全文获取类型
收费全文 | 9874篇 |
免费 | 1775篇 |
国内免费 | 1159篇 |
专业分类
化学 | 7397篇 |
晶体学 | 97篇 |
力学 | 474篇 |
综合类 | 112篇 |
数学 | 965篇 |
物理学 | 3763篇 |
出版年
2024年 | 40篇 |
2023年 | 219篇 |
2022年 | 375篇 |
2021年 | 404篇 |
2020年 | 456篇 |
2019年 | 508篇 |
2018年 | 407篇 |
2017年 | 367篇 |
2016年 | 561篇 |
2015年 | 552篇 |
2014年 | 636篇 |
2013年 | 772篇 |
2012年 | 947篇 |
2011年 | 901篇 |
2010年 | 673篇 |
2009年 | 574篇 |
2008年 | 653篇 |
2007年 | 605篇 |
2006年 | 486篇 |
2005年 | 384篇 |
2004年 | 282篇 |
2003年 | 256篇 |
2002年 | 291篇 |
2001年 | 266篇 |
2000年 | 157篇 |
1999年 | 203篇 |
1998年 | 155篇 |
1997年 | 96篇 |
1996年 | 95篇 |
1995年 | 62篇 |
1994年 | 73篇 |
1993年 | 62篇 |
1992年 | 57篇 |
1991年 | 53篇 |
1990年 | 43篇 |
1989年 | 38篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1959年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Hydroxyapatite coating on porous silicon substrate obtained by precipitation process 总被引:2,自引:0,他引:2
Chen Shaoqiang Zhu Ziqiang Zhu Jianzhong Zhang Jian Shi Yanling Yu Ke Wang Weiming Wang Xiaohua Feng Xiao Luo Laiqiang Shao Li 《Applied Surface Science》2004,230(1-4):418-424
Hydroxyapatite Ca10(PO4)6(OH)2 (HAP) is known as a bioactive and biocompatible material, HAP coatings were used to improve the biocompatible of substrate by many researcher, In this work, HAP thin films on porous silicon (PS) substrates have been prepared by aqueous precipitation method with rapid thermal annealing (RTA) processes. The HAP films had been prepared under the annealing temperature ranging from 300 to 1000 °C. By the measurement of X-ray diffraction (XRD), it was found that for the crystallinity optimization, the heat-treatment at 850–950 °C for 1 h would be favorable. Atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements reveal a dense and smooth surface of the HAP film, and tightly adherence of the coating on porous silicon substrate after sintered. Thus, by this method, porous silicon could be increased its bioactivity and so that could be used in the biomedical area. 相似文献
23.
Zhongfan Jia Qiang Fu Junlian Huang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(12):3836-3842
A new stratagem for the synthesis of amphiphilic graft copolymers of hydrophilic poly(ethylene oxide) as the main chain and hydrophobic polystyrene as the side chains is suggested. A poly(ethylene oxide) with pending 2,2,6,6‐tetramethylpiperidine‐1‐oxyls [poly(4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐co‐ethylene oxide)] was first prepared by the anionic ring‐opening copolymerization of ethylene oxide and 4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl, and then the graft copolymerization of styrene was completed with benzoyl peroxide as the initiator in the presence of poly(4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐co‐ethylene oxide). The polymerization of styrene was under control, and comblike, amphiphilic poly(ethylene oxide)‐g‐polystyrene was obtained. The copolymer and its intermediates were characterized with size exclusion chromatography, 1H NMR, and electron spin resonance in detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3836–3842, 2006 相似文献
24.
Activated carbon fiber (ACF) as extraction fiber for solid-phase microextraction (SPME) and its application for the analysis of banned organochlorine pesticides (OCPs) were investigated. Firstly, ACF was activated by different concentration of zinc chloride, which indicated that ACF activated by 60% zinc chloride had a reasonable specific surface area, pore volume and pore distribution. Secondly, the parameters for the ACF-SPME procedure, the adsorption and desorption conditions, were also optimized when coupled with gas chromatography-mass spectrometry (GC-MS). Thirdly, the ACF-SPME was used to analyze 17 kinds of OCPs in water. The linearity of most pesticides was found to be between 0.2 and 50 microg/l with GC-MS under the selected ion monitoring (SIM) acquisition mode. The limits of detection (LOD) at the sub microg/l were obtained. The work demonstrated here shows that ACF is a promising alternative for the SPME procedure. 相似文献
25.
Jia Chaohua 《数学学报(英文版)》1993,9(3):321-336
LetP(x) denote the greatest prime factor of IIz<n≤x+x1/2
n. In this paper, we prove thatP(x)>x
0.723 holds true for a sufficiently largex.
Project supported by the Tian Yuan Itam in the National Natural Science Foundation of China. 相似文献
26.
线圈型全光纤偏振器的研究 总被引:2,自引:0,他引:2
本文采用等效电流法对线圈型全光纤偏振器进行了分析计算.对应于保偏光纤中两正交传输基模的消光比,提出了一种分析保偏光纤弯曲损耗的新方法,这种方法基于将保偏光纤两个不同偏振模式分别等效为两个普通圆光纤的基模,等效参数通过测量不同偏振模式的模场半径来确定.实验证明这种理论计算方法与实验结果一致.最终,我们研制出的线圈型光纤偏振器在1.31μm工作波长下,实测消光比达30dB以上,工作偏振模式插入损耗≤3dB. 相似文献
27.
28.
29.
Borohydride exchange resin-transition metal(Co,Ni,Cu,)compoundsystems reduced C=C double to C-C single bond in ethanol. 相似文献
30.