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   1852篇
  免费   52篇
  国内免费   21篇
电工技术   33篇
综合类   4篇
化学工业   378篇
金属工艺   57篇
机械仪表   63篇
建筑科学   47篇
矿业工程   5篇
能源动力   111篇
轻工业   97篇
水利工程   28篇
石油天然气   6篇
无线电   206篇
一般工业技术   440篇
冶金工业   206篇
原子能技术   25篇
自动化技术   219篇
  2023年   27篇
  2022年   69篇
  2021年   92篇
  2020年   82篇
  2019年   63篇
  2018年   69篇
  2017年   80篇
  2016年   70篇
  2015年   50篇
  2014年   80篇
  2013年   138篇
  2012年   69篇
  2011年   94篇
  2010年   66篇
  2009年   81篇
  2008年   83篇
  2007年   57篇
  2006年   51篇
  2005年   20篇
  2004年   24篇
  2003年   29篇
  2002年   19篇
  2001年   18篇
  2000年   29篇
  1999年   30篇
  1998年   57篇
  1997年   36篇
  1996年   48篇
  1995年   20篇
  1994年   21篇
  1993年   30篇
  1992年   15篇
  1991年   23篇
  1990年   14篇
  1989年   21篇
  1988年   13篇
  1987年   16篇
  1986年   8篇
  1985年   19篇
  1984年   17篇
  1983年   10篇
  1982年   14篇
  1981年   6篇
  1980年   4篇
  1979年   10篇
  1978年   4篇
  1977年   8篇
  1976年   8篇
  1975年   4篇
  1974年   3篇
排序方式: 共有1925条查询结果,搜索用时 31 毫秒
31.
Tractor driving imposes a lot of physical and mental stress upon the operator. If the operator's seat is not comfortable, his work performance may be poor and there is also a possibility of accidents. The optimal design of tractor seat may be achieved by integrating anthropometric data with other technical features of the design. This paper reviews the existing information on the tractor seat design that considers anthropometry and biomechanical factors and gives an approach for seat design based on anthropometric data. The anthropometric dimensions, i.e. popliteal height sitting (5th percentile), hip breadth sitting (95th percentile), buttock popliteal length (5th percentile), interscye breadth (5th and 95th percentile) and sitting acromion height (5th percentile) of agricultural workers need to be taken into consideration for design of seat height, seat pan width, seat pan length, seat backrest width and seat backrest height, respectively, of a tractor. The seat dimensions recommended for tractor operator's comfort based on anthropometric data of 5434 Indian male agricultural workers were as follows: seat height of 380 mm, seat pan width of 420–450 mm, seat backrest width of 380–400 mm (bottom) and 270–290 mm (top), seat pan length of 370±10 mm, seat pan tilt of 5–7° backward and seat backrest height of 350 mm.

Relevance to industry

The approach presented in this paper for tractor seat design based on anthropometric considerations will help the tractor seat designers to develop and introduce seats suiting to the requirements of the user population. This will not only enhance the comfort of the tractor operators but may also help to reduce the occupational health problems of tractor operators.  相似文献   

32.

Data quality became significant with the emergence of data warehouse systems. While accuracy is intrinsic data quality, validity of data presents a wider perspective, which is more representational and contextual in nature. Through our article we present a different perspective in data collection and collation. We focus on faults experienced in data sets and present validity as a function of allied parameters such as completeness, usability, availability and timeliness for determining the data quality. We also analyze the applicability of these metrics and apply modifications to make it conform to IoT applications. Another major focus of this article is to verify these metrics on aggregated data set instead of separate data values. This work focuses on using the different validation parameters for determining the quality of data generated in a pervasive environment. Analysis approach presented is simple and can be employed to test the validity of collected data, isolate faults in the data set and also measure the suitability of data before applying algorithms for analysis. On analyzing the data quality of the two data sets on the basis of above-mentioned parameters. We show that validity for data set 1 was found to be 75% while it was found to be 67% only for data set 2. Availability and data freshness metrics performance were analyzed graphically. It was found that for data set 1, data freshness was better while availability metric was found better for data set 2. Usability obtained for data set 2 was 86% which was higher as compared to data set 1 whose usability metric was 69%. Thus, this work presents methods that can be leveraged for estimating data quality that can be beneficial in various IoT based industries which are essentially data centric and the decisions made by them depends upon the validity of data.

