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   17131篇
  免费   803篇
  国内免费   42篇
电工技术   247篇
综合类   44篇
化学工业   3881篇
金属工艺   347篇
机械仪表   432篇
建筑科学   990篇
矿业工程   68篇
能源动力   300篇
轻工业   2040篇
水利工程   94篇
石油天然气   23篇
武器工业   1篇
无线电   1184篇
一般工业技术   3766篇
冶金工业   1740篇
原子能技术   143篇
自动化技术   2676篇
  2023年   168篇
  2022年   169篇
  2021年   303篇
  2020年   236篇
  2019年   239篇
  2018年   461篇
  2017年   411篇
  2016年   525篇
  2015年   428篇
  2014年   562篇
  2013年   1147篇
  2012年   785篇
  2011年   1003篇
  2010年   799篇
  2009年   782篇
  2008年   890篇
  2007年   837篇
  2006年   663篇
  2005年   560篇
  2004年   493篇
  2003年   431篇
  2002年   410篇
  2001年   353篇
  2000年   310篇
  1999年   269篇
  1998年   376篇
  1997年   310篇
  1996年   267篇
  1995年   199篇
  1994年   196篇
  1993年   195篇
  1992年   169篇
  1991年   131篇
  1990年   123篇
  1989年   117篇
  1988年   126篇
  1987年   110篇
  1986年   101篇
  1985年   185篇
  1984年   176篇
  1983年   111篇
  1982年   115篇
  1981年   127篇
  1980年   116篇
  1979年   118篇
  1978年   110篇
  1977年   90篇
  1976年   87篇
  1975年   77篇
  1973年   80篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
81.
A study was made of the appraisers' effect on the estimation of metabolic rate with the Edholm scale and a table of the ISO 7243 heat stress standard. The appraisers, five experienced and five inexperienced persons, estimated the metabolic rate of three different work tasks from videotapes. Analysis of variance indicated significant ( [Formula: see text] ) differences in the appraisers' recordings of the activities. The appraisers were grouped according to the similarity of the estimated values they gave. The groups thus contained both experienced and inexperienced appraisers, and it was not possible to classify the appraisers into experienced and inexperienced groups according to their earlier experience. The metabolic rates according to the Edholm scale were higher than according to the ISO 7243 table. The differences in metabolic rates given by the individual observers varied from 38 to 118 W/m(2). The variations in the estimation of metabolic rates were greater when the Edholm scale was used. This variation caused considerable variation also in the predicted mean vote, PMV index. It is recommended that the appraisers be selected carefully, because it is not possible to know whether a randomly selected appraiser is an 'average' or an 'extreme' appraiser without a test. Before conducting extensive field surveys where several appraisers estimate the metabolic rates, it would be useful to arrange training in order to calibrate the levels of the Edholm scale as well as ISO method among the appraisers because training clearly unified the estimation.  相似文献   
82.
Certain tasks, such as formal program development and theorem proving, fundamentally rely upon the manipulation of higher-order objects such as functions and predicates. Computing tools intended to assist in performing these tasks are at present inadequate in both the amount of knowledge they contain (i.e., the level of support they provide) and in their ability to learn (i.e., their capacity to enhance that support over time). The application of a relevant machine learning technique—explanation-based generalization (EBG)—has thus far been limited to first-order problem representations. We extend EBG to generalize higher-order values, thereby enabling its application to higher-order problem encodings.Logic programming provides a uniform framework in which all aspects of explanation-based generalization and learning may be defined and carried out. First-order Horn logics (e.g., Prolog) are not, however, well suited to higher-order applications. Instead, we employ Prolog, a higher-order logic programming language, as our basic framework for realizing higher-order EBG. In order to capture the distinction between domain theory and training instance upon which EBG relies, we extend Prolog with the necessity operator of modal logic. We develop a meta-interpreter realizing EBG for the extended language, Prolog, and provide examples of higher-order EBG.  相似文献   
83.
The effect of birefringence induced in a single-mode fiber by a lateral force has been applied to measure the absolute value of force or pressure with high resolution. A sensor configuration with an extended detecting surface has been investigated by means of calibrated weights. The sensor is sensitive to an incremental force of 2 x 10(-3) N, independently of the length of the fiber. The maximum force applied was 10 N/m of fiber length.  相似文献   
84.
Single crystals of nearly stoichiometric Fe3Si were creep-deformed at temperatureT = 450 to 850° C and applied stress=40 to 250 MPa. While the temperature dependence of the steady-state creep rate of crystals with less than 25 at% Si can be described by an exponential function exp (–H exp/kT), the Fe-26 at% Si samples show an exponential dependence only below 500° C and above 600° C. At intermediate temperatures the dependence is weak. It is suggested that in this intermediate range two phases exist. The experimental results are consistent with the assumption that the phase boundaries do not hinder dislocation movement, and that the disocation velocity in the two phases is different.  相似文献   
85.
86.
Conventional access methods cannot be effectively used in large Scientific/Statistical Database (SSDB) applications. A file structure (called bit transposed file (BTF)) is proposed which offers several attractive features that are better suited for the special characteristics that SSDBs exhibit. This file structure is an extreme version of the (attribute) transposed file. The data are stored by vertical bit partitions. The bit patterns of attributes are assigned using one of several data encoding methods. Each of these encoding methods is appropriate for different query types. The bit partitions can also be compressed using a version of the run length encoding scheme. Efficient operators on compressed bit vectors have been developed and form the basis of a query language. Because of the simplicity of the file structure and query language, optimization problems for database design, query evaluation, and common subexpression removal can be formalized and efficient exact solution or near optimal solution can be achieved. In addition to selective power with low overheads for SSDBs, the BTF is also amenable to special parallel hardware. Results from experiments with the file structure suggest that this approach may be a reasonable alternative file structure for large SSDBs.  相似文献   
87.
