全文获取类型
收费全文 | 686篇 |
免费 | 38篇 |
国内免费 | 2篇 |
专业分类
化学 | 591篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 74篇 |
物理学 | 52篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 40篇 |
2021年 | 45篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 31篇 |
2015年 | 23篇 |
2014年 | 22篇 |
2013年 | 35篇 |
2012年 | 44篇 |
2011年 | 43篇 |
2010年 | 27篇 |
2009年 | 31篇 |
2008年 | 39篇 |
2007年 | 49篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 29篇 |
2003年 | 34篇 |
2002年 | 24篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有726条查询结果,搜索用时 15 毫秒
701.
3D‐printed photo‐spectroelectrochemical devices for in situ and in operando X‐ray absorption spectroscopy investigation
下载免费PDF全文
![点击此处可从《Journal of synchrotron radiation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
702.
Adsorption and conformational change of myoglobin on biomimetic hydroxyapatite nanocrystals functionalized with alendronate 总被引:2,自引:0,他引:2
Iafisco M Palazzo B Falini G Foggia MD Bonora S Nicolis S Casella L Roveri N 《Langmuir : the ACS journal of surfaces and colloids》2008,24(9):4924-4930
The chemical conjugation of bisphosphonates (BPs), specifically alendronate, to hydroxyapatite could be an effective means to impart to it fine-tuned bioactivity. Horse heart myoglobin (Mb), a well-characterized protein, has been adsorbed onto biomimetic hydroxyapatite nanocrystals (nHA) and onto the nHA/alendronate conjugate powdered samples. The obtained materials have potential use in bone implantation and as prospective drug-delivery devices. The kinetic absorption of Mb onto nHA is dramatically affected by its functionalization with alendronate. The covering of the nHA surface by alendronate inhibits the adsorption of myoglobin. The adsorption mechanisms of the protein were studied by spectroscopic techniques (UV-vis and surface-enhanced Raman spectroscopy). The results indicate that the protein changes conformation upon adsorption on the inorganic substrate. In particular, the interaction with nHA alters the coordination state of the iron in the heme through the formation of a hexacoordinated low-spin Mb heme, possibly involving the distal histidine. Instead, the covering of the nHA surface by alendronate does not adsorb the protein but preserves the coordination state of the heme moiety. This study could be of significance either in the field of biomaterials science, in particular, to fine tune a bone-specific drug delivery device and to test nHA as a new support for heterogeneous catalysis, improving the understating of enzyme immobilization. 相似文献
703.
Tanase S Marques-Gallego P Browne WR Hage R Bouwman E Feringa BL Reedijk J 《Dalton transactions (Cambridge, England : 2003)》2008,(15):2026-2033
The reactivity towards H(2)O(2) of the complexes [Fe(pca)(2)(py)(2)].py (1) and Na(2){[Fe(pca(3))](2)O}.2H(2)O.CH(3)CN (2) (where pca(-) is pyrazine-2-carboxylate) and their catalytic activity in the oxidation of hydrocarbons is reported. Addition of H(2)O(2) to 1 results in the formation of a dinuclear Fe(III)-(mu-O)-Fe(III) species characterized spectroscopically and by cyclic voltammetry. By contrast, treatment of 2 with H(2)O(2) results in the formation of mononuclear iron(II) complexes, [Fe(pca)(2)(solvent)(2)]. The experimental results indicate that the catalytic activity of the starting complexes 1 and 2 is strongly dependent on the species formed in solution. 相似文献
704.
