全文获取类型
收费全文 | 114476篇 |
免费 | 11177篇 |
国内免费 | 6214篇 |
专业分类
电工技术 | 7977篇 |
技术理论 | 9篇 |
综合类 | 9057篇 |
化学工业 | 17765篇 |
金属工艺 | 6630篇 |
机械仪表 | 7515篇 |
建筑科学 | 8690篇 |
矿业工程 | 3634篇 |
能源动力 | 3185篇 |
轻工业 | 9714篇 |
水利工程 | 2464篇 |
石油天然气 | 5571篇 |
武器工业 | 1242篇 |
无线电 | 13018篇 |
一般工业技术 | 12637篇 |
冶金工业 | 5039篇 |
原子能技术 | 1639篇 |
自动化技术 | 16081篇 |
出版年
2024年 | 661篇 |
2023年 | 2145篇 |
2022年 | 4066篇 |
2021年 | 5423篇 |
2020年 | 4102篇 |
2019年 | 3169篇 |
2018年 | 3604篇 |
2017年 | 4145篇 |
2016年 | 3611篇 |
2015年 | 5042篇 |
2014年 | 6571篇 |
2013年 | 7660篇 |
2012年 | 8527篇 |
2011年 | 8885篇 |
2010年 | 8035篇 |
2009年 | 7463篇 |
2008年 | 7333篇 |
2007年 | 7025篇 |
2006年 | 6276篇 |
2005年 | 5195篇 |
2004年 | 3685篇 |
2003年 | 2861篇 |
2002年 | 2748篇 |
2001年 | 2280篇 |
2000年 | 2186篇 |
1999年 | 1913篇 |
1998年 | 1357篇 |
1997年 | 1172篇 |
1996年 | 1087篇 |
1995年 | 838篇 |
1994年 | 683篇 |
1993年 | 479篇 |
1992年 | 373篇 |
1991年 | 282篇 |
1990年 | 223篇 |
1989年 | 197篇 |
1988年 | 156篇 |
1987年 | 78篇 |
1986年 | 80篇 |
1985年 | 41篇 |
1984年 | 45篇 |
1983年 | 32篇 |
1982年 | 29篇 |
1981年 | 26篇 |
1980年 | 27篇 |
1979年 | 14篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1959年 | 10篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Si3N4 ceramic was jointed to itself using a filler alloy of Cu76.5Pd8.5Ti15, and the mechanical properties of the jointwere measured and analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15, the SisN4/SisN4 joints were obtained bybrazing at 1373~1473 K f 相似文献
12.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
13.
Min Song Weiying Zhu 《Communications Letters, IEEE》2004,8(7):479-481
This letter analyzes the saturated throughput for multicast switches with multiple input queues per input port. Under the assumptions of a Poisson uniform traffic model and random packet scheduling policy, we derive the multicast switch saturated throughput under different fanouts. To verify the analysis, extensive simulations are conducted with different switch sizes and fanouts. It is shown that the theoretical analysis and the simulation results have a discrepancy less than 1.9%. Results from this letter can be used as a guidance to design the optimal queuing for multicast switches. 相似文献
14.
激光水下成像技术及其进展 总被引:6,自引:0,他引:6
介绍了近年发展起来的三种主要的激光水下成像方法,即常规水下激光成像、高分辨率水下激光三维成像和偏振激光成像,分析了它们各自的工作原理、特点以及各自的发展状况。 相似文献
15.
16.
带隔板底水油藏油井临界产量计算公式 总被引:25,自引:9,他引:16
本给出了带隔板底水油藏油井的监界产量计算公式,它适用于所有带隔板底水油藏的油井。 相似文献
17.
1 INTRODUCTIONParticlesreinforcedtitaniumalloymatrixcomposites(TMCp)havewideapplicationfieldsfortheirattractivehighspecificstreng 相似文献
18.
通过密度测定和DSC热分析,观测了超高分子量聚乙烯的辐射效应。实验结果表明:在吸收剂量0—1.13MGy范围内,密度随吸收剂量的增加而增大,熔化热和熔点也有所增加,特别是在低剂量范围内增加十分明显。以上结果都说明,超高分子量聚乙烯在辐照过程中,结晶在完善或有新的结晶形成 相似文献
19.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration 相似文献
20.
Fernandez E.B. Gudes E. Haiyan Song 《Knowledge and Data Engineering, IEEE Transactions on》1994,6(2):275-292
The integration of object-oriented programming concepts with databases is one of the most significant advances in the evolution of database systems. Many aspects of such a combination have been studied, but there are few models to provide security for this richly structured information. We develop an authorization model for object-oriented databases. This model consists of a set of policies, a structure for authorization rules, and algorithms to evaluate access requests against the authorization rules. User access policies are based on the concept of inherited authorization applied along the class structure hierarchy. We propose also a set of administrative policies that allow the control of user access and its decentralization. Finally, we study the effect of class structuring changes on authorization 相似文献