全文获取类型
收费全文 | 1051篇 |
免费 | 29篇 |
国内免费 | 7篇 |
专业分类
化学 | 723篇 |
晶体学 | 11篇 |
力学 | 46篇 |
数学 | 126篇 |
物理学 | 181篇 |
出版年
2024年 | 5篇 |
2023年 | 8篇 |
2022年 | 73篇 |
2021年 | 40篇 |
2020年 | 44篇 |
2019年 | 32篇 |
2018年 | 40篇 |
2017年 | 35篇 |
2016年 | 56篇 |
2015年 | 29篇 |
2014年 | 22篇 |
2013年 | 88篇 |
2012年 | 62篇 |
2011年 | 59篇 |
2010年 | 39篇 |
2009年 | 39篇 |
2008年 | 45篇 |
2007年 | 36篇 |
2006年 | 35篇 |
2005年 | 26篇 |
2004年 | 17篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 10篇 |
2000年 | 14篇 |
1999年 | 6篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1961年 | 3篇 |
排序方式: 共有1087条查询结果,搜索用时 31 毫秒
991.
This Note is concerned with the severely ill-posed Cauchy–Stokes problem. This inverse problem is rephrased into an optimization one: An energy-like error functional is introduced. We prove that the optimality condition of the first order is equivalent to solving an interfacial equation which turns out to be a Cauchy–Steklov–Poincaré operator. Numerical trials highlight the efficiency of the present method. To cite this article: A. Ben Abda et al., C. R. Mecanique 337 (2009). 相似文献
992.
Silicon dioxide was formed by oxidizing porous silicon film and annealed, in a next step, at 920 °C with lithium nitrate embedded in its structure. These operations have produced the two lithium silicates, Li2Si2O5 and Li2SiO3, as it has been confirmed by the X-ray diffraction measurements. At relative high temperature (230 °C), the experimental ionic conductivity of this achieved sample has doubled in presence of ozone flow. A comparison with other samples, prepared with varieties of metallic nitrates and by following the same experimental procedures as for the former one, has proved that the sample prepared with zirconium was also good for ozone detection. 相似文献
993.
N. A. Kalanda L. I. Gurskii A. M. Saad V. M. Truhan T. V. Haliakevich 《Crystal Research and Technology》2008,43(6):599-605
Based on the data of X‐ray phase and microstructure analysis, the sample composition was optimized in order to provide maximum size of the textured macrograins of YBa2Cu3O7‐δ and of the crystallites in the Y2BaCuO5‐BaCuO2‐CuO, Y2Cu2O5‐BaCuO2 systems. The growth rate has been studied and the YBa2Cu3O7‐δ growth activation energy has been calculated for the samples of Y2BaCuO5+3BaCuO2+2.3CuO, Y2BaCuO5+3BaCuO2+0.6CuO, and Y2Cu2O5+3.5BaCuO2 compounds in the temperature range of 1240‐1270K for the case of use of the Y2Cu2O5 and Y2BaCuO5 precursors with an average grain diameter of 10 μm and 1mm. A crystallization mechanism of YBa2Cu3O7‐δ in the Y2BaCuO5‐BaCuO2‐CuO and Y2Cu2O5‐BaCuO2 systems in the case of different sizes of Y2BaCuO5 and Y2Cu2O5 precursor grains was proposed and validated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
994.
Laura Ielo Saad Touqeer Alexander Roller Thierry Langer Wolfgang Holzer Vittorio Pace 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2501-2506
A conceptually novel, high‐yielding, mono‐ or bis‐homologation was realized with lithium halocarbenoids and enables the one‐step, fully chemocontrolled assembly of a new class of quaternary trifluoromethyl aziridines. Trifluoroacetimidoyl chlorides (TFAICs) act as convenient electrophilic platforms, enabling the addition of either one or two homologating elements by simply controlling the stoichiometry of the process. Mechanistic studies highlighted that the homologation event, carried out with two different carbenoids (LiCH2Cl and LiCH2F), leads to fluoromethyl analogues in which the first nucleophile is employed for constructing the cycle and the second for decorating the resulting molecular architecture. 相似文献
995.
