全文获取类型
收费全文 | 14473篇 |
免费 | 2975篇 |
国内免费 | 1425篇 |
专业分类
化学 | 3210篇 |
晶体学 | 190篇 |
力学 | 1597篇 |
综合类 | 247篇 |
数学 | 2504篇 |
物理学 | 11125篇 |
出版年
2024年 | 26篇 |
2023年 | 163篇 |
2022年 | 333篇 |
2021年 | 404篇 |
2020年 | 432篇 |
2019年 | 355篇 |
2018年 | 378篇 |
2017年 | 499篇 |
2016年 | 602篇 |
2015年 | 541篇 |
2014年 | 806篇 |
2013年 | 1059篇 |
2012年 | 875篇 |
2011年 | 987篇 |
2010年 | 922篇 |
2009年 | 940篇 |
2008年 | 960篇 |
2007年 | 921篇 |
2006年 | 939篇 |
2005年 | 849篇 |
2004年 | 835篇 |
2003年 | 698篇 |
2002年 | 633篇 |
2001年 | 521篇 |
2000年 | 496篇 |
1999年 | 423篇 |
1998年 | 376篇 |
1997年 | 305篇 |
1996年 | 269篇 |
1995年 | 190篇 |
1994年 | 174篇 |
1993年 | 130篇 |
1992年 | 110篇 |
1991年 | 106篇 |
1990年 | 97篇 |
1989年 | 98篇 |
1988年 | 72篇 |
1987年 | 54篇 |
1986年 | 66篇 |
1985年 | 48篇 |
1984年 | 31篇 |
1983年 | 14篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Considering the octet baryons in relativistic mean field theory and selecting entropy per baryon S=l,we calculate and discuss the influence of U bosons on the equation of state,mass-radius,moment of inertia and gravitational redshift of massive protoneutron stars(PNSs).The effective coupling constant gu of U bosons and nucleons is selected from 0 to 70 GeV~(-2).The results indicate that U bosons will stiffen the equation of state(EOS).The influence of U bosons on the pressure is more obvious at low density than high density,while the influence of U bosons on the energy density is more obvious at high density than low density.The U bosons play a significant role in increasing the maximum mass and radius of PNS.When the value of gu changes from 0 to 70 GeV~(-2),the maximum mass of a massive PNS increases from 2.11M_⊙ to 2.58M_⊙,and the radius of a PNS corresponding to PSR J0348+0432 increases from 13.71 km to 24.35 km.The U bosons will increase the moment of inertia and decrease the gravitational redshift of a PNS.For the PNS of the massive PSR J0348+0432,the radius and moment of inertia vary directly with gu,and the gravitational redshift varies approximately inversely with gu. 相似文献
72.
Study of the temperature rise induced by a focusing transducer with a wide aperture angle on biological tissue containing ribs 下载免费PDF全文
We used the spheroidal beam equation to calculate the sound field created by focusing a transducer with a wide aperture angle to obtain the heat deposition, and then we used the Pennes bioheat equation to calculate the temperature field in biological tissue with ribs and to ascertain the effects of rib parameters on the temperature field. The results show that the location and the gap width between the ribs have a great influence on the axial and radial temperature rise of multilayer biological tissue. With a decreasing gap width, the location of the maximum temperature rise moves forward; as the ribs are closer to the transducer surface, the sound energy that passes through the gap between the ribs at the focus decreases,the maximum temperature rise decreases, and the location of the maximum temperature rise moves forward with the ribs. 相似文献
73.
Carrier-envelope phase measurement using plasmonic-field-enhanced high-order harmonic generation of H atom in few-cycle laser pulses 下载免费PDF全文
We investigate the plasmonic-field-enhanced high-order harmonic generation (HHG) of H atom driven by few-cycle laser pulses, by solving the time-dependent Schrödinger equation (TDSE). Compared with the homogeneous field, HHG spectra generated by inhomogeneous field exhibit two-plateau structure. We analyze the origin of the two plateaus by using the semiclassical trajectory method. Our results from both classical and TDSE simulations show that the cutoffs of the two plateaus are dramatically affected by the carrier-envelope phase (CEP) of laser pulse in the inhomogeneous field, even for a little longer pulse. Thus, we can determine the CEP of driving laser based on the cutoff position of HHG generated in the inhomogeneous field. 相似文献
74.
In this paper the repulsive effects in the Kerr and Kerr--Newman fields are
discussed. The contributions made by all parameters of the fields and test
particles to the repulsive effects are also discussed, and the accretive
effect on interstellar dust, i.e. the distribution of dust is calculated.
The discussion is also carried out on the slow rotation of the Kerr field in
which the effect is related to the positions and velocities of the particles
and the orientations of their trajectories as well. 相似文献
75.
