全文获取类型
收费全文 | 6186篇 |
免费 | 943篇 |
国内免费 | 652篇 |
专业分类
化学 | 1968篇 |
晶体学 | 136篇 |
力学 | 1310篇 |
综合类 | 106篇 |
数学 | 1278篇 |
物理学 | 2983篇 |
出版年
2024年 | 11篇 |
2023年 | 60篇 |
2022年 | 100篇 |
2021年 | 141篇 |
2020年 | 127篇 |
2019年 | 125篇 |
2018年 | 118篇 |
2017年 | 190篇 |
2016年 | 252篇 |
2015年 | 179篇 |
2014年 | 305篇 |
2013年 | 450篇 |
2012年 | 359篇 |
2011年 | 441篇 |
2010年 | 371篇 |
2009年 | 406篇 |
2008年 | 410篇 |
2007年 | 456篇 |
2006年 | 385篇 |
2005年 | 395篇 |
2004年 | 318篇 |
2003年 | 300篇 |
2002年 | 269篇 |
2001年 | 208篇 |
2000年 | 197篇 |
1999年 | 174篇 |
1998年 | 139篇 |
1997年 | 122篇 |
1996年 | 84篇 |
1995年 | 95篇 |
1994年 | 90篇 |
1993年 | 81篇 |
1992年 | 57篇 |
1991年 | 52篇 |
1990年 | 39篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 30篇 |
1981年 | 14篇 |
1980年 | 20篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 11篇 |
1974年 | 4篇 |
排序方式: 共有7781条查询结果,搜索用时 250 毫秒
81.
The stationary and time-dependent aerodynamic coefficients of a slender blunt cone with a flap located near the base section of the model are experimentally investigated. The freestream parameters (M∞ = 6, Re L = 0.88 × 107, and γ = 1.4) ensured a turbulent regime of flow over the conical surface and the flap. At high angles of attack (α ~ 10°) laminar-turbulent transition is observable in the separation zone on the leeward side of the body. Emphasis is placed on the determination of the trimming angles of attack for different positions of the center of rotation and the static and dynamic stability coefficients (the model oscillation damping coefficient). 相似文献
82.
利用双模模态域光纤传感器的模间干涉感知薄板结构中应变的变化、获得薄板结构振动变化状况,进一步利用压电体作为动元件,减小振幅,实现振动的主动控制,采用振型叠加法和直接积分相结合的方法,从理论上论证薄板分别受到正弦波激振力,脉冲激振力和方波激振力时的振动主动控制,并由脉冲激振下的响应得到控制前后的幅频特性曲线和相频特性曲线.。 相似文献
83.
GENERAL SOLUTION OF PLANE PROBLEM OF PIEZOELECTRIC MEDIA EXPRESSED BY "HARMONIC FUNCTIONS 总被引:4,自引:0,他引:4
I.IntroductionBecauseofthecouplingcharacteristicbetweenthemechanicaldeformationandthee1ectricaleffect,piezoelectricmaterialshavebeenwidelyusedintransducersandsmartstructures.Moreandmoreattentionshavebeenpaidonsuchmaterials,andgreatadvanceshavebeenmadeinva… 相似文献
84.
85.
颗粒介质的弹塑性动态本构关系研究 总被引:3,自引:0,他引:3
本文运用多刚体系统动力学和微结构连续力学的理论方法,考虑了颗粒体的拓扑结构及颗粒体之间的局部非线性相互作用,通过引进恢复系数,导出了适合于大变形运动(包括平动与转动)情况下,颗粒体间的滑移和分离的客观弹塑性本构关系。 相似文献
86.
Qing Lu N.V. Suryanarayana Christodoulous Christodoulu 《Experimental Thermal and Fluid Science》1993,7(4):354-361
A technique for measuring condensate film thickness using an ultrasonic transducer is described. In the experiment, the condensate film thickness with R-113 and FC-72 (a fluorinert compound developed by the 3M Company) condensing on the horizontal lower surface of a rectangular duct was measured at several locations. From the measured values a power law relation between the condensate film thickness and the axial distance from the leading edge of the condensing surface was derived by regression analysis. Assuming a linear temperature profile in the condensate film, local and average heat transfer coefficients were computed from the condensate film thickness. The average heat transfer coefficients were compared with the values obtained by measuring the heat transfer rate to the coolant. The two values were within ±12% of each other. As yet there is no satisfactory analytical model to predict the local heat transfer coefficient even in the annular condensation regime. One of the main difficulties in modeling the condensation is the lack of a suitable model to predict the interfacial shear stress. With the measurement of the film thickness it is possible to determine the interfacial shear stress. It is hoped that the shear stresses so determined will lead to the development of a satisfactory model for interfacial shear stress with condensation. 相似文献
87.
A compartmental model is developed to estimate flow parameters of a shallow aquifer affected by water loads in surface reservoirs and to evaluate its nonsteady flow distribution. The method incorporates temporal piezometric head measurements and sampling of water for dissolved chemicals and isotopes analyses. Each compartment is governed by a set of equations describing the conservation of linear momentum and mass balance expressions for water, isotopes, and dissolved chemicals. The number of compartmental balance expressions always must be greater than that of the unknown flow parameters associated with each compartment. An optimization method is described to yield spatial distribution of aquifer storativity, transmissivity, porosity, leakage, and compliance coefficients and fluxes leaking into an aquifer's lower boundary. Future predictions of an aquifer's piezometric head distribution in a compartmental system is formulated on the basis of the estimated flow parameters and the leakage components.Compartmental modelling which incorporates concentrations of environmental tracers, may yield efficiency in computing resources and accuracy enhancement for predicting an aquifer's flow regime. 相似文献
88.
89.
The paper presents a theoretical method to investigate the multiple scattering of shear waves and dynamic stress around a circular cavity in a semi-infinite functionally graded piezoelectric material. The analytical solutions of wave fields are expressed by employing wave function expansion method and the expanded mode coefficients are determined by satisfying the boundary conditions of the cavity. Image method is used to satisfy the free boundary condition of the semi-infinite structure. According to the analytical expression of this problem, the numerical solutions of the dynamic stress concentration factor around the cavity are presented. The effects of the piezoelectric property, the buried depth of the cavity, the incident wave number and the nonhomogeneous parameter of materials on the dynamic stress around the cavity are analyzed. Analyses show that the piezoelectric property has great effect on the dynamic stress in the region of intermediate frequency and the effect increases with increasing wave number. When the nonhomogeneous parameter of materials is less than zero, it has less influence on the maximum dynamic stress around the cavity; however, it has greater influence on the distribution of the dynamic stress around the cavity. When the nonhomogeneous parameter of materials is greater than zero, it has greater influence on both the maximum dynamic stress and the distribution of dynamic stress around the cavity, especially in the case that the buried depth is comparatively small. 相似文献
90.
研究了含直线裂纹系的压电材料平面应力问题单个裂纹和双裂纹问题的封闭解答表明,在裂纹尖端,应力、电场强度和电位移有1/2阶的奇异性并与前人结果比较了产生电场奇异性的物理因素 相似文献