全文获取类型
收费全文 | 257篇 |
免费 | 30篇 |
专业分类
化学 | 218篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 42篇 |
物理学 | 22篇 |
出版年
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 12篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 13篇 |
2013年 | 18篇 |
2012年 | 20篇 |
2011年 | 18篇 |
2010年 | 14篇 |
2009年 | 16篇 |
2008年 | 19篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 13篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有287条查询结果,搜索用时 31 毫秒
101.
I‐Ling Lin I‐Hsiang Chen Chi‐Fong Lin Yu‐Hsiang Lo Sheng‐Huei Yang Shinne‐Ren Lin Ming‐Jung Wu 《中国化学会会志》2008,55(3):668-674
A series of 1‐(6‐(2‐(2‐arylethynyl)phenyl)hexyn‐5‐yl)piperidin‐2‐ones 2a‐j were synthesized and their antitumor activities were evaluated. Of these compounds, 1‐(6‐(2‐(2‐(4‐nitrophenyl)ethynyl)phenyl)hexyn‐5‐yl)piperidin‐2‐one ( 2j ) showed the highest potency of growth inhibition activity, especially against the RPMI‐8226 (0.4 μM) and SR (0.02 μM) cell lines of human leukemia. Compound 2j also induced significant apoptotic progress in the cell cycle assay with the K‐562 cell line. 相似文献
102.
Wu MY Chen BG Chang CD Huang MH Wu TG Chang DM Lee YJ Wang HC Lee CI Chern CL Liu RH 《Journal of chromatography. A》2008,1204(1):81-86
A two-step derivatization approach has been developed to enable the simultaneous analysis of glyoxal, methylglyoxal, and 3-deoxyglucosone by the most efficient and widely applied GC-MS methodology. These three analytes are reactive carbonyl compounds associated with the formation of advanced glycation and lipoxidation end products, a process thought to contribute to uremic toxicity and referred to as "carbonyl stress". Effective analysis of these compounds would facilitate understanding these compounds' role in diabetes-related complications. Plasma samples were deproteinized by acetonitrile, followed by a two-step derivatization approach. Pooled plasma samples from healthy individuals were used as the "blank" for preparing calibration standards. The concentrations of the analytes in the "blank" were first determined by standard addition method. Calibration parameters were accordingly established and used to analyze these compounds in plasma samples collected from healthy individuals and diabetic patients. Analytical findings are comparable with those reported in the literature. Quantitation data can be further improved by making available and using isotopically labeled analogs of these analytes as the internal standards. 相似文献
103.
Experimental and Theoretical Charge Density Study on Di‐2‐pyrazylamine (Hdpza) Molecule in Crystal 下载免费PDF全文
Electron density distribution of Di‐2‐pyrazylamine ( Hdpza ) is studied both by single‐crystal X‐ray diffraction method at 100K and theoretical calculation. Structural determination reveals that Hdpza molecules crystalize in a syn‐anti conformation with an intramolecular C? H?N hydrogen bond between two pyrazine rings and then gather together via two intermolecular N? H?N and C? H?N hydrogen interaction and π? π stacking interaction between pyrazine rings. Charge density analysis is made in terms of deformation density (Δπ), Laplacian distribution and topological analysis of total electron density based on multipole model and theoretical calculation. The agreement between experiment and theory is good. The topological properties at bond critical points of C? C and C? N bonds reveal a covalent bond character, and those of intermolecular interactions, such as hydrogen bonds and π? π stacking interactions, reveal a closed‐shell interaction. The potential energy curve of Hdpza molecule shows that the syn‐anti conformation is the most stable one (global minima) than the other two of syn‐syn and anti‐anti conformations. 相似文献
104.
Force Spectroscopy of Metal–Crown Ether Multivalency: Effect of Local Environments on Energy Landscape and Sensing Kinetics 下载免费PDF全文
Dr. Ting‐Yang Kuo Dr. Wei‐Hsiang Tseng Prof. Dr. Chun‐hsien Chen 《Angewandte Chemie (International ed. in English)》2015,54(32):9213-9217
Sandwich complexation involving alkali or alkaline‐earth metals, multivalency, and effects associated with local environments is widely encountered in biological and synthetic systems yet the mechanic properties remain unexplored. Herein, AFM (atomic force microscopy)‐based single‐molecule force spectroscopy is employed to investigate a classical model of Mn+[15C5]2, a metal cation hosted jointly by two 15‐crown‐5 moieties immobilized on both the substrate and the AFM tip. Factors reportedly promoting the recognition performance are examined. The rupture force required to break apart Mn+[15C5]2 is found to be in the order of tens of pico‐Newton, e.g., fβ=31 pN for K+[15C5]2. The presence of a second functional group, carboxylate, confers K+[15C5]2 with a longer lifetime (from 13 to 16 ms), faster association (from 0.4 to 1.3×106 M ?1 s?1), and slower dissociation (from 77 to 62 s?1). The effect of local environments is significant on association yet less critical on dissociation pathways. 相似文献
105.
