全文获取类型
收费全文 | 484385篇 |
免费 | 7876篇 |
国内免费 | 2098篇 |
专业分类
电工技术 | 8869篇 |
综合类 | 1046篇 |
化学工业 | 68587篇 |
金属工艺 | 17645篇 |
机械仪表 | 13548篇 |
建筑科学 | 12554篇 |
矿业工程 | 1334篇 |
能源动力 | 12817篇 |
轻工业 | 48994篇 |
水利工程 | 4019篇 |
石油天然气 | 2986篇 |
武器工业 | 12篇 |
无线电 | 59587篇 |
一般工业技术 | 85313篇 |
冶金工业 | 105765篇 |
原子能技术 | 6683篇 |
自动化技术 | 44600篇 |
出版年
2021年 | 3106篇 |
2020年 | 2267篇 |
2019年 | 2906篇 |
2018年 | 4903篇 |
2017年 | 5032篇 |
2016年 | 5894篇 |
2015年 | 4440篇 |
2014年 | 6580篇 |
2013年 | 21341篇 |
2012年 | 12904篇 |
2011年 | 17964篇 |
2010年 | 13046篇 |
2009年 | 14694篇 |
2008年 | 15412篇 |
2007年 | 15443篇 |
2006年 | 14330篇 |
2005年 | 15627篇 |
2004年 | 14522篇 |
2003年 | 14028篇 |
2002年 | 12393篇 |
2001年 | 12825篇 |
2000年 | 11164篇 |
1999年 | 12516篇 |
1998年 | 34690篇 |
1997年 | 23853篇 |
1996年 | 17715篇 |
1995年 | 13037篇 |
1994年 | 11301篇 |
1993年 | 11110篇 |
1992年 | 7425篇 |
1991年 | 7218篇 |
1990年 | 6731篇 |
1989年 | 6415篇 |
1988年 | 6306篇 |
1987年 | 5129篇 |
1986年 | 5050篇 |
1985年 | 6144篇 |
1984年 | 5416篇 |
1983年 | 4905篇 |
1982年 | 4596篇 |
1981年 | 4691篇 |
1980年 | 4401篇 |
1979年 | 3960篇 |
1978年 | 3813篇 |
1977年 | 5087篇 |
1976年 | 7460篇 |
1975年 | 3234篇 |
1974年 | 3010篇 |
1973年 | 3074篇 |
1972年 | 2431篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A new supported liquid membrane (SLM) system was prepared for the selective transport of bismuth ions from the aqueous feed into the aqueous permeate phase. The support of the SLM was a thin porous polypropylene or polyvinylidene fluoride membrane impregnated with diisooctyldithiophosphinic acid (Cyanex 301) as mobile carrier in 4‐chloroacetophenon as organic solvent. Cyanex 301 acts as a highly selective carrier for the uphill transport of bismuth ions through the SLM. In the presence of HNO3 as a metal ion acceptor in the strip solution, the transport of bismuth ions into the strip side reached 70 % of the initial feed concentration after 3.5 hours. The selectivity and efficiency of bismuth transport from aqueous solutions containing different mixtures of cations were investigated. In the presence of P2O72– ions as suitable masking agent in the feed solution, the interfering effects of other cations were completely eliminated. The selective transport of bismuth through SLM is superior to liquid‐liquid extraction or through bulk liquid membranes. This is due to the high efficiency. The SLM reduces the solvent requirements, combines extraction and stripping operations in a single process and allows the use of highly selective extractants. The system may be applied to samples containing very low bismuth concentrations. 相似文献
992.
As a result of shrinking fossil fuels, biomass as a regenerative energy source gains importance. To realize biomass projects it is essential to investigate in convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses are indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available, it will be shown, which biomass is suitable for fixed bed or fluidized bed gasifiers. 相似文献
993.
994.
Significant increases in the activity of vanadium(III) amidinate catalysts for ethylene polymerization have been obtained by immobilization on a MgCl2‐based support prepared by reaction of AlEt3 with a MgCl2/ethanol adduct. Catalyst immobilization and activation on this type of support prevents the rapid decay in activity observed under homogeneous polymerization conditions with unsupported catalysts. Stable polymerization activity is also observed with analogous titanium(III) complexes. Polyethylene with narrow molecular weight distribution and spherical particle morphology is obtained without reactor fouling. Copyright © 2005 Society of Chemical Industry 相似文献
995.
