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131.
研制了一台多参数的主被动船载蓝绿光海洋激光雷达系统(BLOL),它可用于我国东海海域的海色遥感印证。该海洋激光雷达系统能被动地测量离水辐亮度Lw,主动测量漫散射衰减系数k和叶绿素a浓度C。雷达系统安装在青岛海洋大学的调查船上(约2500吨位),曾在21个站位进行了实验。实验的区域从上海东开始到冲绳岛附近。用该海洋激光雷达系统测量的结果与用传统的方法测量的结果符合的很好。 相似文献
132.
133.
传统古戏台下设瓮助声乃广为流传的说法,在国外亦有类似记述。作者对此作了考据和声学分析,认为事属妄传,当予澄清。 相似文献
134.
A method for estimating the plucking point of guitar tones is proposed. The algorithm is based on investigating the time lag between two consecutive pulses arriving at the bridge of the guitar. The signal is detected with an under-saddle pickup attached to the bridge. The method determines the minimum of the autocorrelation function for one period of the signal. The time lag of the minimum can be converted into the distance from the bridge where the string was plucked. The results obtained with the method are good, the error remains smaller than one centimetre, except for a few outliers. The algorithm is easy to implement and can be used to analyse playing styles. The efficiency of the method gives the potential to also use it in real-time computer music applications. 相似文献
135.
根据三维动画的制作原理,提出了三维动画技术在海态雷达演示系统应用中的方法和途径,通过对海态雷达演示系统片头制作的分析和海流、海浪场演示的技术实现做了初步的探讨,并对提高3DS的运行效率进行了分析. 相似文献
136.
The performance test of a shell-and-plate type evaporator (total surface area 21.95 m2, length 1450 mm, width 235 mm, 100 plates) for ocean thermal energy conversion (OTEC) plants is reported. Freon 22 (R22) and ammonia (NH3) were used as the working fluid. Empirical correlations are proposed for predicting the boiling heat transfer and the heat transfer coefficients on the water side. The water-side pressure drop is about 2.9 × 104 N/m2 when the warm water velocity is 0.7 m/s. The water-side friction factor is obtained. 相似文献
137.
Summary In this paper the eigenperiods of the Tyrrhenian Sea are examined by a hydrodinamical model in two dimensions. The knowledge
of these eigenperiods is important to evaluate the seiches that often appear, in some point or circumstance, stronger than
the tides. This investigation is performed by energizing the basin through the Sardinia channel, in the same way as it was
already done for the tides. This excitation simulates a large set of waves inducing oscillations inside the basin. The periods
of the waves are narrow and their amplitude equal. An analogous method of investigation is that of the fluorescence. In addition,
the results are compared with those previously obtained leaving the basin swinging, after having increased the sea level by
a uniform displacement. The response of the bidimensional model agrees with that of a monodimensional one as far as possible;
thus the last one can give useful information, also for a sea that does not have a channel shape, like the Tyrrhenian Sea.
Nevertheless, this basin has other openings, besides the Sardinia channel, it seems that they do not influence the eigenperiod
behaviour. This has been confirmed by performing the same computations over a sea 500 m less deep: the uniform lowering of
the sea surface is equivalent to close the four minor openings. The results carried out in this case agree with the previous
one. Among all the periods pointed out by our investigation, one is always exhibited in every point and by each system. The
period is that of 5.70 h and it can be considered a fundamental mode of the Tyrrhenian Sea. 相似文献
138.
《Wave Motion》2020
A finite volume full-wave method is used to simulate nonlinear dissipative acoustic propagation in ducts with a circular cross-section. Thermoviscous dissipative effects, due to bulk viscosity and shear viscosity in the boundary layer adjacent to the duct walls, are also considered. The propagation is assumed to be axisymmetric, and two different geometries are considered: a straight cylindrical tube, and a cylindrical tube joined smoothly to a slowly-flaring bell. Of special interest is the study of the onset of standing waves in the nonlinear regime. The full-wave numerical scheme is particularly well-adapted for this purpose, as it is not necessary to impose boundary conditions at the open end of the duct. A simplified model of excitation is adopted, where the lips are replaced by a spring–mass system which behaves like a pressure valve with a single degree of freedom. The full system behaves as expected, with a feedback cycle established between the pressure valve and the air column. The simulation is validated successfully in the linear regime using a theoretical solution. It is shown that increasing the stiffness of the lips leads to discrete jumps in playing frequency, which is behaviour typical of brass instruments. In the nonlinear regime, shock formation is observed for sufficiently high amplitudes of oscillation, and the radiation of these shock waves by the open end of the ducts can be visualised in the time-domain, along with edge-diffraction effects. The formation and evolution of standing waves in the nonlinear regime, where the effect of these shocks is very noticeable, is also examined. 相似文献
139.
140.
Backing effects on the underwater acoustic absorption of a viscoelastic polymer slab embedded with locally resonant scatterers are reported. The polymer slab is embedded with two layers of locally resonant scatterers, i.e. Al spheres coated by soft silicon rubber. Theoretical absorption coefficients of the polymer slab under different backings using a layer multiple scattering method show good agreement with the experimental results, which supports unambiguously the experimental observation. Then relations between the resonance modes and the low-frequency absorption peaks of the composite slab are clarified to address the absorption mechanisms. It shows that the mass of the steel backing affects evidently the low-frequency absorption, the absorption peak shifts to lower frequency range while increasing the backing mass. 相似文献