  相似文献   
33.
In this report, we studied various structural and optical properties of pure and copper-doped cadmium oxide (CdO) thin films. Nanostructured Cu-doped CdO films were deposited using sol–gel spin-coating technique. The structural and morphological changes have been observed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) studies. The optical and electrical properties of the pure and Cu-doped CdO thin films were studied by UV–vis spectroscopy and four-point probe method, respectively. The XRD peaks show the formation of nanocrystalline CdO with cubic face-centered crystal structure. The band gaps of the as deposited films were found in the range of 2.32–2.73 eV, while after doping, it decreases due to structural deformation. The electrical resitivity was found to decrease approximately ~10 in Cu-doped CdO thin films.  相似文献   
34.
Drawing planar graphs using the canonical ordering   总被引:4,自引:0,他引:4  
G. Kant 《Algorithmica》1996,16(1):4-32
We introduce a new method to optimize the required area, minimum angle, and number of bends of planar graph drawings on a grid. The main tool is a new type of ordering on the vertices and faces of triconnected planar graphs. Using this method linear-time-and-space algorithms can be designed for many graph-drawing problems. Our main results are as follows:
  • Every triconnected planar graphG admits a planar convex grid drawing with straight lines on a (2n?4)×(n?2) grid, wheren is the number of vertices.
  • Every triconnected planar graph with maximum degree 4 admits a planar orthogonal grid drawing on ann×n grid with at most [3n/2]+4 bends, and ifn>6, then every edge has at most two bends.
  • Every planar graph with maximum degree 3 admits a planar orthogonal grid drawing with at most [n/2]+1 bends on an [n/2]×[n/2] grid.
  • Every triconnected planar graphG admits a planar polyline grid drawing on a (2n?6)×(3n?9) grid with minimum angle larger than 2/d radians and at most 5n?15 bends, withd the maximum degree.
  • These results give in some cases considerable improvements over previous results, and give new bounds in other cases. Several other results, e.g., concerning visibility representations, are included.  相似文献   
    35.
    Intelligent computing system (ICS) and knowledge-based system (KBS) have been widely used in the detection and interpretation of EMG (electromyography) based diseases. Heuristic-based detection methods of EMG parameters for a particular disease have also been reported in the literature but little effort has been made by researchers to combine rule-based reasoning (RBR) and case-based reasoning of KBS, and ANN (artificial neural nets) of ICS. Integrating the methods in KBS and ICS improves the computational and reasoning efficiency of the problem-solving strategy. We have developed an integrated model of CBR and RBR for generating cases, and ANN for matching cases for the interpretation and diagnosis of neuromuscular diseases. We have hierarchically structured the neuromuscular diseases in terms of their physio-pyscho (muscular, cognitive and psychological) parameters and EMG based parameters (amplitude, duration, phase etc.). Cumulative confidence factor is computed at different node from lowest to highest level of hierarchal structure in the process of diagnosis of the neuromuscular diseases. The diseases considered are Duchenne muscular dystrophy, Polymyostits, Endocrine myopathy, Metabolic myopathy, Neuropathy, Poliomyletis and Myasthenia gravis. The basic objective of this work is to develop an integrated model of RBR, CBR and ANN in which RBR is used to hierarchically correlate the sign and symptom of the disease and also to compute cumulative confidence factor (CCF) of the diseases. CBR is used for diagnosing the neuromuscular diseases and to find the relative importance of sign and symptoms of a diseases to other diseases and ANN is used for matching process in CBR.  相似文献   
    36.
    Fractional advection–dispersion equation (FADE) is a generalization of the classical ADE in which the first order time derivative and first and second order space derivatives are replaced by Caputo derivatives of orders 0<α?1, 0<β?1 and 1<γ?2, respectively. We use Caputo definition to avoid (i) mass balance error, (ii) hyper-singular improper integral, (iii) non-zero derivative of constant, and (iv) fractional derivative involved in the initial condition which is often ill-defined. We present an analytic algorithm to solve FADE based on homotopy analysis method (HAM) which has the advantage of controlling the region and rate of convergence of the solution series via the auxiliary parameter ? over the variational iteration method (VIM) and homotopy perturbation method (HPM). We find that the proposed method converges to the numerical/exact solution of the ADE as the fractional orders α, β, γ tend to their integral values. Numerical examples are given to illustrate the proposed algorithm. Example 5 describes the intermediate process between advection and dispersion via Caputo fractional derivative.  相似文献   
