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   3156篇
  免费   98篇
  国内免费   1篇
电工技术   65篇
综合类   5篇
化学工业   1032篇
金属工艺   58篇
机械仪表   41篇
建筑科学   198篇
矿业工程   30篇
能源动力   33篇
轻工业   369篇
水利工程   10篇
石油天然气   1篇
无线电   206篇
一般工业技术   459篇
冶金工业   288篇
原子能技术   35篇
自动化技术   425篇
  2022年   30篇
  2021年   40篇
  2020年   35篇
  2019年   30篇
  2018年   43篇
  2017年   49篇
  2016年   72篇
  2015年   91篇
  2014年   80篇
  2013年   120篇
  2012年   122篇
  2011年   168篇
  2010年   116篇
  2009年   114篇
  2008年   121篇
  2007年   145篇
  2006年   124篇
  2005年   118篇
  2004年   104篇
  2003年   76篇
  2002年   76篇
  2001年   55篇
  2000年   55篇
  1999年   59篇
  1998年   86篇
  1997年   69篇
  1996年   66篇
  1995年   57篇
  1994年   69篇
  1993年   43篇
  1992年   49篇
  1991年   45篇
  1990年   28篇
  1989年   38篇
  1988年   24篇
  1987年   32篇
  1986年   33篇
  1985年   40篇
  1984年   44篇
  1983年   36篇
  1982年   36篇
  1981年   29篇
  1980年   28篇
  1978年   28篇
  1977年   29篇
  1976年   32篇
  1975年   37篇
  1974年   22篇
  1973年   25篇
  1970年   30篇
排序方式: 共有3255条查询结果,搜索用时 15 毫秒
161.
Gallasch BA  Spiteller G 《Lipids》2000,35(9):953-960
The previously unknown linoleic acid peroxidation product 9,12-dioxo-10(Z)-decenoic acid (Z5) was detected in lentil seed fluor (Lens culinaris Medik.) by electron impact mass spectrometry (El-MS) after derivatization with pentafluorobenzyl-hydroxylamine-hydrochloride, methylation of acidic groups with diazomethane, and protection of hydroxylic groups with N-methyl-N-trimethylsilyl-trifluoroacetamide. The structure of the natural product was confirmed by synthesis of Z5, 9,12-dioxo-10(E)-decenoic acid, and derivatives. EI-MS, nuclear magnetic resonance and gas chromatographic data of these compounds and synthetic intermediates are discussed.  相似文献   
162.
Zusammenfassung  Der vom Bundesamt für Sicherheit in der Informationstechnik (BSI) entwickelte Ansatz des IT-Grundschutzes war bereits Gegenstand von Beitr?gen in der DuD. Inzwischen hat das „Grundschutzhandbuch“ Eingang in die internationale Standard-Familie ISO 2700x gefunden. Der Autor berichtet über die Erfahrungen mit den ersten durchgeführten Zertifizierungen nach dem neuen ISO-Standard auf der Basis von IT-Grundschutz. Dr. Gerhard Weck: Leiter IT Security Consulting. der INFODAS GmbH K?ln. Derzeitiger Arbeitsschwerpunkt: Entwicklung und Vermittlung von Sicherheitskonzepten. Lizenzierter ISO 27001/IT-Grundschutz-Auditor. Autor bzw. Koautor mehrerer Bücher. Fellow der GI. Mitglied des Pr?sidiums-Arbeitskreises „Datenschutz und IT-Sicherheit“ der GI, Sprecher der Security SIG der HP User Society DECUS München e.V.  相似文献   
163.
In this paper we present a novel approach for the specification of user rights in the context of an object oriented use case driven development process. Basically, we extend the specification of methods by a permission section describing the right of some actor to call the method of an object. Our approach is both role based and context based while allowing for permissions to be specified at a fine-grained data-dependent level. We use first-order logic with a built-in notion of objects and classes (provided with an algebraic semantics) as our syntactic and semantic framework. In the second part of the paper, we demonstrate the application of this approach in a model-based context to generate permissions in distributed peer-to-peer networks.  相似文献   
164.
In this paper we develop an easily applicable algorithmic technique/tool for developing approximation schemes for certain types of combinatorial optimization problems. Special cases that are covered by our result show up in many places in the literature. For every such special case, a particular rounding trick has been implemented in a slightly different way, with slightly different arguments, and with slightly different worst case estimations. Usually, the rounding procedure depended on certain upper or lower bounds on the optimal objective value that have to be justified in a separate argument. Our easily applied result unifies many of these results, and sometimes it even leads to a simpler proof.  相似文献   
165.
This experimental analog component study compared two ways of administrating relaxation, either via a computer or by a therapist. The second phase of applied relaxation was used, which is called “release-only relaxation”. Sixty participants from a student population were randomized to one of three groups: computer-administered relaxation, therapist-administered relaxation, or a control group in which participants surfed on the Internet. Outcome was measures using psychophysiological responses and self-report. Objective psychophysiological data and results on the subjective visual analogue scale suggest that there was no difference between the two forms of administration. Both experimental groups became significantly more relaxed than the control group that surfed on the Internet. Practical applications and future directions are discussed.  相似文献   
166.
