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991.
992.
Wei Song Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1996,34(14):2945-2953
The effect of reaction conditions, including catalyst concentration, temperature, and immobilization on support, have been investigated for syndioselective propylene polymerization by the “bare” zirconocenium ion generated from 1,1-diphenyl-methylidene(1-η5-cyclopentadienyl)(9-η5-fluorenyl)zirconium-dichloride precursor (2). Neither variation of the catalyst concentration nor immobilization of 2 on silica support affect the syndiospecificity of polymerization. The stereoregularity of the syndiotactic polypropylene, as judged from the melting transition temperature and homosteric r-pentad population by 13C-NMR, were found to be proportional to polymer molecular weight. These behaviors are compared with a typical isoselective catalyst ethylenebis(4,5,6,7-tetrahydroindenyl) Zr precursor (4). They are in close resemblance in the case of the S-enantiomeric complex of 4, but the racemic mixture of 4 is markedly inferior. The origins of stereo- and regio-errors are discussed. © 1996 John Wiley & Sons, Inc. 相似文献
993.
Fengfu Li Yingtai Jin Chunlei Song Yonghua Lin Fengkui Pei Fosong Wang Ninghai Hu 《应用有机金属化学》1996,10(10):761-771
Three new lanthanide (Ln)–alkylaluminium (Al) bimetallic complexes with the formula [(μ-CF3CO2)2Ln(μ-CF3CHO2)AlR2 · 2THF]2 (Ln=Nd, Y, R=i-C4H9 (i-Bu); Ln=Eu, R=C2H5(Et); THF=tetrahydrofuran) were synthesized by the reaction of Ln(CF3CO2)3 (Ln=Nd, Y) with HAl (i-Bu)2 and of Eu(CF3CO2)3 with AlEt3, respectively. Their crystal structures were determined by X-ray diffraction at 233 K. [(μ-CF3CO2)2Nd (μ-CF3CHO2)Al(i-Bu)2 · 2THF]2 (Nd–Al) and [(μ-CF3CO2)2Y(μ-CF3CHO2)Al(i- Bu)2 · 2THF]2 (Y–Al) are isomorphous and crystallize in space group P 1 with a =12.441(3) Å [12.347(5) Å for Y–Al], b =12.832(3) Å [12.832(4) Å], c =11.334(3) Å [11.292(8) Å], α=104.93 (2)° [104.45(4)°], β=98.47(2)° [98.81(4)°], γ=64.60(2)° [64.30(3)°], R =0.519 [0.113], R w=0.0532 [0.110], Z =1 and [(μ-CF3CO2)2Eu(CF3 CHO2)AlEt2 · 2THF]2(Eu–Al) in space group P 21/ n with a =11.913(6) Å, b =14.051(9) Å, c =17.920(9) Å, α=101.88(11)°, β=γ=90°, R =0.0509, R w=0.0471 and Z =2. The six CF3CO 相似文献
994.
Effect of Cu Ions on the Dipole Moments and Polarization of Strontium Barium Niobate Single Crystals
H. R. Xia C. J. Wang H. Yu H. C. Chen Y. Y. Song 《Crystal Research and Technology》1996,31(7):889-895
The crystal growth, the ferroelectric hysteresis loops, and the infrared reflectivity spectra of coppermodified strontium barium niobate (SBN) single crystals are reported. Compared with the undoped SBN crystals, the copper-modified crystals have stable hysteresis loops, the spontaneous polarization of which is about 0.30 C/m2, but that of the undoped SBN crystals is only about 0.12 C/m2. Their coercive field strength is all about 340 V/mm. The experimental results of the infrared spectra show that the infrared reflectivities vary as the orientations of the dipole moments owing to the copper-doping. The c-axis becomes the most stable orientation of the dipole moments, and the polarization will be locked and won't recede if the copper-modified crystals are polarized into monodomains. 相似文献
995.
996.
