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   2063篇
  免费   43篇
  国内免费   4篇
电工技术   73篇
综合类   1篇
化学工业   592篇
金属工艺   46篇
机械仪表   31篇
建筑科学   37篇
能源动力   79篇
轻工业   127篇
水利工程   2篇
无线电   254篇
一般工业技术   337篇
冶金工业   329篇
原子能技术   54篇
自动化技术   148篇
  2023年   10篇
  2022年   24篇
  2021年   28篇
  2020年   19篇
  2019年   28篇
  2018年   24篇
  2017年   24篇
  2016年   39篇
  2015年   26篇
  2014年   34篇
  2013年   86篇
  2012年   53篇
  2011年   101篇
  2010年   68篇
  2009年   90篇
  2008年   81篇
  2007年   69篇
  2006年   78篇
  2005年   60篇
  2004年   66篇
  2003年   86篇
  2002年   56篇
  2001年   44篇
  2000年   48篇
  1999年   58篇
  1998年   140篇
  1997年   80篇
  1996年   73篇
  1995年   70篇
  1994年   51篇
  1993年   44篇
  1992年   38篇
  1991年   29篇
  1990年   26篇
  1989年   25篇
  1988年   25篇
  1987年   23篇
  1986年   19篇
  1985年   19篇
  1984年   16篇
  1983年   16篇
  1982年   12篇
  1981年   21篇
  1980年   14篇
  1979年   8篇
  1978年   6篇
  1977年   21篇
  1976年   12篇
  1975年   4篇
  1967年   3篇
排序方式: 共有2110条查询结果,搜索用时 15 毫秒
71.
Photo- and Electrochromism of Polyoxometalates and Related Materials   总被引:2,自引:0,他引:2  
Yamase T 《Chemical reviews》1998,98(1):307-326
  相似文献   
72.
Fe3+-ESR measurements are carried out for the samples of (La1–xSrx)2Cu1–yFeyO4–z. Peak-peak width Hpp of the signals decreases with falling temperature until minimum value and rises sharply with further decreasing temperature, which is approximated by Hpp = C0 +C1/T + BT. The Hpp behavior at high temperature and at low temperature can be analyzed by Korringa mechanism and slowing down of Fe3+ spin fluctuation, respectively. From the analysis of coefficient B's of Korringa terms, C0 and g-shift, it is revealed that the magnetic interaction of Fe3+ with hole carriers and Ce2+ spins depends strongly on hole density.  相似文献   
73.
The crop developmental stage represents essential information for irrigation scheduling/fertilizer management, understanding seasonal ecosystem carbon dioxide (CO2) exchange, and evaluating crop productivity. In this study, we devised an approach called the Two-Step Filtering (TSF) for detecting the phenological stages of maize and soybean from time-series Wide Dynamic Range Vegetation Index (WDRVI) data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) 250-m observations. The TSF method consists of a Two-Step Filtering scheme that includes: (i) smoothing the temporal WDRVI data with a wavelet-based filter and (ii) deriving the optimum scaling parameters from shape-model fitting procedure. The date of key crop development stages are then estimated by using the optimum scaling parameters and an initial value of the specific phenological date on the shape model, which are preliminary defined in reference to ground-based crop growth stage observations. The shape model is a crop-specific WDRVI curve with typical seasonal features, which were defined by averaging smoothed, multi-year WDRVI profiles from MODIS 250-m data collected over irrigated maize and soybean study sites.In this study, the TSF method was applied to MODIS-derived WDRVI data over a 6-year period (2003 to 2008) for two irrigated sites and one rainfed site planted to either maize or soybean as part of the Carbon Sequestration Program (CSP) at the University of Nebraska-Lincoln. A comparison of satellite-based retrievals with ground-based crop growth stage observations collected by the CSP over the six growing seasons for these three sites showed that the TSF method can accurately estimate the date of four key phenological stages of maize (V2.5: early vegetative stage, R1: silking stage, R5: dent stage and R6: maturity) and soybean (V1: early vegetative stage, R5: beginning seed, R6: full seed and R7: beginning maturity). The root mean square error (RMSE) of phenological-stage estimation for maize ranged from 2.9 [R1] to 7.0 [R5] days and from 3.2 [R6] to 6.9 [R7] days for soybean, respectively. In addition, the TSF method was also applied for two years (2001 and 2002) over eastern Nebraska to test its ability to characterize the spatio-temporal patterns of these key phenological stages over a larger geographic area. The MODIS-derived crop phenological stage dates agreed well with the statistical crop progress data reported by the United State Department of Agriculture (USDA) National Agricultural Statistics Service (NASS) for eastern Nebraska's three crop agricultural statistic districts (ASDs). At the ASD-level, the RMSE of phenological-stage estimation ranged from 1.6 [R1] to 5.6 [R5] days for maize and from 2.5 [R7] to 5.3 [R5] days for soybean.  相似文献   
74.
