全文获取类型
收费全文 | 1059篇 |
免费 | 12篇 |
国内免费 | 68篇 |
专业分类
化学 | 836篇 |
晶体学 | 6篇 |
力学 | 27篇 |
综合类 | 1篇 |
数学 | 1篇 |
物理学 | 268篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 10篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 22篇 |
2018年 | 21篇 |
2017年 | 25篇 |
2016年 | 28篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 43篇 |
2012年 | 53篇 |
2011年 | 84篇 |
2010年 | 53篇 |
2009年 | 64篇 |
2008年 | 63篇 |
2007年 | 74篇 |
2006年 | 71篇 |
2005年 | 60篇 |
2004年 | 60篇 |
2003年 | 34篇 |
2002年 | 35篇 |
2001年 | 27篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 25篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 3篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 2篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1969年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有1139条查询结果,搜索用时 15 毫秒
31.
Christian J. Simensen 《Fresenius' Journal of Analytical Chemistry》1978,292(3):207-212
Summary A quantitative gas-chromatographic method (molecular sieve column, FID) for the determination of Al4C3 in aluminium and magnesium has been developed. The effect of methane from external sources has been investigated and eliminated. Metallographic analysis of carbides in polished specimens were consistent with the gas-chromatographic measurements within a factor of 2. The discrepancy can be explained by the large uncertainties in light microscopy analysis of the small carbides. Analysis of commercial magnesium shows that the metal contains ca. 2–9 ppm of Al4C3. The concentration of carbides in aluminium from the electrolysis cell is in the range of 10–35 ppm and in the final product of ca. 2–12 ppm Al4C3. CaC2 has been detected in a few magnesium and aluminium samples by means of gas-chromatography and microprobe analysis.
Gas-chromatographische Analyse von Carbiden in Aluminium und Magnesium
Zusammenfassung Zur Bestimmung von Al4C3 in Aluminium und Magnesium wurde eine quantitative gas-chromatographische Methode (MolekularsiebSäule, FID) entwickelt. Der Einfluß von Methan aus äußeren Quellen, wurde untersucht und ausgeschaltet. Die metallographischen Untersuchungen von Carbiden an polierten Proben stimmten mit den Ergebnissen der gas-chromatographischen Messungen mit einem Faktor von 2 überein. Der Unterschied kann durch die großen Unsicherheiten bei der lichtmikroskopischen Analyse der kleinen Carbide erklärt werden. Die Analyse des technisch reinen Magnesiums zeigt, daß das Metall ca. 2–9 ppm Al4C3 enthält. Die Konzentration von Carbiden in elektrolytisch raffiniertem Aluminium liegt im Bereich 10–35 ppm und im Endprodukt bei ca. 2–12 ppm Al4C3. CaC2 wurde in einigen Magnesium- und Aluminiumproben mit Hilfe von gas-chromatographischen und Mikrosondenuntersuchungen festgestellt.相似文献
32.
Chung‐Cheng Chang Kuo‐Ching Yang Jeng‐Gong Guo Leigh‐May Huang Li‐Chyung Wang Gene‐Hsiang Lee Shie‐Ming Peng 《中国化学会会志》2003,50(5):965-971
The insertion reaction of CS2 with Mg(NR2)2 (R= Et, iPr), MgR′2 (R′= Et, Ph) and R″MgBr (R″= iPr, Ph) respectively lead solid products, Mg(S2CNR2)2(THF)n ( 1 : R= Et, n=2; 2 : R= iPr, n=1), Mg(S2C′R)2(THF)2 ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S2C″R) (THF)3 ( 5 : ″R= iPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with 1H, 13C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography. 相似文献
33.
Hydrothermal investigations in the system MgO/B2O3/P2O5(/H2O) yielded two new magnesium borophosphates, Mg2(H2O)[BP3O9(OH)4] and Mg(H2O)2[B2P2O8(OH)2]·H2O. The crystal structures were solved by means of single crystal X‐ray diffraction. While the acentric crystal structure of Mg2(H2O)[BP3O9(OH)4] (orthorhombic, P212121 (No. 19), a = 709.44(5) pm, b = 859.70(4) pm, c = 1635.1(1) pm, V = 997.3(3) × 106 pm3, Z = 4) contains 1D infinite chains of magnesium coordination octahedra interconnected by a borophosphate tetramer, Mg(H2O)2[B2P2O8(OH)2]·H2O (monoclinic, P21/c (No. 14), a = 776.04(5) pm, b = 1464.26(9) pm, c = 824.10(4) pm, β = 90.25(1)°, V = 936.44(9) × 106 pm3,Z = 4) represents the first layered borophosphate with 63 net topology. The structures are discussed and classified in terms of structural systematics. 相似文献
34.
35.
Conductivity as a Sensor for Monitoring Relative Magnesium Corrosion Rates in Real‐time,in Serum‐containing Media under Cell Culture Conditions 下载免费PDF全文
Kolade Ojo Tracy Hopkins Madhura Joshi Pravahan Salunke Guangqi Zhang Keaton Nahan Zhannping Zhang Daoli Zhao Sarah K. Pixley Vesselin Shanov William R. Heineman 《Electroanalysis》2016,28(12):3000-3008
Because controlling the corrosion rate of magnesium metal will be crucial to the success of biomedical implants containing pure magnesium or magnesium alloys, many ways have been sought to improve in vitro tests to analyze corrosion rates, and also to identify new methods of preparing or post‐processing magnesium. In this work, for an in vitro assay, we explored the use of a commercially available conductivity sensor to study magnesium corrosion under cell culture conditions that duplicate many physiologically appropriate parameters. With this sensor, we studied the corrosion of two previously untested magnesium single crystal samples that differed in surface treatments that could alter corrosion rates. The results show that the relative conductivity changes in (mS/cm) over the total time of immersion were proportional to the corrosion rates in (mm/y) and also to the total magnesium released, as detected by inductively coupled plasma mass spectrometry (ICP‐MS). 相似文献
36.
37.
38.
A water circulation system with the almost same element composition and socket type was adopted in coral Acropora culture under different seawater pH value conditions and the data of the relationship between boron isotopic compositions of coral and seawater pH value by thermoelectric ionization mass spectrometer were obtained. According to the correlations between αcarb-3 of coral and the pH value of cultured seawater, αcarb-3 was not a constant but related to pH value, indicating that B(OH)3 also incorporated carbonate. Therefore, the theoretical formula could not be used to calculate the seawater pH value from the δ11Bcarb value of the measured marine biological carbonate. The empirical equations obtained experimentally would be an alternative method to calculate the seawater pH value. In addition, the mixed precipitation of CaCO3 and Mg(OH)2 was found in aquaculture tanks with high pH value, and the δ11B of the solid was significantly higher than that of cultured seawater. The result indicated that the presence of Mg(OH)2 had a significant effect on the boron isotope fractionation, which deserved our attention. 相似文献
39.
Slow evaporation of an aqueous solution containing l-threonine and magnesium sulphate heptahydrate, results in the fractional crystallization of the less soluble l-threonine crystal and not any novel optoelectronic ‘magnesium sulfate admixtured l-threonine’ crystal as reported by Puhal Raj et al. in Optik, 124 (2013) 6887–6891. 相似文献
40.