全文获取类型
收费全文 | 63073篇 |
免费 | 5888篇 |
国内免费 | 3342篇 |
专业分类
电工技术 | 4237篇 |
技术理论 | 4篇 |
综合类 | 4491篇 |
化学工业 | 10341篇 |
金属工艺 | 3724篇 |
机械仪表 | 4164篇 |
建筑科学 | 4751篇 |
矿业工程 | 1461篇 |
能源动力 | 1790篇 |
轻工业 | 4551篇 |
水利工程 | 1279篇 |
石油天然气 | 2805篇 |
武器工业 | 512篇 |
无线电 | 7868篇 |
一般工业技术 | 8200篇 |
冶金工业 | 2740篇 |
原子能技术 | 807篇 |
自动化技术 | 8578篇 |
出版年
2024年 | 263篇 |
2023年 | 958篇 |
2022年 | 1840篇 |
2021年 | 2564篇 |
2020年 | 1848篇 |
2019年 | 1631篇 |
2018年 | 1763篇 |
2017年 | 2001篇 |
2016年 | 1987篇 |
2015年 | 2656篇 |
2014年 | 3185篇 |
2013年 | 3842篇 |
2012年 | 4124篇 |
2011年 | 4547篇 |
2010年 | 4053篇 |
2009年 | 3723篇 |
2008年 | 3733篇 |
2007年 | 3463篇 |
2006年 | 3426篇 |
2005年 | 2958篇 |
2004年 | 2196篇 |
2003年 | 2076篇 |
2002年 | 2359篇 |
2001年 | 1946篇 |
2000年 | 1603篇 |
1999年 | 1388篇 |
1998年 | 1124篇 |
1997年 | 936篇 |
1996年 | 833篇 |
1995年 | 726篇 |
1994年 | 621篇 |
1993年 | 465篇 |
1992年 | 349篇 |
1991年 | 283篇 |
1990年 | 206篇 |
1989年 | 160篇 |
1988年 | 136篇 |
1987年 | 77篇 |
1986年 | 59篇 |
1985年 | 48篇 |
1984年 | 34篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1959年 | 7篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
采用四组分法从辽河减压渣油中分离出胶质、沥青质,分别考察了它们在分散型催化剂作用下的临氢热反应行为。结果表明,胶质、沥青质一方面要裂化生成较轻的产物;另一方面也要发生缩合反应生成较重的反应产物以及甲苯不溶物。渣油在临氢热反应过程中,沥青质是生焦的主要来源,其次才是胶质。比较了热反应生成的沥青质与原生沥青质之间以及热反应生成的胶质与原生胶质之间化学组成的区别,结果表明,反应生成的沥青质和胶质较原生的沥青质和胶质分子结构缩合程度高,并且反应苛刻度越高,缩合程度也越高。 相似文献
12.
13.
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
14.
表面贴装工艺流程的关键工序之一就是焊膏印刷,其工艺控制的好坏直接影响着装配的线路板的质量。通过对印刷工艺参数的分析,利用试验设计的方法来找出关键工艺参数,并加以优化设定,从而为控制工序参数奠定基础。 相似文献
15.
16.
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
17.
Soo Jin Kim Wha Young Lee Yeungho Park Wansoo Huh Young Gwan Ko 《Polymer Engineering and Science》2003,43(5):1011-1017
Supported zirconcene catalysts on a new support, MgO, were prepared and tested in ethylene polymerization. Three types of impregnation methods were employed to find an optimum supporting method for MgO. The direct impregnation of Cp2ZrCl2 on MgO showed low metal loading and polymerization activity, while the catalyst had a higher metal loading and polymerization activity when MgO was treated with methylaluminoxane (MAO) before supporting. Treatment of MgO with MAO during the supporting step invoked two types of catalytic sites, which was evidenced by the bimodal molecular weight distribution of the polymer products. MgO is considered to have potential as a support for metallocenes. 相似文献
18.
19.
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
20.
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