全文获取类型
收费全文 | 286373篇 |
免费 | 3479篇 |
国内免费 | 734篇 |
专业分类
电工技术 | 5204篇 |
综合类 | 255篇 |
化学工业 | 43282篇 |
金属工艺 | 16693篇 |
机械仪表 | 12071篇 |
建筑科学 | 5483篇 |
矿业工程 | 2803篇 |
能源动力 | 6438篇 |
轻工业 | 15083篇 |
水利工程 | 3959篇 |
石油天然气 | 8741篇 |
武器工业 | 23篇 |
无线电 | 29563篇 |
一般工业技术 | 65502篇 |
冶金工业 | 40437篇 |
原子能技术 | 7593篇 |
自动化技术 | 27456篇 |
出版年
2022年 | 2153篇 |
2021年 | 3138篇 |
2020年 | 2424篇 |
2019年 | 2887篇 |
2018年 | 11915篇 |
2017年 | 12203篇 |
2016年 | 9036篇 |
2015年 | 3235篇 |
2014年 | 4651篇 |
2013年 | 10162篇 |
2012年 | 8719篇 |
2011年 | 15297篇 |
2010年 | 13548篇 |
2009年 | 13015篇 |
2008年 | 12985篇 |
2007年 | 14517篇 |
2006年 | 6043篇 |
2005年 | 8443篇 |
2004年 | 6626篇 |
2003年 | 6262篇 |
2002年 | 5144篇 |
2001年 | 4681篇 |
2000年 | 4459篇 |
1999年 | 4359篇 |
1998年 | 10444篇 |
1997年 | 7392篇 |
1996年 | 5702篇 |
1995年 | 4280篇 |
1994年 | 3762篇 |
1993年 | 3995篇 |
1992年 | 3086篇 |
1991年 | 3124篇 |
1990年 | 2981篇 |
1989年 | 2938篇 |
1988年 | 2945篇 |
1987年 | 2589篇 |
1986年 | 2634篇 |
1985年 | 2929篇 |
1984年 | 2754篇 |
1983年 | 2618篇 |
1982年 | 2353篇 |
1981年 | 2326篇 |
1980年 | 2386篇 |
1979年 | 2384篇 |
1978年 | 2406篇 |
1977年 | 2513篇 |
1976年 | 2909篇 |
1975年 | 2200篇 |
1974年 | 2075篇 |
1973年 | 2175篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
85.
Gel state reactions offer new direction for the reactivity of the organic molecules or metal‐organic materials upon photoirradiation with shorter reaction times and high yields compared to solid and solution states. The restricted molecular movement among the molecules in the soft solids control the stereoselectivity of the photoproducts in the gel state reactions. To date, most of the strategies based on self‐assembly have been demonstrated in the solid state, in particular for [2+2] reactions of olefins and polymerization reactions of diacetylenes via 1,4 addition. The soft materials are of emerging materials in recent days given their many applicative day‐to‐day aspects. This review gives a glimpse of recent reports on pericyclic reactions in the gel state that are designed based on the self‐assembly concept. Also it highlights how such reactions accompany the physical changes in the structure of the gels and stereo controlled products with high yields. 相似文献
86.
87.
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
88.
Dhirendra Kumar Mishra Gopal Pugazhenthi Tamal Banerjee 《International Journal of Hydrogen Energy》2021,46(29):15773-15779
The current work explores the usage of novel synthesized Deep Eutectic Solvent (DES) as a catalyst cum solvent media for the thermal dehydrogenation of chemical hydrides, namely Ammonia Borane (AB) and Ethylene diamine bisborane (EDAB). In the first instance, the quantum chemistry based COSMO-SAC (COnductor like Screening MOdel Segment Activity Coefficient) model was used for the selection of the pertinent solvent. 1-Butyl-3-methylimidazolium methanesulfonate: Imidazole ([BMIM][MeSO3]:[Im]) turned out to be an ideal eutectic mixture with the highest predicted solubility with amine boranes. The DES was synthesized by combining the Hydrogen Bond Acceptor (HBA), namely 1-Butyl-3-methylimidazolium methanesulfonate and Imidazole as Hydrogen Bond Donor (HBD) at a molar ratio of 1:2 and T = 70 °C. The formation of DES was confirmed by recording the NMR spectra. Further, the thermal dehydrogenation study was performed at a vacuum of 4 × 10?2 mbar (gauge pressure) of AB/DES and EDAB/DES systems at 105 °C, where a hydrogen equivalent of 1.40 and 2.55 was produced, respectively. The residual samples were further analyzed through 1H NMR analysis for the reaction mechanism and to confirm the role of Ionic Liquid-based DES as catalyst cum solvent media. 相似文献
89.
90.