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991.
992.
993.
Bijan Saha 《Central European Journal of Physics》2010,8(6):920-923
Different characteristics of matter influencing the evolution of the uUniverse haves been simulated by means of a nonlinear
spinor field. We have considered two cases where the spinor field nonlinearity occurs either as a result of self-action or
due to the interaction with a scalar field. 相似文献
994.
We show that a particle, with positive orbital angular momentum, following an outgoing null/timelike geodesic, shall never reach the closed timelike horizon present in the (4 + 1)-dimensional rotating Gödel black hole space–time. Therefore a large part of this space–time remains inaccessible to a large class of geodesic observers, depending on the conserved quantities associated with them. We discuss how this fact and the existence of the closed timelike curves present in the asymptotic region make the quantum field theoretic study of the Hawking radiation, where the asymptotic observer states are a pre-requisite, unclear. However, the semi classical approach provides an alternative to verify the Smarr formula derived recently for the rotating Gödel black hole. We present a systematic analysis of particle emissions, specifically for scalars, charged Dirac spinors and vectors, from this black hole via the semiclassical complex path method. 相似文献
995.
A critical analysis has been made of the long-term yearly and seasonal variations of ozone concentration at Ahmedabad (23°N,
72.5°E), India and Halley Bay (76°S, 27°W), a British Antarctic Service Station. The effect of O3 depletion on night airglow
emission of Li 6708 ? line at Ahmedabad and Halley Bay has been studied. Calculations based on chemical kinetics show that
the airglow intensity of Li 6708 ? line has also been affected due to the depletion of O3 concentration. The nature of yearly variation and seasonal variation of intensity of Li 6708 ? line for the above two stations
have been shown and compared. It has been shown that the rate of decrease of intensity of Li 6708 ? line was comparatively
higher at Halley Bay due to dramatic decrease of Antarctic O3 concentration. 相似文献
996.
We study molecular transistors where graphene nanoribbons act as three metallic electrodes connected to a ring-shaped 18-annulene molecule. Using the nonequilibrium Green function formalism combined with density functional theory, recently extended to multiterminal devices, we show that these nanostructures exhibit exponentially small transmission when the source and drain electrodes are attached in a configuration with destructive interference of electron paths around the ring. The third electrode, functioning either as an attached infinite-impedance voltage probe or as an "air-bridge" top gate covering half of molecular ring, introduces dephasing that brings the transistor into the "on" state with its transmission in the latter case approaching the maximum limit for a single conducting channel device. The current through the latter device can also be controlled in the far-from-equilibrium regime by applying a gate voltage. 相似文献
997.
Brey WW Edison AS Nast RE Rocca JR Saha S Withers RS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,179(2):290-293
We report a 600-MHz 1-mm triple-resonance high-temperature-superconducting (HTS) probe for nuclear magnetic resonance spectroscopy. The probe has a real sample volume of about 7.5 microl, an active volume of 6.3 microl, and appears to have the highest mass sensitivity at any field strength. The probe is constructed with four sets of HTS coils that are tuned to 1H, 2H, 13C, and 15N, and there is a z-axis gradient. The coils are cooled with a conventional Bruker CryoPlatform to about 20 K, and the sample chamber can be regulated above or below room temperature over a moderate range using a Bruker variable temperature unit. The absolute S/N for 0.1% ethylbenzene is approximately 1/3 that of a conventional 5mm probe with just 1/70 of the sample volume. We demonstrate the utility of this probe for small molecules and proteins with 2D spectra of just 1.7 microg of ibuprofen and 400 microM 15N-labeled ubiquitin. 相似文献
998.
In the present work a simple chemical reduction method is followed to grow CdS nanoparticles at room temperature. The grown
sample is ultrasonicated in acetone. The dispersed sample is characterized using electron diffraction technique. Simultaneously
optical absorption of this sample is studied in the range of 400–700 nm. The photoluminescence spectrum of the sample is also
studied. Results show the formation of nanoparticles. Hence an increase in band gap compared to bulk CdS and the as-prepared
CdS nanoparticles have surface sulphur vacancies.
相似文献
999.
Abhijit Mookerjee Kartick Tarafder Atisdipankar Chakrabarti Kamal Krishna Saha 《Pramana》2008,70(2):221-235
We discuss an application of the generalized augmented space method introduced by one of us combined with the recursion method
of Haydock et al (GASR) to the study of electronic structure and optical properties of random binary alloys. As an example, we have taken
the 50-50 CuZn alloy, where neutron scattering indicates the existence of short-range order.
相似文献
1000.
Electric field distributions and their role in the formation of avalanche due to the passage of heavy ions in parallel grid
avalanche type wire chamber detectors are evaluated using a Monte Carlo simulation. The relative merits and demerits of parallel
and crossed wire grid configurations are studied. It is found that the crossed grid geometry has marginally higher gain at
larger electric fields close to the avalanche region. The spatial uniformity of response in the two wire grid configurations
is also compared.
相似文献