Biotechnology has drastically been advanced by the development of iPS and ES cells, which are representative forms induced pluripotent stem cells. In the micro/nano bio field, the development of cells and Taylor-made medicine for a potential treatment of incurable diseases has been a center of attention. The melting point of gelatin is between 25 and 33 °C, and the sol–gel transition occurs in low temperature. This makes the deformation of this useful biomaterial easy. The examples of gelatin fiber applications are suture threads, blood vessel prosthesis, cell-growth-based materials, filter materials, and many others. Because the cell size differs depending on the species and applications, it is essential to fabricate gelatin fibers of different diameters. In this paper, we have developed a fabrication method for gelatin fibers the coacervation method. We fabricated narrow gelatin fibers having a diameter over 10 μm.  相似文献   
75.
In recently developed intelligent vehicles, warning alarms are often used to prompt avoidance behaviours from drivers facing imminent hazardous situations. However, when critical reaction delays to auditory stimulation are anticipated, the alarm should be activated earlier to compensate for such delays. It was found that reaction times to an auditory stimulus significantly increased in the presence of slow eye movement (SEM), which is known to occur frequently during the wake-sleep transition. The reaction delay could not be attributed to temporal effects such as fatigue and was invariant regardless of response effectors (finger or foot). Moreover, it was found that applied pedal force decreased immediately after an auditory stimulus interrupted SEM. Consequently, it was concluded that SEM can be a good predictor of reaction delays to auditory warning alarms when drivers are in a drowsy state. STATEMENT OF RELEVANCE: The present study demonstrated that simple auditory reaction time significantly increased when SEM emerged. In the design of vehicle safety systems using warning alarms to prompt avoidance behaviours from drivers, such reaction delays during SEM must be taken into account.  相似文献   
76.
A novel method has been developed for measuring direct compressive properties such as strength and elasticity of a series of mesophase-pitch-based and PAN-based carbon fibres about 10 m in diameter by uniaxial and transverse compression tests using a micromechanical tester. The fibres were shaped into cylindrical specimens, with their size ratio of length to diameter kept at about 2 to 3, by separating them from a thin film made by polishing the cut faces of a strand of carbon fibres with epoxy resin as a matrix. Individual cylindrical specimens were stood up or laid down on a glass plate without any fixer for the measurements of axial and transverse compression properties of fibres, respectively. The fibres exhibited non-linear elasticity, with the compressive modulus decreasing with compressive deformation. The direct axial compressive strengths of pitch-based carbon fibres were found to be marginally lower than the indirect ones, whereas there was no significant difference between the two strength values for PAN-based fibres. The pitch-based fibres exhibited smaller average values of axial compressive strength than the PAN-based fibres. The transverse compressive strength, which decreases with an increase in elasticity of carbon fibres, exhibited a considerably lower average value than that of the axial compressive strength. Further, the axial compressive strength was found to be smaller than the direct tensile strength for the fibres.  相似文献   
77.
