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991.
Su-Fan Wang Ji-Kang Feng Chia-Chung Sun Peng Liu Zhen Gao Fan-Ao Kong 《Theoretical chemistry accounts》2001,106(3):163-170
The possible geometrical structures and relative stability of (SiS2)
n
(n=1–6) silicon–sulfur clusters are explored by means of density functional theory quantum chemical calculations. The effects
of polarization functions and electron correlation are included in these calculations. The electronic structures and vibrational
spectra of the most stable geometrical structures of (SiS2)
n
are analyzed by the same method. As a result, the regularity of the (SiS2)
n
cluster growth is obtained, and the calculation may used for predicting the formation mechanism of the (SiS2)
n
cluster.
Received: 17 November 1999 / Accepted: 3 November 2000 / Published online: 3 May 2001 相似文献
992.
Roland Resel Raf Kiebooms Dirk Vanderzande Franz Stelzer 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):433-440
Summary. Poly-(para-phenylene vinylene) (2b, PPV) and poly-(2,5-dimethyl-para-phenylene vinylene) (1b) were prepared via the formation of a double bond by thermal elimination of an octylsulfinyl side group at 200°C under vacuum. X-Ray diffraction
experiments revealed a certain degree of long-range order within both polymers. However, considerable differences in the diffraction
pattern were observed, the packing of the polymer chains within the bulk structure being responsible for these differences.
Within the crystal structure of 2b, neighbouring PPV chains pack in a zig-zag arrangement (herringbone pattern). Analysis of the diffraction pattern of 1b on the basis of the crystal structure of a model compound (2,5,2′,5′-tetramethylstilbene) revealed that the molecular planes
of neighbouring polymer chains pack parallel to each other. A model for the crystal structure of 1b is given. The change of packing from a herringbone to a parallel arrangement of the molecular planes is related to the introduction
of methyl groups as side chains to PPV.
Received December 14, 2000. Accepted (revised) December 20, 2000 相似文献
993.
Daniele Cauzzi Claudia Graiff Chiara Massera Giovanni Predieri Antonio Tiripicchio 《Journal of Cluster Science》2001,12(1):259-271
The reaction of [Ru3(CO)12] with Ph2(pyth)PSe (pyth=5-(2-pyridyl)-2-thienyl) allows to obtain two novel clusters [Ru3(3-Se)2(CO)7{P(pyth)Ph2}2] 1 and [Ru3(3-Se)(-PPh2)(-pyth)(CO)6{P(pyth)Ph2}] 2 in satisfactory yields. The first one exhibits the well-known bicapped, open triangular, 50-electron nido-core, whereas 2, whose crystal structure has been determined, shows the rather rare Ru3Se tetrahedron with the Ph2P and pyth fragments as side-bridging ligands. Morever cluster 2 belongs to the exiguous family of selenido-phosphido clusters not easily achievable by other routes. 相似文献
994.
The fluorescent properties, structure, and electronic structure of the ground and excited singlet and triplet electronic states of the cis and trans forms of 4,5-dihydro-2-(2-furyl)oxazole, 4,4-dihydro-2-(2-thienyl)oxazole, 2-(2-furyl)oxazole (FO), and 2-(2-thienyl)oxazole (TO) have been studied. The orbital nature of the lower excited singlet and triplet states has been studied by the semiempirical INDO/S (valence approximation) and PPP/S ( approximation) methods. It was shown that for FO and TO molecules the lower triplet state is of the * type, for which delocalization of the electronic excitation on atoms is characteristic. In the singlet excitation state inversion was observed of the energy levels of the delocalized * states and n* states localized over several bonds (for the free TO and FO molecules the lower excited singlet states S1* were assigned to * and n* types respectively). Owing to the low position of the T
* and T
n* levels relative to the singlet level of * type, the rate constant for intercombination conversion is greater than the rate constant for radiative decay. Consequently an efficient population of the triplet states of the molecules occurs under conditions of electronic-vibrational excitation. The direction of reactions during synthesis was compared with the localization indices in the ground state for electrophilic, nucleophilic, and radical substitution, and also with the excitation localization numbers L for a wide selection of electronically excited states. It was concluded that the change in the structure of the azole molecule on replacing an O atom by an S atom, or on changing from a partially hydrogenated to a heteroaromatic system, was the main reason for the change of all the spectral parameters characterizing the electronic-vibrational or the spin-orbital interaction of the most reactive groups of atoms in the molecular structure. 相似文献
995.
