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111.
A group of novel 2-aryl imidazole derivatives were synthesized and characterized by NMR spectra, X-ray, mass and CHN analysis.
An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazoles (dmip and dmtip) have been studied using
emission spectroscopy and it was detected that the two distinct ground state rotamers of I and II are responsible for the
normal and the tautomer emission respectively. In hydrocarbon solvent, the tautomer emission predominates over the normal
emission for both dmip and dmtip. This reveal that rotamer II is responsible for the tautomer emission and it is stabler than
rotamer I which causes the normal emission. In alcoholic solvent like ethanol, a dramatic enhancement of normal emission is
observed which was due to increased solvation, the more polar rotamer I become stabler than rotamer II. In dioxane—water mixtures
it is observed that the addition of water inhibits the ESIPT process due to the formation of the intermolecular hydrogen bonding
involving water. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited
states of the imidazole derivatives were performed and discussed. PES calculation indicates that the energy barrier for the
interconversion of two rotamers is too high in the excited state than the ground state. 相似文献
112.
A glassy carbon electrode was modified with Nafion, carbon nanotubes and benzo-18-crown-6 to give an electrode for the selective determination of lead(II) via square wave anodic stripping voltammetry. The use of carbon nanotubes with their extraordinary electrical conductivity and strong adsorption ability warrants high sensitivity. Benzo-18-crown-6 is employed as a “molecular scavenger” because of its excellent selectivity for lead(II). The modified electrode shows enhanced sensitivity, reproducibility and selectivity for lead(II) even without applying an electrical potential during the accumulation time. It responds linearly to lead(II) in the 1 to 30 nM concentration range (with a correlation coefficient of 0.9992) after a 10-min accumulation time. The detection limit is 1 nM. The sensor exhibits excellent selectivity over other heavy metal ions such as Cd(II), Cu(II), Zn(II), and Hg(II). Figure
Bi-functional mixture of carbon nanotube and crown ether is established for square wave anodic stripping voltammetric analysis of lead(II). The glassy carbon electrode modified with Nafion, Carbon Nanotube, and Benzo-18-Crown-6 showed excellent selectivity and also low detection limit (1 nM). 相似文献
113.
114.
The geometries of α- and β-silyl substituted vinyl radicals and of α, β-disilylvinyl radical have been optimised with the
STO-3G and the STO-3G * basis sets. The relative stabilities of various conformera have been determined at the UMP2/6-31G*
level. The stabilisation of vinyl radicals through α-silyl substitution is larger than that due to corresponding alkyl groups.
The presence of an α-silyl group also leads to a tendency towards linearisation of the vinyl radical centre and a corresponding
reduction in the inversion barrier. In marked contrast, the β-silyl effect is negligible. The geometric, conformational and
energetic consequences are insignificant. Overall, the silyl substituent effect at vinyl radicals is very different from that
computed earlier for the vinyl cations, but qualitatively similar to that found in carbanions. 相似文献
115.
116.
Polarized Raman spectra of mixed-valent Sm0.75Y0.25S are presented and compared with those of semiconducting SmS and superconducting YS and TiN. The spectra are explained in terms of cluster deformabilities which also govern the phonon anomalies. The existence of a breathing Γ1+ deformability of Sm in Sm1?xYxS, of S in YS, of N in TiN and a quadrupolar Γ12+ deformability of N in TiN is demonstrated. The relationship between these results and the microscopic theory is discussed. 相似文献
117.
T. Chattopadhyay C. Carlone A. Jayaraman H.G.v. Schnering 《Journal of Physics and Chemistry of Solids》1982,43(3):277-284
The Raman spectrum of crystalline As4S3 has been investigated as a function of temperature from 4 to 430 K at ambient pressure, and as a function of pressure to 70 kbar at ambient temperature. The external mode frequencies which appear clearly separated from the internal modes exhibit stronger pressure and temperature sensitivity compared to the latter modes. At the β-As4S3 to α-As4S3 phase transition near 410 K, the external modes change discontinuously indicating a first-order phase transition. The internal mode frequencies remain practically unaffected. The and data are analyzed using well established approaches. Application of non-hydrostatic pressure (>60 kbar) appears to destroy the crystallinity of As4S3. 相似文献
118.
Aswathy RG Ismail B John RP Nampoothiri KM 《Applied biochemistry and biotechnology》2008,151(2-3):244-255
Lactic acid bacteria were isolated from fermented vegetables, sour dough, milk products, sheep and human excreta. The newly isolated cultures were evaluated for a number of probiotic characteristics like bile salt resistance, salt tolerance in general, survival in low pH, hydrophobicity of the cell surface, resistance to low phenol concentration, antimicrobial activity and susceptibility pattern against vancomycin and erythromycin. The selected cultures were further screened for their ability to produce the nutraceticals such as folic acid and exopolysaccharide (EPS). Two potent isolates, CB2 (from cabbage) and SD2 (from sour dough) were found to produce both extracellular and intracellular folate. One of the isolates from yogurt (MC-1) and the one from whey (W3) produced significant amount of EPS with a maximum production of 8.79 +/- 0.05 g/l by MC-1. 相似文献
119.
Bárcena C Sra AK Chaubey GS Khemtong C Liu JP Gao J 《Chemical communications (Cambridge, England)》2008,(19):2224-2226
Mixed spinel hydrophobic ZnxFe1-xO x Fe2O3 (up to x = 0.34) nanoparticles encapsulated in polymeric micelles exhibited increased T2 relaxivity and sensitivity of detection over clinically used Feridex. 相似文献
120.
We use lattice Monte Carlo simulations to study the thermodynamics of hybridization of single-stranded "target" genes in solution with complementary "probe" DNA molecules immobilized on a microarray surface. The target molecules in our system contain 48 segments and the probes tethered on a hard surface contain 8-24 segments. The segments on the probe and target are distinct, with each segment representing a sequence of nucleotides that interacts exclusively with its unique complementary target segment with a single hybridization energy; all other interactions are zero. We examine how surface density (number of probes per unit surface area) and concentration of target molecules affect the extent of hybridization. For short probe lengths, as the surface density increases, the probability of binding long stretches of target segments increases at low surface density, reaches a maximum at an intermediate surface density, and then decreases at high surface density. Furthermore, as the surface density increases, the target is less likely to bind completely to one probe; instead, it binds simultaneously to multiple probes. At short probe lengths, as the target concentration increases, the fraction of targets binding completely to the probes (specificity) decreases. At long probe lengths, varying the target concentration does not affect the specificity. At all target concentrations as the probe length increases, the fraction of target molecules bound to the probes by at least one segment (sensitivity) increases while the fraction of target molecules completely bound to the probes (specificity) decreases. This work provides general guidelines to maximizing microarray sensitivity and specificity. Our results suggest that the sensitivity and specificity can be maximized by using probes 130-180 nucleotides long at a surface density in the range of 7 x 10(-5)- 3 x 10(-4) probe molecules per nm(2). 相似文献