全文获取类型
收费全文 | 2038篇 |
免费 | 413篇 |
国内免费 | 188篇 |
专业分类
化学 | 1333篇 |
晶体学 | 21篇 |
力学 | 108篇 |
综合类 | 11篇 |
数学 | 272篇 |
物理学 | 894篇 |
出版年
2024年 | 4篇 |
2023年 | 51篇 |
2022年 | 74篇 |
2021年 | 104篇 |
2020年 | 99篇 |
2019年 | 85篇 |
2018年 | 75篇 |
2017年 | 76篇 |
2016年 | 122篇 |
2015年 | 113篇 |
2014年 | 130篇 |
2013年 | 160篇 |
2012年 | 200篇 |
2011年 | 204篇 |
2010年 | 136篇 |
2009年 | 139篇 |
2008年 | 117篇 |
2007年 | 101篇 |
2006年 | 92篇 |
2005年 | 81篇 |
2004年 | 68篇 |
2003年 | 54篇 |
2002年 | 49篇 |
2001年 | 45篇 |
2000年 | 31篇 |
1999年 | 26篇 |
1998年 | 21篇 |
1997年 | 25篇 |
1996年 | 25篇 |
1995年 | 20篇 |
1994年 | 19篇 |
1993年 | 11篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2639条查询结果,搜索用时 0 毫秒
991.
992.
Generation of laser-driven flyer dominated by shock-induced shear bands: A molecular dynamics simulation study 下载免费PDF全文
High-power pulsed lasers provide an ingenious method for launching metal foils to generate high-speed flyers for high-pressure loading in material science or aerospace engineering.At high-temperature and high-pressure laser-induced conditions,the dynamic response of the metals and the mechanism of flyer formation remain unclear.In this study,the overall process of the laser-driven aluminum flyer,including laser ablation,rupture of metal foil,and the generation of the flyer was investigated by molecular dynamics combined with the two-temperature model.It was found that under high laser fluence(over 1.3 J/cm;with 200-fs laser pulse duration),the laser induced a shock wave with a peak pressure higher than25 GPa,which led to shear bands expanding from the edge of the laser ablation zone in the foil.Compared with the cases of low laser fluence less than 0.5 J/cm-1,the shear band induced by high laser fluence promotes the rupture of the foil and results in a high-speed flyer(>1 km/s)with better flatness and integrity.In addition,the shock wavefront was found to be accompanied by aluminum crystal phase transformation from face-centered cubic(FCC)to body-centered cubic structure.The crystal structure reverts with the decrease of pressure,therefore the internal structure of the generated flyer is pure of FCC.The results of this study provide a better understanding of the laser-induced shock effect on the foil rupture and flyer quality and forward the development of the laser-driven flyer. 相似文献
993.
In this paper, a novel mode of free-flow affinity electrophoresis (FFAE) was developed to indirectly enhance the separation of free-flow electrophoresis (FFE). In the mode of FFAE, a Ni(II) with high electric charge density and histidine (His) is chosen as a model ligand and target solute, respectively. Through the controlling of experimental conditions (10 mM pH 6.0 Na(2)HPO(4)-NaH(2)PO(4) with 2.0 mM NiCl(2)·6H(2)O background buffer), Ni(II) can combine with His and the combination leads to the high electric charge density of affinity complex of His-Ni(II) in contrast to the low density of free His molecule. But the ligand has weak interaction with uninterested amino acids. Thus, the mobility of His existing as His-Ni(II) is greatly increased from 14.5×10(-8) m(2) V(-1) s(-1) to 30.2 × 10(-8) m(2) V(-1) s(-1), while those mobilities of uninterested amino acids are almost constant. By virtue of the mode, we developed the FFAE procedure and conducted the relevant experiments. The experiments demonstrated the following merits of the FFAE technique: (i) clear enhancement of separation between the target solute of His and uninterested amino acids; (ii) simplicity, and (iii) low cost. Furthermore, the technique was used for the continuous separation of His from its complex sample, and the purity of His was near to 100%. All of the results demonstrate the feasibility of affinity separation in FFE. The developed FFAE may be used in the separation and pretreatment of some biological molecules (e.g. peptides). 相似文献
994.
Wen‐Zuo Li Yu‐Wei Pei F.‐F. Geng Jian‐Bo Cheng Qing‐Zhong Li Bao‐An Gong 《International journal of quantum chemistry》2012,112(12):2499-2503
Some low‐lying states of the HAlS+ and HSAl+ cations have been studied for the first time by large‐scale theoretical calculations using three methods: complete active space self‐consistent field (CASSCF), complete active second‐order perturbation theory (CASPT2), and density functional theory Becke's three‐parameter hybrid function with the nonlocal correlation of Lee–Yang–Parr (B3LYP) with the contracted atomic natural orbital (ANO‐L) and cc‐pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces (PESs) were optimized at the CASSCF/ANO‐L and B3LYP/cc‐pVTZ levels. The ground and the first excited states of linear HAlS+ are predicted to be X2Π and A2Σ+ states, respectively. For the linear HSAl+ structure, the first excited state is A2Σ+. The X2Π state of linear HSAl+ is a second‐order saddle point, because it has two imaginary frequencies. Two bent global minima M1 and M2 were found along the 12A′ and 12A″ PESs, respectively. The CASPT2/ANO‐L potential energy curves of isomerization reactions were calculated as a function of HAlS bond angle. According to our calculations, the ground‐state HAlS+ is linear, whereas the ground‐state HSAl+ is bent. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
995.
