全文获取类型
收费全文 | 85125篇 |
免费 | 7947篇 |
国内免费 | 4076篇 |
专业分类
电工技术 | 5317篇 |
技术理论 | 5篇 |
综合类 | 5819篇 |
化学工业 | 14188篇 |
金属工艺 | 4871篇 |
机械仪表 | 5426篇 |
建筑科学 | 6595篇 |
矿业工程 | 2074篇 |
能源动力 | 2457篇 |
轻工业 | 6224篇 |
水利工程 | 1655篇 |
石油天然气 | 3889篇 |
武器工业 | 690篇 |
无线电 | 10465篇 |
一般工业技术 | 11065篇 |
冶金工业 | 3607篇 |
原子能技术 | 1105篇 |
自动化技术 | 11696篇 |
出版年
2024年 | 373篇 |
2023年 | 1385篇 |
2022年 | 2523篇 |
2021年 | 3534篇 |
2020年 | 2639篇 |
2019年 | 2258篇 |
2018年 | 2386篇 |
2017年 | 2787篇 |
2016年 | 2669篇 |
2015年 | 3524篇 |
2014年 | 4231篇 |
2013年 | 5177篇 |
2012年 | 5469篇 |
2011年 | 6047篇 |
2010年 | 5345篇 |
2009年 | 4917篇 |
2008年 | 4888篇 |
2007年 | 4518篇 |
2006年 | 4478篇 |
2005年 | 3992篇 |
2004年 | 2834篇 |
2003年 | 2642篇 |
2002年 | 2841篇 |
2001年 | 2375篇 |
2000年 | 2040篇 |
1999年 | 1941篇 |
1998年 | 1639篇 |
1997年 | 1343篇 |
1996年 | 1293篇 |
1995年 | 1108篇 |
1994年 | 930篇 |
1993年 | 707篇 |
1992年 | 528篇 |
1991年 | 430篇 |
1990年 | 313篇 |
1989年 | 251篇 |
1988年 | 224篇 |
1987年 | 140篇 |
1986年 | 103篇 |
1985年 | 74篇 |
1984年 | 62篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 33篇 |
1980年 | 26篇 |
1979年 | 17篇 |
1978年 | 5篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
叙述了石油库在发油过程中的HSE管理;发油过程中的危害识别,包括识别范围和内容;发油过程中风险评价的常用基本方法和常见问题;发油过程中危险源的管理控制,包括建立危险源网络图、加强现场监控和制定应急预案。 相似文献
102.
103.
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
104.
105.
The multihop optical network is the most appropriate solution to satisfy the increasing applications of Internet services. This paper extends the regular Kautz graph to one with multiple layers in order to produce more architectural variations. The connectivity between adjacent layers utilizes the systematic connection patterns of a regular Kautz graph. A routing algorithm based on its property is presented. Optical passive star (OPS) couplers are adopted to implement our new topologies. Three scheduling criteria that can solve the contention problem in the intermediate nodes are evaluated and compared in terms of their capability to improve the accessibility. 相似文献
106.
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
107.
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
108.
Generalized multiuser orthogonal space-division multiplexing 总被引:8,自引:0,他引:8
Zhengang Pan Kai-Kit Wong Tung-Sang Ng 《Wireless Communications, IEEE Transactions on》2004,3(6):1969-1973
This paper addresses the problem of performing orthogonal space-division multiplexing (OSDM) for downlink, point-to-multipoint communications when multiple antennas are utilized at the base station (BS) and (optionally) all mobile stations (MS). Based on a closed-form antenna weight solution for single-user multiple-input multiple-output communications in the presence of other receiver points, we devise an iterative algorithm that finds the multiuser antenna weights for OSDM in downlink or broadcast channels. Upon convergence, each mobile user will receive only the desired activated spatial modes with no cochannel interference. Necessary and sufficient conditions for the existence of OSDM among the number of mobile users, the number of transmit antennas at the BS, and the number of receive antennas at the MS, are also derived. The assumption for the proposed method is that the BS knows the channels for all MS's and that the channel dynamics are quasi-stationary. 相似文献
109.
介绍了土卡河水电站可研阶段通过方案比选后确定的工程规模(特征水位、装机容量)。为保证2006年底第一台机组发电,根据目前的施工进度,需要采用围堰挡水发电,文章简要介绍了第一台机组发电的运行方式。 相似文献
110.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献