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   443061篇
  免费   7517篇
  国内免费   1403篇
电工技术   7859篇
综合类   353篇
化学工业   68463篇
金属工艺   17187篇
机械仪表   14261篇
建筑科学   9618篇
矿业工程   2241篇
能源动力   12638篇
轻工业   35438篇
水利工程   4627篇
石油天然气   8096篇
武器工业   24篇
无线电   50783篇
一般工业技术   89130篇
冶金工业   83079篇
原子能技术   9409篇
自动化技术   38775篇
  2022年   2923篇
  2021年   5024篇
  2020年   3737篇
  2019年   4759篇
  2018年   7841篇
  2017年   7798篇
  2016年   8382篇
  2015年   5440篇
  2014年   8581篇
  2013年   22901篇
  2012年   13622篇
  2011年   17708篇
  2010年   14088篇
  2009年   15573篇
  2008年   15753篇
  2007年   15287篇
  2006年   13552篇
  2005年   12132篇
  2004年   11479篇
  2003年   11259篇
  2002年   10588篇
  2001年   10278篇
  2000年   9675篇
  1999年   10083篇
  1998年   26765篇
  1997年   18410篇
  1996年   13945篇
  1995年   10198篇
  1994年   8938篇
  1993年   9022篇
  1992年   6285篇
  1991年   5935篇
  1990年   5855篇
  1989年   5517篇
  1988年   5226篇
  1987年   4598篇
  1986年   4442篇
  1985年   4999篇
  1984年   4568篇
  1983年   4113篇
  1982年   3797篇
  1981年   3891篇
  1980年   3592篇
  1979年   3410篇
  1978年   3418篇
  1977年   4061篇
  1976年   5508篇
  1975年   2917篇
  1974年   2721篇
  1973年   2807篇
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
961.
Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy)2sb]PF6 and [Ir(dFppy)2sb]PF6 (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy)2sb]PF6 and [Ir(dFppy)2 sb]PF6 in neat films (compared with quantum yields of these complexes dispersed in m‐bis(N‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy)2sb]PF6 and [Ir(dFppy)2sb]PF6 achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W–1) at 2.5 V, and 7.1 % and 26.2 lm W–1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells.  相似文献   
962.
Various influence diagnostics in Multiple Discriminant Analysis can be found in the literature. Almost all of them are based on the overall probability of misclassification. Two case-deletion diagnostics which evaluate the effect of the omission on the linear functions which determine Fisher’s Linear Discriminant Rule are proposed in this paper. Both measures are based on the L 2-norm: The first diagnostic is calculated from the data set and the second diagnostic is calculated in the minimum hypercube which covers it.  相似文献   
963.
Chromium carbide-nickel coatings were deposited onto a technical grade copper substrate by means of a high-velocity plasma jet of a plasmatron operating in specially selected regimes. An analysis of the coatings showed evidence of the formation of a Ni-based solid solution, a complex chromium carbide (Cr7C3), and an fcc crystal phase with a lattice parameter of 3.614 Å. The surface of the coatings exhibits a characteristic relief resulting from a dynamic interaction between melted and fused particles of the initial powder. The local hardness on some areas of the surface and in depth of the coating reaches 66±4.5 HRC, while the coating adhesion strength varies from 25 to 300 MPa.  相似文献   
964.
965.
Evaluated the effects of intraseptal scopolamine hydrobromide (40 μg) injections on Pavlovian (classical) conditioning, with tones used as the CS and a periorbital electric shock train as the UCS, using New Zealand albino rabbits. Eyeblink (EB) and heart rate (HTR) CRs were concomitantly recorded. Although injections of scopolamine into the medial septum impaired the acquisition of the Pavlovian conditioned eyelid reflex, these injections enhanced the magnitude of accompanying Pavlovian conditioned HTR decelerations. However, scopolamine applied to the lateral septal area had no effect on EB conditioning, relative to the vehicle; like medial injections, scopolamine also enhanced the magnitude of the accompanying HTR decelerations. Results are compatible with those of previous investigations indicating that medial septal dysfunction impairs somatomotor conditioning but leaves autonomic conditioning intact and that septal dysfunction produces a parasympathetic bias of the cardiovascular system. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
966.
Specifying concurrent systems with TSL   总被引:1,自引:0,他引:1  
Rosenblum  D.S. 《Software, IEEE》1991,8(3):52-61
The Task Sequencing Language (TSL), which lets programmers specify constraints on the behavior of concurrent programs, is described. The constraints, specified by high-level annotations to Ada programs, are monitored at runtime; when a violation is detected, control is returned to the user, along with information about the nature of the violation. It is argued that such a tool is a necessary crutch for human reasoning capabilities when dealing with the complexities of concurrent process interaction. The first large-scale application of TSL, the specification and validation of a distributed tasking supervisor for Ada, is described  相似文献   
967.
A method for assessing health care technology that models the demand on the clinician's attention exerted by patients' data (diagnostic and therapeutic) can provide a means for simultaneously reducing the cost and improving the quality of health care. The attentional demand exerted by patients' data can be measured by the amount of uncertainty in the data. Uncertainty can be expressed mathematically by the concept of entropy in information theory.  相似文献   
968.
Surface tension as a controlled variable in mechanical dishwashing   总被引:1,自引:0,他引:1  
Using a continuous, in-line, nondestructive technique based on the maximum bubble pressure method, the surface tension of the wash water in a mechanical dishwashing machine has been monitored. This technique has enabled surface tension to be used as a controlled variable, providing feedback to regulate the amount of surfactant added. Assuming the mechanical force of the water spray is adequate to remove bound soil from the dish surface, the food soil may be titrated against surfactant, providing an indirect indication as to when the dishes are clean. This technique also could be applied to a recirculated wash solution for in-place cleaning.  相似文献   
969.
A strategy for the realisation of a product-modulation frequency conversion technique is presented. For maximum efficiency and spectral purity, a pulse-width modulation (PWM) circuit is used. The addition of pulse-width-modulated signals from the three input phases to each of the three output phases is accomplished by time-division multiplexing (TDM). The need for the product modulator to accommodate multiplication by negative numbers is eliminated by a modification to the basic equations.  相似文献   
970.
Hay  S.G. 《Electronics letters》1987,23(15):789-791
A method of designing multiple-beam antennas based on shaping the subreflector of an offset Cassegrain antenna is described. It is applied to a compact system having a diameter of 300? that is required to produce beams up to 4-6°either side of boresight. The performance is shown to be only slightly less than that obtainable by also shaping the main reflector, indicating that efficient multiple-satellite-access antennas can be designed without specially shaped main reflectors.  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