全文获取类型
收费全文 | 27148篇 |
免费 | 1530篇 |
国内免费 | 4224篇 |
专业分类
化学 | 26632篇 |
晶体学 | 547篇 |
力学 | 168篇 |
综合类 | 147篇 |
数学 | 1067篇 |
物理学 | 4341篇 |
出版年
2024年 | 36篇 |
2023年 | 226篇 |
2022年 | 531篇 |
2021年 | 503篇 |
2020年 | 580篇 |
2019年 | 1521篇 |
2018年 | 685篇 |
2017年 | 1500篇 |
2016年 | 927篇 |
2015年 | 840篇 |
2014年 | 1071篇 |
2013年 | 2298篇 |
2012年 | 1644篇 |
2011年 | 1760篇 |
2010年 | 1247篇 |
2009年 | 1502篇 |
2008年 | 1689篇 |
2007年 | 1769篇 |
2006年 | 1651篇 |
2005年 | 1472篇 |
2004年 | 1475篇 |
2003年 | 1189篇 |
2002年 | 1003篇 |
2001年 | 836篇 |
2000年 | 817篇 |
1999年 | 603篇 |
1998年 | 560篇 |
1997年 | 472篇 |
1996年 | 388篇 |
1995年 | 399篇 |
1994年 | 283篇 |
1993年 | 258篇 |
1992年 | 255篇 |
1991年 | 180篇 |
1990年 | 113篇 |
1989年 | 100篇 |
1988年 | 81篇 |
1987年 | 48篇 |
1986年 | 45篇 |
1985年 | 51篇 |
1984年 | 37篇 |
1983年 | 20篇 |
1982年 | 41篇 |
1981年 | 42篇 |
1980年 | 24篇 |
1979年 | 45篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Lianfang Chen Hongmei NieGuangbo Zhang Fuwen GongYuzhu Yang Chengbin GongKun Xiao 《Tetrahedron letters》2014
This Letter aimed to develop an efficient method for the determination of cyanide ion (CN−). A novel colorimetric chemosensor 4-[(1E)-2-(4-hydroxyphenyl)ethenyl]-1-allylpyridinium bromide (HPEAPB) was synthesized. HPEAPB displayed good selectivity toward CN− over other competing anions in ethanol. A color change from yellow to red was immediately observed upon the addition of CN− and the limit of detection (LOD) was 3.4 × 10−6 mol L−1. The sensing mechanism was discussed by UV–vis, 1H NMR titration, and a comparison study. Colorimetric test paper for CN− was prepared by attaching HPEAPB to a chromatography paper, which could be used to detect CN− in environmental samples as simply as a pH-indicator paper for pH value. The LOD of the test paper for CN− was 2.0 × 10−4 mol L−1. This detection method for CN− has potential applications in cyanide ion containing fields by combination of rapid and real-time advantages. 相似文献
992.
G. Satish K. Harsha Vardhan ReddyK. Ramesh B.S.P. Anil KumarY.V.D. Nageswar 《Tetrahedron letters》2014
A simple and efficient, ligand-free C–N cross-coupling of aryl halides/benzyl bromides with trans-4-hydroxy-l-proline has been developed to produce aromatized N-substituted pyrroles, using a catalytic amount of magnetically separable and recyclable CuFe2O4 nanoparticles, in the presence of Cs2CO3 in DMSO at 100 °C. 相似文献
993.
The reaction of 1-aryl-2-(dimethylaminomethylene)butane-1,3-diones with diethyl oxalate in the presence of sodium hydride in THF gave ethyl 5-aroyl-4-oxo-4H-pyran-2-carboxylates, from which 4-oxo-6-aryl-4H-pyran-2-carboxylic acids (6-arylcomanic acids) were obtained in high yields via acid-catalyzed deformylative rearrangement. 5-Aroyl-4-oxo-4H-pyran-2-carboxylic acids (5-aroylcomanic acids) were prepared via а ring-opening/ring-closure sequence by the reaction of 5-aroyl-2-carbethoxy-4-pyrones with piperidine and subsequent basic hydrolysis and acidification. 相似文献
994.
Satyanarayana Reddy Jaggavarapu Anand Solomon Kamalakaran Jagadeesh Babu Nanubolu Venkata Prasad Jalli Sravan Kumar Gangisetty Gopikrishna Gaddamanugu 《Tetrahedron letters》2014
Efficient and facile synthesis of 7H-benzopyrano[3,2-c]coumarins has been achieved by mild base promoted reaction of 4-chloro-3-formylcoumarin with diversely functionalized resorcinols. All the products were obtained as pure precipitates from the reaction mixture and the structure of the product was confirmed by X-ray analysis. 相似文献
995.
Sheng‐Run Zheng Xi‐Ling Wen Zi‐Meng Liu Tao Xie Jing‐Bo Tan Jun Fan Shuang‐Shuang Hou Wei‐Guang Zhang 《无机化学与普通化学杂志》2014,640(10):2057-2061
Two coordination polymers (CPs), namely, [Cu(Hptz)2(Hhba)2]n ( 1 ) [Hptz = 5‐(4‐pyridyl)‐1H‐tetrazole, H2hba = 2‐hydroxybenzoic acid] and [Zn3(ptz)2(hpa)2]n ( 2 ) (H2hpa = 2‐hydroxy‐2‐phenylacetic acid), were synthesized by solvothermal reactions. Both complexes were characterized by elemental analysis, infrared spectroscopy, powder X‐ray diffraction, thermogravimetric analysis, and single‐crystal X‐ray diffraction analysis. Compound 1 exhibits a 2D (4,4) network, where each layer connects to four adjacent layers to construct a 3D supramolecular framework. Compound 2 has a 3D framework structure composed of 1D SUBs, which are formed by both carboxyl and tetrazole groups. The complexes represent two rare examples of CPs constructed from Hptz and organic carboxyl acid ligands. Complex 2 exhibits intense, red‐shifted emissions in the visible region at room temperature. 相似文献
996.
997.
998.
Xin Ma Lien B. Lai Stella M. Lai Akiko Tanimoto Mark P. Foster Vicki H. Wysocki Venkat Gopalan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(43):11667-11671
We demonstrate that surface‐induced dissociation (SID) coupled with ion mobility mass spectrometry (IM‐MS) is a powerful tool for determining the stoichiometry of a multi‐subunit ribonucleoprotein (RNP) complex assembled in a solution containing Mg2+. We investigated Pyrococcus furiosus (Pfu) RNase P, an archaeal RNP that catalyzes tRNA 5′ maturation. Previous step‐wise, Mg2+‐dependent reconstitutions of Pfu RNase P with its catalytic RNA subunit and two interacting protein cofactor pairs (RPP21⋅RPP29 and POP5⋅RPP30) revealed functional RNP intermediates en route to the RNase P enzyme, but provided no information on subunit stoichiometry. Our native MS studies with the proteins showed RPP21⋅RPP29 and (POP5⋅RPP30)2 complexes, but indicated a 1:1 composition for all subunits when either one or both protein complexes bind the cognate RNA. These results highlight the utility of SID and IM‐MS in resolving conformational heterogeneity and yielding insights on RNP assembly. 相似文献
999.
1000.
Fanzhi Yang Karsten Rauch Katharina Kettelhoit Lutz Ackermann 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(42):11467-11470
Versatile ruthenium(II) complexes allow for site‐selective C H oxygenations with weakly‐coordinating aldehydes. The challenging C H functionalizations proceed with high chemoselectivity by rate‐determining C H metalation. The new method features an ample substrate scope, which sets the stage for the step‐economical preparation of various bioactive heterocycles. 相似文献