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   5066篇
  免费   163篇
  国内免费   11篇
电工技术   51篇
综合类   1篇
化学工业   928篇
金属工艺   85篇
机械仪表   86篇
建筑科学   306篇
矿业工程   18篇
能源动力   132篇
轻工业   467篇
水利工程   43篇
石油天然气   38篇
武器工业   1篇
无线电   274篇
一般工业技术   857篇
冶金工业   1002篇
原子能技术   19篇
自动化技术   932篇
  2023年   32篇
  2022年   40篇
  2021年   83篇
  2020年   74篇
  2019年   63篇
  2018年   91篇
  2017年   72篇
  2016年   122篇
  2015年   88篇
  2014年   160篇
  2013年   347篇
  2012年   242篇
  2011年   320篇
  2010年   222篇
  2009年   190篇
  2008年   257篇
  2007年   232篇
  2006年   190篇
  2005年   192篇
  2004年   139篇
  2003年   130篇
  2002年   131篇
  2001年   82篇
  2000年   70篇
  1999年   81篇
  1998年   101篇
  1997年   108篇
  1996年   73篇
  1995年   75篇
  1994年   54篇
  1993年   69篇
  1992年   78篇
  1991年   44篇
  1990年   49篇
  1989年   61篇
  1988年   55篇
  1987年   51篇
  1986年   56篇
  1985年   71篇
  1984年   59篇
  1983年   68篇
  1982年   49篇
  1981年   35篇
  1980年   45篇
  1979年   61篇
  1978年   45篇
  1977年   45篇
  1976年   39篇
  1975年   37篇
  1973年   25篇
排序方式: 共有5240条查询结果,搜索用时 15 毫秒
991.
This paper uses two large databases, one of given names and one of family names, to categorise the names of researchers from Italy, Sweden, the UK and the USA whose papers in astronomy and oncology were published in 2006–2007 and in 2011–2012 by sex (gender) and ethnicity or national origin. For all the countries, there were relatively many more females publishing papers in oncology than in astronomy, but their share of contributions was lower than the percentage of researchers. Sweden and the UK had much higher percentages of both other European and Rest of the World researchers than Italy did. US researchers with non-European names were categorised in six main country groups. The ones with the greatest presence were Chinese (mainly Mandarin) and South Asians (mainly Indians). The method could be adapted to investigate the progress of women in research in many other countries, and the role played by non-national researchers in their scientific output.  相似文献   
992.
Obtaining quantitative information about molecular assemblies with high spatial and temporal resolution is a challenging task in fluorescence microscopy. Single‐molecule techniques build on the ability to count molecules one by one. Here, a method is presented that extends recent approaches to analyze the statistics of coincidently emitted photons to enable reliable counting of molecules in the range of 1–20. This method does not require photochemistry such as blinking or bleaching. DNA origami structures are labeled with up to 36 dye molecules as a new evaluation tool to characterize this counting by a photon statistics approach. Labeled DNA origami has a well‐defined labeling stoichiometry and ensures equal brightness for all dyes incorporated. Bias and precision of the estimating algorithm are determined, along with the minimal acquisition time required for robust estimation. Complexes containing up to 18 molecules can be investigated non‐invasively within 150 ms. The method might become a quantifying add‐on for confocal microscopes and could be especially powerful in combination with STED/RESOLFT‐type microscopy.  相似文献   
993.
In this paper we consider Runge–Kutta discontinuous Galerkin (RKDG) schemes for Vlasov–Poisson systems that model collisionless plasmas. One-dimensional systems are emphasized. The RKDG method, originally devised to solve conservation laws, is seen to have excellent conservation properties, be readily designed for arbitrary order of accuracy, and capable of being used with a positivity-preserving limiter that guarantees positivity of the distribution functions. The RKDG solver for the Vlasov equation is the main focus, while the electric field is obtained through the classical representation by Green’s function for the Poisson equation. A rigorous study of recurrence of the DG methods is presented by Fourier analysis, and the impact of different polynomial spaces and the positivity-preserving limiters on the quality of the solutions is ascertained. Several benchmark test problems, such as Landau damping, the two-stream instability, and the Kinetic Electro static Electron Nonlinear wave, are given.  相似文献   
994.
