全文获取类型
收费全文 | 26843篇 |
免费 | 4855篇 |
国内免费 | 2689篇 |
专业分类
电工技术 | 2831篇 |
技术理论 | 1篇 |
综合类 | 2567篇 |
化学工业 | 4869篇 |
金属工艺 | 1602篇 |
机械仪表 | 2487篇 |
建筑科学 | 1418篇 |
矿业工程 | 1022篇 |
能源动力 | 966篇 |
轻工业 | 1119篇 |
水利工程 | 714篇 |
石油天然气 | 751篇 |
武器工业 | 436篇 |
无线电 | 2551篇 |
一般工业技术 | 4348篇 |
冶金工业 | 927篇 |
原子能技术 | 461篇 |
自动化技术 | 5317篇 |
出版年
2024年 | 217篇 |
2023年 | 672篇 |
2022年 | 1021篇 |
2021年 | 1221篇 |
2020年 | 1418篇 |
2019年 | 1263篇 |
2018年 | 1239篇 |
2017年 | 1438篇 |
2016年 | 1486篇 |
2015年 | 1566篇 |
2014年 | 1873篇 |
2013年 | 2042篇 |
2012年 | 2228篇 |
2011年 | 2217篇 |
2010年 | 1677篇 |
2009年 | 1703篇 |
2008年 | 1493篇 |
2007年 | 1661篇 |
2006年 | 1399篇 |
2005年 | 1141篇 |
2004年 | 916篇 |
2003年 | 714篇 |
2002年 | 580篇 |
2001年 | 557篇 |
2000年 | 463篇 |
1999年 | 440篇 |
1998年 | 335篇 |
1997年 | 265篇 |
1996年 | 218篇 |
1995年 | 195篇 |
1994年 | 141篇 |
1993年 | 130篇 |
1992年 | 116篇 |
1991年 | 59篇 |
1990年 | 61篇 |
1989年 | 59篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 14篇 |
1975年 | 2篇 |
1963年 | 1篇 |
1959年 | 9篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 8 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.
3.
Zenan Yu Julian Moore Jean Calderon Lei Zhai Jayan Thomas 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(39):5289-5295
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets. 相似文献
4.
5.
Abrasive water jet technology can be used for micro-milling using recently developed miniaturized nozzles. Abrasive water jet (AWJ) machining is often used with both the nozzle tip and workpiece submerged in water to reduce noise and contain debris. This paper compares the performance of submerged and unsubmerged abrasive water jet micro-milling of channels in 316L stainless steel and 6061-T6 aluminum at various nozzle angles and standoff distances. The effect of submergence on the diameter and effective footprint of AWJ erosion footprints was measured and compared. It was found that the centerline erosion rate decreased with channel depth due to the spreading of the jet as the effective standoff distance increased, and because of the growing effect of stagnation as the channel became deeper. The erosive jet spread over a larger effective footprint in air than in water, since particles on the jet periphery were slowed much more quickly in water due to increased drag. As a result, the width of a channel machined in air was wider than that in water. Moreover, it was observed that the instantaneous erosion rate decreased with channel depth, and that this decrease was a function only of the channel cross-sectional geometry, being independent of the type of metal, the jet angle, the standoff distance, and regardless of whether the jet was submerged or in air, in either the forward or backward directions. It is shown that submerged AWJM results in narrower features than those produced while machining in air, without a decrease in centerline etch rate. 相似文献
6.
7.
谐波齿轮机构在商业表格印刷机中的应用 总被引:1,自引:1,他引:0
从商业表格印刷机特殊要求出发,以某一具体机型的传动系统为例,提出采用谐波齿轮机构解决纵向套准的问题。并且分析研究了谐波齿轮机构的工作原理及其在商业表格印刷机中的使用。 相似文献
8.
Preparation and properties of nano-sized SnO2 powder 总被引:2,自引:0,他引:2
1 INTRODUCTIONSnO2isoneofthemainmaterialsusedingassensor.Becauseofthehumidityandgassensingfunction,itattractsmoreandmoreattentions.Butthepresentproblemishowtoimprovethestabilityandsensibilityofgassensor.Researchershavetakenmanymeasurestoresolvethisproble… 相似文献
9.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。 相似文献
10.
Bedich ika Helena Bendov Ivan Macha
《Chemical Engineering and Processing: Process Intensification》2005,44(12):1312-1319
A procedure has been proposed for the estimation of the terminal falling velocity of non-spherical particles moving in a Carreau model fluid in the transition flow region. The procedure is based on a modification of the relationship formerly developed for the fall of spherical particles including the particle dynamic shape factor. The suitability of the proposed procedure has been confirmed by good agreement between experimental and calculated terminal falling velocity data. In the experiments, the terminal falling velocity of short cylinders and rectangular prisms in polymer solutions of different measure of shear thinning and elasticity has been measured. 相似文献