全文获取类型
收费全文 | 1258篇 |
免费 | 52篇 |
国内免费 | 5篇 |
专业分类
化学 | 1073篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 157篇 |
物理学 | 70篇 |
出版年
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 38篇 |
2020年 | 23篇 |
2019年 | 19篇 |
2018年 | 18篇 |
2017年 | 17篇 |
2016年 | 44篇 |
2015年 | 37篇 |
2014年 | 35篇 |
2013年 | 57篇 |
2012年 | 78篇 |
2011年 | 88篇 |
2010年 | 50篇 |
2009年 | 51篇 |
2008年 | 75篇 |
2007年 | 79篇 |
2006年 | 79篇 |
2005年 | 71篇 |
2004年 | 63篇 |
2003年 | 64篇 |
2002年 | 43篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1973年 | 3篇 |
排序方式: 共有1315条查询结果,搜索用时 15 毫秒
41.
Luisa Fernanda Rojas Paola Zapata Laura Ruiz-Tirado 《Current Opinion in Green and Sustainable Chemistry》2022
According to the Food and Agriculture Organization of the United Nations, approximately 1.3 billion tons of food is wasted each year, equivalent to approximately one-third of world production. Agri-food wastes are the source of proteins, carbohydrates, lipids, and other essential minerals that have been exploited for value-added products by the development of biorefineries and sustainable business as important elements of circular economies. The innovation and materialization of these types of processes, including the use of disruptive technologies on microbial bioconversion and enzyme technology, such as nanotechnology, metabolic engineering, and multi-omics platforms, increase the perspectives on the waste valorization process. Lignocellulolytic enzymes, pectinases, and proteases are mainly used as catalyzers on agri-food waste treatment, and their production in house might be the trend in near future for agro-industrial countries. Another way to transform the agri-food wastes is via aerobic or anaerobic microbial process from fungal or bacterial cultures; these processes are the key to produce waste enzymes. 相似文献
42.
43.
Yolanda Prieto Marcelo Muoz Vernica Arancibia Mauricio Valderrama Fernando J. Lahoz M. Luisa Martín 《Polyhedron》2007,26(18):5527-5532
The reaction of the dimer complex [{Ru(CO)3Cl2}2] with the ligands 4,6-dichloroquinoline-5,8-dione and 6-methoxybenzo[g]quinoline-5,10-dione in ethanol solution led to the neutral mononuclear complexes of general formula [Ru(CO)2Cl2(κ2-quinolinedione-N,O)]. The complexes were characterized by elemental analysis, IR and RMN spectroscopy, and the molecular structure of [Ru(CO)2Cl2(6-methoxybenzo[g]quinoline-5,10-dione)] was determined by single-crystal X-ray diffraction. The redox chemistry of ligands and complexes was investigated by cyclic voltammetry, and their potential antitumor activity was also evaluated. 相似文献
44.
Francesca Goldoni Dario Iarossi Adele Mucci Luisa Schenetti 《Journal of heterocyclic chemistry》1997,34(6):1801-1804
3,4′-Dibromo-2,2′-bithiophene was converted, in high yield, into the corresponding dibutoxy derivative. The 1H 13C and nmr data are discussed in comparison with those of 3,3′- and 4,4′-dibutoxy-2,2′-bithiophene in relation to regiochemistry. 相似文献
45.
The capacity for anaerobic decolorization of a sulfonated azo dye, Congo Red, by a strain of a sulfate-reducing bacterium
was evaluated. After optimizing the growth rate of the bacteria on a simple carbon source and terminal electron acceptor pair,
lactate and sulfate, respectively, the effect of the dye concentration on their growth rate was analyzed. The decolorization
rate was affected by the dye concentration in the growth medium. The azo-bond cleavage mechanism of reductive decolorization
with the formation of benzidine was consistent with the results, as this metabolite was identified by high-performance liquid
chromatography. Several fractions of the culture medium, including lysed cell extracts, were examined for the capacity to
reduce the azo dye. This reduction capacity was found in the culture medium in which the cells had previously grown. The results
showed that the mechanism of reductive decolorization of this sulfonated azo dye was extracellular and nonenzymatic, consistent
with the production of sulfide anion by the microorganisms while growing on lactate and sulfate. The sulfide anions were the
cause of the reduction leading to the disappearance of color in the medium. To increase the rate of decolorization, the presence
of ferrous ion was also necessary together with the lactate and sulfate substrates. 相似文献
46.
