全文获取类型
收费全文 | 345051篇 |
免费 | 3459篇 |
国内免费 | 1251篇 |
专业分类
化学 | 180198篇 |
晶体学 | 5340篇 |
力学 | 15767篇 |
综合类 | 11篇 |
数学 | 38708篇 |
物理学 | 109737篇 |
出版年
2021年 | 2503篇 |
2020年 | 2742篇 |
2019年 | 2991篇 |
2018年 | 3671篇 |
2017年 | 3590篇 |
2016年 | 5719篇 |
2015年 | 3919篇 |
2014年 | 5749篇 |
2013年 | 15640篇 |
2012年 | 12428篇 |
2011年 | 15238篇 |
2010年 | 10073篇 |
2009年 | 10153篇 |
2008年 | 13907篇 |
2007年 | 14010篇 |
2006年 | 13401篇 |
2005年 | 12122篇 |
2004年 | 11177篇 |
2003年 | 9792篇 |
2002年 | 9506篇 |
2001年 | 11084篇 |
2000年 | 8456篇 |
1999年 | 6581篇 |
1998年 | 5182篇 |
1997年 | 5203篇 |
1996年 | 4892篇 |
1995年 | 4470篇 |
1994年 | 4215篇 |
1993年 | 4031篇 |
1992年 | 4586篇 |
1991年 | 4581篇 |
1990年 | 4235篇 |
1989年 | 4070篇 |
1988年 | 4095篇 |
1987年 | 4056篇 |
1986年 | 3825篇 |
1985年 | 5269篇 |
1984年 | 5489篇 |
1983年 | 4444篇 |
1982年 | 4760篇 |
1981年 | 4646篇 |
1980年 | 4502篇 |
1979年 | 4522篇 |
1978年 | 4668篇 |
1977年 | 4637篇 |
1976年 | 4670篇 |
1975年 | 4443篇 |
1974年 | 4348篇 |
1973年 | 4506篇 |
1972年 | 2791篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
FexNi100−x nanometric films were deposited on SiO2/Si substrates at room temperature using the pulsed laser deposition technique. The targets were Fe-Ni amorphous magnetic foils with composition Fe50Ni50, Fe35Ni65 and Fe22Ni78. Morphological and structural properties of the deposited films were investigated using scanning electron microscopy, Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, and X-ray reflectivity. Electrical and magnetic characteristics of the films were investigated by using the four-point probe and the magneto-optic Kerr effect techniques, respectively. The film properties are strictly dependent on the Fe-Ni compositional ratio. 相似文献
992.
C.M.Lin C.T. Chia Y.J. Shu Y.K. Tseng 《光散射学报》2005,17(3):216-218
Weperformedthehigh-pressureRaman measurementofthethreenanosizedZnOcrystals. Wefoundthesmallerthesize,thehigherthe pressuretoinducethephasetransitionfrom w櫣rzitetorock-saltstructure. High-pressureRamanmeasurementsof nona-shapedZnOcrystalswerepreformed.The… 相似文献
993.
M.D. Williams S.C. Williams S.A. Yasharahla N. Jallow 《Applied Surface Science》2007,253(20):8568-8570
Ultraviolet photoemission spectroscopy is used to study the kinetics of the H-Zn complex deactivation in Zn doped InP(1 0 0). Hydrogen injected into the material electronically passivates the local carrier concentration. Reverse-biased anneals of the InP under ultra-high vacuum show a dramatic change in the work function of the material with increasing temperature. Spectral features are also shown to be sensitive to sample temperature. To our knowledge, we show the first view of hydrogen retrapping at the surface using photoemission spectroscopy. A simple photoelectron threshold energy analysis shows the state of charge compensation of the material. 相似文献
994.
V. Hamplov A. Bubnov M. Ka par V. Novotn D. Pociecha M. Glogarov 《Liquid crystals》2003,30(5):627-631
A new series of chiral liquid crystalline materials having the same rigid core containing a keto group, and various numbers of ( S )-lactate groups in the chiral segment, has been synthesized and studied. All the compounds contain a branched terminal alkyl chain derived from ( S )-2-methylbutanol. The influence of the number of lactate units on mesogenic behaviour has been studied. All the compounds show the paraelectric SmA phase and the ferroelectric SmC * phase over rather wide temperature ranges. The antiferroelectric SmC * A phase was observed for the compound possessing two lactate groups. 相似文献
995.
