全文获取类型
收费全文 | 834篇 |
免费 | 32篇 |
国内免费 | 16篇 |
专业分类
化学 | 503篇 |
晶体学 | 20篇 |
力学 | 24篇 |
数学 | 170篇 |
物理学 | 165篇 |
出版年
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 33篇 |
2012年 | 42篇 |
2011年 | 60篇 |
2010年 | 28篇 |
2009年 | 36篇 |
2008年 | 35篇 |
2007年 | 46篇 |
2006年 | 40篇 |
2005年 | 43篇 |
2004年 | 24篇 |
2003年 | 27篇 |
2002年 | 40篇 |
2001年 | 10篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 14篇 |
1974年 | 15篇 |
1973年 | 8篇 |
1972年 | 9篇 |
排序方式: 共有882条查询结果,搜索用时 15 毫秒
61.
62.
Zusammenfassung Es wird gezeigt, da? ?ls?ure auf anges?uerter Permanganatl?sung einen Film ergibt, der au?erordentlich empfindlich gegenüber
Einwirkungen anderer Flüssigkeiten ist. Die charakteristischen sternf?rmigen Teilchen dieses Filmes werden durch viele organische
Flüssigkeiten und auch durch menschliche Blutseren ver?ndert. Besonders ausgepr?gt ist dies der Fall, wenn die Seren Wassermannreaktion
zeigen, denn dann ist die Ver?nderung der Teilchen sehr einfacher Natur. Diese Reaktion kann aber nicht als wirklich spezifisch
für syphilitische Seren betrachtet werden, da die Seren gewisser Patienten, die jedoch nicht syphilitisch sind, ganz ?hnliche
Reaktionen ergeben.
übersetzt von Rud. Walter (Leipzig).
Die Verfasser danken den Herren Dr. Robb M. D. und Dr. Ross M. B. C. M. für ihre wertvolle Unterstützung bei diesen Untersuchungen. 相似文献
63.
A new algorithm is presented, based on elements of artificial intelligence theory, to determine the fractal properties of the backbone of the incipient infinite cluster. It is found that the fractal dimensionality of the backbone isd
f
BB
=1.61±0.01, the chemical dimensionality isd
t=1.40±0.01, and the fractal dimension of the minimum pathd
min=1.15 ± 0.02 for the two-dimensional triangular lattice. 相似文献
64.
Andreas J. Steiner Georg Schitter Arnold E. Stütz Tanja M. Wrodnigg Chris A. Tarling Stephen G. Withers Don J. Mahuran Michael B. Tropak 《Tetrahedron: Asymmetry》2009,20(6-8):832-835
Cyclisation by double reductive amination of 2-acetamino-2-deoxy-d-xylo-hexos-5-ulose with N-2 protected l-lysine derivatives provided 2-acetamino-1,2-dideoxynojirimycin derivatives without any observable epimer formation at C-5. Modifications on the lysine moiety gave access to lipophilic derivatives that exhibited improved hexosaminidase inhibitory activities. 相似文献
65.
In most papers establishing consistency for learning algorithms it is assumed that the observations used for training are realizations of an i.i.d. process. In this paper we go far beyond this classical framework by showing that support vector machines (SVMs) only require that the data-generating process satisfies a certain law of large numbers. We then consider the learnability of SVMs for α-mixing (not necessarily stationary) processes for both classification and regression, where for the latter we explicitly allow unbounded noise. 相似文献
66.
In this paper we consider what happens when Adams self maps are modified by adding certain unstable maps. The unstable maps which are added are trivial after a single suspension. We can choose the modification so that the maps are still K-theory equivalences but the loops on the map are no longer K-theory equivalences. As a corollary we note that the maps are K-theory equivalences but not v
1-periodic equivalences. Another consequence is the behavior of the cobar spectral sequences for generalized homology theories. Tamaki shows that in certain cases a cobar-type spectral sequence for generalized homology theories is well behaved. The maps we construct give an example where despite the connectivity of the spaces the cobar spectral sequence is still poorly behaved. Finally we use our maps to construct spaces whose Bousfield class is distinct from the cofiber of the Adams map but which becomes the same after one suspension. 相似文献
67.
