全文获取类型
收费全文 | 3768篇 |
免费 | 162篇 |
国内免费 | 27篇 |
专业分类
化学 | 2754篇 |
晶体学 | 12篇 |
力学 | 103篇 |
数学 | 564篇 |
物理学 | 524篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 88篇 |
2021年 | 91篇 |
2020年 | 90篇 |
2019年 | 85篇 |
2018年 | 56篇 |
2017年 | 45篇 |
2016年 | 128篇 |
2015年 | 98篇 |
2014年 | 132篇 |
2013年 | 227篇 |
2012年 | 266篇 |
2011年 | 297篇 |
2010年 | 180篇 |
2009年 | 178篇 |
2008年 | 284篇 |
2007年 | 257篇 |
2006年 | 196篇 |
2005年 | 221篇 |
2004年 | 190篇 |
2003年 | 136篇 |
2002年 | 140篇 |
2001年 | 42篇 |
2000年 | 35篇 |
1999年 | 26篇 |
1998年 | 29篇 |
1997年 | 29篇 |
1996年 | 37篇 |
1995年 | 30篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 22篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有3957条查询结果,搜索用时 187 毫秒
891.
We study the processes of particle acceleration which take place in the field of a rotating black hole as part of a mechanism of formation of galactic jets within the first parsec from the central source, where gravitation is supposed to be dominant. We find the Lorentz factor that a stream of particles acquires as function of distance, when the orbital parameters vary slightly due to a local electromagnetic field or a pressure gradient. 相似文献
892.
Let a,b be singular endomorphisms of a. finite dimensional vector space V and denote by S a the semigroup generated by all the elements g -1ag, where g?Aut(V).The aim of this paper is to prove that b?S a if and only if rank(b) ≥ rank(a). 相似文献
893.
894.
OH-protection of alcohols and phenols by heating the hydroxylated compound with 3,4-dihydro-2H-pyrane in the presence of an AlPO4 or AlPO4-Al2O3 heterogeneous acid catalyst is described. Isolated yields, not optimized, were in the range 50–99%. 相似文献
895.
Eva Mª Barea Dr. Rubén Caballero Francisco Fabregat‐Santiago Dr. Pilar De La Cruz Dr. Fernando Langa Prof. Juan Bisquert Prof. 《Chemphyschem》2010,11(1):245-250
Five new sensitizers for dye sensitized solar cells have been designed consisting of conjugated thienylenevinylene units threaded with alkyl chains to improve solubility and cyanoacetic acid as anchoring group. The conjugation length was increased from 2 to 6 thienylenevinylene units, which resulted in a red‐shift of the optical absorption of the dyes from 550 to 750 nm, improving the spectral overlap with the solar spectrum. The photovoltaic performance of these dyes as sensitizers in mesoporous TiO2 solar cells shows a clear correlation of increasing photocurrent with the extension of the conjugation up to an optimal length. Further extension of the conjugation increases the absorption but additional effects like self‐quenching or recombination processes reduce the photocurrent and photovoltages and consequently the overall efficiency of the DSC. 相似文献
896.
897.
898.
Fernando Mendizabal 《International journal of quantum chemistry》2010,110(6):1279-1286
The interaction between {Au3(CH3N?COCH3)3} and {2,4,7‐trinitro‐9‐fluorenone} and the electronic structure and spectroscopic properties of {Au3(CH3N = COCH3)3}n·{2,4,7‐trinitro‐9‐fluorenone} (n = 1,2) are studied at the HF, MP2, and PBE levels. Secondary π‐interactions (Au‐fluorenone) were found to be the main contribution to short‐range stability in the {Au3(CH3N?COCH3)3}n·{2,4,7‐trinitro‐9‐fluorenone} complex. At the MP2 and PBE levels, Au‐C equilibrium distances of 292.3 and 304.0 pm and interaction energies of 105.3 and 24.9 kJ/mol were found, respectively. The absorption spectra of these complexes were calculated by the single excitation time‐dependent method at the PBE level. The theoretical values obtained are in agreement with the experimental range. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
899.
900.
Marta Borges‐Alvarez Fernando Benavente José Barbosa Victoria Sanz‐Nebot 《Rapid communications in mass spectrometry : RCM》2010,24(10):1411-1418
The native form of Cu,Zn‐superoxide dismutase (SOD‐1) is a homodimer that coordinates one Cu2+ and one Zn2+ per monomer. Cu2+ and Zn2+ ions play crucial roles in enzyme activity and structural stability, respectively. In addition, dimer formation is essential for SOD‐1 functionality, and in humans several SOD‐1 mutant isoforms have been associated with certain types of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder. In this paper we used capillary electrophoresis and mass spectrometry to study the different structures of bovine SOD‐1. The metal ions of the native enzyme (Cu2,Zn2‐dimer SOD‐1) were released in acidic medium in order to obtain apo‐SOD‐1, which is a monomer. Both substances were analyzed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) and capillary electrophoresis with ultraviolet and electrospray ionization mass spectrometry detection (CE/UV and CE/ESI‐MS, respectively). With MALDI‐TOF‐MS, using matrices of sinapinic acid (SA) or 2,5‐dihydroxybenzoic acid (DHB) with or without trifluoroacetic acid (TFA), similar mass spectra were obtained for the metalated and non‐metalated samples. In both cases, an average molecular mass corresponding to the apo‐monomer SOD‐1 was calculated. This finding indicated that the metals were released from the Cu2,Zn2‐dimer SOD‐1 during sample preparation or ionization. For CE/UV and CE/ESI‐MS, two background electrolytes (BGEs) potentially compatible with ESI‐MS detection were used, namely 1 M of acetic acid (pH 2.3) and 10 mM of ammonium acetate (pH 7.3). Using a sheath liquid of 2‐propanol/water (60:40 v/v), with or without 0.1% v/v of formic acid, CE/ESI‐MS sensitivity was enhanced when the acidic BGE and the acidic sheath liquid were used. However, the electrophoretic profiles and the mass spectra obtained suggested that the metals of Cu2,Zn2‐dimer SOD‐1 were released, which generated the apo‐monomer during the electrophoretic separation. The neutral BGE provided enhanced conditions for the detection of the native enzyme. The differences between the mass spectra obtained for the Cu2,Zn2‐dimer and the apo‐monomer forms were significant and the presence of formic acid in the sheath liquid affected only sensitivity. Our results highlight the importance of selecting appropriate non‐denaturing separation and detection conditions to obtain reliable structural information about non‐covalent protein complexes by CE/ESI‐MS. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献