全文获取类型
收费全文 | 12060篇 |
免费 | 2726篇 |
国内免费 | 2241篇 |
专业分类
化学 | 6233篇 |
晶体学 | 90篇 |
力学 | 1163篇 |
综合类 | 24篇 |
数学 | 2306篇 |
物理学 | 7211篇 |
出版年
2024年 | 5篇 |
2023年 | 470篇 |
2022年 | 469篇 |
2021年 | 548篇 |
2020年 | 559篇 |
2019年 | 534篇 |
2018年 | 598篇 |
2017年 | 626篇 |
2016年 | 538篇 |
2015年 | 621篇 |
2014年 | 714篇 |
2013年 | 870篇 |
2012年 | 1026篇 |
2011年 | 1005篇 |
2010年 | 847篇 |
2009年 | 783篇 |
2008年 | 854篇 |
2007年 | 943篇 |
2006年 | 1016篇 |
2005年 | 596篇 |
2004年 | 424篇 |
2003年 | 367篇 |
2002年 | 355篇 |
2001年 | 366篇 |
2000年 | 254篇 |
1999年 | 291篇 |
1998年 | 230篇 |
1997年 | 189篇 |
1996年 | 144篇 |
1995年 | 102篇 |
1994年 | 94篇 |
1993年 | 86篇 |
1992年 | 80篇 |
1991年 | 61篇 |
1990年 | 54篇 |
1989年 | 51篇 |
1988年 | 36篇 |
1987年 | 44篇 |
1986年 | 43篇 |
1985年 | 46篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1971年 | 3篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
141.
以碳酸锶为甲烷吸附活化的模型催化剂,用切换变应答、CH4(CO2)-TPD等技术,对甲烷的吸附、碱性对催化剂性能的影响进行了研究,结果表明,甲烷在碳酸锶上的活化显示出明显的酸碱活化机理特征,瞬变应答及TPD结果均证明,甲烷在碳酸锶表面有较强的吸附,其脱附温度约310℃,关联结果表明,甲烷转化率及C2烃收率与催化剂表面SrO碱性中心浓度有非常一致的顺变关系,因此催化剂表面的酸碱中心可能是甲烷的选择活 相似文献
142.
溶剂热还原合成Cr2O3纳米管(英) 总被引:2,自引:0,他引:2
Cr2O3 nanotubes with diameters of 80 nm and lengths of 550 nm were synthesized in a solvothermal reduction system at 180 ℃. The acetyl acetone (AcAc) and ethylene glycol (EG) were used as the chelate agent and the reductant respectively in the system. An intermediate compound-Cr(Ⅲ)(C5H7O2)3 was formed to force Cr2O3to crystallize along one direction. 相似文献
143.
Polyethylene terephthalate(PET)/polycaprolactone(PCL) segmented copolymers with different hard segment contents and a blend of two of them were studied by using DSC, WAXS, TEM and IR techniques and dynamic mechanical, stress-strain and isothermal crystallization measurements. Emphasis was laid on the studies of influence of compositional heterogeneity on the morphology and properties of these segmented copolymers. It was found that the solution cast specimens of the more heterogeneous sample exhibit better segregation of segments, high crystallinity and melting temperature. They have higher thermal stability of mechanical properties at small deformations. However, they are less stable against large deformations and may become softer than the more homogeneous ones. 相似文献
144.
145.
ZHANG Wei-wei CHEN Yu-chun LUO Zhao-feng WANG Ju-ying MA De-yi 《高等学校化学研究》2007,23(4):404-407
In this study, surface plasmon resonance (SPR) for monitoring 17β-eatradiol (E2) was developed. The small molecule E2 was immobilized on a CM5 sensor chip for an indirect competitive immunoassay to detect E2. The SPR response bahed on the antigen-antibody reaction was measured by injecting the sample solution into the flow system. The limitation of detection was 0.445 μg/L. The developed SPE-SPR system was applied to analyze the seawater samples. Recovery of E2 was 91.6%-93. 1%. Relative standard deviations(RSD) for the E2 assay were between 10.9%-15.1% (n = 3). The range of determination of E2 samples from the sewage in the coastal marine environ-ment was between ND(lower than detection limit) and ca. 11.78 ng/L. 相似文献
146.
Solvent-free organic reactions have been attracting great interest of chemists due to the elimination of the usage of harmful organic solvents,low costs,and simplicity in the procedure1.Solvent-free mechanochemical reactions of fullerenes were explored and are significant for the reactions of fullerenes because the low solubility of fullerenes in common organic solvents requires large quantity of organic solvents and some novel fullerene reactions could only occur in the solid-state reaction2.… 相似文献
147.
Chuan Zhou Tao Juan Li Xin Cui Yao Fu Qing Xiang Guo 《中国化学快报》2007,18(10):1199-1202
The possibility to carry out Cu-catalyzed cross-couplings under ligandless conditions was studied.It was found that by using K_3PO_4 as the base,the cross-coupling could proceed successfully between aryl iodides and several types of nucleophiles.Aryl bromides were completely inactive under the same reaction conditions. 相似文献
148.
Youyi Sun Hongfang Jiu Douguo Zhang Jiangang Gao Bin Guo Qijin Zhang 《Chemical physics letters》2005,410(4-6):204-208
Ag colloidal nanoparticles coated with Eu(TTA)3 · 2H2O complexes were prepared, and it was found that Eu(TTA)3 · 2H2O complexes J-aggregate was formed on the surface of Ag nanoparticles according to a red shift (18.2 nm) in UV–Vis spectra. However, there had similar excitation wavelength, which was attributed to existence of Ag nanoparticles. Highly luminescent properties of Ag colloidal nanoparticles were observed, and it was believed to result from low energy transfer between Eu(III) complexes and Ag and the large electromagnetic field arising from the excitation of surface plasmon polariton of Ag nanoparticles. 相似文献
149.
150.
以生命和表面催化体系为对象,研究了介观化学体系中内涨落对体系非线性动力学行为的调控作用。内涨落可以诱导随机振荡,其强度在体系处于最佳尺度时会出现一个甚至多个极大值,并且在耦合体系中会得到进一步增强,表现为尺度共振效应、尺度选择效应和双重尺度效应,揭示了介观化学体系中尺度效应的新机制。 相似文献