全文获取类型
收费全文 | 196451篇 |
免费 | 2353篇 |
国内免费 | 630篇 |
学科分类
工业技术 | 199434篇 |
出版年
2021年 | 1234篇 |
2019年 | 1280篇 |
2018年 | 2124篇 |
2017年 | 2104篇 |
2016年 | 2171篇 |
2015年 | 1489篇 |
2014年 | 2615篇 |
2013年 | 7951篇 |
2012年 | 4462篇 |
2011年 | 6110篇 |
2010年 | 4930篇 |
2009年 | 5771篇 |
2008年 | 6145篇 |
2007年 | 6196篇 |
2006年 | 5633篇 |
2005年 | 5304篇 |
2004年 | 5249篇 |
2003年 | 5092篇 |
2002年 | 4898篇 |
2001年 | 5305篇 |
2000年 | 4916篇 |
1999年 | 5435篇 |
1998年 | 15616篇 |
1997年 | 10294篇 |
1996年 | 7715篇 |
1995年 | 5746篇 |
1994年 | 4980篇 |
1993年 | 4984篇 |
1992年 | 3347篇 |
1991年 | 3228篇 |
1990年 | 3197篇 |
1989年 | 2997篇 |
1988年 | 2755篇 |
1987年 | 2202篇 |
1986年 | 2270篇 |
1985年 | 2591篇 |
1984年 | 2297篇 |
1983年 | 2046篇 |
1982年 | 1885篇 |
1981年 | 2023篇 |
1980年 | 1778篇 |
1979年 | 1643篇 |
1978年 | 1644篇 |
1977年 | 2015篇 |
1976年 | 2692篇 |
1975年 | 1416篇 |
1974年 | 1358篇 |
1973年 | 1305篇 |
1972年 | 1113篇 |
1971年 | 941篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
Bochkareva N. I. Ivanov A. M. Klochkov A. V. Kogotkov V. S. Rebane Yu. T. Virko M. V. Shreter Y. G. 《Semiconductors》2015,49(6):827-835
Semiconductors - It is shown that the emission efficiency and the 1/f noise level in light-emitting diodes with InGaN/GaN quantum wells correlate with how the differential resistance of a diode... 相似文献
33.
Mechanical durability of extruded fish feed must be optimized to lower economic losses as well as emission of organic matter to aquatic environments. The glass transition hypothesis for viscoelastic biopolymers is demonstrated and confirmed experimentally to be valid for extruded fish feed pellets. It is proposed and demonstrated that it is important to avoid early glass transition onset, to optimize the obtained mechanical durability. From the proposed glass transition hypothesis, immediate process relevance to the pre-drying transport mechanism is demonstrated. Furthermore, measured mechanical durability is found to range from 1.5 to 5.0% loss, for different combinations of drying parameters. 相似文献
34.
35.
36.
37.
Akopdzhanyan T. G. Chemagina E. A. Borovinskaya I. P. 《Russian Journal of Non-Ferrous Metals》2020,61(6):686-690
Russian Journal of Non-Ferrous Metals - The synthesis and sintering of the (AlN)x(SiC)1 – x solid solution have been studied under conditions of self-propagating high-temperature synthesis... 相似文献
38.
Zavadiuk S.V. Loboda P.I. Soloviova T.O. Trosnikova I.Iu. Karasevska O.P. 《Powder Metallurgy and Metal Ceramics》2020,59(1-2):22-28
Powder Metallurgy and Metal Ceramics - The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the... 相似文献
39.
Daniel T. Payne Mandeep K. Chahal V clav B&rcaron ezina Whitney A. Webre Katsuhiko Ariga Francis D Souza Jan Labuta Jonathan P. Hill 《Frontiers of Chemical Science and Engineering》2020,14(1):28
Chiral 1,1’-binaphthyl-linked diporphyrin ‘tweezers’ (R)-1/(S)-1 and the corresponding zinc(II) complexes (R)-2/(S)-2 were prepared as chiral host molecules, and their utility for chiral analyses (especially enantiomeric excess (ee) determinations) were evaluated. Tris(1-n-dodecyl)porphyrins were used for the first time as the interacting units. Host capabilities of the diporphyrin tweezers were investigated by titrations with (R,R)- and (S,S)-cyclohexane-1,2-diamine (CHDA). The host molecules could be used as multichannel probes of ee by using UV-vis, circular dichroism (CD), fluorescence emission and 1H nuclear magnetic resonance (1H-NMR) methods. Chiral configurations could also be differentiated using CD or 1H-NMR spectroscopy. All three optical techniques give good resolution of ee with reasonable sensitivity considering the low concentrations used (ca. 10−6 mol·L−1). The ee determination of CHDA enantiomers using NMR spectroscopy is also possible because of the reasonably well separated resonances in the case of (R,R)- and (S,S)-CHDA. Non-metallated (R)-1/(S)-1 hosts could not be used to detect chiral information in a strongly acidic chiral guest. This work demonstrates the utility of 1,1’-binapthyl-linked chiral hosts for chiral analysis of ditopically interacting enantiomers. 相似文献
40.