全文获取类型
收费全文 | 251183篇 |
免费 | 2109篇 |
国内免费 | 596篇 |
专业分类
电工技术 | 3312篇 |
综合类 | 2434篇 |
化学工业 | 37824篇 |
金属工艺 | 14212篇 |
机械仪表 | 8709篇 |
建筑科学 | 5142篇 |
矿业工程 | 2445篇 |
能源动力 | 3794篇 |
轻工业 | 12348篇 |
水利工程 | 3986篇 |
石油天然气 | 9022篇 |
武器工业 | 12篇 |
无线电 | 23619篇 |
一般工业技术 | 54252篇 |
冶金工业 | 30378篇 |
原子能技术 | 7176篇 |
自动化技术 | 35223篇 |
出版年
2018年 | 17291篇 |
2017年 | 16332篇 |
2016年 | 13216篇 |
2015年 | 2267篇 |
2014年 | 3169篇 |
2013年 | 6514篇 |
2012年 | 7391篇 |
2011年 | 14684篇 |
2010年 | 12613篇 |
2009年 | 10373篇 |
2008年 | 11626篇 |
2007年 | 12541篇 |
2006年 | 4251篇 |
2005年 | 4995篇 |
2004年 | 4745篇 |
2003年 | 4675篇 |
2002年 | 3971篇 |
2001年 | 3555篇 |
2000年 | 3533篇 |
1999年 | 3268篇 |
1998年 | 7068篇 |
1997年 | 5175篇 |
1996年 | 3863篇 |
1995年 | 2925篇 |
1994年 | 2604篇 |
1993年 | 2727篇 |
1992年 | 2266篇 |
1991年 | 2328篇 |
1990年 | 2410篇 |
1989年 | 2317篇 |
1988年 | 2323篇 |
1987年 | 2190篇 |
1986年 | 2246篇 |
1985年 | 2292篇 |
1984年 | 2206篇 |
1983年 | 2135篇 |
1982年 | 1980篇 |
1981年 | 2193篇 |
1980年 | 2053篇 |
1979年 | 2269篇 |
1978年 | 2431篇 |
1977年 | 2430篇 |
1976年 | 3095篇 |
1975年 | 2244篇 |
1974年 | 2307篇 |
1973年 | 2342篇 |
1972年 | 2155篇 |
1971年 | 1911篇 |
1970年 | 1701篇 |
1969年 | 1655篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
An Imhoff tank was reconstructed into a 250 m3 UASB reactor in order to treat a malting plant wastewater. The UASB was inoculated with sludge from an anaerobic lagoon used for slaughterhouse wastewater treatment. After two months of operation the reactor achieved full load with an HRT of 17 h, a COD removal higher than 80% and a biogas production of 300 m3/day (77% average methane content), with an organic loading rate of 3.6 kgCOD/m3.d (0.24 kgCOD/kgVSS.d). A yield coefficient of 0.09 gVSS/gCODrem was found from a mass balance. The fat present in the inoculated sludge (48 mg/gSSV) did not affect the start up performance. Sludge from the inoculum with high content of fat (270 mg/gSSV), was separated by flotation in the first week of operation. The COD removal efficiency was scarcely influenced by the reactor operation temperature (17-25 degrees C). 相似文献
12.
Towards intelligent dressing 总被引:1,自引:0,他引:1
Egana I. Mendikute A. Urionaguena X. Alberdi H. 《IEEE instrumentation & measurement magazine》2006,9(3):38-43
The aim of this article is to state the principles of an intelligent monitoring and control system for the grinding machine, comprising the dressing process as well as grinding stability. 相似文献
13.
V. I. Pipa 《Semiconductors》2006,40(6):665-667
Radiative lifetimes of nondegenerate electrons and holes distributed uniformly in a semiconductor layer either deposited on a substrate or bounded by two dielectric media are calculated. The obtained expression takes into account the radiation reabsorbtion and interference effects and determines the dependences of the radiative lifetimes on the refractive indices of the external media and on the layer thickness. 相似文献
14.
15.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
16.
17.
18.
19.
Fahmy H.I. Develekos G. Douligeris C. 《Selected Areas in Communications, IEEE Journal on》1997,15(2):226-237
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies 相似文献
20.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献