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141.
Li G Dobhal MP Graham A Shibata M Zheng G Kozyrev A Pandey RK 《The Journal of organic chemistry》2003,68(10):3762-3772
The thermolysis products obtained by refluxing a series of vic-dihydroxychlorins in o-dichlorobenzene are characterized. Depending on the nature of substrates, this methodology provides an access for novel carbon-carbon linked chlorin-chlorin dimers and chlorin-porphyrin dimers with fixed and flexible orientations. The configuration of the linkers in the symmetrical and unsymmetrical dimers was confirmed by extensive NMR (COSY, ROESY) and molecular modeling studies. The molecular modeling studies of the energy-optimized dimers with flexible orientation confirmed that one of the chlorin units of the dimeric structure is tilted toward the opposite ring as evident by the shielding effect in the resonances of some of the protons in the (1)H NMR spectroscopy. Among the dimers with fixed orientation, compared to the free-base analogues, the related mono- and di-Zn(II) complexes produced a decreased fluorescence intensity, suggesting a possibility of the faster energy transfer via intersystem crossing (ISC) in the metalated derivatives than the corresponding free-base analogues to produce the corresponding excited triplet states. The photosensitizing efficacy of the monomers and the related dimers was also compared in radiation-induced fibrosarcoma (RIF) tumor cells at variable drug/light doses. In preliminary screening, compared to monomers, the corresponding carbon-carbon linked dimers produced enhanced photosensitizing efficacy. 相似文献
142.
Graham A Li G Chen Y Morgan J Oseroff A Dougherty TJ Pandey RK 《Photochemistry and photobiology》2003,77(5):561-566
An in vitro and in vivo structure-activity relationship study was carried out on a series of benzochlorins with variable lipophilicity. The structural features evaluated in this study include the length of the alkyl or fluoroalkyl groups attached to the six-member exocyclic ring either by an ether or by a carbon-carbon bond. In preliminary in vitro (radiation-induced fibrosarcoma [RIF] cells) and in vivo screening (C3H mice, bearing RIF tumors), all Zn (II) benzochlorins were found to be effective. However, benzochlorins bearing alkyl groups with carbon-carbon bonds showed enhanced efficacy compared with the related alkyl ether analogs. A comparative intracellular localization study of the newly synthesized benzochlorins with Rhodamine-123 indicated that the effective photosensitizers localize in mitochondria, and a displacement study with PK11195 showed their partial affinity for the peripheral benzodiazepine receptor (PBR). Interestingly, compared with the Zn(II) benzochlorin that was found to be quite effective in vivo, the corresponding free-base analog produced less photosensitizing activity and was found to localize in lysosomes. A comparative study with dansyl-proline confirmed the binding of the effective benzochlorins to Site II of human serum albumin (HSA). However, no direct correlation was observed between the binding constant values (to HSA or to PBR) of benzochlorins and their photosensitizing ability. 相似文献
143.
144.
Pandey KK 《Inorganic chemistry》2001,40(20):5092-5096
Ab initio calculations at the SCF, MP2, CASSCF, and CASPT2 levels of theory with basis sets using atomic pseudopotentials have been carried out for the stretched eta(3)-hydridoborate sigma-complex of niobium, [Cl2Nb(H2B(OH)2)], in order to investigate the nature and energetics of the interaction between the transition metal and the eta(3)-hydridoborate ligand. The geometry of the complex [Cl2Nb(H2B(OH)2] and its fragments [Cl2Nb](+) and [H2B(OH)2](-) were optimized at SCF and CASSCF levels. These results are consistent with [Cl2Nb(eta(3)-H2B(OH)2)] being a Nb(III) complex in which both hydrogen and boron of the [eta(3)-H2B(OH)2](-) ligand have a bonding interaction with the niobium preserving stretching B-H bond character. The calculated values of DEF (energy required to restore the fragment from the equilibrium structure to the structure it takes in the complex) for [Cl2Nb](+) are 5.35 kcal/mol at SCF, 3.27 kcal/mol at MP2, 4.80 kcal/mol at CASSCF, and 2.82 kcal/mol at CASPT2 and for [H2B(OH)2](-) 21.13 kcal/mol at SCF, 23.85 kcal/mol at MP2, 20.69 kcal/mol at CASSCF, and 23.48 kcal/mol at CASPT2. Values of INT (stabilization energy resulting from the coordination of distorted ligand to the metal fragment) for the complex [Cl2Nb(H2B(OH)2)] are -239.35 kcal/mol at SCF, -260.00 kcal/mol at MP2, -230.76 kcal/mol at CASSCF, and -252.60 kcal/mol at CASPT2. For the complex [(eta(5)-C5H5)2Nb(H2B(OH)2)], calculations at the SCF and MP2 levels were carried out. Values of INT for [(eta(5)-C5H5)2Nb(H2B(OH)2)] are -169.93 kcal/mol at SCF and -210.62 kcal/mol at MP2. The results indicate that the bonding of the [eta(3)-H2B(OH)2](-) ligand with niobium is substantially stable. The electronic structures of [Cl2Nb(H2B(OH)2)], [(eta(5)-C5H5)2Nb(H2B(OH)2)], and its fragments are analyzed in detail as measured by Mulliken charge distributions and orbital populations. 相似文献
145.
