全文获取类型
收费全文 | 1077篇 |
免费 | 207篇 |
国内免费 | 79篇 |
专业分类
化学 | 390篇 |
晶体学 | 24篇 |
力学 | 42篇 |
综合类 | 9篇 |
数学 | 36篇 |
物理学 | 470篇 |
综合类 | 392篇 |
出版年
2024年 | 4篇 |
2023年 | 2篇 |
2022年 | 19篇 |
2021年 | 14篇 |
2020年 | 25篇 |
2019年 | 27篇 |
2018年 | 37篇 |
2017年 | 30篇 |
2016年 | 42篇 |
2015年 | 37篇 |
2014年 | 51篇 |
2013年 | 92篇 |
2012年 | 83篇 |
2011年 | 97篇 |
2010年 | 71篇 |
2009年 | 66篇 |
2008年 | 62篇 |
2007年 | 80篇 |
2006年 | 59篇 |
2005年 | 54篇 |
2004年 | 55篇 |
2003年 | 51篇 |
2002年 | 40篇 |
2001年 | 35篇 |
2000年 | 28篇 |
1999年 | 39篇 |
1998年 | 20篇 |
1997年 | 19篇 |
1996年 | 7篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1363条查询结果,搜索用时 172 毫秒
91.
SUNYufeng ZHANGGuosheng WEIBingchen LIWeihuo WANGYuren 《科学通报(英文版)》2004,49(6):542-546
In situ synthesized TiC particles and β-Ti dendrites reinforced Cu47Ti34Zr11Ni8 bulk metallic glass (BMG) composite ingots were prepared by the suction casting method.The ingots with diameters from 1 up to 4mm were successfully obtained. It was shown that introducing TiC micro-sized particles into the amorphous matrix did not disturb the glass forming ability (GFA) of the matrix,while the yield strength and ductility could be well improved.The phase constitution, microstructure and elements distribution in the composites were studied by OM, XRD, SEM and EDS.It was shown that the in situ synthesized TiC particles acting as heterogeneous nucleation sites promoted the precipitation of β-Ti dendrites, resulting in the formation of the TiC particles and β-Ti dendrites co-reinforced BMG composites. The compressive tests were employed to probe the yield strength and ductility of BMG composites. 相似文献
92.
A study of ultrasonic velocities and internal friction has been carried out in Pb-Bi alloys in the concentration range of
0 to 49.5 atomic % Bi using the composite oscillator technique. From the velocity and density data a set of elastic constants
namely, Young’s modulus, rigidity modulus, bulk modulus and Poisson’s ratio are estimated. The results are interpreted in
terms of the phase changes occurring in the alloy system. Internal friction is found to be more sensitive than the elastic
constants to the phase changes. 相似文献
93.
J.K. Baria 《Czechoslovak Journal of Physics》2004,54(5):575-595
A simple pseudopotential model is used for the calculation of the temperature dependence of lattice mechanical properties which also depend on the phonon density of states such as lattice heat capacity C
V
, Debye temperature D, harmonic contribution to free energy, thermal pressure, isothermal bulk modulus corrected to the fourth order, volume thermal expansion coefficient , Debye-Waller factor, mean-square displacement, Debye-Waller temperature parameter, and X-ray characteristic temperature M of Cu, Ag, Au, Ni, Pd, Pt, Rh, and Ir. The contribution of d-like electrons is taken into account by introducing repulsive short-range Born-Mayer-like term. Very recently proposed screening function due to Sarkar et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever possible. A good agreement between theoretical investigations and experimental findings show the ability of our model potential to reproduce wide class of properties in noble and transition metals. 相似文献
94.
S.V. Dordevic D.N. Basov R.C. Dynes B. Ruzicka V. Vescoli L. Degiorgi H. Berger R. Gaál L. Forró E. Bucher 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):15-23
We present a comprehensive analysis of the optical constants of the two-dimensional dichalcogenide materials 2
H
-
TaSe
2
and 2
H
-
NbSe
2
, in an attempt to address the physics of two-dimensional correlated systems. The title compounds were studied over several
decades in frequency, from the far-infrared to the ultraviolet. Measurements with linearly polarized light have allowed us
to obtain both the in-plane and out-of-plane components of the conductivity tensor. Although the electromagnetic response
of dichalcogenides is strongly anisotropic, both the in-plane and out-of-plane components of the conductivity tensor share
many common features, including the presence of a well-defined metallic component, as well as a “mid-infrared band”. We discuss
the implications of these results in the context of the spectroscopic results of other classes of low-dimensional conductors
such as the high-temperature superconducting cuprates. In particular, the analysis of the redistribution of the spectral weight
as a function of temperature, as well as the behavior of the quasiparticles relaxation rate, points to significant distinctions
between the charge dynamics of dichalcogenides and other classes of low dimensional conductors.
Received 28 October 2002 / Received in final form 10 March 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: degiorgi@solid.phys.ethz.ch 相似文献
95.
