全文获取类型
收费全文 | 68008篇 |
免费 | 5597篇 |
国内免费 | 5115篇 |
专业分类
化学 | 32504篇 |
晶体学 | 927篇 |
力学 | 4897篇 |
综合类 | 598篇 |
数学 | 11563篇 |
物理学 | 28231篇 |
出版年
2024年 | 111篇 |
2023年 | 610篇 |
2022年 | 1076篇 |
2021年 | 1524篇 |
2020年 | 1720篇 |
2019年 | 1699篇 |
2018年 | 1579篇 |
2017年 | 1884篇 |
2016年 | 2250篇 |
2015年 | 1886篇 |
2014年 | 2697篇 |
2013年 | 5022篇 |
2012年 | 3300篇 |
2011年 | 3797篇 |
2010年 | 2956篇 |
2009年 | 4188篇 |
2008年 | 4278篇 |
2007年 | 4709篇 |
2006年 | 3969篇 |
2005年 | 3161篇 |
2004年 | 2755篇 |
2003年 | 2887篇 |
2002年 | 3279篇 |
2001年 | 2328篇 |
2000年 | 2210篇 |
1999年 | 1860篇 |
1998年 | 1769篇 |
1997年 | 1097篇 |
1996年 | 1046篇 |
1995年 | 874篇 |
1994年 | 948篇 |
1993年 | 672篇 |
1992年 | 742篇 |
1991年 | 476篇 |
1990年 | 441篇 |
1989年 | 334篇 |
1988年 | 315篇 |
1987年 | 304篇 |
1986年 | 269篇 |
1985年 | 234篇 |
1984年 | 251篇 |
1983年 | 138篇 |
1982年 | 204篇 |
1981年 | 187篇 |
1980年 | 118篇 |
1979年 | 154篇 |
1978年 | 111篇 |
1977年 | 92篇 |
1976年 | 44篇 |
1973年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
以六氯环三膦腈(HCCP)为原料合成了六(4-苯基苯氧基)三聚膦腈(HPPCP)和六(4-苯基偶氮苯氧基)三聚膦腈(HPDPCP),运用1HNMR、31P NMR、IR等测试技术对其结构进行了表征。TGA结果表明,两种物质具有良好的热稳定性,HPPCP的最大热分解温度高达455℃,HPDPCP残留率高达62·83%(800℃)。同时紫外光谱研究结果表明,极性溶剂使HPDPCP的紫外吸收波长红移。HPPCP和HPDPCP在阻燃材料方面、HPDPCP在线性或非线性光学以及分子信息存储器件等方面有着潜在的应用前景。 相似文献
992.
Using ClO2 as chemiluminescence (CL) oxidant, a novel homogeneous CL system in neutral and near neutral aqueous solution is proposed in this paper. ClO2 could oxidize sulfite in pH 5.0–8.5 acetate buffer to produce CL emission, and pipemidic acid could sensitize the CL system. The ClO2–SO32−–pipemidic acid reaction was used as a model CL system and explored the possibility of highly active and eco-friendly ClO2 being used as CL oxidant in neutral and near neutral aqueous solution. Combined with flow-injection analysis, the proposed CL system was applied to the automated dissolution testing of pipemidic acid tablet. Compared with the common strong acidic or strong basic CL system, this proposed CL owns its advantages. 相似文献
993.
994.
995.
meso-四(邻烷氧基苯基)卟啉合钴的合成、表征和性能研究 总被引:3,自引:0,他引:3
合成了meso-四(邻烷氧基苯基)卟啉合钴配合物10个,其中未见文献报道的新化合物8个,研究了其合成、分离、纯化方法,首次得到了该系列化合物的晶体或固体。用1H NMR、MS、IR、UV、元素分析等表征确证了其结构,报道和解析了该类卟啉钴配合物的1H NMR特殊波谱现象。用差示扫描量热法(DSC)和偏光显微镜(PM)研究了该系列配合物的液晶性能,发现6个配合物具有液晶性。研究了烷氧基链长、金属离子和分子空间结构对卟啉液晶性能的影响,烷氧基链长的增加、金属配合物的形成有利于液晶性能的改善。 相似文献
996.
Guang-Hua Cui Jian-Rong Li Ruo-Hua Zhang Xian-He Bu 《Journal of Molecular Structure》2005,740(1-3):187-191
Two new coordination polymers, [Eu2(L)3(H2O)2]n 1 and {[Tb2(L)3(H2O)2]·H2O}n 2, (H2L=succinic acid) have been synthesized by the reaction of H2L with nitrate salts of Eu(III) or Tb(III) under hydrothermal conditions. The X-ray diffraction analysis reveals that the two complexes are constructed by L bridging the chains of edge-sharing EuO8(H2O) or TbO8(H2O) polyhedra to form 3D network structure. 1 and 2 possess different topological structures due to the difference in the conformations of L. The solid photoluminescence of 1 and 2 was also investigated in room temperature. 相似文献
997.
Ruiz E Rodríguez-Fortea A Cano J Alvarez S Alemany P 《Journal of computational chemistry》2003,24(8):982-989
The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data. 相似文献
998.
999.
A novel coordination polymer [{Cd(hmbdc)(H2O)3}·2H2O]n (hmbdc=5-hydroxy- isophthalic acid) has been synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P21/c, with a=9.599(3), b=18.699(5), c=7.557(2) (A), β= 108.198(4)°, V=1288.6(6) (A)3, Z=4, Mr=382.60, Dc=1.972 g/cm3, F(000)=760, μ=1.740, the final R=0.0555 and wR=0.0995 for 1732 observed reflections with Ⅰ > 2σ(Ⅰ). The structural analysis shows that the intermolecular hydrogen bonds and π-π interactions result in a three-dimensional supramolecular framework. 相似文献
1000.
Ranjana Yadav 《European Polymer Journal》2007,43(8):3531-3537
Models capable of predicting the maximum extent of conversion (p) of cardanol-based novolac-type phenolic resin, have been developed using response surface methodology to determine the optimum reaction conditions. Three-dimensional response surface and their contour plot were drawn. The maximum extent of conversion (98.93%) was predicted when the cardanol was condensed with formaldehyde (molar ratio 1:0.652) at 119.84 °C for a time period of 3 h with the catalyst (e.g., citric acid) concentration of 1.988% of total volume of cardanol and formaldehyde. The pH of the reaction mixture was maintained at 3.0. These predicted values for optimum process conditions were in good agreement with experimental data. 相似文献