全文获取类型
收费全文 | 1808篇 |
免费 | 297篇 |
国内免费 | 865篇 |
专业分类
化学 | 2377篇 |
晶体学 | 323篇 |
力学 | 14篇 |
综合类 | 15篇 |
数学 | 9篇 |
物理学 | 232篇 |
出版年
2024年 | 5篇 |
2023年 | 20篇 |
2022年 | 73篇 |
2021年 | 86篇 |
2020年 | 86篇 |
2019年 | 70篇 |
2018年 | 65篇 |
2017年 | 99篇 |
2016年 | 128篇 |
2015年 | 112篇 |
2014年 | 136篇 |
2013年 | 307篇 |
2012年 | 196篇 |
2011年 | 183篇 |
2010年 | 142篇 |
2009年 | 158篇 |
2008年 | 164篇 |
2007年 | 190篇 |
2006年 | 176篇 |
2005年 | 154篇 |
2004年 | 124篇 |
2003年 | 107篇 |
2002年 | 72篇 |
2001年 | 25篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有2970条查询结果,搜索用时 15 毫秒
1.
Chunlin Li Yilu Fu Guozhu Bian Tiandou Hu Yaning Xie Jing ZhanDepartment of Chemical Physics University of Science and Technology of China Hefei China Institute of High Energy Physics Chinese Academy of Sciences Beijing China 《天然气化学杂志》2003,12(3)
The Ni/CeO2-ZrO2-Al2O3 catalyst with different Al2O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and Al2O3 is stronger than that between NiO and CeO2-ZrO2.The addition of Al2O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess Al2O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity. 相似文献
2.
1 INTRODUCTION donor due to the presence of the protonated carboxyl group; (d) it can form short bridges via one car- Coordination polymers are of great interest due to boxylato end or long bridges via the benzene ring[7]. their physical properties and potential applications in We believe that coordination functionality of isoph- functional materials[1~3]. Aromatic polycarboxylic acids thalate can lead to interesting structures. In this com- such as 1,2,4,5-benzenetetracarboxylic acid[4],… 相似文献
3.
HUANG Xi-He SHENG Tian-Lu XIANG Sheng-Chang FU Rui-Biao HU Sheng-Min LI Ya-Min WU Xin-Tao ② 《结构化学》2007,26(2):161-164
The hydrothermal reaction of 1,2-dicyanobenzene with NaN3 in the presence of CuCl2, 2,2′-bipyridine and H2O affords a novel dinuclear copper(II)-ditetrazolate, [Cu(bpy)- (pdtz)]2 (Hpdtz = 5,5′-1,2-phenylene-ditetrazole, bpy = 2,2′-bipyridine). The pdtz ligand is generated in situ through Sharpless 2 3 cycloaddition reaction. Its crystal structure was deter- mined by single-crystal X-ray diffraction method. The crystal crystallizes in the monoclinic system, space group P21/n with a = 8.2096(16), b = 18.580(4), c = 11.838(2) , β = 103.12(3)o, V = 1758.5(6) 3, Z = 2, Mr = 863.83, Dc = 1.631 g/cm3, F(000) = 876 and μ = 1.272 mm-1. In this novel dinuclear structure, the pdtz ligand adopts a peculiar μ2-η1,η2 coordination mode. 相似文献
4.
对国产GYQG球形硅胶施加高压水热处理并进行扩孔,制备了用于高效液相色谱法的大孔硅胶填料,考察了扩孔压力,扩孔温度和扩孔时间对平均孔径和比表面积的影响。并将产品日本SIL-3003×10^-8m硅胶进行了物理性质和孔分布的对比实验,结果表明GYQG硅胶扩孔后平均孔径为20~30nm接近日本SIL-3003×10^-8m硅前平平均孔径25nm。display structure 相似文献
5.
G.T. Chandrappa N. Steunou S. Cassaignon C. Bauvais P.K. Biswas J. Livage 《Journal of Sol-Gel Science and Technology》2003,26(1-3):593-596
Vanadium oxide nanotubes (VO
x
-NT) have been prepared by mixing hexadecylamine with V2O5·nH2O gels. This procedure was followed by an hydrothermal treatment (150–180°C, 2–7 days) which leads to a large quantity of VO
x
-NT. SEM and XRD analysis have been used to optimize the temperature and reaction time required for production of VO
x
-Nt and morphology of the nanotubes investigated by TEM. 相似文献
6.
