全文获取类型
收费全文 | 116406篇 |
免费 | 10004篇 |
国内免费 | 5571篇 |
专业分类
电工技术 | 7438篇 |
技术理论 | 7篇 |
综合类 | 8209篇 |
化学工业 | 19099篇 |
金属工艺 | 6657篇 |
机械仪表 | 7674篇 |
建筑科学 | 9022篇 |
矿业工程 | 3112篇 |
能源动力 | 3341篇 |
轻工业 | 8076篇 |
水利工程 | 2209篇 |
石油天然气 | 6495篇 |
武器工业 | 996篇 |
无线电 | 13687篇 |
一般工业技术 | 14456篇 |
冶金工业 | 4999篇 |
原子能技术 | 1317篇 |
自动化技术 | 15187篇 |
出版年
2024年 | 492篇 |
2023年 | 1881篇 |
2022年 | 3389篇 |
2021年 | 4700篇 |
2020年 | 3579篇 |
2019年 | 3038篇 |
2018年 | 3297篇 |
2017年 | 3697篇 |
2016年 | 3456篇 |
2015年 | 4703篇 |
2014年 | 5866篇 |
2013年 | 6852篇 |
2012年 | 7388篇 |
2011年 | 8251篇 |
2010年 | 7306篇 |
2009年 | 6741篇 |
2008年 | 6716篇 |
2007年 | 6207篇 |
2006年 | 6272篇 |
2005年 | 5333篇 |
2004年 | 3902篇 |
2003年 | 3599篇 |
2002年 | 3838篇 |
2001年 | 3257篇 |
2000年 | 2784篇 |
1999年 | 2810篇 |
1998年 | 2323篇 |
1997年 | 1978篇 |
1996年 | 1784篇 |
1995年 | 1504篇 |
1994年 | 1244篇 |
1993年 | 925篇 |
1992年 | 741篇 |
1991年 | 514篇 |
1990年 | 396篇 |
1989年 | 315篇 |
1988年 | 249篇 |
1987年 | 154篇 |
1986年 | 125篇 |
1985年 | 83篇 |
1984年 | 65篇 |
1983年 | 47篇 |
1982年 | 53篇 |
1981年 | 40篇 |
1980年 | 33篇 |
1979年 | 14篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1959年 | 5篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Climate change raises many concerns for urban water management because of the effects on all aspects of the hydrological cycle. Urban water infrastructure has traditionally been designed using historical observations and assuming stationary climatic conditions. The capability of this infrastructure, whether for storm-water drainage, or water supply, may be over- or under-designed for future climatic conditions. In particular, changes in the frequency and intensity of extreme rainfall events will have the most acute effect on storm-water drainage systems. Therefore, it is necessary to take future climatic conditions into consideration in engineering designs in order to enhance water infrastructure investment planning practices in a long time horizon. This paper provides the initial results of a study that is examining ways to enhance urban infrastructure investment planning practices against changes in hydrologic regimes for a changing climate. Design storms and intensity-duration-frequency curves that are used in the engineering design of storm-water drainage systems are developed under future climatic conditions by empirically adjusting the general circulation model output, and using the Gumbel distribution and the Chicago method. Simulations are then performed on an existing storm-water drainage system from NE Calgary to investigate the resiliency of the system under climate change. 相似文献
4.
5.
Effect of modified atmosphere packaging on the shelf-life of coated, whole and sliced mushrooms 总被引:2,自引:0,他引:2
Whole and sliced fresh mushrooms (Agaricus bisporus) were packaged with PVC wrap or two polyolefins (PD-941 and PD-961) films after coating with CaCl2 and chitosan. Package gas composition, color, weight loss and maturity were measured during storage at 12 °C and 80%RH. For PD-961, the highest in-package concentration occurred during the first day of storage regardless of treatments, while wrap and PD-941 showed varying degrees in-package concentration with different processes and coatings. The whiteness of whole mushrooms varied significantly with the type of coating, but not with the type of films. The extent of darkening was greater in coated whole mushrooms than in sliced ones. Weight loss occurred in all packages and varied from 3 (g/100 g) to about 7 (g/100 g) after 6 days of storage. Due to a lower permeability, PD-961 packages had the lowest weight loss. The type of packaging films significantly affected the maturity index, where PD-961 most effectively lowered maturity index for both whole and sliced mushrooms, thus extending the shelf-life. The type of coating did not appear to affect maturity index except for the wrap package where chitosan coating markedly lowered the maturity index of sliced mushrooms. 相似文献
6.
连续油管技术与装备发展综述 总被引:41,自引:14,他引:27
自世界上第一台连续油管作业机问世至今,连续油管作业技术与装备已经过了40多年的发展历程,以其占地面积小、作业成本低、搬迁安装方便、保护油层、增加油井产量和使用范围广等诸多不可比拟的优势,得到迅速发展,并广泛应用于钻井、完井、试油、采油、修井和集输等各个作业领域。实践表明,连续油管作业技术与装备是一项具有巨大潜力和生命力的实用性技术。目前,该项技术的应用日趋活跃,备受关注。在总结连续油管作业技术与装备的发展现状和展示其发展趋势的基础上,客观地分析了国内连续油管技术与装备的应用与研究现状,提出相应的发展对策。 相似文献
7.
结合工程实例,介绍了我国第一座可拆装高架火炬的基本原理及组成,并对可拆装高架火炬与普通高架火炬在安全、技术、安装、维修、占地面积、投资等方面进行了比较,还分析了高架火炬未来的发展趋势. 相似文献
8.
9.
10.
Jin Tae Kim Keun Byoung Yoon Choon-Gi Choi 《Photonics Technology Letters, IEEE》2004,16(7):1664-1666
A novel fabrication process using a hot embossing technique has been developed for micromechanical passive alignment of polymer planar lightwave circuit (PLC) devices. With only one step of embossing, single-mode waveguide straight channels and micropedestals for passive aligning are simultaneously defined on a polymer thin film with an accuracy of /spl plusmn/0.5 /spl mu/m. This process reduces the steps for fabricating alignment structures. A fabricated polymer PLC chip and fibers are combined on a v-grooved silicon optical bench (SiOB) in a flip-chip manner. The process provides a coupling loss as low as 0.67 dB per coupling face and a cost-effective packaging solution for various polymer PLC devices. 相似文献