全文获取类型
收费全文 | 436862篇 |
免费 | 4874篇 |
国内免费 | 1237篇 |
专业分类
化学 | 234335篇 |
晶体学 | 6493篇 |
力学 | 18788篇 |
综合类 | 13篇 |
数学 | 50053篇 |
物理学 | 133291篇 |
出版年
2021年 | 3783篇 |
2020年 | 4201篇 |
2019年 | 4530篇 |
2018年 | 5865篇 |
2017年 | 5748篇 |
2016年 | 8852篇 |
2015年 | 5576篇 |
2014年 | 8557篇 |
2013年 | 20225篇 |
2012年 | 15701篇 |
2011年 | 19320篇 |
2010年 | 13526篇 |
2009年 | 13387篇 |
2008年 | 17690篇 |
2007年 | 17598篇 |
2006年 | 16299篇 |
2005年 | 14589篇 |
2004年 | 13555篇 |
2003年 | 11921篇 |
2002年 | 11747篇 |
2001年 | 13443篇 |
2000年 | 10094篇 |
1999年 | 7928篇 |
1998年 | 6576篇 |
1997年 | 6321篇 |
1996年 | 6087篇 |
1995年 | 5482篇 |
1994年 | 5404篇 |
1993年 | 5206篇 |
1992年 | 5840篇 |
1991年 | 5937篇 |
1990年 | 5668篇 |
1989年 | 5478篇 |
1988年 | 5497篇 |
1987年 | 5381篇 |
1986年 | 5095篇 |
1985年 | 6570篇 |
1984年 | 6702篇 |
1983年 | 5306篇 |
1982年 | 5392篇 |
1981年 | 5376篇 |
1980年 | 4962篇 |
1979年 | 5355篇 |
1978年 | 5497篇 |
1977年 | 5389篇 |
1976年 | 5336篇 |
1975年 | 4917篇 |
1974年 | 4890篇 |
1973年 | 4882篇 |
1972年 | 3455篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
We study networks of coupled phase oscillators and show that
network architecture can force relations between average
frequencies of the oscillators. The main tool of our analysis is
the coupled cell theory developed by Stewart, Golubitsky, Pivato,
and Torok, which provides precise relations between network
architecture and the corresponding class of ODEs in RM and
gives conditions for the flow-invariance of certain polydiagonal
subspaces for all coupled systems with a given network
architecture. The theory generalizes the notion of fixed-point
subspaces for subgroups of network symmetries and directly extends
to networks of coupled phase oscillators. For systems of coupled phase oscillators (but not generally for ODEs in RM, where M ≥ 2), invariant polydiagonal subsets of
codimension one arise naturally and strongly restrict the network
dynamics. We say that two oscillators i and j coevolve if the polydiagonal θi = θj is flow-invariant, and show that the average frequencies of these
oscillators must be equal. Given a network architecture, it is shown that coupled cell theory
provides a direct way of testing how coevolving oscillators form
collections with closely related dynamics. We give a
generalization of these results to synchronous clusters of phase
oscillators using quotient networks, and discuss implications for
networks of spiking cells and those connected through buffers that
implement coupling dynamics. 相似文献
993.
S. M. Arabei D. V. Novik T. A. Pavich K. N. Solov’ev 《Journal of Applied Spectroscopy》2006,73(4):511-521
We have studied the fluorescence and fluorescence excitation spectra at 300 K, 77 K, and 4.2 K for silicate gel matrices colored
with meso-tetrapropylporphin by impregnation of the matrix with a solution of the pigment. Comparison of the data obtained
with the absorption spectra in acidified solutions and analysis of the low-temperature fine-structure vibronic spectra, and
also taking into account data obtained earlier for octaethylporphin in a xerogel showed formation of two cationic forms of
meso-tetrapropylporphin in the gel matrix: the short-wavelength form has a dicationic structure, while the long-wavelength form
has a monocationic structure. We have traced out the correlations of the vibrational structure in the spectra of the dicationic
form with data for the porphin dication, and we have drawn a number of conclusions concerning the normal vibrational modes
that are active in the vibronic fluorescence and absorption spectra of the studied cationic forms. Using the AM1 semiempirical
quantum chemical method, we optimized the geometry of the mesotetrapropylporphin dication: the most stable of the possible
conformers is the dication structure with saddleshaped macrocycle nonplanarity.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 453–461, July–August, 2006. 相似文献
994.
