全文获取类型
收费全文 | 29739篇 |
免费 | 2852篇 |
国内免费 | 1274篇 |
专业分类
电工技术 | 876篇 |
综合类 | 2046篇 |
化学工业 | 10064篇 |
金属工艺 | 1782篇 |
机械仪表 | 1400篇 |
建筑科学 | 2319篇 |
矿业工程 | 398篇 |
能源动力 | 2860篇 |
轻工业 | 1951篇 |
水利工程 | 374篇 |
石油天然气 | 702篇 |
武器工业 | 152篇 |
无线电 | 924篇 |
一般工业技术 | 4640篇 |
冶金工业 | 1023篇 |
原子能技术 | 213篇 |
自动化技术 | 2141篇 |
出版年
2024年 | 107篇 |
2023年 | 499篇 |
2022年 | 839篇 |
2021年 | 1132篇 |
2020年 | 1062篇 |
2019年 | 956篇 |
2018年 | 746篇 |
2017年 | 919篇 |
2016年 | 871篇 |
2015年 | 852篇 |
2014年 | 1553篇 |
2013年 | 1650篇 |
2012年 | 2166篇 |
2011年 | 2209篇 |
2010年 | 1791篇 |
2009年 | 1744篇 |
2008年 | 1548篇 |
2007年 | 2039篇 |
2006年 | 1672篇 |
2005年 | 1508篇 |
2004年 | 1325篇 |
2003年 | 1167篇 |
2002年 | 925篇 |
2001年 | 778篇 |
2000年 | 708篇 |
1999年 | 619篇 |
1998年 | 491篇 |
1997年 | 409篇 |
1996年 | 327篇 |
1995年 | 246篇 |
1994年 | 235篇 |
1993年 | 194篇 |
1992年 | 149篇 |
1991年 | 99篇 |
1990年 | 77篇 |
1989年 | 59篇 |
1988年 | 42篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1964年 | 2篇 |
1956年 | 1篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
941.
本文阐述应用计算机辅助技术进行工业产品造型设计,文中用两个案例介绍了使用UG软件对工业产品--玩具结构及外形设计的流程和技巧. 相似文献
942.
An exact approach for free vibration of an isotropic rectangular plate carrying a line-concentrated mass and with a line-translational spring support or carrying a line-spring-mass system is presented in this paper. The mode shape function of vibration of such a plate is expressed in terms of the four fundamental solutions derived in this paper. The main advantage of the proposed method is that the resulted frequency equation for such a rectangular plate can be conveniently obtained from a second-order determinant. The proposed method is thus computationally efficient due to the significant decrease in the determinant order as compared with previously developed procedures which usually led to an eighth-order determinant for solving the title problem. Two numerical examples are given to illustrate the efficiency of the proposed method and to investigate the effects of the location and the magnitude of a line-concentrated mass and elastic line-support as well as the influence of the aspect ratio on the natural frequencies of a rectangular plate. 相似文献
943.
944.
HC轧机板形板凸度控制特性的计算机模拟 总被引:1,自引:0,他引:1
用三次样条流线条元法分析带材的三维塑性变形,用影响系数法分析辊系的弹性变形用,BP神经网络方法对轧后带材板形进行模式识别,将三者联立,对900mmHC轧机板形板凸度控制特性进行了计算机模拟。结果表明:HC轧机控制二次板形能力很强,对四次及更高次板形控制能力较弱;中间辊横移和工作辊弯辊对板形板凸度的控制需要相互配合。对板凸度的控制应着重在开始道次进行。 相似文献
945.
为了满足曲线的设计要求,针对六次Said-Ball曲线不能调整曲线形状的不足,一个含有双形状参数的六次多项式基函数被给出,探讨了所构造的基函数的性质。基于该基函数定义了带有双形状参数的六次Said-Ball扩展曲线,分析了2段扩展曲线连续拼接应满足的条件。在给定控制多边形的情况下,通过改变形状参数值,可以调整曲线形状,增强了曲线的表达能力,弥补了六次Said-Ball曲线不能调整曲线形状的不足。该方法是不仅实用而且有效,在计算机辅助几何设计中可以得到广泛地应用。 相似文献
946.
