全文获取类型
收费全文 | 1183篇 |
免费 | 56篇 |
国内免费 | 8篇 |
专业分类
化学 | 756篇 |
晶体学 | 9篇 |
力学 | 46篇 |
数学 | 250篇 |
物理学 | 186篇 |
出版年
2023年 | 14篇 |
2022年 | 25篇 |
2021年 | 23篇 |
2020年 | 34篇 |
2019年 | 25篇 |
2018年 | 27篇 |
2017年 | 19篇 |
2016年 | 70篇 |
2015年 | 28篇 |
2014年 | 39篇 |
2013年 | 89篇 |
2012年 | 102篇 |
2011年 | 98篇 |
2010年 | 60篇 |
2009年 | 37篇 |
2008年 | 70篇 |
2007年 | 70篇 |
2006年 | 56篇 |
2005年 | 68篇 |
2004年 | 22篇 |
2003年 | 31篇 |
2002年 | 29篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 10篇 |
1972年 | 4篇 |
1970年 | 2篇 |
1966年 | 4篇 |
排序方式: 共有1247条查询结果,搜索用时 15 毫秒
71.
72.
Bonhommeau S Bréfuel N Pálfi VK Molnár G Zwick A Salmon L Tuchagues JP Sanchez Costa J Létard JF Paulsen H Bousseksou A 《Physical chemistry chemical physics : PCCP》2005,7(15):2909-2914
A quasi-quantitative photo-induced low-spin (LS)-->high-spin (HS) conversion of FeII ions has been observed in the [Fe(TRIM)2]Cl2 complex by irradiating the sample with blue light (488 nm) at 10 K. The time dependence of the HS-->LS relaxation has been studied between 10 K and 44 K by means of magnetic susceptibility measurements. These relaxation curves could be satisfactorily fitted by mono-exponential decays including tunnelling effect except for temperatures below 30 K. The introduction of a distribution of vibrational frequencies into this model improved significantly the fits in the low-temperature range and gave a good agreement with the experimental data in the whole temperature range suggesting a multi-rate relaxation process in this complex. 相似文献
73.
Natalia Castro Christine Raynaud Antoine Rouilly Luc Rigal Christian Quellet 《高分子科学杂志,C辑:聚合物评论》2016,56(1):137-186
Encapsulation of flavor and aroma compounds has been largely explored in order to meet appraisal demands from consumers by improving the impact of flavor during the consumption of food products. Even though several techniques have been used for encapsulating volatile compounds, i.e., spray drying, fluidized bed coating, coacervation, and melt extrusion, those most frequently used in the food industry are spray drying and melt extrusion. In this article, the different techniques of encapsulation of flavors and fragrances in polymer-based matrices by extrusion are reviewed and partly re-defined, emphasizing the differences between the various techniques reported so far and the role of matrix types, additives, and operative conditions. Also, the role of water as a key parameter for controlled release and shelf stability of the delivery system will be discussed. 相似文献
74.
Baeten V von Holst C Garrido A Vancutsem J Michotte Renier A Dardenne P 《Analytical and bioanalytical chemistry》2005,382(1):149-157
In this paper we present an alternative method for detection of meat and bone meal (MBM) in feedstuffs by near-infrared microscopic (NIRM) analysis of the particles in the sediment fraction (dense fraction (d >1.62) from dichloroethylene) of compound feeds. To apply this method the particles of the sediment fraction are spread on a sample holder and presented to the NIR microscope. By using the pointer of the microscope the infrared beam is focussed on each particle and the NIR spectrum (1112–2500 nm) is collected. This method can be used to detect the presence of MBM at concentrations as low as 0.05% mass fraction. When results from the NIRM method were compared with the classical microscopic method, a coefficient of determination (R2) of 0.87 was obtained. The results of this study demonstrated that this method could be proposed as a complementary tool for the detection of banned MBM in feedstuffs by reinforcement of the monitoring of feeds. 相似文献
75.
Ben Yahia H Gaudin E Darriet J Banks M Kremer RK Villesuzanne A Whangbo MH 《Inorganic chemistry》2005,44(9):3087-3093
A new magnetic oxide, CuMnVO4, was prepared, and its crystal structure was determined by single-crystal X-ray diffraction. The magnetic properties of CuMnVO4 were characterized by magnetic susceptibility and specific heat measurements, and the spin exchange interactions of CuMnVO4 were analyzed on the basis of spin-polarized electronic band structure calculations. CuMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra containing high-spin Mn2+ cations. Our work shows that CuMnVO4 undergoes a three-dimensional antiferromagnetic transition at approximately 20 K. Both the intrachain and interchain spin exchanges are antiferromagnetic, and the interchain spin exchange is not negligible compared to the intrachain spin exchange. 相似文献
76.
