全文获取类型
收费全文 | 1082篇 |
免费 | 20篇 |
国内免费 | 188篇 |
专业分类
化学 | 776篇 |
晶体学 | 7篇 |
力学 | 31篇 |
数学 | 22篇 |
物理学 | 454篇 |
出版年
2023年 | 12篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 59篇 |
2014年 | 45篇 |
2013年 | 74篇 |
2012年 | 55篇 |
2011年 | 106篇 |
2010年 | 69篇 |
2009年 | 102篇 |
2008年 | 86篇 |
2007年 | 67篇 |
2006年 | 78篇 |
2005年 | 64篇 |
2004年 | 56篇 |
2003年 | 52篇 |
2002年 | 31篇 |
2001年 | 23篇 |
2000年 | 27篇 |
1999年 | 23篇 |
1998年 | 20篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1290条查询结果,搜索用时 15 毫秒
111.
Fabrice P. L. Andrieux Colin Boxall Robin J. Taylor 《Journal of solution chemistry》2008,37(11):1511-1527
Studies of the thermodynamics of formation of the acetohydroxamatoiron(III) complexes were carried out in acidic media at
temperatures ranging from 293 to 323 K. Through the isolation of the unique UV–visible spectra of all three complexes, it
was possible to determine their formation constants and deduce enthalpies and entropies of formation as well as their molar
absorptivities. The enthalpies of formation of the mono-, bis- and trisacetohydroxamatoiron(III) complexes were found to be
−56.4, −17.09 and +19.74 kJ⋅mol−1, respectively. Following the determination of the enthalpy and entropy of formation of these complexes, speciation diagrams
were calculated for the complexes at temperatures ranging from 293 to 323 K. 相似文献
112.
基于G4方法, 计算了1,3-丁二烯框架燃烧反应机理中102个物种的热力学数据, 并考察了振动非谐性、 频率校正因子以及受阻内转动对结果的影响. 结果表明, 考虑振动非谐性或采用不同的频率校正因子, 对热力学数据的影响不大; 考虑内转动后, 对热力学数据有较大影响. 而且考虑内转动后, 得到的热力学数据与实验热力学数据吻合得更好. 用所得热力学数据模拟了1,3-丁二烯的绝热燃烧温度以及点火延迟时间, 结果显示, 要得到可靠的绝热火焰温度, 对小分子(如CO和CO2等)的热力学数据需要采用实验结果. 将用所得热力学数据模拟得到的点火延迟时间, 与机理本身的热力学数据所得点火延迟时间进行对比, 二者差别显著, 表明所得热力学数据主要通过改变一些反应的逆反应速率常数来影响点火延迟时间. 进一步确定了用所得热力学数据对点火延迟时间有显著影响的一些物种. 相似文献
113.
114.
M. Marqués 《Journal of Physics and Chemistry of Solids》2008,69(9):2277-2280
We report first principles results of a detailed investigation directed to elucidate mechanistic aspects of the zircon-reidite phase transition in ZrSiO4. The calculated thermodynamic boundary is located around 5 GPa, and the corresponding thermal barrier, estimated from temperatures at which the transition is observed at zero and high pressure, is 133 kJ/mol. Under a martensitic perspective, we examine two different transition pathways at the thermodynamic transition pressure. First, the direct, displacive-like, tetragonal I41/a energetic profile is computed using the c/a ratio as the transformation parameter, and yields a very high activation barrier (236 kJ/mol). Second, a quasi-monoclinic unit cell allows us to characterize a transition path from zircon (β=90°) to reidite (β=114.51°) with an activation barrier of around 80 kJ/mol at β=104°. This energy is somewhat lower than our previous estimation and supports the reconstructive nature of the transformation at the thermodynamic transition pressure. 相似文献
115.
Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere. 相似文献
116.
Summary Adsorption properties of activated carbon cloth were investigated by gas-solid chromatography. Retention of several organic
compounds was measured in the temperature range from 200 to 250°C. The gas/solid distribution coefficients and the related
thermodynamic function of adsorption at zero surface coverage were determined. The obtained experimental data were used to
explain the adsorbent-adsorbate interaction. 相似文献
117.
S.I. Lopatin S.M. Shugurov Z.G. Turnina 《The Journal of chemical thermodynamics》2006,38(12):1706-1710
In the present study, the stability of gaseous barium silicates was confirmed by the high temperature mass spectrometry. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined for gaseous barium silicates as (−510 ± 15) kJ · mol−1 and (−884 ± 18) kJ · mol−1 at 298 K; standard atomization enthalpies as (1637 ± 17) kJ · mol−1 and (2318 ± 20) kJ · mol−1 at 298 K for BaSiO2 and BaSiO3, respectively. Based on the results obtained the critical analysis of the literature data was carried out. 相似文献
118.
The structural, phase transition, elastic, lattice dynamic and thermodynamic properties of rare-earth compounds PrP and PrAs with NaCl (B1), CsCl (B2), ZB (B3), WC (Bh) and CuAu (L10) structures are investigated using the first principles calculations within the generalized gradient approximation (GGA). For the total-energy calculation, we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab-initio Simulation Package (VASP). Specifically, some basic physical parameters, e.g. lattice constants, bulk modulus, elastic constants, shear modulus, Young's modulus and Poison's ratio, are predicted. The obtained equilibrium structure parameters are in excellent agreement with the experimental and theoretical data. The temperature and pressure variations of the volume, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature are calculated in wide pressure and temperature ranges. The phonon dispersion curves and corresponding one-phonon density of states (DOS) for both compounds are also computed in the NaCl (B1) structure. 相似文献
119.
120.
根据原子分子反应静力学与群论,确定了H2、D2和T2的基电子状态为1∑+g(D∞v),SnH、SnD和SnT的基电子状态为2∑+( C∞v).应用基函数SDD**和6-311G**,密度泛函B3P86方法,计算了氢同位素分子及其锡化物的结构、能量E、定容热容Cv和熵S.H2 (D2, T2) ,SnH(D , T)和SnH2(D2, T2)的基电子状态分别为1∑+g(D∞h ),2∑+(C∞v)和3B1(C2v).H2、D2和T2的离解能为4.591 8 eV,SnH(D, T)分子的离解能为2.714 7 eV,SnH2(D2, T2)分子的离解能为4.833 9 eV.用总能量中的电子和振动能量近似代表SnHn、SnDn和SnTn(n=1,2)分子处于固态时的能量,用总熵中的电子和振动熵近似代表SnH、 SnD和SnT分子处于固态时的熵,从而计算了锡与H2、D2和T2反应过程的△Hf°,△Sf°,△Gf°和平衡压力, 并导出他们与温度的函数关系.X 相似文献