全文获取类型
收费全文 | 10235篇 |
免费 | 1440篇 |
国内免费 | 1074篇 |
专业分类
化学 | 7151篇 |
晶体学 | 332篇 |
力学 | 886篇 |
综合类 | 82篇 |
数学 | 275篇 |
物理学 | 4023篇 |
出版年
2024年 | 23篇 |
2023年 | 81篇 |
2022年 | 266篇 |
2021年 | 271篇 |
2020年 | 318篇 |
2019年 | 292篇 |
2018年 | 293篇 |
2017年 | 359篇 |
2016年 | 412篇 |
2015年 | 323篇 |
2014年 | 435篇 |
2013年 | 1022篇 |
2012年 | 524篇 |
2011年 | 539篇 |
2010年 | 400篇 |
2009年 | 490篇 |
2008年 | 578篇 |
2007年 | 620篇 |
2006年 | 595篇 |
2005年 | 562篇 |
2004年 | 549篇 |
2003年 | 466篇 |
2002年 | 475篇 |
2001年 | 391篇 |
2000年 | 377篇 |
1999年 | 346篇 |
1998年 | 263篇 |
1997年 | 250篇 |
1996年 | 210篇 |
1995年 | 202篇 |
1994年 | 177篇 |
1993年 | 168篇 |
1992年 | 134篇 |
1991年 | 47篇 |
1990年 | 54篇 |
1989年 | 41篇 |
1988年 | 40篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1976年 | 7篇 |
1973年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
在当代经济学的语境下,本文从一种广义的制度分析新视角,首次重新解读了马克思(以及恩格斯)著作中的制度经济论述。通过深入细致的思想梳理、观点辨析、理论提炼与重构工作发现,马克思的经济学是经济思想史上第一个重要的制度经济学分析体系。这一分析体系既包含有关社会经济制度问题的基本概念与原理的“一般性分析”,也包括关于资本主义市场经济制度的历史特性的“专门性分析”。两个分析层次之间具有内在的逻辑联系,反映了从“一般”到“特殊”的创新性理论演绎思路。对马克思的制度经济学分析体系的重新发掘与提炼表明,马克思的制度经济思想不仅在制度经济思想史上占具至关重要的地位,而且对于丰富和推进当代制度经济理论发展也具有重要的学术启示与借鉴意义。 相似文献
62.
口述史在社会学中的意义,不仅在于可以通过口述记忆研究个人在大叙事中的生命沉浮,更在于它提供了深挖人的精神世界的社会性的方法。其主要研究对象,可称之为记忆社区的问题。记忆社区至少包括三个维度:地点、时间和人物。它以个人的口述为起点,基于人的生命实践,富含主体性和情感性特征,但其勾勒出的是一个囫囵的整体,有极强的社会性特征,蕴含丰富的社会和文化意义。口述记忆中的文化是一种经由个体化实践而感悟出的文化感,家庭中的“义务感”是它的一个典型形式,其表现为社会力的方式,成为黏合社区的重要机制。记忆社区本质上是人和物的混融,它呈现的社区形象是一个有机整体。口述史能够作为社区研究方法,不仅在于它呈现了独特的记忆社区,还在于指明了社会建设和基层社会治理的深层机制,这便是从人心的角度,揭示了人之安所遂生的社区力量。记忆社区概念提醒我们,历史上积淀下来的社区文化和社会底蕴是值得探究和善用的凝聚社区的相对稳固的机制。 相似文献
63.
以氯化锶和硼酸氢铵为原料,采用液相沉淀法制备了片状水合硼酸锶(SrB6O10•5H2O)粉体,并用XRD、FT-IR及SEM进行了表征。利用热重分析法对片状纳米硼酸锶粉体的脱水热分解动力学进行了研究,分别采用 Coats- Redfern 方程和 Flynn-Wall-Ozawa(FWO)法对热重分析数据进行了处理和拟合,初步确定了水合硼酸锶的四步脱水过程及相应的热分解反应机理,得到各步反应的表观活化能和指前因子。 相似文献
64.
Die Autoren machen mit aktivierungsanalytischen Untersuchungen am Reaktor der Technischen Universität Budapest bekannt. Der thermische Neutronenfluβ war 2·1011 ncm?28?1, und es wurde ein Ge(Li)-Detektor mit 25 cm3 Volumen und einer Energieauflösung von 2 keV angewendet. Die untersuchten Tomatenproben enthielten durchschnittlich 85% Trockensubstanz. Es wurden folgende Konzentrationen an Spurenelementen ermittelt (in mg/kg): Br: 50,1; Mn: 10,2; Zn: 9,3; Cu: 6,6; As: 0,051; Sb:0,030; Au: 0,005. 相似文献
65.
The refined grains in both as-cast Mg-10Y-1Zn-2Zr (WZ101?K, wt.%) and Mg-10Y-1Al (WA101, wt.%) alloys have been found to have superior thermal stability after solution treatment. Plate-shaped, but different polytypes of long-period stacking ordered (LPSO) phases distributed along grain boundaries are considered as the predominant inhibitors of grain growth. Based on the plate-shaped features of the LPSO phases, a modified Zener’s model is established and the predicted limiting grain sizes are in a good agreement with the experimental results. Therefore, this model has strong potential for designing advanced Mg-RE-based alloys with high strength and high creep resistance at high temperatures. 相似文献
66.
