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   1643篇
  免费   56篇
  国内免费   10篇
电工技术   23篇
综合类   2篇
化学工业   362篇
金属工艺   44篇
机械仪表   52篇
建筑科学   34篇
矿业工程   2篇
能源动力   97篇
轻工业   122篇
水利工程   12篇
石油天然气   4篇
无线电   214篇
一般工业技术   358篇
冶金工业   167篇
原子能技术   17篇
自动化技术   199篇
  2024年   5篇
  2023年   28篇
  2022年   71篇
  2021年   89篇
  2020年   77篇
  2019年   57篇
  2018年   89篇
  2017年   67篇
  2016年   76篇
  2015年   46篇
  2014年   63篇
  2013年   118篇
  2012年   71篇
  2011年   87篇
  2010年   67篇
  2009年   42篇
  2008年   53篇
  2007年   67篇
  2006年   32篇
  2005年   31篇
  2004年   23篇
  2003年   14篇
  2002年   27篇
  2001年   24篇
  2000年   14篇
  1999年   18篇
  1998年   41篇
  1997年   42篇
  1996年   26篇
  1995年   13篇
  1994年   15篇
  1993年   16篇
  1992年   11篇
  1991年   16篇
  1990年   8篇
  1989年   8篇
  1988年   9篇
  1987年   10篇
  1986年   11篇
  1985年   8篇
  1984年   13篇
  1983年   11篇
  1982年   6篇
  1981年   10篇
  1980年   8篇
  1979年   9篇
  1978年   9篇
  1977年   10篇
  1976年   16篇
  1973年   5篇
排序方式: 共有1709条查询结果,搜索用时 15 毫秒
11.
Several studies have indicated that slip-resistant shoes may have a positive effect on reducing the risk of slips and falls, a leading cause of injury at work. Few studies, however, have examined how duration of shoe usage affects their slip-resistance properties. This study examined the association between the duration of slip-resistant shoes usage and the self-reported rate of slipping in limited-service restaurant workers. A total of 475 workers from 36 limited-service restaurants in the USA were recruited to participate in a 12-week prospective study of workplace slipping. Of the 475 participants, 83 reported changing to a new pair of shoes at least once during the 12-week follow-up. The results show that slip-resistant shoes worn for less than six months were moderately more effective than those worn for more than six months. Changing to a new pair of shoes among those wearing slip-resistant shoes at baseline was associated with a 55% reduction in the rate of slipping (RR = 0.45, 95% CI = 0.23–0.89). Further research is needed to develop criteria for the replacement of slip-resistant shoes.

Practitioner Summary: The duration of usage impacts the slip-resistance properties of slip-resistant shoes. Slip-resistant shoes worn for less than six months were moderately more effective in reducing slips than slip-resistant shoes worn for more than six months. Shoe use policies should not only encourage or require their use but also include guidance on replacing slip-resistant shoes at regular intervals.  相似文献   

12.
The aqueous polymerization of acrylamide initiated by potassium permanganate/β-hydroxybutyric acid has been studied volumetrically at 35 ± 0.01°C in an inert medium. The rate of polymerization shows nearly square root dependence on β-hydroxybutyric acid at low concentration (3.12 – 12.5 · 10?3 mol dm?3). The order with respect to potassium permanganate has been found to be 0.6 indicating thereby a bimolecular mode of termination. The polymerization rate has been varied linearly at low monomer concentrations i.e. from 2.5 –7.0 · 10?2 mol dm?3. The dependence of number average degree of polymerization on the initial rate of polymerization and temperature has been determined. The over-all activation energy has been found to be 51.66 kJ mol?1. A kinetic reaction scheme is proposed on the basis of experimental results.  相似文献   
13.
Summary The mixed boundary-values problem of elasticity with parabolic boundary when the prescribed displacement is parabolic has been reduced to the solution of the non-homogeneous Hilbert problem following the method of complex variable. The result has been compared with that obtained byParia [5] for parabolic boundary with prescribed constant displacement as a particular case.
Zusammenfassung Das gemischte Randwertproblem der Elastizitätstheorie wird für parabolische Berandung auf die Lösung des inhomogenen Hilbert-Problems unter Benützung der komplexen Methode zurückgeführt. Die Randverschiebung wird durch ein Polynom zweiten Grades dargestellt. Das Ergebnis wird mit dem vonParia [5] verglichen, das als Sonderfall konstante Verschiebungen am parabolischen Rand vorschreibt.