The significance of laboratory sample preparation for the determination of two important mycotoxins, ochratoxin A (OTA) and deoxynivalenol (DON), in wheat was investigated by comparing water-slurry mixing and dry-milling procedures. The distribution of OTA and DON in 10 kg samples of naturally contaminated wheat was established by analyzing one hundred 100 g subsamples of each sample. A normal distribution and a good repeatability of DON measurements was observed for both water-slurry mixing (mean 2290 microg/kg, CV 4.6%, median 2290 microg/kg) and dry milling (mean 2310 microg/kg, CV 6.4%, median 2290 microg/kg) procedures. For OTA determinations, reliable results could be obtained only by slurry mixing sample preparation (mean 2.62 microg/kg, CV 4.0%, median 2.62 microg/kg), whereas dry-milling comminution resulted in an inhomogeneous distribution with a high variability (mean 0.83 microg/kg, CV 75.2%, median 0.60 microg/kg) and a positive skewness (2.12). Ad hoc experiments were performed on different size portions of the same sample (10 kg) to assess accuracy and precision of the comminution/homogenization procedures (slurry mixing and dry milling). Very good results were obtained for DON determination with both procedures in terms of accuracy (>98.7% of the "weighted value") and precision (CV <3%). For OTA determination good results were only obtained by slurry mixing (99.4% of the "weighted value," CV 10%), whereas dry milling provided results with low accuracy (43.2% of the "weighted value") and high variability (CV 110%). This study clearly demonstrated that sample preparation by slurry mixing is strictly necessary to obtain reliable laboratory samples for OTA determination in wheat to minimize misclassification of acceptable/rejectable lots, mainly within official control. 相似文献
705.
Dunkelberger AD Kieda RD Shin JY Rossi Paccani R Fusi S Olivucci M Crim FF 《The journal of physical chemistry. A》2012,116(14):3527-3533
Recent experimental and theoretical studies on N-alkylated indanylidene pyrroline Schiff bases (NAIP) show that these compounds exhibit biomimetic photoisomerization analogous to that in the chromophore of rhodopsin. The NAIP compounds studied previously isomerize rapidly and often evolve coherently on the ground-electronic surface after reaction. We present the results of transient electronic absorption spectroscopy on dMe-OMe-NAIP, a newly synthesized NAIP analogue that differs from other NAIP compounds in the substituents on its pyrrolinium ring. Following excitation with 400 nm light, dMe-OMe-NAIP relaxes from the electronic-excited state in less than 500 fs, which is slower than in other analogues, and does not show the prominent oscillations observed in other NAIP compounds. A reduction in the amount of twisting between the rings caused by removal of the methyl group is likely responsible for the slower isomerization. Measurements in solvents of varying viscosity and structure suggest that intramolecular processes dominate the relaxation of nascent photoproducts. 相似文献
706.
A tetraethylene glycol dimethylether-lithium bis(oxalate)borate (TEGDME-LiBOB) electrolyte for advanced lithium ion batteries 总被引:1,自引:0,他引:1
Dong-Ju LeeJusef Hassoun Stefania PaneroYang-Kook Sun Bruno Scrosati 《Electrochemistry communications》2012,14(1):43-46
Tetraethylene glycol dimethylether-lithium bis(oxalate)borate (TEGDME-LiBOB) electrolyte is here studied. Electrochemical impedance spectroscopy (EIS) measurements demonstrate that the electrolyte has conductivity higher than 10− 3 S cm− 1 at room temperature and about 10− 2 S cm− 1 at 60 °C, while thermogravimetry indicates a stability extending up to 180 °C. Sweep voltammetry of the electrolyte shows anodic stability extending over 4.6 V vs. Li and cathodic peak at about 1.5 V vs. Li/Li+, caused by a decomposition of LiBOB salt, and following prevented by using a pre-treated Sn-C anode. Furthermore, LiFePO4 electrode is successfully used as cathode in a lithium cell using the TEGDME-LiBOB electrolyte. The promising electrochemical results, the low cost and the very high safety level candidate the electrolyte here reported as a valid alternative to the conventional electrolyte based on fluorinated salts presently used in the lithium ion battery field. 相似文献
707.
Attanasi OA Bartoccini S Favi G Giorgi G Perrulli FR Santeusanio S 《The Journal of organic chemistry》2012,77(2):1161-1167
By highly efficient, one-pot, three-component reactions, combining one set of 1,2-diaza-1,3-dienes (DDs), primary amines, and isothiocyanates in a different sequential order of addition, heterocyclic skeletal diversity can be achieved. The key feature discriminating the different heterocyclic core formation is the availability of the N or S heteronucleophile to give the first Michael addition step affording regioselective substituted 2-thiohydantoins or 2-iminothiazolidinones. The hydrazone or enehydrazino side chain at the 5-position of both heterocycles represents a valuable functionality to reach novel 5-hydroxyethylidene derivatives difficult to obtain by other methods. 相似文献
708.
