全文获取类型
收费全文 | 1258篇 |
免费 | 46篇 |
国内免费 | 5篇 |
专业分类
化学 | 813篇 |
晶体学 | 14篇 |
力学 | 46篇 |
数学 | 139篇 |
物理学 | 297篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 36篇 |
2021年 | 47篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 39篇 |
2017年 | 24篇 |
2016年 | 37篇 |
2015年 | 46篇 |
2014年 | 40篇 |
2013年 | 100篇 |
2012年 | 105篇 |
2011年 | 98篇 |
2010年 | 63篇 |
2009年 | 66篇 |
2008年 | 72篇 |
2007年 | 68篇 |
2006年 | 49篇 |
2005年 | 42篇 |
2004年 | 46篇 |
2003年 | 32篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有1309条查询结果,搜索用时 924 毫秒
991.
Priscilla Mendes Arruda Antônio Canal Neto Mauro Cesar Martins Campos Henrique Raulino Coelho da Cruz Fábio Alves dos Santos 《International journal of quantum chemistry》2015,115(2):77-83
The Monte Carlo simulated annealing method is adapted to optimize correlated Gaussian‐type functions in nonrelativistic molecular environments. Starting from an atom‐centered atomic Gaussian basis set, the uncontracted functions are reoptimized in the molecular environments corresponding to the H2O, CN?, N2, CO, BF, NO+, CO2, and CS systems. These new molecular adapted basis sets are used to calculate total energies, harmonic vibrational frequencies, and equilibrium geometries at a correlated level of theory. The present methodology is a simple and effective way to improve molecular correlated wave functions, without the need to enlarge the molecular basis set. Additionally, this methodology can be used to generate hierarchical sequences of molecular basis sets with increasing size, which are relevant to establish complete basis set limits. © 2014 Wiley Periodicals, Inc. 相似文献
992.
Dr. Vinayaraj Ozhukil Kollath Freya Van den Broeck Dr. Krisztina Fehér Prof. José C. Martins Dr. Jan Luyten Dr. Karl Traina Dr. Steven Mullens Prof. Rudi Cloots 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(29):10497-10505
Biocompatible inorganic nano‐ and microcarriers can be suitable candidates for protein delivery. This study demonstrates facile methods of functionalization by using nanoscale linker molecules to change the protein adsorption capacity of hydroxyapatite (HA) powder. The adsorption capacity of bovine serum albumin as a model protein has been studied with respect to the surface modifications. The selected linker molecules (lysine, arginine, and phosphoserine) can influence the adsorption capacity by changing the electrostatic nature of the HA surface. Qualitative and quantitative analyses of linker‐molecule interactions with the HA surface have been performed by using NMR spectroscopy, zeta‐potential measurements, X‐ray photoelectron spectroscopy, and thermogravimetric analyses. Additionally, correlations to theoretical isotherm models have been calculated with respect to Langmuir and Freundlich isotherms. Lysine and arginine increased the protein adsorption, whereas phosphoserine reduced the protein adsorption. The results show that the adsorption capacity can be controlled with different functionalization, depending on the protein–carrier selections under consideration. The scientific knowledge acquired from this study can be applied in various biotechnological applications that involve biomolecule–inorganic material interfaces. 相似文献
993.
Synthesis of 1‐Arylethyl‐2‐arylethylamino‐5‐trifluoroacetyl‐1,2,3,4‐tetrahydropyridines and Related Compounds with Potential Cell Efflux Pump Inhibition 下载免费PDF全文
Nilo Zanatta Marcio M. Lobo Josiane M. dos Santos Laura de A. Souza Valquiria P. de Andrade Helio G. Bonacorso Marcos A. P. Martins 《Journal of heterocyclic chemistry》2015,52(6):1776-1781
This study reports a simple, fast, and efficient method for the synthesis of a new series of 1‐arylethyl‐2‐arylethylamino‐5‐trifluoroacetyl‐1,2,3,4‐tetrahydropyridines and related compounds from the reaction of 2‐alkoxy‐5‐trifluoroacetyl‐3,4‐dihydro‐2H‐pyrans with 2‐arylethanamines and related 2‐ethanamines. The desired tetrahydropyridines were obtained in excellent yields (90–98%), through a reaction that can be described as an AAB′ three‐component reaction protocol following an ANRORC‐type mechanism. 相似文献
994.