  相似文献   
14.
15.
This paper investigates a new method to solve the inverse problem of Rutherford backscattering (RBS) data. The inverse problem is to determine the sample structure information from measured spectra, which can be defined as a function approximation problem. We propose using radial basis function (RBF) neural networks to approximate an inverse function. Each RBS spectrum, which may contain up to 128 data points, is compressed by the principal component analysis, so that the dimensionality of input data and complexity of the network are reduced significantly. Our theoretical consideration is tested by numerical experiments with the example of the SiGe thin film sample and corresponding backscattering spectra. A comparison of the RBF method with multilayer perceptrons reveals that the former has better performance in extracting structural information from spectra. Furthermore, the proposed method can handle redundancies properly, which are caused by the constraint of output variables. This study is the first method based on RBF to deal with the inverse RBS data analysis problem.  相似文献   
16.
The Journal of Supercomputing - In the Attribute-Based Encryption (ABE) scheme, patients encrypt their electronic health record (EHR), attach the appropriate attributes with it, and outsource them...  相似文献   
17.
Cloud computing is an Information Technology deployment model established on virtualization. Task scheduling states the set of rules for task allocations to an exact virtual machine in the cloud computing environment. However, task scheduling challenges such as optimal task scheduling performance solutions, are addressed in cloud computing. First, the cloud computing performance due to task scheduling is improved by proposing a Dynamic Weighted Round-Robin algorithm. This recommended DWRR algorithm improves the task scheduling performance by considering resource competencies, task priorities, and length. Second, a heuristic algorithm called Hybrid Particle Swarm Parallel Ant Colony Optimization is proposed to solve the task execution delay problem in DWRR based task scheduling. In the end, a fuzzy logic system is designed for HPSPACO that expands task scheduling in the cloud environment. A fuzzy method is proposed for the inertia weight update of the PSO and pheromone trails update of the PACO. Thus, the proposed Fuzzy Hybrid Particle Swarm Parallel Ant Colony Optimization on cloud computing achieves improved task scheduling by minimizing the execution and waiting time, system throughput, and maximizing resource utilization.  相似文献   
18.
The Cu2Zn1?xCdxSnS4 quinternary alloy nanostructures with different Cd contents were grown using spin coating technique on porous silicon (63.93 %) substrate. The structural properties of Cu2Zn1?xCdxSnS4/PS were investigated by X-ray diffraction and field emission-scanning electron microscope (FE-SEM). The optical properties studied through photoluminescence technique, indicated that the band gap is shifted as Cd content increases from 1.84 eV at x = 0 to 1.76 eV at x = 1. The electrical characterization of the Ag/n-PS/Cu2Zn1?xCdxSnS4/Ag diode through current to voltage (I–V) characterization shows the highest photo-response of (value if any) at Cu2Zn0.4Cd0.6SnS4 composition.  相似文献   
19.
A novel bacterial foraging technique for edge detection   总被引:2,自引:0,他引:2  
A new approach for edge detection using a combination of bacterial foraging algorithm (BFA) and probabilistic derivative technique derived from Ant Colony Systems, is presented in this paper. The foraging behavior of some species of bacteria like Escherichia coli can be hypothetically modeled as an optimization process. A group of bacteria search for nutrients in a way that maximizes the energy obtained per unit time spent during the foraging. The proposed approach aims at driving the bacteria through the edge pixels. The direction of movement of the bacteria is found using a direction probability matrix, computed using derivatives along the possible directions. Rules defining the derivatives are devised to ensure that the variation of intensity due to noise is discarded. Quantitative analysis of the feasibility of the proposed approach and its comparison with other standard edge detection operators in terms of kappa and entropy are given. The effect of initial values of parameters of BFA on the edge detection is discussed.  相似文献   
20.
The Internet infrastructure must evolve from best-effort service to meet the needs of different customers and applications. With Internet traffic differentiation, service providers can support a range of offerings, such as loss or delay bounds and network bandwidth allocation, to meet different performance requirements. The differentiated services (Diffserv) architecture provides a scalable approach, in which network access (or edge) devices aggregate traffic flows onto provisioned pipes that traverse a streamlined network core. We have identified the key requirements for provisioning Diffserv functions on Internet servers. Based on these requirements, we have implemented, and deployed, a policy-based architecture on IBM's AIX operating system that provides Diffserv services to both QoS-aware and -unaware applications  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