David Doran Yousef M. Abul‐Haija Leroy Cronin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(33):11375-11378
Living systems are characterised by an ability to sustain chemical reaction networks far‐from‐equilibrium. It is likely that life first arose through a process of continual disruption of equilibrium states in recursive reaction networks, driven by periodic environmental changes. Herein, we report the emergence of proto‐enzymatic function from recursive polymerisation reactions using amino acids and glycolic acid. Reactions were kept out of equilibrium by diluting products 9:1 in fresh starting solution at the end of each recursive cycle, and the development of complex high molecular weight species is explored using a new metric, the Mass Index, which allows the complexity of the system to be explored as a function of cycle. This process was carried out on a range of different mineral environments. We explored the hypothesis that disrupting equilibrium via recursive cycling imposes a selection pressure and subsequent boundary conditions on products. After just four reaction cycles, product mixtures from recursive reactions exhibit greater catalytic activity and truncation of product space towards higher‐molecular‐weight species compared to non‐recursive controls. 相似文献
996.
A systematically designed practical approach was carried out for the optimization of an anion selective electrode for the determination of an anionic laxative, docusate sodium (DS). The PVC membrane composition and the sensor assembly were systematically optimized. Different sensors were fabricated using tetradodecylammonium bromide (TDAB), tridodecylmethylammonium bromide, tetraheptylammonium bromide as ion exchangers. The effect of ionophore was evaluated using four different host‐guest ionophores, namely; calix[8]arene, β‐cylodextrin, hydroxypropyl‐β‐cylodextrin and carboxymethyl‐β‐cylodextrin to reach the optimum membrane composition. Sensors were constructed in both liquid membrane and solid contact sensor‐assemblies. The slope, linear range, LOQ and response time for each sensor was calculated to assess their performance characteristics. Best Nernstian slope of ?61.38 mV/decade and lowest quantification limit of 7.62×10?7 M was achieved by the sensor containing TDAB as ion exchanger and Calix[8]arene as ionophore in the PVC matrix using the gold wire solid contact sensor assembly. Electrode selectivity was assured in the presence of DS potential degradation product, common interfering ions and industrial excipients of tablet and gel formulations. Validation was carried out regarding the ICH validation parameters. 相似文献
997.
ABSTRACTLipids and DNAs are two major building blocks of life. Interestingly, by chemically linking these two natural compounds together, synthetic lipid-DNA conjugates exhibit several attractive features for cell membrane studies. These lipid-DNA conjugates are amphiphilic macromolecules combining the cell membrane insertion capability of lipids with the properties of DNAs in precise hybridization and programmability. These supramolecular conjugates have demonstrated exciting applications from generating cell membrane nanopores to transmembrane cargo deliveries, and from analyzing cell membrane events to tissue engineering. In this review, we will discuss the design, structures, and biological applications of lipid-DNA conjugates, with an emphasis on their functions on live cell membranes. We expect, in the near future, significant advancement in our ability to understand, control, and apply these cell membrane-modified lipid-DNA conjugates. 相似文献
998.
Srinivasa Rao Jada Katherine McMillan Ahmad S. Hamzah Mohammad S. Saad Nordin H. Lajis Malcolm F.G. Stevens Carl H. Schwalbe Johnson Stanslas 《Journal of chemical crystallography》2006,36(2):93-97
The title compound, 3-{2-[decahydro-6-hydroxy-5-(hydroxymethyl)-5,8a-dimethyl-2-methylene-1-napthalenyl]ethylidene}dihydro-4-acetoxy-2(3H)-furanone, C22H32O6, was synthesised from andrographolide. It crystallizes in the orthorhombic system with a = 7.4219(12), b = 11.8411(10), c = 23.777(4) Å in space group P212121. While the stereochemical relation between rings is slightly changed from the starting material, acetylation of the hydroxyfuranone moiety completely abolishes O--HO hydrogen bonding there, leaving a C--HO interaction. The hydrogen-bonded chains at the opposite end of the andrographolide molecule persist but reverse direction. 相似文献
999.
1000.