Studies on CdS nanoparticles dispersed in silica matrix prepared by sol-gel technique 总被引:2,自引:0,他引:2
B. Bhattacharjee S.K. Bera D. Ganguli S. Chaudhuri A.K. Pal 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):3-9
SiO2/CdS-nanoparticle composite films (SiO2:CdS=85:15, 80:20, 75:25 and 70:30) were prepared by the sol-gel route. The films were characterized by studying microstructural
(XRD and TEM) and optical (transmittance and photoluminescence) properties. Band gaps of these films annealed at different
temperatures (373-473 K) for different times (10-120 min) indicated that the signature of nanocrystallinity is retained throughout
the range of our experimental conditions. A thermal diffusion process controlled growth in the crystallite size with increasing
annealing time and temperature. The average radii of the nanoparticles varied as the cube root of the annealing time but showed
exponential dependence on the inverse of annealing temperature. Photoluminescence (PL) studies of the composite films indicated
excitonic transitions. Theoretical analysis of the line shapes of the PL peaks recorded at 300 K and 80 K could be accounted
for by the combined effects of size distribution and phonon broadening. It was observed that the deformation potential (E
d) effectively controlled the line shapes of the PL measurements.
Received 24 May 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: msakp@mahendra.iacs.res.in 相似文献
96.
97.
A. A. Zakharenko 《Pramana》2007,69(4):617-629
In this work, the experimental results of the creation of the second non-dispersive Zakharenko wave (C
ph = C
g ≠ 0) in the negative roton branch (the so-called second sound) of the bulk elementary excitations (BEEs) energy spectra are
introduced. Several BEE signals detected by a bolometer situated in the isotopically pure liquid helium-II at low temperatures
∼100 mK are shown, which give evidence of negative roton creation in the liquid by helium atomic beams striking the liquid
surface. The negative roton signals were clearly distinguished by the following ways: the negative roton signal created by
helium atomic beams appeared earlier than the positive roton signal created by the beams, and presence of both positive and
negative roton signals together. It is natural that the negative roton creation by the beams requires the 4He-atom energies ∼12 K, while the positive roton creation by the atomic beams requires energies ∼35 K. Therefore, successive
increase in the heater power resulting in an increase in the 4He-atom energies gives solid evidence that the negative rotons are first created in the liquid by the helium atomic beams.
相似文献
98.
The general effective-medium dispersion relations are derived for surface-localized magnetic polaritons which propagate parallel to the surface between a superlattice and semi-infinite bulk material, as applied to ferromagnetic and antiferromagnetic superlattices, in the situation when a static magnetic field is applied in the plane of the layers and parallel to the magnetization. The dependence of the energy of the surface waves on the volume fraction of the ferromagnetic superlattice component and the influence of the external magnetic field on the spectrum of the surface magnetic polaritons for the antiferromagnetic superlattice are investigated. The spectrum of the surface-localized magnetic polaritons which appear at the junction of the magnetic (ferromagnetic and antiferromagnetic) superlattice with the magnetic material are more complex, in contrast to the cases of semi-infinite magnetic material or semi-infinite magnetic SL. It is essential that in all cases in the presence of the external magnetic field the spectrum of the magnetic polaritons are non-reciprocal. The properties of surface polaritons are discussed in detail for the system ferromagnetic superlattice (YIG/non magnet)/YAG and the antiferromagnetic superlattice (MnF2/ZnF2)/FeF2. 相似文献
99.
Ming Liu Yafei Wang Zhiyong Zhang Jianming Li Yu Liu Hua Tan Meijun Ni Gangtie Lei Meixiang Zhu Weiguo Zhu 《Journal of polymer science. Part A, Polymer chemistry》2011,49(17):3874-3881
To exploit an effective way to improve polymeric photovoltaic performance, a series of dithiophene‐benzothiadiazole‐alt‐fluorene copolymers containing carbazole groups at C‐9 positions of the alternating fluorene units (PFO‐FCz‐DBT) were synthesized and characterized. The effect of the carbazole groups on the optophysical, electrochemical, and photovoltaic properties of these copolymers was investigated. By comparison, this type of copolymers with carbazole units exhibited significantly improved photovoltaic properties than poly(2,7‐(9,9‐dioctyl‐fluorene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole) (PFO‐DBT) in the bulk heterojunction solar cells. A maximum power‐conversion efficiency (PCE) of 2.41% and a highest short‐circuit current density (Jsc) of 9.68 mA cm?2 were obtained for the PFO‐FCz‐DBT30, which are about two times higher than the corresponding levels for the PFO‐DBT30. This work demonstrated that introducing a hole‐transporting carbazole unit into copolymer is a simple and effective method to improve the Jsc and PCE. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
100.
Chunhui Duan Wanzhu Cai Chengmei Zhong Yanhu Li Xiaohui Wang Fei Huang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2011,49(20):4406-4415
Three narrow‐band‐gap conjugated copolymers based on indenofluorene and triphenylamine with pendant donor‐π‐acceptor chromophores were successfully synthesized by post‐functionalization approach. All the polymers have good solubility in common solvents and excellent thermal stability. The photophysical properties, energy levels and band gaps of the polymers were well manipulated by introducing different acceptor groups onto the end of their conjugated side chains. By using different acceptor groups, the band gaps of the polymers were narrowed from 1.86 to 1.53 eV by lowering their lowest unoccupied molecular orbital levels, whereas their relatively deep highest occupied molecular orbital levels of approximately ?5.35 eV were maintained. Bulk‐heterojunction solar cells with these polymers as electron donors and (6,6)‐phenyl‐C71‐butyric acid methyl ester as acceptor showed power conversion efficiencies as high as 3.1% and high open circuit voltages more than 0.88 eV. The relationships between the performance and film morphology, energy levels, charge mobilities were discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献