全文获取类型
收费全文 | 462篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
化学 | 347篇 |
力学 | 7篇 |
数学 | 43篇 |
物理学 | 99篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 32篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 25篇 |
2014年 | 19篇 |
2013年 | 20篇 |
2012年 | 42篇 |
2011年 | 37篇 |
2010年 | 17篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 20篇 |
2006年 | 16篇 |
2005年 | 16篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1990年 | 2篇 |
1987年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1964年 | 2篇 |
1963年 | 5篇 |
1958年 | 2篇 |
1956年 | 1篇 |
1942年 | 1篇 |
1914年 | 1篇 |
排序方式: 共有496条查询结果,搜索用时 218 毫秒
1.
Spyridon Koutsoukos Frederik Philippi Francisco Malaret Tom Welton 《Chemical science》2021,12(20):6820
There are thousands of papers published every year investigating the properties and possible applications of ionic liquids. Industrial use of these exceptional fluids requires adequate understanding of their physical properties, in order to create the ionic liquid that will optimally suit the application. Computational property prediction arose from the urgent need to minimise the time and cost that would be required to experimentally test different combinations of ions. This review discusses the use of machine learning algorithms as property prediction tools for ionic liquids (either as standalone methods or in conjunction with molecular dynamics simulations), presents common problems of training datasets and proposes ways that could lead to more accurate and efficient models.In this review article, the authors discuss the use of machine learning algorithms as tools for the prediction of physical and chemical properties of ionic liquids. 相似文献
2.
3.
Kristian Hougaard Frederik D. Nielsen 《Journal of Optical and Fiber Communications Reports》2004,1(1):63-83
In this paper we will present an overview of the use
of photonic crystal fibers as fiber amplifiers. We
will describe the basic concepts of optical
amplification, and how to do numerical modelling of
such components. We will then identify advantages
and disadvantages of amplifiers based on PCF
technology compared to conventional fibers, and then
go into greater detail on some of these specific
applications, such as low pump power amplifiers, and
high-power double-clad amplifiers and lasers. 相似文献
4.
The Bekenstein–Hawking entropy of certain black holes can be computed microscopically in string theory by mapping the elusive
problem of counting microstates of a strongly gravitating black hole to the tractable problem of counting microstates of a
weakly coupled D-brane system, which has no event horizon, and indeed comfortably fits on the head of a pin. We show here
that, contrary to widely held beliefs, the entropy of spherically symmetric black holes can easily be dwarfed by that of stationary
multi-black-hole “molecules” of the same total charge and energy. Thus, the corresponding pin-sized D-brane systems do not
even approximately count the microstates of a single black hole, but rather those of a zoo of entropically dominant multicentered
configurations.
Fourth Award in the 2007 Essay Competition of the Gravity Research Foundation. 相似文献
5.
6.
7.
M. Heber Chr Liedtke H. Korte E. Hoffmann-Posorske A. Donella-Deana L. A. Pinna J. Perich E. Kitas R. B. Johns H. E. Meyer 《Chromatographia》1992,33(7-8):347-350
Summary Capillary electrophoresis is a novel technique in the non-radioactive determination of phosphoamino acids. The main advantage of the method presented is the high selectivity and the ability to separate all phosphoamino acid derivatives. Non-radioactive determination of PTH or dabsyl phosphoamino acids by capillary electrophoresis provides a fast and simple screening procedure for all O-phosphorylated amino acids in protein and peptides in the low picomolar range. 相似文献
8.
An accurate primary Fourier transform infrared (FTIR) method for the determination of moisture in mineral and ester based lubricants has been developed based on the extraction of moisture into dry acetonitrile. FTIR evaluation of acetonitrile extracts from new and used lubricants as well as common lubricant additives and contaminants which might co-extract indicated that phenolic constituents interfered significantly with moisture measurements. By measuring moisture at 3676 cm−1 on the shoulder of the asymmetric OH stretching band, spectral interferences from extracted phenolic constituents were minimized. The spectra of calibration standards (0-2100 ppm), prepared by gravimetric addition of water to dry acetonitrile, were recorded in a 1000-μm CaF2 transmission flow cell and produced linear standard curves having an S.D. of ∼±20 ppm. Lubricant sample preparation involved the vigorous shaking (20 min) of a 1:1.5 (w/v) mixture of lubricant and dry acetonitrile, centrifugation to separate the phases, acquisition of the FTIR spectrum of the upper acetonitrile layer, and subtraction of the spectrum of the dry acetonitrile used for extraction. A Continuous Oil Analyzer and Treatment (COAT®) FTIR system was programmed to allow the automated analysis of acetonitrile extracts, and the methodology was validated by analyzing 58 new and used oils, independently analyzed by the Karl Fischer (KF) method. Linear regression of FTIR versus KF results for these oils produced a linear plot with a between-method S.D. of ±80 ppm. As implemented on the COAT® system, this FTIR method is capable of analyzing 72 acetonitrile extracts/h and provides a high-speed alternative to the KF titrimetric procedures for the determination of water in lubricants. 相似文献
9.
Irmgard Heber 《Colloid and polymer science》1967,215(2):145-149
Zusammenfassung Steigert man für das Poly?thylen die Kristallisationstemperatur, so findet man Kristallformen in der folgenden Reihenfolge:
rautenf?rmige Einkristalle— rautenf?rmige Einkristalle mit abgeschnittenen spitzen Ecken (“truncated lozenge crystals”)-l?ngliche
sechseckf?rmige Einkristalle, bei denen die kristallographische b-Achse der orthorhombischen Elementarzelle in Richtung der l?ngsten Ausdehnung des Kristalls liegt. Diese l?nglichen Sechsecke
lagern sich zu Sph?rolithen zusammen, und zwar so, da? die kristallographische b-Achse radial liegt, wie es auch bei den aus der Schmelze gewachsenen Sph?rolithen der Fall ist. Damit sind für das Poly?thylen
übergangsformen zwischen den Einkristallen und Sph?rolithen aufgezeigt.
Sph?rolithe, die aus der L?sung gewachsen sind, zeigen im Polarisationsmikroskop nur dann ein konzentrisches Ringsystem, wenn
bei der Bildung der Sph?rolithe ein Mindestangebot an Substanz vorhanden ist. Die Ringbreite nimmt dann mit steigender Kristallisationstemperatur
zu. Bei aus der Schmelze gewachsenen Poly?thylen-Sph?rolithen ist mit der Bildung von nicht-kristallographischen Verzweigungen
eine Drehung der Indikatrix verbunden. Vermutlich wird also auch bei aus der L?sung gewachsenen Sph?rolithen das Ringsystem
auf dem Auftreten von Verzweigungen infolge hohen Angebotes von kristallisierender Substanz beruhen.
Summary With increasing temperature of crystallization polyethylene crystallizes from solution as lozenge single crystals, truncated lozenge crystals and longish hexagonal crystals, with the crystallographic b-axis along the long diagonal. In the solutions longish hexagonal crystal plates are able to cluster and to form spherulites, in which their crystallographic b-axes are oriented radially like the b-axes in spherulites grown from the melt. Various transition species have been observed. In polarised light the spherulites grown from solution show a concentric ring-system only, if during the crystallization a sufficient quantity of polyethylene is present. The ring-width increases with increasing crystallization temperature. Further it is shown that in polyethylene spherulites grown from the melt the rotation of the indicatrix is connected with a non-crystallographic branching. We suppose, that also for the solution-grown spherulites the ring-system depends on branching.相似文献
10.