全文获取类型
收费全文 | 15486篇 |
免费 | 1841篇 |
国内免费 | 951篇 |
专业分类
电工技术 | 1590篇 |
技术理论 | 5篇 |
综合类 | 1287篇 |
化学工业 | 1428篇 |
金属工艺 | 797篇 |
机械仪表 | 1199篇 |
建筑科学 | 2903篇 |
矿业工程 | 1334篇 |
能源动力 | 681篇 |
轻工业 | 276篇 |
水利工程 | 757篇 |
石油天然气 | 522篇 |
武器工业 | 153篇 |
无线电 | 1167篇 |
一般工业技术 | 1640篇 |
冶金工业 | 683篇 |
原子能技术 | 225篇 |
自动化技术 | 1631篇 |
出版年
2024年 | 53篇 |
2023年 | 247篇 |
2022年 | 436篇 |
2021年 | 562篇 |
2020年 | 557篇 |
2019年 | 456篇 |
2018年 | 422篇 |
2017年 | 579篇 |
2016年 | 664篇 |
2015年 | 716篇 |
2014年 | 1249篇 |
2013年 | 980篇 |
2012年 | 1304篇 |
2011年 | 1260篇 |
2010年 | 987篇 |
2009年 | 944篇 |
2008年 | 786篇 |
2007年 | 977篇 |
2006年 | 818篇 |
2005年 | 720篇 |
2004年 | 572篇 |
2003年 | 486篇 |
2002年 | 429篇 |
2001年 | 445篇 |
2000年 | 303篇 |
1999年 | 268篇 |
1998年 | 188篇 |
1997年 | 179篇 |
1996年 | 129篇 |
1995年 | 131篇 |
1994年 | 117篇 |
1993年 | 51篇 |
1992年 | 46篇 |
1991年 | 44篇 |
1990年 | 41篇 |
1989年 | 26篇 |
1988年 | 22篇 |
1987年 | 19篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
This paper addresses the problem of designing controllers that are robust to a great uncertainty in a time constant of the plant. Plants must be represented by minimum phase rational transfer functions of an arbitrary order. The design specifications are: (1) a phase margin for the nominal plant, (2) a gain crossover frequency for the nominal plant, (3) zero steady state error to step commands, and (4) a constant phase margin for all the possible values of the time constant (T): 0<T<∞. We propose a theorem that defines the structure of the set of controllers that fulfil these specifications and show that it is necessary for these robust controllers to include a fractional-order PI term. Examples are developed for both stable and unstable plants, and the results are compared with a standard PI controller and a robust controller designed using the QFT methodology. 相似文献
102.
针对工程等级高、过水流量大、抗震设防要求高的引水工程,渡槽结构型式选择存在工程技术难题,根据引水工程渡槽槽墩较高、荷载大、结构断面大、沉降变形影响因素较为复杂特点,进行了渡槽支承型式、槽身截面形式、渡槽墩身的比选。结果表明:简支结构具有减少施工难度和不均匀沉降对槽体结构应力影响,简化结构受力条件,简支结构较为有利优点。空心重力墩具有节省材料,充分利用材料强度,刚度较大,墩身质量较轻,抗震能力和抗冲击强,高度较大优点,对类似工程设计具有参考意义。 相似文献
103.
《Expert systems with applications》2014,41(15):6596-6610
The Bayesian learning provides a natural way to model the nonlinear structure as the artificial neural networks due to their capability to cope with the model complexity. In this paper, an evolutionary Monte Carlo (MC) algorithm is proposed to train the Bayesian neural networks (BNNs) for the time series forecasting. This approach called as Genetic MC is based on Gaussian approximation with recursive hyperparameter. Genetic MC integrates MC simulations with the genetic algorithms and the fuzzy membership functions. In the implementations, Genetic MC is compared with the traditional neural networks and time series techniques in terms of their forecasting performances over the weekly sales of a Finance Magazine. 相似文献
104.
借助Lyapunov函数稳定性理论和最优化理论研究了永磁同步电动机系统解的界,得到了它的界估计。通过计算机模拟,数值模拟验证了计算理论的可行性。 相似文献
105.
106.
We determined the optimal reaction conditions to minimize the energy cost and the quantities of by‐products for a poly(ethylene terephthalate) process by using the iterative dynamic programming (IDP) algorithm. Here, we employed a sequence of three reactor models: the semibatch transesterification reactor model, the semibatch prepolymerization reactor model, and the rotating‐disc‐type polycondensation reactor model. We selectively chose or developed the reactor models by incorporating experimentally verified kinetic models reported in the literature. We established the model for the entire reactor system by connecting the three reactor models in series and by resolving some joint problems arising when different types of reactor models were interconnected. On the basis of the simulation results of the reactor system, we scrutinized the cause and effect between the reaction conditions and the final quality of the polymer product. Here, we set up the optimization strategy by using IDP on the basis of the integrated reactor model, and the process variables with significant influence on the properties of polymer were selected as control variables with the help of a simulation study. With this method, we could refine the reaction conditions at the end of each iteration step by contracting the spectra of control regions, and the iteration process finally stopped when the profile of the optimal trajectory converged. We also took the constraints on the control variables into account to guarantee polymer quality and to suppress side reactions. Constituting six different strategies by setting weighting vectors differently, we examined the differences in optimal trajectories, the trend of optimality, and the quality of the final polymer product. For each of the strategies, we conducted the optimization to examine whether the number‐average degree of polymerization approached the desired value. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 993–1008, 2002 相似文献
107.
J. Popplewell 《Chemical Engineering Communications》1988,67(1):243-257
Magnetic measurements on ferrofluids can be used to determine the magnetic concentration which may be as large as 15% by volume in a very viscous fluid. Additional information on the particle size distribution parameters and the mode of magnetisation can be obtained from an analysis of the magnetisation curve. Magnetic studies are also invaluable for a correct interpretation of the magnetic dichroism, birefringence and small angle neutron scattering (SANS) data. Measurements on a ferrofluid after freezing enables the shape anisotropy to be determined and the degree of particle elongation (∼15%) calculated. 相似文献
108.
结合遥感影像、野外调查和水沙数据,以冲积大河为研究对象,分析中国大河的河型分布及成因。中国大河的冲积河段以弯曲与辫状河型为主,局部河段为分汊与网状河型。综合考虑河型分布的一般性和特殊性,认为相对输沙率(来沙量与输沙能力之比)、相对河岸侵蚀切应力(近岸水流切应力与河岸临界抗冲切应力之比)和河谷地形控制(如节点和宽度)是决定河型成因的3个最主要的因素。 相似文献
109.
110.