全文获取类型
收费全文 | 1900篇 |
免费 | 45篇 |
国内免费 | 4篇 |
专业分类
化学 | 1350篇 |
晶体学 | 29篇 |
力学 | 15篇 |
数学 | 87篇 |
物理学 | 468篇 |
出版年
2023年 | 18篇 |
2022年 | 11篇 |
2021年 | 18篇 |
2020年 | 29篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 26篇 |
2015年 | 33篇 |
2014年 | 29篇 |
2013年 | 90篇 |
2012年 | 72篇 |
2011年 | 85篇 |
2010年 | 52篇 |
2009年 | 49篇 |
2008年 | 118篇 |
2007年 | 109篇 |
2006年 | 118篇 |
2005年 | 94篇 |
2004年 | 110篇 |
2003年 | 72篇 |
2002年 | 73篇 |
2001年 | 37篇 |
2000年 | 51篇 |
1999年 | 47篇 |
1998年 | 18篇 |
1997年 | 32篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 33篇 |
1993年 | 30篇 |
1992年 | 38篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 23篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 21篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 20篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有1949条查询结果,搜索用时 15 毫秒
991.
Rakesh Malik Subhalakshmi Lamba Ajay Gupta Akihisa Inoue 《Journal of magnetism and magnetic materials》2010,322(23):3742-9998
The magnetic properties of nickel ferrite nanoparticles in the form of powders, prepared by the sol-gel process and subjected to different annealing temperatures, were investigated using both static and dynamic measurements namely hysteresis, zero field cooled-field cooled magnetization (ZFC-FC) measurements and Mössbauer spectroscopy. The Transmission Electron Microscopy (TEM) studies reveal particle sizes for the as-prepared particles which increases upto 52 nm with annealing. A bimodal distribution, upto an annealing temperature of was observed. ZFC-FC measurements for the as-prepared samples reveal twin peaks, indicative of the bimodal size distribution. ZFC-FC measurements performed for fields varying from 100 Oe to 3 kOe show a superparamagnetic phase with blocking temperatures between 320 and . Numerical simulations for the ZFC-FC studies indicate that the signature of the bimodal size distribution can be seen only at very low fields. The variation of coercivity with particle size, as determined from the hysteresis measurements, shows a transition from a single domain to a multi domain state for particle sizes larger than 35 nm. Mössbauer measurements performed at room temperature for the as-prepared sample shows a six finger pattern for the samples with higher particle size and a doublet pattern for the samples with smaller particle size, which is indicative of their superparamagnetic nature. 相似文献
992.
Toshihiko Maeda Tairiku Tashiro Shigeru Horii 《Physica C: Superconductivity and its Applications》2010
Samples with nominal compositions of x = 0–0.1 in (Bi(1+3x)/3Cu(2?3x)/3)Sr2(RE1?xCax)Cu2Oz ((Bi,Cu)-“1-2-1-2”; RE: Y or rare-earth element) were synthesized by a solid-state reaction method and characterized by means of X-ray diffractometry (XRD). It is confirmed that the (Bi,Cu)-“1-2-1-2” forms only when RE = Y, Dy and Ho. Single- or nearly single-phase samples are obtained for x = 0–0.05 and the Ca-free composition of this compound is determined to be (Bi1/3Cu2/3)Sr2RECu2Oz. Since ionic radii of Y, Dy and Ho are very close to each other and this seems to be an essential factor for the stability of the (Bi,Cu)-“1-2-1-2”. 相似文献
993.
A nine-layered skin tissue model is newly developed for the Monte Carlo simulation of spectral reflectance. The derivation
of the necessary parameters for each of the nine layers in the simulation is presented, in which the parameters used in the
conventional three-layered model are modified on the basis of some histological findings on skin and reported examples. Using
appropriate optical and geometrical parameters, simulated spectra can be produced that agree well with measured spectra. This
approach provides a flexible means of spectral fitting to measured results and of estimating changes in the parameters of
skin tissue. 相似文献
994.
Hidetaka Tsujimoto Yuichiro Honda Takeshi Maeda Yoshiaki Sakurai 《Journal of luminescence》2010,130(2):217-1978
A new series of heteroleptic cyclometalated platinum(II) complexes Pt-1a-f was synthesized, employing 2-arylpyridine (or 1-arylisoquinoline) (HC∧N-1) and 1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dione (HO∧O-1) for cyclometalation and as ancillary ligands, respectively, and photoluminescent properties were investigated. Focusing on red-shifted phosphorescence, C∧N ligands containing π-extended aromatics and electron-rich heterocycles were examined. All obtained complexes exhibited photoluminescence at ambient temperature, and the emission maxima ranged from green (λPL=518 nm) to far red (λPL=708 nm). The large Stokes shifts of more than 100 nm and sub-microsecond or microsecond emission lifetimes revealed that these complexes are phosphorescent emissive. The quantum yield of Pt-1 ranged from 0.02 to 0.59 at ambient temperature and decreased as the emission maximum was red-shifted. In comparison with the reference platinum(II) complexes, Pt-2 bearing an aliphatic ancillary ligand, such as 2,2,6,6-tetramethylheptane-3,5-dionate (O∧O-2), the ligand O∧O-1 did not significantly affect the photoluminescence emission maxima, indicating that the energy gap between the singlet ground state and the triplet level was predominantly dependent on the C∧N ligand. 相似文献
995.
