全文获取类型
收费全文 | 222篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 94篇 |
力学 | 9篇 |
数学 | 86篇 |
物理学 | 38篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 10篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 17篇 |
2008年 | 7篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 13篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有227条查询结果,搜索用时 15 毫秒
101.
We show that there exist informationally incomplete phase space observables such that the Cartesian margins are informationally equivalent with position and momentum. This shows that it is possible to reconstruct the position and momentum distributions of a quantum system from the statistics of a single observable, and thus a single measurement, even though the state of the system is not uniquely determined by the statistics. 相似文献
102.
A. Lehmuskero V. Kontturi J. Hiltunen M. Kuittinen 《Applied physics. B, Lasers and optics》2010,98(2-3):497-500
Different colors on stainless steel have been obtained by heating the surfaces with laser. The colors have been modeled as an effective sum of small color pixels, each of them consisting of certain thickness of chromium oxide. We have considered the utilization of the technique into color pixeling and presented a qualitative relation between the energy, the color, and the chromium oxide layer thickness. 相似文献
103.
Abstract Aliphatic polyesters, such as poly(lactic acids), need high molecular weight for acceptable mechanical properties. This can be achieved through ring-opening polymerization of lactides. The lactide route is, however, relatively complicated, and alternative polymerization routes are of interest. In this paper we report the properties of a polymer made by a two-step process: first a condensation polymerization of lactic acid and then an increase of the molecular weight with diisocyanate. The end product is then a thermoplastic poly(ester-urethane). The hydroxylterminated prepolymer was made with condensation polymerization of L–lactic acid and a small amount of 1,4-butanediol. The polymerization was performed in the melt under nitrogen and reduced pressure. The preparation of poly(ester-urethane) was done in the melt using aliphatic diisocyanates as the chain extenders reacting with the end groups of the prepolymer. The polymer samples were carefully characterized, including preliminary degradation studies. The results indicate that this route to convert lactic acid into thermoplastic biodegradable polymer has high potential. Lactic acid is converted into a mechanically attractive polymer with high yield, which could make the polymer suitable for high volume applications. The mechanical properties of the poly(ester-urethane) are comparable with those of poly(lactides). Capillary rheometer measurements indicate that the polymer is processible both by injection molding and extrusion. 相似文献
104.
Carbohydrate analysis is an important source of the information required for understanding and control of pulp and paper processes. The behavior of cellulose and hemicelluloses in the process, carbohydrate–lignin interactions, and the enzymatic treatment of fibers are examples of situations for which reliable, fast, qualitative, and quantitative methods are required. New uses of lignocellulosic material have further increased the need for carbohydrate analysis. This review collates and summarizes the most important findings and approaches in the analysis of wood-based carbohydrates by use of capillary zone electrophoresis and provides an analysis of the effect of different conditions on the separation, showing the advantages and limitations of the methods used. It provides guidelines for achieving higher quality and improved separation efficiency in carbohydrate analysis. Figure
Kraft pulping process and future possibilities for hemicellulose recovery 相似文献
105.
The number of negative squares of all self-adjoint extensions of a simple symmetric operator of defect one with finitely many negative squares in a Krein space is characterized in terms of the behaviour of an abstract Titchmarsh-Weyl function near 0 and ∞. These results are applied to a large class of symmetric and self-adjoint indefinite Sturm-Liouville operators with indefinite weight functions. 相似文献
106.
Miia Hiltunen Simon Riihelä Sirkka Liisa Maunu 《Journal of Polymer Science.Polymer Physics》2009,47(19):1869-1879
The syntheses and rheological behavior of ethyl hydroxyethyl cellulose (EHEC)‐based graft‐copolymers were studied. Copolymers were prepared by grafting EHEC with acrylamide (Aam) via reversible addition fragmentation chain transfer (RAFT) polymerization. Hydroxyl groups of EHEC were esterified with a carboxylic acid functional chain transfer agent (CTA) to prepare EHEC‐macroCTAs with different degrees of substitution. EHEC‐macroCTAs were characterized by ATR‐FTIR, 13C NMR, and SEC, and elemental analysis was used to quantify the degree of CTA substitution. EHEC‐macroCTAs with different degrees of substitution were copolymerized with acrylamide by “grafting from” technique. Formation of new cellulose‐based copolymers was comprehensively confirmed by 1H NMR, ATR‐FTIR, and SEC measurements. Further, the associations of EHEC‐g‐PAam copolymers in water were studied at various concentrations and temperatures by means of UV–vis spectroscopy, fluorescence spectroscopy, and rheological measurements. The results indicate that copolymers have both intra and intermolecular association in water depending on the amount of grafts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1869–1879, 2009 相似文献
107.
Jussi Väisälä 《Results in Mathematics》2005,48(1-2):184-195
We show that quasihyperbolic geodesics exist in convex domains in reflexive Banach spaces and that quasihyperbolic geodesies are quasiconvex in the norm metric in convex domains in all normed spaces. 相似文献
108.
Jussi Klemelä 《Computational Statistics》2005,20(2):349-368
Summary We present algorithms for finding the level set tree of a multivariate density estimate. That is, we find the separated components
of level sets of the estimate for a series of levels, gather information on the separated components, such as volume and barycenter,
and present the information together with the tree structure of the separated components. The algorithm proceeds by first
building a binary tree which partitions the support of the density estimate, followed by bottom-up travels of this tree during
which we join those parts of the level sets which touch each other. As a byproduct we present an algorithm for evaluating
a kernel estimate on a large multidimensional grid. Since we find the barycenters of the separated components of the level
sets also for high levels, our method finds the locations of local extremes of the estimate.
Writing of this article was financed by Deutsche Forschungsgemeinschaft under project MA1026/8-1. 相似文献
109.
This paper studies a telecommunications company's optimal networkinvestment strategies. The objective of the company is to maximizethe value of the network. According to our numerical exampleswe are not able to consider a single point-to-point connectionseparately from the network, because the network demands andcapacities affect each other. Therefore, the whole network structurehas to be considered in the point-to-point investments. 相似文献
110.
Tero Kumpulainen Jussi Pekkanen Jani Valkama Jarmo Laakso Reijo Tuokko Matti Mäntysalo 《Optics & Laser Technology》2011,43(3):570-576
New manufacturing methods are being sought for electronics production. Printable electronics is a promising method for producing low cost and large-scale electronics. In printable electronics nanoparticle inks printed on the surface of substrate contain additives, such as dispersing agent and carrier fluids that provide good printing properties by changing the viscosity and separating the nanoparticles of the ink. In the sintering process ink particles are heated to a certain, ink-specific temperature. During the sintering process the carrier fluid and dispersing agents are evaporated from the ink. Additional heating after evaporation causes the nanoparticles to start to agglomerate. A small particle size allows the use of a considerably lower sintering temperature than with bulk silver, for example 220 °C. The sintering process is usually utilized with a convection oven, with a long sintering time, and the thermal load on the surrounding material can become too great as components and patterns are formed from layers of different type inks. Hence, alternative sintering methods are sought. This paper describes tests done with two different types of laser; pulsed and continuous wave lasers. Laser sintering enables short sintering times and selective sintering, making it possible for printed structures to contain fragile active components produced with other technologies. 相似文献