全文获取类型
收费全文 | 24750篇 |
免费 | 1053篇 |
国内免费 | 324篇 |
专业分类
电工技术 | 508篇 |
综合类 | 547篇 |
化学工业 | 4857篇 |
金属工艺 | 578篇 |
机械仪表 | 817篇 |
建筑科学 | 1032篇 |
矿业工程 | 183篇 |
能源动力 | 660篇 |
轻工业 | 2627篇 |
水利工程 | 281篇 |
石油天然气 | 183篇 |
武器工业 | 27篇 |
无线电 | 2625篇 |
一般工业技术 | 3407篇 |
冶金工业 | 3991篇 |
原子能技术 | 188篇 |
自动化技术 | 3616篇 |
出版年
2023年 | 169篇 |
2022年 | 546篇 |
2021年 | 711篇 |
2020年 | 377篇 |
2019年 | 451篇 |
2018年 | 540篇 |
2017年 | 471篇 |
2016年 | 560篇 |
2015年 | 467篇 |
2014年 | 701篇 |
2013年 | 1319篇 |
2012年 | 1050篇 |
2011年 | 1298篇 |
2010年 | 968篇 |
2009年 | 1040篇 |
2008年 | 1021篇 |
2007年 | 1007篇 |
2006年 | 870篇 |
2005年 | 734篇 |
2004年 | 786篇 |
2003年 | 991篇 |
2002年 | 1268篇 |
2001年 | 1055篇 |
2000年 | 629篇 |
1999年 | 574篇 |
1998年 | 1359篇 |
1997年 | 894篇 |
1996年 | 660篇 |
1995年 | 450篇 |
1994年 | 340篇 |
1993年 | 367篇 |
1992年 | 206篇 |
1991年 | 160篇 |
1990年 | 155篇 |
1989年 | 145篇 |
1988年 | 140篇 |
1987年 | 121篇 |
1986年 | 119篇 |
1985年 | 161篇 |
1984年 | 87篇 |
1983年 | 99篇 |
1982年 | 85篇 |
1981年 | 103篇 |
1980年 | 106篇 |
1979年 | 63篇 |
1978年 | 52篇 |
1977年 | 102篇 |
1976年 | 194篇 |
1975年 | 52篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
We present our experience withEuLisp as a teaching language, focussing on the level of the language which was specifically designed for this purpose (level-0).EuLisp has been used in undergraduate and postgraduate teaching since 1990, in lectures and laboratories, where in many cases it has replaced Scheme or Common Lisp. It has been used extensively in programming courses, parallelism courses, as a vehicle for advanced courses in symbolic computing and programming language design; it has also been used as a platform for final year undergraduate projects. This experience has demonstrated thatEuLisp is well suited to teaching and far reaching in its capabilities: it supports the relevant concepts in a consistent and versatile framework, so that the language serves to facilitate the educational process. The discussion is illustrated with examples, and where appropriate we draw a comparison with the Lisp dialects used previously in these courses. 相似文献
83.
84.
R. A. Minamisawa L. E. R. Santos M. A. Parada K. R. P. Daghastanli P. Ciancaglini A. De Almeida 《仪器科学与技术》2013,41(1):97-104
Abstract Techniques applying digital images increasingly have been used in biology, medicine, physics, and other research areas. The image coordinates can represent light intensities values to be detected by a CCD. Based on this concept, a photometric system composed of a LED source and a digital camera as a detector was used for optical density measurements. Standards for permanganate, glucose, and protein solutions were determined by colorimetric methods using our device. Samples of protein of Pasteurella mutocida bacteria membrane and, also, fractions of rabbit kidney membrane, rich in Na, K‐ATPase, with unknown concentrations were dosed through the Hartree method using our photometric system. 相似文献
85.
J. De Vries 《Theory of Computing Systems》1975,9(1):46-50
LetG denote an infinite,-compact, locally compact topological group. In this paper a construction is given for a topological transformation groupH
G with the Hilbert spaceL
2
(G × G) as a phase space such that any topological transformation group (G, X, ) can be embedded inH
G
, providedX is a separable metrizable space and is a bounded action. The class of such topological transformation groups contains all actions ofG on separable, metrizable, locally compact spaces. 相似文献
86.
