全文获取类型
收费全文 | 33779篇 |
免费 | 2089篇 |
国内免费 | 62篇 |
专业分类
电工技术 | 298篇 |
综合类 | 17篇 |
化学工业 | 7464篇 |
金属工艺 | 618篇 |
机械仪表 | 733篇 |
建筑科学 | 1093篇 |
矿业工程 | 67篇 |
能源动力 | 870篇 |
轻工业 | 6491篇 |
水利工程 | 354篇 |
石油天然气 | 242篇 |
武器工业 | 1篇 |
无线电 | 1660篇 |
一般工业技术 | 5453篇 |
冶金工业 | 5961篇 |
原子能技术 | 124篇 |
自动化技术 | 4484篇 |
出版年
2024年 | 80篇 |
2023年 | 336篇 |
2022年 | 469篇 |
2021年 | 954篇 |
2020年 | 813篇 |
2019年 | 920篇 |
2018年 | 1540篇 |
2017年 | 1450篇 |
2016年 | 1505篇 |
2015年 | 1164篇 |
2014年 | 1376篇 |
2013年 | 2857篇 |
2012年 | 2112篇 |
2011年 | 1986篇 |
2010年 | 1637篇 |
2009年 | 1471篇 |
2008年 | 1478篇 |
2007年 | 1327篇 |
2006年 | 935篇 |
2005年 | 752篇 |
2004年 | 712篇 |
2003年 | 727篇 |
2002年 | 603篇 |
2001年 | 455篇 |
2000年 | 404篇 |
1999年 | 433篇 |
1998年 | 2106篇 |
1997年 | 1322篇 |
1996年 | 826篇 |
1995年 | 485篇 |
1994年 | 372篇 |
1993年 | 393篇 |
1992年 | 118篇 |
1991年 | 115篇 |
1990年 | 94篇 |
1989年 | 88篇 |
1988年 | 114篇 |
1987年 | 116篇 |
1986年 | 90篇 |
1985年 | 96篇 |
1984年 | 85篇 |
1983年 | 62篇 |
1982年 | 57篇 |
1981年 | 80篇 |
1980年 | 87篇 |
1978年 | 53篇 |
1977年 | 131篇 |
1976年 | 248篇 |
1975年 | 54篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
1.
ABSTRACTIn this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory. 相似文献
2.
J Comas I Rodríguez-Roda M Poch K V Gernaey C Rosen U Jeppsson 《Water science and technology》2006,53(4-5):303-311
Wastewater treatment plant operators encounter complex operational problems related to the activated sludge process and usually respond to these by applying their own intuition and by taking advantage of what they have learnt from past experiences of similar problems. However, previous process experiences are not easy to integrate in numerical control, and new tools must be developed to enable re-use of plant operating experience. The aim of this paper is to investigate the usefulness of a case-based reasoning (CBR) approach to apply learning and re-use of knowledge gained during past incidents to confront actual complex problems through the IWA/COST Benchmark protocol. A case study shows that the proposed CBR system achieves a significant improvement of the benchmark plant performance when facing a high-flow event disturbance. 相似文献
3.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
4.
5.
6.
Su M.F. Reda Taha M.M. Christodoulou C.G. El Kady I. 《Photonics Technology Letters, IEEE》2008,20(10):761-763
Processing methods used in photonics and nanotechnology possess many limitations restricting their application areas such as high cost, inability to produce fine details, problems with scalability, and long processing time. Proximity field nanopatterning is a lithography method which surpasses these limitations. By using interference patterns produced by a two-dimensional phase mask, the technique is able to generate a submicron detailed exposure on a millimeter-size slab of light sensitive photopolymer, which is then developed like a photographic plate to reveal three-dimensional interference patterns from the phase mask. While it is possible to use simulations to obtain the interference patterns produced by a phase mask, realizing the mask dimensions necessary for producing a desired interference pattern is analytically challenging due to the intricacies of light interactions involved in producing the final interference pattern. An alternative method is to iteratively optimize the phase mask until the interference patterns obtained converge to the desired pattern. However, depending on the optimization technique used, one either risks a significant probability of failure or requires a prohibitive number of iterations. We argue that an optimization technique that is to take advantage of the physics of the problem using machine learning methods (here fuzzy learning) can lead to competent mask design. This technique is described in this letter. 相似文献
7.
Larissa Canilha Walter Carvalho Marco Giulietti Maria Das Graças Almeida Felipe João Batista Almeida E Silva 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):715-721
BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry 相似文献
8.
9.
10.
In this article, a general synthesis method is proposed for the design of discontinuous feedback strategies leading to asymptotically stabilizing sliding regimes. The method is applicable to the class of nonlinear dynamical systems possessing constant equilibrium points. A family of nonlinear stabilizing sliding manifolds, parametrized by generic desired equilibrium point, is specified on the basis of the extended linearization approach. Some examples including simulations are presented for illustrative purposes.
Editor: S. Zak 相似文献