全文获取类型
收费全文 | 59789篇 |
免费 | 8069篇 |
国内免费 | 3341篇 |
专业分类
电工技术 | 9854篇 |
技术理论 | 5篇 |
综合类 | 5913篇 |
化学工业 | 10759篇 |
金属工艺 | 1738篇 |
机械仪表 | 3619篇 |
建筑科学 | 8316篇 |
矿业工程 | 1282篇 |
能源动力 | 6099篇 |
轻工业 | 1452篇 |
水利工程 | 1813篇 |
石油天然气 | 1607篇 |
武器工业 | 472篇 |
无线电 | 3637篇 |
一般工业技术 | 6031篇 |
冶金工业 | 1836篇 |
原子能技术 | 906篇 |
自动化技术 | 5860篇 |
出版年
2024年 | 259篇 |
2023年 | 999篇 |
2022年 | 1747篇 |
2021年 | 2007篇 |
2020年 | 2121篇 |
2019年 | 1885篇 |
2018年 | 1748篇 |
2017年 | 2055篇 |
2016年 | 2179篇 |
2015年 | 2396篇 |
2014年 | 3689篇 |
2013年 | 3755篇 |
2012年 | 4172篇 |
2011年 | 4693篇 |
2010年 | 3489篇 |
2009年 | 3595篇 |
2008年 | 3452篇 |
2007年 | 3982篇 |
2006年 | 3624篇 |
2005年 | 3205篇 |
2004年 | 2556篇 |
2003年 | 2364篇 |
2002年 | 1904篇 |
2001年 | 1572篇 |
2000年 | 1331篇 |
1999年 | 1093篇 |
1998年 | 863篇 |
1997年 | 783篇 |
1996年 | 679篇 |
1995年 | 564篇 |
1994年 | 446篇 |
1993年 | 350篇 |
1992年 | 315篇 |
1991年 | 220篇 |
1990年 | 223篇 |
1989年 | 194篇 |
1988年 | 162篇 |
1987年 | 99篇 |
1986年 | 76篇 |
1985年 | 62篇 |
1984年 | 77篇 |
1983年 | 53篇 |
1982年 | 38篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1966年 | 8篇 |
1959年 | 15篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
191.
相转移法制备高纯超细TiO2技术研究 总被引:9,自引:0,他引:9
报道了用相转移法制备高纯超细TiO2的新技术;探讨了Ti(Ⅳ)从有机相转移到水相发生水解反应的机理 ;通过TG-DTA分析以及XRD物相分析对水解产物的组成、热分解机理,晶型转变规律进行了研究,建立了水解产物焙烧的最佳温度。 相似文献
193.
F. Cœuret E. Oliveira Vilar E. Bezerra Cavalcanti 《Journal of Applied Electrochemistry》2002,32(10):1175-1182
The paper deals with carbon fibre cloth electrodes, employed in the fabrication of composite materials. The electrical conductivity of single bundles, groups of bundles and cloth is studied. Ohm's law applies to the electrical conduction in the direction of the fibre length, but bundle conductivity decreases with the number of fibres in the bundle. Electrochemical mass transfer between a flowing electrolyte and a cloth arranged as a flow-through or a flow-by porous electrode indicates the existence of double porosity in the material. Due to double porosity, only the external surface of the cloth works as an electrode. This finding shows that the material is not suitable for such an application. 相似文献
194.
Ricardo Garcia-Padron Dan Loyd Stefan Sjökvist 《Subsurface Sensing Technologies and Applications》2002,3(2):125-150
One promising method of locating buried objects, such as land mines, is to use optical systems for detecting contrasts in surface temperature. With enhanced knowledge about the interacting physical processes behind these temperature contrasts, it is possible to improve detection precision. In such a context, moisture movement in the soil and moisture evaporation from the surface have been found to be of particular interest. This study was based on indoor experiments on wet and dry sand exposed to radiation from a solar panel. Simulations of heat and moisture transfer conducted with a one-dimensional model are also presented for the experiments. The calculations were successful in accurately predicting surface temperatures for both wet and dry sand, making it possible to predict surface temperatures under different conditions. These findings will contribute to increasing the probability of successful detection of buried objects under real conditions using optical methods. 相似文献
195.
The hydrodynamic characteristics and mass transfers of halide quaternary salts between two immiscible phases in a stirred membrane permeation cell were investigated. The concentration of quaternary salt, temperature, solvent and the four kinds of halide quaternary salts were evaluated to achieve the extractive optimum condition. The diffusivity, overall mass‐transfer coefficients and individual mass‐transfer coefficients were determined and correlated in terms of the conventional Sh‐Re‐Sc relationship. The transfer time of quaternary salts across the membrane and the thickness of the hydrodynamic diffusion boundary layer were determined as well, so as to characterize the extractive phenomenon of quaternary salts between the two phases that is useful in phase‐transfer catalysis. 相似文献
196.
An investigation of pore cracking in titanium welds 总被引:1,自引:0,他引:1
T. Khaled 《Journal of Materials Engineering and Performance》1994,3(1):21-36
Two welded Ti-6A1-4V pressure vessels leaked prematurely in service. The leaks were caused by cracks emanating from weld porosity.
The cracks originated during fabrication, with subsequent growth in service leading to the formation of the leak paths. Pore
cracking is thought to be caused by a mechanism that involves both sustained-load and cyclic contributions, with the former
being the more prominent. It is shown that the tendency for cracking is influenced by pore position and that pore size is
not a deciding factor in that regard. The factors that govern pore cracking are discussed, and the possible role of interstitial
embrittlement is assessed. 相似文献
197.
L. Z. Jin 《Journal of Materials Engineering and Performance》1994,3(6):734-739
Chloride-induced stress-corrosion cracking (SCC) is one of the failure modes of stainless steels. Highly alloyed austenitic
stainless steels S32654, S31254, and N08028, and duplex grades S32750 and S31803 possess much improved resistance to SCC compared
with S30400 and S31600 steels. With the development of a database, SSData, experimental data collected from calcium chloride
tests, autoclave tests, and drop evaporation tests were evaluated. Stress-corrosion cracking data generated by autoclave tests
agreed well with the practical service conditions and can be used to discriminate alloys for SCC resistance in sodium chloride
solution. Drop evaporation test data can be used in situations where evaporation may occur and cyclic loading may be involved.
The SCC resistance of alloys under each method increased with increasing molybdenum equivalent Mo + 0.25Cr + 0.1Ni. For a
given alloy, the testing result depends on the stress state and environment; different test methods can give different ranking
orders concerning SCC resistance. The performance of duplex stainless steels in a chloride-containing environment at higher
temperatures was not as good as expected when dynamic loading was involved. 相似文献
198.
Mao Ze yu Chen Chang zhi Department of Hydraulic Engineering Tsinghua University Beijing P.R.China 《水动力学研究与进展(B辑)》1999,(3)
1. INTRODUCTIONThesimulationofstreamwatertemperatureissignificantlyimportantforthestudyofnumericalmodelingofrivericeprocesses[1] .Historically,themathematicalmodelingofthetransportandfateofheatinawaterbodyhasbeenthesubjectofextensivestudyforvariousre… 相似文献
199.
200.
由于悬空侧壁部分的变形状态是圆锥形零件成形的关键,而径向拉应力是实现悬空部分成形的必要条件,同时也是该部分冲压成形成败的关键为此,经力学分析得出了侧壁部分径向拉应力的解析式和造成圆锥形零件破裂的最大径向拉应力的计算式。同时分析了圆锥形零件的成形载荷。 相似文献