全文获取类型
收费全文 | 1051篇 |
免费 | 51篇 |
国内免费 | 2篇 |
专业分类
化学 | 754篇 |
晶体学 | 15篇 |
力学 | 13篇 |
数学 | 57篇 |
物理学 | 265篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 32篇 |
2021年 | 34篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 52篇 |
2017年 | 34篇 |
2016年 | 58篇 |
2015年 | 41篇 |
2014年 | 108篇 |
2013年 | 106篇 |
2012年 | 68篇 |
2011年 | 72篇 |
2010年 | 38篇 |
2009年 | 31篇 |
2008年 | 42篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 22篇 |
2004年 | 29篇 |
2003年 | 18篇 |
2002年 | 21篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 9篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有1104条查询结果,搜索用时 15 毫秒
71.
Fructos MR Belderrain TR Nicasio MC Nolan SP Kaur H Díaz-Requejo MM Pérez PJ 《Journal of the American Chemical Society》2004,126(35):10846-10847
The complex IPrCuCl (1) catalyzes the transfer of the :CHCO2Et group from ethyl diazoacetate (EDA) to unsaturated and saturated substrates (olefins, amine, alcohols) with very high yields. In the absence of substrate, the complex 1 does not react with EDA to give the diazo coupling products (fumarate and maleate), a rare example in the field of metal-catalyzed diazocompounds decomposition. 相似文献
72.
73.
A metastable state, characterized by a low degree of mass localization, is identified using density-functional theory (DFT). This free energy minimum, located through the proper evaluation of competing terms in the free energy functional, is independent of the specific form of the DFT used. Computer simulation results on particle motion indicate that this heterogeneous state corresponds to the deeply supercooled state. 相似文献
74.
Dibromoacetyl benzene derivatives on condensation with thiourea give 2-amino-4-arylthiazoles instead of the expected 2-amino-4-aryl-5-bromothiazoles. Attempts have been made to find the reaction pathway. 相似文献
75.
Rajnish Moudgil Damanjit Kaur Rachita Vashisht Prasad V Bharatam 《Journal of Chemical Sciences》2000,112(6):623-629
Ab initio HF/6-31+G*, MP2/6-31+G*, B3LYP/6-31+G* level calculations have been performed on HSe-NH2 to estimate the Se-N rotational barriers and N-inversion barriers. Two conformers have been found withsyn andanti arrangement of the NH2 hydrogens with respect to Se-H bond. The N inversion barriers in selenamide are 1.65, 2.47, 1.93 kcal/mol and the Se-N rotational
barriers are 6.58, 6.56 and 6.12 kcal/mol respectively at HF/6-31+G*, MP2/6-31+G* and B3LYP/6-31+G* levels respectively. The
nN →Σ *Se-H negative hyperconjugation is found to be responsible for the higher rotational barriers. 相似文献
76.
77.
S. B. Beri K. B. Bhalla R. Bhanja A. Bharti V. S. Bhatia G. Claesson S. Garpman S. K. Gupta V. K. Gupta N. Y. Herrstrom B. Jakobsson R. Joseph G. L. Kaul G. Kaur M. Kaur S. Kitroo V. Kumar S. Lokanathan I. Lund L. K. Mangotra I. S. Mitra S. Mookerjee B. Norén A. Oskarsson I. Otterlund Y. Prakash S. Persson N. K. Rao S. Sankhyadhar S. Satti M. M. Sherif K. Söderström S. K. Tuli 《Zeitschrift für Physik A Hadrons and Nuclei》1987,327(4):431-441
40Ar-emulsion interactions are studied, to investigate the question of anomalons, in twoG- 5 emulsion stacks. In about 4600 primary interactions, projectile fragments of Z≧2 for all generations have been followed until they interact or leave the stack. After careful estimation of charges of these fragments, variation of their mean free paths is studied as a function of distance from the preceding interaction. Generation effect,N h dependence and production angle effect are investigated. In addition multi-chain events are analysed separately. Our results do not show anomalons at the 6% level and are consistent with non-occurrence of anomalons. However, this experiment is not sensitive enough to rule out anomalons (with a mfp of the order of 2 to 3 cm) produced at about 1% (or less) level. 相似文献
78.
A novel, efficient and protecting group free enantioselective synthetic approach of (?)-(R)-1 and (+)-(S)-rolipram 2 is described employing the organocatalyzed asymmetric Michael addition, Henry condensation, Wittig olefination and reductive lactamization reactions as key steps. 相似文献
79.
The preparation of some novel 3-(arylideneamino)-3a,8a-dihydroxy-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazole-2,8-diones 8(i–xiv) and 3-(arylideneamino)-3a,8a-dihydroxy-2-thioxo-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazol-8(2H)-ones 9(i–xiv) have been reported through one-pot catalyst-free reaction of aldehydes, semicarbazide hydrochloride/thiosemicarbazide with ninhydrin. All the synthesized compounds have been screened for antimicrobial activity and some of them were observed to possess broad spectrum antibacterial potential as well as significant antagonistic potential against fungal pathogens. 相似文献
80.
Vinod Chhokar Meenakshi Sangwan Vikas Beniwal Kiran Nehra Kaur S. Nehra 《Applied biochemistry and biotechnology》2010,160(8):2256-2264
Tannase from Aspergillus awamori MTCC 9299 was purified using ammonium sulfate precipitation followed by ion-exchange chromatography. A purification fold
of 19.5 with 13.5% yield was obtained. Temperature of 30 °C and pH of 5.5 were found optimum for tannase activity. The effects
of metals and organic solvents on the activity of tannase were also studied. Metal ions Mg+2, Mn+2, Ca+2, Na+, and K
+
stimulated the tannase activity, while Cu+2, Fe+3, and Co+2 acted as inhibitors of the enzyme. The addition of organic solvents like acetic acid, isoamylalcohol, chloroform, isopropyl
alcohol, and ethanol completely inhibited the enzyme activity. However, butanol and benzene increased the enzyme activity. 相似文献