首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20076篇
  免费   562篇
  国内免费   42篇
电工技术   226篇
综合类   5篇
化学工业   3033篇
金属工艺   457篇
机械仪表   453篇
建筑科学   758篇
矿业工程   70篇
能源动力   465篇
轻工业   1614篇
水利工程   153篇
石油天然气   133篇
无线电   1905篇
一般工业技术   3554篇
冶金工业   5419篇
原子能技术   168篇
自动化技术   2267篇
  2022年   171篇
  2021年   270篇
  2020年   205篇
  2019年   248篇
  2018年   297篇
  2017年   256篇
  2016年   290篇
  2015年   258篇
  2014年   467篇
  2013年   894篇
  2012年   694篇
  2011年   884篇
  2010年   637篇
  2009年   595篇
  2008年   785篇
  2007年   733篇
  2006年   675篇
  2005年   594篇
  2004年   484篇
  2003年   492篇
  2002年   450篇
  2001年   406篇
  2000年   376篇
  1999年   424篇
  1998年   1363篇
  1997年   875篇
  1996年   638篇
  1995年   449篇
  1994年   410篇
  1993年   423篇
  1992年   296篇
  1991年   254篇
  1990年   270篇
  1989年   230篇
  1988年   227篇
  1987年   212篇
  1986年   204篇
  1985年   264篇
  1984年   216篇
  1983年   212篇
  1982年   210篇
  1981年   184篇
  1980年   197篇
  1979年   134篇
  1978年   138篇
  1977年   248篇
  1976年   319篇
  1975年   139篇
  1974年   127篇
  1973年   110篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
MAN is but a part of the universe; his capabilities make him a significant link, in the cycle of life. To ensure this life, man must live in harmony with his environment. Recently, a disharmony has been discovered which could have grave effects upon the existence of man. It appears that man in his great thrust forward is destroying his own environment. The gravity of this threat to man's own existence carries some intrinsic problems of its own: man must allow his reason rather than his emotion to take command.  相似文献   
53.
A multiplexing, demodulating, and recording telemetry system designed to process multiple pulse-coded temperature channels is described. The system provides complete control of recording and multiplexing sequences and timing, and gives a single analog signal in response to each sample of pulse-coded data. It identifies all channels and indicates to a computer when a new data sample is to be processed. The system is self-calibrating to maintain accuracy over extended data collection periods, and is inexpensive.  相似文献   
54.
55.
Electroantennograms (EAGs) from male and femaleIps avulsus, I. calligraphus, andI. grandicollis to their pheromones and selected host odorants or kairomones verified the presence of antennal olfactory receptors in both sexes of each species capable of detecting ipsdienol, ipsenol,cis- andtrans-verbenol,endo-brevicomin -pinene, frontalin, and verbenone. Each species possesses receptors with lower thresholds and in greater abundance for the compounds they produce and to which they are behaviorally most responsive. Detection of bothIps andDendroctonus pheromones by the three cohabiting species provides a sensory basis for olfactory interactions among the species. Differences in both threshold and saturation levels for EAGs for the various behavioral chemicals could denote differences in specific behavioral roles for each compound.Texas Agricultural Experiment Station Paper Number TA-22463. This research was supported in part by McIntire-Stennis Project 1525, USDA-CR grants 85-CRCR-1-1856 and 86-CRCR-2019 and NATO Collaborative Research Grant 86-0710. The findings, opinions, and recommendations expressed herein are those of the authors and not necessarily those of the U.S. Department of Agriculture. All programs and information of the Texas Agricultural Experiment Station are available without regard to race, ethnic origin, religion, sex, or age.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.  相似文献   
56.
The study of a three-phase catalytic slurry reactor for SO2 oxidation on activated carbon has been conducted with a dynamic response technique. The analysis of zero and first temporal moments of the gas for temperatures between 10 and 26°C provides individual measurements of the adsorption, desorption and surface reaction rate constants and their energies of activation. A parallel first-moment analysis was carried out for O2 adsorption onto carbon to obtain the necessary equilibrium constants for temperatures used in the SO2-oxidation calculations. With second moment analysis of adsorption data, we find the adsorption kinetic constants with and without reaction are in quantitative agreement. By evaluating the separate temperatu effect on the adsorption/desorption, and surface reaction rates, we conclude that neither step is controlling at temperatures up to 26°C. The values the several kinetic and equilibrium constants agree well with those found by other authors.  相似文献   
57.
Journal of the American Oil Chemists' Society - Scanning electron microscopy was used to study the crystal structure of hydrogenated Canola oil. Fixation of the samples was carried out at 10 C...  相似文献   
58.
Even chain sodium alkanesulfonates from the Strecker reaction, odd chain sodium alkanesulfonates from the alkaline decarboxylation of α-sulfo acids, and sodium 1-hydroxy-2-alkanesulfonates from the reduction of esters of α-sulfo acids were compared with respect to Krafft point, critical micelle concentration, detergency and foam height. Sodium alkanesulfonates and crude fusion products from the α-sulfo acids (mixtures of alkanesulfonates of one less carbon atom with a lesser amount of a soap of two less carbon atoms) are more soluble and have better detergent and foaming properties. Sodium 1-hydroxy-2-alkanesulfonates resemble monosodium salts of α-sulfo acids. Alkanesulfonic acids and 1-hydroxy-2-alkane-sulfonic acids obtained from the sodium salts by ion exchange have lower Krafft points and are more readily soluble. The critical micelle concentrations of 1-hydroxy-2-alkanesulfonic acids and α-sulfo acids are nearly the same and about equal to those of alkanesulfonic acids of one less carbon atom. Presented at the AOCS meeting in Toronto, Canada, 1962. A laboratory of the E. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.  相似文献   
59.
We demonstrate the enhanced capacities of our analysis toolset for three-dimensional data. In particular, we provide supporting evidence for some of the conclusions reached in our previous studies of two-dimensional avalanching heaps. Segregation by self-diffusion is shown to take place in three-dimensional assemblies and self-diffusion velocities are shown to be of a comparable order of magnitude to those found in plane-strain situations. The effect on assembly evolution by discrete avalanching of the availability of a third dimension for translation is investigated. The discrete wavelet transform is again shown to be a useful component of the toolset in coupling process variables in the context of the discrete defining events associated with assembly evolution. In particular, we move towards the determination of time constants by correlating wavelet coefficients with a time shift.  相似文献   
60.
Edward G. Smith  Ian D. Robb 《Polymer》1974,15(11):713-716
These investigations are concerned with water-polymer interactions in polymer latices. It is known that water can act as a plasticizer for many solid polymers and cause a reduction in the glass transition temperature, Tg, of the amorphous regions. Experiments were carried out to determine whether pulsed n.m.r. techniques could be used to study the Tg of a polymer suspension and hence the influence of water and electrolyte on it. From T1 and T2 proton relaxation measurements as a function of temperature on polystyrene latex systems it was shown that the presence of water lowers the Tg of the polymer particles (by about 10°C), the effect being slightly greater in the presence of concentrated electrolyte. The extent of electrolyte penetration into the particles was deduced by studying relaxation as a function of particle diameter in latices containing paramagnetic Mn2+ ions. Using simple theories of relaxation and spin diffusion it was concluded that for all but the smallest particles electrolyte penetration is restricted to a very thin shell of the order of 1 nm. These conclusions were supported by the results of similar measurements on PTFE particles.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号