Biosynthesis‐Assisted Structural Elucidation of the Bartolosides,Chlorinated Aromatic Glycolipids from Cyanobacteria 下载免费PDF全文
Dr. Pedro N. Leão Hitomi Nakamura Margarida Costa Dr. Alban R. Pereira Prof. Rosário Martins Prof. Vitor Vasconcelos Prof. William H. Gerwick Prof. Emily P. Balskus 《Angewandte Chemie (International ed. in English)》2015,54(38):11063-11067
The isolation of the bartolosides, unprecedented cyanobacterial glycolipids featuring aliphatic chains with chlorine substituents and C‐glycosyl moieties, is reported. Their chlorinated dialkylresorcinol (DAR) core presented a major structural‐elucidation challenge. To overcome this, we discovered the bartoloside (brt) biosynthetic gene cluster and linked it to the natural products through in vitro characterization of the DAR‐forming ketosynthase and aromatase. Bioinformatic analysis also revealed a novel potential halogenase. Knowledge of the bartoloside biosynthesis constrained the DAR core structure by defining key pathway intermediates, ultimately allowing us to determine the full structures of the bartolosides. This work illustrates the power of genomics to enable the use of biosynthetic information for structure elucidation. 相似文献
995.
996.
F.M.L. Almeida Jr. Y.A. Coutinho J.A. Martins Simñoes M.A.B. do Vale S. Wulck 《The European Physical Journal C - Particles and Fields》2001,22(2):277-281
The possibility of detecting single heavy Dirac and/or Majorana neutrinos at LEP II is investigated for heavy neutrino masses
in the range . We study the process as a clear signature for heavy neutrinos. Numerical estimates for cross sections and distributions for the signal and the
background are calculated and a Monte Carlo reconstruction of final state particles after hadronization is presented.
Received: 20 September 2001 / Published online: 12 November 2001 相似文献
997.
Marcos A. P. Martins Rogrio A. Freitag Adriano Da Rosa Alex F. C. Flores Nilo Zanatta Helio G. Bonacorso 《Journal of heterocyclic chemistry》1999,36(1):217-220
A one-pot synthesis of 1-methyl- and 1-phenylpyrazole-3(5)-ethyl esters 2,3a-e by the cyclocondensation of β-alkoxyvinyl trichloromethyl ketones 1a-e with methyl and phenyl hydrazine hydrochloride under mild conditions, is reported. A study using compounds 1a-e with different substituents proved that these are versatile building blocks for the synthesis of pyrazole derivatives, having a 3(5)-ethoxycarbonyl substituent in good yields (60–89%). The hydrazine and β-alkoxyvinyl trichloromethyl ketone substituent effects on the reaction regiochemistry on the formation of the 1,3- and 1,5-isomer were observed. 相似文献
998.
