全文获取类型
收费全文 | 76057篇 |
免费 | 6722篇 |
国内免费 | 5155篇 |
学科分类
工业技术 | 87934篇 |
出版年
2024年 | 201篇 |
2023年 | 1232篇 |
2022年 | 1806篇 |
2021年 | 2765篇 |
2020年 | 2436篇 |
2019年 | 2021篇 |
2018年 | 1797篇 |
2017年 | 2359篇 |
2016年 | 2714篇 |
2015年 | 2712篇 |
2014年 | 3834篇 |
2013年 | 4232篇 |
2012年 | 4785篇 |
2011年 | 5727篇 |
2010年 | 4117篇 |
2009年 | 4838篇 |
2008年 | 4208篇 |
2007年 | 5017篇 |
2006年 | 4795篇 |
2005年 | 3998篇 |
2004年 | 3304篇 |
2003年 | 3053篇 |
2002年 | 2582篇 |
2001年 | 2223篇 |
2000年 | 1929篇 |
1999年 | 1538篇 |
1998年 | 1204篇 |
1997年 | 953篇 |
1996年 | 854篇 |
1995年 | 728篇 |
1994年 | 658篇 |
1993年 | 558篇 |
1992年 | 494篇 |
1991年 | 386篇 |
1990年 | 307篇 |
1989年 | 209篇 |
1988年 | 159篇 |
1987年 | 134篇 |
1986年 | 116篇 |
1985年 | 129篇 |
1984年 | 112篇 |
1983年 | 77篇 |
1982年 | 85篇 |
1981年 | 69篇 |
1980年 | 60篇 |
1979年 | 58篇 |
1977年 | 59篇 |
1976年 | 63篇 |
1975年 | 74篇 |
1974年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 217 毫秒
991.
微波辐射下一步合成2-甲氧基-3-氰基-4-芳基吡啶和2-氨基-3-氰基-4-芳基吡喃衍生物 总被引:1,自引:0,他引:1
2,5-双亚苄基环戊酮与丙二腈在氢氧化钠-甲醇或哌啶-乙醇中,经微波辐射一步合成了2-甲氧基-3-氰基-4-芳基吡啶和2-氨基-3-氰基-4-芳基吡喃衍生物,反应在3-9mi内完成,产率56%-78%。 相似文献
992.
993.
994.
Li Jianxiong R. Gries G. Gries K. N. Slessor G. G. S. King W. W. Bowers R. J. West 《Journal of chemical ecology》1993,19(6):1057-1062
Of the four possible stereoisomers of 5,11-dimethylheptadecane, the major sex pheromone component of the eastern hemlock looper (EHL),Lambdina fiscellaria fiscellaria Guen., and the western hemlock looper (WHL),Lambdina fiscellaria lugubrosa Hulst, (5R,11S)-5,11-dimethylheptadecane was the only stereoisomer eliciting electrophysiological responses by male EHL and WHL antennae. In field bioassays with EHL and WHL populations, traps baited with (5R,11S)-5, 11-dimethylheptadecane caught as many males as did traps baited with all four stereoisomers combined or a synthetic mixture of 5,11-dimethylheptadecanes. Catches in traps baited with the other three stereoisomers did not significantly differ from those in the unbaited control traps. We conclude that male antennae lack chemoreceptors for the other three stereoisomers of 5,11-dimethylheptadecane and hypothesize that only (5R,115)-5,11-dimethylheptadecane is produced by female EHLs and WHLs. 相似文献
995.
996.
介绍了1,4-环己烷二甲酸的物化性质、性能特点及应用,并综述了其专利制备技术的研究进展。 相似文献
997.
Naoufal Bahlawane Edgar Fischer Rivera Katharina Kohse-Hinghaus Armin Brechling Ulf Kleineberg 《Applied catalysis. B, Environmental》2004,53(4):245-255
The chemical vapor deposition method was used to deposit thin films of cobalt oxide starting with cobalt (II) acetylacetonate and oxygen. The deposition process was investigated and the obtained films were identified as a cubic spinel-type polycrystalline Co3O4 with a crystallite size of 30–40 nm. The coating was carbon-free and the surface oxygen concentration was measured to be 66 at.% with AES analysis. Smooth and highly uniform thin films were deposited on planar stainless steel substrates and subjected to TPR and catalysis tests that show positive correlation. The apparent activation energy of Co3O4 reduction to CoO was measured to be (33±5) kJ/mol. The catalytic activity of Co3O4 was investigated toward the conversion of both propane and ethanol to carbon dioxide. Though the catalytic action was registered at the same temperature, the deactivation process was seen to be different. The catalytic conversion of ethanol induces a fast deactivation process, which was linked to its high ability to reduce Co3O4. 相似文献
998.
A new CVD method without vacuum condition(CVDWV)was designed in this study,ithad been found that by modifying the flow rate of the carrier gas(N_2)and the temperature of sur-face reaction,silicon saturator and sample tube,the amount of silica deposited on the external sur-face of the zeolite could be precisely controlled,The changes in the physicochemical properties ofzeolite,such as pore-opening size,acidity and reaction property were investigated.The results ob-tained showed that:modification of the improved CVD method did not change the internal structureand acidity of the zeolite,but could bring about significant change of pore-opening size and reactionproperty as desired. 相似文献
999.
对6种苯并噻唑偶氮吡唑化合物的分析特性进行了探讨,着重研究了4—(6′—甲基苯并噻唑-2′-偶氮)-3,5-二氨基吡唑(MBTAP)与钯离子显色反应的光度性质。在非离子表面活性剂 Brij35存在下与钯离子形成橙红色的配合物。适宜的 pH 值范围为9.0~10.5.配合物的最大吸收波长为510nm,表观摩尔吸光系数为3.01×10~4L·mol~(-1)·cm~(-1)。钯在0~14μg/25mL,范围内服从比尔定律.显色体系可稳定11h。在柠檬酸存在下可消除 Fe~(3+)、Co~(2+)、Cu~(2+)、Ni~(2+)等离子的干扰。 相似文献
1000.