全文获取类型
收费全文 | 61868篇 |
免费 | 5375篇 |
国内免费 | 3073篇 |
专业分类
电工技术 | 3920篇 |
技术理论 | 4篇 |
综合类 | 4320篇 |
化学工业 | 9795篇 |
金属工艺 | 3375篇 |
机械仪表 | 3927篇 |
建筑科学 | 4534篇 |
矿业工程 | 1312篇 |
能源动力 | 1698篇 |
轻工业 | 4376篇 |
水利工程 | 1188篇 |
石油天然气 | 2639篇 |
武器工业 | 484篇 |
无线电 | 7644篇 |
一般工业技术 | 7761篇 |
冶金工业 | 4450篇 |
原子能技术 | 761篇 |
自动化技术 | 8128篇 |
出版年
2024年 | 240篇 |
2023年 | 877篇 |
2022年 | 1679篇 |
2021年 | 2361篇 |
2020年 | 1710篇 |
2019年 | 1530篇 |
2018年 | 1622篇 |
2017年 | 1830篇 |
2016年 | 1840篇 |
2015年 | 2475篇 |
2014年 | 2973篇 |
2013年 | 3631篇 |
2012年 | 3890篇 |
2011年 | 4299篇 |
2010年 | 3880篇 |
2009年 | 3540篇 |
2008年 | 3568篇 |
2007年 | 3297篇 |
2006年 | 3278篇 |
2005年 | 2832篇 |
2004年 | 2091篇 |
2003年 | 2000篇 |
2002年 | 2270篇 |
2001年 | 1892篇 |
2000年 | 1520篇 |
1999年 | 1374篇 |
1998年 | 1680篇 |
1997年 | 1244篇 |
1996年 | 1014篇 |
1995年 | 848篇 |
1994年 | 698篇 |
1993年 | 581篇 |
1992年 | 348篇 |
1991年 | 293篇 |
1990年 | 218篇 |
1989年 | 181篇 |
1988年 | 154篇 |
1987年 | 96篇 |
1986年 | 81篇 |
1985年 | 65篇 |
1984年 | 32篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 35篇 |
1980年 | 36篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 45篇 |
1976年 | 90篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
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
4.
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
5.
6.
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
7.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
8.
9.
Combining ideal beamforming and Alamouti space-time block codes 总被引:3,自引:0,他引:3
The simplest Alamouti space-time block code is coupled with a larger number of transmit antennas via ideal beamforming to achieve higher diversity gain. It is shown that the combined system can remain both full diversity and full code rate without orthogonality loss. Simulation results show a significant performance gain over the conventional space-time block codes. 相似文献
10.
地理信息系统是利用现代计算机图形和数据库技术来处理地理空间及其相关数据的计算机系统,是融地理学、测量学、几何学、计算机科学和应用对象为一体的综合性高新技术。在石油天然气管道的管理向现代化、科学化和智能化方向发展的过程中,地理信息系统是有利的辅助手段之一。文章对地理信息系统发展、基本功能要求、建设内容及其在石油天然气管道中的应用进行了论述。 相似文献