全文获取类型
收费全文 | 601篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 408篇 |
晶体学 | 4篇 |
力学 | 17篇 |
数学 | 72篇 |
物理学 | 121篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 18篇 |
2020年 | 18篇 |
2019年 | 11篇 |
2018年 | 18篇 |
2017年 | 12篇 |
2016年 | 26篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 32篇 |
2012年 | 33篇 |
2011年 | 42篇 |
2010年 | 25篇 |
2009年 | 21篇 |
2008年 | 39篇 |
2007年 | 45篇 |
2006年 | 27篇 |
2005年 | 24篇 |
2004年 | 39篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有622条查询结果,搜索用时 15 毫秒
141.
Javier E. Alfonso-Ramos Ruben Van Lommel David Hernández-Castillo Prof. Frank De Proft Roy González-Alemán Prof. Erik V. Van der Eycken Gerardo M. Ojeda-Carralero 《European journal of organic chemistry》2023,26(3):e202201028
1,3-Dipolar cycloadditions are the preferred method to generate five-membered heterocyclic rings. Surprisingly, cycloadditions based on acyl-isocyanide ylides have remained underexplored by the chemical community. Acyl-isocyanide ylides readily react with dipolarophiles, such as substituted alkenes, to yield Δ1-pyrroline derivatives. As an explanation for the observed reactivity of this reaction is lacking, extensive density functional theory calculations were performed to scrutinize the mechanistic features of the transformation. Herein we explain the experimental outcome of the reaction using a variety of reactivity theories and predict opposed regioselectivity for electron-poor and electron-rich dipolarophiles. With the insights obtained, we hope to incentivize the design of new cycloaddition reactions based on the acyl-isocyanide ylides motif. 相似文献
142.
Elena Ochoa Ochoa Gerardo Gómez Ávalos Jaime E. Muñoz Rivera 《Mathematical Methods in the Applied Sciences》2020,43(17):9805-9813
We consider the Timoshenko model with partial dissipative boundary condition with delay, and we prove that the solution decays exponentially to zero, provided the wave speed are equal; this improve earlier result due to Bassam et al and Muñoz Rivera and Naso. Moreover, consider the exponential stability to the corresponding semilinear problems. 相似文献
143.
Marco Antonio Ibarra-Valencia Gerardo Pvel Espino-Solis Blanca Elisa Estrada Gerardo Corzo 《Molecules (Basel, Switzerland)》2021,26(18)
In vitro assays of phagocytic activity showed that the peptide Pin2[G] stimulates phagocytosis in BMDM cells from 0.15 to 1.25 μg/mL, and in RAW 264.7 cells at 0.31 μg/mL. In the same way, the peptide FA1 induced phagocytosis in BMDM cells from 1.17 to 4.69 μg/mL and in RAW 264.7 cells at 150 μg/mL. Cytokine profiles of uninfected RAW 264.7 showed that Pin2[G] increased liberation TNF (from 1.25 to 10 μg/mL) and MCP-1 (10 μg/mL), and FA1 also increased the release of TNF (from 18.75 to 75 μg/mL) but did not increase the liberation of MCP-1. In RAW 264.7 macrophages infected with Salmonella enterica serovar Typhimurium, the expression of TNF increases with Pin2[G] (1.25–10 μg/mL) or FA1 (18.75–75 μg/mL). In these cells, FA1 also increases the expression of IL-12p70, IL-10 and IFN-γ when applied at concentrations of 37.5, 75 and 150 μg/mL, respectively. On the other hand, stimulation with 1.25 and 10 μg/mL of Pin2[G] promotes the expression of MCP-1 and IL-12p70, respectively. Finally, peptides treatment did not resolve murine gastric infection, but improves their physical condition. Cytokine profiles showed that FA1 reduces IFN-γ and MCP-1 but increases IL-10, while Pin2[G] reduces IFN-γ but increases the liberation of IL-6 and IL-12p70. This data suggests a promising activity of FA1 and Pin2[G] as immunomodulators of gastric infections in S. Typhimurium. 相似文献
144.
145.
Horacio J. Salavagione Gerardo Martínez Rafael Gómez José L. Segura 《Journal of polymer science. Part A, Polymer chemistry》2010,48(16):3613-3622
A new material has been prepared by covalent attachment of a perylene derivative, N‐(carboxyphenyl)‐N′‐(8‐pentadecyl)perylene‐3,4:9,10‐bis(dicarboximide) (PDI‐COOH), to poly(vinyl alcohol) (PVA) by esterification. The perylenediimide (PDI)‐modified PVA polymers are soluble in water and dimethylsulfoxide (DMSO). This solubility is conferred to the insoluble perylene derivative by the water‐soluble polymer. The materials have been characterized by hydrogen‐nuclear magnetic resonance, Fourier transform infrared spectra, X‐ray diffraction, and X‐ray photoelectron spectroscopy confirming the covalent attachment of the PDI to the polymer chains. The significant changes in the crystalline parameters and the thermal stability observed for the polymer after the esterification also confirm the covalent linkage with PDI. In addition, the PDI‐modified PVA shows good fluorescence both in solution (quantum yield ~0.2–0.25) and in solid suggesting that the PDI retains largely its photochemical and photophysical properties after immobilization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3613–3622, 2010 相似文献
146.