Some of the systems used in natural language generation (NLG), a branch of applied computational linguistics, have the capacity to create or assemble somewhat original messages adapted to new contexts. In this paper, taking Bernard Williams’ account of assertion by machines as a starting point, I argue that NLG systems meet the criteria for being speech actants to a substantial degree. They are capable of authoring original messages, and can even simulate illocutionary force and speaker meaning. Background intelligence embedded in their datasets enhances these speech capacities. Although there is an open question about who is ultimately responsible for their speech, if anybody, we can settle this question by using the notion of proxy speech, in which responsibility for artificial speech acts is assigned legally or conventionally to an entity separate from the speech actant.  相似文献   
995.
Abstract

Recent data breaches at major retailers have created an extra awareness of information security risks within the IT internal auditors. This article focuses on top security topics which every internal auditor must consider before they finalize their audit plans  相似文献   
996.
Modelling class B G-protein-coupled receptors (GPCRs) using class A GPCR structural templates is difficult due to lack of homology. The plant GPCR, GCR1, has homology to both class A and class B GPCRs. We have used this to generate a class A–class B alignment, and by incorporating maximum lagged correlation of entropy and hydrophobicity into a consensus score, we have been able to align receptor transmembrane regions. We have applied this analysis to generate active and inactive homology models of the class B calcitonin gene-related peptide (CGRP) receptor, and have supported it with site-directed mutagenesis data using 122 CGRP receptor residues and 144 published mutagenesis results on other class B GPCRs. The variation of sequence variability with structure, the analysis of polarity violations, the alignment of group-conserved residues and the mutagenesis results at 27 key positions were particularly informative in distinguishing between the proposed and plausible alternative alignments. Furthermore, we have been able to associate the key molecular features of the class B GPCR signalling machinery with their class A counterparts for the first time. These include the [K/R]KLH motif in intracellular loop 1, [I/L]xxxL and KxxK at the intracellular end of TM5 and TM6, the NPXXY/VAVLY motif on TM7 and small group-conserved residues in TM1, TM2, TM3 and TM7. The equivalent of the class A DRY motif is proposed to involve Arg2.39, His2.43 and Glu3.46, which makes a polar lock with T6.37. These alignments and models provide useful tools for understanding class B GPCR function.  相似文献   
997.
Umkehrwalze A was the original reflector used in the version of the Enigma machine employed by the German armed services. Its wiring was originally deduced by the Polish cryptanalyst Marian Rejewski in December 1932 or January 1933, but details of the wiring have not previously been published. Sufficient information to recover the wiring analytically is provided in a wartime document by Alan Turing, and other sources have been found to confirm the solution. This paper presents the wiring, along with alternative methods of recovering it from Turing's data.  相似文献   
998.
The three renewable energy technologies discussed in this paper are based on water, but differ markedly in terms of the size of the available potential resource, the maturity of the associated conversion technologies, the extent to which they have been exploited to date, and the current research effort being devoted to their future development. Hydro-electricity and tidal power are both very mature technologies. The exploitation of Australia's relatively limited potential for hydro-electric development began over a century ago and the opportunities for further hydro-electric development are now very restricted. The country's significant tidal power resources, on the other hand, have not been exploited for electricity generation to date, but continual assessment of the feasibility of tidal power projects has been undertaken over the past half century. Although Australia has large ocean wave energy resources, ocean wave energy conversion technology is not yet fully commercial and no commercial wave generation plants are operating in Australia. A small number of wave energy conversion devices, however, are at the pilot testing stage.  相似文献   
999.
Do-it-yourself (DIY) is a staple element of the spare time activities of many households, but little is known about the extent to which basic repair work is carried out through DIY and about the quality of this work. Through secondary analyses of UK government data (English House Condition Survey and Family Expenditure Survey), this paper examines the scale of DIY work by owner-occupiers, how work is organized, the interrelationship of DIY work, the use of unpaid help, and the use of contractors. It considers the types of work carried out, the characteristics of those who tackle DIY or use unpaid help, the dwelling types most likely to experience DIY work, and the motivations of and constraints on those home-owners who do it. The paper concludes with a discussion on the policy implications of these findings for government and the building industry. Although most DIY work is cosmetic and does not deal with basic repair and maintenance, the sheer scale of DIY ensures that it makes a contribution to improving housing conditions. The provision of more advice, information and education by government, local authorities and the private sector could ensure that more DIY work is of better quality and that home owners give priority to essential repairs whether or not they tackle these themselves.  相似文献   
1000.
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