全文获取类型
收费全文 | 24821篇 |
免费 | 2297篇 |
国内免费 | 1767篇 |
专业分类
电工技术 | 1067篇 |
技术理论 | 13篇 |
综合类 | 2597篇 |
化学工业 | 3279篇 |
金属工艺 | 1607篇 |
机械仪表 | 1169篇 |
建筑科学 | 3324篇 |
矿业工程 | 1208篇 |
能源动力 | 885篇 |
轻工业 | 1206篇 |
水利工程 | 602篇 |
石油天然气 | 3888篇 |
武器工业 | 134篇 |
无线电 | 1381篇 |
一般工业技术 | 2110篇 |
冶金工业 | 1343篇 |
原子能技术 | 180篇 |
自动化技术 | 2892篇 |
出版年
2024年 | 121篇 |
2023年 | 405篇 |
2022年 | 743篇 |
2021年 | 937篇 |
2020年 | 972篇 |
2019年 | 772篇 |
2018年 | 645篇 |
2017年 | 817篇 |
2016年 | 899篇 |
2015年 | 1063篇 |
2014年 | 1753篇 |
2013年 | 1620篇 |
2012年 | 1993篇 |
2011年 | 2062篇 |
2010年 | 1490篇 |
2009年 | 1442篇 |
2008年 | 1234篇 |
2007年 | 1529篇 |
2006年 | 1475篇 |
2005年 | 1244篇 |
2004年 | 1023篇 |
2003年 | 884篇 |
2002年 | 701篇 |
2001年 | 575篇 |
2000年 | 522篇 |
1999年 | 381篇 |
1998年 | 314篇 |
1997年 | 278篇 |
1996年 | 230篇 |
1995年 | 180篇 |
1994年 | 137篇 |
1993年 | 83篇 |
1992年 | 82篇 |
1991年 | 59篇 |
1990年 | 50篇 |
1989年 | 49篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1954年 | 1篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The proliferating need for sustainability intervention in food grain transportation planning is anchoring the attention of researchers in the interests of stakeholders and environment at large. Uncertainty associated with food grain supply further intensifies the problem steering the need for designing robust, cost-efficient and sustainable models. In line with this, this paper aims to develop a robust and sustainable intermodal transportation model to facilitate single type of food grain commodity shipments while considering procurement uncertainty, greenhouse gas emissions, and intentional hub disruption. The problem is designed as a mixed integer non-linear robust optimisation model on a hub and spoke network for evaluating near optimal shipment quantity, route selection and hub location decisions. The robust optimisation approach considers minimisation of total relative regret associated with total cost subject to several real-time constraints. A version of Particle Swarm Optimisation with Differential Evolution is proposed to tackle the resulting NP-hard problem. The model is tested with two other state-of the art meta-heuristics for small, medium, and large datasets subject to different procurement scenarios inspired from real time food grain operations in Indian context. Finally, the solution is evaluated with respect to total cost, model and solution robustness for all instances. 相似文献
2.
In this research, we propose a novel framework referred to as collective game behavior decomposition where complex collective behavior is assumed to be generated by aggregation of several groups of agents following different strategies and complexity emerges from collaboration and competition of individuals. The strategy of an agent is modeled by certain simple game theory models with limited information. Genetic algorithms are used to obtain the optimal collective behavior decomposition based on history data. The trained model can be used for collective behavior prediction. For modeling individual behavior, two simple games, the minority game and mixed game are investigated in experiments on the real-world stock prices and foreign-exchange rate. Experimental results are presented to show the effectiveness of the new proposed model. 相似文献
3.
The penalized calibration technique in survey sampling combines usual calibration and soft calibration by introducing a penalty term. Certain relevant estimates in survey sampling can be considered as penalized calibration estimates obtained as particular cases from an optimization problem with a common basic structure. In this framework, a case deletion diagnostic is proposed for a class of penalized calibration estimators including both design-based and model-based estimators. The diagnostic compares finite population parameter estimates and can be calculated from quantities related to the full data set. The resulting diagnostic is a function of the residual and leverage, as other diagnostics in regression models, and of the calibration weight, a singular feature in survey sampling. Moreover, a particular case, which includes the basic unit level model for small area estimation, is considered. Both a real and an artificial example are included to illustrate the diagnostic proposed. The results obtained clearly show that the proposed diagnostic depends on the calibration and soft-calibration variables, on the penalization term, as well as on the parameter to estimate. 相似文献
4.
Combinatorial auction is a useful trade manner for transportation service procurements in e-marketplaces. To enhance the competition of combinatorial auction, a novel auction mechanism of two-round bidding with bundling optimization is proposed. As the recommended the auction mechanism, the shipper/auctioneer integrates the objects into several bundles based on the bidding results of first round auction. Then, carriers/bidders bid for the object bundles in second round. The bundling optimization is described as a multi-objective model with two criteria on price complementation and combination consistency. A Quantum Evolutionary Algorithm (QEA) with β-based rotation gate and the encoding scheme based on non-zero elements in complementary coefficient matrix is developed for the model solution. Comparing with a Contrast Genetic Algorithm, QEA can achieve better computational performances for small and middle size problems. 相似文献
5.
针对流体输送埋地管道泄漏问题,设计了一种利用管道机器人携带封堵气囊进行快速应急封堵修复的埋地管道泄漏内封堵装置。采用矩阵变换方法建立了牵引系统驱动轮过弯方程,利用MATLAB软件对过弯方程进行了验证,同时利用ADAMS软件仿真分析过弯路径与驱动轮转角对牵引系统行走速度的影响。研究结果表明:由两个串联封堵器组成的应急封堵系统可满足复杂工况下的管道泄漏封堵要求;牵引系统驱动轮在弯管内部行走时,单轮速度呈周期性变化,但三个驱动轮整体周期运动特性一致;驱动轮转角在25°~40°时,牵引系统行走速度与驱动轮转角成正比,且转角为30°时驱动效果最好。该内封堵装置的结构设计可为管道泄漏应急封堵领域装备的研发提供重要参考。 相似文献
6.
7.
通过认真学习《细节决定成败》,结合井矿盐开采的实际,分别以生产过程中的三个细节为主,讨论了在采输卤生产技术控制中的细节的重要性。 相似文献
8.
9.
10.