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991.
In this paper it has been shown that the neutrino bulk viscous stresses can give rise to the late time acceleration of the universe. It is found that a number of spatially flat FRW models with a negative deceleration parameter can be constructed using neutrino viscosity and one of them mimics a ΛCDM model. This does not require any exotic dark energy component or any modification of gravity. 相似文献
992.
The self-assembly of non-toxic well-consumed small caffeine molecules into well-defined structures has important implications
for future medical applications seeking to target the transport of small drugs in human body. Particularly, the solvation
of the microenvironments of the self assembly ultimately dictates the interaction with the drug molecules and their therapeutic
efficacy. We present femtosecond-resolved studies of the dynamics of aqueous solvation within self-assembled dimeric structure
of caffeine molecules. We have placed small hydrophobic probes 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran
(DCM), coumarin 500 (C500) into the caffeine dimer to enable spectroscopic examinations of the interior. While molecular modeling
and NMR studies of the probes in the caffeine dimers reveal a well-defined location (stacked in between two caffeine molecules),
dynamical light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy, densimetric and sonometric experiments explore
the structural evolution of the dimer upon complexation with the probes. We have extended our studies in various temperatures
in order to explore structural evolution of the self assembled structure and consequently the dynamics of solvation in the
interior of the dimer. Picoseconds/femtosecond resolved dynamics and the polarization gated spectroscopic studies unravel
the hydration and energetics associated with activated viscous flow of the confined probes. Our studies indicate that the
interior of the caffeine dimer is well-solvated; however, the dynamics of solvation is retarted significantly compared to
that in bulk water, clearly revealing the dimers maintain some ordered water molecules. We have also explored the consequence
of the retarded dynamics of solvation on the photo-induced electron transfer (ET) reaction of a model probe, 2-(p-toluidino)
naphthalene-6-sulfonate (TNS) encapsulated in the dimer. 相似文献
993.
Positive feedback and cooperativity in the regulation of gene expression are generally considered to be necessary for obtaining
bistable expression states. Recently, a novel mechanism of bistability termed emergent bistability has been proposed which
involves only positive feedback and no cooperativity in the regulation. An additional positive feedback loop is effectively
generated due to the inhibition of cellular growth by the synthesized proteins. The mechanism, demonstrated for a synthetic
circuit, may be prevalent in natural systems also as some recent experimental results appear to suggest. In this paper, we
study the effects of additive and multiplicative noise on the dynamics governing emergent bistability. The calculational scheme
employed is based on the Langevin and Fokker-Planck formalisms. The steady state probability distributions of protein levels
and the mean first passage times are computed for different noise strengths and system parameters. In the region of bistability,
the bimodal probability distribution is shown to be a linear combination of a lognormal and a Gaussian distribution. The variances
of the individual distributions and the relative weights of the distributions are further calculated for varying noise strengths
and system parameters. The experimental relevance of the model results is also pointed out. 相似文献
994.
Ritu Mishra Rupendranath Banerjee Subrata Mukhopadhyay 《Journal of Physical Organic Chemistry》2012,25(12):1193-1197
Copper(II) dramatically catalyzes the oxidation of thiols by a superoxide bridging two CoIII ions. The catalyzed path overwhelmingly dominates over the uncatalysed path and is first order in the superoxo complex concentration. The first‐order rate constants show a first‐order dependence in [Cu2+], a second‐order dependence in [thiol] and linearly varies with [H+]?3. On the basis of observed kinetics reported here, it is proposed that Cu(II) reacts with two thiol molecules to form a CuII(thiol)2 complex, an electron is transferred from one ligated thiol to the CuII center to form CuI(thiol) and a thiyl radical. The copper(I)‐thiol complex is oxidized by the conjugate base of the title complex to regenerate CuII(thiol). A CuII/I catalytic cycle is thus believed to be responsible for the observed catalysis. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
995.
R. K. Varma S. B. Banerjee A. Ambastha 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(2):38
Experimental results are presented here reporting the detection of a curl-free vector potential on the macro-scale as contrasted
with the detection on the micro-scale à la Aharonov-Bohm. Such a detection is attributed to the ‘quantum modulation’ of the
plane wave state of the guiding centre motion of a charged particle in a magnetic field, which is generated concomitantly
with the excitation of its Landau levels in a scattering episode, through the mechanism of quantum entanglement between the
parallel and perpendicular degrees of freedom of the particle. Such a ‘quantum modulation’ is also a matter wave, but on the
macro-scale, and leads to the ‘sensing’ of the curl-free vector potential on the macro-scale. Thus while the Aharonov-Bohm
effect is attributed to the sensing of the curl-free vector potential by the de Broglie wave, its sensing on the macro-scale
is attributed to the modulation of the de Broglie wave. 相似文献
996.
