全文获取类型
收费全文 | 2130篇 |
免费 | 111篇 |
国内免费 | 33篇 |
专业分类
化学 | 1464篇 |
晶体学 | 15篇 |
力学 | 151篇 |
数学 | 345篇 |
物理学 | 299篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 43篇 |
2021年 | 79篇 |
2020年 | 93篇 |
2019年 | 100篇 |
2018年 | 120篇 |
2017年 | 99篇 |
2016年 | 169篇 |
2015年 | 119篇 |
2014年 | 164篇 |
2013年 | 253篇 |
2012年 | 181篇 |
2011年 | 164篇 |
2010年 | 138篇 |
2009年 | 121篇 |
2008年 | 103篇 |
2007年 | 75篇 |
2006年 | 51篇 |
2005年 | 36篇 |
2004年 | 26篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 13篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有2274条查询结果,搜索用时 0 毫秒
51.
Mehdi Sahihi Zobeideh Heidari-Koholi Abdol-Khalgh Bordbar 《Journal of Macromolecular Science: Physics》2013,52(12):2311-2323
The interaction of quercetin, quercitrin, and rutin, as natural polyphenolic compounds, with β-lactoglobulin (BLG) using molecular docking and molecular dynamics simulation methods was examined. Molecular docking studies showed that quercetin and quercitrin were bounded to the internal cavity of protein, while rutin was bounded to the entrance of the cavity because of its large structural volume. It was found that there were one-, three-, and four-hydrogen bond interactions between BLG and quercetin, quercitrin, and rutin respectively. This showed that with an increase in the number of OH groups in the flavonoid structure, there was an increase in the number of hydrogen bond interactions. The binding constants for the binding of quercetin, quercitrin, and rutin to BLG were 1.2 × 106, 1.9 × 106, and 7.4 × 104 M?1 respectively. The results of molecular dynamics simulation showed that the root mean square deviation (RMSD) of non-liganded BLG and BLG–ligand complexes reached equilibration after 3500 ps. The study of the radius of gyration revealed that BLG and BLG–ligand complexes were stabilized around 2500 ps, and unlike the two other complexes, there was no conformational change for BLG–quercetin. Finally, analyzing the RMS fluctuations suggested that the structure of the ligand binding site remained approximately rigid during simulation. 相似文献
52.
An efficient synthesis of 2-(3-alkyl-4-oxo-2- thioxo-1,3-thiazinan-5-yl)acetic acids is described via a three-component reaction
between primary amines, CS2, and itaconic anhydride. 相似文献
53.
A coefficient inverse problem of the one-dimensional parabolic equation is solved by a high-order compact finite difference method in this paper. The problem of recovering a time-dependent coefficient in a parabolic partial differential equation has attracted considerable attention recently. While many theoretical results regarding the existence and uniqueness of the solution are obtained, the development of efficient and accurate numerical methods is still far from satisfactory. In this paper a fourth-order efficient numerical method is proposed to calculate the function u(x,t) and the unknown coefficient a(t) in a parabolic partial differential equation. Several numerical examples are presented to demonstrate the efficiency and accuracy of the numerical method. 相似文献
54.
Five new Ni(II) Schiff base complexes [NiLx(Solv)2] denoted by NiLx, x = 1–5, were synthesized and characterized. The Schiff base ligands were synthesized from the condensation of 5-bromo-2-hydroxy-3-nitrobenzaldehyde with different aliphatic and aromatic diamines. The X-ray crystal structure of NiL3 was determined. The ligands and complexes were tested as antibacterial agents against two gram(+) and two gram(?) human pathogenic bacteria. The complexes showed moderate antibacterial activity against both gram type bacteria. The new Ni(II) complexes showed enhanced antibacterial activity compared to the previously reported Cu(II) complexes of the same ligands. 相似文献
55.
