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   74778篇
  免费   709篇
  国内免费   689篇
电工技术   1428篇
综合类   47篇
化学工业   11179篇
金属工艺   3444篇
机械仪表   2637篇
建筑科学   1639篇
矿业工程   503篇
能源动力   1851篇
轻工业   6377篇
水利工程   845篇
石油天然气   2303篇
武器工业   41篇
无线电   7194篇
一般工业技术   16447篇
冶金工业   12408篇
原子能技术   2628篇
自动化技术   5205篇
  2022年   573篇
  2021年   903篇
  2020年   695篇
  2019年   777篇
  2018年   1549篇
  2017年   1562篇
  2016年   1760篇
  2015年   944篇
  2014年   1555篇
  2013年   3562篇
  2012年   2354篇
  2011年   2817篇
  2010年   2367篇
  2009年   2638篇
  2008年   2615篇
  2007年   2551篇
  2006年   2181篇
  2005年   1911篇
  2004年   1837篇
  2003年   1787篇
  2002年   1704篇
  2001年   1677篇
  2000年   1669篇
  1999年   1563篇
  1998年   3667篇
  1997年   2597篇
  1996年   1935篇
  1995年   1521篇
  1994年   1325篇
  1993年   1348篇
  1992年   994篇
  1991年   1052篇
  1990年   1072篇
  1989年   1052篇
  1988年   941篇
  1987年   874篇
  1986年   877篇
  1985年   934篇
  1984年   778篇
  1983年   770篇
  1982年   677篇
  1981年   692篇
  1980年   665篇
  1979年   648篇
  1978年   622篇
  1977年   774篇
  1976年   932篇
  1975年   582篇
  1974年   551篇
  1973年   544篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Designs of 2 types of dried balanced food mixtures ("Unipit-1" and "Unipit-2") intended for complete recovery nutrition of patients with retained and disordered digestive function have been validated. The chemical composition of these products has been presented. The results of clinical trials have proved the high therapeutic effectiveness of "Unipit-1" and "Unipit-2" in rehabilitation of neurosurgical patients.  相似文献   
993.
The tensile strength of glass optical fibres when coated with various polymers has been measured as a function of -ray dose. Fibres protected with acrylate, silicone + acrylate or polyimide coatings showed little degradation after receiving a total dose of 1 MGy (they retained >95% of their preirradiated strength). For a fibre with an extruded nylon overcoat the nylon became very brittle after 0.5 MGy, but as far as could be assessed, the strength of the central glass fibre was little affected. Two other types of fibre, both protected with fluorinated polymers, were severely weakened after 0.1 MGy (their tensile strength being reduced to < 40% of their pre-irradiated strength). Experimental results are given supporting the hypothesis that the degradation results from gaseous fluorine-containing species chemically attacking the surface of the glass fibre.  相似文献   
994.
Cybernetics and Systems Analysis - The author proposes a matrix method for constructing an order N discrete cosine-sine type VII transform. Based on the method, two order 8 integer cosine-sine type...  相似文献   
995.
The Lake Basaka catchment (Ethiopia) has undergone a significant land use–land cover (LULC) change and lake level rise over the past five decades. Significant quantities of water and sediment flow annually into the lake through erosion processes. An appropriate method of estimating the surface run‐off from such ungauged and dynamic catchment is extremely important for delineating sensitive areas (based on run‐off responses) to be protected and for development of suitable measures to reduce run‐off and associated soil loss. Reliable prediction of run‐off, however, is very difficult and time‐consuming for catchments such as that of Lake Basaka. The present study estimated the dynamics of surface (direct) run‐off using the NRCS‐CN model in ArcGIS, assisted by remote sensing and ancillary data. The results indicated the Lake Basaka catchment experienced significant temporal and spatial variability in its run‐off responses, depending on the rainfall (amount and distribution) pattern and LULC changes. A significant run‐off increase occurred after 1973, consistent with significant LULC changes and lake level increments occurring after that period. A reduced vegetation cover also resulted in increased run‐off coefficient of the lake catchment from 0.11 in the 1970s to 0.23 in the 2000s, indicating the important need to consider possible future LULC evolution when forecasting the lake catchment run‐off behaviour.  相似文献   
996.
Power Technology and Engineering - The problem of electrical safety involving the assessment of hazardous factors during repair of overhead transmission lines is considered. The conditions of...  相似文献   
997.
A solution to the problem of realization of an acoustically transparent body in a far field is proposed using active quenching of the diffracted field by quenching means placed on the surface of the body.  相似文献   
998.
This work presents a method of formation of an accurate self-similar solution of the problem of hydrodynamic calculation of a wedge-shaped support (slide block, guide) operating in the presence of a lubricating material and melt of the guide. Based on the equation of motion of an viscous incompressible liquid for a “thin layer” and the expression for the energy dissipation rate, an analytical dependence is obtained for the profile of the melted surface of the guide. In addition, the main performance characteristics of the friction couple considered are defined. The influence of the parameter specified by the melt of the guide on the bearing capacity and friction force is estimated.  相似文献   
999.
Various methods of spectral-spatial classification of hyperspectral data are reviewed. Papers devoted to the most popular ways of using spatial information for increasing the accuracy of classification maps are considered. It is shown that the best results are obtained by using preprocessing of “raw” data before the procedures of pixel-wise spectral classification. Disadvantages, limits, and possible directions for developing existing methods are investigated and analyzed.  相似文献   
1000.
Conclusions 1. The specific resistance of soil not only beneath the cone of the penetrometer but also against the friction couple should be used to define the prediction of the strength and deformation characteristics of silty-clayey soils more precisely from static-penetration data, and the type of clayey soils should also be considered for the strength characteristics.2. For penetrometers equipped with radiation-logging apparatus, it is possible to evaluate mechanical characteristics of soils under field conditions, using the soil's density in addition to the penetration parameters q and f.3. In developing regional statistical relationships, it should be remembered that the extent to which q and f influence . c, and E is determined largely by what types of soil the statistical sample represents and in what range the physical indicators of its conditions vary.4. To define the recommendations of Construction Rule and Regulation 1.02.07-87 more precisely, it is expedient to use resultant correlation relationships (6)–(8) to evaluate , c, and E from static-penetration data for the genetic groups of quartenary deposits investigated.Translated from Osnovaniya, Fundamenty i Mekhanika Grungov, No. 4, pp. 21–24, July–August, 1990.  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