The mid-infrared (1500-3800 cm−1) absorption spectrum of gaseous nitric oxide has been studied at low temperature (99 K) with a long absorption path (160 m) in order to observe weak combination, difference, and overtone bands of the NO dimer. About ten new bands were assigned with greater or lesser certainty. Combined with previous results, they lead to a set of 12 secure and 7 tentative vibrational term values for (NO)2, essentially doubling our knowledge of NO dimer vibrational states. The strongest non-fundamental bands in this region, other than the ν1 (symmetric N-O stretch) + ν5 (asymmetric N-O stretch) overtone, involve combinations of ν5 with ν3 (intermolecular stretch). Excitation of ν5 results in increased frequencies for the intermolecular modes ν2, ν3, and ν4. A new value of 155.5 cm−1 was obtained for ν4, the elusive infrared-inactive out-of-plane fundamental vibration. 相似文献
76.
ZnO naorods on ZnO-coated seed substrates were fabricated by solution chemical method from Zn(NO3)2/NaOH under assisted electrical field. The working mechanism of electrical field was analyzed and the factors affecting the rod growth such as potential, precursor concentration and growth temperature were elucidated. The structural and optical properties are characterized by SEM, TEM, XRD, HRTEM and UV-vis. The results indicated that the nanorods have wurtzite structure without electrical field and are primarily of zincite structure under electrical field; when the electrical field is 1.1-1.3 V, not only the elevation of ion diffusion and adsorption lower the crystallite/solution interfacial energy and then the crystal nucleation barrier by increasing charge intensity, but also the production of H+ through oxidation of OH− increases properly the degree of solution supersaturation near the substrate, and thus lowers the activation energy. Both the two processes do favor to rod growth. With increasing precursor concentration in this system, the average diameter and length of ZnO nanorods increase, leading to decreasing of optical transmittance. The maximum rod growth rate at given concentration of Zn2+ occurs at a specific temperature. 相似文献
77.
L. C. Cortés-Cuautli G. F. Torres del Castillo 《International Journal of Theoretical Physics》2006,45(9):1783-1790
It is shown that, in the standard framework of non-relativistic quantum mechanics, the presence of a magnetic field implies that there are no operators representing those translations or rotations that do not leave invariant the magnetic field, and the corresponding components of the linear or angular momentum are undefined.
Pacs: 03.65.-w. 02.20.-a 相似文献
78.
A planar metamaterial structure consisting of two layers of split-ring resonator (SRR) arrays is demonstrated to form the
image of a point source with subwavelength resolution. The source frequency is swept through the resonance gap of the metamaterial
layers and the lateral field intensity distribution is recorded on the transmission side of the metamaterial. When the source
is tuned to the resonance frequency of SRRs, the metamaterial acts as a high permeability medium and a distinct image with
subwavelength resolution in the lateral direction is obtained. Increasing the distance between the individual SRR layers reduces
the interlayer coupling, and the intensity and spatial resolution of the image decrease rapidly. 相似文献
79.
Christopher?J.?FewsterEmail author Izumi?ojima Martin?Porrmann 《Letters in Mathematical Physics》2005,73(1):1-15
In this Letter we try to settle some confused points concerning the use of the notion of p-nuclearity in the mathematical and physical literature, pointing out that the nuclearity index in the physicists’ sense vanishes for any p> 1. Our discussion of these issues suggests a new perspective, in terms of ε-entropy and operator spaces, which might permit connections to be drawn between phase space criteria and quantum energy inequalities.Mathematics Subject Classification (2000): 81T05, 47B10, 47L25. 相似文献
80.
In this paper we present an axiomatic, geometric, formulation of electromagnetism with only one axiom: the field equation for the Faraday bivector field F. This formulation with F field is a self-contained, complete and consistent formulation that dispenses with either electric and magnetic fields or the electromagnetic potentials. All physical quantities are defined without reference frames, the absolute quantities, i.e., they are geometric four-dimensional (4D) quantities or, when some basis is introduced, every quantity is represented as a 4D coordinate-based geometric quantity comprising both components and a basis. The new observer-independent expressions for the stress-energy vector T(n) (1-vector), the energy density U (scalar), the Poynting vector S and the momentum density g (1-vectors), the angular momentum density M (bivector) and the Lorentz force K ((1-vector) are directly derived from the field equation for F. The local conservation laws are also directly derived from that field equation. The 1-vector Lagrangian with the F field as a 4D absolute quantity is presented; the interaction term is written in terms of F and not, as usual, in terms of A. It is shown that this geometric formulation is in a full agreement with the Trouton-Noble experiment. 相似文献