Omar Snchez Estrella Asp María C Martí Marlene Roeckel 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(11):1261-1267
Most of the kinetic studies on nitrification have been performed in diluted salts medium. In this work, the ammonia oxidation rate (AOR) was determined by respirometry at different ammonia (0.01 and 33.5 mg N‐NH3 L?1), nitrite (0–450 mg N‐NO2? L?1) and nitrate (0 and 275 mg N‐NO3? L?1) concentrations in a saline medium at 30 °C and pH 7.5. Sodium azide was used to uncouple the ammonia and nitrite oxidation, so as to measure independently the AOR. It was determined that ammonia causes substrate inhibition and that nitrite and nitrate exhibit product inhibition upon the AOR. The effects of ammonia, nitrite and nitrate were represented by the Andrews equation (maximal ammonia oxidation rate, rAOMAX, = 43.2 [mg N‐NH3 (g VSSAO h)?1]; half saturation constant, KSAO, = 0.11 mg N‐NH3 L?1; inhibition constant KIAO, = 7.65 mg N‐NH3 L?1), by the non‐competitive inhibition model (inhibition constant, KINI, = 176 mg N‐NO2? L?1) and by the partially competitive inhibition model (inhibition constant, KINA, = 3.3 mg N‐NO3? L?1; α factor = 0.24), respectively. The rAOMAX value is smaller, and the KSAO value larger, than the values reported in diluted salts medium; the KIAO value is comparable to those reported. Process simulations with the kinetic model in batch nitrifying reactors showed that the inhibitory effects of nitrite and nitrate are significant for initial ammonia concentrations larger than 100 mg N‐NH4+ L?1. Copyright © 2005 Society of Chemical Industry 相似文献
996.
Spatially distributed data are often encountered in the biological sciences. Representation and analysis of such data requires specific tools. A simple geographical information system is presented, which allows representation and elementary analysis of geographically coded information. The system handles two kinds of data: maps and facts, where map data describe the basis on which the fact data are located. Maps consist of objects described through a set of coordinates, while for facts a coordinate pair is associated with an unlimited number of data records containing five fields: a date, an element from a list, a two-character code, an integer number and a real number. The input data can be displayed interactively on screen by logically combining selection criteria for each field. The facts corresponding to the selected criteria are either displayed as such, or are clustered and displayed as polygons or pies. A short example showing a possible application of the program is presented and advantages as well as limitations are discussed. 相似文献
997.
Alphorn, a software environment for programming distributed computer systems, is described. Programs running on different computers, possibly of different types and running different operating systems, communicate in a client-server relationship by means of remote procedure calls. This efficient construct structures programs neatly. The paper covers distributed process control, Alphorn's object-based programming style, remote procedure calls, the service interface language, configuration, runtime and debugging, and fault tolerance support 相似文献
998.
Learning to Perceive and Act by Trial and Error 总被引:5,自引:1,他引:4
This article considers adaptive control architectures that integrate active sensory-motor systems with decision systems based on reinforcement learning. One unavoidable consequence of active perception is that the agent's internal representation often confounds external world states. We call this phoenomenon perceptual aliasingand show that it destabilizes existing reinforcement learning algorithms with respect to the optimal decision policy. We then describe a new decision system that overcomes these difficulties for a restricted class of decision problems. The system incorporates a perceptual subcycle within the overall decision cycle and uses a modified learning algorithm to suppress the effects of perceptual aliasing. The result is a control architecture that learns not only how to solve a task but also where to focus its visual attention in order to collect necessary sensory information. 相似文献
999.
J.A. Bakken L. Barone D. Braun M. Caillat C. Dionisi C. Dor H. Elmamouni F. Ferroni G.L. Grazer J.T. He R. Herbiet B. Ille P. Lecomte E. Longo P.F. Loverre Y.S. Lu J.P. Martin U. Micke R.P. Mount P.A. Pirou H.-G. Sander D. Schmitz M. Schneegans D.P. Stickland R.L. Sumner K.L. Tung E. Valente M. Vivargent 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,228(2-3):294-302
A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained (
) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement. 相似文献
1000.