The aim of this study was to investigate the psychometric properties of Internet administered questionnaires used in panic research. Included were 494 people who had registered for an Internet-based treatment program for panic disorder (PD). Participants were randomly assigned to fill in the questionnaires either on the Internet or the paper-and-pencil versions, and then to fill in the same questionnaires again the next day using the other format. The questionnaires were the body sensations questionnaire [BSQ; Chambless, D. L., Caputo, G. C., Bright, P., & Gallagher, R. (1984). Assessment of fear of fear in agoraphobics: the body sensations questionnaire and the agoraphobic cognitions questionnaire. Journal of Consulting and Clinical Psychology, 52, 1090–1097], agoraphobic cognitions questionnaire [ACQ; Chambless, D. L., Caputo, G. C., Bright, P., & Gallagher, R. (1984). Assessment of fear of fear in agoraphobics: the body sensations questionnaire and the agoraphobic cognitions questionnaire. Journal of Consulting and Clinical Psychology, 52, 1090–1097], mobility inventory [MI; Chambless, D. L., Caputo, G., Jasin, S., Gracely, E. J., & Williams, C. (1985). The mobility inventory for agoraphobia. Behaviour Research and Therapy, 23, 35–44], beck anxiety inventory [BAI; Beck, A. T., Epstein, N., Brown, G., & Steer, R. A. (1988). An inventory for measuring clinical anxiety: psychometric properties. Journal of Consulting and Clinical Psychology, 56, 893–897], beck depression inventory II [Beck, A. T., & Steer, R. A. (1996). Beck Depression Inventory. Manual, Svensk version (Swedish version). Fagernes, Norway: Psykologiförlaget, AB], quality of life inventory [QOLI; Frisch, M. B., Cornell, J., Villanueva, M., & Retzlaff, P. J. (1992). Clinical validation of the quality of life inventory. A measure of life satisfaction for use in treatment planning and outcome assessment. Psychological Assessment, 4, 92–101], and montgomery Åsberg depression rating scale [MADRS; Svanborg, P., & Åsberg, M. (1994). A new self-rating scale for depression and anxiety states based on the comprehensive psychopathological rating scale. ACTA Psychiatrica Scandinavica, 89, 21–28]. Results showed largely equivalent psychometric properties for the two administration formats (Cronbach’s α between 0.79 and 0.95). The results also showed high and significant correlations between the Internet and the paper-and-pencil versions. Analyses of order effects showed an interaction effect for the BSQ and the MI (subscale Accompanied), a main effect was identified for ACQ, MI-Alone, BAI and BDI II. However, in contrast to previous research, the Internet version did not consistently generate higher scores and effect sizes for the differences were generally low. Given the presence of an interaction effect, we recommend that the administration format should be stable in research across measurement points. Finally, the findings suggest that Internet versions of questionnaires used in PD research can be used with confidence.  相似文献   
167.
To produce high stressed automotive components like engine frames and cylinder heads in foundry industry often AlSi7Mg alloys are used. During mould filling and casting melt flow affects the development of the microstructure, which defines the mechanical properties. In this paper the microstructure formation in AlSi7Mg0.3 and AlSi7Mg0.6 alloys during directional solidification is investigated. To induce a forced melt flow a rotating magnetic field is applied. For that purpose a Bridgman‐type gradient furnace is equipped with a rotary ring magnet. For detailed investigation of the shape of the solid‐liquid interface and the primary dendrite spacing a decanting device is used. As a result, the forced melt flow substantially changes the dendritic solidification microstructure. The rotating magnetic field generates a radial secondary flow in and ahead of the mushy zone, which causes an enrichment of eutectics in the centre of the samples. At lower solidification velocities this locally leads to the transition to mixed columnar‐equiaxed or even to equiaxed growth. In that case the solid‐liquid interfaces of the decanted samples show a significant depression in the centre part. In the out‐of‐centre region columnar growth still exists and the primary dendrite spacing decreases with increasing melt flow.  相似文献   
168.
In order to produce new high Mn‐high C austenitic steels (Rm>700 MPa), different tests and methods were used to determine a suitable window of process parameters. In‐situ melting hot tensile tests and hot compression tests were carried out to investigate the hot ductility, fracture characteristics and flow behaviour during continuous casting and hot deformation of 3 steels with Mn and C contents between 9‐23% and 0.6‐0.9%, respectively. The results show that these steels are susceptible to interdendritic fracture at high temperatures. Decreasing Mn content improves the reduction of area at high temperatures to 60% or more. Hot deformation loads for processing the investigated steels are not higher in comparison to the stainless steel 1.4301.  相似文献   
169.
We present the Vienna Schrödinger-Poisson Solver (VSP), a multi-purpose quantum mechanical solver for investigations on nano-scaled device structures. VSP includes a quantum mechanical solver for closed as well as open boundary problems on fairly arbitrary one-dimensional cross sections within the effective mass framework. For investigations on novel gate dielectrics VSP holds models for bulk and interface trap charges, and direct and trap assisted tunneling. Hetero-structured semiconductor devices, like resonant tunneling diodes (RTD), can be treated within the closed boundary model for quick estimation of resonant energy levels. The open boundary model allows evaluation of current voltage characteristics.  相似文献   
170.
Dirty RF: A New Paradigm   总被引:1,自引:0,他引:1  
The implementation challenge for new low-cost low-power wireless modem transceivers has continuously been growing with increased modem performance, bandwidth, and carrier frequency. Up to now we have been designing transceivers in a way that we are able to keep the analog (RF) problem domain widely separated from the digital signal processing design. However, with today’s deep sub-micron technology, analog impairments – “dirt effects” – are reaching a new problem level which requires a paradigm shift in the design of transceivers. Examples of these impairments are phase noise, non-linearities, I/Q imbalance, ADC impairments, etc. In the world of “Dirty RF” we assume to design digital signal processing such that we can cope with a new level of impairments, allowing lee-way in the requirements set on future RF sub-systems. This paper gives an overview of the topic and presents analytical evaluations of the performance losses due to RF impairments as well as algorithms that allow to live with imperfect RF by compensating the resulting error effects using digital baseband processing.  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