Li-Zhao Huang Yue Shui Wei Chen Zhong-Ming Li Hong-Tao Song Guang-Ai Sun Jia-Zhuang Xu Gan-Ji Zhong Dong Liu 《高分子科学》2021,39(3):365-376
The correlation between aggregates and bound rubber structures in silicone rubbers(S(phr)) with various silica fractions(ΦSi) has been investigated by contrast matching small-angle neutron scattering(SANS), swelling kinetics, and low-field nuclear magnetic resonance(NMR).Mixed solvents with deuterated cyclohexane fractions of 4.9% and 53.7% were chosen to match the scattering length densities of the matrix(SMP(phr)) and the filler(SMS(phr)), respectively. All the data consistently suggest that:(i) There is a critical threshold ΦSic between 10 and 30 phr;below ΦSic, the isolated aggregates are dominant, while beyond ΦSic, some rubber fraction is trapped among the agglomerate;(ii) ΦSiindependent thicknesses around 7.5 nm(NMR) and 8.6 nm(SANS) suggest that the bound rubber formation is determined by inherent properties of the components, and the power-law around 4.2 suggests an exponential changed gradient density of the bound rubber;(iii) SMS(80) presents a bicontinuous bound rubber with three characteristic lengths of 41, 100, and 234 nm. The expanded correlation length, a 20 nm smaller aggregate sizes suggest that such existent bicontinuous network in dry samples with less ΦSi is kind of impacted by swelling. With the obtained bound rubber models, the reinforcing mechanism of filled silicone rubber is elucidated. 相似文献
997.
Kunqian Mu Kaiwen Jiang Yue Wang Zihan Zhao Song Cang Kaishun Bi Qing Li Ran Liu 《Molecules (Basel, Switzerland)》2022,27(3)
β-cyclodextrin has a unique annular hollow ultrastructure that allows encapsulation of various poorly water-soluble drugs in the resulting cavity, thereby increasing drug stability. As a bioactive molecule, the metabolism of β-cyclodextrin is mainly completed by the flora in the colon, which can interact with API. In this study, understanding the in vivo fate of β-cyclodextrin, a LC-MS/MS method was developed to facilitate simultaneous quantitative analysis of pharmaceutical excipient β-cyclodextrin and API dextromethorphan hydrobromide. The established method had been effectively used to study the pharmacokinetics, tissue distribution, excretion, and metabolism of β-cyclodextrin after oral administration in rats. Results showed that β-cyclodextrin was almost wholly removed from rat plasma within 36 h, and high concentrations of β-cyclodextrin distributed hastily to organs with increased blood flow velocities such as the spleen, liver, and kidney after administration. The excretion of intact β-cyclodextrin to urine and feces was lower than the administration dose. It can be speculated that β-cyclodextrin metabolized to maltodextrin, which was further metabolized, absorbed, and eventually discharged in the form of CO2 and H2O. Results proved that β-cyclodextrin, with relative low accumulation in the body, had good safety. The results will assist further study of the design and safety evaluation of adjuvant β-cyclodextrin and promote its clinical development. 相似文献
998.
999.
We conduct extensive research into the structures of BexZn1-xOO ternary alloys in a pressure range of 0-60GPa,using the ab initio total energy evolutionary algorithm and total energy calculations,finding several metastable structures.Our pressure-composition phase diagram is constructed using the enthalpy results.In addition,we calculate the electronic structures of the BexZn1-xOO structures and investigate the bandgap values at varying pressures and Be content.The calculated results show that the bandgap of the BexZn1-xOO ternary alloys increases with an increase in Be content at the same pressure.Moreover,the bandgap of the BexZn1-xOO ternary alloys increases with the increasing pressure with fixed Be content.At the same Be content,the formation enthalpy of the BexZn1-xOO ternary alloys first decreases,then increases with the increasing pressure. 相似文献
1000.
Meccanica - In this work, a bond-based peridynamic de-icing model has been developed to simulate the thermo-mechanical ice removal process of frozen structures. In the proposed numerical method,... 相似文献