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   2509篇
  免费   12篇
电工技术   9篇
化学工业   58篇
金属工艺   2篇
机械仪表   11篇
建筑科学   4篇
能源动力   9篇
轻工业   27篇
水利工程   1篇
石油天然气   2篇
无线电   25篇
一般工业技术   43篇
冶金工业   2307篇
原子能技术   2篇
自动化技术   21篇
  2019年   4篇
  2018年   2篇
  2016年   2篇
  2015年   4篇
  2014年   4篇
  2013年   5篇
  2012年   8篇
  2011年   7篇
  2010年   14篇
  2009年   4篇
  2008年   10篇
  2007年   8篇
  2006年   6篇
  2005年   7篇
  2004年   10篇
  2003年   13篇
  2002年   5篇
  2001年   4篇
  2000年   8篇
  1999年   80篇
  1998年   765篇
  1997年   453篇
  1996年   281篇
  1995年   160篇
  1994年   124篇
  1993年   127篇
  1992年   20篇
  1991年   22篇
  1990年   21篇
  1989年   29篇
  1988年   20篇
  1987年   23篇
  1986年   24篇
  1985年   28篇
  1983年   4篇
  1982年   10篇
  1981年   16篇
  1980年   14篇
  1979年   4篇
  1978年   11篇
  1977年   41篇
  1976年   74篇
  1975年   6篇
  1974年   4篇
  1973年   5篇
  1968年   2篇
  1967年   5篇
  1959年   4篇
  1948年   2篇
  1890年   3篇
排序方式: 共有2521条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
The first case of the unstable Hb Genova as a result of sporadic mutation is described. It is found in a 3-year-old Canadian boy of East Indian extraction with chronic Heinz body haemolytic anaemia.  相似文献   
35.
The thermal energy available from high-temperature magma is calculated to be 8 × 1014 kcal/km3 and an upper bound for volcanic energy of 3 × 1018 kcal/volcano is determined. Approximately one-third of the energy may be obtained between about 750 and 1150 °C (i.e. above the solidification temperature of the magma), while the remaining two-thirds is available from magma in the solid state between ambient and around 750 °C. Gas dissolved in the magma possesses about 4% of the thermal energy and a large portion of that energy is potentially available as high-temperature steam. After removal of water, the gas remaining is a low-Btu gas with a heat of combustion of about 0.3 kcal/l. Utilization of both the thermal and combustion energy is the subject of current research projects.  相似文献   
36.
Three representatives of a novel class of amide (isopeptide) glycoconjugates have been synthesised: N alpha-D-galacturonoyl-L-lysine and N epsilon-D-galacturonoyl-L-lysine and N epsilon-D-polygalacturonoyl-L-lysine. Galacturonoyl-lysine amide bonds were labile in 2 M trifluoroacetic acid at 120 degrees and in alkali, but relatively stable in cold acid. The amide bonds were resistant to digestion by Driselase, Pronase and trypsin. The polysaccharide backbone of N epsilon-D-polygalacturonoyl-L-lysine was hydrolysed by Driselase to yield two major ninhydrin-positive compounds which were shown by 1H and 13C NMR spectroscopy to be tri- and tetra-alpha-(1-->4)-D-galacturonoyl-L-lysines. To investigate the possible natural occurrence of N-galacturonoyl isopeptide bonds, we fed cell-suspension cultures of spinach and tomato with D-[6-14C]glucuronic acid, which radio-labels pectic polysaccharides. The radioactive cell walls were digested with, sequentially, Driselase, mild acid, and proteinases. On electrophoresis at pH 2.0, several of the radioactive digestion-products were cathodic. Some of the cathodic products yielded [14C]galacturonic acid upon complete acid hydrolysis. The existence of these products is compatible with the presence of novel N-galacturonoyl isopeptide bonds, which could serve as cross-links in plant cell walls.  相似文献   
37.
Electrochromic fabric devices represent a further extension to the plethora of available literature on conductive fabrics. This article contains a brief overview of electrochromic devices, electrochromic polymers, conductive materials, conductive fabrics, and electrochromic fabric devices. A tabulated list of the perceived colour of a number of electrochromic polymers that is contained herein is designed to serve as an aide to colour mixing studies. The challenges of optimisation and commercialisatiion of electrochromic fabric devices and their mitigating factors are conjectured, along with some future potential applications for electrochromic fabric device technologies.  相似文献   
38.
Here, we describe the development of a reacting flow multi-species/combustion methodology, implemented as an extension to the differential reduced ejector analysis (DREA) computer program [Mathematical and computer modeling, vol. 31, 2000, p. 21; Appl. Math. Model. 25 (2001) 427; Comput. Math. Appl. 43(10–11); NASA Contractor Report, 1998]. Use of the single fluid IVP solver framework that was developed for the original DREA model has been directly coupled into the combustion formulation. With these modifications, the analysis has an elementary single step reaction Fuel+Oxidizer→Product combustion capability. Though approximate in nature, the simplicity and efficiency of the DREA formulation make it suitable for its original niche, namely design and preliminary design environments where more complex and expensive models may be inappropriate.  相似文献   
39.
Issues and Techniques in Networked-Based Distributed Healthcare: Overview   总被引:1,自引:0,他引:1  
For telemedicine to reach its potential in the Internet2 environment,significant progress must be made in a number of areas. The emergingtelecommunications will include the Internet2 between medicalinstitutions and emerging broadband loop and wireless technologiesfor interconnections to homes. Within the technical environment,problems that must be addressed include the development of robotic-controlled,remote-monitoring devices unique to the various medical specialties;the encoding, transmission, and decoding of raw data specificto the specialized needs of various medical application areas;and the reduction of data for storage and retrieval in patientrecords. Institutionally, human factor and information accessissues with respect to physicians, patients, and non-physicianhealthcare providers must be addressed; healthcare insuranceprovider policies, government regulation, and state licensinglaws must be adapted for a new paradigm of healthcare delivery;and the philosophy of capital investment for the delivery ofhealthcare must be revised.Many current practiceswill be supplanted by home healthcare alternatives, the use ofpatient-initiated preventive healthcare initiatives, and remote-clinicactivity. These applications will result in central record archivingsystems; the need for encryption schemes, virus protection, andvandalism protection; extensive, additional connectivity betweenhealthcare providers and professionals; and new commercial playersin the healthcare arena.The hot applicationareas will include women's health, children's health, healthcarefor senior citizens, home healthcare, well-patient monitoring,and early-detection of medical problems.  相似文献   
40.
Quarterly Time-Series Forecasting With Neural Networks   总被引:2,自引:0,他引:2  
Forecasting of time series that have seasonal and other variations remains an important problem for forecasters. This paper presents a neural network (NN) approach to forecasting quarterly time series. With a large data set of 756 quarterly time series from the M3 forecasting competition, we conduct a comprehensive investigation of the effectiveness of several data preprocessing and modeling approaches. We consider two data preprocessing methods and 48 NN models with different possible combinations of lagged observations, seasonal dummy variables, trigonometric variables, and time index as inputs to the NN. Both parametric and nonparametric statistical analyses are performed to identify the best models under different circumstances and categorize similar models. Results indicate that simpler models, in general, outperform more complex models. In addition, data preprocessing especially with deseasonalization and detrending is very helpful in improving NN performance. Practical guidelines are also provided.  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