全文获取类型
收费全文 | 536165篇 |
免费 | 10151篇 |
国内免费 | 2303篇 |
专业分类
电工技术 | 9860篇 |
综合类 | 555篇 |
化学工业 | 79425篇 |
金属工艺 | 19516篇 |
机械仪表 | 16888篇 |
建筑科学 | 14195篇 |
矿业工程 | 1052篇 |
能源动力 | 15196篇 |
轻工业 | 51391篇 |
水利工程 | 3911篇 |
石油天然气 | 2468篇 |
武器工业 | 28篇 |
无线电 | 74749篇 |
一般工业技术 | 100701篇 |
冶金工业 | 101087篇 |
原子能技术 | 7026篇 |
自动化技术 | 50571篇 |
出版年
2022年 | 2616篇 |
2021年 | 4549篇 |
2020年 | 3154篇 |
2019年 | 3870篇 |
2018年 | 5885篇 |
2017年 | 5938篇 |
2016年 | 6499篇 |
2015年 | 5245篇 |
2014年 | 8604篇 |
2013年 | 25769篇 |
2012年 | 14755篇 |
2011年 | 20691篇 |
2010年 | 16018篇 |
2009年 | 18216篇 |
2008年 | 19018篇 |
2007年 | 18936篇 |
2006年 | 17108篇 |
2005年 | 15779篇 |
2004年 | 15166篇 |
2003年 | 14718篇 |
2002年 | 14087篇 |
2001年 | 14185篇 |
2000年 | 13075篇 |
1999年 | 13971篇 |
1998年 | 33513篇 |
1997年 | 23771篇 |
1996年 | 18723篇 |
1995年 | 14197篇 |
1994年 | 12557篇 |
1993年 | 12092篇 |
1992年 | 8697篇 |
1991年 | 8372篇 |
1990年 | 7850篇 |
1989年 | 7451篇 |
1988年 | 7015篇 |
1987年 | 5791篇 |
1986年 | 5758篇 |
1985年 | 6903篇 |
1984年 | 6369篇 |
1983年 | 5502篇 |
1982年 | 5169篇 |
1981年 | 5088篇 |
1980年 | 4748篇 |
1979年 | 4530篇 |
1978年 | 4176篇 |
1977年 | 5097篇 |
1976年 | 7063篇 |
1975年 | 3425篇 |
1974年 | 3283篇 |
1973年 | 3149篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
921.
Ignatius Y. Chan 《Microscopy research and technique》1987,5(2):181-188
A new transmission electron microscopy (TEM) specimen preparation procedure for high temperature experiments using a controlled atmosphere specimen holder (HTCASH) has been developed. It is designed for studying the microstructure of catalyst specimens before and after treatments in various gases. The procedure involved (1) finding a new formula for the embedding material, (2) devising a new method of making specimen supports, and (3) developing a method for removing the embedding material after the specimen has been microtomed. These techniques were then brought together to produce the ideal specimens for the HTCASH experiments. As an extra benefit, this procedure is also suitable for preparing specimens for ultrahigh resolution imaging experiments. The application of the new procedure in HTCASH experiments is illustrated through a high temperature reduction of a Co/SiO2-923 catalyst. 相似文献
922.
923.
924.
Imre T.G. Cronje W.A. van Wyk J.D. Ferreira J.A. 《Industry Applications, IEEE Transactions on》2002,38(6):1613-1621
This paper covers the experimental investigation and theoretical calculation of losses in a planar inductor under load. Finite-element software is used to perform the loss calculations. Thermally controlled experiments are performed for a range of frequencies to validate the corresponding finite-element method loss calculations. The thermal dependence of the loss mechanisms is also considered. 相似文献
925.
We have designed, developed, and tested a very promising thermal image analysis method for polygraph testing. The method achieved a correct classification rate of CCR= 84% on the test population to our avail. This method, once refined, can serve as an additional channel for increasing the reliability and accuracy of traditional polygraph examination. We extract subtle facial temperature fluctuation patterns through nonlinear heat transfer modeling. The modeling transforms raw thermal data to blood flow rate information. Then, we use the slope of the average periorbital blood flow rate as the feature of a binary classification scheme. The results come to support our previous laboratory findings about the importance of periorbital blood flow in anxious states. 相似文献
926.
In this paper, the space-vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and to analyze power sources and loads with different connections (delta and wye). This method can also be applied to analyze steady-state (or transient phenomena) and unbalanced sources, including harmonics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits. 相似文献
927.
The flow and heat transfer characteristics of a pair of embedded counter-rotating vortices are studied experimentally. In order to control the strength of longitudinal vortices, angle of attack of the vortex generators is varied from ±20° to ±45°, and the spacing between the vortex generators is 4 cm apart. The heat transfer measurements using thermo-chromatic liquid crystal are made to provide the local surface distributions of heat transfer coefficients. The following conclusions are obtained from the present experiment. For the common-flow-down cases, two maximum values in the local heat transfer distributions exist for the three angles of attack. With the common-flow-up cases, only one maximum value exists. The common-flow-down cases show better heat transfer characteristics than the common-flow-up cases. 相似文献
928.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
929.
In Malaysia, no long-term daylight data are measured. It was only recently that the need to measure the availability of daylight became urgent when the importance of daylighting in buildings was rediscovered. The hourly daylight availability has been simulated for the Malaysian sky using daylight modelling techniques based on empirical and measured solar irradiation and cloud cover data. This paper presents the techniques involved in producing exterior illuminance data. These data were then compared with measured illuminance at Shah Alam and Bangi, Malaysia. The global illuminance levels are generally high, with values exceeding 80,000 lux at noon during the months when solar irradiation is highest. Even during the months when the ground receives less solar irradiation, the peak illuminance can reach 60,000 lux. Applications and uses of such data are in daylighting design, both for visual and thermal comfort, task illuminance and energy-conscious design of buildings. Recommendations are made at the end of the paper on the various climatic data that are required to be measured for overall daylighting design applications. 相似文献
930.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene. 相似文献