全文获取类型
收费全文 | 1206篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
化学 | 909篇 |
晶体学 | 3篇 |
力学 | 22篇 |
数学 | 174篇 |
物理学 | 123篇 |
出版年
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 9篇 |
2016年 | 20篇 |
2015年 | 11篇 |
2014年 | 21篇 |
2013年 | 28篇 |
2012年 | 43篇 |
2011年 | 40篇 |
2010年 | 23篇 |
2009年 | 24篇 |
2008年 | 46篇 |
2007年 | 49篇 |
2006年 | 40篇 |
2005年 | 33篇 |
2004年 | 31篇 |
2003年 | 28篇 |
2002年 | 39篇 |
2001年 | 20篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 22篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1991年 | 18篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 19篇 |
1986年 | 22篇 |
1985年 | 29篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 27篇 |
1981年 | 29篇 |
1980年 | 27篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1972年 | 10篇 |
1966年 | 9篇 |
1965年 | 11篇 |
1963年 | 7篇 |
1961年 | 7篇 |
排序方式: 共有1231条查询结果,搜索用时 23 毫秒
81.
82.
Johann Schröder 《Mathematische Zeitschrift》1966,92(1):75-94
Ohne Zusammenfassung 相似文献
83.
84.
Velcicky J Lanver A Lex J Prokop A Wieder T Schmalz HG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):5087-5110
A diversity-oriented, enantioselective synthesis of new (monoprotected) carbocyclic nucleoside analogues (CNAs) with the nucleobase attached to a 3-hydroxymethyl-4-trialkylsilyloxymethylcyclopent-2-en-1-yl scaffold was developed. As a key intermediate, racemic (5SR,8RS)-8-allyloxy-2-trimethylsilyl-7-oxa-bicyclo[3.3.0]-oct-1-en-3-one was prepared from 1,1-diallyloxy-3-trimethylsilyl-2-propyne in a cobalt-mediated Pauson-Khand reaction. The enantiomerically pure material was obtained through efficient kinetic resolution (selectivity factor s >/= 40 at -78 degrees C) by means of an oxazaborolidine-catalyzed borane reduction (CBS reduction) with catecholborane. The absolute configuration of the resolved products was determined by CD spectroscopy, Mosher ester analysis, and chemical correlation. Subsequent steps involve diastereoselective ketone reduction and fully regio- and diastereoselective introduction of the nucleobase through Pd(0)-catalyzed allylic substitution. The generality of the method was demonstrated by preparation of CNAs in both enantiomeric series with all five natural nucleobases, as well as 5-bromouracil, 5-fluorouracil, and 6-chloropurine. Screening of the various compounds in a cytotoxicity assay with BJAB and ALL tumor cell lines revealed that some of the compounds possess pronounced antitumoral properties (LD50 values down to 9 microM, as determined by lactate dehydrogenase release after 48 h). By measuring DNA fragmentation, it could be shown that the activity results from induction of apoptosis. 相似文献
85.
Dreer S Wilhartitz P Piplits K Mayerhofer K Foisner J Hutter H 《Analytical and bioanalytical chemistry》2004,379(4):599-604
Gate oxynitride structures of TFT-LCDs were investigated by SIMS, and successful solutions are demonstrated to overcome difficulties arising due to the charging effects of the multilayer systems, the matrix effect of the method, and the small pattern sizes of the samples. Because of the excellent reproducibility achieved by applying exponential relative sensitivity functions for quantitative analysis, minor differences in the barrier gate-oxynitride composition deposited on molybdenum capped aluminium-neodymium metallisation electrodes were determined between the centre and the edge of the TFT-LCD substrates. No differences were found for molybdenum-tungsten metallisations. Furthermore, at the edge of the glass substrates, aluminium, neodymium, and molybdenum SIMS depth profiles show an exponential trend. With TEM micrographs an inhomogeneous thickness of the molybdenum capping is revealed as the source of this effect, which influences the electrical behaviour of the device.The production process was improved after these results and the aging behaviour of TFT-LCDs was investigated in order to explain the change in control voltage occurring during the lifetime of the displays. SIMS and TEM show an enrichment of neodymium at the interface to the molybdenum layer, confirming good diffusion protection of the molybdenum barrier during accelerated aging. The reason for the shift of the control voltage was finally located by semi-quantitative depth profiling of the sodium diffusion originating from the glass substrate. Molybdenum-tungsten was a much better buffer for the highly-mobile charge carriers than aluminium-neodymium. Best results were achieved with PVD silicon oxynitride as diffusion barrier and gate insulator deposited on aluminium-neodymium metallisation layers. 相似文献
86.
87.
88.
Johann Steiner Hans-Gert Bernstein Hendrik Bielau Annika Berndt Ralf Brisch Christian Mawrin Gerburg Keilhoff Bernhard Bogerts 《BMC neuroscience》2007,8(1):2
Background
S100B is considered an astrocytic in-situ marker and protein levels in cerebrospinal fluid (CSF) or serum are often used as biomarker for astrocytic damage or dysfunction. However, studies on S100B in the human brain are rare. Thus, the distribution of S100B was studied by immunohistochemistry in adult human brains to evaluate its cell-type specificity. 相似文献89.
90.
Zur mechanischen Kubatur 总被引:5,自引:0,他引:5
Johann Radon 《Monatshefte für Mathematik》1948,52(4):286-300
Ohne Zusammenfassung 相似文献