全文获取类型
收费全文 | 2059篇 |
免费 | 70篇 |
国内免费 | 137篇 |
专业分类
化学 | 632篇 |
晶体学 | 26篇 |
力学 | 413篇 |
综合类 | 1篇 |
数学 | 474篇 |
物理学 | 720篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 40篇 |
2021年 | 33篇 |
2020年 | 41篇 |
2019年 | 29篇 |
2018年 | 33篇 |
2017年 | 32篇 |
2016年 | 44篇 |
2015年 | 59篇 |
2014年 | 72篇 |
2013年 | 162篇 |
2012年 | 96篇 |
2011年 | 225篇 |
2010年 | 137篇 |
2009年 | 171篇 |
2008年 | 158篇 |
2007年 | 141篇 |
2006年 | 146篇 |
2005年 | 96篇 |
2004年 | 85篇 |
2003年 | 80篇 |
2002年 | 52篇 |
2001年 | 33篇 |
2000年 | 48篇 |
1999年 | 23篇 |
1998年 | 27篇 |
1997年 | 27篇 |
1996年 | 24篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 3篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2266条查询结果,搜索用时 15 毫秒
31.
对用调制差热分析(MDTA)准恒温法测样品热容量的情形进行了讨论。通过结合最基本的热传导定律和MDTA模型,指出了目前国际上测量样品热容量的准恒温法只能得到在所测温度范围内的物质热容量平均值,调制温度的幅度越大或调制频率越高,所得到的热容量数据越平滑。在所测温度范围内样品热容量基本不变时,用MDTA准恒温法较好;但当样品热容量在所测温度范围内有明显变化时,用传统差热分析法(DTA)更好一些。 相似文献
32.
Andrzej Czopnik Nataly Shitsevalova Alexander Krivchikov Vasyl Pluzhnikov Yuriy Paderno 《Journal of solid state chemistry》2004,177(2):507-514
We have measured heat capacity and thermal expansion of rare earth dodecaborides REB12 (RE=Y, Tb-Tm, Lu). YB12 and LuB12 are diamagnetics whereas the other dodecaborides are ordered antiferromagnetically. The amplitude of the heat capacity discontinuity at the Néel temperature and the shape of the heat capacity variation in the critical region for all these antiferromagnetics are characteristics for amplitude-modulated magnetic structures. In the ordered state TbB12 reveals two first-order phase transitions, most likely due to magnetic structure changes. The heat capacity of ErB12 just below the Néel point shows an anomaly of unclear origin. From the Schottky contribution to the heat capacity we have determined crystal field parameters. They are completely different than that is estimated from Point Charge Model. 相似文献
33.
Benzofuro[2,3-b]benzofuran-2,3,8,9-tetracarboxylic dianhydride (BBTDA) is introduced as a monomer for the synthesis of a series of novel polyimides with enhanced high thermal stability. Polyimides derived from BBTDA and aromatic diamines showed high glass transition (Tg>296 °C) and degradation (T5>455 °C) temperatures, and were soluble in organic solvents (i.e. N-methyl pyrrolidone (NMP), N,N′-dimethylformamide (DMF), N,N′-dimethylacetamide (DMAc)). The polymerization yielded high-molecular-weight polyimides with inherent viscosities ranging from 1.75 to 2.14 dl/g. The polymers were characterized by IR and elemental analysis. 相似文献
34.
《Thermochimica Acta》2003,401(2):169-173
The heat capacity and the heat content of gallium nitride were measured by calvet calorimetry (320-570 K) and by drop calorimetry (670-1270 K), respectively. The temperature dependence of the heat capacity in the form Cpm=49.552+5.440×10−3T−2.190×106T−2+2.460×108T−3 was derived by the least squares method. Furthermore, thermodynamic functions calculated on the basis of our experimental results and literature data on the molar entropy and the heat of formation of GaN are given. 相似文献
35.
Heat exchange plays an important role in hydrodynamical systems, which is
an interesting topic in theory and application. In this paper, the authors consider the
global stability of steady supersonic Rayleigh flows for the one-dimensional compressible
Euler equations with heat exchange, under the small perturbations of initial and boundary
conditions in a finite rectilinear duct. 相似文献
36.
It is shown that new parametersX can be defined such that the heat capacity CxT(S/T)x is negative, even when the canonical ensemble [i.e., at fixed T=(U/S)Y and YX] is stable. This implies an extension of the classical theory of polytropes from ideal gases to general fluids. As examples of negative heat capacity systems we treat blackbody radiation and general gas systems with nonsingular T. For the case of a simple ideal gas we even exhibit an apparatus which enforces a constraint X(p, V)=const that makes Cx<0. We then show that it is possible to infer the statistical mechanics of canonicallyunstable systems-for which even the traditional heat capacities are negative-by imposing constraints that stabilize the associated noncanonical ensembles. Two explicit models are discussed. 相似文献
37.
ZHANG Xiaoping CHEN Shuixia ZENG Hanmin Department of Environmental Science Engineering South China University of Technology Guangzhou P. R. China Key Laboratory of Polymeric Composite & Functional Materials The Ministry of Education of China Materials Science Institute Zhongshan University 《Chinese Journal of Reactive Polymers》2002,(2)
1. INTRODUCTION Study on the deposition of metal ions on ACFs indicated that such a process consists of several consecutive steps [1]: (1) transfer of the solvated ions (metal ions) from the bulk solution to the proximity of the ACFs surface; (2) absorpt… 相似文献
38.
A systematic investigation was performed to elucidate the cause of spontaneous ignition of Refuse Derived Fuel (RDF) and Meat Bone Meal (MBM). Heat generation in both RDF and MBM with addition of water liquid and vapor at room temperature was determined by isothermal calorimetry. Compared with water liquid, the heat of wetting by sorption of water vapor at 80% relative humidity and 25 °C was larger, which can raise the temperature of RDF and MBM more than 30 and 56 °C, respectively. Heat generation due to fermentation occurred and the temperature of RDF and MBM reached or exceeded 80 °C after 5 days for RDF and 4 days for MBM at 100% RH. The spontaneous ignition for RDF and MBM results from heat of wetting and fermentation at room temperature and a further exothermic reaction at higher temperature. 相似文献
39.
Heat conduction, convection and radiolysis of the
The calorimeter allows the water absorbed dose, a measure of radiotherapy, to be measured according to its definition. Different detector types are used in the PTB calorimeter; this paper discusses heat conduction, convection and the radiolysis of the
system for a ‘sealed’ detector. The ‘sealed’ detector allows the calorimeter to be operated at room temperature in the case of 60Co-γ-radiation. 相似文献
Full-size image
40.
A. Krauss 《Thermochimica Acta》2006,445(2):126-132
A transportable water calorimeter for the determination of the quantity of absorbed dose to water in radiotherapy beams has been developed at the PTB and is presented in detail in this investigation. Heat conduction effects occurring in the calorimeter are studied for different lateral sizes of high-energy photon beams, for different depth dose distributions of electron beams and for a scanned-beam irradiation with a heavy ion beam. The corresponding correction factors are calculated and arguments are given under which conditions these can adequately be applied. 相似文献