We consider the spatial power spectra associated with fluctuations of quadratic operators in field theory, such as quantum stress tensor components. We show that the power spectrum can be negative, in contrast to most fluctuation phenomena where the Wiener-Khinchin theorem requires a positive power spectrum. We show why the usual argument for positivity fails in this case, and discuss the physical interpretation of negative power spectra. Possible applications to cosmology are discussed. 相似文献
106.
Su TR Lin JJ Chiu CC Chen JY Su JH Cheng ZJ Hwang WI Huang HH Wu YJ 《Electrophoresis》2012,33(7):1139-1152
The extracts from soft corals have been increasingly investigated for biomedical and therapeutic purposes. The aim of this study is to examine and analyze the anti-tumor effects of the genus Sinularia extract sinularin on A2058 melanoma cells using MTT assay, cell migration assay, wound healing assay, flow cytometric analysis, and proteomic analysis. Sinularin dose-dependently (1-5 μg/mL) inhibited melanoma cell proliferation while the treatment at identical concentrations suppressed cell migration. Sinularin dose-dependently enhanced apoptotic melanoma cells and caused tumor cell accumulation at G2/M phase, indicating that sinularin exerts apoptosis-induced and cell cycle-delayed activities in A2058 melanoma cells. Comparative proteomic analysis was conducted to investigate the effects of sinularin at the molecular level by comparison between the protein profiling of melanoma cells treated with sinularin and without the treatment. Thirty-five differential proteins (13 upregulated and 22 downregulated) concerning the treatment were identified by liquid chromatography-tandem mass spectrometry. Proteomic data and Western blot displayed the levels of several tumor inhibitory or apoptosis-associated proteins including annexin A1, voltage-dependent anion-selective channel protein 1 and prohibitin (upregulated), heat shock protein 60, heat shock protein beta-1, and peroxiredoxin-2 (downregulated) in A2058 melanoma cells exposed to sinularin. Increased expression of p53, cleaved-caspase-3, cleaved-caspase-8, cleaved-caspase-9, p21, and Bax and decreased expression of Bcl-2 in sinularin-treated melanoma cells suggest that the anti-tumor activities of sinularin against melanoma cells are particularly correlated with these pro-apoptotic factors. These data provide important information for the mechanisms of anti-tumor effects of sinularin on melanoma cells and may be helpful for drug development and progression monitoring of human melanoma. 相似文献
107.
Chuan‐Yien Liu Hsin‐Ta Wang Wen‐Chun Chung Yi‐Ting Cheng Yi‐Ting Chen Mei‐Lin Ho Chih‐Chieh Wang Gene‐Hsiang Lee Hwo‐Shuenn Sheu 《中国化学会会志》2012,59(9):1070-1079
Three coordination polymers, {[Cd(3‐bpd)2(NCS)2]×C2H5OH}n ( 1 ), {[Cd(3‐bpd)(dpe)(NO3)2]×(3‐bpd)}2 ( 2 ), {[Cd(dpe)2(NCS)2]×3‐bpd×2H2O}n ( 3 ) (3‐bpd = 1,4‐bis(3‐pyridyl)‐2,3‐diaza‐1,3‐butadiene; dpe = 1,2‐bis(4‐pyridyl)ethane), were prepared and structurally characterized by a single‐crystal X‐ray diffraction method. In compound 1 , each Cd(II) ion is six‐coordinate bonded to six nitrogen atoms from four 3‐bpd and two NCS? ligands. The 3‐bpd acts as a bridging ligand connecting the Cd(II) ion to generate a 2D layered metal‐organic framework (MOF) by using a rhomboidal‐grid as the basic building units with the 44 topology. In compound 2 , the Cd(II) ion is also six‐coordinate bonded to four nitrogen atoms of two 3‐bpd, two dpe and two oxygen atoms of two NO3? ligands. The 3‐bpd and dpe ligands both adopt bis‐monodentate coordination mode connecting the Cd(II) ions to generate a 2D layered MOF by using a rectangle‐grid as the basic building units with the 44 topology. In compound 3 , two crystallographically independent Cd(II) ions are both coordinated by four nitrogen atoms of dpe ligands in the basal plane and two nitrogen atom of NCS? in the axial sites. The dpe acts as a bridging ligand to connect the Cd(II) ions forming a 2D interpenetrating MOFs by using a square‐grid as the basic unit with the 44 topology. All of their 2D layered MOFs in compounds 1 ‐ 3 are then arranged in a parallel non‐interpenetrating ABAB—packing manner in 1 and 2 , and mutually interpenetrating manner in 3 , respectively, to extend their 3D supramolecular architectures with their 1D pores intercalated with solvent (ethanol in 1 or H2O in 3 ) or free 3‐bpd molecules in 2 and 3 , respectively. The photoluminescence measurements of 1 ‐ 3 reveal that the emission is tentatively assigned to originate from π‐π* transition for 1 and 2 and probably due to ligand‐center luminescence for compounds 3 , respectively. 相似文献
108.
