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991.
We propose a color vision model that can be used to predict color appearance in mesopic vision as well as photopic and scotopic vision. It is based on a two-stage model which consists of the cone and opponent stages and it assumes rod intrusion at the opponent stage. The model has the following features to describe the color appearance in mesopic vision. First, it includes a gradual and nonlinear shift in spectral luminous efficiency from V (LD) to V (LD) to cope with the spectral sensitivity difference between photopic and scotopic vision and the nonlinearity of rod influence on the luminance channel. Second, the model assumes decrease of the chromatic component with decreasing illuminance to explain the reduction of saturation at low illuminance levels. Third, it assumes that red/green and yellow/blue components change with illuminance levels independently, thus explaining hue shifts with decreasing illuminance. We applied the model for color appearance simulation of natural scenes in a mesopic visual environment. 相似文献
992.
Xinhuan Feng Lei Sun Yange Liu Lingyun Xiong Shuzhong Yuan Guiyun Kai Xiaoyi Dong 《Optical and Quantum Electronics》2004,36(10):919-926
A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated. 相似文献
993.
Sergio Albeverio Agnieszka Kozak Yuri Kozitsky 《Communications in Mathematical Physics》2004,251(1):1-25
We study the two-dimensional gauge theory of the symmetric group Sn describing the statistics of branched n-coverings of Riemann surfaces. We consider the theory defined on the disc and on the sphere in the large-n limit. A non trivial phase structure emerges, with various phases corresponding to different connectivity properties of the covering surface. We show that any gauge theory on a two-dimensional surface of genus zero is equivalent to a random walk on the gauge group manifold: in the case of Sn, one of the phase transitions we find can be interpreted as a cutoff phenomenon in the corresponding random walk. A connection with the theory of phase transitions in random graphs is also pointed out. Finally we discuss how our results may be related to the known phase transitions in Yang-Mills theory. We discover that a cutoff transition occurs also in two dimensional Yang-Mills theory on a sphere, in a large N limit where the coupling constant is scaled with N with an extra logN compared to the standard t Hooft scaling. 相似文献
994.
Frequency domain (FD) fluorescence lifetime data was collected for a series of 20 crude petroleum oils using a 405 nm excitation
source and over a spectral range of ~426 to ~650 nm. Average fluorescence lifetimes were calculated using three different
models: discrete multi-exponential, Gaussian distribution, and Lorentzian distribution. Fitting the data to extract accurate
average lifetimes using the various models proved easier and less time consuming for the FD data than with Time Correlated
Single Photon Counting (TCSPC) methods however the analysis of confidence intervals to the computed average lifetimes proved
cumbersome for both methods. The uncertainty in the average lifetime was generally larger for the discrete lifetime multi-exponential
model when compared to the distribution-based models. For the lifetime distributions, the data from the light crude oils with
long lifetimes generally fit to a single decay term. Heavier oils with shorter lifetimes required multiple decay terms. The
actual value for the average lifetime is more dependant on the specific fitting model employed than the data acquisition method
used. Correlations between average fluorescence lifetimes and physical and chemical parameters of the crude oils were made
with a view to developing a quantitative model for predicting the gross chemical composition of crude oils. It was found that
there was no significant benefit gained by using FD over TCSPC other than more rapid data analysis in the FD case. For the
FD data the Gaussian distribution model for fluorescence lifetime gave the best correlations with chemical composition allowing
a qualitative correlation to some bulk oil parameters.
相似文献
Alan G. RyderEmail: |
995.
25 fs pulses with energy up to 0.8 mJ from a multi-pass amplifier system have been spectrally broadened from 460 nm to 950
nm due to strong self-phase modulation (SPM) effect in a gas filled hollow fiber. Using a set of chirped mirrors, the ultra-broadband
dispersion compensation was achieved, and the compressed pulses reached their transform limit. Under optimized conditions
we achieved pulses with duration of 5.1 fs and with energy of 400 μJ, corresponding to the peak power up to 80 GW.
Supported by the National Natural Science Foundation of China (Grant Nos. 60608003, 60490280, 60225005 and 60621063) 相似文献
996.
997.
Amorphous gallium nitride (a-GaN) thin films were deposited on glass substrate by electron beam evaporation technique at room
temperature and high vacuum using N
2 as carrier gas. The structural properties of the films was studied by X-ray diffraction (XRD) and scanning electron microscope
(SEM). It was clear from XRD spectra and SEM study that the GaN thin films were amorphous. The absorbance, transmittance and
reflectance spectra of these films were measured in the wavelength range of 300–2200 nm. The absorption coefficient spectral
analysis in the sharp absorption region revealed a direct band gap of E
g = 3:1 eV. The data analysis allowed the determination of the dispersive optical parameters by calculating the refractive
index. The oscillator energy E
0 and the dispersion energy E
d, which is a measure of the average strength of inter-band optical transition or the oscillator strength, were determined.
Electrical conductivity of a-GaN was measured in a different range of temperatures. Then, activation energy of a-GaN thin
films was calculated which equalled E
a = 0:434 eV. 相似文献
998.
999.
The dynamics of information traffic over scale-free networks has been investigated systematically. A series of routing strategies
of data packets have been proposed, including the local routing strategy, the next-nearest-neighbour routing strategy, and
the mixed routing strategy based on local static and dynamic information. The capacity of the network can be quantified by
the phase transition from free flow state to congestion state. The optimal parameter values of each model leading to the highest
efficiency of scale-free networked traffic systems have been found. Moreover, we have found hysteretic loop in networked traffic
systems with finite packets delivering ability. Such hysteretic loop indicates the existence of the bi-stable state in the
traffic dynamics over scale-free networks.
相似文献
1000.
Yuanyuan Li Jie Sun Li Wang Peng Zhan Zhishen Cao Zhenlin Wang 《Applied Physics A: Materials Science & Processing》2008,92(2):291-294
A sensor based on surface plasmon resonance (SPR) of plasmonic crystals fabricated via a colloidal-crystal-assisted templating
method is studied. Plasmonic crystals are prepared by depositing a thin gold (Au) layer onto a two-dimensional array of polystyrene
spheres self-assembled on a quartz substrate. The enhanced transmission as a result of the SPR of Au plasmonic crystals, which
are immersed in different ambient liquids, are measured and compared with that of polystyrene (PS) microsphere templates of
different sizes, both before and after removal of Au nanoprisms formed on the quartz substrate through pores among the spheres.
It is found that the measured sensitivities exhibit a linear dependence on the refractive index of the surrounding medium
and are linked to coupling effects between SPRs on the corrugated Au film and nanoislands. The feasibility of the SPR system
in molecular monolayer detection is further demonstrated through a formation of alkanethiolate self-assembled monolayers on
the Au film surface, which causes a 4 nm red-shift of the main SPR.
PACS 07.07.Df; 73.20.Mf; 78.66.-w; 81.16.Dn 相似文献