全文获取类型
收费全文 | 13436篇 |
免费 | 130篇 |
国内免费 | 312篇 |
专业分类
化学 | 3665篇 |
晶体学 | 7篇 |
力学 | 76篇 |
综合类 | 44篇 |
数学 | 5598篇 |
物理学 | 3700篇 |
无线电 | 788篇 |
出版年
2024年 | 8篇 |
2023年 | 41篇 |
2022年 | 58篇 |
2021年 | 48篇 |
2020年 | 93篇 |
2019年 | 97篇 |
2018年 | 116篇 |
2017年 | 127篇 |
2016年 | 132篇 |
2015年 | 50篇 |
2014年 | 158篇 |
2013年 | 774篇 |
2012年 | 491篇 |
2011年 | 614篇 |
2010年 | 498篇 |
2009年 | 2917篇 |
2008年 | 2338篇 |
2007年 | 991篇 |
2006年 | 642篇 |
2005年 | 485篇 |
2004年 | 392篇 |
2003年 | 263篇 |
2002年 | 224篇 |
2001年 | 181篇 |
2000年 | 171篇 |
1999年 | 137篇 |
1998年 | 226篇 |
1997年 | 202篇 |
1996年 | 67篇 |
1995年 | 264篇 |
1994年 | 218篇 |
1993年 | 180篇 |
1992年 | 247篇 |
1991年 | 215篇 |
1990年 | 74篇 |
1989年 | 74篇 |
1988年 | 41篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
We add to the known examples of complete Kähler manifolds with negative sectional curvature by showing that the following three classes of domains in euclidean spaces also belong: perturbations of ellipsoidal domains in ?n, intersections of complex-ellipsoidal domains in ?2, and intersections of fractional linear transforms of the unit ball in ?2. In the process, we prove the following theorem in differential geometry: in the intersection of two complex-ellipsoidal domains in ?2, the sum of the Bergman metrics is a Kähler metric with negative curvature operator. 相似文献
192.
A decorated lattice is suggested and the Ising model on it with three kinds
of interactions K1,
K2, and
K3 is studied. Using an equivalent transformation, the square decorated Ising lattice is transformed into a regular square Ising lattice with nearest-neighbor, next-nearest-neighbor, and four-spin interactions, and the critical fixed point is found at
K1=0.5769,
K2=-0.0671, and
K3=0.3428, which determines the critical temperature of the system. It is also found that this system and
the regular square Ising lattice, and the eight-vertex model belong to the
same universality class. 相似文献
193.
The plastic flow of a foam results from bubble rearrangements. We study their occurrence in experiments where a foam is forced to flow in 2D: around an obstacle; through a narrow hole; or sheared between rotating disks. We describe their orientation and frequency using a topological matrix defined in the companion paper (F. Graner, B. Dollet, C. Raufaste, and P. Marmottant, this issue, 25 (2008) DOI 10.1140/epje/i2007-10298-8), which links them with continuous plasticity at large scale. We then suggest a phenomenological equation to predict the plastic strain rate: its orientation is determined from the foam's local elastic strain; and its rate is determined from the foam's local elongation rate. We obtain a good agreement with statistical measurements. This enables us to describe the foam as a continuous medium with fluid, elastic and plastic properties. We derive its constitutive equation, then test several of its terms and predictions. 相似文献
194.
E. Floriani R. Lima R. Vilela Mendes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):295-302
In this paper, we examine the effects of the
gravitational field on the dynamical evolution of the cavity-field
entropy and the creation of the Schr?dinger-cat state in the
Jaynes-Cummings model. We consider a moving two-level atom
interacting with a single mode quantized cavity-field in the
presence of a classical homogeneous gravitational field. Based on
an
su(2) algebra, as the dynamical symmetry group of the model, we derive the reduced density operator of the cavity-field
which includes the effects of the atomic motion and the gravitational field. Also, we obtain the exact solution and the approximate
solution for the system-state vector, and examine the atomic dynamics. By considering the temporal evolution of the
cavity-field entropy as well as the dynamics of the Q-function of the cavity-field we study the effects of the gravitational
field on the generation of the Schr?dinger-cat states of the cavity-field by using the Q-function,
field entropy and approximate solution for the system-state vector. The results show that the
gravitational field destroys the generation of the Schr?dinger-cat state of the cavity-field. 相似文献
195.
S. Canulescu T. Lippert A. Wokaun 《Applied Physics A: Materials Science & Processing》2008,93(3):771-778
The mass distributions of the species generated by laser ablation from a La0.6Ca0.4MnO3 target using laser irradiation wavelengths of 193 nm, 266 nm and 308 nm have been investigated with and without a synchronized
gas pulse of N2O. The kinetic energies of the species are measured using an electrostatic deflection energy analyzer, while the mass distributions
of the species were analyzed with a quadrupole mass filter.
In vacuum (pressure 10−7 mbar), the ablation plume consists of metal atoms and ions such as La, Ca, Mn, O, LaO, as well as multiatomic species, e.g.
LaMnO+. The LaO+ diatomic species are by far the most intense diatomic species in the plume, while CaO and MnO are only detected in small
amounts.