Hsiao‐Fen Wang Kuang‐Hway Yih Weng‐Feng Zeng Shou.‐Ling Huang Gene‐Hsiang Lee 《中国化学会会志》2012,59(8):989-994
Reactions of the thiocarbamoyl‐molybdenum complex [Mo(CO)2(η2‐SCNMe2)(PPh3)2Cl] 1 , and ammonium diethyldithiophosphate, NH4S2P(OEt)2, and potassium tris(pyrazoyl‐1‐yl)borate, KTp, in dichloromethane at room temperature yielded the seven coordinated diethyldithiophosphate thiocarbamoyl‐molybdenum complexe [Mo(CO)2{η2‐S2P(OEt)2}(η2‐SCNMe2)(PPh3)] β‐3 , and tris(pyrazoyl‐1‐yl)borate thiocabamoyl‐molybdenum complex [Mo(CO)2(η3‐Tp)(η2‐SCNMe2)(PPh3)] 4 , respectively. The geometry around the metal atom of compounds β‐3 and 4 are capped octahedrons. The α‐ and β‐isomers are defined to the dithio‐ligand and one of the carbonyl ligands in the trans position in former and two carbonyl ligands in the trans position in later. The thiocabamoyl and diethyldithiophosphate or tris(pyrazoyl‐1‐yl)borate ligands coordinate to the molybdenum metal center through the carbon and sulfur and two sulfur atoms, or three nitrogen atoms, respectively. Complexes β‐3 and 4 are characterized by X‐ray diffraction analyses. 相似文献
109.
Prof. Hsien‐Ming Kao Chih‐Hsuan Chung Dr. Diganta Saikia Shih‐Hsiang Liao Pei‐Ying Chao Yu‐Han Chen Prof. Kevin C.‐W. Wu 《化学:亚洲杂志》2012,7(9):2111-2117
Functionalization of periodic mesoporous organosilicas (PMOs) with high loadings of pendant organic groups to form bifunctional PMOs with ordered mesostructures remains a challenging objective. Herein, we report that well‐ordered ethane‐bridged PMOs functionalized with exceptionally high loadings of pendant carboxylic acid groups (up to 80 mol % based on silica) were synthesized by the co‐condensation of 1,4‐bis(trimethoxysilyl)ethane (BTME) and carboxyethylsilanetriol sodium salt (CES) with Pluronic P123 as the template and KCl as an additive under acidic conditions. The bifunctional materials were characterized by using a variety of techniques, including powder X‐ray diffraction, nitrogen‐adsorption/desorption, TEM, and solid‐state 13C and 29Si NMR spectroscopy. Zeta‐potential measurements showed that the surface negative charges increased with increasing the CES content. This property makes them potential candidates for applications in drug adsorption. The excellent adsorption capacity of these bifunctional PMOs towards an anticancer drug (doxorubicin) was also demonstrated. 相似文献
110.
Annamalai Senthilvelan Dr. I.‐Ting Ho M. Sc. Kai‐Chi Chang Dr. Gene‐Hsiang Lee Dr. Yi‐Hung Liu M. Sc. Wen‐Sheng Chung Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(25):6152-6160
Chemodosimeter : Upon titration with CuII, the fluorescence of 1 showed strong fluorescence enhancement because the metal ion helps to lock the conformation of the fluorophores. CuII was reduced to CuI by the free phenolic OH group of 1 , the phenol was then oxidised by CuII and assisted in the trapping of CuI. Ditopic behaviour was observed for 1? CuI, which showed further enhancement of its fluorescence intensity upon complexation with anions (as depicted, A?=CH3COO? or F?).