全文获取类型
收费全文 | 16859篇 |
免费 | 577篇 |
国内免费 | 324篇 |
专业分类
电工技术 | 266篇 |
综合类 | 1047篇 |
化学工业 | 3541篇 |
金属工艺 | 552篇 |
机械仪表 | 954篇 |
建筑科学 | 359篇 |
矿业工程 | 118篇 |
能源动力 | 311篇 |
轻工业 | 776篇 |
水利工程 | 97篇 |
石油天然气 | 500篇 |
武器工业 | 57篇 |
无线电 | 889篇 |
一般工业技术 | 3152篇 |
冶金工业 | 417篇 |
原子能技术 | 39篇 |
自动化技术 | 4685篇 |
出版年
2023年 | 61篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 31篇 |
2018年 | 978篇 |
2017年 | 1224篇 |
2016年 | 1253篇 |
2015年 | 542篇 |
2014年 | 193篇 |
2013年 | 116篇 |
2012年 | 624篇 |
2011年 | 1015篇 |
2010年 | 61篇 |
2009年 | 121篇 |
2008年 | 134篇 |
2007年 | 154篇 |
2006年 | 161篇 |
2005年 | 4231篇 |
2004年 | 3157篇 |
2003年 | 2325篇 |
2002年 | 408篇 |
2001年 | 172篇 |
2000年 | 41篇 |
1999年 | 104篇 |
1998年 | 178篇 |
1997年 | 92篇 |
1996年 | 62篇 |
1995年 | 31篇 |
1994年 | 40篇 |
1993年 | 77篇 |
1992年 | 73篇 |
1991年 | 50篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1984年 | 5篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1933年 | 1篇 |
1932年 | 2篇 |
1929年 | 3篇 |
1923年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
991.
992.
E.?Keshavarzi M.?Vahedpour S.?AlaviEmail author B.?Najafi 《International Journal of Thermophysics》2004,25(6):1747-1762
The high-frequency shear modulus, G, and shear relaxation time, shear, are obtained using the Zwanzig–Mountain equation for soft-sphere and Lennard-Jones potentials. The Hansen and Weis soft-sphere radial distribution function and the Matteoli–Mansoori Lennard-Jones radial distribution function are used in the equation. The shear relaxation times of different isotherms for both of these fluids pass through a minimum at a reduced density of about 0.7, which indicates a change from fluid-like behavior to viscoelastic behavior. The origins of this common density point are discussed. It is also shown that for the Lennard-Jones fluid, if the ratio of the reduced relaxation time to a power of the reduced temperature is plotted as a function of the reduced density, all isotherms become superimposed on a single curve. 相似文献
993.
J.?BrilloEmail author I.?Egry H.?S.?Giffard A.?Patti 《International Journal of Thermophysics》2004,25(6):1881-1888
The density of liquid Cu-Au alloys is measured using the technique of electromagnetic levitation, which entails producing a shadow image of the sample. The shadow is recorded by a digital CCD-camera, and the volume of the sample is calculated by an image processing algorithm. The density and thermal expansion of several alloys and the pure elements copper and gold are investigated at various temperatures above their melting points. In addition, the densities are also investigated as a function of the gold concentration at constant temperature. The measured values agree with literature data and with predictions obtained by molecular dynamics. It was found from data analysis that the ideal solution model applies. 相似文献
994.
M.?A.?Al-NimrEmail author A.?F.?Khadrawi 《International Journal of Thermophysics》2004,25(6):1953-1964
The transient thermal behavior of a stagnant gas confined in a horizontal microchannel is investigated analytically under the effect of the dual-phase-lag heat conduction model. The microchannel is formed from two infinite horizontal parallel plates where the upper plate is heated isothermally and the lower one is kept adiabatic. The model that combines both the continuum approach and the possibility of slip at the boundary is adopted in this study. The effects of the Knudsen number Kn, the thermal relaxation time q, and the thermal retardation time T on the microchannel thermal behavior are investigated using three heat conduction models. It is found that the deviations between the predictions of the parabolic and the hyperbolic models are insignificant. On the other hand, the deviations between the parabolic and dual-phase-lag models are significant under the same operating conditions. 相似文献
995.
