全文获取类型
收费全文 | 2820篇 |
免费 | 104篇 |
国内免费 | 12篇 |
专业分类
化学 | 1783篇 |
晶体学 | 5篇 |
力学 | 79篇 |
数学 | 511篇 |
物理学 | 558篇 |
出版年
2023年 | 17篇 |
2022年 | 23篇 |
2021年 | 41篇 |
2020年 | 54篇 |
2019年 | 50篇 |
2018年 | 35篇 |
2017年 | 41篇 |
2016年 | 76篇 |
2015年 | 59篇 |
2014年 | 88篇 |
2013年 | 130篇 |
2012年 | 165篇 |
2011年 | 219篇 |
2010年 | 139篇 |
2009年 | 111篇 |
2008年 | 176篇 |
2007年 | 195篇 |
2006年 | 159篇 |
2005年 | 128篇 |
2004年 | 122篇 |
2003年 | 110篇 |
2002年 | 100篇 |
2001年 | 39篇 |
2000年 | 44篇 |
1999年 | 30篇 |
1998年 | 37篇 |
1997年 | 37篇 |
1996年 | 34篇 |
1995年 | 23篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 31篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1974年 | 14篇 |
排序方式: 共有2936条查询结果,搜索用时 218 毫秒
101.
Dr. Liangliang Song Prof. Dr. Erik V. Van der Eycken 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):121-144
Polycycles are abundantly present in numerous advanced chemicals, functional materials, bioactive molecules and natural products. However, the strategies for the synthesis of polycycles are limited to classical reactions and transition metal-catalyzed cross-coupling reactions, requiring pre-functionalized starting materials and lengthy synthetic operations. The emergence of novel approaches shows great promise for the fields of organic/medicinal/materials chemistry. Among them, transition metal-catalyzed C−H activation followed by intermolecular annulation reactions prevail, due to their straightforward manner with high atom- and step-economy, providing rapid, concise and efficient methods for the construction of diverse polycycles. Several strategies have been developed for the synthesis of polycycles, relying on sequential multiple C−H activation/annulation, or combination of C−H activation/annulation and further interaction with a proximal group, or merger of C−H activation with a cycloaddition reaction, or in situ formation of the directing group. These are attractive, efficient, step- and atom-economic methods starting from commercially available materials. This Minireview will provide an introduction to transition metal-catalyzed C−H activation for the synthesis of polycycles, helping researchers to discover indirect connections and reveal hidden opportunities. It will also promote the discovery of novel synthetic strategies relying on C−H activation. 相似文献
102.
103.
104.
105.
Ly Dieu Ha Poul Erik Hansen Fritz Duus Hung Dinh Pham Lien‐Hoa D. Nguyen 《Magnetic resonance in chemistry : MRC》2012,50(3):242-245
Four new prenylated depsidones, oliveridepsidones A–D, were isolated from the bark of Garcinia oliveri collected in Vietnam. Their structures were elucidated using mainly NMR techniques (1H and 13C NMR, HMQC, HMBC and NOE experiments). Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
106.
107.
Dr. Alexander Hoffmann Cooper Citek Dr. Stephan Binder Arne Goos Prof. Dr. Michael Rübhausen Oliver Troeppner Prof. Dr. Ivana Ivanović‐Burmazović Prof. Dr. Erik C. Wasinger Prof. Dr. T. Daniel P. Stack Prof. Dr. Sonja Herres‐Pawlis 《Angewandte Chemie (International ed. in English)》2013,52(20):5398-5401
108.
109.
Poul Erik Hansen Bahjat A. Saeed Rita S. Rutu Teobald Kupka 《Magnetic resonance in chemistry : MRC》2020,58(8):750-762
1J(15N,H) coupling constants for enaminones and NH-forms of intramolecularly hydrogen-bonded Schiff bases as model compounds for sp2-hybridized nitrogen atoms are evaluated using density functional theory (DFT) to find the optimal functionals and basis sets. Ammonia is used as a test molecule and its one-bond coupling constant is compared with experiment. A methylamine Schiff base of a truncated molecule of gossypol is used for checking the performance of selected B3LYP, O3LYP, PBE, BHandH, and APFD density functionals and standard, modified, and dedicated basis sets for coupling constants. Both in vacuum and in chloroform, modeled by the simple continuum model of solvent, the modified basis sets predict significantly better the 1J(15N,H) value in ammonia and in the methylamine Schiff base of a truncated molecule of gossypol than the standard basis sets. This procure is then used on a broad set of intramolecularly hydrogen-bonded molecules, and a good correlation between calculated and experimental one-bond NH coupling constants is obtained. The 1J(15N,H) couplings are slightly overestimated. The calculated data show for hydrogen-bonded NH interatomic distances that the calculated values depend on the NH bond lengths. The shorter the bond lengths, the larger the 1J(15N,H). A useful correlation between 1J(15N,H) and NH bond length is derived that enables realistic predictions of one-bond NH coupling constants. The calculations reproduce experimentally observed trends for the studied molecules. 相似文献
110.
Giuseppe Spedalotto Dr. Robert Gericke Marta Lovisari Dr. Erik R. Farquhar Dr. Brendan Twamley Dr. Aidan R. McDonald 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(51):11983-11990
Hydroxide-bridged high-valent oxidants have been implicated as the active oxidants in methane monooxygenases and other oxidases that employ bimetallic clusters in their active site. To understand the properties of such species, bis-μ-hydroxo-NiII2 complex ( 1 ) supported by a new dicarboxamidate ligand (N,N′-bis(2,6-dimethyl-phenyl)-2,2-dimethylmalonamide) was prepared. Complex 1 contained a diamond core made up of two NiII ions and two bridging hydroxide ligands. Titration of the 1 e− oxidant (NH4)2[CeIV(NO3)6] with 1 at −45 °C showed the formation of the high-valent species 2 and 3 , containing NiIINiIII and NiIII2 diamond cores, respectively, maintaining the bis-μ-hydroxide core. Both complexes were characterised using electron paramagnetic resonance, X-ray absorption, and electronic absorption spectroscopies. Density functional theory computations supported the spectroscopic assignments. Oxidation reactivity studies showed that bis-μ-hydroxide-NiIII2 3 was capable of oxidizing substrates at −45 °C at rates greater than that of the most reactive bis-μ-oxo-NiIII complexes reported to date. 相似文献