全文获取类型
收费全文 | 1969篇 |
免费 | 79篇 |
国内免费 | 8篇 |
专业分类
化学 | 1291篇 |
晶体学 | 11篇 |
力学 | 34篇 |
数学 | 277篇 |
物理学 | 443篇 |
出版年
2023年 | 10篇 |
2022年 | 27篇 |
2021年 | 43篇 |
2020年 | 36篇 |
2019年 | 36篇 |
2018年 | 22篇 |
2017年 | 34篇 |
2016年 | 51篇 |
2015年 | 59篇 |
2014年 | 73篇 |
2013年 | 109篇 |
2012年 | 119篇 |
2011年 | 129篇 |
2010年 | 71篇 |
2009年 | 95篇 |
2008年 | 147篇 |
2007年 | 117篇 |
2006年 | 103篇 |
2005年 | 95篇 |
2004年 | 87篇 |
2003年 | 66篇 |
2002年 | 92篇 |
2001年 | 34篇 |
2000年 | 34篇 |
1999年 | 36篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 23篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1931年 | 3篇 |
排序方式: 共有2056条查询结果,搜索用时 15 毫秒
951.
Torres José L. Grethlein Hans E. Lynd Lee R. 《Applied biochemistry and biotechnology》1989,(1):621-633
High energy costs are associated with the recovery of ethanol from fermentation broths. This paper discusses a computer simulation
of the Dartmouth Process, which aims to reduce these costs by the use of IHOSR distillation, extensive heat integration, and
extractive distillation using a salt.
To resolve the uncertainty in modeling alcohol-water-salt vapor-liquid equilibrium, a new and more accurate activity coefficient
model was used. An Aspen™ model was used to generate capital and energy costs for a range of ethanol concentrations in the
feed. Simulation results show that the Dartmouth Process offers substantial economic advantages over benzene azeotropic distillation,
particularly at low feed concentrations. 相似文献
952.
L. Lima S. Olivares F. Martínez J. Torres D. de la Rosa C. Sepúlveda 《Journal of Radioanalytical and Nuclear Chemistry》1998,237(1-2):35-40
PIXE studies on pure metal targets surrounded by insulating material produced enhanced X-ray yields at comparatively low proton
energies. Specially prepared metal discs of selected transition elements were embedded in Macor target holders and irradiated
with 700 keV protons. Improved X-ray yields of up to more than 300% were observed. It was found that the enhanced yields were
affected by the incident beam current due to a “leakage” effect. The recorded time-dependent spectra showed similar charge
build-up and discharge patterns as those originally obtained for non-conducting samples. A possible mechanism for the enhancement
is discussed. 相似文献
953.
Mantilla A Tzompantzi F Ferrat G López-Ortega A Romero E Ortiz-Islas E Gómez R Torres M 《Chemical communications (Cambridge, England)》2004,(13):1498-1499
Oligomerization reaction was carried out at room temperature using sulfated titania as catalyst. Total isobutene conversion was obtained with high stability for a long period of time. In case of deactivation, total reactivation of the catalyst was reached. 相似文献
954.
Summary The synthesis and analytical properties of di(2-pyridyl) methylene 2-furoylhydrazone (DPFH) are described. The solubility, spectral characteristics, andpK values are reported, as well as the absorptivity of metal chelates formed. The reaction between iron and DPFH has been studied by spectrophotometry. The green 12 iron: DPFH complex (=8.4×103l·-mole–1·cm–1 at 620 nm) is formed at pH 5.3–11.3. The effect of interferences has been studied and the method applied to the determination of iron in cement, with good results.
Di-(2-pyridyl)methylen-2-furoylhydrazon als analytisches Reagens zur spektrophotometrischen Bestimmung von Eisenspuren
Zusammenfassung Synthese und analytische Eigenschaften von Di(2-pyridylmethylen-2-furoylhydrazon wurden beschrieben. Die Löslichkeit, die Spektraleigenschaften, diepK-Werte und die Absorptivität seiner Metall-Chelate wurden angegeben. Der grüne 12-Komplex mit Eisen bildet sich bei pH 5, 3-11, 3. Störfaktoren wurden untersucht und die Eisenbestimmung in Zement beschrieben.相似文献
955.
