全文获取类型
收费全文 | 1861篇 |
免费 | 56篇 |
国内免费 | 17篇 |
专业分类
化学 | 1043篇 |
晶体学 | 14篇 |
力学 | 61篇 |
数学 | 521篇 |
物理学 | 295篇 |
出版年
2023年 | 11篇 |
2022年 | 87篇 |
2021年 | 83篇 |
2020年 | 62篇 |
2019年 | 56篇 |
2018年 | 68篇 |
2017年 | 40篇 |
2016年 | 81篇 |
2015年 | 76篇 |
2014年 | 77篇 |
2013年 | 133篇 |
2012年 | 122篇 |
2011年 | 144篇 |
2010年 | 96篇 |
2009年 | 82篇 |
2008年 | 100篇 |
2007年 | 79篇 |
2006年 | 90篇 |
2005年 | 71篇 |
2004年 | 65篇 |
2003年 | 39篇 |
2002年 | 54篇 |
2001年 | 20篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有1934条查询结果,搜索用时 0 毫秒
151.
Tomasz Gubica Jadwiga Stroka Andrzej Temeriusz Marianna Kańska 《Journal of Physical Organic Chemistry》2011,24(12):1229-1234
Ten nitrophenyl N‐glycosides have been studied electrochemically in neutral (at pH 7) water–organic solutions by cyclic voltammetry using static mercury drop electrode. For all compounds under investigation the two electrochemical processes have been observed: the four‐electron irreversible reduction of their nitro groups to the corresponding phenylhydroxylamine derivatives, as well as the two‐electron quasi‐reversible process between phenylhydroxylamine and nitroso derivatives. For three compounds the additional electrochemical processes have been also observed, which can be connected with the formation of azoxybenzene derivatives. The potentials of both redox processes: a two‐electron quasi‐reversible R? NHOH/R? NO (Ef) and four‐electron irreversible R? NO2/R? NHOH (Epc(I)) systems have been determined and discussed according to crystal structures of selected compounds. Ef and Epc(I) depended strongly on the positive mesomeric effect (caused by glycosidic nitrogen atom), as well as on the intramolecular hydrogen bond between electroactive nitro group and the hydrogen atom at the glycosidic atom observed in N‐o‐nitrophenyl‐2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐glucopyranosylamine. Moreover, the chirality of selected reactants has had the pronounced effect on the Epc(I). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
152.
This paper presents a system that accurately measures the distance travelled by ultrasound waves through the air. The simple design of the system and its obtained accuracy provide a tool for non-contact distance measurements required in the laser’s optical system that investigates the surface of the eyeball. 相似文献
153.
In this Letter, we introduce an algorithm that overcomes limitations in shape measurement by holographic microscopic methods in cases of micro-optical elements with high NA, such as microlenses. The presented algorithm provides a simple method for shape reconstruction from interferometrically measured phase. The algorithm is based on the analysis of local ray transition through the measured object. We develop algorithms for holographic configurations working in transmission and reflection. The accuracy of the developed algorithms is proved by experiments and extensive simulations. We present an experiment in a holographic Mach-Zehnder configuration where we have measured and successfully reconstructed the height distribution of spherical and cylindrical microlenses with NA up to 0.3. 相似文献
154.
Tomasz ?ojewski Jacek Bagniuk Andrzej Ko?odziej Joanna ?ojewska 《Applied Physics A: Materials Science & Processing》2011,105(3):753-761
This study proposes a method to estimate the lipid content in binding media in paintings that can be used at any laboratory
equipped with an infrared spectrometer. The lipid content estimator, termed greasiness index (GI), is defined as a ratio of
lipid ν(C=O) and protein amide I bands at 1743 and 1635 cm−1, respectively. Three Fourier transform infrared (FTIR) sampling techniques were evaluated for GI determination: reflective
attenuated total reflection—ATR, specular reflection microscopy—μSR and photoacoustic—PAS. A set of model painting samples containing three tempera binding media (casein, egg, egg + oil),
seven pigments and one varnish type were used in the study. Multivariate analysis was used to evaluate the resulting data.