The interaction of a reactive N2O gas pulse with the ablation plume leads to an increase in plume reactivity, which is desired when thin manganite films are
grown, in order to incorporate the necessary amount of oxygen into the film. The N2O gas pulse appears to have a significant influence on the oxidation of the Mn species in the plume, and on the creation of
negative ions, such as LaO−,O− and O2−. 相似文献
196.
M. S. B. Darby T. C. May-Smith R. W. Eason 《Applied Physics A: Materials Science & Processing》2008,93(2):477-481
We have demonstrated pulsed laser deposition of Nd-doped gadolinium gallium garnet on Y3Al5O12 by the simultaneous ablation of two separate targets of Nd:Gd3Ga5O12 (GGG) and Ga2O3. Such an approach is of interest as a method of achieving stoichiometry control over films whilst the growth parameters are
kept constant and optimal for high quality crystal growth. We show here how the stoichiometry and resultant lattice parameter
of a film can be controlled by changing the relative deposition rates from the two targets. Films have been grown with enough
extra Ga to compensate for the deficiency that commonly occurs when depositing only from a GGG target. We have also grown
crystalline GGG films with an enriched Ga concentration, and this unconventional approach to film stoichiometry control may
have potential applications in the fabrication of films with advanced compositionally graded structures. 相似文献
197.
G. P. Gupta A. Z. Msezane 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(2):157-160
Excitation energies from ground state for 97 fine-structure levels as well as oscillator strengths and radiative decay rates
for all electric-dipole-allowed and intercombination transitions among the fine-structure levels of the terms belonging to
the (1s
22s
22p
6)3s
23p, 3s
3
p
2, 3s
23d, 3p
3, 3s3p3d, 3p
23d, 3s3d
2, 3s
24s, 3s
24p, 3s
24d, 3s
24f, and 3s3p4s configurations of Co XV are calculated, using extensive configuration-interaction (CI) wave functions, obtained with the
CIV3 computer code of Hibbert. The important relativistic effects in intermediate coupling are included through the Breit-Pauli
approximation via spin-orbit, spin-other-orbit, spin-spin, Darwin and mass correction terms. Small adjustments to the diagonal
elements of the Hamiltonian matrices have been made. Our calculated excitation energies, including their ordering, are in
excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute
for Standards and Technology (NIST) wherever available. The mixing among several fine-structure levels is found to be very
strong, with most of the strongly mixed levels belonging to the (1s
22s
22p
6)3p
23d and 3s3d
2 configurations. The strong mixing among several fine-structure levels makes it very difficult to identify them uniquely.
Perhaps, that may be the reason for the lack of both experimental and theoretical results for these levels. We believe that
our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work.
From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. In this calculation
we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available. 相似文献
198.
B. Sen B. Das P. Chatterjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(2):211-216
Nonlinear dust acoustic solitary waves in a dusty plasma are studied for nonzero kinematic viscosity. Sagdeev’s potential
can be obtain upto any order in ϕ. The existence of soliton solution is determined by pseudopotential approach. It is seen
that the electron inertia has a significant effect on the existence of solitary waves in presence of kinematic viscosity. 相似文献
199.
H. Kim G. P. Kushto R. C. Y. Auyeung A. Piqué 《Applied Physics A: Materials Science & Processing》2008,93(2):521-526
Fluorine-doped tin oxide (FTO) thin films have been investigated as an alternative to indium tin oxide anodes in organic photovoltaic
devices. The structural, electrical, and optical properties of the FTO films grown by pulsed laser deposition were studied
as a function of oxygen deposition pressure. For 400 nm thick FTO films deposited at 300°C and 6.7 Pa of oxygen, an electrical
resistivity of 5×10−4 Ω-cm, sheet resistance of 12.5 Ω/□, average transmittance of 87% in the visible range, and optical band gap of 4.25 eV were obtained. Organic photovoltaic (OPV)
cells based on poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunctions were prepared on FTO/glass electrodes and the device performance was investigated as a function of FTO
film thickness. OPV cells fabricated on the optimum FTO anodes (∼300–600 nm thick) exhibited power conversion efficiencies
of ∼3%, which is comparable to the same device made on commercial ITO/glass electrodes (3.4%). 相似文献
200.
S. Gaspard M. Oujja R. de Nalda M. Castillejo L. Bañares S. Lazare R. Bonneau 《Applied Physics A: Materials Science & Processing》2008,93(1):209-213
We have recently shown that irradiation of self-standing films of the biopolymers collagen and gelatine with single femtosecond
laser pulses produces a nanofoaming layer with regular bubble size which can be controlled by wavelength selection. Following
these initial studies, here we report on the temporal evolution of the foaming effect by measurements in situ and in real
time of the change in the transmittance of a cw probe HeNe laser through the irradiated films. Self standing films of the
biopolymers were irradiated with 90 fs laser pulses at 800, 400, and 266 nm. For fluences below and above the modification
threshold a permanent attenuation of the transmission occurs (increasing with fluence). The initial decay of the transmission
is fast (around few tens of ns), and is followed by dynamics in the longer timescale (micro and milliseconds). The temporal
evolution of the transmission measured upon fs laser irradiation is similar with that determined in the irradiation of the
biopolymer films at 248 nm with 25 ns laser pulses. The method allows separating in time the different processes occurring
after irradiation that lead to a permanent nanofoaming structure, while the results allow us to understand the mechanisms
of femtosecond laser processing of the biopolymers and their interest in biomedical applications. 相似文献