全文获取类型
收费全文 | 12681篇 |
免费 | 2531篇 |
国内免费 | 2307篇 |
专业分类
化学 | 9320篇 |
晶体学 | 275篇 |
力学 | 793篇 |
综合类 | 162篇 |
数学 | 1450篇 |
物理学 | 5519篇 |
出版年
2024年 | 36篇 |
2023年 | 232篇 |
2022年 | 411篇 |
2021年 | 462篇 |
2020年 | 606篇 |
2019年 | 589篇 |
2018年 | 524篇 |
2017年 | 497篇 |
2016年 | 676篇 |
2015年 | 687篇 |
2014年 | 797篇 |
2013年 | 1016篇 |
2012年 | 1304篇 |
2011年 | 1280篇 |
2010年 | 958篇 |
2009年 | 965篇 |
2008年 | 1046篇 |
2007年 | 895篇 |
2006年 | 770篇 |
2005年 | 647篇 |
2004年 | 481篇 |
2003年 | 364篇 |
2002年 | 374篇 |
2001年 | 318篇 |
2000年 | 272篇 |
1999年 | 222篇 |
1998年 | 148篇 |
1997年 | 127篇 |
1996年 | 123篇 |
1995年 | 94篇 |
1994年 | 98篇 |
1993年 | 70篇 |
1992年 | 74篇 |
1991年 | 60篇 |
1990年 | 66篇 |
1989年 | 44篇 |
1988年 | 31篇 |
1987年 | 20篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1966年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
191.
A microemulsion electrokinetic chromatography method has been firstly used for the separation of the therapeutically important xanthones from Securidaca inappendiculata. The separation of the nine xanthones was systematically optimized with respect to pH, composition of microemulsion,addition of cyclodextrins, applied voltage and column temperature. Baseline separation was successfully achieved for the nine xanthones, which was also compared with that by micellar electrokinetic chromtography. 相似文献
192.
Li Ting Chai Yang Zhou Li Wei Wei Wang Quan Rui Wang Feng Gang Tao 《中国化学快报》2007,18(12):1460-1462
Nation-Teflon bimembrane was used as an efficient support for the preparation and application of heterogeneous palladium catalysts.The supported palladium catalysts exhibit high activity and stability in the Suzuki cross-coupling of aryl bromides with arylboronic acids to afford the corresponding biaryls in good to excellent yields,and can be readily recovered and reused several times without significant loss of activity. 相似文献
193.
Conducting polyaniline-zirconium dioxide (PANI/ZrO2) composites were synthesized by ‘in situ’ deposition technique in the presence of hydrochloric acid (HCl) as dopant by adding the fine grade powder (average particle size of approximately 20 nm) of ZrO2 into the polymerization reaction mixture of aniline. The composites obtained were characterized by infrared spectra (IR) and X-ray diffraction (XRD) and thermogravimetric analysis (TGA). TG curves and DTG curves of the composites suggest that the thermal degradation process of PANI/ZrO2 composites proceeds in two-steps and the composites are more thermally stable than that of the pure PANI. The improvement in the thermal stability for the composites is attributed to the interaction between PANI and ZrO2, which restricts the thermal motion of PANI chains and shields the degradation of PANI in the composites. 相似文献
194.
195.
Ning GL Li XC Munakata M Gong WT Maekawa M Kamikawa T 《The Journal of organic chemistry》2004,69(4):1432-1434
Phenyl-substituted cyclopentadienes are proved to form phenylated pyrylium cations in the presence of silver(I) perchlorate by insertion of an oxygen atom into the cyclopentadiene-ring. Three phenylated pyrylium compounds, [(Ph(5)C(5)O(+))(ClO(4)(-))](2)(CH(2)Cl(2)) (1), Ag(ClO(4))(H(2)O)(Ph(4)HC(5)O(+)) (ClO(4)(-)) (2), and (Ph(3)H(2)C(5)O(+))(ClO(4)(-)) (3) have been synthesized and characterized. A possible reaction pathway and formation mechanism of the pyrylium cation are proposed and discussed. 相似文献
196.
197.
The complex Cu2(μ-dppb)2(μ-Cl)2 has been synthesized from the reaction of CuCl, dppb and (n-Bu)4NCl. The crystal belongs to the triclinic with space group P1. The unit cell parameters are: a=9.939(4)?, b=10.083(6)?, c=14.104(5)?, α=76.46(3)°, β=71.02(2)°, γ=70.87(5)°. The single crystal X-ray diffraction analysis reveals that it has a bi-ring structure with a symmetry center at the middle of two Copper atoms. The outer ring is a 14-membered ring of Cu-dppb-Cu-dppb, and the inner ring is a 4-membered ring composed of two Cl- and two Cu(Ⅰ). Investigation of third-order optical nonlinearity shows that it exhibits considerable nonlinear absorptive and self-defocusing effect with α2=1.75×10-13m·W-1 and n2=3.19×10-18m2·W-1. CCDC: 193113. 相似文献
198.
Tao Miao 《Tetrahedron letters》2007,48(1):95-99
The immobilization of copper in organic-inorganic hybrid materials catalyzing the Ullmann reaction has been described. Phenols reacted with aryl iodides, aryl bromides and aryl chlorides smoothly in the presence of a 3-(2-aminoethylamino)propyl functionalized silica gel immobilized copper catalyst. The protocol involved the use of DMSO as the solvent, and potassium fluoride as the base. The reactions generated the corresponding cross-coupling products in good to excellent yields. Furthermore, the silica-supported copper could be recovered and recycled by a simple filtration of the reaction solution and used for 10 consecutive trials without loss of its reactivity. 相似文献
199.
通过结合杂化密度泛函和前线轨道理论与弹性散射格林函数方法研究了BE- MP(benzene-1,4-di-ethynyl-4-mercaptophenyl)和TEMP(thiophene-2,5-di-ethynyl-4- mercaptophenyl)两分子结的输运性质。基于杂化密度泛函方法计算两扩展分子电子结构的基础上,计算了两分子的输运性质.计算结果显示:电流增加来源于电极和分子轨道的共振;电导曲线呈现出平台特征.在此基础上从扩展分子A(Au-BEMP-Au)中间的苯环的旋转而引起电流减小的角度解释了负微分电阻现象. 相似文献
200.
杂原子B—ZSM—35沸石的干法合成,表征及CO+H2反应性能的研究 总被引:4,自引:2,他引:4
首次利用吸附态模板剂在Na2O-SiO2-B2O3-DEA干粉体系中合成了杂原子B-SZM-35沸石,XRD,SEM,IR,及CO加氢反应研究了其物理化学特性。结果表明,B原子同晶取代Al原子进入ZSM-35沸石骨加。 相似文献