68.
Low levels of water (limit of detection 2-5 mg kg1?)can be determined in a non-polar organic solvents such as benzene, 1,2-dichloroethane (DCE) and n-hexane by utilizing the reaction of water with SnCl4 or SbCl5. The reaction results of hydrolysis in halide and is accompanied by a decrease in optical absorption. With SnSl4, the reaction is monitored near 300 nm and with SbCl5 it is monitored at lower wavelengths (350-420). Niether reactons proceeds well in media containing only DCE and n-hexane. For this reason, the arrangemens involves a halide reagent dissolved in benzene which is merged with a benzene/n-hexane/DCE carrier stream into which samlpe is injected. A configuration in which only 2μl of a concentrated halide reagent solution is injected into the flowing sample stream is also shown to be viable for the determination of water in benzene. A membrane-permeation-based calibration method for preparing trace water standards is described. 相似文献
69.
Kapuruge Don Kunkuma Amila Somarathne Ekenechukwu C. Okafor Daiki Sugawara Akihiro Hayakawa Hideaki Kobayashi 《Proceedings of the Combustion Institute》2021,38(4):5163-5170
This study examined the effects of OH concentration and temperature on the NO emission characteristics of turbulent, non-premixed methane (CH4)/ammonia (NH3)/air swirl flames in two-stage combustors at high pressure. Emission data were obtained using large-eddy simulations with a finite-rate chemistry method from model flames based on the energy fraction of NH3 (ENH3) in CH4/NH3 mixtures. Although NO emissions at the combustor exit were found to be significantly higher than those generated by CH4/air and NH3/air flames under both lean and stoichiometric primary zone conditions, these emissions could be lowered to approximately 300 ppm by employing far-rich equivalence ratios (?) of 1.3 to 1.4 in the primary zone. This effect was possibly due to the lower OH concentrations under far-rich conditions. An analysis of local flame characteristics using a newly developed mixture fraction equation for CH4/NH3/air flames indicated that the local temperature and NO and OH concentration distributions with local ? were qualitatively similar to those in NH3/air flames. That is, the maximum local NO and OH concentrations appeared at local ? of 0.9, although the maximum temperature was observed at local ? of 1.0. Both the temperature and OH concentration were found to gradually decrease with the partial replacement of CH4 with NH3. Consequently, NO emissions from CH4/NH3 flames were maximized at ENH3 in the range of 20% to 30%, after which the emissions decreased. Above 2100 K, the NO emissions from CH4/NH3 flames increased exponentially with temperature, which was not observed in NH3/air flames because of the lower flame temperatures in the latter. But, the maximum NO concentration in CH4/NH3 flames was occurred at a temperature slightly below the maximum temperature, just as in NH3/air flames. The apparent exponential increase in NO emissions from CH4/NH3 flames is attributed to a similar trend in the OH concentration at high temperatures. 相似文献
70.
Ali Izadi-Najafabadi Takeo Yamada Don N. Futaba Hiroaki Hatori Sumio Iijima Kenji Hata 《Electrochemistry communications》2010,12(12):1678-1681
We report the energy and power voltage-dependencies of supercapacitors using single-walled carbon nanotube electrodes. The energy density was dependent on the cell-voltage cubed (up to 4 V: E = 1.43 × V3). The cubic relationship was attributed to the linear increase of the capacitance as a function of voltage, enabled by electrochemical doping. Furthermore, while up to 3.5 V, the maximum power rating of the nanotube electrodes increased as a function of the cell-voltage squared, beyond 3.5 V, a decline in power was observed as a result of depletion of the electrolyte's ions. 相似文献