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   25285篇
  免费   158篇
  国内免费   769篇
电工技术   331篇
综合类   138篇
化学工业   2696篇
金属工艺   813篇
机械仪表   1291篇
建筑科学   1616篇
矿业工程   630篇
能源动力   113篇
轻工业   5426篇
水利工程   448篇
石油天然气   581篇
武器工业   103篇
无线电   1310篇
一般工业技术   8358篇
冶金工业   427篇
原子能技术   222篇
自动化技术   1709篇
  2022年   37篇
  2021年   63篇
  2018年   41篇
  2016年   36篇
  2015年   69篇
  2014年   105篇
  2013年   114篇
  2012年   2640篇
  2011年   3517篇
  2010年   740篇
  2009年   402篇
  2008年   2265篇
  2007年   2113篇
  2006年   1838篇
  2005年   1590篇
  2004年   1229篇
  2003年   1159篇
  2002年   1011篇
  2001年   865篇
  2000年   786篇
  1999年   549篇
  1998年   301篇
  1997年   299篇
  1996年   285篇
  1995年   235篇
  1994年   224篇
  1993年   140篇
  1992年   204篇
  1991年   212篇
  1990年   216篇
  1989年   210篇
  1988年   219篇
  1987年   221篇
  1986年   219篇
  1985年   274篇
  1984年   218篇
  1983年   220篇
  1982年   226篇
  1981年   189篇
  1980年   135篇
  1979年   127篇
  1978年   88篇
  1976年   28篇
  1975年   42篇
  1974年   34篇
  1965年   52篇
  1964年   42篇
  1958年   31篇
  1957年   33篇
  1956年   37篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
132.
The Institute of Medicine's (IOM) exhaustive study on the computerized patient record is finally complete. One of the study's first recommendations is to establish an institute for the computer-based patient record to get the ball rolling. Computers in Healthcare Editor Carolyn Dunbar asks a key leader of the IOM study, Richard Dick, Ph.D., why the ball is now rolling and picking up speed rapidly toward a true electronic medical record.  相似文献   
133.
布隆迪共和国的小水电蕴藏量极为丰富.20世纪80年代完成的水电蕴藏量调查结果表明,41项已认定工程的可开发总装机容量可达300 MW.目前,正在逐个研究、筛选,以确定最佳坝址,而且将对确定的项目进行可行性研究,并逐步予以实施.  相似文献   
134.
气候变化很可能对欧洲莱茵河的径流造成影响。需要用领先的科学和技术知识去加强适应性战略,以应对河道径流变化,关键在于认识气候的潜在影响以及社会与自然体系适应气候变化的能力。这两者无论是在个体、地方、区域,再到国际等各个层面上都具有很大的不确定度。提出了面临的三大挑战。在制定适应性战略时如何应对气候变化产生的不确定度是第一大挑战。研究发现,为支撑流域适应性规划而对不确定度进行传播一般仅占现有不确定度的一小部分,如只利用一种模型或一种情景以及一种方法去考虑不确定度。第二大挑战是克服目前科学家提供的科学知识与决策者所需知识之间的失配问题。早期使用"政策风险评估法"的经验表明,该法可以更好地满足决策者的需求。第三大挑战是如何恰当地将莱茵河流域的跨境特点纳入到研究工作和政策制定中来,从整个流域层面而不是单一流域内层面进行综合分析,进而提出并实施适应性方案,这样可以提供新的机遇,但也面临着许多实际性的挑战。  相似文献   
135.
For gas puff Z-pinches, the K-shell x-ray yield is maximized with the use of a multi-shell nozzle. Optimization of the yield, verification of hydrodynamic models of the nozzle flows, and plausible MHD code modeling of the implosions require data on the radial and axial (R,Z) distribution of mass in the nozzle's flow field. Interferometry is a well-established technique for acquiring such data. We describe the development and use of a two-dimensional interferometer with emphasis on the required data reduction methods. We also show that the instrument can derive the flow from each individual nozzle in a multi-shell system.  相似文献   
136.
