全文获取类型
收费全文 | 20443篇 |
免费 | 1515篇 |
国内免费 | 41篇 |
专业分类
电工技术 | 279篇 |
综合类 | 19篇 |
化学工业 | 4874篇 |
金属工艺 | 756篇 |
机械仪表 | 1151篇 |
建筑科学 | 435篇 |
矿业工程 | 13篇 |
能源动力 | 755篇 |
轻工业 | 1919篇 |
水利工程 | 65篇 |
石油天然气 | 28篇 |
无线电 | 3161篇 |
一般工业技术 | 4262篇 |
冶金工业 | 1888篇 |
原子能技术 | 235篇 |
自动化技术 | 2159篇 |
出版年
2023年 | 199篇 |
2022年 | 325篇 |
2021年 | 566篇 |
2020年 | 409篇 |
2019年 | 523篇 |
2018年 | 589篇 |
2017年 | 663篇 |
2016年 | 742篇 |
2015年 | 676篇 |
2014年 | 925篇 |
2013年 | 1367篇 |
2012年 | 1330篇 |
2011年 | 1562篇 |
2010年 | 1100篇 |
2009年 | 1087篇 |
2008年 | 1042篇 |
2007年 | 808篇 |
2006年 | 736篇 |
2005年 | 638篇 |
2004年 | 604篇 |
2003年 | 574篇 |
2002年 | 509篇 |
2001年 | 410篇 |
2000年 | 360篇 |
1999年 | 392篇 |
1998年 | 704篇 |
1997年 | 506篇 |
1996年 | 315篇 |
1995年 | 267篇 |
1994年 | 243篇 |
1993年 | 233篇 |
1992年 | 168篇 |
1991年 | 138篇 |
1990年 | 128篇 |
1989年 | 124篇 |
1988年 | 79篇 |
1987年 | 76篇 |
1986年 | 72篇 |
1985年 | 93篇 |
1984年 | 86篇 |
1983年 | 58篇 |
1982年 | 47篇 |
1981年 | 45篇 |
1980年 | 46篇 |
1979年 | 45篇 |
1978年 | 35篇 |
1977年 | 56篇 |
1976年 | 89篇 |
1975年 | 44篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
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
42.
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
43.
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
44.
45.
A logic language is suitable for specification if it is equipped with features for data abstraction and modularization. In this paper, an effective mechanism to incorporate function and type into logic programming is presented as the means to embed data abstraction mechanism into logic programming. This incorporation is essentially based on Horn clause logic with equality and a polymorphic type system that is an extension of Mycroft and O’Keefe’s system. This paper also presents an implementation based on Warren Abstract Machine (WAM) and shows the performance, along with a comparison with WAM. 相似文献
46.
A series of polyurethane block copolymers based on hydroxy-terminated polydimethylsiloxane and poly(propylene glycol) soft segments of molecular weights 1818 and 2000, respectively, were synthesized. The hard segments consisted of 4,4′-diphenylnethane diisocyanate and 1,4-butanediol as the chain extender. Samples with different molar ratios were prepared. We tried to synthesize polydimethylsiloxane-based polyurethanes (PDMS-PU) containing a hard block as major fraction and a soft block as minor fraction for preparing toughened rigid systems. After a study of the pure polydimethylsiloxane-based polyurethane and poly(propylene glycol)-based polyurethane (PPG-PU), (mixed polyol)-based block copolymers and blends of PDMS-PU and PPG-PU were synthesized, and characterized by means of differential scanning calorimetry, tensile testing and scanning electron microscopy. In (mixed polyol)-based copolymers and lower hard-segment content blends, macro-phase separation occurred, but blends with higher hard-segment contents showed significant reduction in amounts of phase separation. 相似文献
47.
48.
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
49.
50.
A simple amplitude shift keying (ASK) optical link is demonstrated by using a low-cost self-pulsating laser diode and an envelope detector for a low-cost broadband local area network. A link sensitivity of -22 dBm was achieved at 200 Mbit/s. Because the self-pulsation frequency can be tuned by the bias current, frequency division multiplexing can be simply implemented for multiuser applications 相似文献