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   709177篇
  免费   4160篇
  国内免费   2277篇
电工技术   11969篇
综合类   3203篇
化学工业   103596篇
金属工艺   27283篇
机械仪表   21022篇
建筑科学   18299篇
矿业工程   2855篇
能源动力   17443篇
轻工业   62183篇
水利工程   7191篇
石油天然气   8276篇
武器工业   57篇
无线电   86888篇
一般工业技术   134087篇
冶金工业   118198篇
原子能技术   12783篇
自动化技术   80281篇
  2021年   4680篇
  2020年   3742篇
  2019年   4654篇
  2018年   20328篇
  2017年   19389篇
  2016年   16912篇
  2015年   6072篇
  2014年   9326篇
  2013年   28501篇
  2012年   18284篇
  2011年   30574篇
  2010年   24454篇
  2009年   24380篇
  2008年   26714篇
  2007年   27856篇
  2006年   18449篇
  2005年   18053篇
  2004年   17703篇
  2003年   17337篇
  2002年   16284篇
  2001年   15825篇
  2000年   14992篇
  1999年   15579篇
  1998年   36335篇
  1997年   26379篇
  1996年   20482篇
  1995年   15977篇
  1994年   14196篇
  1993年   13916篇
  1992年   10279篇
  1991年   9887篇
  1990年   9444篇
  1989年   9134篇
  1988年   8663篇
  1987年   7546篇
  1986年   7556篇
  1985年   8845篇
  1984年   8231篇
  1983年   7314篇
  1982年   6867篇
  1981年   6864篇
  1980年   6616篇
  1979年   6351篇
  1978年   6082篇
  1977年   7107篇
  1976年   9526篇
  1975年   5171篇
  1974年   4991篇
  1973年   4898篇
  1972年   4056篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
The identification of adequate wastewater treatment for small communities is a complex problem since it demands a combination of data from different sources, such as aspects of the community and landscape, the receiving environment and the available wastewater treatment technologies. The Catalan Water Agency (Agència Catalana de l'Aigua) considered using an EDSS (Environmental Decision Support System) as a tool to help water managers select the most adequate treatment for the urban wastewater of nearly 3,500 small communities in Catalonia (Spain). From that moment, EDSS was applied to all the river basins in Catalonia. In this paper the authors present the results obtained for the 76 small communities located in one of these river basins: the Fluvia River Basin. The characteristics of the community used in the reasoning process of the EDSS, the list of selected wastewater treatment alternatives, the technical environmental justification for the selected treatments and the reasons for discarding, favouring or disadvantaging them are presented. Finally, some results for the Fluvia River Basin are compared with those obtained in other Catalan river basins with different characteristics in order to evaluate which are the significant features in identifying adequate wastewater treatments.  相似文献   
122.
Continuous simulation is performed using the US Environmental Protection Agency (USEPA) Storm Water Management Model (SWMM) to evaluate regional differences around the United States in hydrologic and water quality performance of wet-weather controls. Controls are characterised as being limited by peak inflow rate (i.e. any device with little or no storage, such as screens, filters and some proprietary devices) or by storage capacity (e.g., ponds, tanks). For flow-limited devices, results are presented in the form of percentage of annual runoff volume captured (passing through the device) for a given inflow capacity. For storage-limited devices, results are presented in two forms: percentage of annual runoff volume captured as a function of unit basin size and drawdown (drain) time, and as a percentage of total suspended solids captured, for the same two variables. Regional differences are apparent, driven mainly by variations in rainfall patterns around the country.  相似文献   
123.
124.
V. Ya. Chubar' Zaporozhe Machine Building Institute. Translated from Problemy Prochnosti, No. 3, pp. 62–65, March, 1989.  相似文献   
125.
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables.  相似文献   
126.
Fiber cross sections for use in textiles and composites are becoming more and more complex. Shape impacts fiber or filaments properties and therefore the yarn and fabric characteristics. This paper presents the influence of the fiber cross section on the fabric surface characteristics. The material used was polyester staple fibers, of four different shapes: round, scalloped oval, cruciform and hexachannel. All fibers had the same cut length with different fineness. Yarns obtained from these fibers had nominally the same yarn count, torsion value and structure. Plain jersey fabrics were knitted from each of the yarns under identical conditions and then relaxed prior to testing. Friction behavior was evaluated and a roughness-friction criterion developed. An indirect measurement of the real area of contact was obtained in order to provide roughness and friction properties. The influence of fiber cross section on yarn bending rigidity and on the state of the knitted fabric surface was characterized.  相似文献   
127.
128.
New thermodynamic data for the In–Sb system are obtained and compared with calculation results available in the literature. An isothermal vacuum cell and a procedure for electrolyte preparation are described which ensure high measurement accuracy.  相似文献   
129.
A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In 0.12Ga0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In0.12Ga0.88As was estimated to be about 380 meV  相似文献   
130.
The results of a computer simulation of the initial stages of the nucleation and growth of gold on NaCl(100) are presented. A potential energy scaling Monte Carlo model employing a 50 × 50 array, mobile monomers, dimers and trimers, and gold atom vertical “roll up” was used. The parameters in the model were obtained from the work of Robinson and Robins, other published sources and/or found by calculation. Simulations of the migration of single gold adatoms over the surface permitted the determination of the diffusion coefficient as a function of the reciprocal temperature which returned the same activation energy given by the potential field, thus indicating the consistency of the model. Initial cluster densities were determined using deposition rates of Rd = 1015cm-2s-1 and Rd = 1014cm-2s-1 over the temperature range T=200–425 K. Initial cluster growth was found to occur primarily by surface phase transport and resulted in clusters that were shaped like very thin disks. Using the equations from the work of Velfe and coworkers, calculations were made to extrapolate the computer simulation data in order to permit an indirect comparison with the data of Robinson and Robins. Good agreement was achieved. Initial condensation coefficients determined over a 250 ms interval showed that α ≈ 0 at T > 425 K and α ≈ 1 at T < 325 K for a deposition rate of Rd=1015 cm-2 s-1.  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