The feasibility of anaerobic ammonium oxidation (anammox) process to treat wastewaters containing antibiotics and heavy metals (such as the liquid fraction of the anaerobically digested swine manure) was studied in this work. The specific anammox activity (SAA) was evaluated by means of manometric batch tests. The effects of oxytetracycline, sulfathiazole, copper and zinc were studied. The experimental data of the short-term assays were fitted with an inhibition model to identify the half maximal inhibitory concentration (IC(50)). After 24 h exposures, IC(50)-values equal to 1.9, 3.9, 650 and 1,100 mg L(-1) were identified for copper, zinc, sulfathiazole and tetracycline respectively. The effect of prolonged exposure (14 days) to oxytetracycline and sulfathiazole was studied by means of repeated batch-assays. Anabolism and catabolism reactions were active during the inhibition tests indicating that anammox bacteria could grow even in the extreme conditions tested. Considering the average concentrations expected in swine wastewaters, the inhibitors studied do not seem to represent a problem for the application of the anammox process. However, in order to verify the effect of these compounds on the growth of anammox bacteria, continuous culture experiments could be conducted.  相似文献   
137.
Here we describe a novel, hand-held reference point indentation (RPI), instrument that is designed for clinical measurements of bone material properties in living patients. This instrument differs from previous RPI instruments in that it requires neither a reference probe nor removal of the periosteum that covers the bone, thus significantly simplifying its use in patient testing. After describing the instrument, we discuss five guidelines for optimal and reproducible results. These are: (1) the angle between the normal to the surface and the axis of the instrument should be less than 10°, (2) the compression of the main spring to trigger the device must be performed slowly (>1 s), (3) the probe tip should be sharper than 10 μm; however, a normalized parameter with a calibration phantom can correct for dull tips up to a 100 μm radius, (4) the ambient room temperature should be between 4?°C and 37 °C, and (5) the effective mass of the bone or material under test must exceed 1 kg, or if under 1 kg, the specimen should be securely anchored in a fixation device with sufficient mass (which is not a requirement of previous RPI instruments). Our experience is that a person can be trained with these guidelines in about 5 min and thereafter obtain accurate and reproducible results. The portability, ease of use, and minimal training make this instrument suitable to measure bone material properties in a clinical setting.  相似文献   
138.
Since 2009, the Spallation Neutron Source (SNS) has been producing neutrons with ion beam powers near 1 MW, which requires the extraction of ~50 mA H(-) ions from the ion source with a ~5% duty factor. The 50 mA are achieved after an initial dose of ~3 mg of Cs and heating the Cs collar to ~170 °C. The 50 mA normally persist for the entire 4-week source service cycles. Fundamental processes are reviewed to elucidate the persistence of the SNS H(-) beams without a steady feed of Cs and why the Cs collar temperature may have to be kept near 170 °C.  相似文献   
139.
140.
Life cycle assessment (LCA) allows evaluating the potential environmental impacts of a product or a service in relation to its function and over its life cycle. In past LCAs applied to wastewater treatment plants (WWTPs), the system function definition has received little attention despite its great importance. This has led to some limitations in LCA results interpretation. A new methodology to perform LCA on WWTPs is proposed to avoid those limitations. It is based on net environmental benefit (NEB) evaluation and requires assessing the potential impact of releasing wastewater without and with treatment besides assessing the impact of the WWTP's life cycle. The NEB allows showing the environmental trade-offs between avoided impact due to wastewater treatment and induced impact by the WWTP's life cycle. NEB is compared with a standard LCA through the case study of a small municipal WWTP consisting of facultative aerated lagoons. The NEB and standard LCA show similar results for impact categories solely related to the WWTP's life cycle but differ in categories where wastewater treatment environmental benefit is accounted for as NEB considers influent wastewater quality whereas standard LCA does not.  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