Beef adductor muscles were incubated for 4 h post mortem at 10°C and for 4 h and 6 h post mortem at 30°C, 37°C and 42°C. Half of the muscles were cooked just after incubation and the other half was first stored for two days at 4°C and then cooked. Meat kept for 4 h or 6 h at 42°C and for 6 h at 37°C and cooked at once had a significantly (p<0·05) lower shear force than meat kept for 4 h at 37°C, 4 h at 30°C, 6 h at 30°C or 4 h at 10°C. The respective significant differences were also found when the meat was cooked two days after incubation. Organoleptic evaluation showed that meat incubated for 6 h at 37°C or for 4 h at 42°C was not significantly more tender than other samples. However, meat kept for 6 h at 42°C was more tender (p<0·5) than the other samples. After two days of storage, meat incubated for 6 h at 37°C and for 6 h at 42° was more tender (p<0·05) than meat kept for 6 h at 30°C. It was concluded that high temperature conditioning at 37°C or higher for 6 h (4 h at 42°C) just after slaughter makes meat more tender than conventional cooling systems.  相似文献   
88.
Asymmetrically cracked specimens fail with considerably less ductility than symmetrically cracked ones, due to the crack progressing along a shear band into pre-damaged material. A formulation for the accumulation of damage ahead of an asymmetric crack is presented, based on strain increments following a power law relation. These results are integrated both numerically and approximately.The crack growth per unit displacement increases approximately as the logarithm of the total crack advance per inclusion spacing , and varies inversely as the critical fracture strain c. This provides a basis for predicting large-scale, fully plastic fracture from asymmetric weld defects, using small-scale laboratory specimens.
Résumé Les éprouvettes fissurées de manière asymétrique se rompent avec beaucoup moins de ductilité que celles qui sont fissurées de manières symétrique, en raison du fait que la fissure se développe suivant une bande de cisaillement dans un matériau préendommagé. On Présente une formulation de l'accumulation du dommage en avant d'une fissure asymétrique, en se basant sur des gradients de déformations répartis selon une loi quadratique. L'interprétation des résultats est effectuée par voie numérique et par approximation.On constate que le croissance d'une fissure par unité de déplacement est sensiblement proportionnelle au logarithme de l'avancement total de la fissure rapporté à l'espacement entre deux inclusions , et en raison inverse de la déformation critique à la rupture c. Ceci fournt une base pour prédire une rupture à plus grande échelle et en conditions tout à fait plastiques, qui résulteront de défauts de soudage asymétriques, et ce en utilisant des éprouvettes réduites de laboratoire.
  相似文献   
89.
Zusammenfassung Die massive Bedrohung durch Nuklearwaffen, die den Supermächten die Möglichkeit zur Auslöschung allen Lebens auf der Erde geben, erfordert eine Entscheidungsfindung oftmals innerhalb weniger Minuten. Dies hat beide Seiten zum Aufbau von Frühwarn- und Entscheidungssystemen (FWES) veranlaßt, durch deren Einsatz ein atomarer Angriff noch innerhalb der Raketenflugzeit erkannt werden soll. In diesem FWES spielt die Verarbeitung und Weiterleitung von Informationen durch den Computer eine kriegsentscheidende Rolle: Die Informatik ist zu einer der wichtigsten Grundlagenwissenschaften in der Rüstungsforschung geworden. Dieser Artikel gibt eine Übersicht über die Funktionsweise computergestützter FWES und zeigt Fehlerquellen auf, die es möglich und sogar wahrscheinlich machen, daß eine Verkettung unglücklicher Umstände zu einem Nuklearkrieg aus Versehen führen kann.
Liste der Abkürzungen ANMCC Alternate National Military Command Center - BMWES Ballistic Missile Early Warning System - CSS Communication System Segment - EMP Elektromagnetischer Puls - FWES Frühwarn- und Entscheidungssystem - ICBM Intercontinental Ballistic Missile - JCS Joint Chief of Staff - NCS NORAD Computer System - NMCC National Military Command Center - NORAD North American Aerospace Defense Command Center - PAC Pacific Command - PARCS Perimeter Acquisition Radar Attack Characterization System - SAC Strategic Air Command - SCC Space Computational Center - SLBM Submarine-launched Ballistic Missiles - WWMCCS World Wide Military Command and Control System  相似文献   
90.
This paper introduces a certain graphical coalitional game where the internal topology of the coalition depends on a prescribed communication graph structure among the agents. The game Value Function is required to satisfy four Axioms of Value. These axioms make it possible to provide a refined study of coalition structures on graphs by defining a formal graphical game and by assigning a Positional Advantage, based on the Shapley value, to each agent in a coalition based on its connectivity properties within the graph. Using the Axioms of Value the graphical coalitional game can be shown to satisfy properties such as convexity, fairness, cohesiveness, and full cooperativeness. Three measures of the contributions of agents to a coalition are introduced: marginal contribution, competitive contribution, and altruistic contribution. The mathematical framework given here is used to establish results regarding the dependence of these three types of contributions on the graph topology, and changes in these contributions due to changes in graph topology. Based on these different contributions, three online sequential decision games are defined on top of the graphical coalitional game, and the stable graphs under each of these sequential decision games are studied. It is shown that the stable graphs under the objective of maximizing the marginal contribution are any connected graph. The stable graphs under the objective of maximizing the competitive contribution are the complete graph. The stable graphs under the objective of maximizing the altruistic contribution are any tree.  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