全文获取类型
收费全文 | 20637篇 |
免费 | 3345篇 |
国内免费 | 2360篇 |
专业分类
化学 | 14367篇 |
晶体学 | 184篇 |
力学 | 1163篇 |
综合类 | 119篇 |
数学 | 2843篇 |
物理学 | 7666篇 |
出版年
2024年 | 88篇 |
2023年 | 454篇 |
2022年 | 679篇 |
2021年 | 747篇 |
2020年 | 889篇 |
2019年 | 812篇 |
2018年 | 721篇 |
2017年 | 691篇 |
2016年 | 1016篇 |
2015年 | 1004篇 |
2014年 | 1137篇 |
2013年 | 1513篇 |
2012年 | 1735篇 |
2011年 | 1821篇 |
2010年 | 1274篇 |
2009年 | 1137篇 |
2008年 | 1292篇 |
2007年 | 1154篇 |
2006年 | 1022篇 |
2005年 | 920篇 |
2004年 | 734篇 |
2003年 | 639篇 |
2002年 | 710篇 |
2001年 | 555篇 |
2000年 | 454篇 |
1999年 | 445篇 |
1998年 | 355篇 |
1997年 | 323篇 |
1996年 | 346篇 |
1995年 | 308篇 |
1994年 | 242篇 |
1993年 | 170篇 |
1992年 | 171篇 |
1991年 | 167篇 |
1990年 | 130篇 |
1989年 | 98篇 |
1988年 | 55篇 |
1987年 | 63篇 |
1986年 | 74篇 |
1985年 | 53篇 |
1984年 | 35篇 |
1983年 | 28篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1957年 | 4篇 |
1910年 | 3篇 |
1905年 | 2篇 |
1904年 | 2篇 |
1902年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
饮食中微量元素砷的分布规律与人体健康关系 总被引:3,自引:1,他引:2
采用催化动力学光度法测定了六大类(共三十种)样品中的总砷含量,探讨了砷在食品中的分布规律,建立了砷在人体中的安全系效和积累系效的效学评价公式,用于评价砷与人体健康的关系,这对人们选择食物有一定的指导意义。 相似文献
52.
53.
Qixin Guo Mitsuhiro NishioHiroshi Ogawa Akira Yoshida 《Solid State Communications》2003,126(11):601-604
Temperature dependence of optical reflectance spectra in vacuum ultraviolet region for aluminum nitride has been measured on high-quality single crystal with synchrotron radiation. The dominant structure due to the interband transition is observed at photon energy around 7.7 eV. With decreasing temperature, the energy position of the dominant structure in the reflectance spectra shifts towards higher energy. The experimental data has been fitted to the Bose-Einstein expression and the obtained parameter related to the strength of the electron-phonon interactions is much smaller than that for the peak at 6.2 eV, suggesting that the higher-lying interband transition energy decreases more slowly with increasing temperature in aluminum nitride (AlN). 相似文献
54.
Y. Gu Igor L. Kuskovsky R.D. Robinson G.F. Neumark S.P. Guo M.C. Tamargo 《Solid State Communications》2005,134(10):677-681
The composition and size of optically active CdxZn1−xSe/ZnSe quantum dots are estimated with a previously developed method. The results are then compared with those obtained for CdxZn1−xSe/Zn0.97Be0.03Se QDs. We show that introducing Be into the barrier material enhances both Cd composition and quantum size effect of optically active quantum dots. 相似文献
55.
56.
GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point optical monitoring method. 相似文献
57.
58.
The permittivity and loss of poly(methyl methacrylate) (PMMA) network crosslinked with trimethylol-1,1,1 propane and its interpenetrating network polymers with 10, 34, and 50% (by weight) poly(urethane) have been measured from 100 to 400 K over a frequency range of 12 to 1 × 105 Hz. Two relaxation processes, γ and β, are observed in the PMMA network, and a third process, αpu, in the 10% poly(urethane) IPN. At higher concentrations of poly(urethane), the γ process is removed from the temperature-frequency range of our study. Crosslinking in pure PMMA slows the segmental motions involved in the β process and raises its activation energy. Physical aging of the 10 wt% poly(urethane)-PMMA causes its γ process to become indiscernible and the αpu process to become better resolved. A discussion of these results in terms of local regions of segmental motion is provided. 相似文献
59.
60.
A new porphyrin, peroxyacetic acid uroporphyrin I, has been isolated from the urine of patients with congenital erythropoietic porphyria by reversed phase high performance liquid chromatography. The porphyrin was characterized by high resolution mass spectrometry and by typical chemical reactions of a peroxyacid. 相似文献