997.
Hand–arm vibration syndrome (HAVS) is collectively a vasospastic and neurodegenerative occupational disease. One of the major symptoms of HAVS is vibration white finger (VWF) caused by exaggerated vasoconstriction of the arteries and skin arterioles. While VWF is a very painful and costly occupational illness, its pathology has not been well understood. In this study a small artery is modeled as a fluid filled elastic tube whose diameter changes along the axial direction. Equations of motion are developed by considering interactions between the fluid, artery wall and soft-tissue bed. It is shown that the resulting wave equation is the same as that of the basilar membrane in the cochlea of mammals. Therefore, the artery system shows a spatial resonance as in the basilar membrane, which responds with the highest amplitude at the location determined by the vibration frequency. This implies that a long-term use of one type of tool will induce high-level stresses at a few identical locations of the artery that correspond to the major frequency components of the tool. Hardening and deterioration of the artery at these locations may be a possible cause of VWF. 相似文献
998.
Two protocols for deterministic secure quantum communication (DSQC) using GHZ-like states have been proposed. It is shown that one of these protocols is maximally efficient and that can be modified to an equivalent protocol of quantum secure direct communication (QSDC). Security and efficiency of the proposed protocols are analyzed and compared. It is shown that dense coding is sufficient but not essential for DSQC and QSDC protocols. Maximally efficient QSDC protocols are shown to be more efficient than their DSQC counterparts. This additional efficiency arises at the cost of message transmission rate. 相似文献
999.
The binding of 8-anilinonaphthalene sulfonate to concanavalin A has been investigated. Isothermal titration calorimetry (ITC) and circular dichroism studies have been performed under different experimental conditions to understand the binding quantitatively and evaluate contributions of different forces responsible for it. Isothermal titration calorimetric results of concanavalin A with ANS at pH 5.2 and 2.5, where it exists as a dimer, indicated binding heterogeneity and two classes of noninteracting sites. Enhancement of the binding constants from native to pH 2.5 suggests that the ANS binding is strongly influenced by the protein charge and the favorable alteration in the structure of concanavalin A as suggested by near-UV CD results. No binding was observed with the tetrameric form of concanavalin A, indicating shielding of sites due to dimerization of canonical dimers. The results have also demonstrated existence of a hydrophobic binding site that is distinct from the saccharide binding site. 相似文献
1000.
Verma R Sharma A Banerjee I Kargupta K 《Journal of colloid and interface science》2006,296(1):220-232
The instability, morphology and pattern formation engendered by the van der Waals force in a thin liquid film of thickness h confined between two closely placed solid surfaces (at distance d > h) are investigated based on nonlinear 3D simulations. The initial and the final stages of dewetting and pattern formation are found to be crucially dependent on the volumetric (thickness) ratio of air and liquid and its deviation from the location of the maximum of the spinodal parameter versus volumetric ratio curve. On a low energy surface, relatively thinner films and wider air gaps favor initial dewetting of the lower plate by the formation of holes, whereas thicker films with thinner air gaps initially evolve by the formation of columns/bridges that join the upper plate. In the later stage of evolution, the initial holes in thinner films evolve into columns/drops, while a rapid coalescence of columns in the thicker films eventually causes formation of holes. Thus, a phase inversion, either from liquid-in-air to air-in-liquid dispersion or vice versa, occurs during the final stages of evolution. A thin film confined between two high-energy solid surfaces forms columns (bridges) only when its mean thickness, h0, is greater than a critical thickness (hc) or the air gap is smaller than a critical distance. The patterns can be aligned by using a topographically patterned confining surface. Conditions on pattern periodicity, amplitude, and the volumetric ratio of air and liquid in the gap are explored for the formation of various types of ordered patterns including annular rings of columns, concentric ripples, parallel channels and a rectangular array of complex features. The results are of significance in soft lithographies such as LISA, soft stamping and capillary force lithography. 相似文献