Carmen Diez-Pardos Alvaro Valdés Rita Prosmiti Pablo Villarreal Gerardo Delgado-Barrio 《Theoretical chemistry accounts》2007,118(3):511-517
In the present study, the validity of the pairwise additivity of the interactions, derived from the Rg2 and Rg-dihalogen CCSD(T) potentials, is investigated by means of ab initio electronic structure and quantum-mechanical calculations. The topology of the potential surfaces of three different types
of Rg2–dihalogen vdW complexes is studied and general trends within the Rg2–dihalogen family are discussed. Calculations of vibrational energies, including all five intermolecular degrees of freedom,
are performed on such pairwise-additive potentials. The results are compared with experimental data from high-resolution spectroscopy,
and provide further information on the additivity of the intermolecular forces for the He2-dihalogen trimers.
Contribution to the Serafin Fraga Memorial Issue. 相似文献
147.
Gerardo Cisneros 《Journal of computational chemistry》1993,14(4):452-454
We present an improvement to Johnson, Gill, and Pople's results for reducing the cost of using the McMurchie–Davidson RNLM recurrence relation for one-center integrals. Recursive replacement of singly referenced and single-term auxiliary integrals results in floating point operation (FLOP ) savings of up to 11% and explicit auxiliary integral calculation reductions of up to 76% with respect to the full list and up to 46% with respect to FLOP-reduced lists with no replacement. The programs are written in the string-manipulation language Convert; one of the programs automatically generates a FORTRAN subroutine given an integral list. © 1993 John Wiley & Sons, Inc. 相似文献
148.
Gerardo F. Torres del Castillo 《Communications in Mathematical Physics》1984,92(4):485-490
The equations for theD(k, 0) Killing spinor fields are integrated assuming that the left conformal curvature does not vanish and that eitherk 2, 4, 6, ..., or the Einstein vacuum field equations are satisfied. 相似文献
149.
A comparative study of the physicochemical properties of perfluorinated and hydrogenated amphiphiles
Blanco E González-Pérez A Ruso JM Pedrido R Prieto G Sarmiento F 《Journal of colloid and interface science》2005,288(1):247-260
In this work we studied and compared the physicochemical properties of perfluorinated (sodium perfluoroheptanoate, C7FONa, and perfluorooctanoate, C8FONa) and hydrogenated (sodium octanoate, C8HONa, decanoate, C10HONa, and dodecanoate, C12HONa) amphiphiles. First, we determined their Krafft points to study the solubility and appropriate temperature range of micellization of these compounds. The critical micelle concentration (cmc) and ionization degree of micellization (beta) as a function of temperature (T) were estimated from conductivity data. Plots of cmc vs T appear to follow the typical U-shaped curve with a minimum T(min). The results show that the surfactants with CF2/CH2 ratio of 1.5 between alkyl chains (C12HONa-C8FONa and C10HONa-C7FONa) have nearly the same minimum value for cmc against temperature. The comparison between the cmc of hydrogenated amphiphiles and the corresponding perfluorinated amphiphiles must be done at this point. Thermodynamic functions of micellization were obtained by applying different theoretical models and choosing the one that best fit our experimental data. Although perfluorinated and hydrogenated amphiphiles present similar thermodynamic behavior, we have found a variation of 1.3 to 1.7 in the CF2/CH2 ratio, which did not remain constant with temperature. In the second part of this study the apparent molar volumes and adiabatic compressibilities were determined from density and ultrasound velocity measurements. Apparent molar volumes at infinite dilution presented the ratio 1.5 between alkyl chains again. However, apparent molar volumes upon micellization for sodium perfluoroheptanoate indicated a different aggregation pattern. 相似文献
150.
Sabín J Prieto G Messina PV Ruso JM Hidalgo-Alvarez R Sarmiento F 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):10968-10975
This work deals with the effect of Ca2+ and La3+ on the colloidal stability of phosphatidylcholine (PC) liposomes in aqueous media. As physical techniques, nephelometry, photon correlation spectroscopy, electrophoretic mobility, and surface tension were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersity values were observed as La3+ concentration increases, suggesting that this cation induces the aggregation of liposomes. However, changes in polydispersity were not observed with Ca2+, suggesting a coalescence mechanism or fusion of liposomes. The stability factor (W), calculated from the nephelometry measurements indicated that aggregation/fusion occurs at a critical concentration (c.c.) of 0.3 and 0.7 M for La3+ and Ca2+, respectively. To gain a better insight into the interaction mechanism between the liposomes and the studied ions, the interaction between PC monolayers and Ca2+ and La3+ was studied. Changes in the surface area per lipid molecule (A0) in the monolayer at the c.c. values were found for both ions, with a more pronounced effect in the case of Ca2+. This corresponds with a larger reduction of the steric repulsive interaction between the headgroups at the phospholipid membrane (pi(head)). The experimental result validates the hypothesis made on the liposome fusion in the presence of Ca2+ and liposome aggregation in the presence of La3+. These aggregation mechanisms have also been confirmed by transmission electron microscopy. 相似文献