Pet'kov V. I. Orlova A. I. Kazantsev G. N. Samoilov S. G. Spiridonova M. L. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):623-632
A5–4xZrxZr(PO4)3 (A=Na, K;0≤x≤1.25), Na1-xCd0.5xZr2(PO4)3 (0≤x≤1), Na5–xCd0.5xZr(PO4)3 (0≤x≤4) compositions which belong to the NZP structural family were synthesized using the sol-gel method. The lattice thermal
expansion of members of these rows were determined up to 600°C by high-temperature X-ray diffractometry. The axial thermal
expansion coefficients change from -5.8·10-6to 7.5·10-6 °C-1 (αa) and from 2.6·10–6 to 22·10–6 °C-1 (αc). These results, in addition to those for other NZP compounds allow us to explain their low thermal expansion. The mechanism
can be attributed to strongly bonded three-dimensional network structure, the existence of structural holes capable to damp
some of the thermal vibrations and anisotropyin the thermal expansion of the lattice.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
SiO2–Al2O3 aerogels and xerogels with a Si to Al molar ratio r
Si/Al varying from 0.25 to 20, were made by sol-gel process in acidic conditions at pH 2 and respectively dried by the CO2 supercritical method and by solvent evaporation. The Al precursor was also chelated with ethylacetoacetate, which made it possible to study the structure and texture of such gels in conditions favorable to the formation of mixed Al–O–Si bonds. Nitrogen adsorption isotherms according to the Brunauer, Emmett and Teller method (BET), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR), Fourier Transformed Infrared Spectroscopy (FTIR) and Infrared absorbance spectra after Temperature Programmed Desorption (TPD) of pyridine, showed that the Si–O infrared asymmetric stretching vibration and the Bronsted acidity relative to the Lewis acidity, depended on the ratio of AlIV to Si atoms. 相似文献
997.
998.
本文通过将抗癌活性化合物cis-[RuCl2(Me2SO)4]与L-组氨酸在乙醇溶液中或在溶剂热条件下反应,均得到了配合物[RuCl(Me2SO)2(L-His)](1).X-射线单晶结构分析表明该配合物的晶体属变形八面体,空间群P3121,a=b=14.0575(16)A,c=15.637(3)A,分子中含一个结晶水.该配合物中L-组氨酸配体分别通过氨基氮、咪唑氮、羧基氧与中心原子钌(Ⅱ)配位. 相似文献
999.
一维链状有机锡配位聚合物[(PhCH2)3Sn·(O2CC5H4N)·(H2O)]n的合成及晶体结构 总被引:7,自引:0,他引:7
[(PhCH2)3Sn·(O2CC5H4N)·(H2O)]n was synthesized by the reaction of 4-pyridine car-boxylic acid with the tribenzyltin oxide and was characterized by IR,1H NMR and MS.Its crystal structure was determined by X-ray single crystal diffraction.The crystal belongs to monoclinic.The space group P21/c with unit cell parameters a=1.2241(8)nm,b=0.9660(6)nm,c=2.3708(15)nm,β=102.722(12)°,V=2.734(3)nm3,Z =4,Dc=1.298g·cm-3.In crystal,the tin atom rendered five-coordinate in a trigo nal bipyramidal structure which is bridged by 4-pyridine carboxy-late into one-dimensional chain polymers. 相似文献
1000.
一维链状配位聚合物[Co(imbz)2(H2O)2]n[imbz=4′-(1-咪唑基亚甲基)苯甲酸根]的合成及晶体结构 总被引:1,自引:0,他引:1
A new coordination polyme[Co (imbz)2(H2O)2]n[imbz =4'-(imidazol-1-ylmethyl)benzoate anion]was synthesized and characterized by x-ray crystallography.The title complex crystallizes in monoclinic,space group P21/c,a=10.910(2),b=8.8720(18),c=11.252(2)Å,β=92.20(3)°,V=1088.3(4)Å3,Z =2,Dc=1.518g·cm-3,μ=0.836cm-1,F(000)=514,R=0.0679,wR=0.1710.Each Co(Ⅱ)atom has a distorted octahedral coordination geometry and is six-coord-inated by two water molecules and fou rimbz ligands.Each imbz ligand connects two Co(Ⅱ) to gen-erate an infinite 1Dtwisted chain structure. 相似文献