全文获取类型
收费全文 | 1348篇 |
免费 | 40篇 |
国内免费 | 9篇 |
专业分类
化学 | 967篇 |
晶体学 | 10篇 |
力学 | 28篇 |
数学 | 202篇 |
物理学 | 190篇 |
出版年
2023年 | 16篇 |
2022年 | 25篇 |
2021年 | 48篇 |
2020年 | 27篇 |
2019年 | 41篇 |
2018年 | 32篇 |
2017年 | 35篇 |
2016年 | 55篇 |
2015年 | 41篇 |
2014年 | 41篇 |
2013年 | 86篇 |
2012年 | 79篇 |
2011年 | 90篇 |
2010年 | 49篇 |
2009年 | 50篇 |
2008年 | 98篇 |
2007年 | 91篇 |
2006年 | 86篇 |
2005年 | 67篇 |
2004年 | 59篇 |
2003年 | 27篇 |
2002年 | 32篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 8篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1924年 | 2篇 |
1912年 | 2篇 |
1911年 | 2篇 |
1910年 | 2篇 |
1858年 | 1篇 |
排序方式: 共有1397条查询结果,搜索用时 593 毫秒
191.
Lo Fiego MJ Badajoz MA Silbestri GF Lockhart MT Chopa AB 《The Journal of organic chemistry》2008,73(22):9184-9187
The exceptional leaving group ability of the trimethylstannyl group in electrophilic aromatic substitutions makes possible the synthesis, in a single step, of bi- and triaroylarenes through the catalyst-free, regioselective reaction of bi- and tristannylarenes with different aroyl halides in o-dichlorobenzene as solvent. Specific di- and triketones are obtained in good to excellent yields (45-83%). 相似文献
192.
The 3-oxygenated-cis-dialkyl-2,5-substituted tetrahydrofuran system, present in several natural products, was prepared with good selectivity by acidic cyclization of 5-alkene-1,2,4-triol derivatives. The starting alkenol was obtained in few steps from a chiral cis-diol resulting from microbial oxidation of bromobenzene. The study of the cyclization allowed the rationalization of all experimental results by assuming a complete ionization at the allylic position and a model close to the one proposed by Labelle for homoallylic induction in five-membered ring closures. 相似文献
193.
André Gustavo de A. Fernandes Pedro Ivo da S. Maia Elizeu J. de Souza Sebastião S. Lemos Alzir A. Batista Ulrich Abram Javier Ellena Eduardo E. Castellano Victor M. Deflon 《Polyhedron》2008
Novel rhenium complexes containing the maltolate (mal) or kojate (koj) anions as chelating ligands have been synthesized: [ReOCl(mal)2] (1), [ReOCl2(mal)(PPh3)] (2), [ReOBr2(mal)(PPh3)] (3), [ReOCl2(koj)(PPh3)] (4) and [ReOBr2(koj)(PPh3)] (5). The products have been characterized by FTIR, 1H, 13C, and 31P NMR spectroscopies and elemental analysis. The crystal and molecular structures of all complexes were determined. Complex 1 crystallizes monoclinic, space group C2/c, Z = 8. It contains two O,O′-bidentate maltolate ligands and one chloro ligand at the (ReO)3+ unit, so that a distorted octahedral geometry is adopted by the six-coordinated rhenium(V) center. The chloro ligand occupies a cis position to the oxo ligand. Complexes 2 and 3 are isostructural and crystallize orthorhombic, space group Pbca and Z = 8. The isostructural complexes 4 and 5 crystallize monoclinic, space group P21/n and Z = 4. In complexes 2–5, the (ReO)3+ unit is coordinated by a monoanionic O,O-bidentate unit of the maltolate (2 and 3) or kojate (4 and 5) ligand, one triphenylphosphine and two halogeno ligands (Cl in 2 and 4; Br in 3 and 5), with the rhenium(V) center in a distorted octahedral environment. The halide ligands are in cis positions to each other. 相似文献
194.
