全文获取类型
收费全文 | 181篇 |
免费 | 5篇 |
专业分类
化学 | 142篇 |
晶体学 | 4篇 |
力学 | 5篇 |
数学 | 12篇 |
物理学 | 23篇 |
出版年
2020年 | 2篇 |
2019年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 21篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 6篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1972年 | 4篇 |
1968年 | 1篇 |
1967年 | 4篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1954年 | 1篇 |
1897年 | 1篇 |
排序方式: 共有186条查询结果,搜索用时 937 毫秒
141.
Volker Wulf Nils Wienand Michaela Wirtz Hans-Willi Kling Siegmar Gäb Oliver J. Schmitz 《Journal of chromatography. A》2010,1217(5):749-754
Multidimensional gas-chromatographic analyses of olesochemically based nonionic, anionic and several cationic surfactants in industrial cleaners are demonstrated. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry allows the simultaneous determination of fatty alcohols, fatty alcohol sulphates and alkyl polyglucosides. In addition, the determination of fatty alcohol ethoxylates up to C10EO8 (highest degree of ethoxylation) and C18EO5 (longest C-chain at an ethoxylation degree of five) and the analysis of fatty alcohol alkoxylates that contain ethoxy (EO) and propoxy (PO) groups could be realized. Because of decomposition in the injector and a weak EI-fragmentation, cationic surfactants such as alkyl benzyl dimethyl ammonium chloride could also be identified by their characteristic fragments. Thermogravimetric analyses confirmed that the temperature in a normal GC injector is not high enough to cause thermal decomposition of esterquats. However, we could demonstrate that a modified silylation procedure forms decomposition products of esterquats in the GC injector which are detectable by GC × GC–(TOF)MS and allows the identification of such GC-atypical analytes. 相似文献
142.
Wang S Alekseev EV Miller HM Depmeier W Albrecht-Schmitt TE 《Inorganic chemistry》2010,49(21):9755-9757
Molten methylboronic acid has been used as a reactive flux to prepare the first neptunium(V) borate, NpO(2)[B(3)O(4)(OH)(2)] (NpBO-1), and the first actinide boronate, UO(2)(CH(3)BO(2))(H(2)O) (UCBO-1). NpBO-1 contains cation-cation interactions between the neptunyl units. In contrast, the presence of the methyl groups in the uranyl boronate leads to a one-dimensional structure. 相似文献
143.
K. Wille J. Vanden Bussche H. Noppe E. De Wulf P. Van Caeter C.R. Janssen H.F. De Brabander L. Vanhaecke 《Journal of chromatography. A》2010,1217(43):6616-6622
Perfluorinated compounds (PFCs), which are extensively used in a wide variety of applications because of their specific surfactant properties, have recently appeared as an important new class of global environmental pollutants. Quantitative analysis of PFCs in aqueous matrices remains, however, a challenging task. During this study, a new analytical method for the determination of 14 PFCs in surface-, sewage- and seawater was developed and validated. The target analytes were extracted using solid-phase extraction followed by liquid chromatography coupled to a time-of-flight mass spectrometer (LC–ToF-MS). The use of very narrow mass tolerance windows (<10 ppm) resulted in a highly selective MS-technique for the detection of PFCs in complex aqueous matrices. Validation of this analytical method in surface-, sewage- and seawater resulted in limits of quantification (LOQs) varying from 2 to 200 ng L−1, satisfying recoveries (92–134%), and good linearity (R2 = 0.99 for most analytes). Analysis of samples of the North Sea, the Scheldt estuary, and three harbours of the Belgian coastal region led to the detection of four different PFCs. Perfluorooctane sulfonate (PFOS) was found to be the most abundant PFC in levels up to 38.9 ng L−1. 相似文献
144.
