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   381893篇
  免费   4558篇
  国内免费   1114篇
电工技术   6646篇
综合类   292篇
化学工业   57241篇
金属工艺   17078篇
机械仪表   12172篇
建筑科学   8455篇
矿业工程   3155篇
能源动力   9394篇
轻工业   28390篇
水利工程   4823篇
石油天然气   10585篇
武器工业   28篇
无线电   42216篇
一般工业技术   79302篇
冶金工业   68211篇
原子能技术   10348篇
自动化技术   29229篇
  2021年   3485篇
  2019年   3377篇
  2018年   5833篇
  2017年   5941篇
  2016年   6346篇
  2015年   3831篇
  2014年   6425篇
  2013年   16853篇
  2012年   10113篇
  2011年   13358篇
  2010年   10788篇
  2009年   12139篇
  2008年   12335篇
  2007年   12309篇
  2006年   10511篇
  2005年   9744篇
  2004年   9040篇
  2003年   8898篇
  2002年   8443篇
  2001年   8565篇
  2000年   8232篇
  1999年   8410篇
  1998年   20649篇
  1997年   14569篇
  1996年   11372篇
  1995年   8407篇
  1994年   7513篇
  1993年   7515篇
  1992年   5835篇
  1991年   5694篇
  1990年   5380篇
  1989年   5401篇
  1988年   5264篇
  1987年   4581篇
  1986年   4551篇
  1985年   5201篇
  1984年   4859篇
  1983年   4564篇
  1982年   4090篇
  1981年   4170篇
  1980年   4082篇
  1979年   4150篇
  1978年   4140篇
  1977年   4525篇
  1976年   5688篇
  1975年   3693篇
  1974年   3526篇
  1973年   3634篇
  1972年   3112篇
  1971年   2873篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Kulyako  Yu. M.  Trofimov  T. I.  Samsonov  M. D.  Myasoedov  B. F. 《Radiochemistry》2003,45(5):503-505
It was shown for the first time that weighable amounts of uranium dioxide and its mixtures with Np, Pu, and Am in the form of solid solutions can be efficiently and quantitatively dissolved in the presence of tributyl phosphate saturated with HNO3. Individual PuO2 and NpO2 are not dissolved under these conditions. In treatment of a mechanical mixture of UO2 with PuO2 or NpO2, uranium is completely dissolved, while plutonium and neptunium remain in the precipitate.  相似文献   
992.
993.
Horizontal subsurface flow constructed wetlands have proven their efficiency in treating wastewater and removing the pollutants of concern. Treatment efficiency depends on the wastewater residence time, which is a function of the hydraulic loading and the physical conditions of the constructed filter system, which can be described with effective parameters such as: hydraulic conductivity, porosity, dispersivity etc. Because spatial variability is often scale dependent, these effective parameters may be affected by the scale of the system being studied. In this paper the results of tracer experiments in constructed filters using saturated horizontal flow at three scales (small and medium lab scales and full-scale system) using the same filter media is reported. Light-weight aggregate (filter media termed Filtralite-P) was used at all scales. Increasing the scale was associated with increasing dispersivity, meanwhile hydraulic conductivity experienced dramatic reduction and variation by increasing the examined scale. Observed changes in the hydraulic parameters indicate that heterogeneity at different scales should be taken into account when the performance of LWA filters are evaluated from small-scale experiments.  相似文献   
994.
The structure of the biological module of the computer database in the ISIS/Base format of the Information System for Antitumor Agents of the GU Blokhin Cancer Research Center (CRC), RAMS, is given and the organizational and technological aspects of its loading, editing, retrieval, and use are described.  相似文献   
995.
The salient features of using a solid substance to cool the core of a nuclear reactor and the associated advantages and limitations are examined. Conceptual proposals concerning the core design and the arrangement of the in-reactor space of a high-temperature nuclear reactor with a solid coolant are presented. Evaluated data and some results for a model reactor are presented. __________ Translated from Atomnaya énergiya, Vol. 103, No. 3, pp. 156–161, September, 2007.  相似文献   
996.
We investigate thin poly(3‐hexylthiophene‐2,5‐diyl)/[6,6]‐phenyl C61 butyric acid methyl ester (P3HT/PCBM) films, which are widely used as active layers in plastic solar cells. Their structural properties are studied by grazing‐incidence X‐ray diffraction (XRD). The size and the orientation of crystalline P3HT nanodomains within the films are determined. PCBM crystallites are not detected in thin films by XRD. Upon annealing, the P3HT crystallinity increases, leading to an increase in the optical absorption and spectral photocurrent in the low‐photon‐energy region. As a consequence, the efficiency of P3HT/PCBM solar cells is significantly increased. A direct relation between efficiency and P3HT crystallinity is demonstrated.  相似文献   
997.
998.
Mitotic chromosomes of the freshwater snail Pomacea patula catemacensis (Baker 1922) were analyzed on gill tissue of specimens from the type locality (Lake Catemaco, Mexico). The diploid number of chromosomes is 2n = 26, including nine metacentric and four submetacentric pairs; therefore, the fundamental number is FN = 52, No sex chromosomes could be identified. The same chromosome number and morphology were already reported for P. flagellata, i.e., the other species of the genus living in Mexico. The basic haploid number for family Ampullariidae was reported to be n = 14 in the literature; so, its reduction to n = 13 is probably an apomorphy of the Mexican Pomacea snails. Lanistes bolteni, from Egypt, also shows n = 13, but its karyotype is much more asymmetrical, and seems to have evolved independently from P. flagellata and P. patula catemacensis. The nominotypical subspecies, P. patula patula (Reeve 1856), is a poorly known taxon, whose original locality is unknown. A taxonomical account is presented here, and a Mexican origin postulated as the most parsimonious hypothesis.  相似文献   
999.
A novel online technique for monitoring the insulation condition of ac machine stator windings is proposed in this paper. The concept is to measure the differential leakage currents of each phase winding from the terminal box in a noninvasive manner to assess the insulation condition during motor operation. The conventional differential CTs used for phase fault protection can be replaced with high performance current sensors to measure the leakage current with higher accuracy. Indicators for insulation condition such as the capacitance and dissipation factor are calculated based on the measurements to provide a low cost solution for online insulation condition assessment. A simplified online insulation system model is derived for analysis and interpretation of the measured data. Experimental results on a 15-hp induction motor under simulated insulation degradation conditions show that the proposed technique is a very sensitive method capable of detecting incipient signs of insulation degradation.  相似文献   
1000.
Drives to increase the volume of customers who use self-service channels are a common strategic goal. The promise of significant cost reduction is a tempting carrot. Couple this with the vision of customers benefiting from quick, effective and usable contact channels, avoiding human error (except perhaps their own!) or potential frustration at being passed around to an ‘appropriate’ contact centre advisor is a very worthy vision … but is it as simple as this? In this discussion paper the authors speculate that self-service, while potentially being a revenue-saving opportunity, could also erode customer satisfaction and loyalty. Self-service doubtless appeals to some customers, but is it what all customers want? Do organisations understand enough about customer experience to enable them to build successful self-service channels, i.e. those that are useful, usable and used by customers? Do businesses really want to lose the opportunity to actually talk to customers and gain insight and knowledge about them? What impact will increased levels of self-service have on more traditional channels, such as customer contact centres? This paper also discusses evidence that self-service can actually serve to increase communication between organisations and customers across multiple channels. For many organisations, the Internet has actually resulted in more calls to the contact centre, not less. The seductive promise of self-service to cut costs through reducing call volumes may be an empty one.  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