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171.
Ingrid Biehl Johannes Buchmann Safuat Hamdy Andreas Meyer 《Designs, Codes and Cryptography》2002,25(3):223-236
We present RDSA, a variant of the DSA signature scheme, whose security is based on the intractability of extracting roots in a finite abelian group. We prove that RDSA is secure against an adaptively chosen message attack in the random oracle model if and only if computing roots in the underlying group is intractable. We report on a very efficient implementation of RDSA in the class group of imaginary quadratic orders. We also show how to construct class groups of algebraic number fields of degree < 2 in which RDSA can be implemented. 相似文献
172.
Hemodynamic forces within the human carotid artery are well known to play a key role in the initiation and progression of
vascular diseases such as atherosclerosis. The degree and extent of the disease largely depends on the prevailing three-dimensional
flow structure and wall shear stress (WSS) distribution. This work presents tomographic PIV (Tomo-PIV) measurements of the
flow structure and WSS in a physiologically accurate model of the human carotid artery bifurcation. The vascular geometry
is reconstructed from patient-specific data and reproduced in a transparent flow phantom to demonstrate the feasibility of
Tomo-PIV in a complex three-dimensional geometry. Tomographic reconstruction is performed with the multiplicative line-of-sight
(MLOS) estimation and simultaneous multiplicative algebraic reconstruction (SMART) technique. The implemented methodology
is validated by comparing the results with Stereo-PIV measurements in the same facility. Using a steady flow assumption, the
measurement error and RMS uncertainty are directly inferred from the measured velocity field. It is shown that the measurement
uncertainty increases for increasing light sheet thickness and increasing velocity gradients, which are largest near the vessel
walls. For a typical volume depth of 6 mm (or 256 pixel), the analysis indicates that the velocity derived from 3D cross-correlation
can be measured within ±2% of the maximum velocity (or ±0.2 pixel) near the center of the vessel and within ±5% (±0.6 pixel)
near the vessel wall. The technique is then applied to acquire 3D-3C velocity field data at multiple axial locations within
the carotid artery model, which are combined to yield the flow field and WSS in a volume of approximately 26 mm × 27 mm × 60 mm.
Shear stress is computed from the velocity gradient tensor and a method for inferring the WSS distribution on the vessel wall
is presented. The results indicate the presence of a complex and three-dimensional flow structure, with regions of flow separation
and strong velocity gradients. The WSS distribution is markedly asymmetric confirming a complex swirling flow structure within
the vessel. A comparison of the measured WSS with Stereo-PIV data returns an acceptable agreement with some differences in
stress magnitude. 相似文献
173.
174.
We investigate the cavity optomechanical properties of an antiferromagnetic Bose-Einstein condensate, where the role of the mechanical element is played by spin-wave excitations. We show how this system can be described by a single rotor that can be prepared deep in the quantum regime under realizable experimental conditions. This system provides a bottom-up realization of dispersive rotational optomechanics, and opens the door to the direct observation of quantum spin fluctuations. 相似文献
175.
It is still a matter of debate to understand the equation of state of cold matter with supra-nuclear density in compact stars because of unknown non-perturbative strong interaction between quarks. Nevertheless, it is speculated from an astrophysical view point that quark clusters could form in cold quark matter due to strong coupling at realistic baryon densities. Although it is hard to calculate this conjectured matter from first principles, one can expect that the inter-cluster interaction will share some general features with the nucleon-nucleon interaction successfully depicted by various models. We adopt a two-Gaussian component soft-core potential with these general features and show that quark clusters can form stable simple cubic crystal structure if we assume that the wave function of quark clusters have a Gaussian form. With this parametrization, the Tolman-Oppenheimer-Volkoff equation is solved with reasonably constrained parameter space to give mass-radius relations of crystalline solid quark stars. With baryon number densities truncated at 2n0 at surface and the range of the interaction fixed at 2 fm we can reproduce similar mass-radius relations to that obtained with bag model equations of state. The maximum mass ranges from 0.5M⊙ to 3M⊙. The recently measured high pulsar mass ( 2M⊙) is then used to constrain the parameters of this simple interaction potential. 相似文献
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179.
纳米氢氧化钴原位修饰碳糊电极固-液微萃取及电化学检测辛硫磷 总被引:1,自引:0,他引:1
运用纳米氢氧化钴原位修饰碳糊电极微分脉冲伏安(DPV)法检测了辛硫磷。在外加电位下辛硫磷分子被萃取到电极表面,并与纳米氢氧化钴相互作用形成络合物,在-0.489 V处得到1还原峰,且还原峰电流随扫速线性增长,表明电极上的还原过程受吸附控制。吸附过程满足Temkin等温吸附模型。pH与电位的关系表明辛硫磷的还原过程为1电子1个质子反应。运用交流阻抗方法考察了反应过程,并辅以理论计算,表明反应为自发过程,计算结果与循环伏安法一致。采用该体系检测辛硫磷,其还原峰电流与辛硫磷浓度的对数分别在3.333×10~(-13)~3.333×10~(-8) mol/L和3.333×10~(-8)~3.333×10~(-6) mol/L范围内呈线性关系,检出限(S/N=3)可达3.333×10~(-13) mol/L。该方法具有良好的重现性及选择性,用于菠菜中辛硫磷农药的检测,结果满意。 相似文献
180.