全文获取类型
收费全文 | 493篇 |
免费 | 37篇 |
专业分类
化学 | 422篇 |
晶体学 | 6篇 |
力学 | 17篇 |
数学 | 12篇 |
物理学 | 73篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 6篇 |
2021年 | 18篇 |
2020年 | 28篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 23篇 |
2015年 | 15篇 |
2014年 | 23篇 |
2013年 | 39篇 |
2012年 | 46篇 |
2011年 | 51篇 |
2010年 | 27篇 |
2009年 | 21篇 |
2008年 | 35篇 |
2007年 | 22篇 |
2006年 | 18篇 |
2005年 | 13篇 |
2004年 | 15篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有530条查询结果,搜索用时 15 毫秒
41.
A biomaterial supported organocatalyst, readily synthesized by the reaction of chemically modified sulfonic group containing expanded corn starch with pyridine exhibited excellent catalytic activity for the synthesis of β-amino carbonyls in excellent yields via aza-Michael addition of amines to electron deficient alkenes. A remarkable enhancement in the reaction rates was observed with the prepared bifunctional organocatalyst in comparison to the either starch grafted sulfonic acid or the corresponding homogeneous pyridinium p-toluenesulfonate. 相似文献
42.
A molecular dynamics study of the interaction of oleate and dodecylammonium chloride surfactants with complex aluminosilicate minerals 总被引:1,自引:0,他引:1
Rai B Sathish P Tanwar J Pradip Moon KS Fuerstenau DW 《Journal of colloid and interface science》2011,362(2):510-516
Surface characteristics of complex aluminosilicate minerals like spodumene [LiAl(SiO(3))(2)], jadeite [NaAl(SiO(3))(2)], feldspar [KAlSi(3)O(8)], and muscovite [K(2)Al(4)(Al(2)Si(6)O(20))(OH)(4)]) are modeled. Surface energies are computed for the cleavage planes of these minerals. Adsorption mechanisms of anionic chemisorbing type oleate and cationic physisorbing type dodecylammonium chloride molecules on two different crystal planes, that is (110) and (001), of spodumene and jadeite are studied in terms of the surface-surfactant interaction energies computed using molecular dynamics (MD) simulations. The conclusions drawn from purely theoretical computations match remarkably well with our experimental results. 相似文献
43.
Lingam Venkata Reddy Mamatha Nakka Alishetty Suman Soumen Ghosh Madeleine Helliwell Khagga Mukkanti Alok Kumar Mukherjee Sarbani Pal 《Journal of heterocyclic chemistry》2011,48(3):555-562
Reduction of nimesulide followed by treating the N‐acyl derivative of resulting arylamine with Vilsmeier‐Haack reagent provided novel 2‐chloro‐3‐formylquinoline derivatives. The construction of quinoline ring using Vilsmeier‐Haack reagent afforded an unexpected compound, N‐(2‐chloro‐3‐formyl‐7‐phenoxy quinolin‐6‐yl)formamide, in addition to the expected product. The structure of this unexpected quinoline derivative was established via single‐crystal X‐ray analysis and its formation could be explained by an unprecedented N‐S bond cleavage under Vilsmeier‐Haack reaction conditions. The 2‐chloro‐3‐formylquinoline derivatives obtained were converted to a number of corresponding Schiff bases with potential pharmacological importance. J. Heterocyclic Chem., 2011. 相似文献
44.
Starcević K Karminski-Zamola G Piantanida I Zinić M Suman L Kralj M 《Journal of the American Chemical Society》2005,127(4):1074-1075
Spectroscopic titrations and thermal denaturation experiments show that "acyclic" analogue 1 does not bind to ds-DNA, but under same conditions "cyclic" 2 strongly interacts with ds-DNA and ds-RNA by intercalation into the double helix. Besides, 2 is significantly more effective in inhibition of the tumor cell growth in vitro than 1. We have shown that it is possible to efficiently and irreversibly convert "DNA inactive" compound 1 into "DNA active" compound 2 by light irradiation of the aqueous solutions of the former. This strategy offers a new and attractive approach to photoinduced anticancer therapy. 相似文献
45.
Andrés F. Lasagni Peng Shao Charles M. Shaw Suman Das 《Applied Surface Science》2010,256(6):1708-9305
A simple optical interference method for the fabrication of simply periodic and periodic with a substructure on poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) using femtosecond laser interference patterns is demonstrated. The femtosecond laser pulse was split by a diffractive beam splitter and overlapped with two lenses. Homogeneous periodic arrays could be fabricated even using a single laser pulse. In addition, multipulse irradiation resulted in reproducible sub-wavelength ripples oriented perpendicularly to the laser polarization with spatial period from 170 to 220 nm (around one-fourth of the laser wavelength). In addition, the observed size of the spatial period was not affected by the number of incident laser pulses or accumulated energy density. Using high energy pulses it was possible to completely remove the PEDOT:PSS layer without inducing damage to the underneath substrate. 相似文献
46.