Antoine Aboukais Elena A. Zhilinskaya Jean-Franois Lamonier Igor N. Filimonov 《Colloids and surfaces. A, Physicochemical and engineering aspects》2005,260(1-3):199-207
Oxygen adsorption experiments were performed on evacuated and prereduced CeO2/SiO2 and CeO2/Al2O3 catalysts with and without platinum. Considerable amounts of the superoxide radical ions were stabilized on all the samples. Signal parameters suggest Ce4+–O2− positioning for all detectable superoxide species. Physisorbed oxygen broadens O2− signal beyond detection for all the alumina-based samples, while the same procedure for all the silica-based samples did not change signal shape of O2− species. Detectable O2− species are localized in the bulk of ceria and the nature of support (silica or alumina) determines the number of oxygen vacancies and the rate of electron transfer. XRD data suggest that for alumina-based samples small and/or thin islands of ceria dominate, while comparatively large ceria particles are stabilized on the surface of silica-based samples with the same ceria content. Average size of ceria crystallites is still not determining factor and cannot account for the observed differences. Higher concentrations of paramagnetic species may be stabilized on alumina-based samples and thus, sensor-like behavior towards gaseous oxygen at room temperature was detected for them—oxygen admission reversibly changes superoxide lineshape. For silica samples, only minor changes of O2− lineshapes were typical upon the change of the partial pressure of oxygen at ambient and low temperatures. Addition of platinum has little effect on parameters of the O2− signal, except an enhancement of the superoxide decay in the reducing media. Possible site for O2− stabilization inside the lattice of CeO2 was proposed and relevance of the observed effects to the redox catalysis discussed. 相似文献
77.
Sylvie Malo Antoine Maignan Sylvain Marinel Maryvonne Hervieu Kenneth R. Poeppelmeier Bernard Raveau 《Solid State Sciences》2005,7(12):1492
Recently, the ferroelectromagnet YMnO3 has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature 80 K) and ferroelectricity (Curie temperature 914 K). There have been no reports of complete YMn1−xMxO3 solid solutions in which substitution of the foreign M cation preserves the hexagonal P63cm structure. In contrast there exist several homeotypic phases with the general formula, Ln1+nCunMO3+3n (n=1 (M=Ti), 2 (M=V) and 3 (M=Mo); Ln: lanthanide). Several YMn1−x(Cu3/4Mo1/4)xO3 compounds have been synthesized. The solid solution, from YMnO3 (x=0) to YCu3/4Mo1/4O3 (x=1) has been characterized by X-ray diffraction and transmission electron microscopy study. For 0<x<0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P63cm, of YMnO3. The Mn-free end member, x=1, crystallizes in a complex multiple cell, the superstructure being associated to Cu3+/Mo6+ cationic ordering. Dilution of the Mn3+ magnetic array by the paramagnetic (Cu2+) and diamagnetic (Mo6+) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x0.5 compositions. 相似文献
78.
79.
Angela Milinkovic Dr. Antoine Dupé Ao. Univ.-Prof. Dr. Ferdinand Belaj Univ.-Prof. Dr. Nadia C. Mösch-Zanetti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(55):e202201867
Molybdenum(VI) bis(imido) complexes [Mo(NtBu)2(LR)2] (R=H 1 a ; R=CF3 1 b ) combined with B(C6F5)3 ( 1 a /B(C6F5)3, 1 b /B(C6F5)3) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H2 and Et3SiH affords ion pairs [Mo(NtBu)(NHtBu)(LR)2][HB(C6F5)3] (R=H 2 a ; R=CF3 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H2O leads to [Mo(NtBu)(NHtBu)(LR)2][(HO)B(C6F5)3] (R=H 3 a ; R=CF3 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of [HB(C6F5)3]−. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(LR)2][{PhCH2O}B(C6F5)3] (R=H 4 a ; R=CF3 4 b ). Catalysis occurs at [HB(C6F5)3]− while [Mo(NtBu)(NHtBu)(LR)2]+ (R=H or CF3) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC). 相似文献
80.
Dr. Raphaël Nougué Dr. Shintaro Takahashi Dr. Aymeric Dajnak Dr. Eddy Maerten Dr. Antoine Baceiredo Dr. Nathalie Saffon-Merceron Prof. Vicenç Branchadell Dr. Tsuyoshi Kato 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202037
Several base-stabilized silyliumylidene ions ( 2 and 3 ) with different ligands were synthesized. Their behaviour appeared strongly dependent on the nature of ligand. Indeed, in contrast to the poorly reactive silyliumylidene ions 3 c,d stabilized by strongly donating ligands (DMAP, NHC), the silylene- and sulfide-supported one ( 2-H and 3 a ) exhibits higher reactivity toward various small molecules. Furthermore, their capability to successively activate multiple small molecules was clearly demonstrated by processes involving successive reactions with silane/formamide, CO2 and H2. Moreover, HBPin adduct of 3 a ( 8-C ) catalyzes the hydroboration of pyridine. Of particular interest, silylene-supported silyliumylidene complex 2-H is one of the rare species able to activate two H2 molecules. 相似文献