Emiliano Braña Delfina Quiñone Sebastián Martínez Joaquín Grassi Ignacio Carrera Julia Torres 《Journal of Coordination Chemistry》2016,69(24):3650-3663
Three new polynuclear compounds based on a dicarboxylic acid ligand are reported. In particular, two Cu(II) coordination compounds, [Cu2(H2O)6(Hbzlidp)2](CF3SO3)2·2H2O (1) and [Cu(NO3)(Hbzlidp)]∞ (2) (bzlidp2? = N-benzyliminodipropionate anion), and a Ni(II) dinuclear compound, [Ni2(H2O)4(bzlidp)2] (3), were synthesized and characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction. Different structures were obtained depending on the reaction conditions. The structural analyses reveal that 1 was formed by dinuclear [Cu2(H2O)6(Hbzlidp)2]2+ units built by two copper(II) ions joined through two Hbzlidp? ligands, while 2 was formed by pairs of Cu(II) centers bridged by four syn,syn carboxylate groups to generate “paddle wheel” units. The dinuclear copper units are arranged in a rhombus type grid, in a 2-D layer structure. In both cases, the N was protonated and not coordinated to the metal center. Compound 3 was formed by [Ni2(H2O)4(bzlidp)2] neutral dinuclear units, with octahedral Ni(II) centers. Solution studies of the ligand–M(II) systems (M(II) = Mn, Co, Ni, Cu, Zn, Cd, and Pb) were also carried out. 相似文献
956.
Liliane Henrique Torres Mohana Zorkot de Carvalho Patrícia da Silva Melo Eneida de Paula Adelir Aparecida Saczk Luciana de Matos Alves Pinto 《Journal of inclusion phenomena and macrocyclic chemistry》2018,91(1-2):9-15
Benzocaine (BZC), is a local anesthetic widely used in topical formulations as well as in throat pastilles. A disadvantage is that the compound presents low aqueous solubility. The present work describes the preparation and characterization of an inclusion complex between BZC and β-cyclodextrin (β-CD), followed by cytotoxicity assays. The association constant (Ka) was calculated using solubility isotherms, at different temperatures, and an HPLC procedure, at room temperature, employing a reverse phase C18 column, with a mobile phase consisting of water/acetonitrile. Ka obtained with solubility isotherms at temperatures of 25, 35, and 45 °C were 229.8, 317.1, and 520.3 M?1, respectively. Employing HPLC, Ka was 38.0 M?1. The difference in the Ka value could be explained because HPLC analyses were conducted using organic solvent, which affected the host–guest interaction. Moreover, the continuous flow could have altered the degree of association of the drug with β-CD. The BZC/CD inclusion complex was characterized using infrared spectroscopy, thermogravimetry, and X-ray diffraction. Analysis showed a good agreement with literature, suggesting that the complex was established. Cytotoxicity assays using fibroblast V79 cells showed that BZC/CD formulation was not cytotoxic, demonstrating its potential to reduce the toxicity of the anesthetic. The assays demonstrated an effective interaction between BZC and CD, and that the inclusion complex was less toxic to V79 cells than the plain BZC, turning it a good alternative to decrease its toxicity when administered to patients. 相似文献
957.
958.
M. Villar Navarro M. Ramos Payán R. Fernández‐Torres M. A. Bello López 《Biomedical chromatography : BMC》2013,27(2):246-253
In this paper two applications of three‐phase HF‐LPME for the determination of pharmaceuticals in human urine are proposed: a capillary electrophoresis with a photodiode array detection method for the analysis of seven nonsteroidal anti‐inflammatory drugs (NSAIDs) and a high‐performance liquid chromatographic with photo diode array and fluorescence detection method for the determination of four sulfonamides and their corresponding N4‐acetyl‐metabolites. Q3/2 Accurel® polypropylene hollow fibers were used for both procedures. Dihexyl ether was used as the supported liquid membrane for the determination of anti‐inflammatories and 1‐octanol for sulfonamides. An aqueous solution (pH 12) was used in both procedures as the acceptor phase and as the donor phase an aqueous solution (pH 2), and a 2 m Na2SO4 aqueous solution (pH 4) was used for the determination of the anti‐inflammatories and sulfonamides. The detection limits obtained were between 0.25 (naproxen) and 0.86 ng/mL (aceclofenac) for the determination of anti‐inflammatories and 7 × 10?4 (sulfamethoxazole) and 0.048 ng/mL (N4‐acetyl‐sulfamethazine) for sulfonamides. The method was successfully applied to the determination of the analytes in human urine. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
959.
960.