Evgeny V. Nazarchuk Oleg I. Siidra Dr. Sergey V. Krivovichev Thomas Malcherek Wulf Depmeier 《无机化学与普通化学杂志》2009,635(8):1231-1235
Two new mixed alkaline uranyl molybdates CsNa3[(UO2)4O4Mo2O8] ( 1 ) and Cs2Na8[(UO2)8O8(Mo5O20)] ( 2 ) have been obtained by high‐temperature solid state reactions. Their crystal structures have been solved by direct methods: Compound 1 : triclinic, P , a = 6.46(1), b = 6.90(1), c = 11.381(2) Å, α = 84.3(1), β = 91.91(1), γ = 80.23(1)°, V = 488.6(2) Å3, R1 = 0.06 for 2865 unique reflections with |Fo| ≥ 4σF; Compound 2 : orthorhombic, Ibam, a = 6.8460(2), b = 23.3855(7), c = 12.3373(3) Å, V = 1975.2(1) Å3, R1 = 0.049 for 2120 unique reflections with |Fo| ≥ 4σF. The structure of 1 contains complex sheets of UrO5 pentagonal bipyramids and molybdenum polyhedra. The sheets have [(UO2)2O2(MoO5)] composition. Natrium and cesium atoms are located in the interlayer space. Cesium atoms are situated between the molybdenum clusters, whereas natrium atoms are segregated between the uranyl complexes. The large Cs+ ions are localized between the Mo2O9 groups and force the molybdenum polyhedra to rotate relative to the [(UO2)2O2(MoO5)] sheets. Such rotation is impossible for U6+ polyhedra due to their rigid edge‐sharing complexes. The distance between the U6+ polyhedra vertices of neighboring layers is 3.8 Å, that allows the Na+ ion to be positioned between the uranyl groups. The crystal structure of 2 is based upon a framework consisting of [(UO2)2O2(MoO5)] sheets parallel to (010). The sheets are linked into a 3‐D framework by sharing vertices with the Mo(2)O4 tetrahedra, located between the sheets. Each MoO4 tetrahedron shares two of its corners with two MoO6 octahedra in the sheet above, and the other two with MoO6 octahedra of the sheet below. Thus four MoO6 octahedra and one MoO4 tetrahedron form chains of composition Mo5O18. The resulting framework has a system of channels occupied by the Cs+ and Na+ ions. 相似文献
145.
Imane Belkyal Dr. Mohamed El Azhari Yuandong Wu Wolfgang Bensch Wulf Depmeier 《无机化学与普通化学杂志》2009,635(11):1600-1603
The single crystal structure of RbPbPS4 was determined at 293 K. The compound crystallizes in the orthorhombic space group Pnma (No. 62) with a = 17.486(1) Å, b = 6.7127(5) Å, c = 6.4191(5) Å, V = 753.5(1) Å3, Z = 4. Differential scanning calorimetry shows a reversible structural phase transition at 182 K on cooling and at 184 K on heating. The phase transition is attributed to the displacement of the lead atoms which are located on the mirror planes at room temperature. In the low temperature modification, the Pb2+ ions are moved away from the mirror plane thus changing the coordination number from seven at low temperature to six at room temperature. The low temperature phase of RbPbPS4 is non‐centrosymmetric with space group P212121, which is a maximal translationengleiche subgroup index 2 (t2) of Pnma. The analysis demonstrates that the phase transition is of second order, or at least nearly so. 相似文献
146.
Importance of the Anchor Group Position (Para versus Meta) in Tetraphenylmethane Tripods: Synthesis and Self‐Assembly Features
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Marcin Lindner Dr. Michal Valášek Jan Homberg Kevin Edelmann Dr. Lukas Gerhard Prof. Dr. Wulf Wulfhekel Dr. Olaf Fuhr Tobias Wächter Prof. Dr. Michael Zharnikov Dr. Viliam Kolivoška Dr. Lubomír Pospíšil Dr. Gábor Mészáros Dr. Magdaléna Hromadová Prof. Dr. Marcel Mayor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(37):13218-13235
The efficient synthesis of tripodal platforms based on tetraphenylmethane with three acetyl‐protected thiol groups in either meta or para positions relative to the central sp3 carbon for deposition on Au (111) surfaces is reported. These platforms are intended to provide a vertical arrangement of the substituent in position 4 of the perpendicular phenyl ring and an electronic coupling to the gold substrate. The self‐assembly features of both derivatives are analyzed on Au (111) surfaces by low‐temperature ultra‐high‐vacuum STM, high‐resolution X‐ray photoelectron spectroscopy, near‐edge X‐ray absorption fine structure spectroscopy, and reductive voltammetric desorption studies. These experiments indicated that the meta derivative forms a well‐ordered monolayer, with most of the anchoring groups bound to the surface, whereas the para derivative forms a multilayer film with physically adsorbed adlayers on the chemisorbed para monolayer. Single‐molecule conductance values for both tripodal platforms are obtained through an STM break junction experiment. 相似文献
147.
