全文获取类型
收费全文 | 17665篇 |
免费 | 2753篇 |
国内免费 | 3148篇 |
专业分类
化学 | 13739篇 |
晶体学 | 247篇 |
力学 | 996篇 |
综合类 | 283篇 |
数学 | 2164篇 |
物理学 | 6137篇 |
出版年
2024年 | 41篇 |
2023年 | 350篇 |
2022年 | 662篇 |
2021年 | 663篇 |
2020年 | 761篇 |
2019年 | 746篇 |
2018年 | 594篇 |
2017年 | 607篇 |
2016年 | 915篇 |
2015年 | 915篇 |
2014年 | 1040篇 |
2013年 | 1383篇 |
2012年 | 1383篇 |
2011年 | 1528篇 |
2010年 | 1201篇 |
2009年 | 1080篇 |
2008年 | 1233篇 |
2007年 | 1123篇 |
2006年 | 1053篇 |
2005年 | 873篇 |
2004年 | 779篇 |
2003年 | 620篇 |
2002年 | 694篇 |
2001年 | 539篇 |
2000年 | 434篇 |
1999年 | 363篇 |
1998年 | 283篇 |
1997年 | 219篇 |
1996年 | 231篇 |
1995年 | 162篇 |
1994年 | 178篇 |
1993年 | 149篇 |
1992年 | 113篇 |
1991年 | 124篇 |
1990年 | 125篇 |
1989年 | 62篇 |
1988年 | 55篇 |
1987年 | 44篇 |
1986年 | 48篇 |
1985年 | 51篇 |
1984年 | 22篇 |
1983年 | 31篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1957年 | 4篇 |
1936年 | 5篇 |
1928年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
铬(Ⅲ)邻菲咯啉,8—羟基喹啉配合物/Y型分子筛的制备及苯酚催化羟化 总被引:2,自引:0,他引:2
制备了铬(Ⅲ)邻菲咯啉,8-羟基喹啉配合物/Y型分子筛,利用元素分析,SEM,UV-VisBET及XRD等方法确定了分子筛选笼中金属配合物的生在及其晶体结构,考察了实验参数对苯酚转化率及产物选择性的影响。 相似文献
82.
83.
84.
Ye Qing Li Ming Lu Chun Xu Lu Sai Jian Zhu Qi Fa Liu 《中国化学快报》2007,18(11):1313-1315
A novel and simple procedure for synthesis of azanucleoside by Mitsunobu reaction between N-(p-nitrobenzyloxycarbonyl)- trans-4-hydroxy-D-proline methyl ester obtained from trans-4-hydroxy-L-proline after six-step reaction and 2-fluoro-6-azidopurine is described,and azanucleoside is fluorinated by new fluridizer 2,2-difluoro-1,3-dimethylimidazolidine (DFI).All reactions could be carded out under mild condition. 相似文献
85.
Studies on fluorenscence resonance energy transfer between CdS nanoparticles and DOCAI dyes 总被引:1,自引:0,他引:1
Lun Wang Yan Liu Hong Qi Chen A Ni Liang Fa Gong Xu 《中国化学快报》2007,18(3):369-372
The water-soluble CdS nanoparticles were synthesized in aqueous solution. A novel fluorescence resonance energy transfer (FRET) system with CdS nanoparticles as energy donors and 3,30-diethyl-oxadicarbocyanine iodide (DOCAI) dyes as energy accepter has been developed. 相似文献
86.
Multicomponent Na2V6O16.3H2O (barnesite) single-crystalline nanobelts were synthesized by a direct reaction-crystallization growth of bulk V2O5 and NaF powders under hydrothermal treatment without using any templates or catalysts. This new strategy could be extended to prepare other one-dimensional multicomponent nanomaterials including ammonium, alkali-metal or alkali-earth metal vanadium oxide bronzes and other transition metal oxyfluorides. This is an efficient and mild solution method with clear advantages over the traditional high-temperature approach for the large-scale production of 1D multicomponent nanomaterials. The applicability of this approach toward the preparation of other inorganic systems, such as tungstates and molybdates, will be explored. 相似文献
87.
Preparation of flame retardant polyamide 6 composite with melamine cyanurate nanoparticles in situ formed in extrusion process 总被引:1,自引:0,他引:1
This paper is focused on in situ preparation of melamine cyanurate (MCA) nanoparticles from reaction of melamine (MEL) and cyanuric acid (CA) and their flame retardant polyamide 6 (PA6) composite in the extrusion process through a novel reactive processing method. Fourier transform infrared (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were utilized to characterize the in situ formed MCA nanoparticles and their blends with PA6. Introduction of pentaerythritol (LTP) and water-bound plasticizer dioctyl phthalate (DPT) into the extrusion reaction system greatly inhibits the evaporation of water required for melamine and cyanuric acid reaction at high temperature (higher than 180 °C), laying a foundation for successful in situ preparation of MCA through reactive processing. XRD and FT-IR measurements indicate that under the effect of pentaerythritol, dioctyl phthalate and water, melamine really reacts with cyanuric acid to in situ form MCA in extrusion process. The reaction degree is close to 100%. A very important finding through SEM is that the in situ formed MCA particles, which were found to have aspect ratio of about 7.5, radial size in the range of 70-300 nm (mostly 70-90 nm) and crystallite size of less than 22 nm, are uniformly dispersed in the matrix PA6 at nanoscale. The in situ formed MCA nanoparticles greatly improve the flame retardancy and the mechanical properties of flame-retarded PA6 materials, and the introduced plasticizer dioctyl phthalate also ameliorates the related impact property. The obtained flame-retarded PA6 materials have good comprehensive performance with flame retardancy UL-94 V-0 rating at 1.6 and 3.2 mm thickness, tensile strength 48.0 MPa, elongation at break 106.3% and Izod notched impact strength 8.92 kJ/m2. Compared with flame-retarded PA6 material with in situ formed MCA, the one prepared through conventional blending of PA6 with commercial MCA product has improved tensile strength but deteriorated impact strength and flame retardancy. 相似文献
88.
89.
90.