全文获取类型
收费全文 | 15515篇 |
免费 | 935篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 167篇 |
综合类 | 43篇 |
化学工业 | 3265篇 |
金属工艺 | 307篇 |
机械仪表 | 317篇 |
建筑科学 | 690篇 |
矿业工程 | 45篇 |
能源动力 | 508篇 |
轻工业 | 1260篇 |
水利工程 | 124篇 |
石油天然气 | 51篇 |
无线电 | 1118篇 |
一般工业技术 | 3040篇 |
冶金工业 | 2278篇 |
原子能技术 | 119篇 |
自动化技术 | 3146篇 |
出版年
2023年 | 146篇 |
2022年 | 287篇 |
2021年 | 571篇 |
2020年 | 377篇 |
2019年 | 382篇 |
2018年 | 496篇 |
2017年 | 461篇 |
2016年 | 531篇 |
2015年 | 465篇 |
2014年 | 594篇 |
2013年 | 1074篇 |
2012年 | 980篇 |
2011年 | 1167篇 |
2010年 | 813篇 |
2009年 | 755篇 |
2008年 | 799篇 |
2007年 | 786篇 |
2006年 | 587篇 |
2005年 | 513篇 |
2004年 | 380篇 |
2003年 | 391篇 |
2002年 | 344篇 |
2001年 | 218篇 |
2000年 | 190篇 |
1999年 | 211篇 |
1998年 | 225篇 |
1997年 | 199篇 |
1996年 | 192篇 |
1995年 | 184篇 |
1994年 | 158篇 |
1993年 | 150篇 |
1992年 | 119篇 |
1991年 | 75篇 |
1990年 | 124篇 |
1989年 | 117篇 |
1988年 | 81篇 |
1987年 | 93篇 |
1986年 | 106篇 |
1985年 | 101篇 |
1984年 | 90篇 |
1983年 | 79篇 |
1982年 | 96篇 |
1981年 | 90篇 |
1980年 | 71篇 |
1979年 | 70篇 |
1978年 | 64篇 |
1977年 | 76篇 |
1976年 | 63篇 |
1975年 | 45篇 |
1974年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 378 毫秒
201.
Daniel E. Miller Julie R. Vale 《Mathematics of Control, Signals, and Systems (MCSS)》2014,26(2):177-214
In this paper we consider the problem of adaptively stabilizing, and providing step tracking for, an uncertain linear time-varying system. We propose an adaptive pole placement controller which solves the problem for a single-input single-output plant whose parameters switch at a moderate rate among the elements of a compact set. The output feedback controller incorporates an integrator, and its action emulates the behaviour of a pole placement state feedback compensator; the controller is periodic and mildly nonlinear, is easy to implement, is noise tolerant, and tolerates a degree of unmodelled dynamics. 相似文献
202.
Dr. Christoph Goebel Prof.?Dr. Hans-Arno Jacobsen Victor del Razo Mag.? Christoph Doblander Dipl.-Ing. Jose Rivera Dipl-Inform.?Wirt Jens Ilg Dr. Christoph Flath Prof.?Dr. Hartmut Schmeck Prof.?Dr. Christof Weinhardt Dipl-Inform. Daniel Pathmaperuma Prof.?Dr. Dr.?h.?c. Hans-Jürgen Appelrath Prof.?Dr. Michael Sonnenschein Prof.?Dr. Sebastian Lehnhoff Prof.?Dr. Oliver Kramer Prof.?Dr. Thorsten Staake Prof.?Dr. Elgar Fleisch Prof.?Dr. Dirk Neumann Prof.?Dr. Jens Strüker Dr. Koray Erek Prof.?Dr. Rüdiger Zarnekow Dr. Holger Ziekow Prof.?Dr. J?rg L?ssig 《WIRTSCHAFTSINFORMATIK》2014,56(1):31-39
Due to the increasing importance of producing and consuming energy more sustainably, Energy Informatics (EI) has evolved into a thriving research area within the CS/IS community. The article attempts to characterize this young and highly dynamic field of research by describing current EI research topics and methods and provides an outlook of how the field might evolve in the future. It is shown that two general research questions have received the most attention so far and are likely to dominate the EI research agenda in the coming years: How to leverage information and communication technology (ICT) to (1) improve energy efficiency, and (2) to integrate decentralized renewable energy sources into the power grid. Selected EI streams are reviewed, highlighting how the respective research questions are broken down into specific research projects and how EI researchers have made contributions based on their individual academic background. 相似文献
203.
