全文获取类型
收费全文 | 15634篇 |
免费 | 372篇 |
国内免费 | 343篇 |
专业分类
电工技术 | 326篇 |
综合类 | 562篇 |
化学工业 | 3202篇 |
金属工艺 | 1033篇 |
机械仪表 | 1130篇 |
建筑科学 | 891篇 |
矿业工程 | 159篇 |
能源动力 | 2725篇 |
轻工业 | 718篇 |
水利工程 | 599篇 |
石油天然气 | 363篇 |
武器工业 | 65篇 |
无线电 | 603篇 |
一般工业技术 | 2127篇 |
冶金工业 | 455篇 |
原子能技术 | 347篇 |
自动化技术 | 1044篇 |
出版年
2024年 | 15篇 |
2023年 | 157篇 |
2022年 | 210篇 |
2021年 | 299篇 |
2020年 | 285篇 |
2019年 | 255篇 |
2018年 | 244篇 |
2017年 | 299篇 |
2016年 | 304篇 |
2015年 | 402篇 |
2014年 | 688篇 |
2013年 | 1118篇 |
2012年 | 768篇 |
2011年 | 1243篇 |
2010年 | 810篇 |
2009年 | 942篇 |
2008年 | 816篇 |
2007年 | 892篇 |
2006年 | 815篇 |
2005年 | 803篇 |
2004年 | 665篇 |
2003年 | 695篇 |
2002年 | 592篇 |
2001年 | 429篇 |
2000年 | 311篇 |
1999年 | 361篇 |
1998年 | 303篇 |
1997年 | 265篇 |
1996年 | 244篇 |
1995年 | 198篇 |
1994年 | 146篇 |
1993年 | 143篇 |
1992年 | 112篇 |
1991年 | 91篇 |
1990年 | 89篇 |
1989年 | 75篇 |
1988年 | 68篇 |
1987年 | 56篇 |
1986年 | 33篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 21篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The objective of this paper is to prove that the Clausius inequality must be re-stated to have general applicability for heat transfer involving radiative fluxes. The integrand (đQ/T) of the Clausius expression applies to heat conduction and convection, but does not hold for most radiative transfer scenarios, with the exception of reversible infinitesimal net blackbody radiation transfer. In other cases involving radiative transfer, the equality holds for a cycle even though irreversible heat addition by radiative transfer occurs. This is without the erroneous presumption of entropy destruction anywhere in the cycle. Thus, the Clausius inequality indicates reversibility for a cycle that includes an irreversible process. Further, in some radiative cases the quantity đQ/T, where T is the boundary temperature, is not the entropy transfer at the system boundary, and in fact, primarily represents entropy production within the system. It is also clear that in another case considered, the quantity đQ/T had no physical meaning whatsoever. Consequently, the Clausius expression has been re-stated so that it is applicable to cycles with processes involving any form of heat transfer. A new integrand (đQcc/T + đSNet,Rad) is presented, allowing the Clausius inequality to generally apply to all heat transfer scenarios. The work in this paper emphasizes the need to re-state other fundamental equations allowing applicability to all heat transfer processes, and draws attention to the unique character of radiative entropy calculations. 相似文献
32.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters. 相似文献
33.
V. Anjos M.J.V. Bell E.F. da Silva Jr. R.W.A. Franco I.A. Esquef 《Microelectronics Journal》2005,36(11):977-980
In this paper we report the use of photothermal techniques such as Thermal lens (TL) spectrometry, Photoacoustic and heat capacity, ρcp, to determine the thermo-optical parameters, such as thermal conductivity (K), thermal diffusivity (D), specific heat (cp) and the optical path dependence with temperature (ds/dT), of an undoped polycrystalline 3C-SiC. To our knowledge, this is the first time that Thermal lens technique is used for wide band-gap systems. Results obtained for the polycrystalline sample with TL technique indicates that ds/dT is negative at room temperature. Moreover, the obtained values of thermal diffusivity and thermal conductivity are in good agreement with that found in the literature, indicating that the phototermal techniques can be used to obtain the referred parameters in circumstances where other techniques cannot be used, for example, in harsh environments. 相似文献
34.
George Weiss 《Mathematics of Control, Signals, and Systems (MCSS)》1991,4(2):193-203
We give an elementary proof of the well-known fact that shift-invariant operators onL
2[0, ∞) are represented by transfer functions which are bounded and analytic on the right open half-plane. We prove a generalization
to Banach space-valuedL
p
-functions, where 1≤p<∞. We show that the result no longer holds forp=∞.
This research was supported partially by the Weizmann Fellowship, and partially by the Air Force Office of Scientific Research
under Contract F49620-86-C-0111. 相似文献
35.
36.
Sirisha Nerella Debendra K. Das Godwin A. Chukwu Abhijit Y. Dandekar Santanu Khataniar Shirish L. Patil 《Petroleum Science and Technology》2003,21(7):1275-1294
Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this article, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and the second as a commingled mixture with crude oil. These results show that the pumping power and heat loss for GTL are less than that of the crude oil for the same volumetric flow rate. Therefore, GTL can be transported through TAPS using existing equipment at pump stations. 相似文献
37.
A. N. Karapetyan I. A. Gribova A. P. Krasnov Yu. N. Studnev A. K. Pogosyan K. V. Oganesyan 《Journal of Friction and Wear》2007,28(6):546-550
The results of investigation of the modification of the Armenian minerals with fluorine-containing oligomers show that a modified product appears when the mineral fillers are treated with fluoroalkanes. The product preserves the structure of the fillers with a “grafted” fluoroalkane layer in which chlorine atoms locate mainly over their periphery. The composite materials based on heterochained polymers and the modified fillers possess a stronger wear resistance and a low friction coefficient. 相似文献
38.
Giulio Croce Paola Dagaro Carlo Nonino 《International Journal of Heat and Mass Transfer》2007,50(25-26):5249-5259
39.
This study develops a mathematical model for coupled heat and mass transfer in an unsaturated porous slab exposed to a flowing hot gas. Effects of the initial saturation conditions on associated variables, i.e., total pressure, temperature, moisture content, and multiphase flow, are studied. The Newton-Raphson method based on a finite volume technique is applied. This study emphasizes the influence of initial saturation level and gravitational effect in heat and multiphase flow phenomena associated with this system. Gravity enhances the downward flow of liquid within the porous slab. Pressure buildup occurs near the interface between the wet and the dry zone. However, it appears that the order of magnitude to the total pressure is small. This study explains the fundamental mechanism of multiphase flow that involves heat and mass transfer in a heated unsaturated porous slab. 相似文献
40.
London Resin (LR) White is a commonly used resin for embedding specimens to be used for immuno- and/or cytochemical studies. In some instances, due to either the properties of the specimen or the availability of various reagents and equipment, it becomes necessary and/or more convenient to polymerize LR White using heat rather than chemical accelerators or UV light. It is known, however, that heat can reduce or even eliminate the anti genicity of the tissue being embedded. It is therefore desirable to polymerize specimens at the lowest temperature possible and to remove the specimens from the oven as soon as polymerization is complete. We have developed a technique that provides a visual marker that allows the exothermic polymerization of LR White to be monitored, thus minimizing the amount of time a specimen must stay in the oven while excluding oxygen from capsules of polymerizing LR White. 相似文献