    37.
    A 33.7 MHz heavy-ion radio frequency quadrupole (RFQ) linear accelerator has been designed, built, and tested. It is a four-rod-type RFQ designed for acceleration of 1.38 keVu, qA> or =116 ions to about 29 keVu. Transmission efficiencies of about 85% and 80% have been measured for the unanalyzed and analyzed beams, respectively, of oxygen ((16)O(2+), (16)O(3+), (16)O(4+)), nitrogen ((14)N(3+), (14)N(4+)), and argon ((40)Ar(4+)). The system design and measurements along with results of beam acceleration test will be presented.  相似文献   
    38.
    Concurrent programs that embed specifications of synchronizations in the body of their component are difficult to extend and modify. Small changes in a concurrent program, particularly changes in the interactions among components, may require re-implementation of a large number of components. Even specifications of components cannot be reused easily. This paper presents a concurrent program composition mechanism in which both specification and implementation of computations and interactions are completely separated. Separation of specifications and implementations facilitates extensions and modifications of programs by allowing one to separately change the implementations of computations and interactions. It also supports their reusability. The paper also describes the design and implementation of a concurrent object-oriented programming language based on this model, including a compiler for the language, and reports on the execution behavior of programs written in the language.  相似文献   
    39.
    Quantitative proteomics can be used for the identification of cancer biomarkers that could be used for early detection, serve as therapeutic targets, or monitor response to treatment. Several quantitative proteomics tools are currently available to study differential expression of proteins in samples ranging from cancer cell lines to tissues to body fluids. 2-DE, which was classically used for proteomic profiling, has been coupled to fluorescence labeling for differential proteomics. Isotope labeling methods such as stable isotope labeling with amino acids in cell culture (SILAC), isotope-coded affinity tagging (ICAT), isobaric tags for relative and absolute quantitation (iTRAQ), and (18) O labeling have all been used in quantitative approaches for identification of cancer biomarkers. In addition, heavy isotope labeled peptides can be used to obtain absolute quantitative data. Most recently, label-free methods for quantitative proteomics, which have the potential of replacing isotope-labeling strategies, are becoming popular. Other emerging technologies such as protein microarrays have the potential for providing additional opportunities for biomarker identification. This review highlights commonly used methods for quantitative proteomic analysis and their advantages and limitations for cancer biomarker analysis.  相似文献   
    40.
    Creep fracture behaviour of pure aluminium-matrix composites with 10–30 vol% SiC particulates at 623 K is reported. A comparison of tensile and compression creep data shows the existence of a transition stress. Above this transition stress no steady state creep is observed in tension. This transition stress is related to a transition from intergranular to transgranular fracture. The origin of transition stress is perhaps associated with the diffusional relaxation of stress concentration at the matrix/particle interface by lattice diffusion. The intergranular creep fracture of composites appears to be similar to that of unreinforced aluminium and it is power-law creep controlled. The transgranular creep fracture occurs by void nucleation and growth. The nucleation strain for voids is quite small and hence the tertiary stage starts before the end of the primary stage. The ductile fracture models overestimate the strain to fracture and do not predict the observed stress dependence of strain to fracture.  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