全文获取类型
收费全文 | 17175篇 |
免费 | 1453篇 |
国内免费 | 1172篇 |
专业分类
化学 | 10375篇 |
晶体学 | 594篇 |
力学 | 619篇 |
综合类 | 46篇 |
数学 | 343篇 |
物理学 | 7823篇 |
出版年
2024年 | 26篇 |
2023年 | 189篇 |
2022年 | 344篇 |
2021年 | 391篇 |
2020年 | 470篇 |
2019年 | 370篇 |
2018年 | 328篇 |
2017年 | 376篇 |
2016年 | 645篇 |
2015年 | 466篇 |
2014年 | 600篇 |
2013年 | 1261篇 |
2012年 | 981篇 |
2011年 | 1031篇 |
2010年 | 872篇 |
2009年 | 1099篇 |
2008年 | 1078篇 |
2007年 | 1347篇 |
2006年 | 1262篇 |
2005年 | 889篇 |
2004年 | 881篇 |
2003年 | 719篇 |
2002年 | 545篇 |
2001年 | 443篇 |
2000年 | 413篇 |
1999年 | 359篇 |
1998年 | 374篇 |
1997年 | 275篇 |
1996年 | 335篇 |
1995年 | 281篇 |
1994年 | 240篇 |
1993年 | 184篇 |
1992年 | 152篇 |
1991年 | 103篇 |
1990年 | 99篇 |
1989年 | 62篇 |
1988年 | 56篇 |
1987年 | 33篇 |
1986年 | 40篇 |
1985年 | 50篇 |
1984年 | 40篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 24篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Visible and NIR luminescence of nanocrystalline β-Ga2O3:Er prepared by solution combustion synthesis
In this paper we report on facile solution combustion synthesis of erbium doped β-Ga2O3 with urea as fuel. The product was characterized using powder X-ray diffraction and transmission electron microscopy (TEM). X-ray diffraction and TEM showed that the material is nanostructured. Luminescence properties of β-Ga2O3:Er are studied with excitation in near infrared (Nd:YAG laser at 1064 nm) and visible (argon laser at 514.5 nm). A strong NIR emission of Er3+ in the window of minimal optical loss in silica based optical fibers, due to the 4I13/2→4I15/2 transition at 1.55 μm has been observed. Codoping with Yb3+ significantly increases the intensity of that important emission. 相似文献
172.
173.
Davor Pavuna Daniel Ariosa Dominique Cloetta Claudia Cancellieri Mike Abrecht 《Pramana》2008,70(2):237-243
Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T
c superconductors (HTSC) under different degrees of epitaxial (compressive vs. tensile) strain. In overdoped and underdoped
in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La2 − x
Sr
x
CuO4 (LSCO) films we almost double T
c to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES
data under tensile strain exhibit the dispersion that is three-dimensional, yet T
c drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the two-dimensional character of the dispersion and increases T
c, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established
the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual
lattice of cuprates is like a ‘Napoleon-cake’, i.e. rigid CuO2 planes alternating with softer ‘reservoir’, that distort differently under strain, our data rule out all oversimplified two-dimensional
(rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T
c.
相似文献
174.
Makoto Nakanishi Yukiyasu Matsuno Jun Takada 《Journal of Physics and Chemistry of Solids》2008,69(1):49-54
The influence of composition on the structural ordering and magnetism in the VxNb1+yS2 system has been investigated by X-ray diffraction and magnetic measurements. Stoichiometric V1/3NbS2 did not exhibit the structural ordering of vanadium between the NbS2 layers. In the ordered structure, the vanadium composition deviated from the ideal value of to both higher and lower values, while the niobium composition was in the range of 0.05?y?0.18. Excess niobium, y>0, is thought to play an essential role in the structural ordering in this system. For samples with excess niobium and ordered structures, a magnetic transition was observed at 20-50 K, depending on the composition. The spontaneous magnetization of 3-5×10−3 μB/V atom is thought to be intrinsic to this system. The magnetization curves consisted of a constant and a proportional parts of the magnetic field, which correspond to the spontaneous magnetization and high-field susceptibility, respectively. The magnetization curves and the temperature dependencies of the high-field susceptibility were quite similar to those of the canted antiferromagnetic NiS2. A correlation between the structural and magnetic ordering is suggested. 相似文献
175.