催化裂化USY/ZnO/Al2O3脱硫添加剂的高温水热失活 总被引:3,自引:0,他引:3
对USY/ZnO/Al2O3汽油催化裂化脱硫添加剂经高温水热老化处理前后的脱硫性能进行了考察,发现老化后添加剂的脱硫性能大幅度下降.采用XRD和IR等技术对USY/ZnO/Al2O3添加剂在高温和高温水热条件下失活的原因进行了研究.结果表明,在高温下,ZnO可与USY沸石中的铝发生固相反应生成ZnAl2O4尖晶石,从而造成USY晶体结构崩塌,转变成无定形状态.在ZnO含量较高的条件下,ZnO可继续与USY晶体结构崩塌后生成的无定形的硅和铝的氧化物反应,生成Zn2SiO4硅锌矿和ZnAl2O4尖晶石结构.这一方面使添加剂失去了可形成硫化物吸附中心的ZnO,另一方面破坏了硫化物的裂化活性组分USY,从而造成添加剂脱硫性能下降甚至失去脱硫活性.ZnO对USY的破坏作用主要与温度有关.在USY/ZnO/Al2O3体系中,ZnO被ZnO与Al2O3之间形成的锌铝尖晶石膜固定并与USY隔离,单纯的高温条件对添加剂的破坏不显著,而水蒸气可以促进ZnO的移动,有利于ZnO与USY的接触,因此在高温和有水蒸气存
在的条件下添加剂的结构易遭到破坏. 相似文献
7.
配合物形成的三维超分子体系—[Ni(C_6H_4O_2N)_2(H_2O)_4]的水热法合成、晶体结构及热分析 总被引:7,自引:0,他引:7
采用水热法用Ni(NO3)26H2O和异烟酸制备出了一种新的由配合物形成的三维超分子体系—[Ni(C6H4O2N)2(H2O)4],并通过X射线衍射对其晶体结构进行了测定。 该晶体属三斜晶系,空间群为Pī, 所得晶胞参数为: a = 6.9228(4), b = 9.6664(19),c = 6.322(1) , a = 96.86(3), b = 113.33(3), g = 110.35(3)°, V = 347.6(1) 3, Z = 1, Mr = 374.98, Dc = 1.791 g/cm3, F(000) = 194, m = 1.443 mm-1。用1362个可观察的 (I > 2s(I))衍射点,修正123个结构参数, 最终偏离因子R = 0.0444,wR = 0.1271。在组成该化合物的基本结构单元[Ni(C6H4O2N)2(H2O)4]中,Ni处于1个稍微拉长的八面体的中心; 各个结构单元之间通过氢键OH…O相互连接,形成了无限伸展的具有层状结构的三维超分子体系。 另外,从差热及热重曲线可以看出,该化合物加热到154 ℃时开始分解, 首先失去4个H2O,再失去2个异烟酸根,最后残余物为NiO。 相似文献
8.
9.
The hydrothermal reaction of VOSO4, As2O3, CoC2O4·2H2O and 2,2-bipy yields a novel arsenic-vanadate [CoII(2,2-bpy)2]2[AsIII8VIV 14O42(H2O)]·H2O (1), which is characterized by IR, elemental analysis, TGA, magnetic susceptibility and single crystal X-ray diffraction analysis. X-ray diffraction shows that compound 1 is the first example of tubular arsenic–vanadium cluster containing infinite {[Co(2,2-bpy)2]2[As8V14O42(H2O)]} chain constructed from [As8V14O42(H2O)] clusters interconnected through [Co(2,2-bpy)]2+ units. Crystal data: 1, orthorhombic, P 212121, a=12.1401(2) Å, b=15.8722(1) Å, c=39.9533(5) Å, Z=4.Graphical Abstract: A novel polyoxoarsenicvanadate, [CoII(2,2-bipy)2]2 [AsIII8VIV 14O42(H2O)]·H2O, is depicted along with a tubular hybrid solid with a rhombic tube formed within the chain. 相似文献
10.
Wataru Ueda Kenzo Oshihara Damien Vitry Tokio Hisano Youhei Kayashima 《Catalysis Surveys from Japan》2002,6(1-2):33-44
Mo-V-M(=Al, Ga, Bi, Sb and Te)–O mixed oxide catalysts were synthesized hydrothermally for the first time, characterized structurally, and tested for ethane and propane oxidation after activation by various ways. These catalysts were black solids of rod-shaped (fiber like) crystals, which had a layer structure in the direction of fiber axis and a high dimensional arrangement of metal octahedra in the cross-section plane. These fresh crystalline materials became active for catalytic oxidation of alkanes after heat-treatment at 600 °C and subsequent grinding in order to increase exposed plane of the cross-section. The resulting catalysts were very active for an oxidative dehydrogenation of ethane with 80% of the ethylene selectivity in the reaction temperature range of 300 to 400 °C and also showed about 50% selectivity to acrylic acid in the propane oxidation. Multi-functional character which derived from the high dimensional structure of the catalysts and mechanism of the selective alkane oxidation were discussed. 相似文献