全文获取类型
收费全文 | 15262篇 |
免费 | 1071篇 |
国内免费 | 42篇 |
专业分类
电工技术 | 192篇 |
综合类 | 18篇 |
化学工业 | 3464篇 |
金属工艺 | 582篇 |
机械仪表 | 776篇 |
建筑科学 | 365篇 |
矿业工程 | 27篇 |
能源动力 | 526篇 |
轻工业 | 1477篇 |
水利工程 | 64篇 |
石油天然气 | 45篇 |
武器工业 | 3篇 |
无线电 | 2310篇 |
一般工业技术 | 3089篇 |
冶金工业 | 1815篇 |
原子能技术 | 157篇 |
自动化技术 | 1465篇 |
出版年
2023年 | 121篇 |
2022年 | 231篇 |
2021年 | 408篇 |
2020年 | 293篇 |
2019年 | 329篇 |
2018年 | 419篇 |
2017年 | 454篇 |
2016年 | 521篇 |
2015年 | 460篇 |
2014年 | 643篇 |
2013年 | 1024篇 |
2012年 | 891篇 |
2011年 | 1079篇 |
2010年 | 785篇 |
2009年 | 779篇 |
2008年 | 766篇 |
2007年 | 595篇 |
2006年 | 497篇 |
2005年 | 428篇 |
2004年 | 415篇 |
2003年 | 403篇 |
2002年 | 327篇 |
2001年 | 309篇 |
2000年 | 273篇 |
1999年 | 272篇 |
1998年 | 634篇 |
1997年 | 463篇 |
1996年 | 294篇 |
1995年 | 233篇 |
1994年 | 229篇 |
1993年 | 219篇 |
1992年 | 148篇 |
1991年 | 139篇 |
1990年 | 113篇 |
1989年 | 119篇 |
1988年 | 85篇 |
1987年 | 63篇 |
1986年 | 72篇 |
1985年 | 82篇 |
1984年 | 80篇 |
1983年 | 58篇 |
1982年 | 55篇 |
1981年 | 51篇 |
1980年 | 54篇 |
1979年 | 45篇 |
1978年 | 35篇 |
1977年 | 61篇 |
1976年 | 91篇 |
1975年 | 44篇 |
1973年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
The deactivation characteristics of Pd/SiO2 in the selective hydrogenation of acetylene were correlated with changes in the amount of the C4 species produced. The amounts of butenes produced changed in parallel with the catalyst activity, indicating that the rate limiting step for butene production was the same as that for acetylene hydrogenation. On the other hand, the amount of 1,3-butadiene produced changed, showing a maximum with catalyst deactivation because 1,3-butadiene is an intermediate in the sequential reaction process which involves both the production and consumption of 1,3-butadiene. This was verified by a simultaneous TG/reaction experiment showing that 1,3-butadiene was a precursor of green oil. The catalyst showed a self-regenerative behavior in its activity and the amounts of C4 species produced during the early stage of deactivation because two opposite factors, which contributed to either the lowering or the promotion of activity, were involved in the process. A specific type of polymer species, produced during the initial period of deactivation, is proposed to be responsible for the promotion of catalyst activity. 相似文献
23.
Takuma Suzuki Hang-Ju Ko Agus Setiawan Jung-Jin Kim Koh Saitoh Masami Terauchi Takafumi Yao 《Materials Science in Semiconductor Processing》2003,6(5-6):519-521
We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH3 is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH3 pre-exposure helps form a Zn3N2 layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar. 相似文献
24.
Dynamic RSVP protocol 总被引:5,自引:0,他引:5
Geng-Sheng Kuo Po-Chang Ko 《Communications Magazine, IEEE》2003,41(5):130-135
RSVP is a resource reservation setup protocol that can be used by a host to request specific QoS for multicast multimedia flows on the Internet. Multiprotocol label switching (MPLS) architecture also needs RSVP. The fact that the resolutions of the display system used in different receiver nodes might have different, multi-resolution characteristics is supported in the MPEG-4 standard, and the EZW compression algorithm can cease decoding at any point in the bitstream. However, RSVP does not provide a more flexible mechanism. In this article we propose an extension of RSVP to provide the needed mechanism, coined dynamic RSVP (DRSVP), to dynamically adjust reserved resources on nodes without much effort. It provides different video resolutions to different receiver nodes with different needed reserved resources. Therefore, it does not waste precious Internet resources to transmit unnecessary multimedia packets. 相似文献
25.
R Albrecht TC Awes C Baktash P Beckmann F Berger R Bock G Claesson G Clewing L Dragon A Eklund RL Ferguson A Franz S Garpman R Glasow HA Gustafsson HH Gutbrod J Idh P Jacobs K Kampert BW Kolb P Kristiansson IY Lee H Loehner I Lund FE Obenshain A Oskarsson I Otterlund T Peitzmann S Persson F Plasil AM Poskanzer M Purschke H Ritter S Saini R Santo HR Schmidt T Siemiarczuk SP Sorensen E Stenlund ML Tincknell GR Young 《Canadian Metallurgical Quarterly》1991,44(6):2736-2752
26.
AB Young 《Canadian Metallurgical Quarterly》1997,153(8-9):496-498
The gene for Huntington's disease is widely expressed in brain and yet the illness is characterized pathologically by a distinct regional pattern of cell death. Various theories for this selective vulnerability have been offered but the most compelling remains that of abnormal energy metabolism. These issues are reviewed. 相似文献
27.
Hansen P.B. Raybon G. Koren U. Miller B.J. Young M.G. Newkirk M.A. Chien M.-D. Tell B. Burrus C.A. 《Electronics letters》1993,29(9):739-741
A 2 cm long three-contact multisection laser has been fabricated for modelocking at very low repetition rates. Active modelocking yields 8.0-12.3 ps pulses at 2.2, 4.3 and 6.5 GHz corresponding to the fundamental, first, and second harmonics of the cavity resonance frequency. This device demonstrates the feasibility of fabricating monolithic pulse sources operating at rates as low as the OC-48 Sonet transmission rate (2.488 Gbit/s).<> 相似文献
28.
29.
30.
Robotic synthesis is making possible the synthesis of large, systematically designed sets of compounds. We analyze a 512-compound set that is a 2(9) full factorial experimental design using a recursive partitioning algorithm, FIRM, and a high-dimension visualization tool, TempleMVV. These techniques are used to quickly and easily identify the main trends in the data set and also identify unusual observations. We show that analytical and visualization methods can be used synergistically to analyze a large, complex, high-dimensional data set. We also show that a fractional factorial design of 128 compounds would give essentially the same information. 相似文献