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   199674篇
  免费   2306篇
  国内免费   613篇
电工技术   3468篇
综合类   149篇
化学工业   28963篇
金属工艺   8049篇
机械仪表   6068篇
建筑科学   4811篇
矿业工程   1303篇
能源动力   5127篇
轻工业   17115篇
水利工程   2297篇
石油天然气   4040篇
武器工业   8篇
无线电   23066篇
一般工业技术   40013篇
冶金工业   37229篇
原子能技术   5086篇
自动化技术   15801篇
  2021年   1606篇
  2019年   1568篇
  2018年   2573篇
  2017年   2645篇
  2016年   2775篇
  2015年   1794篇
  2014年   3074篇
  2013年   8939篇
  2012年   5050篇
  2011年   7021篇
  2010年   5589篇
  2009年   6350篇
  2008年   6443篇
  2007年   6511篇
  2006年   5579篇
  2005年   5228篇
  2004年   5006篇
  2003年   4887篇
  2002年   4525篇
  2001年   4657篇
  2000年   4579篇
  1999年   4726篇
  1998年   11373篇
  1997年   8120篇
  1996年   6408篇
  1995年   4673篇
  1994年   4271篇
  1993年   4073篇
  1992年   3223篇
  1991年   3076篇
  1990年   2870篇
  1989年   2951篇
  1988年   2826篇
  1987年   2398篇
  1986年   2308篇
  1985年   2715篇
  1984年   2505篇
  1983年   2345篇
  1982年   2090篇
  1981年   2203篇
  1980年   2029篇
  1979年   2124篇
  1978年   2120篇
  1977年   2366篇
  1976年   3189篇
  1975年   1833篇
  1974年   1761篇
  1973年   1772篇
  1972年   1443篇
  1971年   1339篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Wastewater discharge from coal refining plants contains a number of biologically toxic compounds; 2000-2500 mg/l of COD of which 40% is composed of phenol, 100-400 mg/l of thiocyanate, 10-40 mg/l of cyanide, 100-250 mg/l of NH4+-N and 150-300 mg/l of total nitrogen. In order to treat this kind of high strength wastewater, we have developed a high performance biofilm process using fluidizing bio-carriers of the tube chip type. The fluidizing biofilm carriers are made of a composite of polyethylene and several inorganic materials, whose density is controlled at 0.97-0.98 g/ml. The fluidizing biofilm carriers show sound fluidization characteristics inside bioreactors. The wastewater is treated using three consecutive series reactors in oxic-anoxic-oxic arrangement. Each reactor is charged with the fluidizing biofilm carriers of 50 vol%. Furthermore, newly cultured active microorganisms for the thiocyanate biodegradation are added in the biofilm process. At total hydraulic retention time of 2.2 days, this process can achieve steady state removal efficiencies: COD, 99%; thiocyanate, 99%; NH4+-N, 99% and total nitrogen, 90%.  相似文献   
62.
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem.  相似文献   
63.
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies.  相似文献   
64.
Filled fibrous sorbents modified with transition metal ferro- and ferricyanides capable to recover americium(III) and rare-earth metals(III) from nitric acid solutions were prepared. The most complete and rapid recovery is attained on complex-forming and cation-exchange sorbents (as filled fibrous materials) saturated with nickel ions. The sorbents are characterized by good kinetic properties and can be used for recovery of the above metals.  相似文献   
65.
During experiments on the MSL-1 (first microgravity science laboratory) mission of the space shuttle (STS-83 and STS-94, April and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the nondeforming droplet, the resultant magnetohydrodynamic (MHD) flow inside the drop can be inferred from motion of impurity particulates on the surface. In the experiments, subsequent to melting, Joule heating produces a continuous reduction of viscosity of the fluid resulting in an acceleration of the flow with time. These observations indicate formation of a pair of co-rotating toroidal flow structures inside the spheroidal drop that undergo flow instabilities. As the fluid temperature rises, the amplitude of the secondary flow increases, and beyond a point, the tracers exhibit noncoherent chaotic motion signifying emergence of turbulence inside the drop. Assuming that the observed laminar-turbulent transition is shear-layer type, the internal structure of the toroidal loops is used to develop a semiempirical correlation for the onset of turbulence. Our calculations indicate that the suggested correlation is in modest agreement with the experimental data, with the transition occurring at a Reynolds number of 600.  相似文献   
66.
Bestehen ausreichende Anhaltspunkte für die Hochwassergef?hrdung, ist die Gemeinde verpflichtet, sich durch Nachforschungen Gewissheit über das Vorliegen oder Nichtvorliegen eines Hochwasserabflussgebietes gem § 38 Abs 3 WRG zu verschaffen. Liegt ein solches vor, hat sie gem § 12 Abs 1 Z 2 krnt GplG dieses im Fl?chenwidmungsplan ersichtlich zu machen. Erteilt die Gemeinde eine Baubewilligung ohne diese von der Erteilung einer wasserrechtlichen Bewilligung abh?ngig zu machen, haftet sie für die Kosten der Bauführung, die bei gesetzes-konformer Vorgangsweise unterlassen worden w?re.  相似文献   
67.
Thompson  J.B. Reed  K. 《Software, IEEE》2005,22(6):96-97
Undergraduate software engineering education is now well established in many countries, and many of these degree programs have received formal accreditation by the relevant country's professional body for computing. SE 2004 represents an enormous effort by numerous individuals across the discipline. Its quality has been clearly recognized by the sponsoring organizations. The developmental team confidently looks forward to the volume's use and to your participation in future evaluations and in the next phase of development. The volume provides usable results for those in emerging economies who wish to enter the software engineering community, and we know that individual project members and the participating national bodies are ready to assist.  相似文献   
68.
The maximum-likelihood technique is applied to determine the coordinates of moving targets in a three-dimensional bistatic forward-scattering radar. The potential accuracy of the coordinates’ determination is estimated. Simulation results are presented.  相似文献   
69.
Industry widely uses rotary valves and blow tanks for the pneumatic conveying of products, each having their pros and cons depending on the specific application. This article shows the differing results obtained when low-velocity conveying a product through a common pipeline using both a drop-through rotary valve and a bottom-discharge blow tank feeder. A number of issues arise in the rotary valve system, the main one being rotary valve air leakage. A blow tank system, on the other hand, does not leak, as it is an enclosed system. The experimental results show dramatic differences in product throughput. Further exploration leads to a novel modification being made to the rotary valve system in an attempt to increase its capacity. The result of this modification shows a slight increase in output tonnage, but still significantly less than that obtained from the blow tank.  相似文献   
70.
An algorithm was obtained for restoration of a continuous process from a finite number of its equispaced discrete samples. The necessary and sufficient sampling conditions were formulated.  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