995.
996.
Cardy's formula for some dependent percolation models 总被引:2,自引:0,他引:2
F. Camia C. M. Newman V. Sidoravicius 《Bulletin of the Brazilian Mathematical Society》2002,33(2):147-156
We prove Cardy's formula for rectangular crossing probabilities in dependent site percolation models that arise from a deterministic cellular automaton with a random initial state. The cellular automaton
corresponds to the zero-temperature case of Domany's stochastic Ising ferromagnet on the hexagonal lattice (with alternating
updates of two sublattices) [7]; it may also be realized on the triangular lattice 𝕋 with flips when a site disagrees with
six, five and sometimes four of its six neighbors.
Received: 24 December 2001 相似文献
997.
Several illusions of vision are considered on the basis of a neurophysiological holographic model of visual perception at the level of the eye’s and the retina. It is suggested that the eye’s optical system forms a spatial spectrum of the observed object rather than its image on the retina. The spectrum is encoded by active anisotropic quasi-crystalline structures of rod rhodopsins and cone iodopsins, and a complex Fourier hologram of the observed object consisting of two quadrature components is recorded. The holographic hypothesis is confirmed by the results obtained by digital simulation. 相似文献
998.
Parametric interactions in nonlinear crystals represent a powerful tool in the optical manipulation of information, both in the classical and the quantum regime. Here, we analyze in detail classical and quantum aspects of three-and five-mode parametric interactions in x(2) nonlinear crystals. The equations of motion are explicitly derived and then solved within the parametric approximation. We describe several applications, including holography, all-optical gates, generation of entanglement, and telecloning. Experimental results on the photon distributions and correlations of the generated beams are also reported and discussed. 相似文献
999.
We describe the formation of a narrow beam for intensity-modulated electromagnetic radiation propagating through highly scattering materials. We propose to use this beam to reconstruct images, similar to X-ray back-projection techniques. For sufficiently high modulation frequency, the photon density wave is primarily carried by photons that suffer small or no large-angle scattering, which gives rise to the beam’s narrow divergence. The beam-narrowing concept is supported by large-scale numerical simulations to examine the quality of the imaging. 相似文献
1000.
In mountain-rescue operations injured people are generally exposed to vibrations and shocks that can be potential causes of physical conditions worsening. Such vibrations can derive both from patient's body manipulations (e.g. when it is being loaded and immobilized on a stretcher) and from forces coming from the transport devices and vehicles. Despite the general feeling that during this kind of operations the levels of transmitted vibrations to the injured can be quite large and potentially dangerous, there is practically no study in literature providing reliable parameters (i.e. measurements) to support or dismiss these beliefs. This paper reports the results of a measurement campaign carried-out in order to outline, identify and quantify the excitations a human body is exposed to, during typical transportation phases related to mountain-rescue operations. The work mainly presents and discusses the experimental setup with the aim of focusing on the problems related to this kind of measurements; the results of the experimental campaign carried-out for the measurement of the vibrations undergone by a human body during a simulated rescue operation are presented and discussed as well. Such simulation includes three phases of transportation: on a hand-held stretcher, on an ambulance and on a helicopter. The work is not intended to supply a complete characterization and analysis of vibrations transmission during any rescue operation but just to provide a preliminary overview and to define a measurement method that can be applied for a more comprehensive characterization. With such aims measurements were carried out in on-field situations stated as “typical” by rescue experts and data then analyzed both with standard procedures and algorithms (e.g. ISO 2631s weighting curves) and with the commonly used statistical indexes; in the analysis it is important to be aware that standardized measurement procedures and indexes, created to verify comfort or health-risks of workers, might not fit the case of a generic patient who experienced a serious mountain accident. The work includes also a laboratory activity mainly related to mechanical characterization of the stretcher used in the field tests. The most interesting result of the study is the comparison of the vibration levels in the various rescue phases that, even when using different indicators, shows that the most critical issue is due to hand transportation despite the bad judgment usually expressed for helicopter flight. 相似文献