Synthesis, DNA-binding and antiproliferative properties of acridine and 5-methylacridine derivatives
Several acridine derivatives were synthesized and their anti-proliferative activity was determined. The most active molecules were derivatives of 5-methylacridine-4-carboxylic acid. The DNA binding properties of the synthesized acridines were analyzed by competitive dialysis and compared with the anti-proliferative activities. While inactive acridine derivatives showed high selectivity for G-quadruplex structures, the most active 5-methylacridine-4-carboxamide derivatives had high affinity for DNA but showed poor specificity. An NMR titration study was performed with the most active 5-methylacridine-4-carboxamide, confirming the high affinity of this compound for both duplex and quadruplex DNAs. 相似文献
709.
Hannes Kopitz Daniel A. Cashman Stefania Pfeiffer‐Marek Holger Gohlke 《Journal of computational chemistry》2012,33(9):1004-1013
The harmonic model is the most popular approximation for estimating the “configurational” entropy of a solute in molecular mechanics/Poisson‐Boltzmann solvent accessible surface area (MM/PBSA)‐type binding free energy calculations. Here, we investigate the influence of the solvent representation in the harmonic model by comparing estimates of changes in the vibrational entropies for 30 trypsin/ligand complexes on ligand binding. Second derivatives of Amber generalized Born (GB) solvation models are available in the nucleic acid builder code. They allow one to use these models for the calculation of vibrational entropies instead of using a simpler solvation model based on a distance‐dependent dielectric (DDD) constant. Estimates of changes in the vibrational entropies obtained with a DDD model are systematically and significantly larger, by on average, 6 kcal mol?1 (at T = 300 K), than estimates obtained with a GB model and so are more favorable for complex formation. The difference becomes larger the more the vibrational entropy contribution disfavors complex formation, that is, the larger the ligand is (for the complexes considered here). A structural decomposition of the estimates into per‐residue contributions reveals polar interactions between the ligand and the surrounding protein, in particular involving charged nitrogens, as a main source of the differences. Snapshots minimized with the DDD model showed a structural deviation from snapshots minimized in explicit water that is larger by, on average, 0.5 Å RMSD compared to snapshots that were minimized with GBHCT. As experimental vibrational entropies of biomacromolecules are elusive, there is no direct way to establish a solvent model's superiority. Thus, we can only recommend using the GB harmonic model for vibrational entropy calculations based on the reasoning that smaller structural deviations should point to the implicit solvent model that closer approximates the energy landscape of the solute in explicit solvent. © 2012 Wiley Periodicals, Inc. 相似文献
710.
Morkovská P Hromadová M Pospísil L Giannarelli S 《Langmuir : the ACS journal of surfaces and colloids》2006,22(4):1896-1902
The first example of the effect of an electric double layer on the reduction of electrochemically generated radical species is reported. The anion radical of methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate (pesticide bifenox) is electrochemically reduced in acetonitrile to a phenylhydroxylamine derivative in a process involving three electrons. This heterogeneous reaction is strongly influenced by the concentration and nature of the cation of the indifferent electrolyte. Depending on the type of tetraalkylammonium cation, the redox potential changes by 0.45 V. The kinetic parameters were obtained for five tetraalkylammonium hexafluorophosphate salts. The Frumkin correction, which assumes that the outer Helmholtz plane coincides with the reaction site, was applied to kinetic data of the radical anion reduction. The correction of the apparent rate accounted for the observed effect only in the case of tetramethylammonium salt. The presence of higher tetraalkylammonium homologues causes deviations from the predicted dependence of the electron-transfer rate on the phi2 potential of the outer Helmholtz plane. Hence, the nature of the cation of the electrolyte exerts a further effect extending beyond the electrostatic repulsion only. The corrected rate of electron transfer decreases exponentially with increasing size of the alkyl chain of the indifferent electrolyte cation in the order methyl > ethyl > propyl > butyl > hexyl. The rate decay is characterized by an exponent beta = 0.83. This confirms that the reaction plane for the reduction of the bifenox radical anion is different for each electrolyte. Due to this fact the Frumkin correction cannot fully account for the observed dependence of the heterogeneous rate on the solution composition. The observed effect is not specific to the bifenox radical. A similar influence of the concentration and nature of the cation of the indifferent electrolyte was observed for other nitro compounds, namely, nitrobenzene, nitrobenzoate, and nitrofen. 相似文献