全文获取类型
收费全文 | 406138篇 |
免费 | 4793篇 |
国内免费 | 1365篇 |
专业分类
电工技术 | 7592篇 |
综合类 | 318篇 |
化学工业 | 60506篇 |
金属工艺 | 16473篇 |
机械仪表 | 13541篇 |
建筑科学 | 8430篇 |
矿业工程 | 2158篇 |
能源动力 | 11611篇 |
轻工业 | 28595篇 |
水利工程 | 4276篇 |
石油天然气 | 7918篇 |
武器工业 | 17篇 |
无线电 | 49464篇 |
一般工业技术 | 83476篇 |
冶金工业 | 75291篇 |
原子能技术 | 9192篇 |
自动化技术 | 33438篇 |
出版年
2022年 | 2590篇 |
2021年 | 3957篇 |
2020年 | 2992篇 |
2019年 | 3855篇 |
2018年 | 6538篇 |
2017年 | 6523篇 |
2016年 | 6994篇 |
2015年 | 4370篇 |
2014年 | 7192篇 |
2013年 | 20169篇 |
2012年 | 11523篇 |
2011年 | 15395篇 |
2010年 | 12253篇 |
2009年 | 13801篇 |
2008年 | 14181篇 |
2007年 | 13928篇 |
2006年 | 12509篇 |
2005年 | 11194篇 |
2004年 | 10583篇 |
2003年 | 10474篇 |
2002年 | 9887篇 |
2001年 | 9778篇 |
2000年 | 9181篇 |
1999年 | 9560篇 |
1998年 | 24392篇 |
1997年 | 16747篇 |
1996年 | 12839篇 |
1995年 | 9553篇 |
1994年 | 8396篇 |
1993年 | 8413篇 |
1992年 | 6083篇 |
1991年 | 5716篇 |
1990年 | 5704篇 |
1989年 | 5334篇 |
1988年 | 5056篇 |
1987年 | 4441篇 |
1986年 | 4316篇 |
1985年 | 4828篇 |
1984年 | 4441篇 |
1983年 | 4020篇 |
1982年 | 3667篇 |
1981年 | 3750篇 |
1980年 | 3441篇 |
1979年 | 3338篇 |
1978年 | 3357篇 |
1977年 | 3771篇 |
1976年 | 4869篇 |
1975年 | 2866篇 |
1974年 | 2680篇 |
1973年 | 2745篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
151.
To convey the dynamic information related to traffic conditions in various parts of a city, we propose an environment utilizing the technology of smart phones to provide information anywhere and anytime. Called ";The Interactive Traffic Beat Project,"; it uses a Web-based service to deliver this information to people through their cell phones at the right time so that valuable time can be saved and the chaos on the roads can be managed. 相似文献
152.
Residual stress as measured quantity in quality assurance The x‐ray method is used in the Volkswagen Automotive Group at different world‐wide locations as a standard procedure to determine residual stress. As an important measured quantity in the quality assurance residual stresses are specified in drawings of different components (e.g. gears, coil springs). Measurements are carried out during quality assurance, production, damage analyse, technical development department and design control of components from suppliers. An optimum efficiency can be achieved, if it exists a unique correlation between residual stress values and loading capacity of components, and if the processes to introduce residual stress can be optimized using residual stress measurements during the production. 相似文献
153.
A. K. Srivastava Ram M. Shrestha S. C. Srivastava Rabin Shrestha Dharam Paul 《国际能源研究杂志》2003,27(7):671-685
The power sector in India at present comprises of five separate regional electricity grids having practically no integrated operation in between them. This study analyses the utility planning, environmental and economical effects of integrated power sector development at the national level in which the regional electric grids are developed and operated as one integrated system. It also examines the effects of selected CO2 emission reduction targets in the power sector and the role of renewable power generation technologies in India. The study shows that the integrated development and operation of the power system at the national level would reduce the total cost including fuel cost by 4912 million $, total capacity addition by 2784 MW, while the emission of CO2, SO2 and NOx would be reduced by 231.6 (1.9%), 0.8 (0.9%), 0.4 (1.2%) million tons, respectively, during the planning horizon. Furthermore, the study shows that the expected unserved energy, one of the indices of generation system reliability, would decrease to 26 GWh under integrated national power system from 5158 GWh. As different levels of CO2 emission reduction targets were imposed, there is a switching of generation from conventional coal plants to gas fired plants, clean coal technologies and nuclear based plants. As a result the capacity expansion cost has increased. It was found that wind power plant is most attractive and economical in the Indian perspective among the renewable options considered (Solar, wind and biomass). Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
154.
