全文获取类型
收费全文 | 53542篇 |
免费 | 12796篇 |
国内免费 | 4565篇 |
专业分类
化学 | 54073篇 |
晶体学 | 791篇 |
力学 | 1533篇 |
综合类 | 297篇 |
数学 | 4012篇 |
物理学 | 10197篇 |
出版年
2024年 | 35篇 |
2023年 | 307篇 |
2022年 | 496篇 |
2021年 | 747篇 |
2020年 | 1855篇 |
2019年 | 3216篇 |
2018年 | 1573篇 |
2017年 | 1290篇 |
2016年 | 4112篇 |
2015年 | 4330篇 |
2014年 | 4387篇 |
2013年 | 5374篇 |
2012年 | 4705篇 |
2011年 | 3930篇 |
2010年 | 4246篇 |
2009年 | 4195篇 |
2008年 | 3879篇 |
2007年 | 3065篇 |
2006年 | 2805篇 |
2005年 | 2830篇 |
2004年 | 2373篇 |
2003年 | 2051篇 |
2002年 | 2770篇 |
2001年 | 1973篇 |
2000年 | 1773篇 |
1999年 | 766篇 |
1998年 | 313篇 |
1997年 | 229篇 |
1996年 | 204篇 |
1995年 | 188篇 |
1994年 | 174篇 |
1993年 | 140篇 |
1992年 | 80篇 |
1991年 | 103篇 |
1990年 | 67篇 |
1989年 | 48篇 |
1988年 | 43篇 |
1987年 | 21篇 |
1986年 | 29篇 |
1985年 | 34篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1975年 | 5篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
831.
Jun WANG Kai Ying LIU Li WANG Ji Ling BAI 《中国化学快报》2006,17(1):49-52
The techniques of combinatorial chemistry have recently been applied to the discovery of new asymmetric catalyst for a variety of organic transformations1-3. Using combina- torial methods, it is straightforward to generate thousands of potential asymmetri… 相似文献
832.
Ming‐Zhong Wang Yan‐Yan Zhang Shun‐Lin Li Xiang‐Hai Cai Xiao‐Dong Luo 《Helvetica chimica acta》2006,89(12):3104-3108
A new norsesquiterpene named eupatorone (= (4S,4aR,6R)‐1‐acetyl‐6‐(acetyloxy)‐4,4a,5,6‐tetrahydro‐4,7‐dimethylnaphthalen‐2(3H)‐one; 1 ) and a new sesquiterpene derivative named 2‐deoxo‐2‐(acetyloxy)‐9‐oxoageraphorone (= (1R,4S,4aR,6R,8aS)‐6‐(acetyloxy)‐3,4,4a,5,6,8a‐hexahydro‐4,7‐dimethyl‐1‐(1‐methylethyl)naphthalen‐2(1H)‐one; 2 ), together with the five known cadinene derivatives 3 – 7 were isolated from the flower of Eupatorium adenophorum (Spreng. ). Their structures were established by extensive NMR experiments, including 1D and 2D NMR. 相似文献
833.
834.
Chun‐Xiang Wang Chen‐Xia Du Zhi‐Feng Li 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):m488-m490
In the title compound, [Zn(C17H10N5O)2(H2O)2]·4H2O, cyclic water hexamers forming one‐dimensional metal–water chains are observed. The water clusters are trapped by the co‐operative association of coordination interactions and hydrogen bonds. The ZnII ion resides on a centre of symmetry and is in an octahedral coordination environment comprising two O atoms and two N atoms from two 2′‐(4,5‐diazafluoren‐9‐ylidene)picolinohydrazidate ligands and two water molecules. 相似文献
835.
Layer-by-layer fluorescent conjugated polyelectrolyte films have been studied. The photoluminescence of conjugate polyelectrolytes was observed to be highly tunable during this film assembly process. Efficient photoinduced electron transfer from thus prepared highly luminescent film to a natural electron-transfer protein cytochrome c has also been observed. 相似文献
836.
Complete 1H and 13C NMR assignments of four new steroidal glycosides from a gorgonian coral Junceella juncea 总被引:2,自引:0,他引:2
Four new cholest-type steroidal glycosides, junceellosides A-D, isolated from the EtOH/CH(2)Cl(2) extracts of the South China Sea gorgonian coral Junceella juncea, were identified. Complete assignments of the (1)H and (13)C NMR chemical shifts for these compounds were achieved by means of one- and two-dimensional NMR techniques, including (1)H-(1)H COSY, HSQC, HMBC and NOESY spectra. 相似文献
837.
A series of 1-(2,4-dichlorophenoxyacetoxy)alkylphosphonic acid dimethyl esters 5 and its corresponding phosphonate monosalts 6 were synthesized as potential herbicide. The phosphonate monosalts can be prepared from 1-(2,4-dichlorophenoxyacetoxy)alkylphosphonic acid dimethyl esters 5, which were synthesized by the condensation of O,O-dimethyl-1-hydroxyalkylphosphonates with dichlorophenoxyacetic chloride. This method provides a simple and efficient procedure for the synthesis of phosphonate derivatives containing sensitive groups to acid, base or water such as carboxylate ester bond; and the herbicidal activity of title compounds was evaluated in a set of experiments in greenhouse. Most of the compounds exhibited notable herbicidal activity. 相似文献
838.
Three new alkaloids, longistylumphyllines A–C (1–3), together with the six known alkaloids deoxycalyciphylline B, deoxyisocalyciphylline B, methyl homosecodaphniphyllate, daphnicyclidin A, daphnicyclidin B, and daphnicyclidin F, were isolated from the stems and leaves of Daphniphyllum longistylum. Their structures and relative configuration were elucidated on the basis of spectroscopic data, especially 1D and 2D NMR techniques. 相似文献
839.
840.
Xu‐Cheng Fu Xiao‐Yan Wang Ming‐Tian Li Xiao‐Tao Deng Cheng‐Gang Wang 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m343-m345
The title complex, {[Cu2(C8H4O4)2(C3H4N2)4(H2O)]·H2O}n, is a three‐dimensional polymer formed through bridging by phthalate dianions of two different CuII cations and a network of O(N)—H⋯O hydrogen bonds. The Cu—O and Cu—N interaction distances are in the ranges 2.0020 (16)–2.4835 (17) and 1.968 (2)–1.9855 (19) Å, respectively. The structure is composed of alternating polymer chains parallel to the c axis, with a shortest Cu⋯Cu distance of 6.3000 (5) Å. 相似文献