Bearden IG Bøggild H Boissevain J Christiansen PH Conin L Dodd J Erazmus B Esumi S Fabjan CW Ferenc D Franz A Gaardhøje JJ Hansen AG Hansen O Hardtke D van Hecke H Holzer EB Humanic TJ Hummel P Jacak BV Kaimi K Kaneta M Kohama T Kopytine M Leltchouk M Ljubicic A Lörstad B Maeda N Martin L Medvedev A Murray M Ohnishi H Paic G Pandey SU Piuz F Pluta J Polychronakos V Potekhin M Poulard G Reichhold D Sakaguchi A Schmidt-Sørensen J Simon-Gillo J Sondheim W Sugitate T Sullivan JP Sumi Y Willis WJ 《Physical review letters》2001,87(11):112301
Two-particle interferometry of positive kaons is studied in Pb+Pb collisions at mean transverse momenta
approximately 0.25 and 0.91 GeV/c. A three-dimensional analysis was applied to the lower p(T) data, while a two-dimensional analysis was used for the higher p(T) data. We find that the source-size parameters are consistent with the m(T) scaling curve observed in pion-correlation measurements in the same collisions, and that the duration time of kaon emission is consistent with zero within the experimental sensitivity. 相似文献
146.
The rf pulse response of I=3/2 spin system experiencing first order quadrupolar splitting is studied using density matrix approach. A general expression is derived in terms of spin populations, quadrupole splitting and duration and amplitude of the rf pulse for calculating the NMR signal arising due to the centre line and satellite resonances for the situation where the impressed rf pulse excites the resonances selectively as well as non-selectively. The necessary 4×4 transformation matrix obtained analytically by diagonalyzing the Hamiltonian are used to get the expression for the centre line response. The satellite signals are obtained in the same way but by using the numerical values of the roots of the related quartics. The widths of the corresponding π/2-pulses are calculated for different initial spin populations. The variations of this pulse-width and the corresponding signal amplitude as a function of satellite splitting are studied. 相似文献
147.
M. K. Pandey R. K. Dubey D. N. Tripathi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):275-279
The Classical Trajectory Monte Carlo (CTMC) Method has
been used to calculate the differential, partial and total single electron
capture cross sections for the collision of H+/D+ with Ca and Mg
atoms in the energy range of 1–100 keV. The differential cross sections
at angles near the diffraction limit (<0.1○) in both systems
show a forward peak followed by an asymptotic fall at higher angles. Total
and partial capture cross sections are found to be in good agreement with
the experimental observations. Oscillations in the partial capture cross sections have been explained due to the swapping
of the field electron.
Isotope effect in the electron transfer is reported to be negligible. 相似文献
148.
Anirudh Pradhan Purnima Pandey Kanti Jotania Mahesh Kumar Yadav 《International Journal of Theoretical Physics》2007,46(11):2774-2787
Plane symmetric viscous fluid cosmological models of the universe with a variable cosmological term are investigated. The
viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient of shear
viscosity is to be proportional to rate of expansion in the model. We have also obtained a special model in which the shear
viscosity is assumed to be zero. The cosmological constant Λ is found to be a decreasing function of time and a positive which is supported by results from recent supernovae Ia observations.
Some physical and geometric properties of the models are also discussed. 相似文献
149.
Abhishek Verma Swati Nagpal Praveen K. Pandey P. K. Bhatnagar P. C. Mathur 《Journal of nanoparticle research》2007,9(6):1125-1131
Quantum Dots of CdS
x
Se1−x
embedded in borosilicate glass matrix have been grown using Double-Step annealing method. Optical characterization of the
quantum dots has been done through the combinative analysis of optical absorption and photoluminescence spectroscopy at room
temperature. Decreasing trend of photoluminescence intensity with aging has been observed and is attributed to trap elimination.
The changes in particle size, size distribution, number of quantum dots, volume fraction, trap related phenomenon and Gibbs
free energy of quantum dots, has been explained on the basis of the diffusion-controlled growth process, which continues with
passage of time. For a typical case, it was found that after 24 months of aging, the average radii increased from 3.05 to
3.12 nm with the increase in number of quantum dots by 190% and the size-dispersion decreased from 10.8% to 9.9%. For this
sample, the initial size range of the quantum dots was 2.85 to 3.18 nm. After that no significant change was found in these
parameters for the next 12 months. This shows that the system attains almost a stable nature after 24 months of aging. It
was also observed that the size-dispersion in quantum dots reduces with the increase in annealing duration, but at the cost
of quantum confinement effect. Therefore, a trade off optimization has to be done between the size-dispersion and the quantum
confinement. 相似文献
150.
José R. B. Gomes Emanuel A. Sousa Jorge M. Gonçalves Luís Gales Ana M. Damas Paula Gomes Siddharth Pandey William E. Acree Jr Maria D. M. C. Ribeiro da Silva 《Journal of Physical Organic Chemistry》2007,20(7):491-498
The gaseous standard molar enthalpies of formation of two 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐1,4‐dioxide has been obtained by X‐ray crystallography showing that the two N? O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas‐phase after computations performed at the B3LYP/6‐311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N? O bonds for quinoxaline 1,4‐dioxide derivatives. As found previously, similar N? O bond lengths in quinoxaline‐1,4‐dioxide compounds are not linked with N? O bonds having the same strength. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献