Y Lan XJ Loh J Geng Z Walsh OA Scherman 《Chemical communications (Cambridge, England)》2012,48(70):8757-8759
Core-shell polymeric microspheres with a cleavable shell were prepared in water using cucurbit[8]uril to bring together functional polymeric microspheres and functional polymers. This supramolecular approach was employed to switch the cytotoxicity of the polymeric microspheres, leading to potential applications in the eradication of cancer cells. 相似文献
996.
D Jiao J Geng XJ Loh D Das TC Lee OA Scherman 《Angewandte Chemie (International ed. in English)》2012,51(38):9633-9637
Tricky triggering: Supramolecular peptide amphiphiles were prepared by host-guest complexation of pyrene-labeled peptides and viologen lipid with cucurbit[8]uril. They self-assemble into vesicles, which are responsive to a variety of external triggers. Both "switching on" and "switching off" of fluoresence and cytotoxicity is demonstrated in?vitro. 相似文献
997.
Qiao X Chang H Huang L Zhang J Tian H Geng Y Yan D 《Physical chemistry chemical physics : PCCP》2012,14(29):10279-10284
The growth process and phase state of 5,5'-bis(3'-fluoro-biphenyl-4-yl)-2,2'?:?5',2'- terthiophene (m-F2BP3T) thin films were investigated by atomic force microscopy (AFM), in-plane and out-of-plane X-ray diffraction (XRD), and selected area electron diffraction (SAED). Two meso-phases (thin film phases) of m-F2BP3T films on SiO(2) surface were obtained in the early stages. The m-F2BP3T films initially exhibited two-dimensional (2D) layers (≤4 ML) followed by three-dimensional (3D) island growth. The film structure evolved two thin film phases in the first four layers and the bulk phase was formed from the fifth layer, which occurred concomitantly with the change of the growth mode. Moreover, the variation of weak epitaxy growth behavior of ZnPc from 2D to 3D growth further reflects that the phase state of the first three layers is different from that of the fourth layer, in spite of ZnPc crystals showing just one orientation corresponding to commensurate epitaxy. The novel phase behavior is closely related to the synergistic effects of the outstanding soft matter properties, limited elasticity of organic molecules, and strain originating from the SiO(2) substrate. This study investigates novel phase behavior in organic thin films and provides significant insight into the mechanism of the phase transition. 相似文献
998.
Discovering potent inhibitors against c-Met kinase: molecular design, organic synthesis and bioassay
Liang Z Ding X Ai J Kong X Chen L Chen L Luo C Geng M Liu H Chen K Jiang H 《Organic & biomolecular chemistry》2012,10(2):421-430
The receptor tyrosine kinase c-Met is an attractive target for therapeutic treatment of cancers nowadays. The discovery of small molecule inhibitors is of special interest in the blockade of the c-Met kinase pathway. Here, we initiated our study from compound 1a, a novel inhibitor against c-Met kinase. A substructure similarity search against the SPECS database and chemical synthesis methods were performed to obtain a series of pyrazolidine-3,5-dione derivatives. Through the enzyme-based assay against c-Met kinase, 4 compounds (1c, 1e, 1m and 1o) showed potential inhibitory activity, with IC(50) values mostly less than 10 μM. Based on the structure-activity relationship (SAR) and binding mode analysis, a focused combinatorial library was designed by the LD1.0 program. Taking into account ADMET properties and synthesis accessibility, seven candidate compounds (5a-g) were successfully synthesized. The activity of the most potent compounds 5b (IC(50) = 0.46 μM) was 20 fold higher than that of the lead 1a. Taken together, our findings identified the pyrazolidine-3,5-dione derivatives as potent inhibitors against c-Met kinase and demonstrated the efficiency of the strategy in the development of small molecules against c-Met kinase. 相似文献
999.
The stable dinuclear [Cu(μ‐C2O4)Cu]2+ entity is facially coordinated at each end by a N‐nitrile functionalized triazamacrocycle, 1, 4, 7‐tris(cyanomethyl)‐1, 4, 7‐triazacyclononane ( L ), to generate a centrosymmetric compound [Cu2 L 2(μ‐C2O4)](ClO4)2 · 4DMF ( 1 ) containing a bis‐bidentate oxalate bridge. The variable‐temperature magnetic measurement for the crystallographically characterized compound exhibits quite strong antiferromagnetic coupling interaction between two oxalate‐linked CuII atoms separated by 5.149 Å with a singlet‐triplet energy gap of –345.5 cm–1. On the other hand, a mononuclear CoIII compound [Co L (N3)3] · 2.5H2O ( 2 ) with monodentate azide terminal groups was synthesized. Structural elucidation by X‐ray diffraction shows that the compound has crystallographically imposed C3 symmetry. Enantiomerically pure crystals were obtained upon crystallization indicated by a Flack parameter of 0.04(5). 相似文献
1000.
In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au-Au, Au-Pd, and Au-Pt core-shell nanostructures with typical porous shells. Moreover, the Au-Au isomeric core-shell nanostructure is reported for the first time. The lower oxidation states of Au(I), Pd(II), and Pt(II) are supposed to contribute to the formation of porous core-shell nanostructures instead of yolk-shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au-Pd core-shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core-shell nanostructures. As expected, the Au-Pd core-shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44?mV and 32?mV), a much improved CO tolerance (I(f)/I(b) is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au-M (M = Au, Pd, and Pt) core-shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface-enhanced Raman scattering, and so forth. 相似文献