The redistribution of components in the crystal layer-melt system at the main stages of fractional crystallization on cooled walls is studied. Mathematical solutions that can be used for calculating the fraction of trapped melt and the value of effective distribution (partition) coefficient in the crystallization of systems of different types are obtained. The kinetics of diffusion of impurities and migration of liquid inclusions under the action of temperature gradients at the growth and diffusion-washing stages of a two-phase crystal layer is studied. Simple relations for calculating the holdup of a melt and the maximal degree to which the main component can be purified in the partial melting (sweating) of crystal layers are derived. The theoretical results are compared with the experimental data obtained in the fractional crystallization of organic mixtures and freezing of aqueous solutions. Comparative analysis of the efficiency of the studied stages of fractional crystallization is accomplished and some practical recommendations are formulated. 相似文献
155.
Hydroprocessing catalysts based on Ni, Co, Mo and W are used in various refinery processing applications where several deactivation mechanisms become of importance (coke formation, active phase sintering, metals deposition, poisoning) in the catalyst's life cycle. The life cycle of commercial hydroprocessing catalysts is very complex and includes the catalyst production, sulfidation, use, oxidative regeneration followed by re-sulfidation and reuse or, if reuse is not possible, recycling or disposal. To understand the changes in catalyst properties taking place during a life cycle, the catalyst quality in the different stages can be best monitored by using advanced analytical techniques. The catalyst's life cycle is further complicated by numerous technical, environmental and organizational issues involved. In principle, different companies can be involved in each of the life cycle steps. Leading catalyst manufacturers, together with specialized firms, offer refineries a total catalyst management concept, starting with the purchase of the fresh catalyst and ending with its final recycling or disposal. Total catalyst management includes a broad range of services, ensuring optimal timing during the change-out process, reliable, smooth and safe operations, minimal downtime and maximum catalyst and unit performance. 相似文献
156.
J. Pujara M. A. Siddiqui Z. Liu P. Bjegovic S. S. Takagaki P. Y. Li S. Ramaswamy 《Drying Technology》2008,26(3):341-348
This is part II of a study reported earlier on a method to characterize the air flow and water removal characteristics during vacuum dewatering. This article presents experimental data and analysis of results from the use of a cyclically actuated vacuum dewatering device for removing moisture from wetted porous materials such as paper with the intermittent application of vacuum and accompanying air flow though the material. Results presented include sheet moisture content as a function of residence time and hence water removal rate under a variety of process conditions. Also, experimental results on air flow through the wet porous structure and hence the role and importance of air flow during vacuum dewatering are presented. Vacuum dewatering process conditions include exit solids content between 11 and 20% solid under applied vacuum conditions of 13.5 to 67.7 kPa (4 to 20 in. Hg). Regression analysis indicated that the exit sheet moisture content exhibited a nonlinear relationship with residence time with exit solids reaching a plateau after a certain residence time. Final moisture content correlated linearly with the average overall flow rate of air through the paper sample and the basis weight of the material. 相似文献
157.
Yu. F. Patrakov E. S. Pavlusha N. I. Fedorova Yu. A. Strizhakova 《Solid Fuel Chemistry》2008,42(1):10-13
The results of the thermal solution of oil shale in benzene in a flow unit under supercritical conditions are reported. It was found that the conversion of shale organic matter into liquid products increased by a factor of 2.5 with an increase in the solvent pressure from 5 to 15 MPa. 相似文献
158.
D. Ballutaud F. Jomard T. Kociniewski E. Rzepka H. Girard S. Saada 《Diamond and Related Materials》2008,17(4-5):451-456
Hot filament and microwave plasma CVD micro- nanocrystalline diamond films are analysed by visible and ultra-violet excitation source Raman spectroscopy. The sample grain size varies from 20 nm to 2 μm. The hydrogen concentration in samples is measured by SIMS and compared to the grain size, and to the ratio of sp2 carbon bonds determined by Raman spectroscopy from the 1332 cm− 1 diamond peak and the sp2 1550 cm− 1 G band. Hydrogen concentration appears to be proportional to the sp2 bonds ratio. The 3000 cm− 1 CHx stretching mode band intensity observed on the Raman spectra is decreasing with the G band intensity. Thermal annealing modifies the sp2 phase structure and concentration, as hydrogen outdiffuses. 相似文献
159.
A model of contact thermolysis was constructed based on a combined set of equations for heat transfer from a magmatic intrusion to a coal bed and the kinetics of thermal coal conversion. This model was illustrated by the generation of petroleum hydrocarbons deep in the earth by the thermolysis of the sapropelic matter of boghead. 相似文献
160.
P. S. Gordienko V. A. Kolzunov L. G. Zorina T. A. Kaidalova S. B. Yarusova 《Theoretical Foundations of Chemical Engineering》2008,42(5):680-683
The possibility of processing fluorine-containing wastes of fluorite ore, which include fluorite, calcite, quartz, and anorthite, has been investigated. A manufacturing flow chart of the complex processing of the ore waste materials with the production of sodium fluoride, alumina, soda ash, and raw materials suitable for the production of Portland cement and wollastonite is suggested. 相似文献