全文获取类型
收费全文 | 9225篇 |
免费 | 411篇 |
国内免费 | 61篇 |
专业分类
化学 | 6329篇 |
晶体学 | 93篇 |
力学 | 280篇 |
数学 | 808篇 |
物理学 | 2187篇 |
出版年
2023年 | 46篇 |
2022年 | 135篇 |
2021年 | 226篇 |
2020年 | 178篇 |
2019年 | 172篇 |
2018年 | 172篇 |
2017年 | 144篇 |
2016年 | 296篇 |
2015年 | 269篇 |
2014年 | 353篇 |
2013年 | 596篇 |
2012年 | 743篇 |
2011年 | 823篇 |
2010年 | 469篇 |
2009年 | 386篇 |
2008年 | 616篇 |
2007年 | 580篇 |
2006年 | 512篇 |
2005年 | 473篇 |
2004年 | 408篇 |
2003年 | 325篇 |
2002年 | 326篇 |
2001年 | 216篇 |
2000年 | 177篇 |
1999年 | 129篇 |
1998年 | 69篇 |
1997年 | 79篇 |
1996年 | 95篇 |
1995年 | 81篇 |
1994年 | 75篇 |
1993年 | 57篇 |
1992年 | 60篇 |
1991年 | 47篇 |
1990年 | 51篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1972年 | 9篇 |
排序方式: 共有9697条查询结果,搜索用时 46 毫秒
341.
342.
343.
344.
345.
Marine Rémy Dr. Iwona Nierengarten Boram Park Dr. Michel Holler Dr. Uwe Hahn Dr. Jean-François Nierengarten 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(33):8492-8499
Stable pillar[5]arene-containing [2]rotaxane building blocks with pentafluorophenyl ester stoppers have been efficiently prepared on a multi-gram scale. Reaction of these building blocks with various nucleophiles gave access to a wide range of [2]rotaxanes with amide, ester or thioester stoppers in good to excellent yields. The rotaxane structure is fully preserved during these chemical transformations. Actually, the addition-elimination mechanism at work during these transformations totally prevents the unthreading of the axle moiety of the mechanically interlocked system. The stopper exchange reactions were optimized both in solution and under mechanochemical solvent-free conditions. While amide formation is more efficient in solution, the solvent-free conditions are more powerful for the transesterification reactions. Starting from a fullerene-functionalized pillar[5]arene derivative, this new strategy gave easy access to a photoactive [2]rotaxane incorporating a C60 moiety and two Bodipy stoppers. Despite the absence of covalent connectivity between the Bodipy and the fullerene moieties in this photoactive molecular device, efficient through-space excited state interactions have been evidenced in this rotaxane. 相似文献
346.
Two series of new thermotropic compounds with two terminal mesogenic units, p-oxybenzylidene-p-substituted anilines, attached to both ends of a central polymethylene spacer were prepared. The first series of compounds has central polymethylene spacers of varying length, while the second has different substituents on the aniline moiety of the mesogenic groups which are bracketing the central decamethylene spacer. The mesomorphic properties of the compounds were investigated by differential scanning calorimetry and on the hot-stage of a polarizing microscope. A thermodynamic analysis of the phase transitions of the compounds was made and the results are explained in relation to their structure. 相似文献
347.
Aryl pyridyl ethers were prepared from phenols and active halopyridines under essentially neutral condition via fluoride ion assisted reaction. 相似文献
348.
Aldoximes are readily dehydrated to nitriles with Raney nickel in refluxing 2-propanol. 相似文献
349.
350.
Light intensity and image visualization of GDI injector sprays according to nozzle hole arrangements
The light intensity measurement and image visualization of multi-hole injection spray due to different hole arrangements and hole numbers were investigated. The light intensities and behavior characteristics of the GDI spray were analyzed through the axial and diagonal spray penetration, cone angle, and spray area from the spray images by using the image visualization system and image analysis system. The atomization performance of GDI injectors was analyzed by the local and overall Sauter mean diameter (SMD) measurement. 相似文献