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   20975篇
  免费   570篇
  国内免费   28篇
电工技术   279篇
综合类   16篇
化学工业   3920篇
金属工艺   314篇
机械仪表   378篇
建筑科学   1220篇
矿业工程   117篇
能源动力   585篇
轻工业   1597篇
水利工程   179篇
石油天然气   205篇
武器工业   1篇
无线电   1513篇
一般工业技术   3269篇
冶金工业   5137篇
原子能技术   194篇
自动化技术   2649篇
  2022年   151篇
  2021年   243篇
  2020年   186篇
  2019年   247篇
  2018年   289篇
  2017年   285篇
  2016年   345篇
  2015年   259篇
  2014年   417篇
  2013年   1229篇
  2012年   739篇
  2011年   961篇
  2010年   748篇
  2009年   737篇
  2008年   948篇
  2007年   958篇
  2006年   776篇
  2005年   790篇
  2004年   635篇
  2003年   634篇
  2002年   575篇
  2001年   405篇
  2000年   351篇
  1999年   379篇
  1998年   590篇
  1997年   464篇
  1996年   436篇
  1995年   411篇
  1994年   334篇
  1993年   379篇
  1992年   312篇
  1991年   205篇
  1990年   277篇
  1989年   319篇
  1988年   231篇
  1987年   256篇
  1986年   260篇
  1985年   316篇
  1984年   308篇
  1983年   262篇
  1982年   256篇
  1981年   242篇
  1980年   200篇
  1979年   207篇
  1978年   199篇
  1977年   219篇
  1976年   217篇
  1975年   195篇
  1974年   176篇
  1973年   157篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
In today's competitive world, many organizations are pursuing total quality improvement programs, and as a result of these initiatives, are seeking to define world class capabilities. The organizations with these aspirations are trying to improve product and service quality, business process quality, or delivered quality, and are becoming aware that information technology is playing a more substantial role in realizing these quality goals.  相似文献   
142.
Overcoming contextual limitations on problem-solving transfer.   总被引:1,自引:0,他引:1  
Five experiments investigated transfer from multiple analogs to a superficially dissimilar target problem. When subjects explicitly compared the analogs and then immediately attempted to solve the target problem in the context of a single experiment, transfer was obtained with significant frequency even without a hint that the analogs and target were related. Prehint transfer was sharply reduced or eliminated when the source analogs and the target were presented in different contexts, even when the transfer test was immediate. However, prehint transfer was enhanced, even after a context shift and a week-long delay between reading the source analogs and solving the problem, when the following conditions were met: The target problem was reworded slightly to emphasize a structural feature that it shared with the analogs; three rather than two source analogs were provided; and detailed, schema-oriented questions were used to help subjects focus on the problem-relevant aspects of the stories. Although spontaneous transfer between small numbers of dissimilar analogs is difficult to obtain, it can be achieved by manipulations that foster abstraction of a problem schema from the training examples. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
143.
144.
Broadband dielectric measurements (10 -2 to 3 GHz) are reported on the effects of exposure of thick film adhesive-bonded structures to moisture. Measurement of the dielectric properties over a broad frequency range allows identification of water both in voids and as a molecular dispersion in the matrix. Changes in the low frequency region of the dielectric spectrum can be attributed to a combination of processes associated with plasticisation of the adhesive, interfacial polarisation effects, and hydration of the surface oxide layer. The data obtained are complemented by mechanical testing and failure analysis of the bond structure measured as a function of the time of exposure. This study indicates that for thick film adhesives the ageing characteristics are apparently independent of the surface treatment. In one of the joints studied an additional feature is identified which appears to correlate with the premature aging of the joint structure.  相似文献   
145.
A structured in-depth interview employing standardized criteria was used to determine the prevalence of lifetime and current alcohol dependence (alcoholism) in unselected consecutive patients admitted to a regional Level I trauma center. Of 629 patients, 157 (25.0%) were current alcoholics at the time of injury. An additional 87 (13.8%) were diagnosed as lifetime non-current alcoholics. There was no significant difference in the rates of current alcohol dependence among patients injured in vehicular crashes (23.5%), other unintentional trauma victims (29.3%), and those injured as a result of violence (24.6%). Of BAC + (blood alcohol concentration positive) patients, 54.5% were current alcoholics. However, 14.4% of alcohol-negative patients were also diagnosed as alcohol dependent.  相似文献   
146.
