全文获取类型
收费全文 | 1501篇 |
免费 | 35篇 |
国内免费 | 9篇 |
专业分类
化学 | 1057篇 |
晶体学 | 15篇 |
力学 | 33篇 |
数学 | 171篇 |
物理学 | 269篇 |
出版年
2022年 | 17篇 |
2021年 | 25篇 |
2020年 | 24篇 |
2019年 | 35篇 |
2018年 | 27篇 |
2017年 | 15篇 |
2016年 | 57篇 |
2015年 | 34篇 |
2014年 | 44篇 |
2013年 | 101篇 |
2012年 | 83篇 |
2011年 | 95篇 |
2010年 | 58篇 |
2009年 | 58篇 |
2008年 | 77篇 |
2007年 | 57篇 |
2006年 | 61篇 |
2005年 | 57篇 |
2004年 | 52篇 |
2003年 | 43篇 |
2002年 | 45篇 |
2001年 | 22篇 |
2000年 | 23篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 47篇 |
1995年 | 29篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有1545条查询结果,搜索用时 156 毫秒
941.
S. Krishna Prasad K. L. Sandhya Geetha G. Nair Uma S. Hiremath C. V. Yelamaggad S. Sampath 《Liquid crystals》2013,40(10):1121-1125
The behaviour of the anisotropic electrical conductivity of liquid crystal–gold nanoparticle (LC‐GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol‐capped GNPs has been investigated. The nematic–isotropic transition of the composite decreases nearly linearly with increasing X, the concentration of GNP (in weight %) at a rate of about 1°C /weight %. The inclusion of GNPs increases the electrical conductivity of the system with the value increasing by more than two orders of magnitude for X = 5%. However, the anisotropy in conductivity, defined as the ratio of the conductivity along (σ∥) and orthogonal (σ⊥) to the director shows a much smaller but definite decrease as X increases. 相似文献
942.
A. Selvaraj S. Sivakumar A. K. Ramasamy V. Balasubramanian 《Research on Chemical Intermediates》2013,39(6):2287-2302
Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO2 in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO2 was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO2 was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO2 was 39.5, 86.0, and 96.3 mg g?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO2 when compared with that of undoped TiO2. Moreover, the degradation of RY 84 on N-doped TiO2 in sunlight was faster than the commercial Aeroxide® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO2. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO2. 相似文献
943.
Ingrid C. Hoeger Sandeep S. Nair Arthur J. Ragauskas Yulin Deng Orlando J. Rojas J. Y. Zhu 《Cellulose (London, England)》2013,20(2):807-818
Laboratory mechanical softwood pulps (MSP) and commercial bleached softwood kraft pulps (BSKP) were mechanically fibrillated by stone grinding with a SuperMassColloider®. The extent of fibrillation was evaluated by SEM imaging, water retention value (WRV) and cellulase adsorption. Both lignin content and mechanical treatment significantly affected deconstruction and enzymatic saccharification of fibrillated MSP and BSKP. Fibrillation of MSP and BSKP cell walls occurs rapidly and then levels off; further fibrillation has only limited effect on cell wall breakdown as measured by water retention value and cellulase adsorption. Complete (100 %) saccharification can be achieved at cellulase loading of 5 FPU/g glucan for BSKP after only 15 min fibrillation with energy input of 0.69 MJ/kg. However, the presence of lignin in MSP affects the extent of fibrillation producing fibrils mainly above 1 μm. Lignin binds nonproductively to cellulases and blocks cellulose thereby reducing its accessibility. As a result, the cellulose saccharification efficiency of MSP fibrils (6 h of fibrillation, energy input of 13.33 MJ/kg) was only 55 % at same cellulase loading of 5 FPU/g glucan. 相似文献
944.
