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121.
P. N. Shankar 《Pramana》2005,65(3):437-455
We consider in a frame fixed to a bubble translating with steady speedU, the inviscid, axisymmetric, irrotational motion of the liquid past it. If all speeds are normalized byU and lengths by {ie437-1}, whereT is the surface tension of the liquid-bubble interface, it can be shown that the unknown bubble shape and field depend on
a single parameter {ie437-2} alone, where the pressures are the ones in the bubble and far away respectively. WhenΓ is very large the bubble is almost spherical in shape while for Γ<- Γ* ≈ -0.315, bubbles whose exteriors are simply connected do not exist. We solve the non-linear, free boundary problem for the
whole range Γ* < Γ < ∞ by the use of an analytical representation for the bubble shape, a surface singularity method to compute potential
flows and a generalized Newton’s method to continue inΓ. Apart from providing explicit representations for bubble shapes and detailed numerical values for the bubble parameters,
we show that the classical linearized solution for largeΓ is a very good approximation, surprisingly, to as low values of Γ as 2. We also show that Miksiset al [1] is inaccurate over the whole range and in serious error for large and smallΓ. These have been corrected. 相似文献
122.
123.
The general dynamical equations for perfect fluid filled spheres with an outward flux of photons are derived. The vital role
played by the energy density of the free gravitational field in accelerating photon production has been emphasized. It is
pointed out that even when the material energy density is finite, the energy density of the free gravitational field can take
infinitely large values resulting in vanishing surface area of the star. A generalized Schwarzschild interior solution with
conformally flat geometry but with photon emission has been obtained. It is pointed out that the interior conformal coordinate
system bears a strong resemblance to the exterior Krushkal coordinates. It is shown that for spherical star the invariant
velocity of the fluid particles, falling towards the centre, is proportional to its radius suggesting that the outer envelopes
collapse at a faster rate than the core part. It is shown that the interior radiating solution can be matched with generalized
Schwarzchild exterior solution. 相似文献
124.
L.A. Crum 《Ultrasonics》1984,22(5):215-223
A general review is given of the mechanism of rectified diffusion. The equations that describe the threshold acoustic pressure amplitude as well as the growth rate are presented. Simplified versions of the complicated threshold equation are also obtained for two regions that are of particular interest. Graphical representations of the equations for a variety of physical parameters are given as well as a comparison between the available measurements and the theoretical predictions. Finally, some suggested areas of future research in this area are presented. 相似文献
125.
A zero-curvature criterion is proposed to determine the practical collapse load. Six tests have been carried out on spherical pressure vessels with cylindrical nozzle. Results of these tests and other experimental data quoted from different references are discussed in order to compare the new criterion with various previously proposed criteria. It is concluded that: (1) the zero-curvature point is a characteristic point of the experimental curve and that the new criterion is an objective criterion without any artificial coefficient. (2) the deviation of the collapse load estimated by the new criterion is smaller than that estimated by other criteria.Supported by the Chinese National Foundation of Natural Science. 相似文献
126.
Hideatsu Maeda 《Journal of Polymer Science.Polymer Physics》1994,32(1):91-97
Near-infrared, viscometric, and calorimetric measurements were made on aqueous poly(vinyl methyl ether) (PVME) solutions at temperatures between 15 and 43°C. We found a hydrogen-bonded structure of water around the polymer chain (a polymer-water complex), which is characterized by two distinct hydration numbers (i.e., 2.7 and 5.0 water molecules on each monomer unit of the chain) by analyzing the concentration dependence of endothermic enthalpies at a cloud point temperature, ca. 35°C. In particular, the 2.7 water-polymer complex has been suggested to be cooperatively formed by using data of the near-infrared (nir) absorption spectrum around 1930 nm. Furthermore, the peak-wavelength of the nir spectrum has been observed to change drastically at the cloud point when the temperature is raised. This can be interpreted as a cooperative collapse of the hydrogen-bonded water structure to free water, resulting in the aggregation of the polymer chains due to the exposure of their hydrophobic groups at the cloud point. © 1994 John Wiley & Sons, Inc. 相似文献
127.
A. Yu. Grosberg 《Journal of statistical physics》1985,38(1-2):149-160
The collapse (globulization) of an ideal heteropolymer chain under the action of an external attractive field is considered. The problem of the collapse of different types of primary structures, including mobile, periodic, large-block, and statistical structures, is formulated. It is shown that for a random heteropolymer, the mathematical image of the globular state is the chain-length independence of the probability distribution of a random thermal distribution function of the end monomer coordinates. The free energy per monomer of a chain in a globular state and local densities of monomers of all types are shown to be a self-averaging quantities. An exactly solvable model is proposed for a globule formed by a statistical heteropolymer chain. In this model, different types of monomers are attracted to different centers by linear elastic forces with identical elastic constants. The modulus of elasticity is obtained for a heteropolymer globule with respect to the attraction of different types of monomers in different directions. It is shown that this modulus is higher for a short-periodic polymer than for a statistical one. 相似文献
128.
Bubble dynamics has been recognized as being responsible for many effects in ultrasonic fields, for example cleaning and destruction of surfaces, and emulsification. To improve the performance of ultrasonic devices which make use of these effects some knowledge of the dynamics of cavitation bubbles is needed. One of the main means of studying bubble dynamics is high speed photography in conjunction with some suitable bubble production mechanism to get rid of the statistical appearance of bubbles encountered in ultrasonic cavitation. Results of jet and vortex ring formation obtained mainly with spark-and laser-produced bubbles are reported and demonstrated in a series of frames. 相似文献
129.
M.A. Margulis 《Ultrasonics》1985,23(4):157-169
Contemporary ideas on the nature of cavitation are reviewed in this paper. The general theories of sonoluminescence and sonochemical reactions, the origin, stability and splitting of cavitation bubbles, the dynamics of cavitation field evolution, the peculiarities of cavitation effects at low intensity and low-frequency acoustic oscillations, the sonoluminescence quenching effect and some questions on the energetics of cavitation fields are discussed. The electrical theory of the splitting of cavitation bubbles may, as shown in the paper, become an alternative to the thermal theories of cavitation in the future. 相似文献
130.
Ramesh Chander Kapoor 《Pramana》1976,7(5):334-343
Gravitational recoil of a gigantic black hole (M∼108–9 M⊙) formed in the nonspherical collapse of the nuclear part of a typical galaxy can take place with an appreciable speed as
a consequence of the anisotropic emission of gravitational radiation. Accretion of gaseous matter during its flight through
the galaxy results in the formation of a glowing shock front. The accompanying stellar captures can lead to the formation
of an accretion disk-star system about the hole. Consequently, the hole can become “luminous” enough to be observable after
it emerges out of the galaxy. The phenomenon seems to have an importance in relation to the observations of quasar-galaxy
association in a number of cases. 相似文献