An experimental study was conducted to examine the effectiveness of sodium carbonate in alkali, surfactant and polymer combined slugs in recovering waterflood residual oil. The effects of sodium carbonate concentration on the slug viscosity, interfacial tension, and phase behavior were first examined. Core flood experiments were conducted with unfired linear Berea sandstone cores. The incremental oil recovery, oil cut, residual resistance factor, and chemical propagation were measured for each flood.A significant oil bank was formed for all combined slugs having sodium carbonate concentration ≥1 wt%. The incremental oil recovery, oil cut and the injectivity of the combined slugs greatly improved as sodium carbonate concentration was increased. The effect of sodium carbonate concentration on chemical propagation was dramatic for the synthetic surfactant; a slight delay in surfactant breakthrough and a much slower rate of surfactant propagation were observed at high sodium carbonate concentrations.The results obtained in the present study indicate that the residual oil was recovered by two mechanisms: low interfacial tension and wettability reversal. The former mechanism is dominant at sodium carbonate concentrations ≤1 wt%, whereas the latter plays an important role only at high sodium carbonate concentrations.  相似文献   
147.
A thermogravimetric method for the measurement of carbon, nitrogen, and oxygen in aluminum nitride is described. Since carbon oxidation occurs at lower temperatures than the oxidation of the aluminum compounds, thermogravimetric analyses in the respective temperature regimes can yield measurement of the oxygen, nitrogen, and carbon content. Thermogravimetric analyses were performed on mixtures of aluminum nitride and carbon with various concentrations in order to evaluate the accuracy of this method. The results were compared with those obtained by the hot gas extraction method. Errors produced by overlapping of the temperature ranges of the reactions were evaluated and experimental conditions were optimized to minimize error. This method can produce reliable results at elemental concentrations higher than a few percent. The absolute errors of the C/AI, N/Al, and O/Al atomic ratios were less then 0.02. The detection limit was evaluated to 0.2 wt% of each element. The applicability of the method to the study of the kinetics of the nitridation reaction was demonstrated.  相似文献   
148.
The effect of cooking on proteins from acha and durum wheat was assessed from an analysis of protein extractability, gel electrophoretic profiles, in-vitro protein digestibility (IVPD) and the amino acid compositions of wholemeal flour and residue proteins. Heating wholemeal flour samples at 100–140°C (t = 10–40 min) resulted in 0–30% and 45–55% decreases in acha and durum protein solubility, respectively. In general, high molecular weight (30–70 k Da) protein subunits were more susceptible to heat damage. For both cereals, sodium dodecyl sulphate (SDS; 10 g litre?1) and/or dithiothrcitol (DTT; 10 mM ) increased protein solubility in unheated and heated samples. The IVPD index was 90–91% and was not significantly altered by cooking (100–120°C, t = 40 min). Cooking at extreme temperatures (140°C, t = 40 min) reduced the IVPD by 8% (P = 0.05). Osborne fractionation resulted in a durum or acha residue level of 7.8% or 55.2%. Treatment with solvent containing propanol, SDS and/or DTT at room temperature followed by SDS-polyacrylamide gel electrophoresis of non-solubilised proteins showed that the glutelin fraction of acha, with the exception of a 65 kDa subunit, was insoluble owing to strong inter-subunit hydrophobic and disulphide interactions. Wholemeal acha flour and residue protein showed a significantly greater level of hydrophobic and sulphur amino acids as well as glutamine which is associated with H-bonding. The possibility that cereal protein solubility is also dependent on protein-carbohydrate links is discussed.  相似文献   
149.
Although all-optical networks were being thought about almost ten years ago, until recently it would have been premature to talk about such networks as being truly usable. Now, ways of removing most of the roadblocks to practicality have come clearly into view. It is generally agreed that time-division packet switching in the form of asynchronous transfer mode (ATM) is likely to constitute the next generation of networking, both local and wide area; but what about the generation after that? While people are evolving SONET/ATM, the present Internet, and such emerging ambitions as the National Information Infrastructure (NII), in order to serve the needs anticipated for the next decade, optical fiber is being steadily installed at a rate of 700 miles per day in the United States alone. Furthermore, this resource is being extended steadily outward from the telco or cable provider backbone into customer premises, so that within the lifetime of the ATM generation, we may expect extremely rich fiber connectivity of a large number of homes and offices  相似文献   
150.
Presents the Multicultural Counseling Inventory (MCI), a self-report instrument that measures multicultural counseling competencies. Study 1 comprised 604 psychology students, psychologists, and counselors in a midwestern state. In Study 2, respondents were a national random sample of 320 university counselors. Instrument analysis included exploratory principal-axis factor analysis with oblique rotation, assessment of factor congruence between the factor structures of the 2 samples, LISREL confirmatory factor analysis to test the relative goodness of fit of 6 competing factor models of the MCI, and tests of internal consistency reliabilities. Results indicate that the MCI has 4 factors: Multicultural Counseling Skills, Multicultural Awareness, Multicultural Counseling Relationship, and Multicultural Counseling Knowledge. A higher order, more general multicultural counseling factor is also discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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