The sensitivity of Paramecium tetraurelia (=P. aurelia syngen 4) cells to pulse treatments with various doses of Actinomycin D (AMD) was estimated by comparing the generation times of treated and untreated sister cells. It was found that the delay of division in treated cells depended on the concentration of AMD, on their "age" at the time of the pulse treatment, and on their individual sensitivity. Sensitivity of Paramecium to AMD changes during the cell cycle in a predictable way. About 3 1/2 hr before the normally expected cell fission (total generation time approximately 5 1/2 hr) there is a decrease of sensitivity. Thereafter, the cell enters a new stage with a progressive increase of sensitivity. This 2nd phase ends at the "transition point" (approximately 2 hr before cell division), when sensitivity drops abruptly. The division process itself may be altered and slowed down by high concentrations of AMD, even if the drug is applied after the transition point, but this process can never be completely annulled. The impairment of the division mechanism may lead to morphologic anomalies in the offspring. Resorption of oral anlagen in P. tetraurelia probably never occurs during the cell cycle after AMD treatment. The reason for individual variability of the cells, mechanisms controlling development, and the question of an obligate sequence of gene action in each cell cycle are discussed. 相似文献
87.
S. Bazzarri G. Cicoli P. De Felice G. Rossi F. Sedda 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2006,560(2):640-642
Experimental tests are described to check solid 241Am radioactive sources used to monitor operation of liquid xenon detectors. In particular, radioactive leakage was tested in extreme temperature conditions following immersion in liquid nitrogen for different time periods. No radioactivity loss was detected from the sources considered. The paper describes the source characteristics, test methods and results obtained. 相似文献
88.
A New Distribution System Reconfiguration Approach Using Optimum Power Flow and Sensitivity Analysis for Loss Reduction 总被引:2,自引:0,他引:2
Gomes F.V. Carneiro S. Jr. Pereira J.L.R. Vinagre M.P. Garcia P.A.N. De Araujo L.R. 《Power Systems, IEEE Transactions on》2006,21(4):1616-1623
This paper presents a new approach for distribution system reconfiguration (DSR) based on optimum power flow (OPF) in which the branch statuses (open/close) are represented by continuous functions. In the proposed approach, all branches are initially considered closed, and from the OPF results, a heuristic technique is used to determine the next loop to be broken by opening one switch. Then the list of switches that are candidates to be opened is updated, and the above process is repeated until all loops are broken, making the distribution system radial. This paper includes results and comparisons on test systems utilized in three classical papers published in the technical literature, as well as in a previous paper by the authors. Results obtained on a real large-scale distribution system are also presented 相似文献
89.
柳德荣 《湖南纺织高等专科学校学报》2005,15(4):1-3
如何吸引外商直接投资已成为各地区政策制定者共同关注的焦点。对不同地区利用外商直接投资绩效、潜力进行对比已成为政策制定的重要工具。对湖南省各市、州利用外商直接投资绩效、潜力进行了研究,供政府部门政策制定时参考。 相似文献
90.
J.M. Peza-Tapia V.M. Snchez-Resndiz M.L. Albor-Aguilera J.J. Cayente-Romero L.R. De Len-Gutirrez M. Ortega-Lpez 《Thin solid films》2005,490(2):142-145
The structural, electrical and optical properties of Na-doped CuInS2 thin films grown by spray pyrolysis were studied. These films crystallized in the sphalerite structure of CuInS2, and showed to contain traces of indium sulfide and CuIn5S8 as impurity phases. All films were In-rich and showed p-type conductivity. The film conductivity was strongly affected by Na-doping, which decreased from 10−2 to 10−5 S/cm by increasing the [Na]/[Cu] ratio from 0.005 to 0.03 in the spray solution. The band gap energy was observed to increase, from 1.4 to 1.45 eV, with increasing the [Na]/[Cu] ratio. Our results suggested that Na could be an effective acceptor impurity in sprayed CuInS2. 相似文献