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   813643篇
  免费   11078篇
  国内免费   2453篇
电工技术   14821篇
综合类   825篇
化学工业   121862篇
金属工艺   29764篇
机械仪表   23141篇
建筑科学   21106篇
矿业工程   2936篇
能源动力   22223篇
轻工业   75095篇
水利工程   7354篇
石油天然气   10699篇
武器工业   49篇
无线电   97217篇
一般工业技术   153281篇
冶金工业   160139篇
原子能技术   14249篇
自动化技术   72413篇
  2021年   6658篇
  2020年   4821篇
  2019年   6130篇
  2018年   10299篇
  2017年   10121篇
  2016年   10729篇
  2015年   7871篇
  2014年   12917篇
  2013年   37875篇
  2012年   21084篇
  2011年   29565篇
  2010年   23177篇
  2009年   26062篇
  2008年   27120篇
  2007年   27036篇
  2006年   23928篇
  2005年   21991篇
  2004年   21197篇
  2003年   20900篇
  2002年   19962篇
  2001年   19970篇
  2000年   18537篇
  1999年   19775篇
  1998年   49547篇
  1997年   35181篇
  1996年   27178篇
  1995年   20768篇
  1994年   18217篇
  1993年   17782篇
  1992年   12858篇
  1991年   12254篇
  1990年   11798篇
  1989年   11448篇
  1988年   10788篇
  1987年   9390篇
  1986年   9242篇
  1985年   10802篇
  1984年   10096篇
  1983年   8866篇
  1982年   8305篇
  1981年   8385篇
  1980年   7931篇
  1979年   7733篇
  1978年   7337篇
  1977年   8892篇
  1976年   11969篇
  1975年   6291篇
  1974年   5988篇
  1973年   5977篇
  1972年   4870篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
921.
Examined the association between self-monitoring and occupational preferences. 237 undergraduates completed Snyder and Gangestad's (1986) revised self-monitoring scale and Holland's (1977) Vocational Preference Inventory (VPI). Regression analyses showed that men who valued congruence between their beliefs and behavior (i.e., low self-monitors) preferred social occupations. Men who were inclined to modify their behavior to fit social situations (i.e., high self-monitors) preferred enterprising occupations. In contrast, high self-monitoring women preferred artistic occupations. It is argued that these gender-neutral occupations permit high self-monitoring women to use their social skills but without the constraints found in male dominated enterprising occupations. Results support the assumption that people prefer occupations compatible with their social skills. Implications for career counseling and further research are noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
922.
This article traces the connection between expert systems used as consultants in medicine and their design for instructional purposes in education. It is suggested that there are important differences between these applications. Recognizing these differences leads to the view that the development of intelligent computer-assisted instructions (ICAI) should be guided by empirical research into social/psychological consequences and by ethical inquiries into the acceptability of those consequences. Three proposals are put forward: (1) that the pedagogical role of intelligent CAI be clarified, (2) that forms of intelligent CAI be developed that aim primarily at refining rather than replacing human judgements, and (3) that ICAI research and development projects contain components which address ethical and social/psychological components and which are equitably-funded, integral parts of the overall development effort.This work was supported in part by funds from the Foundation of the University of North Carolina at Charlotte and from the State of North Carolina. An earlier version of this paper was read at the Human Dimension in Artificial Intelligence Symposium held at the University of Kentucky (April 1988).  相似文献   
923.
The electronic band structure of ZrO2 is calculated for the fluorite structure using the self-consistent augmented-plane-wave method in the muffin-tin approximation. The crystal charge density is then site decomposed by fitting Slater orbitals to the wave functions in the muffin tins. The resultant charge densities for Zr4+ and O2− are then used in the Gordon-Kim method to derive pair potentials, from which a number of structural, elastic, and thermodynamic properties are calculated and compared with experimental results and similar calculations for MgO.  相似文献   
924.
Fatty acid esters, high in linoleic acid, were prepared and stored for long-term engine tests. Storage tests with these esters were undertaken to obtain more information on optimal storage requirements and general stability characteristics. Samples were kept at three temperature levels (20 C, 30 C and fluctuating around 50 C) for a 90-day period and were removed at regular intervals for chemical and physical analysis. The influence of air, temperature, light, TBHQ and contact with mild steel was evaluated by comparing the free fatty acid, peroxide, anisidine, ultraviolet absorption, viscosity and induction periods. A statistical model was used to evaluate the data and to reduce the large number of data points to comparable curves. Storage of esters in contact with air, especially at a temperature above 30 C, resulted in significant increases in peroxide, ultraviolet absorption, free fatty acid, viscosity and anisidine values. Exclusion of air retarded oxidation at all temperature levels. A direct relationship between viscosity increases and oxidation parameters was evident. Exposure to light caused a small increase in the oxidation parameters of esters stored at the highest temperature level. Addition of TBHQ prevented oxidation of samples stored under moderate conditions. Under unfavorable storage conditions the anti-oxidant was no longer effective. Mild steel had very little effect on the oxidation parameters. Only the anisidine values of samples stored at the highest temperature level were slightly increased. Methyl esters performed slightly better than ethyl esters during the storage test. The following practical guidelines for storage of fatty acid ester fuels are: (i) airtight containers should be used; (ii) the storage temperature should be <30 C; (iii) mild steel (rust free) containers may be used, and (iv) TBHQ has a beneficial effect on oxidation stability.  相似文献   
925.
926.
The synthesis of hydrocarbons via hydrogenation of carbon monoxide was investigated over cobalt—nickel—zirconia catalysts of various compositions in combination with zeolite HZSM-5 in “mixed bed” and “follow bed” arrangements. These combinations resulted in the formation of aromatics in amounts as high as 30-35 wt% under relatively mild operating conditions (1 atm, 250–280°C). Although the olefinicity of C2 and C3 fractions in the product stream was higher in the mixed bed compared to the follow bed arrangement, the selectivities to aromatics were comparable in the two bed arrangements. The aromatic selectivity was found to be sensitive to operating conditions. The formation of aromatics was favored at high HZSM-5/metal catalyst ratios, low space velocities and high reaction temperatures. The product distributions obtained using various metal/zeolite bifunctional catalysts have been discussed.  相似文献   
927.
This paper considers the integration of alternative technical systems (TS) belonging to a wider class of competing TS, into a supersystem. The paper introduces the notion of alternative TS, shows the peculiarities of their incorporation into a supersystem, reveals the mechanisms used for such incorporation, and shows areas of application for the suggested method.  相似文献   
928.
929.
Ellagic acid (2, 3, 7, 8‐tetrahydroxy(1)benzopyrano(5, 4, 3‐cde)(1)benzopyran‐5, 10‐dione) was selected as a model pollutant which is present in the tannic fraction of cork processing wastewater. The ultrafiltration of aqueous ellagic acid solutions through three membranes was studied in tangential UF laboratory equipment. Two of the membranes were polyethersulfone (Biomax10K and Biomax5K, with MWCO of 10000 and 5000 Da, respectively), and the third made of regenerated cellulose (Ultracel5K, with MWCO of 5000 Da). The water hydraulic permeability was evaluated for each membrane. The evolution of the permeate flow rate with processing time was followed, and the influence of the main operating variables (feed flow rate, trans‐membrane pressure and nature of the membranes) on the permeate flux was also established. According to the hypothesis of the film theory, the intrinsic and apparent rejection coefficients, as well as the mass transfer coefficients, were also determined, and the values obtained were discussed as a function of the operating conditions used.  相似文献   
930.
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