全文获取类型
收费全文 | 3904篇 |
免费 | 138篇 |
国内免费 | 5篇 |
专业分类
化学 | 2629篇 |
晶体学 | 41篇 |
力学 | 76篇 |
数学 | 273篇 |
物理学 | 1028篇 |
出版年
2023年 | 41篇 |
2022年 | 67篇 |
2021年 | 65篇 |
2020年 | 100篇 |
2019年 | 121篇 |
2018年 | 74篇 |
2017年 | 75篇 |
2016年 | 134篇 |
2015年 | 93篇 |
2014年 | 133篇 |
2013年 | 264篇 |
2012年 | 266篇 |
2011年 | 318篇 |
2010年 | 199篇 |
2009年 | 162篇 |
2008年 | 233篇 |
2007年 | 198篇 |
2006年 | 179篇 |
2005年 | 150篇 |
2004年 | 124篇 |
2003年 | 80篇 |
2002年 | 81篇 |
2001年 | 60篇 |
2000年 | 60篇 |
1999年 | 47篇 |
1998年 | 30篇 |
1997年 | 24篇 |
1996年 | 39篇 |
1995年 | 29篇 |
1994年 | 36篇 |
1993年 | 43篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 20篇 |
1988年 | 22篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 30篇 |
1980年 | 20篇 |
1979年 | 27篇 |
1978年 | 16篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1957年 | 13篇 |
排序方式: 共有4047条查询结果,搜索用时 0 毫秒
871.
Polymer nanocomposites containing different concentrations of Au nanoparticles have been investigated by small angle X‐ray scattering and electronic absorption spectroscopy. The variation in the surface plasmon resonance (SPR) band of Au nanoparticles with concentration is described by a scaling law. The variation in the plasmon band of ReO3 nanoparticles embedded in polymers also follows a similar scaling law.
872.
Super Sensitization: Grand Charge (Hole/Electron) Separation in ATC Dye Sensitized CdSe,CdSe/ZnS Type‐I,and CdSe/CdTe Type‐II Core–Shell Quantum Dots 下载免费PDF全文
Tushar Debnath Partha Maity Dr. Hirendra N. Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13305-13313
Ultrafast charge‐transfer dynamics has been demonstrated in CdSe quantum dots (QD), CdSe/ZnS type‐I core–shell, and CdSe/CdTe type‐II core–shell nanocrystals after sensitizing the QD materials by aurin tricarboxylic acid (ATC), in which CdSe QD and ATC form a charge‐transfer complex. Energy level diagrams suggest that the conduction and valence band of CdSe lies below the LUMO and the HOMO level of ATC, respectively, thus signifying that the photoexcited hole in CdSe can be transferred to ATC and that photoexcited ATC can inject electrons into CdSe QD, which has been confirmed by steady state and time‐resolved luminescence studies and also by femtosecond time‐resolved absorption measurements. The effect of shell materials (for both type‐I and type‐II) on charge‐transfer processes has been demonstrated. Electron injection in all the systems were measured to be <150 fs. However, the hole transfer time varied from 900 fs to 6 ps depending on the type of materials. The hole‐transfer process was found to be most efficient in CdSe QD. On the other hand, it has been found to be facilitated in CdSe/CdTe type‐II and retarded in CdSe/ZnS type‐I core–shell materials. Interestingly, electron injection from photoexcited ATC to both CdSe/CdTe type‐II and CdSe/ZnS type‐I core–shell has been found to be more efficient as compared to pure CdSe QD. Our observation suggests the potential of quantum dot core–shell super sensitizers for developing more efficient quantum dot solar cells. 相似文献
873.
Akashdeep Nath Vikas Kumar Ayushi Shukla Prof. Hirendra Nath Ghosh Prof. Sukhendu Mandal 《Angewandte Chemie (International ed. in English)》2023,62(31):e202308034
We demonstrate direct evidence of photoinduced through-space intervalence charge transfer (IVCT) between two cofacially arranged redox-active pairs in metal–organic frameworks and their dynamic variation with their molecular separation. Two homologous MOFs [Co2(NDC)2(DPTTZ)2]. DPTTZ. DMF, 1 and [Co2(BDC)2(DPTTZ)2]. DMF, 2 (where NDC=naphthalene dicarboxylate, BDC=benzene dicarboxylate, DPTTZ=N, N′-di(4-pyridyl)thiazolo-[5,4-d]thiazole, DMF=N, N′-dimethyl formamide) are considered for this, whose intra-dimer distance of redox-active DPTTZ ligands differs ca. 1 Å from one system to another. Spectroelectrochemical study detects the formation of IVCT band at the NIR region between cofacially oriented DPTTZ molecules in both MOFs. Transient spectroscopy shows faster charge separation as well as charge recombination when intra-dimer distance is lesser (in MOF 2 ) due to stronger electronic coupling. We quantify the extent of IVCT by charge transfer integral calculation; and also by optical pump terahertz probe spectroscopy, where MOF 2 shows three times higher carrier mobility due to lesser inter-DPTTZ distance than MOF 1 . These findings reveal a more localized aspect of through-space IVCT between cofacially organized redox-active pair in a three-dimensional framework. 相似文献
874.