Roberto Moreno Soriano Nuria Rojas Emilio Nieto Rosa de Guadalupe González-Huerta Juan Manuel Sandoval-Pineda 《International Journal of Hydrogen Energy》2021,46(51):25944-25953
To keep optimally connected, all electrolysis cell elements is one of the most important design criteria. The optimal distribution of the clamping points is crucial to increasing cell performance. In this work, the compression pressure distribution inside of a 25 cm2 PEM electrolysis cell was evaluated, using different materials: Teflon®, Viton®, ethylene propylene diene monomer rubber (EPDM), and nitrile rubber. Sealing material evaluation was performed taking as performance indicators: total compressed area (%) and compression pressure, for different torques applied. Pressure distribution was obtained by using pressure-sensitive films, analyzing the distribution of pressure points from three-dimensional plots (3D), and quantifying intensities of the images obtained. Results showed that pressure points distribution depends on the stiffness and thickness of the gasket materials. For a tightening torque of 3.70 N m, a pressure of 2.23 MPa is obtained with 85% of the membrane area compressed using nitrile rubber-EPDM gaskets. 相似文献
947.
《Ceramics International》2016,42(16):18681-18691
This work investigates the coarsening of boron carbide grains during the infiltration of porous boron carbide preforms by molten silicon with respect to fabrication of reaction-bonded boron carbide ceramics. Experimental results reveal that the shape of boron carbide grains evolve from the irregular shape to faceted shape due to dissolution-precipitation during infiltration. For infiltration temperatures below 1750 °C, the boron carbide grains are irregular and exhibit an unimodal size distribution, which can be ascribed to the normal grain growth. The growth of the irregular grains follow a cubic law of diffusion control. In contrast, for infiltration temperatures above 1750 °C, the boron carbide grains become faceted and exhibit a bimodal size distribution, indicative of the typical abnormal grain growth. The abnormal growth of faceted grains is proposed to be controlled by coalescence-enhanced two-dimensional nucleation. 相似文献
948.
High Cycle Fatigue (HCF) is a very important topic in mechanical engineering problems. Almost any machine part contains some changes in cross section or boreholes connected with stress concentration. It is the task of shape optimization to improve the strength of machine parts by changing the design at free boundaries. In the past, some work was done with the so-called classical stress concentration factors just to minimize the mentioned stress concentration, also for fatigue. This paper represents a more sophisticated view by including modern Continuum Damage Mechanics (CDM) to model material behavior in HCF. The central question is to design machinery parts so that maximum lifetime is obtained. The whole context for this is developed in this paper, including non-linear finite element algorithms. The paper concludes with numerical and experimental tests for the shape optimization of a notched tension bar in HCF. 相似文献
949.
《分离科学与技术》2012,47(6):950-958
In this work, a new simple correlation has been derived for the prediction of the bulk porosity decline during nanofiltration of a salty (ionic) solution using the PVD membrane. This model has been developed on the basis of the adsorption of the cations available in the feed onto the membrane. Therefore, three adsorption isotherms were tested and fitted to the equilibrium adsorption data, and the Freundlich isotherm was subsequently realized as the best choice. The porosity model included two adjustable parameters which can be determined theoretically and experimentally. Adsorption isotherms were combined for the determination of the first parameter and a novel method called “Flux test” was developed for the other parameter estimation. A reasonable agreement was observed between experimental- and model-predicted porosity. The model's ability of estimation indicates a little decrease at higher pressures due to approaching an unfavorable equilibrium adsorption condition and deviation from the isotherm's parameters from the actual equilibrium amounts to this situation. 相似文献
950.
《分离科学与技术》2012,47(15):3826-3841
Abstract Fouling generally occurs above the so-called “critical flux,” below which steady-state membrane permeability is assumed to be attainable. Operation at sub-critical fluxes can thus be used to minimize membrane fouling. However, rejection behavior may be affected as a consequence of operating within this sub-critical mode that sustains the desirable permeate flux. In this study, the effluent from a synthetic activated sludge production process was used in the assessment of the performance of membrane microfiltration, as a pretreatment in desalination for wastewater reuse. The critical flux was identified using the step-by-step technique. Different operating regimes i.e. above and below the critical flux were used to assess the relationship between solute rejection and membrane fouling. When operating at sub critical mode, rejection was constant even under increasing transmembrane pressure (TMP). This arises mainly from the back transport of particles in the absence of cake formation. Beyond the critical regime, cake formation occurred and rejection increased with increasing TMP. At the critical regime, a decline in rejection was obtained. This rejection behavior was consistent over the three pore sizes that were investigated. Increasing the pore size appears to decrease the rejection at both regimes. This is because larger pore size allows the transmission of smaller particles and a less compact cake formation under and above the critical flux regime respectively. It appears from this study that one may be able to use rejection behavior to confirm and determine the critical flux and adds to the confidence of using the step-by-step method to determine the critical flux. 相似文献