Anahí Sanluis-Verdes Ana Peñaherrera José L. Torán Gustavo Rosero María A. Noriega Betiana Lerner Maximiliano Pérez José M. Casasnovas 《Electrophoresis》2023,44(9-10):864-872
A method development aimed for high-throughput and automated antibody screening holds great potential for areas ranging from fundamental molecular interactions to the discovery of novel disease markers, therapeutic targets, and monoclonal antibody engineering. Surface display techniques enable efficient manipulation of large molecular libraries in small volumes. Specifically, phage display appeared as a powerful technology for selecting peptides and proteins with enhanced, target-specific binding affinities. Here, we present a phage-selection microfluidic device wherein electrophoresis was performed under two orthogonal electric fields through an agarose gel functionalized with the respective antigen. This microdevice was capable of screening and sorting in a single round high-affinity phage-displayed antibodies against virus glycoproteins, including human immunodeficiency virus-1 glycoprotein 120 or the Ebola virus glycoprotein (EBOV-GP). Phages were differentially and laterally swept depending on their antigen affinity; the high-affinity phages were recovered at channels proximal to the application site, whereas low-affinity phages migrated distal after electrophoresis. These experiments proved that the microfluidic device specifically designed for phage-selection is rapid, sensitive, and effective. Therefore, this is an efficient and cost-effective method that allowed highly controlled assay conditions for isolating and sorting high-affinity ligands displayed in phages. 相似文献
195.
Yamile Jalit Marcela C. Rodríguez María D. Rubianes Soledad Bollo Gustavo A. Rivas 《Electroanalysis》2008,20(15):1623-1631
We report the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multiwall carbon nanotubes (MWCNT) in polylysine (Plys) (GCE/MWCNT‐Plys). The resulting electrodes show an excellent electrocatalytic activity towards different bioanalytes like ascorbic acid, uric acid and hydrogen peroxide, with important decrease in their oxidation overvoltages. The dispersion of 1.0 mg/mL MWCNT in 1.0 mg/mL polylysine is highly stable, since after 2 weeks the sensitivity for hydrogen peroxide at GCE modified with this dispersion remained in a 90% of the original value. The MWCNT‐Plys layer immobilized on glassy carbon electrodes has been also used as a platform to build supramolecular architectures by self‐assembling of polyelectrolytes based on the polycationic nature of the polylysine used to disperse the nanotubes. The self‐assembling of glucose oxidase has allowed us to obtain a supramolecular multistructure for glucose biosensing. The influence of glucose oxidase concentration and adsorption time as well as the effect of using polylysine or MWCNT‐Plys as polycationic layers for further adsorption of GOx is also evaluated. 相似文献
196.
Mohallem JR Coura Tde O Diniz LG de Castro G Assafrão D Heine T 《The journal of physical chemistry. A》2008,112(38):8896-8901
The adiabatic finite-nuclear-mass-correction (FNMC) to the electronic energies and wave functions of atoms and molecules is formulated for density-functional theory and implemented in the deMon code. The approach is tested for a series of local and gradient corrected density functionals, using MP2 results and diagonal-Born-Oppenheimer corrections from the literature for comparison. In the evaluation of absolute energy corrections of nonorganic molecules the LDA PZ81 functional works surprisingly better than the others. For organic molecules the GGA BLYP functional has the best performance. FNMC with GGA functionals, mainly BLYP, show a good performance in the evaluation of relative corrections, except for nonorganic molecules containing H atoms. The PW86 functional stands out with the best evaluation of the barrier of linearity of H2O and the isotopic dipole moment of HDO. In general, DFT functionals display an accuracy superior than the common belief and because the corrections are based on a change of the electronic kinetic energy they are here ranked in a new appropriate way. The approach is applied to obtain the adiabatic correction for full atomization of alcanes C(n)H(2n+2), n = 4-10. The barrier of 1 mHartree is approached for adiabatic corrections, justifying its insertion into DFT. 相似文献
197.
