全文获取类型
收费全文 | 42689篇 |
免费 | 3551篇 |
国内免费 | 1794篇 |
专业分类
电工技术 | 2411篇 |
技术理论 | 1篇 |
综合类 | 3092篇 |
化学工业 | 7238篇 |
金属工艺 | 2246篇 |
机械仪表 | 2444篇 |
建筑科学 | 2971篇 |
矿业工程 | 1072篇 |
能源动力 | 1159篇 |
轻工业 | 3516篇 |
水利工程 | 871篇 |
石油天然气 | 2530篇 |
武器工业 | 304篇 |
无线电 | 4925篇 |
一般工业技术 | 5012篇 |
冶金工业 | 2046篇 |
原子能技术 | 501篇 |
自动化技术 | 5695篇 |
出版年
2024年 | 160篇 |
2023年 | 633篇 |
2022年 | 1090篇 |
2021年 | 1586篇 |
2020年 | 1230篇 |
2019年 | 1039篇 |
2018年 | 1170篇 |
2017年 | 1362篇 |
2016年 | 1189篇 |
2015年 | 1639篇 |
2014年 | 2109篇 |
2013年 | 2518篇 |
2012年 | 2830篇 |
2011年 | 3035篇 |
2010年 | 2754篇 |
2009年 | 2650篇 |
2008年 | 2640篇 |
2007年 | 2540篇 |
2006年 | 2482篇 |
2005年 | 2129篇 |
2004年 | 1473篇 |
2003年 | 1266篇 |
2002年 | 1189篇 |
2001年 | 977篇 |
2000年 | 958篇 |
1999年 | 948篇 |
1998年 | 809篇 |
1997年 | 717篇 |
1996年 | 685篇 |
1995年 | 515篇 |
1994年 | 411篇 |
1993年 | 315篇 |
1992年 | 242篇 |
1991年 | 197篇 |
1990年 | 125篇 |
1989年 | 109篇 |
1988年 | 97篇 |
1987年 | 52篇 |
1986年 | 45篇 |
1985年 | 30篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1959年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Feng Yang Mingming Yang Qiong Xia Liang Liang 《International Transactions in Operational Research》2016,23(6):1025-1050
Mathematical models are described for collaborative distribution between two logistics service providers (LSPs). We find that (a) collaborative distribution is conditionally profitable for LSPs, and the conditions for cooperation are given; (b) LSPs save more costs primarily by shortening the delivery distance and decreasing delivery speed; (c) collaborative distribution makes the delivery time either shorter or longer; (d) if one LSP changes its equilibrium price, the total profit conditionally increases, and this condition is related to demand structure and delivery cost structure; and (e) collaborative distribution can solve the personalization of delivery time and reduce pollution to some extent. For the companies sharing the incremental profit, we characterize a transfer payment contract that includes fixed and variable fees. Our findings suggest that LSPs should adopt collaborative distribution to formulate an optimal distribution plan to save costs and shorten the delivery time, and should select partners with smaller cost parameters and both different and moderate speeds. In addition, warehouse and vehicle sharing are beneficial to the implementation of collaborative distribution. 相似文献
992.
993.
994.
Robust adaptive DSC of directly input‐coupled nonlinear systems with input unmodeled dynamics and time‐varying output constraints
下载免费PDF全文
![点击此处可从《国际强度与非线性控制杂志<br>》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this paper, an adaptive robust dynamic surface control is proposed for a class of uncertain nonlinear interconnected systems with time‐varying output constraints and dynamic input and output coupling. The directly coupled inputs and control inputs are both of nonlinear input unmodeled dynamics. To counteract the instable impact of the nonlinear input unmodeled dynamics, normalization signals are designed on the basis of the convergence rates of their Lyapunov functions. With new state variables and control variables being defined, the real control inputs are obtained through solving the equations of intermediate control laws. The time‐varying constraints on output signals are implemented by introducing asymmetric barrier Lyapunov functions. In addition, dynamic signals and decentralized K‐filters are used to deal with the state unmodeled dynamics and to estimate the unmeasurable states, respectively. By the theoretical analysis, the signals in the closed‐loop system are proved to be semi‐globally uniformly ultimately bounded, and the output constraints are guaranteed simultaneously. A numerical example is provided to show the effectiveness of the proposed approach. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
995.
Chao Liu Peifeng Niu Guoqiang Li Xia You Yunpeng Ma Weiping Zhang 《Neural Processing Letters》2017,45(1):299-318
Heat rate value is considered as one of the most important thermal economic indicators, which determines the economic, efficient and safe operation of steam turbine unit. At the same time, an accurate heat rate forecasting is core task in the optimal operation of steam turbine unit. Recently, least squares support vector machine (LSSVM) is being proved an effective machine learning technique for solving nonlinear regression problem with a small sample set. However, it has also been proved that the prediction precision of LSSVM is highly dependent on its parameters, which are hardly choosing for the LSSVM. In the paper, an improved gravitational search algorithm (AC-GSA) is presented to further enhance optimal performance of GSA, and it is employed to serve as an approach for pre-selecting LSSVM parameters. Then, a novel soft computing method, based on LSSVM and AC-GSA, is therefore proposed to forecast heat rate of a 600 MW supercritical steam turbine unit. It combines the merits of the high accuracy of LSSVM and the fast convergence of GSA in order to build heat rate prediction model and obtain a well-generalized model. Results indicate that the developed AC-GSA–LSSVM model demonstrates better regression precision and generalization capability. 相似文献
996.
