全文获取类型
收费全文 | 781篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
化学 | 432篇 |
晶体学 | 6篇 |
力学 | 25篇 |
数学 | 49篇 |
物理学 | 295篇 |
出版年
2023年 | 13篇 |
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 23篇 |
2019年 | 24篇 |
2018年 | 18篇 |
2017年 | 17篇 |
2016年 | 23篇 |
2015年 | 12篇 |
2014年 | 25篇 |
2013年 | 39篇 |
2012年 | 30篇 |
2011年 | 37篇 |
2010年 | 30篇 |
2009年 | 23篇 |
2008年 | 35篇 |
2007年 | 37篇 |
2006年 | 38篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 24篇 |
2002年 | 12篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1933年 | 3篇 |
排序方式: 共有807条查询结果,搜索用时 31 毫秒
721.
Mahandru GM Skauge AR Chowdhury SK Amarasinghe KK Heeg MJ Montgomery J 《Journal of the American Chemical Society》2003,125(44):13481-13485
A new strategy for effecting cascade cyclization processes using nickel enolates has been developed. Nickel enolates may be cleanly generated by the oxidative cyclization of an enal and alkyne with Ni(0), and the resulting enolate may be functionalized by a variety of alkylation processes. Partially and fully intramolecular versions of the process allow the rapid synthesis of complex polycyclics from simple achiral, acyclic precursors. 相似文献
722.
Reactivity of ionic liquids 总被引:2,自引:0,他引:2
Shahana Chowdhury Author Vitae Author Vitae Janet L. Scott Author Vitae 《Tetrahedron》2007,63(11):2363-2389
Ionic liquids are becoming widely used in synthetic organic chemistry and yet relatively little attention has been paid to the intrinsic reactivity of these low temperature molten salts. Clues to the non-innocent nature of many ionic liquids are contained in the reports of altered reactivity of dissolved substrates, unexpected catalytic activity and unforeseen by-product formation. In this review, we focus on the reactivity of ionic liquids, as opposed to reactivity in ionic liquids (although discussion of the latter is often included where it aids understanding of the former). 相似文献
723.
Halder M Chowdhury PK Das R Mukherjee P Atkins WM Petrich JW 《The journal of physical chemistry. B》2005,109(41):19484-19489
The photophysics of hypericin have been studied in its complex with two different isoforms, A1-1 and P1-1, of the protein glutathione S-transferase (GST). One molecule of hypericin binds to each of the two GST subunits. Comparisons are made with our previous results for the hypericin/human serum albumin complex (Photochem. Photobiol. 1999, 69, 633-645). Hypericin binds with high affinity to the GSTs: 0.65 microM for the A1-1 isoform and 0.51 microM for the P1-1 isoform (Biochemistry 2004, 43, 12761-12769). The photophysics and activity of hypericin are strongly modulated by the binding protein. Intramolecular hydrogen-atom transfer is suppressed in both cases. Most importantly, while there is significant singlet oxygen generation from hypericin bound to GST A1-1, binding to GST P1-1 suppresses singlet oxygen generation to almost negligible levels. The data are rationalized in terms of a simple model in which the hypericin photophysics depends entirely upon the decay of the triplet state by two competing processes, quenching by oxygen to yield singlet oxygen and ionization, the latter of these two are proposed to be modulated by A1-1 and P1-1. 相似文献
724.
Sarkar J Chowdhury J Ghosh M De R Talapatra GB 《The journal of physical chemistry. B》2005,109(47):22536-22544
The adsorption of 2-amino-4-methylbenzothiazole (2-AMBT) on colloidal silver particles has been investigated by a surface enhanced Raman scattering (SERS) study. The SERS spectra of the 2-AMBT molecule at varied adsorbate concentrations recorded in different time domains are compared with its Fourier transform infrared (FTIR) spectrum and normal Raman spectrum (NRS) in the bulk and in solution. The experimentally observed SERS spectra are compared with the theoretically modeled surface complexes using ab initio restricted Hatree-Fock (RHF) and density functional theory (DFT) calculations. The most favorable adsorptive sites of the 2-AMBT molecule have been estimated by natural population analysis (NPA) using the above-mentioned high level of theories. The enhancement of the in-plane modes together with the appearance of Ag-N stretching frequency at 215 cm(-1) indicates that the 2-AMBT molecule is adsorbed on the silver surface through the lone pair electrons of both nitrogen atoms with the molecular plane nearly vertical to the surface. 相似文献
725.