996.
D. H. Adams W. Bietenholz 《The European Physical Journal C - Particles and Fields》2004,34(2):245-253
The overlap hypercube fermion is constructed by inserting a lattice fermion with hypercubic couplings into the overlap formula. One obtains an exact Ginsparg-Wilson fermion, which is more complicated than the standard overlap fermion, but which has improved practical properties and is of current interest for use in numerical simulations. Here we deal with conceptual aspects of the overlap hypercube Dirac operator. Specifically, we evaluate the axial anomaly and the index, demonstrating that the correct classical continuum limit is recovered. Our derivation is non-perturbative and therefore valid in all topological sectors. At the non-perturbative level this result had previously only been shown for the standard overlap Dirac operator with Wilson kernel. The new techniques which we develop to accomplish this also for hypercubic kernels are of a general nature and have the potential to be extended to overlap Dirac operators with even more general kernels.Received: 27 October 2003, Published online: 25 February 2004 相似文献
997.
B. Champagnon C. Martinet M. Boudeulle D. Vouagner C. Coussa T. Deschamps L. Grosvalet 《Journal of Non》2008,354(2-9):569-573
Normal silica glass is usually referred to as low density amorphous silica as it can be converted to high density amorphous silica by a hydrostatic pressure (polyamorphic transition). In this work in situ Raman experiments are performed in a diamond anvil cell up to 18 GPa. The pressure effects on the structure of silica after successive compression decompression experiments are analyzed. The mode Grüneisen parameters corresponding to the elastic compression of high density amorphous silica are obtained and compared with those of normal silica. A reorganization of the high density amorphous silica below 3 GPa is evidenced. 相似文献
998.
Recently, Miracle proposed that the intermediate structure in metallic glasses could be usefully characterized as an ordered face centered cubic packing of solute-centered coordination clusters. In this paper we examine the stability of such solute ordered arrangements in binary hard sphere mixtures subject to density maximization through local particle moves. 相似文献
999.
A theoretical approach was made to find out a complete fluorine incorporation zone on a ternary diagram which serves as a useful graphical representation to select the flows of the supplied reagents for incorporation of the suitable amount of fluorine into cladding glass of optical fiber preform made by the MCVD process using CCl2F2 as a source of fluorine under oxygen abundance, oxygen deficiency and intermediate oxygen state conditions. The possible mechanism for incorporation of fluorine into cladding glass of optical fiber is also evaluated on the basis of the thermodynamical data. The fluorine incorporation mechanism in silica glass by the MCVD process is found to be dependent on the CCl2F2/SiCl4 ratio in the input gas mixture. Fluorine doping is found to be effective for removing the strained Si–O–Si bonds, which govern the optical transparency in deep ultra-violet (DUV) and vacuum ultra-violet (VUV) regions. The maximum refractive index depression of ?0.5 × 10?3 is obtained with incorporation of fluorine into silica cladding glass by the MCVD process using CCl2F2 as a dopant precursor with suitable flow of SiCl4 vapor along with O2 through backward deposition pass. The structure of fluorine doped silica glass preform samples containing 1.70–1.79 mol% fluorine incorporated by the MCVD process based on the analyses of 19F MAS spectra done by high-resolution 19F NMR spectroscopy reveal the presence of two distinct types of fluorine environments. The majority of the fluorine environments are formed in SiO1.5F polyhedral and less abundant species is observed to be highly unusual, yielding a fivefold coordinated silicon of the type SiO2F polyhedral which become increased with increasing the fluorine content. 相似文献
1000.
Specific features of the formation of submicron (70–300 nm) inclusions in Ti:sapphire (Al2O3:Ti) grown in a carbon-containing medium have been investigated. These inclusions are caused by deviation from the melt stoichiometry and are formed during the melt-crystal phase transition. These defects are submicropores containing excess aluminum and its suboxides; they can be destroyed by thermal loading of a crystal. 相似文献