Jing Jiang David Lo Jiahuan He Xin Xia Pavneet Singh Kochhar Li Zhang 《Empirical Software Engineering》2017,22(1):547-578
Forking is the creation of a new software repository by copying another repository. Though forking is controversial in traditional open source software (OSS) community, it is encouraged and is a built-in feature in GitHub. Developers freely fork repositories, use codes as their own and make changes. A deep understanding of repository forking can provide important insights for OSS community and GitHub. In this paper, we explore why and how developers fork what from whom in GitHub. We collect a dataset containing 236,344 developers and 1,841,324 forks. We make surveys, and analyze programming languages and owners of forked repositories. Our main observations are: (1) Developers fork repositories to submit pull requests, fix bugs, add new features and keep copies etc. Developers find repositories to fork from various sources: search engines, external sites (e.g., Twitter, Reddit), social relationships, etc. More than 42 % of developers that we have surveyed agree that an automated recommendation tool is useful to help them pick repositories to fork, while more than 44.4 % of developers do not value a recommendation tool. Developers care about repository owners when they fork repositories. (2) A repository written in a developer’s preferred programming language is more likely to be forked. (3) Developers mostly fork repositories from creators. In comparison with unattractive repository owners, attractive repository owners have higher percentage of organizations, more followers and earlier registration in GitHub. Our results show that forking is mainly used for making contributions of original repositories, and it is beneficial for OSS community. Moreover, our results show the value of recommendation and provide important insights for GitHub to recommend repositories. 相似文献
997.
Representative skyline computation is a fundamental issue in database area, which has attracted much attention in recent years. A notable definition of representative skyline is the distance-based representative skyline (DBRS). Given an integer k, a DBRS includes k representative skyline points that aims at minimizing the maximal distance between a non-representative skyline point and its nearest representative. In the 2D space, the state-of-the-art algorithm to compute the DBRS is based on dynamic programming (DP) which takes O(k m 2) time complexity, where m is the number of skyline points. Clearly, such a DP-based algorithm cannot be used for handling large scale datasets due to the quadratic time cost. To overcome this problem, in this paper, we propose a new approximate algorithm called ARS, and a new exact algorithm named PSRS, based on a carefully-designed parametric search technique. We show that the ARS algorithm can guarantee a solution that is at most ?? larger than the optimal solution. The proposed ARS and PSRS algorithms run in O(klog2mlog(T/??)) and O(k 2 log3m) time respectively, where T is no more than the maximal distance between any two skyline points. We also propose an improved exact algorithm, called PSRS+, based on an effective lower and upper bounding technique. We conduct extensive experimental studies over both synthetic and real-world datasets, and the results demonstrate the efficiency and effectiveness of the proposed algorithms. 相似文献
998.
Robust Stochastic Stability and
Control for Uncertain Singular Markovian Jump Systems with Multiplicative Noise
下载免费PDF全文
![点击此处可从《Asian journal of control》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper focuses on the problems of robust stability and stabilization and robust control for uncertain singular Markovian jump systems with (x,v)‐dependent noise. The parameter uncertainties appearing in state, input, disturbance as well as diffusion terms are assumed to be time‐varying but norm‐bounded. Based on the approach of generalized quadratic stability, the memoryless state feedback controller is designed for the robust stabilization problem, which ensures that the resulting closed‐loop system has an impulse‐free solution and is asymptotically stable in the mean square. Furthermore, the results of robust control problem are derived. The desired state feedback controller is presented, which not only meets the requirement of robust stabilization but also satisfies a prescribed performance level. The obtained results are formulated in terms of strict LMIs. What we have obtained can be viewed as corresponding extensions of existing results on uncertain singular systems. A numerical example is finally given to demonstrate the application of the proposed method. 相似文献
999.
Ning Chen Dejie Yu Baizhan Xia Jian Liu Zhengdong Ma 《Structural and Multidisciplinary Optimization》2017,56(6):1259-1270
The aim of this paper is to present a microstructural topology optimization methodology for the structural-acoustic coupled system. In the structural-acoustic system, the structure is considered to be a thin composite plate composed of periodic uniform microstructures. The discrete design variables are used in the microstructural topology optimization, and the constitutive matrix is interpolated by the power-law scheme at the micro scale. The equivalent macro material properties of the microstructure are computed through the homogenization method. The design objective is to minimize the sound pressure level (SPL) in an interior acoustic medium. The sensitivities of the SPL with respect to design variables are derived. The bi-directional evolutionary structural optimization (BESO) method is extended to solve the structural-acoustic coupled optimization problem to find the optimal material distribution of the microstructure. Numerical examples of a hexahedral box and an automobile passenger compartment are given to demonstrate the efficiency of the presented microstructural topology optimization method. 相似文献
1000.
针对现有的无监督作文跑题检测方法中,使用作文内容向量表示作文存在非主题词噪声所导致的相似度不准确问题,该文提出一种基于作文主题词抽取和局部密度阈值选择的无监督作文跑题检测方法。首先使用LDA主题生成模型挖掘待测作文的主题词,并使用分布式表示向量寻找与题目词项语义相似的词,作为对作文题目的主题词扩展,在此基础上使用提出的切题度计算方法计算待测作文的切题度,并使用所提出的基于作文集切题度局部密度的阈值抽取方法动态选取切题阈值,进而实现一种无需训练集和主题无关的无监督作文跑题检测方法。在以英语为母语的学习者和以汉语为母语的学习者所写的8个作文集共9 381篇作文上的实验结果表明,该文提出的作文跑题检测方法能有效识别跑题作文,加入拼写检查预处理后,平均F1值为79.64%,单个作文题目下F1值最好为96.1%。 相似文献