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11.
Wai Tung Lee Xin Tong Dennis Rich Yun Liu Michael Fleenor Akbar Ismaili Joshua Pierce Mark Hagen Jonny Dadras J. Lee Robertson 《Physica B: Condensed Matter》2009,404(17):2670-2672
In recent years, polarized 3He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the 3He gas are the spin-exchange optical pumping (SEOP) method and the meta-stable exchange optical pumping (MEOP) method. At present, the SEOP setup is comparatively compact due to the fact that it does not require the sophisticated compressor system used in the MEOP method. The temperature and the laser power available determine the speed, at which the SEOP method polarizes the 3He gas. For the quantity of gas typically used in neutron scattering work, this speed is independent of the quantity of the gas required, whereas the polarizing time using the MEOP method is proportional to the quantity of gas required. Currently, using the SEOP method to polarize several bar-liters of 3He to 70% polarization would require 20−40 h. This is an order of magnitude longer than the MEOP method for the same quantity of gas and polarization. It would therefore be advantageous to speed up the SEOP process. In this article, we analyze the requirements for temperature, laser power, and the type of alkali used in order to shorten the time required to polarize 3He gas using the SEOP method. 相似文献
12.
G. Kuri G. Materlik V. Hagen R. Wiesendanger 《Applied Physics A: Materials Science & Processing》2001,73(3):265-271
MgO (100) single crystals are implanted with 1.50-MeV Al+ and 3.00-MeV Al2
+ ions at a fluence of 1×1015 Al atoms cm-2 under high-vacuum conditions. The surface morphology of the substrate is measured in air using atomic force microscopy and
X-ray reflectometry followed by computer-simulated spectrum analysis. The ion-irradiated areas are found to protrude to different
heights on the nanometre scale. Small height differences are observed in the areas irradiated by Al+ and Al2
+ ions of comparable energy, dose rate and total fluence. The results indicate that protrusions are most likely caused by implantation-induced
point defects (vacancies) generated in the crystal during implantation. Other possibilities for the cause of protrusions are
discussed. Thermal treatment stimulates a partial recovery of the implantation damage and alters the topography of MgO surfaces.
Received: 22 May 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001 相似文献
13.
C. W. Hagen 《Applied Physics A: Materials Science & Processing》2014,117(4):1599-1605
A perspective is sketched for the field of focused electron beam-induced processing (FEBIP). The FEBIP lithography technique is compared to the very successful resist-based electron beam lithography (EBL) technique. The advantages of FEBIP over EBL are identified, the main advantage being its high spatial resolution. This will enable FEBIP to become an important lithography technique for the fabrication of devices with critical dimension in the range between 1 and 20 nm and serve as a complementary technique to EBL. It will be discussed what needs to be done to achieve this and what the potential applications are. 相似文献
14.
A. Priem P. J. M. van Bentum W. R. Hagen E. J. Reijerse 《Applied magnetic resonance》2001,21(3-4):535-548
Fe(III) and Gd(III) ions in α-alumina (A12O3) exhibit spin states ofS = 5/2 andS = 7/2 respectively. The magnitude of the zero-field interaction (ZFI) (D = 0.10?0.15 cm?1) gives rise to an inter Kramers doublet splitting in the same order of magnitude as the X-band electron paramagnetic resonance (EPR) quantum (0.3 cm?1). It is demonstrated that through a careful step-by-step analysis and spectral simulation of EPR spectra taken at D-band (130 GHz), Q-band (35 GHz), and X-band (9 GHz) at room temperature, the (relative) sign and magnitude of the ZFI parameters, b 2 0 , b 4 0 , and b 4 3 , can be reliably estimated. 相似文献
15.
Hagen Kleinert 《General Relativity and Gravitation》2000,32(5):769-839
I explain the geometric basis for the recently-discovered nonholonomic mapping principle which permits deriving laws of nature in spacetimes with curvature and torsion from those in flat spacetime, thus replacing and extending Einstein's equivalence principle. As an important consequence, it yields a new action principle for determining the equation of motion of a free spinless point particle in such spacetimes. Surprisingly, this equation contains a torsion force, although the action involves only the metric. This force makes trajectories autoparallel rather than geodesic, as a manifestation of inertia. A generalization of the mapping principle transforms path integrals from flat spacetimes to those with curvature and torsion, thus playing the role of a quantum equivalence principle. This generalization yields consistent results only for completely antisymmetric or for gradient torsion. 相似文献
16.
We present a new snapshot technique for performing spectrally resolved Mueller matrix polarimetry. The basic approach is an extension of the channeled spectropolarimetry technique, employing frequency-domain interferometry to encode polarization information into modulation of the spectrum. 相似文献
17.
Trace formulas for pairs of self-adjoint, maximal dissipative and accumulative as well as other types of resolvent comparable operators are obtained. In particular, the existence of a complex-valued spectral shift function for a pair {H′,H} of maximal accumulative operators has been proved. We investigate also the existence of a real-valued spectral shift function. Moreover, we treat in detail the case of additive trace class perturbations. Assuming that H and H′=H+V are maximal accumulative and V is trace class, we prove the existence of a summable complex-valued spectral shift function. We also obtain trace formulas for pairs {H,H?}assuming only that H and H?are resolvent comparable. In this case the determinant of the characteristic function of H is involved in trace formulas. 相似文献
18.
The dual approach to the Ginzburg-Landau theory of a Bardeen-Cooper-Schrieffer superconductor is reviewed. The dual theory describes a grand canonical ensemble of fluctuating closed magnetic vortices, of arbitrary length and shape, which interact with a massive vector field representing the local magnetic induction. When the critical temperature is approached from below, the magnetic vortices proliferate. This is signaled by the disorder field, which describes the loop gas, developing a non-zero expectation value in the normal conducting phase. It therby breaks a global U(1) symmetry. The ensuing Goldstone field is the magnetic scalar potential. The superconducting-to-normal phase transition is studied by applying renormalization group theory to the dual formulation. In the regime of a second-order transition, the critical exponents are given by those of a superfluid with a reversed temperature axis. 相似文献
19.
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