P.?Schley M.?Jaeschke C.?Küchenmeister E.?VogelEmail author 《International Journal of Thermophysics》2004,25(6):1623-1652
A vibrating-wire viscometer of very high precision was used to measure the viscosity of methane and of two natural gases. The experimental data were, in general, taken at temperatures of 260, 280, 300, and 320 K and at pressures up to 20 MPa, and additionally in the case of methane at temperatures of 340 and 360 K and at pressures up to 29 MPa. The estimated uncertainty is ±0.3 and ±0.5% for methane and the natural gases, respectively. The new experimental data for methane were used together with zero-density or low-density viscosity values from this study and from the literature to develop a viscosity equation for natural gas composed of two contributions. The mixing rule of Wilke [J. Chem. Phys. 18: 517 1950] was applied for the zero-density viscosity part which is based on zero-density correlations for twelve components (methane, nitrogen, carbon dioxide, ethane, propane, n- and isobutane, n- and isopentane, n-hexane, n-heptane, and n-octane) and agrees with the values derived from experiment within ±0.3%. The density dependence of the residual viscosity part was correlated with methane data only, neglecting any temperature dependence, whereas the composition dependence is characterized by a pseudo-critical viscosity value. For methane the agreement between the correlated and experimental data is within ±0.5 %. The values predicted with the correlation and the experimental data agree within ±1 % for both the high calorific, H, natural gas and the low calorific, L, natural gas.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A. 相似文献
996.
The solution of three-dimensional planar cracks under shear loading are investigated by the boundary integral equation method. A system of two hypersingular integral equations of a three-dimensional elastic solid with an embedded planar crack are given. The solution of the boundary integral equations is succeeded taking into consideration an appropriate Gauss quadrature rule for finite part integrals which is suitable for the numerical treatment of any plane crack without a polygonal contour shape and permit the fast convergence for the results. The stress intensity factors at the crack front are calculated in the case of a circular and an elliptic crack and are compared with the analytical solution. 相似文献
997.
The purpose of this communication is to present a novel approach to compute the so called Topological Sensitivity (TS) of any variable or functional in elasticity using Boundary Integral Equations (BIEs), and its use as a tool for identification of defects, by itself or in conjunction with zero-order methods, like Genetic Algorithms. The TS of a cost functional provides a measure of the susceptibility of a defect being at a given location. The main contributions are summarized in the following points: 相似文献
998.
A couple of non-convex search strategies, based on the genetic algorithm, are suggested and numerically explored in the context
of large-deflection analysis of planar, elastic beams. The first of these strategies is based on the stationarity of the energy
functional in the equilibrium state and may therefore be considered weak. The second approach, on the other hand, attempts
to directly solve the governing differential equation within an optimisation framework and such a solution may be thought
of as strong. Several numerical illustrations and verifications with ‘exact’ solutions, if available, are provided
For communication 相似文献
999.
A treatise on order in engineering design research 总被引:5,自引:1,他引:4
Engineering design research shows a rather fragmented, if not a chaotic, picture. But does it have a hidden order? Can we explore it, or should we impose a reasoning model? This paper looks for the answer in the purpose of engineering design. It is destined to sustain human existence and well being by virtual creation of artifacts and services for the society. To this end, the engineering design discipline should provide a proper body of knowledge. The design knowledge obtained by empirical exploration and/or rational comprehension should be transformed for practical/pragmatic deployment. It was assumed that this purposely streaming of design knowledge gives a unique rationale for engineering design research. Based on this, a framework of reasoning was constructed, including source, channel, and sink categories of knowledge and research of engineering design, respectively. Within each category, research domains, trajectories, and approaches were identified. The semantic relationships of domains, trajectories, and approaches form a hierarchical structure. The proposed framework enables a grounded argumentation about the order of engineering design research, as well as about the articulation of the engineering design knowledge. 相似文献
1000.
This study describes a scenario-driven conceptual design information model and its formation from the viewpoint of the designers cognition, which is a fundamental part of practical design support tools. Four design meetings were observed in a company, at intervals of several weeks, in order to derive the model. The model consists of information elements generated through the cognitive design problem-solving process, which is a basic design process defined in this study. The study describes the relationship among these information elements, which illustrate the design information model and its formation. The model described in this study is based on scenarios, which promote the evolution of product design. Examples of designers discourse in the design meetings are presented to validate the model. 相似文献