全文获取类型
收费全文 | 29796篇 |
免费 | 2356篇 |
国内免费 | 1212篇 |
专业分类
电工技术 | 1636篇 |
综合类 | 2294篇 |
化学工业 | 5200篇 |
金属工艺 | 1407篇 |
机械仪表 | 1715篇 |
建筑科学 | 2061篇 |
矿业工程 | 724篇 |
能源动力 | 754篇 |
轻工业 | 2702篇 |
水利工程 | 636篇 |
石油天然气 | 1784篇 |
武器工业 | 213篇 |
无线电 | 3282篇 |
一般工业技术 | 3412篇 |
冶金工业 | 1242篇 |
原子能技术 | 342篇 |
自动化技术 | 3960篇 |
出版年
2024年 | 86篇 |
2023年 | 439篇 |
2022年 | 758篇 |
2021年 | 1106篇 |
2020年 | 865篇 |
2019年 | 715篇 |
2018年 | 778篇 |
2017年 | 938篇 |
2016年 | 817篇 |
2015年 | 1160篇 |
2014年 | 1488篇 |
2013年 | 1841篇 |
2012年 | 2050篇 |
2011年 | 2233篇 |
2010年 | 2053篇 |
2009年 | 1951篇 |
2008年 | 1942篇 |
2007年 | 1833篇 |
2006年 | 1791篇 |
2005年 | 1529篇 |
2004年 | 1080篇 |
2003年 | 816篇 |
2002年 | 746篇 |
2001年 | 593篇 |
2000年 | 604篇 |
1999年 | 593篇 |
1998年 | 470篇 |
1997年 | 403篇 |
1996年 | 385篇 |
1995年 | 305篇 |
1994年 | 239篇 |
1993年 | 187篇 |
1992年 | 149篇 |
1991年 | 114篇 |
1990年 | 60篇 |
1989年 | 67篇 |
1988年 | 64篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1959年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
由于密码分析研究的进展及DES自身的弱点,原64比特的DES将不能作为数据加密的标准算法而长期存在。在原来工作的基础上,本文提出了256比特的分组密码方案。密码算法由基于混沌映射的数字滤波器构造。 相似文献
92.
Xia Haihong Zhao Zhixiang Li Jigen Shi Yongqian Han Yinlu Zhu Shengyun Xu Yongli Guan Xialing Cui Baoqun Fu Shinian 《Frontiers of Energy and Power Engineering in China》2007,1(2):135-140
The conceptual study on the accelerator driven system (ADS) that lasted for about five years ended in 1999 in China. As one
project of the National Basic Research Program of China (973 Program) in the energy domain, which is sponsored by the China
Ministry of Science and Technology (MOST), a five-year-program of fundamental research of ADS physics and related technology
was launched in 2000 and passed national review at the end of 2005. The China Institute of Atomic Energy (CIAE), the Institute
of High Energy Physics (IHEP), the Institute of Heavy Ion Physics in Peking University (PKU-IHIP) and other institutions jointly
carried out the research. The research activities were focused on HPPA physics and technology, reactor physics of external
source driven sub-critical assembly, nuclear data base and material study. For HPPA, a high current injector consisting of
an ECR ion source, LEBT and an RFQ accelerating structure of 3.5 MeV was built. In reactor physics study, a series of neutron
multiplication experimental study has been carried out and still being done. The VENUS facility has been constructed as the
basic experimental platform for neutronics study in ADS blanket. It’s a zero power sub-critical neutron multiplying assembly
driven by external neutron produced by a pulsed neutron generator. The theoretical, experimental and simulation study on nuclear
data, material properties and nuclear fuel circulation related to ADS is carrying on to provide the database for ADS system
analysis. The main results on ADS related researches will be reported. 相似文献
93.
94.
95.
96.
97.
Investigation of the reaction mechanism of chloromethane on ZSM5 is a new topic. In this work an in situ FTIR technique was employed to study the conversion processes of chloromethane, the active sites on HZSM5, and the desorption state of surface species. The catalytic conversion of chloromethane to higher hydrocarbons was also studied. It is demonstrated that chloromethane can be reversibly adsorbed on acidic sites of HZSM5 at room temperature. At 100°C chloromethane is irreversibly and dissociatively adsorbed on the strong acidic sites of HZSM5, on which surface methoxyl is formed as proved by infrared characteristic C-H stretchings of-CH3 at 2960 and 2870 cm–1. Alkoxyls are produced and adsorbed on the catalyst surface as characterized by the infrared absorption bands of -CH2-groups at 1460 and 2930 cm–1. At 100°C the adsorbed methoxyl and alkoxyls are the main surface species, and a small amount of aromatics might exist as detected by a characteristic absorption band at 1510 cm–1. Between 100 and 200°C the adsorbed surface methoxyl and alkoxyls are converted to aromatics, and the occupied OH groups partially appear. At temperature higher than 300°C the adsorbed aromatics are thermally desorbed into the gas phase. Aromatics and alkanes are the main products in catalytic conversion. These results reveal that the formation of aromatics from methoxyl and alkoxyls is easier than the desorption of aromatics from HZSM5 catalyst. An alkoxyl mechanism is proposed for the conversion of chloromethane on HZSM5 based upon the experimental results and the three assumptions: (a) The primary C-C bond is formed from surface methoxyl groups via the methoxyl group polarization and C-H bond weakening, (b) The adsorbed alkoxyls are converted to aromatics via hydrogen transfer and bond rearrangement similar to the conventional carbenium ion mechanism for the aromatization of olefins and alkanes on HZSM5. The hydrogen atoms from the aromatization stimulate the desorption of alkoxyls to alkanes. (c) At temperature higher than 300°C surface reactions and desorption of adsorbed species take place simultaneously, determining the product distribution in the catalytic conversion. 相似文献
98.
Manoj Parameswaran Xia Zhao Andrew B. Whinston Fang Fang 《Computer》2007,40(1):40-44
The growing proliferation of malware is raising doubts about the Internet's future. Security measures primarily target inbound traffic, but service providers have no incentive to stop attacks and spam at the source. A proposed certification scheme motivates providers to control outgoing traffic, efficiently increasing overall security while preserving the Internet's open, decentralized structure 相似文献
99.
高瑞霞 《消防技术与产品信息》2005,(3):59-60
设想某一个城镇生产木材调色板的流水线车间里 ,由于电器原因引发了一场火灾 ,致使建筑物坍塌。没有人能够确切地说出有多少工人被埋压在里面 ,更糟的是 ,当毗邻墙体坍塌时 ,隔壁的旧轮胎储藏室也被埋压在下面。于是市消防局派遣一批机器人去现场救援。第一个到达的机器人进入现场调查情况 ,该机器人能忍耐80 0℃的高温炙烤 ,身上安装了摄像机 ,可以给 90 m外的控制室发送图片 ,控制室的指挥人员就可以根据图片决定是否派消防队员冒险进入现场。第二个机器人是无人驾驶卡车 ,进入后便从 75 m远的地方以2 6 gal/ s的速度往火场喷水 ,并用它所… 相似文献
100.