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   9076篇
  免费   550篇
  国内免费   21篇
电工技术   125篇
综合类   18篇
化学工业   2359篇
金属工艺   171篇
机械仪表   207篇
建筑科学   321篇
矿业工程   36篇
能源动力   223篇
轻工业   402篇
水利工程   68篇
石油天然气   28篇
无线电   758篇
一般工业技术   2287篇
冶金工业   982篇
原子能技术   78篇
自动化技术   1584篇
  2023年   153篇
  2022年   374篇
  2021年   418篇
  2020年   285篇
  2019年   246篇
  2018年   301篇
  2017年   255篇
  2016年   349篇
  2015年   298篇
  2014年   438篇
  2013年   550篇
  2012年   547篇
  2011年   623篇
  2010年   423篇
  2009年   412篇
  2008年   433篇
  2007年   416篇
  2006年   324篇
  2005年   252篇
  2004年   222篇
  2003年   201篇
  2002年   192篇
  2001年   122篇
  2000年   113篇
  1999年   119篇
  1998年   193篇
  1997年   155篇
  1996年   105篇
  1995年   83篇
  1994年   73篇
  1993年   90篇
  1992年   53篇
  1991年   50篇
  1990年   50篇
  1989年   37篇
  1988年   44篇
  1987年   40篇
  1986年   34篇
  1985年   42篇
  1984年   38篇
  1983年   32篇
  1982年   27篇
  1981年   27篇
  1980年   23篇
  1979年   19篇
  1978年   28篇
  1977年   24篇
  1976年   60篇
  1975年   28篇
  1971年   19篇
排序方式: 共有9647条查询结果,搜索用时 15 毫秒
991.
This paper presents an optimization procedure which has been developed to select appropriate suspension design parameters for a simple two wheel trailer. A modern approach to the optimization problem has been used applying non-linear programming to the constrained search for the minimum of an objective function. The acceleration response to roadway input of selected points on the load of the trailer has been designated for minimization. This acceleration has an important significance to the trailer design because of its effect on the stable and smooth ride of the trailer. Two computational procedures have been used and the results compared. The first approach involves the linear superposition of responses to a series of discrete sinusoidal inputs while the second applies more contemporary random vibration theory using power spectral density curves to simulate the actual road surfaces. The results of the optimization procedure are then compared with the response characteristics of the original trailer design and demonstrate that a substantial improvement has been made.  相似文献   
992.
One of the commercial challenges today in the gem industry is to quickly identify the origin of color in pink diamonds — natural, treated and synthetic by use of standard and advanced gemological instruments.An analytical technique that is used by many gem labs involves UV fluorescence. The principle factors in the technique are the excitation wavelengths and the emission spectra. No systematic study of fluorescence of pink natural diamonds, pink treated and pink synthetic diamonds has been undertaken. This study is mainly focused on using fluorescence techniques to characterize pink diamonds and to compile a reference library of emission spectra. Longwave (LW) and shortwave (SW) fluorescence of 365, 254 and 220 nm illumination were used in a custom built microscope with a fluorescence camera to record images and a spectrometer to record spectral data with which to establish a correlation with the cause of color.Other advanced instruments (CL imaging, UV–VIS–NIR, FTIR, PL spectroscopy and electrical conductance) were used to establish additional criteria for distinguishing natural, treated and synthetic pink diamonds and to find a correlation with the “EGL USA CIS (Cross-reference Identification System) fluorescence method”.  相似文献   
993.
Chromatographic evidence is presented to show that a methyl-S-methionine sulphonium salt is present in fermented and dried cacao. It is extremely labile and readily decomposes to dimethyl sulphide which contributes to chocolate aroma.  相似文献   
994.
Deoiled herring silage contained an average of 17.6% dry matter (DM) and per 100 g DM: 1.86 MJ GE, 12.1 g N, 5.5 g available lysine and 3.7 g oil. The apparent digestibility coefficients for growing pigs of gross energy (GE) and nitrogen (N) for a diet containing 25% herring silage DM and 75% barley meal DM were 0.83 and 0.91, and the efficiency of retention for digested N was 0.42. The digestible energy (DE) value for the deoiled herring silage was 17.9 MJ DE/kg DM and the digestible nitrogen (DN) value was 119 g DN/kg DM.  相似文献   
995.
Using previously reported methods of sample preparation an essence of coriander leaf was obtained which proved to contain over 25 components. Most of these have been identified, with aliphatic aldehydes providing nearly 90% of the sample. C12 aldehydes are the most abundant.  相似文献   
996.
Using previously reported methods of sample preparation an essence of garden cress was obtained which proved to contain only 11 components. Eight have been identified, all glucosinolate degradation products (isothiocyanates and nitriles), and provide over 95% of the sample. Benzyl derivatives, from glucotropaeolin, are the most abundant. No thiocyanates were obtained.  相似文献   
997.
A method is described by which the S-methylcysteine sulphoxide content of plant material may be determined approximately in a large number of samples with little labour, apparatus or staff. The presence of SMCO in some plants and its absence in others was confirmed and the method was sufficiently sensitive to reveal varietal differences within a species.  相似文献   
998.
Decentralised water supply systems are becoming increasingly affordable and commonplace in Australia and have the potential to alleviate urban water shortages and reduce pollution into natural receiving marine and freshwater streams. Learning processes are necessary to support the efficient implementation of decentralised systems. These processes reveal the complex socio-technical and institutional factors to be considered when developing an enabling environment supporting decentralised water and wastewater servicing solutions. Critical to the technological transition towards established decentralised systems is the ability to create strategic and adaptive capacity to promote learning and dialogue. Learning processes require institutional mechanisms to ensure the lessons are incorporated into the formulation of policy and regulation, through constructive involvement of key government institutions. Engagement of stakeholders is essential to the enabling environment. Collaborative learning environments using systems analysis with communities (social learning) and adaptive management techniques are useful in refining and applying scientists' and managers' knowledge (knowledge management).  相似文献   
999.
As the economy becomes global and ICT-reliant, approaches practiced in enterprise software product development and enterprise resource planning (ERP) system implementation must cope with increasingly complex situations induced by contemporary supply chain and regulations. Compliance with regulations in the market is one aspect of the requirements that enterprise software must meet. Recent research of KPMG IT Advisory has confirmed that where little attention is being paid to the value-added tax (VAT) issues during large ERP projects, there is a higher VAT-risk exposure. In a design-oriented approach, we first identify the stakeholders and their interests in the VAT compliance of ERP systems. Enterprise architecture (EA) and model driven engineering in a multi-level perspective serve as the source of solution patterns. The efficient solution of compliance problems builds upon stakeholders utilizing a set of interdependent models and methods that are suitably allocated to the public and proprietary domains.  相似文献   
1000.
The exact mechanisms relating exposure to ultraviolet (UV) radiation and elevated risk of skin cancer remain the subject of debate. For example, there is disagreement on whether the main risk factor is duration of the exposure, its intensity, or some combination of both. There is also uncertainty regarding the form of the dose-response curve, with many authors believing only exposures exceeding a given (but unknown) threshold are important. This paper explores methods to estimate such thresholds using hierarchical spatial logistic models based on a sample of a cohort of x-ray technologists for whom self-reports of time spent in the sun and numbers of blistering sunburns in childhood are available. A preliminary goal is to explore the temporal pattern of UV exposure and its gradient. Changes would imply that identical exposure self-reports from different calendar years may correspond to differing cancer risks.  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