Athianna Muthusamy Krishnasamy Balaji Salem Chandrasekaran Murugavel 《Journal of polymer science. Part A, Polymer chemistry》2013,51(8):1707-1715
A series of poly(benzylidene‐ether)esters containing a photoreactive benzylidene chromophore in the main chain were synthesized from 2,6‐bis(4‐hydroxy‐3‐methoxybenzylidene)cyclohexanone (BHMBCH) with various aliphatic and aromatic diacid chlorides by an interfacial polycondensation technique. The intrinsic viscosity of the synthesized homo and copolymers determined by Ubbelohde viscometer was found to be 0.12 to 0.17 dL/g. The molecular structure of the monomer and polymers was confirmed by FT‐IR, 1H NMR, and 13C NMR spectral analyses. These polymers were studied for their thermal stability and photochemical properties. Thermal properties were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was found that the polymers were stable up to 280 °C and start degrading thereafter. Increase in acid methylene spacer length decreased the thermal stability. The self‐extinguishing property of the synthesized polymers was studied by calculating the limiting oxygen index (LOI) value using a Van Krevelen's equation. The influence of the length of methylene spacer on phase transition was investigated using DSC and odd‐even effect has been observed. Hot‐stage optical polarizing microscopic (HOPM) study showed that most of the polymers exhibited birefringence and opalescence properties. The photolysis of liquid crystalline poly(benzylidene‐ether)esters revealed that α,β‐unsaturated ketone moiety in the main chain dimerises through 2π + 2π cycloaddition reaction to form a cyclobutane derivative and leads to crosslinking. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
67.
《Analytical letters》2012,45(15):3153-3163
ABSTRACT Thermal lens spectrometry has been used for the determination of iron in calf serum. The method is based on dissociation of Fe3+ from proteins, reduction of Fe3+ to Fe2+ and formation of a coloured complex between Fe2+ and bathophenanthroline. Contrary to the spectrophotometric method, it is shown that thermal lens spectrometry is less sensitive to scattering caused by the presence of small particles remaining in the test solution after the deproteinization step. The background signal is very small and the response is only slightly dependent on the amount of scattering particles. The method is reliable, sensitive and reproducible. The limit of detection for iron is 4 ppb and the relative standard deviation is around 2%. It is expected that the volume of serum sample necessary for an analysis can be reduced to less than 100 μl. 相似文献
68.
Daniel Roca‐Sanjuán Marcus Lundberg David A. Mazziotti Roland Lindh 《Journal of computational chemistry》2012,33(26):2124-2126
In the preceding paper results are presented, which are in serious conflict with state‐of‐the‐art ab initio method. Based on these new results the authors propose a new explanation of the reason for the preferential production of a phosphorescent state. Here we show that these controversial results are flawed, since the model use exclude biradical electron structures. © 2012 Wiley Periodicals, Inc. 相似文献
69.
《Journal of Coordination Chemistry》2012,65(14):2243-2266
AbstractThe Cu(II) ion-based polymeric complexes [Cu(2,2′-bpy).(N3)2]n (I), [Cu2(2,2′-bpy)2.(N3)4]n (II), and monomeric complex [Cu(2,2′-bpy).(NO3)2].5H2O (III) have been synthesized with rigid (–N3) and aromatic (2,2′-bpy = 2,2′-bipyridyl) ligand. The rigid azide group is responsible for the formation of 1-D extended structures in complexes I and II where as in the case of complex III, a monomeric complex is formed due to lack of a bridging group like –N3, resulting in limitation in dimensionality. The thermal stability of the 1-D complexes is comparatively higher than monomeric complex III. Hirshfeld surface analysis has also been applied to investigate other weak interactions and compared with the results from single-crystal X-ray data. Due to the presence of paramagnetic metal centers and long metal···metal distances in complexes I and II and presence of lattice water molecules in complex III, decrease in luminescence intensities have been observed. To attain further insights into the aforementioned interesting species, some chemical concepts such as highest occupied molecular orbital–lowest unoccupied molecular orbital gap, electronic chemical potential, chemical hardness, and electrophilicity index, identified as a derivative of electronic energy, have also been emphasized employing the quantum chemical calculations in the framework of the density functional theory method using the M06-2X/ 6-31G** level of study. Further, these complexes have been used to synthesize copper nanoparticles by applying a green synthetic route. 相似文献
70.
R. C. Gauthier 《Optics & Laser Technology》1994,26(3)
In this paper, light level control is demonstrated using optically induced thermal stress effects in a polarization-maintaining optical fibre. The controlling light beam is absorbed by a blackened segment of the fibre and produces local heating. Light control is demonstrated in the single-ended sensor configuration, which displays a response that cannot be explained from phase delays only, but requires the addition of the coupled mode theory. 相似文献