全文获取类型
收费全文 | 913篇 |
免费 | 125篇 |
国内免费 | 111篇 |
专业分类
化学 | 466篇 |
晶体学 | 4篇 |
力学 | 23篇 |
综合类 | 3篇 |
数学 | 281篇 |
物理学 | 372篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 12篇 |
2019年 | 24篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 24篇 |
2015年 | 24篇 |
2014年 | 32篇 |
2013年 | 74篇 |
2012年 | 35篇 |
2011年 | 28篇 |
2010年 | 35篇 |
2009年 | 56篇 |
2008年 | 66篇 |
2007年 | 79篇 |
2006年 | 59篇 |
2005年 | 49篇 |
2004年 | 78篇 |
2003年 | 52篇 |
2002年 | 53篇 |
2001年 | 36篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 32篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有1149条查询结果,搜索用时 15 毫秒
61.
62.
采用密度泛函B3P86方法和6-311++G(3df,3pf)基组,计算了在-0.05~0.05a.u.外偶极电场作用下,H2O,D2O,T2O,H2,D2,T2,O2的电子能量、核运动能量和熵值,在此基础上通过计算H2O(g)→H2(g)+O2(g)、D2O(g)→D2(g)+O2(g)、T2O(g)→T2(g)+O2(g)的焓变ΔH、熵变ΔS、Gibbs函数变化ΔG,最后得到了H2O,D2O,T2O的可逆分解电压Er.计算结果表明,外偶极电场存在时,H2O,D2O,T2O的Gibbs自由能变ΔG和可逆分解电压Er都有明显的变化,当外偶极电场正方向增加时,其Gibbs自由能变ΔG和可逆分解电压Er均趋于线性增加;当外偶极电场负方向增加时,其Gibbs自由能变ΔG和可逆分解电压Er均趋于线性减小;在相同外偶极电场作用下,Gibbs自由能变ΔG和可逆分解电压Er随H2O,D2O,T2O依次增加. 相似文献
63.
利用XRD,SEM,TEM和振动样品磁强计(VSM)等检测手段对不同磁场强度下水热法制备的钡铁氧体粉末进行了分析.实验结果表明,无磁场下,150℃时得到的产物为BaFe2O4颗粒,而180℃时产物为片状BaFe12O19施加磁场后,150和180℃下水热反应产物都为棒状BaFe12O19随着磁感应强度的增加,水热反应产... 相似文献
64.
以经典热力学第二定律ΔG<0为依据,分析了静态高温高压触媒法合成立方氮化硼(cBN)过程中发生的可能反应.考虑温度和压强对反应物相体积的影响,计算了六方氮化硼(Li3N-hBN)体系中hBN+Li3N→Li3BN2,h BN→cBN及Li3BN2→Li3N+cBN反应在高温高压条件下的ΔG.结果证实,Li3BN2由Li3N与hBN在高温高压(T>1300 K,P>3.0 GPa)条件下反应得到,在cBN的合成(T=1600~1800 K,P=4.6~6.0 GPa)条件下,hBN和Li3BN2都有向cBN转化的倾向,但由hBN向cBN直接转变的反应自由能比Li3BN2分解生成cBN的反应自由能更负,反应的可能性更大.探讨了高温高压条件下立方氮化硼的转变机理。 相似文献
65.
1892年,荷兰物理学家洛伦兹通过创建电子论,为原子内部电子的发现提供了理论基础。1897年,英国物理学家汤姆逊从阴极射线中发现了自由电子,打破了原子不可分的传统观念,由此引发了卢瑟福、玻尔等人对原子内部结构的探索。同时,化学家们将物理学中的电子引入化学,开始用原子结构中的电子来解释化学行为,提出了化学键的电子理论,推动了化学键理论的发展。 相似文献
66.
67.
Summary Sampling from probability density functions (pdfs) has become more and more important in many areas of applied science, and
has therefore been the subject of great attention. Many sampling procedures proposed allow for approximate or asymptotic sampling.
On the other hand, very few methods allow for exact sampling. Direct sampling of standard pdfs is feasible, but sampling of
much more complicated pdfs is often required. Rejection sampling allows to exactly sample from univariate pdfs, but has the
huge drawback of needing a case-by-case calculation of a comparison function that often reveals as a tremendous chore, whose
results dramatically affect the efficiency of the sampling procedure. In this paper, we restrict ourselves to a pdf that is
proportional to a product of standard distributions. From there, we show that an automated selection of both the comparison
function and the upper bound is possible. Moreover, this choice is performed in order to optimize the sampling efficiency
among a range of potential solutions. Finally, the method is illustrated on a few examples. 相似文献
68.
A novel uncertainty propagation method for problems characterized by highly non-linear or discontinuous system responses is presented. The approach is based on a Padé–Legendre (PL) formalism which does not require modifications to existing computational tools (non-intrusive approach) and it is a global method. The paper presents a novel PL method for problems in multiple dimensions, which is non-trivial in the Padé literature. In addition, a filtering procedure is developed in order to minimize the errors introduced in the approximation close to the discontinuities. The numerical examples include fluid dynamic problems characterized by shock waves: a simple dual throat nozzle problem with uncertain initial state, and the turbulent transonic flow over a transonic airfoil where the flight conditions are assumed to be uncertain. Results are presented in terms of statistics of both shock position and strength and are compared to Monte Carlo simulations. 相似文献
69.
We establish a characterization of coagulation-fragmentation processes, such that the induced birth and death processes depicting
the total number of groups at time t≥0 are time homogeneous. Based on this, we provide a characterization of mean-field Gibbs coagulation-fragmentation models,
which extends the one derived by Hendriks et al. As a by-product of our results, the class of solvable models is widened and
a question posed by N. Berestycki and Pitman is answered, under restriction to mean-field models. 相似文献
70.
Isothermal vapor–liquid equilibrium (VLE) and excess enthalpy (HE) data were measured for binary systems required for the design of reactive distillation processes for the methyl acetate production. The isothermal P–x data were measured with the help of a computer-operated static apparatus. A commercial isothermal flow calorimeter was used for the determination of the heats of mixing. Temperature-dependent interaction parameters for the UNIQUAC model were fitted simultaneously to the experimental data from this work and other authors. 相似文献