全文获取类型
收费全文 | 789篇 |
免费 | 79篇 |
国内免费 | 36篇 |
专业分类
化学 | 600篇 |
晶体学 | 11篇 |
力学 | 22篇 |
综合类 | 1篇 |
数学 | 33篇 |
物理学 | 237篇 |
出版年
2024年 | 1篇 |
2023年 | 17篇 |
2022年 | 20篇 |
2021年 | 40篇 |
2020年 | 36篇 |
2019年 | 26篇 |
2018年 | 21篇 |
2017年 | 25篇 |
2016年 | 46篇 |
2015年 | 36篇 |
2014年 | 48篇 |
2013年 | 54篇 |
2012年 | 78篇 |
2011年 | 66篇 |
2010年 | 39篇 |
2009年 | 27篇 |
2008年 | 52篇 |
2007年 | 36篇 |
2006年 | 38篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 22篇 |
2002年 | 16篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有904条查询结果,搜索用时 984 毫秒
1.
In the present work, the use of cylindrical turbulators in a double pipe heat exchanger has been investigated. Cylindrical fin type of turbulators has been placed circumferentially separated by 90° on the outer side of an inner pipe at a regular pitch. Experimental studies were undertaken for different air flow rates in a turbulent regime whose Reynolds number range between 2500 and 10000. Heat transfer characteristics like Nu and friction factor have been experimentally determined. Parametric studies were conducted by changing the pitch and also the orientation of the turbulators. Nu and friction factor were found to increase as the pitch is reduced. A model with alternatively changed orientation outperformed others by exhibiting highest Nu and reduced friction factor. 相似文献
2.
D3h‐Symmetric Porphyrin‐Based Rigid Macrocyclic Ligands for Multicofacial Multinuclear Complexes in a One‐Nanometer‐Sized Cavity 下载免费PDF全文
Yohei Ohkoda Akane Asaishi Tomoya Namiki Tomoaki Hashimoto Midori Yamada Koichiro Shirai Yuta Katagami Dr. Tomoaki Sugaya Prof. Makoto Tadokoro Prof. Akiharu Satake 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(33):11745-11756
The one‐step synthesis of D3h‐symmetric cyclic porphyrin trimers 1 composed of three 2,2′‐[4,4′‐bis(methoxycarbonyl)]bipyridyl moieties and three porphyrinatozinc moieties was achieved from a nickel‐mediated reductive coupling of meso‐5,15‐bis(6‐chloro‐4‐methoxycarbonylpyrid‐2‐yl)porphyrinatozinc. Although cyclic trimers 1 were obtained as a mixture that included other cyclic and acyclic porphyrin oligomers, an extremely specific separation was observed only for cyclic trimers 1 when using columns of silica gel modified with pyrenylethyl, cyanopropyl, and other groups. Structural analysis of cyclic trimers 1 was carried out by means of NMR spectroscopy and X‐ray crystallography. Treatment of an η3‐allylpalladium complex with a cyclic trimer gave a tris(palladium) complex containing three η3‐allylpalladium groups inside the space, which indicated that the bipyridyl moieties inside the ring could work as bidentate metalloligands. 相似文献
3.
4.
5.
Midori Kobayashi Hitoshi Awoki Yoshimi Nakazaki Gisaku Nakamura 《Graphs and Combinatorics》1989,5(1):243-244
In this paper, a perfect one-factorization ofK
36 is given, which is factor-1-rotational. 相似文献
6.
7.
O-Glycosylations using thiomethyl glycosides as donors were compared under both frozen and unfrozen conditions. In the presence of MeOTf as a promoter, enormous rate acceleration was observed when the glycosylation was conducted in p-xylene below its freezing point. 相似文献
8.
Adachi I Aihara H Dijkstra HB Enomoto R Fujii H Fujii K Fujii T Fujimoto J Fujiwara N Hayashii H Higashi S Iida N Imanishi A Ikeda H Ishii T Itoh R Iwasaki H Iwata S Kajikawa R Kamae T Kato S Kawabata S Kichimi H Kishida T Kobayashi M Kuroda S Kusuki N Maruyama A Maruyama K Masuda H Matsuda T Miyamoto A Morimoto T Nakamura K Nitoh O Noguchi S Ochiai F Okuno H Okusawa T Ohshima T Ozaki H Sato T Sai F Shimonaka J Shimozawa K Shirahashi A Sugahara R Sugiyama A Suzuki S Suwada T Takahashi K 《Physical review letters》1988,60(2):97-100
9.
10.
Ye Qing Li Ming Lu Chun Xu Lu Sai Jian Zhu Qi Fa Liu 《中国化学快报》2007,18(11):1313-1315
A novel and simple procedure for synthesis of azanucleoside by Mitsunobu reaction between N-(p-nitrobenzyloxycarbonyl)- trans-4-hydroxy-D-proline methyl ester obtained from trans-4-hydroxy-L-proline after six-step reaction and 2-fluoro-6-azidopurine is described,and azanucleoside is fluorinated by new fluridizer 2,2-difluoro-1,3-dimethylimidazolidine (DFI).All reactions could be carded out under mild condition. 相似文献