Jose G. Trujillo‐Ferrara Rosa Luisa Santilln‐Baca Norberto Farfn‐García Itzia I. Padilla‐Martínez Efrn V. García‐Bez 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(3):o125-o128
The molecular and supramolecular structures of 2‐(1,3‐dioxo‐2,3,3a,4,7,7a‐hexahydro‐1H‐isoindol‐2‐yl)phenyl acetate, C16‐H15NO4, (I), and its para isomer, 4‐(1,3‐dioxo‐2,3,3a,4,7,7a‐hexahydro‐1H‐isoindol‐2‐yl)phenyl acetate, (II), are reported. The torsion angle between the succinimide and benzene rings depends on the position of the acetoxy substitution [89.7 (1) and 61.9 (1)° for (I) and (II), respectively]. The twist of the acetoxy group relative to the mean plane of the benzene ring is almost independent of the acetoxy position [66.0 (1) and 70.0 (1)°]. Packing interactions for both compounds include soft C—H⋯X (X = O and Ph) interactions, forming chains of centrosymmetric dimers and interlinked chains for (I) and (II), respectively. In addition, three perpendicular dipole C=O⋯C=O interactions contribute to the supramolecular structure of (II). 相似文献
47.
del Mar Graciani M Rodríguez A Muñoz M Moyá ML 《Journal of colloid and interface science》2001,235(2):260-264
The reaction of dehydrobromination of 2-(p-nitrophenyl)ethyl bromide with hydroxide ions has been studied in aqueous micellar solutions of N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, SB3-14. The kinetic effects of added salts (NaF, NaCl, NaBr, and NaNO(3)) on the reaction rate in SB3-14 aqueous micellar solutions have also been studied. They were rationalized by considering the binding of the anions, which come from the salt, to the sulfobetaine micelles and their competition with the reactive hydroxide ions for the micellar surface. The equilibrium binding constant of the 2-(p-nitrophenyl)ethyl bromide to the sulfobetaine micelles was estimated by recording the changes in the spectra of the organic substrate when the SB3-14 concentration in the micellar medium changed. This value was in agreement with that obtained from fitting of kinetic data. The second-order rate constant in the micellar pseudophase revealed that the reaction is faster in SB3-14 micelles than in water. This acceleration seems independent of the presence of added salts and can be explained by considering that SB3-14 micelles favor reactions in which charge is delocalized in the transition state. Copyright 2001 Academic Press. 相似文献
48.
49.
Maria Luisa Moyá Antonio Barrios Maria del Mar Graciani Rafael Jiménez Ernestina Muñoz Francisco Sánchez John Burgess 《Transition Metal Chemistry》1991,16(2):165-168
Summary The kinetics of replacement of 4,4-bipyridine, (4,4-bipy), and 4-cyanopyridine, (4-CNpy), by cyanide in [Fe(CN)5-(4,4-bipy)]3-. at 298 K have been studied in binary aqueous mixtures containing different amounts of t-butanol, methanol, glycerol, ethyleneglycol and sucrose. The plots of logarithms of the limiting rate constantsversus the mole fraction of water are linear over the entire composition range studied, showing the importance of solvation phenomena. A different straight line of log (kL/s–1)versus XH2O is obtained for each mixture, indicating the influence of other solvent parameters on the reaction rate. A multiparameter regression of G
exp
with A (acidity vector), B (basicity vector) and GE is used for both reactions; plots of G
calc
versus G
exp
are linear with slopes of near unity. 相似文献
50.
2-and 4-Ethoxymethoxybenzyl methyl ethers were employied as useful starting materials for the synthesis of 1,2- or 1,4-dicarbo-substituted benzenes. The proposed reaction sequence involves connection between the reductive lithiation of benzyl alkyl ethers and the metal-catalyzed cross-coupling reaction of aromatic triflates. 相似文献