首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   193篇
  免费   37篇
  国内免费   58篇
化学   125篇
晶体学   1篇
力学   10篇
综合类   1篇
数学   37篇
物理学   114篇
  2023年   3篇
  2022年   4篇
  2021年   16篇
  2020年   14篇
  2019年   13篇
  2018年   6篇
  2017年   8篇
  2016年   18篇
  2015年   12篇
  2014年   20篇
  2013年   31篇
  2012年   29篇
  2011年   30篇
  2010年   22篇
  2009年   13篇
  2008年   14篇
  2007年   15篇
  2006年   9篇
  2005年   4篇
  2004年   1篇
  2003年   1篇
  2002年   1篇
  2001年   2篇
  1998年   1篇
  1997年   1篇
排序方式: 共有288条查询结果,搜索用时 15 毫秒
1.
《中国化学快报》2020,31(6):1576-1579
Reported herein is the first example of electrochemical selenocyanation of imidazo[1,5-a]quinolines with KSeCN under metal catalyst-and chemical oxidant-free conditions.This sustainable strategy shows a broad scope and great compatibility with functional groups,and affords synthetically and biologically important selenocyanated imidazo[1,5-a]quinolines in good to excellent yields with cheap graphite and Ni plates as the electrodes.The gram-scale synthesis was also successfully conducted,which might demonstrate the potential value of this electrochemical protocol.  相似文献   
2.
我们发展了一种正电子碰撞原子电离的畸变波Born近似方法, 在这个方法中,正负电子偶素通道通过一个ab initio的光学势附加到入射粒子和靶的相互作用势上,且通道对电离作用被第一次被考虑在正电子碰撞原子电离的过程中. 应用这个方法计算了在50 eV入射能量范围氦的电离的三重微分截面,计算结果和实验数据很好的符合.  相似文献   
3.
《中国化学快报》2020,31(7):1855-1858
By virtue of electrochemistry, a series of α,α-dihaloacetophenones were easily obtained with good to excellent yields. This electrochemical procedure was taken in a divided cell with constant current in aqueous media. The reaction can be carried out smoothly at room temperature under metal and oxidant free condition, which provides an eco-friendly synthesis for the α,α-dihaloacetophenone derivatives.  相似文献   
4.
The title compound diethyl 2-(3,4-dichloroisothiazol-5-yl)-4-(trifluoromethyl)-4,5-dihydrothiazol-4-yl-3-methylbenzoate(C15H9Cl2F3N2O2S2, Mr = 441.26) was prepared from methyl 3,4-dichloroisothiazole-5-carboxylate as the starting material by four steps of reaction. Its structure was characterized by IR, 1H-NMR, 13C-NMR, EA and single-crystal X-ray diffraction. The crystal of the title compound belongs to the monoclinic system, space group P21/c with a = 8.8437(18), b = 16.128(3), c = 12.305(3), β = 91.68(3)o, V = 1754.4(6) 3, Z = 4, Dc = 1.671 g/cm3, μ(Mo Ka) = 0.71073 mm-1, F(000) = 888, R = 0.0384 and w R = 0.0778. Weak π-π interactions occur between the isothiazole rings and phenyl rings of adjacent molecules to form a one-dimensional chain and stabilize the crystal structure. Bioassay indicates that the title compound has good activity against the fungi and TMV tested.  相似文献   
5.
In this paper, we consider strong/classical solutions to the 3D compressible Hall-magnetohydrodynamic system. First, we prove the existence of local strong solutions with positive density. Then the existence of global small solutions with small initial data is proved. Optimal time decay rate is also established.  相似文献   
6.
7.
《结构化学》2020,39(9):1689-1693
Hydrothermal reaction of Cu(NO_3)_2·3 H_2O and 4-(4-carboxyphenoxy)isophthalic acid(H_3cpia) results in a two-dimensional coordination polymer based on paddle-wheel-like dinuclear clusters, namely [C_(60)H_(54)Cu_4O_(39)]_n(1). Complex 1 is of triclinic system, space group P1 with a = 10.7318(18), b = 12.267(2), c = 14.528(2) ?, α = 113.560(2)o, β = 96.156(3)o, γ = 103.552(3)o, V = 1660.5(5) ?~3, Z = 1, S = 1.057, F(000) = 842, R = 0.0517 and wR = 0.1426(I 2σ(I)). In this structure, tricarboxylate liagnds are partial deprotonation and potenial proton carriers. Strong antiferromagnetic interaction between Cu~(Ⅱ) ions exists within the Cu_2 cluster and complex 1 exhibits relatively high proton conductivity(σ 1.23 × 10~(-5) S×cm~(-1)) at 76% relative humidity(RH).  相似文献   
8.
设X是维数大于2的Banach空间,映射δ:B(X)→B(X)是2-局部Lie三重导子,则对所有A∈B(X)有δ(A)=[A,T]+φ(A),这里T∈B(X),φ是从B(X)到FI的齐次映射且满足对所有A,B∈B(X)有φ(A+B)=φ(A),其中B是交换子的和.  相似文献   
9.
以“保守系统平衡位置微振动”为例,论述在理论力学中如何适当地整合知识点使之成为一个案例,使学生从具体的案例出发经过思考、分析、讨论,得到可能的解决方案,并进行评价、提炼理论.实践证明,把案例教学引入理论力学教学中,通过多个阶段的实践过程锻炼,有助于学生形成“主体性”和“实践性”的习惯,从而改善课堂教学关系,提高学生的独立学习和实践创新能力.  相似文献   
10.
《Tetrahedron letters》2019,60(24):1620-1623
5-Aryloxazolidines react with active methylene compounds in the presence of catalytic magnesium ethoxide to give methylene-linked 1,3-dicarbonyl compounds, while the similar reaction with 2-oxindoles results in 3-methyl derivatives.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号