Surface-enhanced Raman spectra (SERS) of 5,10,15,20-tetrakis(1-decylpyridium-4-yl)-21H,23H-porphintetrabromide or Por 10 (H(2)Tdpyp) adsorbed on silver hydrosols are compared with the FTIR and resonance Raman spectrum (RRS) in the bulk and in solution. Comparative analysis of the RR and the FTIR spectra indicate that the molecule, in its free state, has D(2h) symmetry rather than C(2v). The SERS spectra, obtained on adsorption of this molecule on borohydride-reduced silver sol, indicate the formation of silver porphyrin. With the change in the adsorbate concentration, the SERS shows that the molecule changes its orientation on the colloidal silver surface. The appearance of longer wavelength band in the electronic absorption spectra of the sol has been attributed to the coagulation of colloidal silver particles in the sol. The long wavelength band is found to be red-shifted with the decrease in adsorbate concentration. The excitation profile study indicates that the resonance of the Raman excitation radiation with the original sol band is more important than that with the new aggregation band for the SERS activity. This indicates a large contribution of electromagnetic effect to surface enhancement. 相似文献
726.
The 4A2 → 2E transition of potassium chromicyanide has been studied under magnetic field. It has been found that the g-value is nearly isotropic, quite unlike the case of ruby. An attempt has been made to explain the zero-field splittings of 2E, 2T1 and 2T2 states and the g-value of the 2E state on the assumption that the distant ions are mainly responsible for lowering of symmetry of the crystal field from Oh. A reasonable choice of parameters can make the calculated values agree with the observed ones. 相似文献
727.
Ahmed Abdullah Fazlul Huq Ashraf Chowdhury Hasan Tayyem Philip Beale Keith Fisher 《BMC chemical biology》2006,6(1):3-9
Background
Cis-planaramineplatinum(II) complexes like their trans isomers are often found to be active against cancer cell lines. The present study deals with the synthesis, characterization and determination of activity of new cis-planaramineplatinum(II) complexes. 相似文献728.
Chemically synthesized conducting polyaniline (PANI) was investigated as adsorbent for its possible application in the removal of organic dyes, such as methylene blue (MB) and procion red (PR) from their aqueous solution. PANI adsorbent behaves as a charged surface upon post‐synthesis treatment of the polymer with acid and base. The adsorbent thus treated shows a high selectivity for the removal of dyes in the adsorption process. The Langmuir adsorption isotherm was used to represent the experimental adsorption data. The cationic dye, MB can be preferentially removed by the base‐treated PANI while the anionic dye, PR is predominately removed by the acid‐treated one. These observations were further evidenced from the measurements of molar conductance and pH of the dye solutions employed for adsorption. The finding can be explained considering the electrostatic nature of adsorption coupled with the morphology of the PANI surface thus treated. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
729.
N. I. Molla S. M. Hossain S. Basunia R. U. Miah M. Rahman D. H. Sikder M. I. Chowdhury 《Journal of Radioanalytical and Nuclear Chemistry》1997,216(2):213-215
The concentration of rare earths and other elements have been determined in the bed sediment samples of Karnafuli estuarine zone in the Bay of Bengal by instrumental neutron activation analysis (INAA). The samples and the standards soil-5, soil-7, coal fly ash and pond sediment were prepared and simultaneously irradiated for short and long time at the TRIGA Mark-II research reactor facility of Atomic Energy Research Establishment, Savar, Dhaka. The maximum themal neutron flux was of the order of 1013 n·cm–2·s–1. After irradiation the radioactivity of the product nuclides was measured by using a high resolution high purity germanium detector system. Analysis of -ray spectra and quantitative analysis of the elemental concentration were done via the software GANAAS, it has been possible to determine the concentration level of 27 elements including the rare earths La, Ce, Sm, Eu, Tb, Dy and Yb and uranium and thorium. 相似文献
730.
Premamoy Ghosh Dilip Kumar Chowdhury 《Journal of polymer science. Part A, Polymer chemistry》1985,23(5):1407-1419
Benzophenone (BP)-sensitized photopolymerization of methyl methacrylate (MMA) in near UV/visible light was studied at 40°C using dimethylaniline maleic acid (DMA—MA) combination as the photoinitiator. An instantaneous 1:1 complexation between DMA and MA takes place when they are mixed together in acetonitrile. Also, instantaneous complex formation occurs between DMA and MMA and between MA and MMA when they are dissolved in MMA in low concentrations, separately. Interestingly, when equimolar proportions of DMA and MA are mixed together in MMA, there is indication for further instantaneous complexation between (DMA—MMA) complex and (MA—MMA) complex forming the actual initiating species in the photopolymerization system. Initiator exponent was 0.28 and monomer exponent varied between 0.0 to 1.8 depending on the nature of the solvent and range of dilution used. Analysis of kinetic data indicates a free radical mechanism for the polymerization with initiator-dependent termination. Chain termination via degradative initiator transfer is quite significant; but the degradative effect becomes much less prominent in the higher range of initiator concentration indicating that the reinitiation reaction following the initiator transfer process assumes more proportionate significance as the initiator concentration is increased, probably as a result of higher reinitiation efficiency. Polymers obtained gave evidence for the incorporation of aromatic (amine) end groups in them. 相似文献