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排序方式: 共有744条查询结果,搜索用时 15 毫秒
731.
Tea (Camellia Sinensis) is the most widely consumed beverage in the world and is known to have therapeutic, antioxidant and nutritional effects.
It contains dimeric flavanols and polyphenols which are known as the most important organic compounds in tea infusions, and
can make strong and stable complexes with metal ions. In this study, we carried out a series of electron paramagnetic resonance
experiments on well-known paramagnetic transition metal ions, namely Mn2+, Fe3+, Cu2+, VO2+, and Cr3+ doped in black tea cultivated along the shore of Black Sea, Turkey, to see the effects and structures formed. 相似文献
732.
Hasan Karabıyık Hande Petek Nazan Ocak İskeleli Çiğdem Albayrak 《Structural chemistry》2009,20(5):903-910
The molecular and crystal structure of (E)-2-Acetyl-4-(2-bromophenyldiazenyl)phenol (1) and (E)-2-Methyl-4-(o-tolyldiazenyl)phenol (2) were characterized and determined by single crystal X-ray diffraction method besides spectroscopic means. The periodic organization
of 1 is stabilized by C–H···O type weak H-bond and Br···O type weak halogen bonding and thus, a two dimensional puckered network
is established almost parallel to () the plane. Molecules of 2 are linked into C(7) chains generated by translation along the [1 0 1] direction with the aid of O–H···N type H-bonds, and these chains are
strengthened by C–H···π interactions involving o-tolylphenol ring. Quantum chemical studies at B3LYP/6-311 ++G(d,p) level reveal that potential barrier of the compounds around
Ar–N torsions is of double minimum character unless it is defected by the presence of o-substituent groups in the vicinity of the azo bridge. The results from crystallographic and quantum chemical studies suggest
that azo benzene compounds may adapt non-planar geometry apart from the most stable planar conformation, which is located
on the secondary minima of double potential barrier regarding rotational motion around Ar–N bonds. 相似文献
733.
U. Amador J.M. Gallardo-Amores G. Heymann H. Huppertz E. Morán M.E. Arroyo y de Dompablo 《Solid State Sciences》2009,11(2):343-348
Olivine-LiCoXO4 (X = P, As) compounds might transform to the denser spinel-type and Na2CrO4-type structures under pressure. In this work, the relative energetic stability of the three polymorphs and the pressure of the possible polymorphic transformations are investigated combining experiments and first principles calculations. Olivine-LiCoAsO4 is predicted to transform to the Na2CrO4-like structure at 0.4 GPa and to the spinel structure at 5.8 GPa (0 K). Quenching HP/HT experiments show that olivine-LiCoAsO4 treated at 6 GPa/1173 K transforms to the spinel-like structure. Computational results indicate that olivine-LiCoPO4 transforms to the Na2CrO4-like form at around 4 GPa (0 K), the latter being the stable form till very high pressures (21.6 GPa). In good agreement with this, olivine-LiCoPO4 when subjected to 6 GPa/1173 K and 15 GPa/1173 K is converted to the Na2CrO4-type polymorph. Crystallographic data of the new compound LiCoPO4 within the Na2CrO4 structural type are provided. 相似文献
734.
735.
The results of first principles calculations of band structure, density of states and electron density topology of CdC2O4 and Ag2C2O4 crystals are presented. The calculations have been performed with WIEN2k ab initio program, using highly precise full potential
linearized augmented plane wave (FP LAPW) method within Density Functional Theory formalism. The obtained SCF electron density
has been used in calculations of Bader’s AIM (atoms in molecules) topological properties of the electron density in crystal.
The obtained results show important similarities in electronic structure and electron density topology of both compounds and
allow supposing, that during the thermal decomposition process these compounds should behave similarly, which is in agreement
with the experiment. 相似文献
736.
We derive explicit and exact expressions for the physical velocity of a free particle comoving with the Hubble flow as measured
by a static observer, and for the frequency shift of light emitted by a comoving source and received, again, by a static observer.
The expressions make it clear that an interpretation of the redshift as a kind of Doppler effect only makes sense when the
distance between the observer and the source vanishes exactly. 相似文献
737.
Çiğdem Albayrak Başak Koşar Mustafa Odabaşoğlu Orhan Büyükgüngör 《Crystallography Reports》2010,55(7):1203-1206
The crystal structure of hexakis(4-phormylphenoxy)cyclotriphosphazene is determined by using X-ray diffraction and then the
molecular structure is investigated with density functional theory (DFT). X-Ray study shows that the title compound has C-H…π
interaction with phosphazene ring. The molecules in the unit cell are packed with Van der Waals and dipole-dipole interactions
and the molecules are packed in zigzag shaped. Optimized molecular geometry is calculated with DFT at B3LYP/6-311G(d,p) level.
The results from both experimental and theoretical calculations are compared in this study. 相似文献
738.
L. Elçi M. Soylak A. Uzun E. Büyükpatır M. Doğan 《Analytical and bioanalytical chemistry》2000,368(4):358-361
A simple flame atomic absorption spectrometric (FAAS) procedure for the determination of lead, bismuth, gold, palladium and cadmium as impurities in Raney nickel and nickel oxide was developed using a preconcentration step on an Amberlite XAD-16 resin packed column. Lead, bismuth, gold, palladium and cadmium were quantitatively recovered and separated from a solution containing 1 M HCl and 0.3 M NaI by the column system. Effects of the various parameters such as reagent concentrations, sample volume, matrix effects, etc. have been investigated. Under optimized conditions, the relative standard deviation of the combined method of sample treatment, preconcentration and determination with FAAS (n = 7) is generally lower than 12%. The limit of detection (3s, n = 20) was between 10–270 ng/g. The results were used for separation and preconcentration of five trace elements from nickel matrices. 相似文献
739.
Ivica Janigov Frantiek Lednickýy Zuzana Ngellov Bohuslav V. Kokta Ivan Chodk 《Macromolecular Symposia》2001,169(1):149-158
Scanning electron microscopy was employed to investigate the effect of peroxide‐initiated crosslinking on behaviour of composites of low‐density polyethylene filled with wood flour. The improved wetting of the filler by the matrix and/or the increase in the matrix/filler adhesion was shown to be the main consequence of crosslinking, with the obvious influence on the physical, especially mechanical properties. 相似文献
740.
Nihal Kan Kaynar Erbil Ağar Hasan Tanak Songul Sahin Orhan Büyükgüngör Metin Yavuz 《Crystallography Reports》2018,63(3):372-374
The molecular structure of the title compound, C14H11ClN2O4, was determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic sp. gr. P21/c with Z = 4. The title compound, C14H11ClN2O4, is a Schiff base which adopts the phenol-imine tautomeric form in the solid state.The molecule is almost planar and the dihedral angle between the planes of two aromatic ring is 2.2(1)°. The molecular structure is stabilized by intramolecular O–H···N hydrogen bond which generates a six-membered ring. In the crystal structure, the molecules are linked together by intermolecular C–H···O interactions. 相似文献