Ranjeet V. Nair Manojkumar R. Shukla Prashant N. Patil Manikrao M. Salunkhe 《合成通讯》2013,43(10):1671-1677
Pseudomonas cepacia lipase supported on ceramic particles (PS-C) offers a simple alternative route for the synthesis of achiral half esters, with very high yields, easy work up and remarkable substrate selectivity, as it cleaves only phenolic esters having a phenyl group (i.e. C6H5-O-CO-C6H5). 相似文献
945.
Samikannu Ramesh Kulanthaivel Sivakumar Chiradeep Panja Pirama Nayagam Arunachalam 《合成通讯》2013,43(23):3544-3551
The synthesis of α-aminonitriles by a direct three component Strecker reaction has been achieved in water, which is found to be an inexpensive, non-toxic and eco-friendly reaction medium for the nucleophilic addition. This protocol is effective to a wide variety of substrates with different functional groups and does not require the use any other catalyst. 相似文献
946.
Goverdhan Mehta Chebiyyam Prabhakar Nacharaju Krishnamurthy Mangalam S. Nair 《合成通讯》2013,43(22):3467-3475
Synthesis of structurally novel aza-and oxa-polyquinanes from the abundantly available cis,syn,cis-triquinane dione 1 via transannular nucleo-phillc additions is reported. 相似文献
947.
An imidazolidin-2-one chiral auxiliary mediated acetate aldol reaction was explored in the enantioselective synthesis of (S)-dapoxetine (SSRI). The diastereoselective aldol adduct was transformed to highly enantiopure (S)-dapoxetine with overall good yield. 相似文献
948.
949.
Shekhar Kumar S. Balasubramonian D. Sivakumar U. Kamachi Mudali R. Natarajan 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(3):883-884
Di-(2-ethyl hexyl) phosphoric acid (hereafter referred as D2EHPA) is an important solvent for solvent extraction industry.
It is also used in nuclear solvent extraction as a solvent for TALSPEAK and REVERSED TALSPEAK processes for actinide (III)–lanthanide
(III) separation. Its PVT properties are not available in literature. In this work, group-contribution approach was used to
predict its PVT properties as well as selected physical properties like normal boiling point. 相似文献
950.
Two new aromatic carboxylic acids, namely, 3,5-bis(benzyloxy)benzoic acid (HL1) and 3,5-bis(pyridine-2-ylmethoxy)benzoic acid (HL2), have been prepared by replacing the hydroxyl hydrogens of 3,5-dihydroxy benzoic acid with benzyl and pyridyl moieties, respectively. The anions derived from HL1 and HL2 have been used for the support of a series of lanthanide coordination compounds [Eu(3+) = 1-2; Tb(3+) = 3-4; Gd(3+) = 5-6]. The new lanthanide complexes have been characterized on the basis of a variety of spectroscopic techniques in conjunction with an assessment of their photophysical properties. Lanthanide complexes 2, 4, and 6, which were synthesized from 3,5-bis(pyridine-2-ylmethoxy)benzoic acid, were structurally authenticated by single-crystal X-ray diffraction. All three complexes were found to exist as infinite one-dimensional (1-D) coordination polymers with the general formula {[Ln(L2)(3)(H(2)O)(2)]·xH(2)O}(n). Scrutiny of the packing diagrams for 2, 4, and 6 revealed the existence of interesting two-dimensional molecular arrays held together by intermolecular hydrogen-bonding interactions. Furthermore, the coordinated benzoate ligands serve as efficient light harvesting chromophores. In the cases of 1-4, the lowest energy maxima fall in the range 280-340 nm [molar absorption coefficient (ε) = (0.39-1.01) × 10(4) M(-1) cm(-1)]. Moreover, the Tb(3+) complexes 3 and 4 exhibit bright green luminescence efficiencies in the solid state (Φ(overall) = 60% for 3; 27% for 4) and possess longer excited state lifetimes than the other complexes (τ = 1.16 ms for 3; 1.38 ms for 4). In contrast to the foregoing, the Eu(3+) complexes 1 and 2 feature poor luminescence efficiencies. 相似文献