全文获取类型
收费全文 | 396篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
化学 | 265篇 |
力学 | 2篇 |
数学 | 91篇 |
物理学 | 39篇 |
出版年
2023年 | 5篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2014年 | 5篇 |
2013年 | 14篇 |
2012年 | 14篇 |
2011年 | 18篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 19篇 |
2007年 | 21篇 |
2006年 | 22篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 14篇 |
1982年 | 4篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有397条查询结果,搜索用时 15 毫秒
301.
Textor A Papastavrou I Siewert J Magull J Kulik A Fiedler HP von Zezschwitz P Grond S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(26):7416-7423
Spirodionic acid (1), a novel microbial metabolite with a spiro[4.5]decene skeleton, the 6-ethyl-2H-pyrone 5, dihydrosarkomycin (6), and other metabolites were isolated from the strain Streptomyces sp. Tü 6077. Structural elucidation was accomplished by NMR spectroscopic and mass-spectrometric studies, and the biosyntheses of compounds 1, 5, and 6 were investigated by feeding experiments with (13)C-labeled precursors. All results indicate a biogenetic sequence with metabolite 5 and sarkomycin (7) as precursors in the formation of spirocyclus 1 through an intermolecular Diels-Alder-type reaction. 相似文献
302.
303.
We compute the asymptotic distribution of the sample covariance matrix for independent and identically distributed random vectors with regularly varying tails. If the tails of the random vectors are sufficiently heavy so that the fourth moments do not exist, then the sample covariance matrix is asymptotically operator stable as a random element of the vector space of symmetric matrices. 相似文献
304.
Ruediger Schueler Juergen Petermann Karl Schulte Hans-Peter Wentzel 《Macromolecular Symposia》1996,104(1):261-268
The conditions to form a conductive network in carbon black filled epoxy resin were examined. It was found that the formation is controlled by particle-particle interaction which can be influenced by shear forces or by the ionic concentration of the resin. Therefore the network morphology and thus the percolation threshold depends strongly upon the processing route. On best conditions the percolation threshold was reduced to 0.06 vol.-%. That a continuous network can form with such a low volume fraction can be explained by the fractal dimension of agglomerates the network is made of. 相似文献
305.
Let be an i.i.d. sequence of -valued random vectors belonging to the generalized domain of semistable attraction of some nonnormal law. Assume further
that is a sequence of positive integer valued random variables such that for some
for some discrete positive random variable D, where we do not assume that and are independent. Let . Then various laws of the iterated logarithm for the norm of as well as the radial projection onto a unit vector θ are presented. 相似文献
306.
307.
Manfred Pinnow Hans-Peter Fink Carola Fanter Jürgen Kunze 《Macromolecular Symposia》2008,262(1):129-139
Highly porous cellulose was formed by gelation of cellulose carbamate solutions in caustic soda. Two methods for gel preparation were optimized for the formation of beads and bulky materials – the chemical precipitation from dilute sulfuric acid and the thermal gelation by annealing at elevated temperatures. Various methods were used for characterizing of the pores of low density materials: scanning electron microscopy, small angle X-ray scattering, mercury intrusion and nitrogen sorption. These methods were optimized and used for characterizing the complete pore system from micro to macro pores. The effects of different preparation (cellulose carbamate concentration in caustic soda) and processing (precipitation, drying and pyrolysis) on the pore structure were studied by the set of complementary methods. Aerocell samples with a minimum density of 0.06 g/cm3 were prepared from cellulose carbamate. They are characterized by a broad pore size distribution ranging from 0.5 nm to 1 mm, specific internal surfaces of up to 660 m2/g and total pore volumes of up to 18 cm3/g. 相似文献
308.
Synthesis of Novel 2-Aminothiophene-3-carboxylates by Variations of the Gewald Reaction 总被引:1,自引:0,他引:1
Hans-Peter Buchstaller Carsten D. Siebert Ralf H. Lyssy Ina Frank Adil Duran Rudolf Gottschlich Christian R. Noe 《Monatshefte für Chemie / Chemical Monthly》2001,132(2):279-293
Summary. The synthesis of the title compounds through variations of the Gewald reaction is presented. Knoevenagel condensation of methylketone derivatives with methyl cyanoacetate and subsequent treatment of the α,β-unsaturated nitriles
with sulfur and amine resulted in the corresponding 2-aminothiophenes 5 or isomers 9 and 10. Reaction of methylketone derivatives bearing a leaving group at the methyl group under modified Gewald conditions selectively led to the formation of 4-substituted 2-aminothiophenes 9a and 12. The introduction of the sulfur atom occurs through nucleophilic displacement with sodium sulfide.
Received July 5, 2000. Accepted (revised) August 23, 2000 相似文献
309.
Hans-Peter Welzel Gerhard Kossmehl Gunnar Engelmann Barbara Neumann Ulla Wollenberger Frieder Scheller Waldfried Plieth 《Macromolecular Symposia》1998,126(1):283-293
The hydroxy group of 3-(2-hydroxyethyl)thiophene was protected as methyl ether 1 and as dimethyl tert-butyl silyl ether 5 before anodic polymerization. The poly[3-(2-methoxyethyl)thiophene] 2 was prepared by electrochemical homopolymerization of 1 . Ether cleavage was carried out in the polymer film 2 and the resulting poly [3-(2-hydroxyethyl)thiophene] ( 3 ) was activated with cyanogen bromide to immobilize alcohol dehydrogenase. Silylether 5 did not undergo homopolymerization but copolymerization of 5 with 3-methylthiophene ( 4 ) was successful. After cleavage of the protecting group the resulting copolymer 7 was activated by cyanuric chloride, and chymotrypsin was immobilized. Electrocopolymerization of thiophene-3-acetic acid ( 8 ) and 3-methylthiophene ( 4 ) under various conditions produces copolymer 9 . By activation of the carboxylic groups with N,N'-dicyclohexylcarbodiimide (DCC) lactate oxidase (LOD) was bond to the surface of the electrode to form a lactate sensor. 相似文献
310.
Dr. Florian Späth Dr. Himadri R. Soni Johann Steinhauer Fabian Düll Dr. Udo Bauer Phillip Bachmann Dr. Wolfgang Hieringer Prof. Dr. Andreas Görling Prof. Dr. Hans-Peter Steinrück Dr. Christian Papp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(37):8884-8893
The interaction of single-layer hexagonal boron nitride (h-BN) on Ni(111) with molecular oxygen from a supersonic molecular beam led to a covalently bonded molecular oxygen species, which was identified as being between a superoxide and a peroxide. This is a rare example of an activated adsorption process leading to a molecular adsorbate. The amount of oxygen functionalization depended on the kinetic energy of the molecular beam. For a kinetic energy of 0.7 eV, an oxygen coverage of 0.4 ML was found. Near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy revealed a stronger bond of h-BN to the Ni(111) substrate in the presence of the covalently bound oxygen species. Oxygen adsorption also led to a shift of the valence bands to lower binding energies. Subsequent temperature-programmed X-ray photoelectron spectroscopy revealed that the oxygen boron bonds are stable up to approximately 580 K, when desorption, and simultaneously, etching of h-BN set in. The experimental results were substantiated by density functional theory calculations, which provided insight to the adsorption geometry, the adsorption energy and the reaction pathway. 相似文献