A good reproducibility of GI was obtained by ATR and PAS but not with μSR. The discriminative power of the technique is higher for unvarnished samples, but, generally, the GI estimator can be used
for the categorisation of binding media in large populations of painting samples analysed with the same FTIR technique (sampling
technique, detection, etc.). 相似文献
155.
Tomasz Tkocz 《Mathematische Nachrichten》2014,287(4):398-404
In this paper we prove the S‐inequality for certain product probability measures and ideals in . As a result, for the Weibull and Gamma product distributions we derive concentration of measure type estimates as well as optimal comparison of moments. 相似文献
156.
We show that many harmonic analysis operators in the Bessel setting,including maximal operators,Littlewood–Paley–Stein type square functions,multipliers of Laplace or Laplace–Stieltjes transform type and Riesz transforms are,or can be viewed as,Calderón–Zygmund operators for all possible values of type parameter λ in this context.This extends results existing in the literature,but being justified only for a restricted range of λ. 相似文献
157.
Tomasz Zok Mariusz Popenda Marta Szachniuk 《Central European Journal of Operations Research》2014,22(3):457-473
Comparison of molecular structures in order to identify their similarity is an important step in solving various problems derived from computational biology, like structure alignment and modelling, motif search or clustering. Thus, there is a constant need for the development of good measures to determine distances between the structures and tools to display these distances in an easily interpretable form. In the paper we present MCQ4Structures, a new method and tool for structural similarity computation based on molecule tertiary structure representation in torsional angle space. We discuss its unique features as compared with the other measures, including RMSD and LGA, and we show its experimental use in comparison of a number of 3D structures as well as evaluation of models predicted within RNA-Puzzles contest. MCQ4Structures software is available as a free Java WebStart application at: http://www.cs.put.poznan.pl/tzok/mcq/. The source code licensed under BSD can be downloaded from the same website. 相似文献
158.
Aleksandra Swiercz Edmund K. Burke Mateusz Cichenski Grzegorz Pawlak Sanja Petrovic Tomasz Zurkowski Jacek Blazewicz 《Central European Journal of Operations Research》2014,22(3):567-589
This paper introduces a new approach to applying hyper-heuristic algorithms to solve combinatorial problems with less effort, taking into account the modelling and algorithm construction process. We propose a unified encoding of a solution and a set of low level heuristics which are domain-independent and which change the solution itself. This approach enables us to address NP-hard problems and generate good approximate solutions in a reasonable time without a large amount of additional work required to tailor search methodologies for the problem in hand. In particular, we focused on solving DNA sequencing by hybrydization with errors, which is known to be strongly NP-hard. The approach was extensively tested by solving multiple instances of well-known combinatorial problems and compared with results generated by meta heuristics that have been tailored for specific problem domains. 相似文献
159.
We prove that if A ? {1, ..., N} has no nontrivial solution to the equation x 1 + x 2 + x 3 + x 4 + x 5 = 5y, then \(|A| \ll Ne^{ - c(\log N)^{1/7} } \) , c > 0. In view of the well-known Behrend construction, this estimate is close to best possible. 相似文献
160.
Leszek Pazderski Tomasz Pawlak Jerzy Sitkowski Lech Kozerski Edward Szłyk 《Magnetic resonance in chemistry : MRC》2010,48(6):450-457
1H, 13C and 15N NMR studies of iron(II), ruthenium(II) and osmium(II) tris‐chelated cationic complexes with 2,2′‐bipyridine and 1,10‐phenanthroline of the general formula [M(LL)3]2+ (M = Fe, Ru, Os; LL = bpy, phen) were performed. Inconsistent literature 1H signal assignments were corrected. Significant shielding of nitrogen‐adjacent protons [H(6) in bpy, H(2) in phen] and metal‐bonded nitrogens was observed, being enhanced in the series Ru(II) → Os(II) → Fe(II) for 1H, Fe(II) → Ru(II) → Os(II) for 15N and bpy → phen for both nuclei. The carbons are deshielded, the effect increasing in the order Ru(II) → Os(II) → Fe(II). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献