Seyyed Javad Sabounchei Hassan Nemattalab Sadegh Salehzadeh Sima Khani Mehdi Bayat Hamid Reza Khavasi 《Polyhedron》2008
Reaction of phosphorus ylide Ph3PCHC(O)C6H4Cl (Y1) with HgX2 (X = Cl, Br and I) and ylide (p-tolyl)3PCHC(O)CH3 (Y2) with HgI2 in equimolar ratios using methanol as solvent leads to binuclear products. The bridge-splitting reaction of binuclear complex [(Y1) · HgCl2]2 by DMSO yields a mononuclear complex containing DMSO as ligand. O-coordination of DMSO is revealed by single crystal X-ray analysis in mononuclear complex of [(Y1) · HgCl2 · DMSO]. C-coordination of ylides is confirmed by X-ray structure of binuclear complex [(Y2) · HgI2]2. Characterization of the obtained compounds was also performed by elemental analysis, IR, 1H, 31P, and 13C NMR. Theoretical studies on mercury(II) complexes of Y1 show that formation of mononuclear complexes in DMSO solution in which DMSO acts as a ligand, energetically is more favorable than that of binuclear complexes. 相似文献
56.
The design of catalysts for the chemical recycling of plastic waste will benefit greatly from an intimate knowledge of the interfacial polymer–catalyst interactions that determine reactant and product distributions. Here, we investigate backbone chain length, side chain length, and concentration effects on the density and conformation of polyethylene surrogates at the interface with Pt(111) and relate them to experimental product distributions resulting from carbon–carbon bond cleavage. Using replica-exchange molecular dynamics simulations, we characterize the polymer conformations at the interface by the distributions of trains, loops, and tails and their first moments. We find that the preponderance of short chains, in the range of 20 carbon atoms, lies entirely on the Pt surface, whereas longer chains exhibit much broader distributions of conformational features. Remarkably, the average length of trains is independent of the chain length but can be tuned via the polymer–surface interaction. Branching profoundly impacts the conformations of long chains at the interface as the distributions of trains become less dispersed and more structured, localized around short trains, with the immediate implication of a wider carbon product distribution upon C–C bond cleavage. The degree of localization increases with the number and size of the side chains. Long chains can adsorb from the melt onto the Pt surface even in melt mixtures containing shorter polymer chains at high concentrations. We confirm experimentally key computational findings and demonstrate that blends may provide a strategy to reduce the selectivity for undesired light gases.The design of catalysts for the chemical recycling of plastic waste will benefit greatly from an intimate knowledge of the interfacial polymer–catalyst interactions that determine reactant and product distributions. 相似文献
57.
Sadegh Salehzadeh Yasin Gholiee Mehdi Bayat 《International journal of quantum chemistry》2011,111(14):3608-3615
For the first time, a simple methodology is reported for theoretical calculation of microscopic protonation constants of polybasic molecules in solution. Density functional theory study was used for complete microequilibrium analysis of spermine, H2N(CH2)3NH(CH2)4NH(CH2)3NH2, a linear tetraamine with 16 known microspecies. A general thermodynamic cycle is proposed to calculate protonation microconstants of polybasic molecules using calculated micro‐ΔG values in aqueous solution. The microscopic protonation constants were determined with considering both the most abundant and most stable conformers for all microspecies. The results show that the microscopic protonation constants derived from the most abundant conformers (i.e., linear conformers in which the intramolecular hydrogen bonding does not exist) are in good agreement with the corresponding available experimental data. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
58.
59.
Mehdi Sharifi Ali Akbar Alizadeh Maryam Hamzeh-Mivehroud Siavoush Dastmalchi 《Journal of the Iranian Chemical Society》2018,15(11):2519-2531
TNF-α is a crucial cytokine in the process of inflammatory diseases. The adverse effect of TNF-α is mostly mediated by interaction of TNF-α with TNF-α receptor type I (TNFR1); therefore, discovery of molecules which can bind to TNFR1 preventing TNF-α-receptor complex formation would be of great interest. In the current study, using GRID/GOLPE program, a 3D-QSAR study was conducted on a series of synthetic TNFR1 binders, which resulted in a 3D-QSAR model with appropriate power of predictivity in internal (r2?=?0.94 and q2LOO?=?0.74) and external (r2?=?0.66 and SDEP?=?0.42) validations. The structural features of TNFR1 inhibitors essential for exerting activity were explored by analyzing the contour maps of the 3D-QSAR model showing that steric interactions and hydrogen bonds are responsible for exerting TNFR1 inhibitory activity. To propose potential chemical entities for TNFR1 inhibition, PubChem database was searched and the selected compounds were virtually tested for anti-TNFR1 activity using the generated model, resulting in two potential anti-TNFR1 compounds. Finally, the possible interactions of the compounds with TNFR1 were investigated using docking studies. The findings in the current work can pave the way for designing more potent anti-TNFR1 inhibitors. 相似文献
60.