全文获取类型
收费全文 | 18379篇 |
免费 | 1632篇 |
国内免费 | 1206篇 |
专业分类
电工技术 | 819篇 |
技术理论 | 1篇 |
综合类 | 3783篇 |
化学工业 | 1693篇 |
金属工艺 | 624篇 |
机械仪表 | 1017篇 |
建筑科学 | 903篇 |
矿业工程 | 334篇 |
能源动力 | 491篇 |
轻工业 | 608篇 |
水利工程 | 580篇 |
石油天然气 | 1299篇 |
武器工业 | 248篇 |
无线电 | 1425篇 |
一般工业技术 | 2890篇 |
冶金工业 | 489篇 |
原子能技术 | 370篇 |
自动化技术 | 3643篇 |
出版年
2024年 | 56篇 |
2023年 | 163篇 |
2022年 | 279篇 |
2021年 | 297篇 |
2020年 | 390篇 |
2019年 | 438篇 |
2018年 | 459篇 |
2017年 | 492篇 |
2016年 | 534篇 |
2015年 | 504篇 |
2014年 | 805篇 |
2013年 | 1180篇 |
2012年 | 1228篇 |
2011年 | 1222篇 |
2010年 | 986篇 |
2009年 | 977篇 |
2008年 | 1020篇 |
2007年 | 1120篇 |
2006年 | 1080篇 |
2005年 | 909篇 |
2004年 | 826篇 |
2003年 | 754篇 |
2002年 | 651篇 |
2001年 | 530篇 |
2000年 | 527篇 |
1999年 | 533篇 |
1998年 | 462篇 |
1997年 | 417篇 |
1996年 | 387篇 |
1995年 | 385篇 |
1994年 | 303篇 |
1993年 | 257篇 |
1992年 | 224篇 |
1991年 | 199篇 |
1990年 | 160篇 |
1989年 | 134篇 |
1988年 | 100篇 |
1987年 | 57篇 |
1986年 | 43篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
41.
本文将等效介电常数近似分析方法在应用范围和处理方法上进行了一些改进.发展为双等效介电常数近似分析法,然后用它来分析矩形介质波导阵列.推得两个一维周期的耦合特征方程。如果将Macatili方法应用范围扩展用来研究该波导阵列也会得到同样的结果,它们都能在二维平面上较准确地反应出通带和阻带等主要周期特性。 相似文献
42.
43.
An equation of state for 1,1-difluoroethane (HFC 152a, CH3CHF2) has been developed on the basis of reliable experimental data including PVT, liquid Cp, and saturated-liquid-density data measured by our group. It is a non-dimensionalized virial equation whose functional form is the same as that originally developed for 1,1,1,2-tetrafluoroethane (HFC 134a) in our group. The effective range is for pressures up to 15 MPa, temperatures from 230 to 450 K, and densities to 1000 kg m−3. The equation represents reliable PVT measurements within ± 1% in pressure for the superheated vapour and supercritical fluid, while within ±0.5% in density for the compressed liquid. In addition, it should be noted that the equation represents the other essential thermodynamic properties including vapour pressures, saturated-liquid/ vapour densities, isobaric/isochoric specific heats and sound velocity in both the liquid and gaseous phase of HFC 152a. 相似文献
44.
Sensitivity analysis is used to show how uncertainties in basic factors, such as heat transfer, pressure drop, compressor efficiency, and thermophysical properties, influence the result of heat pump cycle performance estimations. By comparing the results of this analysis with uncertainty levels of estimations and experimental determinations, it is established to what extent improvements in accuracy are needed. The investigation was carried out for several different applications and, as working fluids, both pure substances and non-azeotropic mixtures were examined. It was found that evaporation heat transfer and compressor efficiency are two areas where improvements are needed. It is also shown that estimates using very accurate, substance-specific, equations of state differ from those using more general types by up to 1 % for COP and 2% for capacity. 相似文献
45.
基于(I)报根据pVT和Tμp图形的相似性和Patel-Teja状态方程建立的预测纯流体气、液相粘度的统一模型,通过引入常规的状态方程参数的混合规则,将其应用于二元轻烃混合物共计1894个数据点及模拟天然气高压粘度的预测,平均相对误差分别为13.78%和16.75%;应用于油藏原油和天然气高压粘度的预测,结果优于现有的有关油气藏流体粘度模型. 相似文献
46.
1 Introduction For increasing the output energy of laser, the pumping power must be enhanced. But the cooperative effect will arise and cause spontaneous radiation light in laser medium sample when the pumping power is high e- nough without the resonator. The spontaneous radiation light is coherent light between laser and fluorescent. It will compete the upper energy level population with ex- cited radiation, and the loss increase. In solid laser medium, such as Nd∶YAG, the Nd ion densityi… 相似文献
47.
Quasi-static and dynamic crushing behaviors of aluminum and steel tubes with a cutout 总被引:3,自引:0,他引:3
Tubular members are commonly used as an energy absorber in engineering structures and many such members have a cutout. In this study, the crushing behaviors of tubes with a cutout are characterized and the effects of cutout on the energy absorption capabilities of these tubes are quantified. Systematic parametric studies were carried out to study the effect of material properties, including yield and ultimate strength of material, strain rate effect, location of cutout, tube length and impact speed on the crushing behaviors and energy absorption capacity of aluminum and steel tubes. First, a numerical model was constructed with a commercial explicit finite element code. It will be first proven that the numerical simulation can produce sufficiently accurate results in an economic manner. Subsequently, the crushing behavior of aluminum and steel tubes with a cutout was experimentally characterized and their energy absorption capacity was evaluated in terms of mean crushing force, peak crushing force and specific energy absorption (SEA). Tubes of various lengths with a cutout located at different locations, subject to both quasi-static and dynamic impact loadings were considered. For steel tubes, the numerical simulation investigated the influence of the strain rate effect and variation in strain hardening ratio of the material. Empirical equations describing the mean and peak crushing forces of aluminum and steel tubes with a cutout were developed using linear and nonlinear regression methods applied to the results obtained from the numerical and experimental studies. 相似文献
48.
Matthew Caurie 《International Journal of Food Science & Technology》2005,40(3):295-303
An equation has been derived to calculate the water activity (Aw) of multicomponent mixtures of solutes and non‐solutes. The equation is based on a previous Caurie adsorption equation and it depends on the number of component ingredients and the initial moisture contents of the ingredients in the mixture. Solute and non‐solute/water interaction effects in solution were identified as playing important roles in determining accurate equilibrium Aws of the aqueous mixtures. The new equation allows for interaction effects in mixed solution/suspensions and has been tested on model foods (the data was taken from the literature) containing up to five solutes and non‐solute components. The equation displays a high degree of accuracy. Unlike the Ross equation, which applies only approximately to mixtures of dilute solutions, the new equation applies to mixtures at all solution concentrations and to wet solids. 相似文献
49.
50.
采用了一个既能提高立方型状态方程比体积计算精度,又不影响气液平衡条件的简单摩尔修正项来改进PR方程比体积的计算。本文对19种低温流体给出其修正项的值,计算饱和蒸气和液体比体积,并与未修正的PR方程的计算值比较,结果表明这种修正能显著提高低温流体(包括量子流体氢、氦和强极性的氨气)饱和液体比体积的计算精度,并对蒸气比体积的计算也略有改进。 相似文献