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   18977篇
  免费   677篇
  国内免费   44篇
电工技术   237篇
综合类   24篇
化学工业   3739篇
金属工艺   468篇
机械仪表   397篇
建筑科学   948篇
矿业工程   108篇
能源动力   600篇
轻工业   1634篇
水利工程   172篇
石油天然气   68篇
无线电   1457篇
一般工业技术   3365篇
冶金工业   3424篇
原子能技术   116篇
自动化技术   2941篇
  2023年   123篇
  2022年   210篇
  2021年   330篇
  2020年   234篇
  2019年   270篇
  2018年   368篇
  2017年   378篇
  2016年   413篇
  2015年   338篇
  2014年   513篇
  2013年   1218篇
  2012年   825篇
  2011年   1166篇
  2010年   799篇
  2009年   829篇
  2008年   930篇
  2007年   871篇
  2006年   759篇
  2005年   743篇
  2004年   594篇
  2003年   541篇
  2002年   526篇
  2001年   332篇
  2000年   303篇
  1999年   328篇
  1998年   355篇
  1997年   298篇
  1996年   326篇
  1995年   303篇
  1994年   289篇
  1993年   262篇
  1992年   259篇
  1991年   162篇
  1990年   230篇
  1989年   203篇
  1988年   167篇
  1987年   166篇
  1986年   156篇
  1985年   187篇
  1984年   197篇
  1983年   162篇
  1982年   170篇
  1981年   168篇
  1980年   143篇
  1979年   165篇
  1978年   123篇
  1977年   121篇
  1976年   162篇
  1975年   125篇
  1973年   108篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Integrating working and learning is seen as a desirable alternative to traditional training regimes. An integrated approach to working and learning is more gradual, contextual, problem oriented and cost effective. Knowledge technology aims to catalyze workplace learning, but requires the right organisational culture and brings additional costs regarding the articulation, representation and transmission of knowledge. Our approach reduces these costs by making articulation a natural part of collaborative working, designing for both informal and formal knowledge, and facilitating the transition of socially situated knowledge through enriched documents. To be successful, our approach has certain prequesites concerning organisational culture, and the nature of shared documents, organisational knowledge and work activities.  相似文献   
72.
73.
The surface of glass beads of average particle size 100m was modified (a) by incorporating extra hydroxyl groups by chemcial treatment, and (b) by applying a thin coating of polymethacrylic acid (PMA) on the glass surface. The corresponding chemical changes were investigated using infrared spectroscopy. The tensile behaviour of a glass bead-filled PVC composite prepared with surface-modified glass beads, showed the following effects: (a) hydroxyl groups incorporated on to the glass surface did not affect the glass-PVC interface and hence did not change the tensile behaviour of the composite; (b) PMA coating on the glass surface caused improvement in the tensile behaviour in the low strain region and deterioration in the high region. An SEM study of the fractured surface suggested debonding at the glass-PVC interface in the first case, and failure of the PVC-PMA interface in the second case.  相似文献   
74.
Normalized Difference Vegetation Index (NDVI), which is a measure of vegetation vigour, and lake water levels respond variably to precipitation and its deficiency. For a given lake catchment, NDVI may have the ability to depict localized natural variability in water levels in response to weather patterns. This information may be used to decipher natural from unnatural variations of a given lake’s surface. This study evaluates the potential of using NDVI and its associated derivatives (VCI (vegetation condition index), SVI (standardised vegetation index), AINDVI (annually integrated NDVI), green vegetation function (F g ), and NDVIA (NDVI anomaly)) to depict Lake Victoria’s water levels. Thirty years of monthly mean water levels and a portion of the Global Inventory Modelling and Mapping Studies (GIMMS) AVHRR (Advanced Very High Resolution Radiometer) NDVI datasets were used. Their aggregate data structures and temporal co-variabilities were analysed using GIS/spatial analysis tools. Locally, NDVI was found to be more sensitive to drought (i.e., responded more strongly to reduced precipitation) than to water levels. It showed a good ability to depict water levels one-month in advance, especially in moderate to low precipitation years. SVI and SWL (standardized water levels) used in association with AINDVI and AMWLA (annual mean water levels anomaly) readily identified high precipitation years, which are also when NDVI has a low ability to depict water levels. NDVI also appears to be able to highlight unnatural variations in water levels. We propose an iterative approach for the better use of NDVI, which may be useful in developing an early warning mechanisms for the management of lake Victoria and other Lakes with similar characteristics.  相似文献   
75.
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   
76.
随着对能源问题和环境问题的日益重视,各种可替代传统石化能源方式的新能源方式纷纷涌现。其中,太阳能是一种资源最丰富的可再生清洁能源,而且可以认为是一种用之不竭的能源方式。近年来,太阳能发电技术也进入快速发展的时期。而且与新兴的纳米技术相结合,有望为绿色能源的发展带来革命性的变化。  相似文献   
77.
Single-chip heterogeneous multiprocessors (SCHMs) are arising to meet the computational demands of portable and handheld devices. These computing systems are not fully custom designs traditionally targeted by the design automation community, general-purpose designs traditionally targeted by the computer architecture community, nor pure embedded designs traditionally targeted by the real-time community. An entirely new design philosophy will be needed for this hybrid class of computing. The programming of the device will be drawn from a narrower set of applications with execution that persists in the system over a longer period of time than for general-purpose programming. However, the devices will still be programmable, not only at the level of the individual processing element, but across multiple processing elements and even the entire chip. The design of other programmable single chip computers has enjoyed an era where the design tradeoffs could be captured in simulators such as SimpleScalar and performance could be evaluated to the SPEC benchmarks. Motivated by this, we describe new benchmark-based design strategies for SCHMs which we refer to as scenario-oriented design. We include an example and results.  相似文献   
78.
On September 11, 2001, an airliner was intentionally crashed into the Pentagon. It struck at the first elevated slab on the west wall, and slid approximately 310?ft (94.5?m) diagonally into the building. The force of the collision demolished numerous columns and the fa?ade of the exterior wall, and induced damage to first-floor columns and the first elevated slab over an area approximately 90?ft (27.4?m) wide and 310?ft (94.5?m) long. None of the building collapsed immediately. The portion that remained standing, even after an intense fire, sustained substantial damage at the first-floor level.  相似文献   
79.
The present study presents a methodology for detailed reliability analysis of nuclear containment without metallic liners against aircraft crash. For this purpose, a nonlinear limit state function has been derived using violation of tolerable crack width as failure criterion. This criterion has been considered as failure criterion because radioactive radiations may come out if size of crack becomes more than the tolerable crack width. The derived limit state uses the response of containment that has been obtained from a detailed dynamic analysis of nuclear containment under an impact of a large size Boeing jet aircraft. Using this response in conjunction with limit state function, the reliabilities and probabilities of failures are obtained at a number of vulnerable locations employing an efficient first-order reliability method (FORM). These values of reliability and probability of failure at various vulnerable locations are then used for the estimation of conditional and annual reliabilities of nuclear containment as a function of its location from the airport. To study the influence of the various random variables on containment reliability the sensitivity analysis has been performed. Some parametric studies have also been included to obtain the results of field and academic interest.  相似文献   
80.
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