全文获取类型
收费全文 | 24921篇 |
免费 | 1873篇 |
国内免费 | 4327篇 |
专业分类
化学 | 22265篇 |
晶体学 | 446篇 |
力学 | 702篇 |
综合类 | 198篇 |
数学 | 2032篇 |
物理学 | 5478篇 |
出版年
2024年 | 31篇 |
2023年 | 257篇 |
2022年 | 626篇 |
2021年 | 557篇 |
2020年 | 589篇 |
2019年 | 930篇 |
2018年 | 652篇 |
2017年 | 974篇 |
2016年 | 812篇 |
2015年 | 730篇 |
2014年 | 851篇 |
2013年 | 1885篇 |
2012年 | 1577篇 |
2011年 | 1671篇 |
2010年 | 1282篇 |
2009年 | 1599篇 |
2008年 | 1673篇 |
2007年 | 1636篇 |
2006年 | 1582篇 |
2005年 | 1376篇 |
2004年 | 1359篇 |
2003年 | 1100篇 |
2002年 | 1028篇 |
2001年 | 785篇 |
2000年 | 770篇 |
1999年 | 608篇 |
1998年 | 527篇 |
1997年 | 499篇 |
1996年 | 476篇 |
1995年 | 482篇 |
1994年 | 379篇 |
1993年 | 332篇 |
1992年 | 308篇 |
1991年 | 209篇 |
1990年 | 171篇 |
1989年 | 141篇 |
1988年 | 114篇 |
1987年 | 71篇 |
1986年 | 71篇 |
1985年 | 50篇 |
1984年 | 59篇 |
1983年 | 17篇 |
1982年 | 33篇 |
1981年 | 53篇 |
1980年 | 37篇 |
1979年 | 41篇 |
1978年 | 28篇 |
1976年 | 19篇 |
1974年 | 15篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
Mössbauer investigations about iron atom redistribution in oxide films of zirconium alloys subjected to corrosion at 500°C in pure oxygen and water pair have been analysed. The alloys were also subjected to autoclave conditions at a pressure of 10.0 MPa and autoclave conditions at 350°C and at a pressure of 16.8 MPa, using distilled water and water with additives of lithium and fluorine. It is shown that, depending on the corrosion environment, various compounds of iron, such as α-Fe2O3, Fe3O4, and FeO, as solid solutions of iron in ZrO2 are formed in oxide films. 相似文献
54.
55.
The Li oxides species formed on Li over-deposited V2O5 thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V2O5 system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li2O and Li2O2 compounds on the surface. The formation of Li2O2 causes to arise an emission line at about 11.3 eV in the valence band spectra. 相似文献
56.
To find an effective extraction and removal method for palladium(II), which is one of the main fission products from an acidic nuclear spent fuel solution, the extraction behavior of palladium(II) from a nitric acid medium by an acidic chelating extractant, 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5-one (HPMTP) and a tertiary amine of high molecular weight, tri-n-octylamine (TOA), has been studied by spectrophotometry. A noticeable antagonistic extraction effect was observed in the extraction system under the given conditions. To understand this phenomenon, a preliminary investigation was performed to explain the mechanism of this reaction. According to the theory of corresponding solutions (TCS), the association reaction between HPMTP and TOA is proposed in the organic phase. An associated species, HPMTP·TOA, formed through hydrogen bonding in a chloroform medium might be the main reason why an antagonistic extraction effect occurred. The association constant between HPMTP and TOA was calculated to be 2.86±0.05. 相似文献
57.
F. R. Ling B. Wang T. Geng S. Q. Fang W. Yuan D. D. Teng C. X. Guan 《Optics & Laser Technology》2004,36(7):541-544
In this paper experimental studies of nonvolatile photorefractive holographic recording in Ce:Cu:LiNbO3 crystals doped with Sc(0,1,2,3 mol%) were carried out. The Sc:Ce:Cu:LiNbO3 crystals were grown by the Czochralski method and oxidized in Nb2O5 powders. The nonvolatile holographic recording in Sc:Ce:Cu:LiNbO3 crystals was realized by the two-photon fixed method. We found that the recording time of Sc:Ce:Cu:LiNbO3 crystal became shorter with the increase of Sc doping concentration, especially doping with Sc(3 mol%), which exceeds the so-called threshold, and there was little loss of nonvolatile diffraction efficiencies between Sc(3 mol%):Ce:Cu:LiNbO3 and Ce:Cu:LiNbO3 crystals. 相似文献
58.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
59.
60.
本文实验发现具有较大密度和较高速度的93W钨合金长杆模拟弹的穿靶深度反而比密度较小,速度较低的90W钨合金长杆弹的穿靶深度小.针对这一现象,本文从两种材料在侵彻环境下的细观响应特性的差异上给出了有实验根据的合理分析,结论是90W在侵彻环境下较易于形成绝热剪切带,从而在弹头部发生“自锐化”效应所致. 相似文献