全文获取类型
收费全文 | 13026篇 |
免费 | 864篇 |
国内免费 | 105篇 |
专业分类
电工技术 | 315篇 |
综合类 | 184篇 |
化学工业 | 2696篇 |
金属工艺 | 462篇 |
机械仪表 | 749篇 |
建筑科学 | 446篇 |
矿业工程 | 65篇 |
能源动力 | 535篇 |
轻工业 | 919篇 |
水利工程 | 68篇 |
石油天然气 | 244篇 |
武器工业 | 36篇 |
无线电 | 2233篇 |
一般工业技术 | 2555篇 |
冶金工业 | 953篇 |
原子能技术 | 204篇 |
自动化技术 | 1331篇 |
出版年
2024年 | 20篇 |
2023年 | 174篇 |
2022年 | 237篇 |
2021年 | 388篇 |
2020年 | 306篇 |
2019年 | 244篇 |
2018年 | 351篇 |
2017年 | 397篇 |
2016年 | 410篇 |
2015年 | 339篇 |
2014年 | 511篇 |
2013年 | 816篇 |
2012年 | 767篇 |
2011年 | 929篇 |
2010年 | 700篇 |
2009年 | 723篇 |
2008年 | 699篇 |
2007年 | 603篇 |
2006年 | 549篇 |
2005年 | 505篇 |
2004年 | 427篇 |
2003年 | 361篇 |
2002年 | 373篇 |
2001年 | 325篇 |
2000年 | 326篇 |
1999年 | 338篇 |
1998年 | 438篇 |
1997年 | 296篇 |
1996年 | 248篇 |
1995年 | 169篇 |
1994年 | 186篇 |
1993年 | 158篇 |
1992年 | 99篇 |
1991年 | 96篇 |
1990年 | 74篇 |
1989年 | 67篇 |
1988年 | 50篇 |
1987年 | 53篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 20篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 7篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Jokerst N.M. Gaylord T.K. Glytsis E. Brooke M.A. Cho S. Nonaka T. Suzuki T. Geddis D.L. Shin J. Villalaz R. Hall J. Chellapa A. Vrazel M. 《Advanced Packaging, IEEE Transactions on》2004,27(2):376-385
This paper explores design options for planar optical interconnections integrated onto boards, discusses fabrication options for both beam turning and embedded interconnections to optoelectronic devices, describes integration processes for creating embedded planar optical interconnections, and discusses measurement results for a number of integration schemes that have been demonstrated by the authors. In the area of optical interconnections with beams coupled to and from the board, the topics covered include integrated metal-coated polymer mirrors and volume holographic gratings for optical beam turning perpendicular to the board. Optical interconnections that utilize active thin film (approximately 1-5 /spl mu/m thick) optoelectronic components embedded in the board are also discussed, using both Si and high temperature FR-4 substrates. Both direct and evanescent coupling of optical signals into and out of the waveguide are discussed using embedded optical lasers and photodetectors. 相似文献
22.
23.
A route to synthesize ZSM‐5 crystals with a bimodal micro/mesoscopic pore system has been developed in this study; the successful incorporation of the mesopores within the ZSM‐5 structure was performed using tetrapropylammonium hydroxide (TPAOH)‐impregnated mesoporous materials containing carbon nanotubes in the pores, which were encapsulated in the ZSM‐5 crystals during a solid rearrangement process within the framework. Such mesoporous ZSM‐5 zeolites can be readily obtained as powders, thin films, or monoliths. 相似文献
24.
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
25.
中原油田岩石可钻性与声波时差关系研究 总被引:3,自引:0,他引:3
选取中原油田的大量岩心,采用常规岩石力学测试方法测定了岩石的可钻性、声波测试方法测定了岩石和岩屑声波时差,通过对测得的岩石可钻性级值和声波时差进行回归拟合,得出了中原油田岩石可钻性与声波时差的关系式。现场应用表明,该关系式较好地反映了中原油田地层岩石可钻性与声波时差的关系,可以在优选钻头时作为参考或直接应用。 相似文献
26.
Jui-Ting Weng Jiunn Ru Lai Wanjiun Liao 《Wireless Communications, IEEE Transactions on》2006,5(7):1676-1684
In this paper, we analyze node mobility for reliable packet delivery in mobile IP networks. In mobile IP, packets destined to roaming nodes are intercepted by their home agents and delivered via tunneling to their care of addresses (CoA). A mobile node may roam across multiple subnets. At each boundary crossing, a handoff is initiated such that the CoA is updated and a new tunnel is established. We consider both basic mobile IP handoff and smooth handoff. We find that reliable packet delivery in mobile IP networks can be modeled as a renewal process, because the retransmission over a new tunnel after each boundary crossing is independent of the previous history. We then derive the probability distribution of boundary crossings for each successful packet, based on which the packet reliable delivery time can be obtained. Our analytical model is derived based on a general distribution of residence time in a subnet and a general distribution of successful retransmission attempts in each subnet. The results can be readily applied to any distributions for both items. We also provide numerical examples to calculate the probability distribution of boundary crossings, and conduct simulations to validate our analytical results 相似文献
27.
Boon Tiong Tan Siou Teck Chew Mook Seng Leong Ban Leong Ooi 《Microwave Theory and Techniques》2003,51(8):1906-1910
A dual-mode ring bandpass filter with two pairs of capacitors has been designed. The capacitors are used to control the location of the even- and odd-mode frequencies independently, allowing weak coupling for narrow-band filter design with realizable capacitance values. Theoretical expressions have been derived for these frequencies. A 4% bandwidth bandpass filter centered at 1.9 GHz was designed and tested with good agreement between theoretical and measured results. 相似文献
28.
H.S. Seo Y.G. Choi B.J. Park D.H. Cho K.H. Kim 《Photonics Technology Letters, IEEE》2003,15(9):1198-1200
A flat signal gain over in the entire C- and L-bands by erbium (Er) ions' radiative transition and stimulated Raman scattering in an Er-doped germano-silica fiber can be obtained if proper values of the concentration of Er and background loss in a fiber core are obtained during the fiber fabrication process. The optimized conditions for the flat C- and L-band gain are analyzed as functions of Er concentrations. Even for a low-gain value provided by a germano-silica core fiber with a low Er concentration and an optimum fiber length, a relatively low pump is required to obtain the flat gain band. 相似文献
29.
30.
Maenghyo Cho Hee Yuel Roh 《International journal for numerical methods in engineering》2003,56(1):81-115
In the present study first‐order shear deformable shell finite elements based on general curvilinear co‐ordinates are proposed. For the development of the present shell elements, a partial mixed variational functional with independently assumed strains is provided in order to avoid the severe locking troubles known as transverse shear and membrane lockings. Bubble functions are included in the shape function of displacement to improve the performance of the developed element. The proposed assumed strain four‐ and nine‐node elements based on the general tensor shell theory provide an efficient linkage framework for shell surface modelling and finite element analysis. In the several benchmark problems, the present shell elements with exact geometric representations demonstrate their performance compared to previously reported results. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献