Cynthia M. C. Prado-Manso Ednalva A. Vidoto Fbio S. Vinhado Hrica C. Sacco Katia J. Ciuffi Patrícia R. Martins Antnio G. Ferreira John R. Lindsay-Smith Otaciro R. Nascimento Yassuko Iamamoto 《Journal of molecular catalysis. A, Chemical》1999,150(1-2):251-266
The synthesis, characterization and catalytic activity of the cationic iron porphyrins Fe[M(4-N-MePy)TDCPP]Cl2 and Fe[M(4-N-MePy)TFPP]Cl2 in the epoxidation of (Z)-cyclooctene by PhIO in homogeneous solution and supported on silica gel (SG), imidazole propyl gel (IPG) or SG modified with 2-(4-sulfonatophenyl)ethyl groups (SiSO3) have been accomplished. When supported on IPG, both cationic FeP bind to the support via Fe–imidazole coordination. Fe[M(4-N-MePy)TDCPP]IPG contains a mixture of low-spin bis-coordinated FeIIIP and high-spin mono-coordinated FeIIIP species, whereas Fe[M(4-N-MePy)TFPP]IPG only contains high-spin mono-coordinated FeIIIP. These FePIPG catalysts also contain FeIIP species, whose presence was confirmed by EPR spectroscopy using NO as a paramagnetic probe. Both cationic FePs coordinate to SG through Fe–O ligation and they are present as high-spin FeIIIP species. The cationic FePs supported on SiSO3− are also high-spin FeIIIP species and they bind to the support via electrostatic interaction between the 4-N-methylpyridyl groups and the SO3− groups present on the matrix. In homogeneous solution, both Fe[M(4-N-MePy)TDCPP]Cl2 and Fe[M(4-N-MePy)TFPP]Cl2 have similar catalytic activity to Fe(TDCPP)Cl and Fe(TFPP)Cl, leading to cis-epoxycyclooctane yields of 92%. When supported on inorganic matrices, both FePs lead to epoxide yields comparable to their homogeneous analogues and their anchoring enables catalyst recovery and re-use. Recycling of Fe[M(4-N-MePy)TDCPP]SiSO3− shows that this FeP maintains its activity in a second reaction. 相似文献
999.
Phillip Hamer Gabrielle Bourret‐Sicotte George Martins Alison Wenham Ruy S. Bonilla Peter Wilshaw 《固体物理学:研究快报》2017,11(5)
Palladium membranes have been used for decades for the separation of hydrogen from other gasses. In this letter the use of thin palladium leaves to act as sources of atomic hydrogen for silicon samples is explored. It has been assumed in the past that although hydrogen diffuses through palladium in atomic form, the atoms recombine to form molecular hydrogen at the surface. In this letter it is shown that hydrogen supplied to one surface of a palladium leaf can result in atomic hydrogen being released from the opposite surface at low pressure. This is demonstrated through the use of a palladium leaf in a direct plasma system which allows for atomic hydrogen to be supplied to a sample while avoiding exposure to UV radiation from the plasma and high energy charged particles. This method is shown to provide significant atomic hydrogen to silicon samples and improve passivation of silicon surfaces. Method of Shielded Hydrogen Passivation: Schematic of direct plasma chamber with a shield inserted between the plasma and the silicon sample. 相似文献
1000.
S.L. Martins M.G.C. Resende C.C. Ribeiro P.M. Pardalos 《Journal of Global Optimization》2000,17(1-4):267-283
In this paper, we present a parallel greedy randomized adaptive search procedure (GRASP) for the Steiner problem in graphs. GRASP is a two-phase metaheuristic. In the first phase, solutions are constructed using a greedy randomized procedure. Local search is applied in the second phase, leading to a local minimum with respect to a specified neighborhood. In the Steiner problem in graphs, feasible solutions can be characterized by their non-terminal nodes (Steiner nodes) or by their key-paths. According to this characterization, two GRASP procedures are described using different local search strategies. Both use an identical construction procedure. The first uses a node-based neighborhood for local search, while the second uses a path-based neighborhood. Computational results comparing the two procedures show that while the node-based variant produces better quality solutions, the path-based variant is about twice as fast. A hybrid GRASP procedure combining the two neighborhood search strategies is then proposed. Computational experiments with a parallel implementation of the hybrid procedure are reported, showing that the algorithm found optimal solutions for 45 out of 60 benchmark instances and was never off by more than 4% of the optimal solution value. The average speedup results observed for the test problems show that increasing the number of processors reduces elapsed times with increasing speedups. Moreover, the main contribution of the parallel algorithm concerns the fact that larger speedups of the same order of the number of processors are obtained exactly for the most difficult problems. 相似文献