This work focuses on an unexplored aspect of non-symmetric geometry where only the off-diagonal metric components along the extra dimension, in a 5-dimensional spacetime, are non-symmetric. We show that the energy densities of the stationary non-symmetric models are similar to that of brane models thereby mimicking the thick-brane scenario. We find that the massive test particles are confined near the location of the brane for both growing and decaying warp factors. This feature is unique to the non-symmetric nature of our model. We have also studied the dynamical models where standard 4D FLRW brane is embedded. Our analysis shows that the non-symmetric terms deconfine energy density at the early universe while automatically confine at late times. 相似文献
47.
Kalpana Sharma Rishi Pal Chahal Suman Mahendia Anil Kumar Tomar Shyam Kumar 《辐射效应与固体损伤》2013,168(5):378-384
Polyvinyl alcohol films were irradiated to 90 MeV O 6+ and 150 MeV Si 14+ ions at fluence ranging from 1010 to 1012 ions/cm2. The observed changes in optical energy gap of this polymer have been investigated and results are tried to be explained in terms of energy transferred by the incident ions. It has been noticed that the value of optical energy gap decreases with increasing energy loss during the ion–polymer interaction process. 相似文献
48.
The study compares the effect of incorporation of three different groups of anti-hyperlipidemic drugs, namely niacin, simvastatin, and fenofibrate on the phase profile of liposomal membranes of dipalmitoylphosphatidylcholine (DPPC). The fluorescence anisotropy studies, using 1,6-diphenyl-1,3,5-hexatriene as fluorescent probe, have shown that the lipophilic molecule fenofibrate changes phase behavior of DPPC liposomal membrane to a greater extent compared to the changes produced by amphiphilic simvastatin and hydrophilic niacin. This variation in effect can be attributed to the nature of the drug molecules and hence their location in different parts of the liposomal membrane. We have also calculated the changes in van’t Hoff enthalpy values in all these three cases and observed that these values decreased with increase in drug concentrations in the case of simvastatin but for fenofibrate and niacin the effect is completely the reverse. In order to get a better insight, the fraction of motionally restricted lipid molecules has been calculated. 相似文献
49.
Suman Bhandary Ruma Basu Smarajit Manna Sukhen Das Papiya Nandy 《Phase Transitions》2013,86(3):221-227
Membrane fusion is an important process in a wide range of cellular and sub-cellular activities. It is evident that during the intermediate stages of fusion some transitory non-bilayer configurations must appear within the lipid moiety. Using fluorescence techniques, we have studied here the process of aggregation and fusion of liposomes made of lipids, namely 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). When mixed together, the complete fusion between these two liposomes took around 44 h as both DPPC and DMPC favour lamellar configuration. When the mixture was incubated at 42°C the fusion process was completed after 23 h. But, when 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) was added in the liposomal matrix the time for fusion was reduced to 21 h for mixture without incubation and 17 h when the mixture was incubated. This indicates that DPPE having a tendency to assume non-lamellar conformation, promoted destabilisation of the lamellar conformation within the liposome which facilitated the fusion between two apposing bilayers. 相似文献
50.
Suman Gomosta Rongala Ramalakshmi Chinnappa Arivazhagan Anagha Haridas Beesam Raghavendra Kuppaiyandi Maheswari Thierry Roisnel Sundargopal Ghosh 《无机化学与普通化学杂志》2019,645(6-7):588-594
The complexes [Ag{κ3‐S,S′,H‐H2B(mbz)2}(PR3)]x, ( 1 : x = 2, R = Ph; 2 : x = 1, R = Cy) (mbz = 2‐mercaptobenzothiazolyl) and amidine based dihydro(2‐mercaptobenzo‐thiazolyl) borates, [HN=C(Ph)–NH(R)–H2B(mbz)] ( 3 : R = 2,6‐diisopropylphenyl and 4 : R = Ph) were synthesized and characterized by various spectroscopic methods and single‐crystal X‐ray crystallography. Complex [Ag{κ3‐S,S′,H‐H2B(mbz)2}(PPh3)]2 ( 1 ) has a dimeric structure in its crystalline state, in which central silver(I) atoms adopt a distorted trigonal bipyramid arrangement. In contrast, complex [Ag{κ3‐S,S′,H‐H2B(mbz)2}(PCy3)] ( 2 ) has a monomeric structure in its crystalline state, in which the central silver(I) atoms adopt a distorted trigonal planar arrangement. Infrared spectroscopy was utilized as a tool for investigating the presence of M ··· H–B interactions. In addition, density functional theory (DFT) calculations were used to analyse the B–H ··· [M] bonding interaction in the metal borate complexes. 相似文献