The suspension-preheater flash-furnace (SF) process for cement clinkering introduces a calcining flash furnace operating as an integral portion of a suspension preheater, rotary kiln, and clinker cooler system. Preheated raw meal from the suspension preheater is calcined in the flash furnace to 80 to 90 percent decarbonation. The capacity of the SF rotary kiln is increased thereby, since its function is limited to sintering rather than sintering and calcining. The flash furnace incorporates vortex flow to accomplish the mixing of fuel, raw meal, and gases. Effective distribution within the flash furnace limits temperature gradients and eliminates localized elevated temperatures that might otherwise lead to coating and material build-up. Hot combustion gases are recovered from the clinker cooler for use in the flash furnace. An orifice in the kiln gas exit duct serves to balance the parallel gas flows through the kiln and secondary air duct. Operating pressures and temperatures are described. The smaller size of the rotary kiln used in the SF process leads to extended refractory life as demonstrated by operating experience. The SF process is adaptable to the control of internal alkali, sulfur, and chlorine cycles through a gas bypass and through a unique material withdrawal arrangement from the flash furnace. Existing plants may be modified to incorporate the SF process. Nearly 20 commercial scale plants are operating or are being constructed.  相似文献   
78.
Biodegradable plastics can be used as conventional plastics, while on disposal they decompose to water and carbon dioxide by microorganisms existing in natural environment. Products using biodegradable plastics have recently been developed in many companies pursuing ecology. In this study, surface modification of biodegradable plastics was carried out by inert ion beams for improvement of photo deterioration under an ultraviolet ray. The hardness of biodegradable plastics tended generally to decrease with irradiation of an ultraviolet ray. In this method, the hardness of ion-bombarded biodegradable plastics was kept at an initial value under an ultraviolet ray, because the modified layer by ion bombardment intercepted an ultraviolet ray. The hardness of He+ ion-bombarded biodegradable plastics showed larger value than that of Ar+ ion bombardment. He+ ion bombardment at ion energy of 10 keV produced the suitable property with both of high transmittance of a visible ray and high interception of an ultraviolet ray in a surface layer of biodegradable plastics.  相似文献   
79.
Multirobot motion coordination in space and time   总被引:5,自引:0,他引:5  
This paper describes a solution to the multirobot motion planning problem based on a decoupled analysis in the space domain and in the time domain. It investigates the practical use of the notion of motion plan quality and of the motion plan robustness measures for computing safe motions. The use of anytime algorithms allows one to evaluate the opportunity of looking for alternative solution paths by generating small variations of robot motions affecting both its geometrical path and its scheduled velocity. By using the concept of plan robustness, several alternative paths are generated and evaluated through various performance indices and impact factors, using heuristic rules. These indices allow one to know how much a variation affects a given plan. Finally, some recent experiments are outlined.  相似文献   
80.
Sensor Fusion System Using Recurrent Fuzzy Inference   总被引:1,自引:0,他引:1  
In robotic and manufacturing systems, it is difficult to measure the state of systems accurately because of many uncertain factors and noise, and it is very important to estimate the state of systems. We must measure the phenomena of systems by multiple sensors and estimate the state of systems by acquiring information of sensors. However, we can not acquire all of sensor information synchronically, because each sensor has particular sensor information and measuring time. For estimating the state of systems by multiple sensors, a multi-sensor fusion system fusing various sensory information is needed. In this paper, we propose a Recurrent Fuzzy Inference (RFI) with recurrent inputs and apply it to a multi-sensor fusion system for estimating the state of systems. The membership functions of RFI are expressed by Radial Basis Function (RBF) with insensitive ranges. The shape of the membership functions can be adjusted by a learning algorithm. The learning algorithm is based on the steepest descent method and incremental learning which can add new fuzzy rules. The effectiveness of the multi-sensor fusion system using RFI will be shown through a numerical experiment of moving robot and estimation of surface roughness in grinding process.  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