We have studied the effects of controlled ion bombardment on the electronic structure of the Si(0 0 1) surface. The surface was exposed to various doses of Ar+ ions accelerated towards the surface at 500 eV. X-ray photoelectron spectroscopy (XPS) spectra of the irradiated H-terminated Si(0 0 1) surface reveal the appearance of peaks that are associated with the presence of cleaved Si bonds. Ultraviolet photoelectron spectroscopy (UPS) spectra of the irradiated Si(0 0 1)2 × 1 surface show that the dimer dangling-bond surface state decays monotonically with increasing dose. These results, coupled with previous scanning tunneling microscopy (STM) studies, indicate that the breaking of dimers, and possibly the creation of adatom-like defects, during ion irradiation are responsible for the changes in the electronic structure of the valence band for this surface. 相似文献
176.
Andrey V. Lunchev Dr. Samuel A. Morris Dr. Rakesh Ganguly Prof. Andrew C. Grimsdale 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1819-1823
A route to the synthesis of novel 5,7-diazapentacenes and some preliminary studies on their properties is reported. A single crystal X-ray diffraction study of the dihexyl derivative showed it had formed a dimer during the analysis. The materials possess lower lying frontier orbitals than pentacene and may have potential applications in organic electronic devices. This synthetic method may be applicable to the synthesis of other azaacenes. 相似文献
177.
Dr. Wenyan Hao Yuchen Sha Dr. Yi Deng Yi Luo Li Zeng Shan Tang Dr. Yue Weng Prof. Dr. Chien-Wei Chiang Prof. Dr. Aiwen Lei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):4931-4934
An in situ generated oxidation species of nickel quinolinylpropioamide intermediate was produced. Characterization by X-ray absorption near edge structure (XANES) and EPR provides complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved. 相似文献
178.
Dan-Dan Wang Li Song You-Yu Wang Jia-Yu Guo Hang-Yan Shen Xiao-Rong Wang Wen-Xiang Chai 《应用有机金属化学》2020,34(4):e5561
Four new heteroleptic [Cu(NN)P2]+-type cuprous complexes— 1 -TPP, 2 -POP, 3 -Xantphos, and 4 -DPPF—were designed and synthesized using a diimine ligand 2-(2′-pyridyl)benzoxazole (2-PBO) and different phosphine ligands (TPP, triphenylphosphine; POP, bis[2-(diphenylphosphino)phenyl]ether; Xantphos, 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; DPPF, 1,1′-bis(diphenylphosphino)-ferrocene). All complexes were characterized using single-crystal X-ray diffraction, spectroscopic analysis (infrared, UV–Vis.), elemental analysis, and photoluminescence (PL). Single-crystal X-ray diffraction revealed complexes 1 – 4 as isolated cation complex structures with a tetrahedral CuN2P2 coordination geometry and diverse P–Cu–P angles. Their UV–Vis. absorption spectra exhibited a blue-shift sequence in wavelength with an enlarged P–Cu–P angle from 4 to 2 then to 3 and then to 1 . The PL emission peaks of 1 – 3 also exhibited a similar blue-shift sequence ( 2 → 3 → 1 ). Their PL lifetime in microseconds (~7.5, 5.1, and 4.7 μs for 1 , 2 , and 3 , respectively) indicated that their PL behavior represents phosphorescence. Time-dependent density functional theory (TD-DFT) calculation and wavefunction analysis revealed that S1 and T1 states of 1 – 3 should be assigned as metal–ligand and ligand–ligand charge-transfer (ML + L'L)CT states. Their UV–Vis. absorption and phosphorescence should be attributed to the charge transfer from the P–Cu–P segment to the 2-PBO ligand. Therefore, as the P–Cu–P angle increased (lower HOMO), the energy of S1 and T1 states also increased, following the change of PL color. 相似文献
179.
Rebeca G. Castillo Justin T. Henthorn Jeremy McGale Dimitrios Maganas Serena DeBeer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):13065-13075
In recent years, X-ray emission spectroscopy (XES) in the Kβ (3p-1s) and valence-to-core (valence-1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first-row transition metals. In this work, we present an extension of Kβ XES (in both the 4p-1s and valence-to-1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ2 lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase-relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo-containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second-row transition metals, thus providing chemists with a site-specific tool for the elucidation of 4d transition metal electronic structure. 相似文献
180.