Kaye S. Morgan Sarah C. Irvine Yoshio Suzuki Akihisa Takeuchi Karen K.W. Siu 《Optics Communications》2010,283(2):216-19789
A suitably large coherence area is important in coherent X-ray optics, when using techniques such as interferometry or phase contrast imaging (PCI). The work done by Suzuki using a prism interferometer to measure X-ray coherence at 12.4 keV [1] is here extended to consider the use of a diffuser at the bio-medical imaging energy of 25 keV. In order to achieve a broader, more even X-ray field and eliminate speckle, a spinning piece of paper may be used as a rotating random-phase screen to diffuse the hard X-ray beam, but this will concomitantly decrease the magnitude of the complex degree of second-order coherence. We also study the effect of source size and source-to-sample distance on coherence, where imaging area and required flux must be considered. Coherence measurements at the 20XU beamline at the SPring-8 synchrotron are compared to results from wave-optical computer modelling. These show that while the diffuser will decrease the magnitude of the complex degree of coherence, further free-space propagation will lessen this effect. In the design of an experiment, the collimating slit size and use of a diffuser must therefore be balanced with distance from the source, in order to maximise coherence while maintaining the desired field of view and exposure time. 相似文献
996.
Hajime Maeda 《Tetrahedron letters》2005,46(17):3057-3060
Photoreaction of 2,3-dicyanonaphthalene with methoxy-substituted 1,2-diarylcyclopropanes in benzene gave alkylated naphthalene derivatives via excited singlet of 2,3-dicyanonaphthalene. Fluorescence of the photoalkylated products showed intense intramolecular exciplex emission. 相似文献
997.
998.
Effect of oxidation dynamics on the film characteristics of Ce:YIG thin films deposited by pulsed-laser deposition 总被引:1,自引:0,他引:1
Yoshiki Nakata Tatsuo Okada Mitsuo Maeda Sadao Higuchi Kiyotaka Ueda 《Optics and Lasers in Engineering》2006,44(2):147-154
Thin films with different compositions of Ce-substituted yttrium iron garnet (Ce:YIG (Y2CeFe5O12)), Ga-doped Ce:YIG (Ce:Ga:YIG (Y2CeFe4.25Ga0.75O12)), and Gd-doped Ce:YIG (Ce:Gd:YIG (Y1.6CeGd0.4Fe5O12)) were deposited on gadolinium gallium garnet (GGG (Gd3Ga5O12)) substrates in O2 or Ar background gas by pulsed-laser deposition (PLD) technique. Crystalline films were obtained at a lower O2 gas pressure of 20 mTorr or at higher Ar gas pressures of more than 100 mTorr. In addition, the behavior of YO molecules was visualized by two-dimensional laser-induced fluorescence (2D-LIF), in order to investigate the oxidation dynamics in the ablation plume. The oxidation dynamics and the crystallinity had close correlation. 相似文献
999.
1000.
Tsuyoshi Maeda 《Journal of Physics and Chemistry of Solids》2005,66(11):1924-1927
In order to quantitatively evaluate the formation energies of Cu, In/Ga/Al and Se vacancies in chalcopyrite-type CuInSe2 (CIS), CuGaSe2 (CGS) and CuAlSe2 (CAS), first-principles pseudopotential calculations using plane-wave basis functions were performed. All calculations were performed using a supercell with 64 atoms, which was eight times greater than the number of atoms in a primitive cell with eight atoms. The formation energies of point defects were calculated as a function of the atomic chemical potentials of constituent elements. Atomic arrangements around the vacancy were optimized allowing relaxation of the first- and second-nearest-neighbor atoms of the vacancy. The obtained results were as follows: (1) the formation energy of Cu vacancy was smaller than those of the other vacancies in CIS, CGS and CAS. Under the Cu-poor condition, the formation energy of Cu vacancy in CIS was lowest among those in them; (2) the formation energy of Se vacancy in CIS was relatively lower than those in CGS and CAS; (3) the formation energy of (2VCu+InCu) pair in CIS was greatly dependent on the chemical potential of the constituent elements, i.e. Cu, In and Se. On the other hand, the formation energies of (2VCu+GaCu) in CGS and (2VCu+AlCu) in CAS were not largely dependent on the chemical potential of the constituent elements. Under the Cu-poor condition, the formation energy of (2VCu+InCu) pair in CIS was much lower than those of (2VCu+GaCu) in CGS and (2VCu+AlCu) in CAS. 相似文献