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991.
992.
993.
Comets exhibit high (up to 25 %) amount of optical polarization when they are observed through ground based or space telescopes.
These polarizations are caused due to the scattering of cometary dust. The observed linear polarisation of comets is generally
a function of the wavelength of incident light (λ), the scattering angle (θ), the geometrical shape and size of the particle and the composition of dust particles in terms of the complex values of
the refractive index. The scattering properties of cometary dust will help to know the nature of cometary dust. In the present
work, the observed linear polarization data of Comet NEAT are studied through simulations using Ballistic Particle-Cluster
Aggregate (BPCA) and Ballistic Cluster-Cluster Aggregate (BCCA). Using Superposition T-matrix code, the best-fitting values
of complex refractive indices are calculated which can well fit the observed polarization data of Comet NEAT C/2001 Q4. The
best fitting values of complex refractive indices coming out from the present analysis correspond to mixture of both silicates
and organics. 相似文献
994.
Ikonen Jussi Sardini Paul Siitari-Kauppi Marja Martin Andrew 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(1):339-348
Diffusive transport of iodine (I) and tritiated water (HTO) in granodiorite is studied in the framework of the long term diffusion project (LTD) at the Grimsel Test Site, Switzerland. In this paper we modelled the tracer profiles measured in a long term (780 days) in situ diffusion test was carried out as part of LTD. The main outcome of the modelling tends to prove that the in situ apparent diffusion coefficients of I and HTO are close to the reference apparent diffusion coefficient determined in the laboratory (D a = 3 × 10−10 m2 s−1).
相似文献995.
Paul Bracken 《Central European Journal of Physics》2008,6(1):135-140
An effective Hamiltonian for the generalized harmonic oscillator is determined by using squeezed state wavefunctions. The
equations of motion over an extended phase space are determined and then solved perturbatively for a specific choice of the
oscillator parameters. These results are used to calculate the dynamic and geometric phases for the generalized oscillator
with this choice of parameters.
相似文献
996.
997.
Paul J. Szeptycki 《Proceedings of the American Mathematical Society》2002,130(12):3713-3717
An almost disjoint family is said to be soft if there is an infinite set that meets each in a nonempty but finite set. We consider the associated cardinal invariant defined to be the minimal cardinality of an almost disjoint family that is not soft. We show that this cardinal coincides with J. Brendle's cardinal .
998.
Pure-tone threshold estimation from extrapolated distortion product otoacoustic emission I/O-functions in normal and cochlear hearing loss ears 总被引:2,自引:0,他引:2
A new method for direct pure-tone threshold estimation from input/output functions of distortion product otoacoustic emissions (DPOAEs) in humans is presented. Previous methods use statistical models relating DPOAE level to hearing threshold including additional parameters e.g., age or slope of DPOAE I/O-function. Here we derive a DPOAE threshold from extrapolated DPOAE I/O-functions directly. Cubic 2 f1-f2 distortion products and pure-tone threshold at f2 were measured at 51 frequencies between f2=500 Hz and 8 kHz at up to ten primary tone levels between L2=65 and 20 dB SPL in 30 normally hearing and 119 sensorineural hearing loss ears. Using an optimized primary tone level setting (L1 = 0.4L2 + 39 dB) that accounts for the nonlinear interaction of the two primaries at the DPOAE generation site at f2, the pressure of the 2 f1-f2 distortion product pDP is a linear function of the primary tone level L2. Linear regression yields correlation coefficients higher than 0.8 in the majority of the DPOAE I/O-functions. The linear behavior is sufficiently fulfilled for all frequencies in normal and impaired hearing. This suggests that the observed linear functional dependency is quite general. Extrapolating towards pDP=0 yields the DPOAE threshold for L2. There is a significant correlation between DPOAE threshold and pure-tone threshold (r=0.65, p<0.001). Thus, the DPOAEs that reflect the functioning of an essential element of peripheral sound processing enable a reliable estimation of cochlear hearing threshold up to hearing losses of 50 dBHL without any statistical data. 相似文献
999.
Previous studies of behavior and IC single units in the mouse support theoretical expectations that gaps with ramped trailing markers have reduced detectability compared to equivalent gaps with ramped leading markers. In experiment 1, detection probability and response speeds of humans listening for gaps in broadband noise were investigated by independently varying either leading marker fall-time (FT) or trailing marker rise-time (RT). Gaps with silent duration of 1, 4, or 12 ms were presented 2 s into a 3-s noise burst, with either abrupt marker onsets and offsets or linearly ramped RT/FT of 2, 4, or 8 ms durations. Addition of a nonzero RT or FT to the gap silent period increased detectability and also increased reaction speed on trials with "Yes" response, but there was no difference in detectability or response speeds between RT and FT conditions. Experiment 2 extended this finding to gaps having two, one, or no abrupt marker edges. These findings suggest that human listeners do not make use of abrupt onset or offset information to enhance gap detection, but seem to rely on the effective sound level reduction associated with the gap for detection. 相似文献
1000.
Ison JR Virag TM Allen PD Hammond GR 《The Journal of the Acoustical Society of America》2002,112(1):238-246
Listeners asked to detect tones masked by noise hear frequent signals but miss infrequent probes, suggesting that they attend to spectral regions where they expect the signals to occur. The narrow detection pattern centered on the frequent target approximates that obtained in notched noise, indicating that attention is focused on the auditory filter. We measured attention bands in young and elderly listeners (n=5, 4; 20-25 and 62-82 years of age) for targets (800 or 1200 Hz) and infrequent probe signals (target +/-25-100 Hz) masked in wideband noise. We anticipated that their width would increase with age, as has been reported for auditory filters. A yes-no single-interval procedure provided detection probabilities and detection response speeds. Both measures showed near-linear declines with decreasing signal level, and graded decay functions as probe frequency deviated from the target frequency. Probes deviating from the target by 25 to 50 Hz were equivalent to a 2-dB reduction in signal level for both measures. The equivalent rectangular bandwidth (ERB) for detection approximated 11% of the signal frequency for each age group. Confidence intervals (95%) showed that the elderly ERB could be at most only about 20% larger than that of younger listeners. 相似文献