Geschäftsmodelle 总被引:1,自引:1,他引:0
Prof. Dr. Daniel Veit Prof. Eric Clemons Prof. Dr. Alexander Benlian Prof. Dr. Peter Buxmann Prof. Dr. Thomas Hess Prof. Dr. Dennis Kundisch Prof. Dr. Jan Marco Leimeister Prof. Dr. Peter Loos Prof. Dr. Martin Spann 《WIRTSCHAFTSINFORMATIK》2014,56(1):55-64
The business model concept, although a relatively new topic for research, has garnered growing attention over the past decade. Whilst it has been robustly defined, the concept has so far attracted very little substantive research. In the context of the wide-spread digitization of businesses and society at large, the logic inherent in a business model has become critical for business success and, hence, a focus for academic inquiry. The business model concept is identified as the missing link between business strategy, processes, and Information Technology (IT). The authors argue that the BISE community offers distinct and unique competencies (e.g., translating business strategies into IT systems, managing business and IT processes, etc.) that can be harnessed for significant research contributions to this field. Within this research gap three distinct streams are delineated, namely, business models in IT industries, IT enabled or digital business models, and IT support for developing and managing business models. For these streams, the current state of the art, suggest critical research questions, and suitable research methodologies are outlined. 相似文献
204.
This study was designed to test the hypotheses that digestibility and post-absorption metabolism of fish oil are influenced
by impaired lipolysis and by the stereospecific composition of its triacylglycerols. Male Wistar rats were fed nonpurified
diets containing one of the following fat sources: 9% native fish oil (NFO), 9% autorandomized fish oil (RFO), 8.1% fish oil-derived
free fatty acids (FO-FFA) plus 0.9% glycerol, or 9% soybean oil (SO) as a reference fat. In a 24-day balance study, apparent
digestibility of total dietary fat averaged 93.1% in the SO, NFO and RFO groups, and 90.9% in the FO-FFA group. Randomization
of fish oil had no effect on apparent digestibility of individual fatty acids. In rats fed FO-FFA, apparent absorption of
saturated and monounsaturated fatty acids was lower when compared to the NFO and RFO groups. Feeding the FO-FFA diet tended
to increase plasma triglyceride content. The hypocholesterolemic effect of polyunsaturated n−3 fatty acids was not influenced
by the dietary source. Similar effects on fatty acid profiles of plasma and liver phospholipids were caused by the NFO, RFO
and the FO-FFA diets. We conclude that once polyunsaturated n−3 fatty acids are absorbed, their effect on lipid metabolism
is not determined by the dietary source. 相似文献
205.
NH3-NO/NO2 SCR for diesel exhausts after treatment: mechanism and modelling of a catalytic converter
Nova Isabella Ciardelli Cristian Tronconi Enrico Chatterjee Daniel Weibel Michel 《Topics in Catalysis》2007,42(1-4):43-46
We review herein the key mechanistic and kinetic features of the reactions involved in the NH3-NO/NO2 SCR system investigated by dynamic reactive experiments over a V-based commercial powdered catalyst, eventually leading to
the proposal of an original redox scheme which accounts for stoichiometry, selectivity and intrinsic kinetics of the global
SCR process. 相似文献
206.
