全文获取类型
收费全文 | 35489篇 |
免费 | 5999篇 |
国内免费 | 4035篇 |
专业分类
化学 | 24475篇 |
晶体学 | 407篇 |
力学 | 2272篇 |
综合类 | 321篇 |
数学 | 4457篇 |
物理学 | 13591篇 |
出版年
2024年 | 87篇 |
2023年 | 702篇 |
2022年 | 1130篇 |
2021年 | 1263篇 |
2020年 | 1417篇 |
2019年 | 1400篇 |
2018年 | 1198篇 |
2017年 | 1163篇 |
2016年 | 1653篇 |
2015年 | 1662篇 |
2014年 | 2001篇 |
2013年 | 2615篇 |
2012年 | 3177篇 |
2011年 | 3256篇 |
2010年 | 2266篇 |
2009年 | 2220篇 |
2008年 | 2422篇 |
2007年 | 2098篇 |
2006年 | 1904篇 |
2005年 | 1565篇 |
2004年 | 1217篇 |
2003年 | 953篇 |
2002年 | 860篇 |
2001年 | 707篇 |
2000年 | 651篇 |
1999年 | 770篇 |
1998年 | 633篇 |
1997年 | 607篇 |
1996年 | 591篇 |
1995年 | 559篇 |
1994年 | 460篇 |
1993年 | 407篇 |
1992年 | 344篇 |
1991年 | 293篇 |
1990年 | 274篇 |
1989年 | 209篇 |
1988年 | 174篇 |
1987年 | 142篇 |
1986年 | 111篇 |
1985年 | 118篇 |
1984年 | 72篇 |
1983年 | 59篇 |
1982年 | 55篇 |
1981年 | 27篇 |
1980年 | 14篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1959年 | 2篇 |
1957年 | 8篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
981.
982.
983.
Zhigang Liu Renxian Zhou Xiaoming Zheng 《天然气化学杂志》2007,16(2):167-172
The CuO-CeO2 catalyst prepared by chelating method has a superior catalytic performance for the preferential oxidation of CO in rich hydrogen, compared with the CuO-CeO2 catalyst prepared by coprecipitation method. The CO conversions over these catalysts, at 120℃and 120000 ml/(g-h) in the absence of CO2 and H2O, are 99.6% and 88.6%, respectively, and the selectivity of O2 over these catalysts is very close (i.e. 51.3% and 55.8%, respectively). The influence of certain factors such as hydrogen concentration, carbon monoxide concentration, H2O, O2/CO ratios, and space velocity on the catalytic performance of CuO-CeO2 catalyst prepared by chelating method is also studied. The results show that the addition of hydrogen and H2O has a negative effect on the catalytic performance of CuO-CeO2 catalyst, however, the variation of space velocity and the O2/CO ratio causes a comparatively slight influence. 相似文献
984.
We report synthesis of temperature- and redox-responsive multiblock copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined α,ω-bis(dithioester)-functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) were prepared using 1,4-bis(thiobenzoylthiomethyl)benzene and 1,4-bis(2-(thiobenzoylthio)prop-2-yl)benzene as RAFT agents, respectively. Dually responsive multiblock copolymers were synthesized in a single aminolysis/oxidation step from the α,ω-bis(dithioester)-terminated PNIPAM and PDMAEMA. The copolymers and their stimulus-responsive behavior were characterized by size exclusion chromatography, NMR, light scattering and atomic force microscopy. Due to the presence of redox-sensitive disulfide bonds between the blocks, the copolymers were readily reduced to the starting polymer blocks. The presence of temperature-responsive PNIPAM blocks provided the copolymers with the ability to assemble into core-shell nanostructures with hydrophobic PNIPAM as a core and cationic PDMAEMA as stabilizing shell when above the phase transition temperatures of PNIPAM. The temperature-induced assembly of the copolymers also showed substantial pH sensitivity. The phase transition temperature increased with decreasing pH, while molecular weight of the assemblies decreased. 相似文献
985.
流动注射分析光度法同时测定镍和铁 总被引:7,自引:0,他引:7
建立了流动注射(FIA)光度法同时测定镍和铁的新方法,以乙酸-乙酸钠缓冲溶液(PH4.50)作载液,溴化十六烷基三甲胺作增溶剂,记录560nm处Ni(Ⅱ)-Br-PADAP与Fe(Ⅱ)-Br-PADAP的峰值吸收之和746nm处Fe(Ⅱ)-Br-PADAP的吸不度测定了钠基合金中的镍和铁。两咱离子的定量线性范围分别为0.10-1.20mg/lL和0.20-1.60mg/L,检出限为0.02mg/L 相似文献
986.
Li Shu-Min Miao Yan-Gang Zhou Zi-Fang Chen Ji Liu Yao-Yang 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,39(1):29-34
The first Born approximation is used to study the laser-assisted electron capture by a fast proton from a hydrogen atom. The laser modification on differential cross section peaks sharply in the forward direction. With the impact energy increasing, the change in integral cross section becomes notable. The more intense the laser, the greater the cross section is; the lower the frequency, the greater the cross section. 相似文献
987.
988.
989.
A type of high visible-light active titanium oxinitride(TiO2-xNx) powder was prepared by a simple proc-ess:the calcination of the hydrated titanium dioxide at the atmosphere of ammonia-argon using a tu-bular electric furnace at high temperatures. The hydrated titanium dioxide was synthesized as the precursor of TiO2-xNx using titanic acid as raw material,which came from sulfate technique of produc-ing titanium white. The effects of temperature and reaction time on the nitrogen content,grain size and crystal structure were studied. The visible-light activity and photocatalysis capability of the powder were also investigated. 相似文献
990.
The electrochemical behavior and the interaction of alizarin red S (ARS) with calf thymus DNA was investigated on a bare glassy carbon electrode (GCE) and DNA modified GCE (DNA/GCE), respectively. ARS showed a pair of redox peaks at ?0.445 V and ?0.414 V on a bare GCE. On addition of DNA into the ARS solution, the peak current of ARS decreased and the peak potential positively shifted, but without new redox peaks appeared. The ARS reduction peak current increased with immersion time on a DNA/GCE. The results showed that ARS could interact with DNA molecules by intercalative binding mode. The equilibrium constant, binding number and the ratio of binding constant for oxidized and reduced ARS forms were obtained. The DNA damage was directly detected by appearance of guanosine and adenosine bases oxidation signal. The influence of experimental conditions on DNA damage extent was discussed in detail. 相似文献