Rasitha Manha Veedu Niklas Niemeyer Dr. Nils Bäumer Dr. Krishnan Kartha Kalathil Prof. Dr. Johannes Neugebauer Prof. Dr. Gustavo Fernández 《Angewandte Chemie (International ed. in English)》2023,62(49):e202314211
The functionalization of π-conjugated scaffolds with sterically demanding substituents is a widely used tactic to suppress cofacial (H-type) stacking interactions, which may even inhibit self-assembly. Contrary to expectations, we demonstrate herein that increasing steric effects can result in an enhanced thermodynamic stability of H-type supramolecular polymers. In our approach, we have investigated two boron dipyrromethene (BODIPY) dyes with bulky phenyl ( 2 ) and mesityl ( 3 ) meso-substituents and compared their self-assembly in nonpolar media with that of a parent meso-methyl BODIPY 1 lacking bulky groups. While the enhanced steric demand induces pathway complexity, the superior thermodynamic stability of the H-type pathways can be rationalized in terms of additional enthalpic gain arising from intermolecular C−H⋅⋅⋅F−B interactions of the orthogonally arranged aromatic substituents, which overrule their inherent steric demand. Our findings underline the importance of balancing competing non-covalent interactions in self-assembly. 相似文献
198.
Microencapsulation of cinnamon leaf (Cinnamomum zeylanicum) and garlic (Allium sativum) oils in β-cyclodextrin 总被引:1,自引:0,他引:1
J. Fernando Ayala-Zavala Herlinda Soto-Valdez Alberto González-León Emilio Álvarez-Parrilla Olga Martín-Belloso Gustavo A. González-Aguilar 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):359-368
Cinnamon leaf (CLO) and garlic oils (GO) are good antimicrobials, however, their volatility complicates their application
as food preservatives. Hence, microencapsulation of CLO and GO with β-cyclodextrin (β-CD) was studied at 4:96, 8:92, 12:88,
and 16:84 (oil:β-CD) percent weight ratios. Microcapsule characterization included gas chromatography analysis, moisture sorption–desorption
isotherms, infrared spectroscopy (IR), and antifungal activity against Alternaria alternata. Major oil constituents were eugenol for CLO and allyl disulfide for GO. The 16:84 ratio (CLO:β-CD) showed the highest eugenol
content; the allyl disulfide content was higher, but not significantly different (P > 0.05) for the 12:88 and 16:84 ratios. Microcapsules showed lower moisture sorption than β-CD, although during water desorption
there were no difference between them. Hydrogen bonds were detected between oil constituents and β-CD by IR spectroscopy.
CLO:β-CD and GO:β-CD microcapsules displayed good antifungal activity against Alternaria alternata. Therefore, CLO and GO microcapsules can have important applications in the food industry as stable natural antimicrobial
compound systems. 相似文献
199.
Gustavo Pierdominici-Sottile Marcelo A. Martí Juliana Palma 《Chemical physics letters》2008,456(4-6):243-246
We present the results of combined molecular dynamics and full-quantum calculations aimed at elucidating the role of residue Thr122 of the enzyme methylamine dehydrogenase. Calculations were performed on the native structure and the T122A mutant. We found that the presence of Thr122 has a deleterious effect on the proton transfer step that is proposed to determine the rate of the reaction. Besides, at the PM3 level, the substitution of Thr122 by Ala does not significantly modify the preference of the proton by atom OD2 of Asp76. Transmission coefficients obtained form MP2/6-31G(d,p)//PBE/DZP minimum energy paths show that proton tunneling is significant. 相似文献
200.
Phthalic acid, a ubiquitous organic compound found in soil, water, and in domestic and nuclear wastes can affect the mobility and bioavailability of metals and radionuclides. We examined the complexation of uranium with phthalic acid by potentiometric titration, electrospray ionization-mass spectroscopy (ESI-MS), and extended X-ray absorption fine structure (EXAFS) analysis. Potentiometric titration of a 1:1 U/phthalic acid indicated uranyl ion bonding with both carboxylate groups of phthalic acid; above pH 5 the uranyl ion underwent hydrolysis with one hydroxyl group coordinated to the inner-sphere of uranium. In the presence of excess phthalic acid, ESI-MS analysis revealed the formation of both 1:1 and 1:2 U/phthalic acid complexes. EXAFS studies confirmed the mononuclear biligand 1:2 U/phthalic acid complex as the predominant form. These results show that phthalates can form soluble stable complexes with uranium and may affect its mobility. 相似文献