Chemical shift reagents were used to expand the amount of structural information obtainable from NMR studies of derivatives of methyl oleate and elaidate:methylcis-9,10-epoxystearate, methyltrans-9,10-epoxystearate, methyl erythro-9,10-dihydroxystearate, and methyl threo-9,10-dihydroxystearate. Chemical shift reagent studies of methyltrans-9,10-epoxystearate and methyl threo-9,10-dihydroxystearate afforded the most information. Chemical shift reagent studies of methylcis-9,10-epoxystearate and methyl erythro-9,10-dihydroxystearate were decidedly inferior. The series of complementary interpretive techniques previously developed during chemical shift reagent studies of monofunctional fatty esters and model polyfunctional fatty esters were found to be applicable in the current study. However, to avoid ambiguity in several proton assignments, supplementary spin decoupling experiments were necessary. 相似文献
207.
Whentris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octaneodionato)europium (III)—Eu(fod)3—forms a complex with a sufficiently basic functional group in a donor molecule, the change in the magnetic environment of
protons near the coordination site causes their nuclear magnetic resonance (NMR) signals to shift to different positions.
Consequently Eu(fod)3 and other compounds that similarly affect NMR signals have been designated chemical shift reagents (csr). Because of their
ability to shift proton signals, csr substantially increase the amount of structural information that can be obtained from
NMR spectroscopy, frequently converting complicated splitting patterns into first-order spectra. Some generally useful experimental
and interpretive csr techniques are described here using methyl petroselinate and methyl oleate as examples. Csr studies of
methyl petroselinate reveal that the position of the double bond is at C-6, and that there is no chain substitution or branching
before C-9. Csr studies of methyl oleate reveal that the position of the double bond is at or beyond C-9, and that there is
no chain substitution or branching before C-6. Some suggestions are presented for expanding the amount of structural information
that can be obtained by csr studies of unsaturated lipid derivatives.
Presented in part at AOCS Meeting, Atlantic City, October, 1971. 相似文献
208.
H. B. Knight Lee P. Witnauer W. E. Palm R. E. Koos Daniel Swern 《Journal of the American Oil Chemists' Society》1959,36(9):382-388
Summary Thirty-one acyloxy or aryloxy esters prepared from hydroxystearic acids have been evaluated as plasticizers for a vinyl chloride-vinyl
acetate copolymer (95∶5). Many of them were found to be primary plasticizers, having outstanding low-temperature performance
when employed at the 35% level. Formulations with these compounds compared quite favorably in tensile properties with those
containing the di-2-ethylhexyl esters of phthalic, sebacic, azelaic, and adipic acids. Volatility losses were similar to those
of the four di-2-ethylhexyl esters. The loss of plasticizer through migration was equal to or less than that from compositions
containing the esters of sebacic, azelaic, and adipic acids but was greater than that of the phthalate ester.
A mechanistic scheme of plasticizer-polymer interaction has been presented, proposing that the rate of diffusion of plasticizer
through the polymer mass is a controlling factor in both good low-temperature performance and the resulting high migration
losses. Methyl esters, some aromatic esters, and esters containing three or more polar centers have improved permanence but
show a more rapid change in torsional modulus as the temperature is lowered during the determination of the Clash-Berg stiffening
temperature.
Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture. 相似文献
209.
210.
Sam V. Shelton William J. Wepfer Daniel J. Miles 《Chemical Engineering Communications》1988,71(1):39-52
This work deals with the thermal analysis of externally heated porous beds of finite length. A one dimensional model was developed that includes conduction and storage in both the fluid and bed, convective exchange between the fluid and bed, and the effect of adsorption/desorption in the bed. This model results in two coupled differential equations for the fluid and bed temperatures as functions of four independent dimensionless parameters. These equations were solved numerically using finite difference approximations. A truncation error analysis was carried out to maintain an accurate solution. The method of normalization is such that the results of this analysis are of use in bed design when the breakthrough characteristics in finite length beds are of interest. A method to measure bed thermal performance is defined and a means to optimize bed thermal performance is presented. An experiment was conducted to validate the numerically obtained results. A comparison of numerical to experimental results is presented 相似文献