现场试验结果基本吻合。因此应用有限元方法研究车辆/轨道耦合系统是可行和可靠的。 相似文献
993.
994.
On the field method in non-holonomic mechanics 总被引:1,自引:0,他引:1
This paper deals with the generalization of the field method to non-holonomic systems whose motion is subject to either non-linear constraints or those of a higher order, while their motion is modeled by the generalized Lagrange equations of the second kind. Two examples are given to illustrate the theory.The project supported by the Ministry of Science, Technologies and Development, Republic of Serbia (1874) 相似文献
995.
Numerical simulation of unsteady interaction of centrifugal impeller with its diffuser using Lagrangian discrete vortex method 总被引:1,自引:0,他引:1
In this study, an advanced Lagrangian vortex- boundary element method is applied to simulate the unsteady impeller-diffuser interactions in a diffuser pump not only for design but also for off-design considerations. In velocity calculations based on the Biot-Savart law we do not have to grid large portions of the flow field and the calculation points are concentrated in the regions where vorticity is present. Lagrangian representation of the evolving vorticity field is well suited to moving boundaries. An integral pressure equation shows that the pressure distribution can be estimated directly from the instantaneous velocity and vorticity field. The numerical results are compared with the experimental data and the comparisons show that the method used in this study can provide us insight into the complicated unsteady impeller-diffuser interaction phenomena in a diffuser pump. 相似文献
996.
997.
998.
ZhaoYan LinJiahao ZhangYahui AnWei 《Acta Mechanica Solida Sinica》2003,16(3):240-244
A nonlinear seismic analysis method for complex frame structures subjected to stationary random ground excitations is proposed. The nonlinear elasto-plastic behaviors may take place only on a small part of the structure. The Bouc-Wen differential equation model is used to model the hysteretic characteristics of the nonlinear components. The Pseudo Excitation Method (PEM) is used in solving the linearized random differential equations to replace the solution of the less efficient Lyapunov equation. Numerical results of a real bridge show that .the method proposed is effective for practical engineering analysis. 相似文献
999.
Sudhir?S.?Shenoy Norman?J.?WagnerEmail author Jonathan?W.?Bender 《Rheologica Acta》2003,42(4):287-294
A novel electrorheological (ER) effect is presented where the application of an electric field, orthogonal to the vorticity-flow plane, increases the critical hydrodynamic stress required to shear thicken concentrated, colloidal dispersions (the E-FiRST effect). The shear thickening behavior of a Brownian charge stabilized dispersion (226 nm silica in 4-methylcyclohexanol at 53, 50. and 41 vol.%) is studied in the presence of an electric field as a function of the field strength and coupling parameter ( ß) where the latter is a function of a.c. field frequency due to diffusion limitations on the polarization of the particles' double layer. A mechanism is proposed whereby the applied electric field suppresses the formation of the self-organized hydrocluster microstructure responsible for shear thickening, thus delaying the onset of shear thickening to higher applied shear stresses. A Mason-number type scaling law is found to scale the effect, which supports the proposed mechanism. 相似文献
1000.
In the present paper, based on the nonlinear dynamic equation of spacial flexible mechanical arm with dual-link bar, the method of linear quadratic control is used to eliminate the remain vibration of mechanical arm. In the process of computation, the traditional differential algorithm is replaced by the time integration method. Because of taking the more precise time-intervals in the given time-interval and avoiding a lot of computational difficulties, the method of this paper has the characteristics of high precision and unconditional stable. For a typical structure, the precise control law is obtained and the advantages of the algorithm in this paper are shown. 相似文献