Some recent examples of substitution effects in the three partial structures of selected sodalites are presented. Framework-cation, and cage-cation substitution effects are discussed for the series |(EuxCa2–x)4(OH)8|[(Al2+xSi1–x)4O24]-SOD, cage-anion substitutions for |Ca8[(WO4)x(MoO4)1–x]2|[Al12O24]-SOD. While in a first approximation decomposition into partial structures seems reasonable, it is shown that, however, effects arising from substitutions in one partial structure are not limited to it. This is due to the fact that three main interactions have to be considered, namely, cage-cation – framework, cage-anion – framework, and cage-cation – cage-anion interactions. These can be co-operative or competitive and may lead to structural frustrations. 相似文献
148.
Wulf Wulfhekel Dirk Sander Serge Nitsche Frdric Dulot Andr Leycuras Margrit Hanbücken 《Surface science》2004,550(1-3):8-14
A concave-shaped surface has been prepared in a 6H–SiC(0 0 0 1) substrate by mechanical grinding. As a consequence, the different crystallographic planes building up the 6H–SiC polytype are cut under continuously changing polar angles in all azimuthal directions. Through hydrogen etching, this curved surface breaks up into a whole set of surfaces vicinal to the initial 6H(0 0 0 1) orientation. The local structural reorganisation after hydrogen etching has been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Two types of local bond environments are present at the step edges leading to a strong anisotropy in the surface etching with hydrogen. As a result, the distribution of the terrace width and the step heights varies with the azimuthal angle and reflects the sixfold symmetry of the bulk crystal. For most azimuthal directions, an alternation of large and small terraces, separated by steps of 0.75 nm heights (height of half the 6H polytype, three bilayers) is observed and only for well defined azimuthal directions, equally spaced terraces separated by steps of 1.5 nm height (one unit cell of 6H–SiC, six bilayers) are found. In addition, the polar variations have been studied by taking various line-scans along the concave-shaped surface with AFM. It seems that for polar angles above 3°, step bunching of several SiC steps occurs whereas below 3° the bimodal terrace width distribution is observed. 相似文献
149.
150.
Prof. Dr. Hubert K. Stassen Prof. Dr. Ralf Ludwig Dr. Alexander Wulf Prof. Dr. Jairton Dupont 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(23):8324-8335
The formation, stabilisation and reactivity of contact ion pairs of non‐protic imidazolium ionic liquids (ILs) in solution are conceptualized in light of selected experimental evidence as well theoretical calculations reported mainly in the last ten years. Electric conductivity, NMR, ESI‐MS and IR data as well as theoretical calculations support not only the formation of contact ion pairs in solution, but also the presence of larger ionic and neutral aggregates even when dissolved in solvents with relatively high dielectric constants, such as acetonitrile and DMSO. The presence of larger imidazolium supramolecular aggregates is favoured at higher salt concentrations in solvents of low dielectric constant for ILs that contain shorter N‐alkyl side chains associated with anions of low coordination ability. The stability and reactivity of neutral contact species are also dependent on the nature of the anion, imidazolium substituents, and are more abundant in ILs containing strong coordinating anions, in particular those that can form charge transfer complexes with the imidazolium cation. Finally, some ILs display reactivities as contact ion pairs rather than solvent‐separated ions. 相似文献