Nancy Ghosh S Singh N Kaur Nanda G Venugopalan P Bharatam PV Trehan S 《Chemical communications (Cambridge, England)》2003,(12):1420-1421
The origin of diastereoselectivity in the addition of alkyl lithium to chiral Schiff bases has been investigated experimentally and theoretically and the formation of the major diastereomer can be explained from the energy minimized structure of the Schiff base in which the phenyl group has been found to orient in such a manner that it posed lesser steric hindrance to the incoming nucleophile as compared to the alkyl group. 相似文献
875.
In search of novel γ-lactam antibacterial agents as non-β-lactam mimics of some γ-lactam antibiotics, N-aryl modification in the γ-lactam ring has been made to synthesize compounds 4–8 in two to six steps. Compound 4 was synthesized using the intermolecular Michael addition of diethyl N-(6-coumarinyl)-2-aminomalonate and 3-aryl/(2-heteroaryl)acryloyl chloride followed by intramolecular amidification. Hydrolysis and stereoselective decarboxylation of 4 resulted in the formation of trans- γ-lactam carboxylic acids (5), which on side chain homologation followed by saponification of the intermediate γ-lactam monoester (7) afforded γ-lactam carboxylic derivatives 8. Moderate to good bacterial growth inhibition was observed for some of the synthesized compounds against E. coli and S. aureus. 相似文献
876.
Rational Design for Complementary Donor–Acceptor Recognition Pairs Using Self‐Complementary Hydrogen Bonds 下载免费PDF全文
Amrita Sikder Boyli Ghosh Saptarshi Chakraborty Dr. Ankan Paul Dr. Suhrit Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):1908-1913
An adaptable and efficient molecular recognition pair has been established by taking advantage of the complementary nature of donor–acceptor interactions together with the strength of hydrogen bonds. Such distinct molecular recognition propagates in orthogonal directions to effect extended alternating co‐assembly of two different appended molecular entities. The dimensions of the assembled structures can be tuned by stoichiometric imbalance between the donor and acceptor building blocks. The morphology of the self‐assembled material can be correlated with the ratio of the two building blocks. 相似文献
877.
Efficient White‐Light Generation from Ionically Self‐Assembled Triply‐Fluorescent Organic Nanoparticles 下载免费PDF全文
Dr. Susmita Das Tanay Debnath Amrita Basu Dr. Deepanwita Ghosh Prof. Abhijit Kumar Das Dr. Gary A. Baker Prof. Amitava Patra 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(26):8855-8863
Low cost, simple, and environmentally friendly strategies for white‐light generation which do not require rare‐earth phosphors or other toxic or elementally scare species remain an essentially unmet challenge. Progress in the area of all‐organic approaches is highly sought, single molecular systems remaining a particular challenge. Taking inspiration from the designer nature of ionic‐liquid chemistry, we now introduce a new strategy toward white‐light emission based on the facile generation of nanoparticles comprising three different fluorophores assembled in a well‐defined stoichiometry purely through electrostatic interactions. The building blocks consist of the fluorophores aminopyrene, fluorescein, and rhodamine 6G which represent blue, green, and red‐emitting species, respectively. Spherical nanoparticles 16(±5) nm in size were prepared which display bright white‐light emission with high fluorescence quantum efficiency (26 %) and color coordinate at (0.29, 0.38) which lie in close proximity to pure white light (0.33, 0.33). It is noteworthy that this same fluorophore mixture in free solution yields only blue emission. Density functional theory calculations reveal H‐bond and ground‐state proton transfer mediated absolute non‐parallel orientation of the constituent units which result in frustrated energy transfer, giving rise to emission from the individual centers and concomitant white‐light emission. 相似文献
878.
879.
Bittu Saha Bijeta Mitra Dhiraj Brahmin Biswajit Sinha Pranab Ghosh 《Tetrahedron letters》2018,59(41):3657-3663
This is the first reported, unconventional, efficient strategy for the synthesis of quinoxaline from 2 to iodo benzoic acid and sodium azide in presence of organo Cu (II) catalyst. Herein, a very simple, versatile one pot multi-component protocol for the synthesis of biologically active compound, quinoxaline has been described via Schmidt reaction and the nucleophilic substitution reaction. The isolated compounds were characterized by 1H NMR, 13C NMR. Our reported organo catalyst was characterized by single crystal XRD, SEM. 相似文献
880.
Jhantu DasSomnath Ghosh 《Tetrahedron letters》2011,52(52):7189-7194
A new synthetic approach toward the synthesis of flavones and pyranoflavone has been developed by light induced intramolecularphotochemicalWittigreaction in water onto aryloxycarbonyl groups and suitably substituted phosphonium bromides sans any phase transfer catalyst or promoter. 相似文献