全文获取类型
收费全文 | 399篇 |
免费 | 16篇 |
国内免费 | 3篇 |
专业分类
化学 | 263篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 68篇 |
物理学 | 71篇 |
出版年
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 19篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2016年 | 17篇 |
2015年 | 9篇 |
2014年 | 10篇 |
2013年 | 22篇 |
2012年 | 29篇 |
2011年 | 37篇 |
2010年 | 20篇 |
2009年 | 18篇 |
2008年 | 19篇 |
2007年 | 13篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 12篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 4篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1966年 | 3篇 |
1965年 | 4篇 |
1963年 | 3篇 |
1962年 | 3篇 |
1942年 | 2篇 |
1941年 | 2篇 |
1940年 | 2篇 |
1939年 | 3篇 |
1937年 | 3篇 |
1934年 | 2篇 |
排序方式: 共有418条查询结果,搜索用时 15 毫秒
1.
Zusammenfassung Es wurde die Gehaltsänderung der isomorphen Verunreinigung zweier Systeme: Na2SO4·10 H2O/Na2SeO4·10 H2O und Na2SO4·10 H2O/Na2CrO4·10 H2O während der Entwässerung sowohl in deren gesätt. Lösung bei der Übergangstemp. als auch durch Lösungsmittel (CH3OH und C2H5OH) untersucht.Der nach beiden genannten Methoden durchgeführte Entwässerungsprozeß ist von einer Verminderung der isomorphen Verunreinigung begleitet. Der Reinigungskoeffizient (W) hängt mit der Beschaffenheit der isomorphen Verunreinigung und deren Konzentration im ursprünglichen Kristallhydrat zusammen. Wenn die Entwässerung unter Einwirkung organischer Lösungsmittel verläuft, istW auch noch von der Natur des Entwässerungsmittels selbst sowie von der Löslichkeit der isomorphen Verunreinigung im verwendeten Lösungsmittel abhängig.
Mit 2 Abbildungen 相似文献
Dehydration of crystal hydrates as a method of purifying salts, VII: Investigation of the alteration of isomorphous contaminant content during the dehydration ofNa 2 SO 4·10 H2 O in its saturated solution at the transition temperatur and by employing organic solvents
The change in the content of isomorphous contaminant of the two systems Na2SO4·10 H2O/Na2SeO4·10 H2O and Na2SO4·10 H2O/Na2CrO4·10 H2O during dehydratation has been investigated both in their saturated solution at the temperature of transition and by the solvents CH3OH and C2H5OH.The dehydratation process, carried out by either method mentioned, is accompanied with a decrease of the isomorphous contaminant content in the crystalline mass. The coefficient of purification (W) depends on the nature of the isomorphous contaminant and its concentration in the initial crystallohydrate. In the case, when dehydratation takes place under the action of organic solvents,W depends also on the nature of the dehydratation agent itself, as well as on the solubility of the isomorphous contaminant in the employed solvent.
Mit 2 Abbildungen 相似文献
2.
In the present work are brought forth experimental data on the problem of the size of the crystal nucleus in supersatured solutions of sodium sulphate. A method is employed in which two supersaturated solutions of Na2SO4·10H2O are separated by a porous membrane with a various average diameter of the pores and in one supersaturated solution crystallization is being caused. The experiments showed that in case of sizes 10–15 mμ of the pores, the second supersaturated solution does not crystallize. These sizes are from order ofOstwalds experimental crystal nucleus (about 1 mμ) correspond to that estimated byGorbatshev andShlikov (1,2–3,0 μ) and almost coincide with that estimated byGopal (about 10 mμ). 相似文献
3.
The experimental parameters of cathodic stripping chronopotentiometry of chloride at a silver-film electrode are investigated and optimized. The chloride preconcentration is achieved in the form of silver chloride by a controlled potential oxidation of the working electrode under vigorous stirring. Cathodic stripping of the deposit is obtained by the constant current, under the condition of diffusive mass transfer. Deaeration of the solution is not necessary. A detection limit of 35 μ dm−3 (10−6 mol dm−3) is obtained at a deposition time of 180 s, with a reproducibility of 6.7 % (expressed as relative standard deviation, RSD). 相似文献
4.
A simple unequal-sphere packing model is applied to study the iodine (3x3) adlayer on the Pt(111) surface. By using a newly introduced parameter, defined as the average adsorbate height, three characteristic adlattices, (3x3)-sym, (3x3)-asym, and (3x3)-lin, have been selected and characterized in great detail, including the exact adatom registry. The (3x3)-sym iodine adlattice, observed in many experimental studies, appears to be, on average, the closest one to the substrate surface. A special contour plot of average adsorbate height vs X and Y positions of the (3x3) iodine unit cell indicates the existence of two local minima, which are related to preferential formation of (3x3)-sym and (3x3)-asym iodine adlattices. Our model gives good agreement with experimental findings, and explains the mechanism of preferential appearance of (3x3)-sym and (3x3)-asym structures. 相似文献
5.
An amperometric detector with a small thin mercury film electrode is described. The device demonstrates advantageous operational
characteristics such as small dispersion (D<2) and “memory effect” (me<0.6%), extensive maximum sample frequency (msf −200
samples/h), and high sensitivity. It has been proven useful in flow-injection analysis at a constant potential under hydrodynamic
conditions. 相似文献
6.
Nikola Horvacki Filip Andri Uro Gai Dejan urovi
ivoslav Tei Milica Fotiri Aki Duanka Milojkovi-Opsenica 《Molecules (Basel, Switzerland)》2022,27(21)
Domesticated international (standard) apple cultivars, together with resistant apple cultivars are the core of the Serbian apple production. Furthermore, autochthonous cultivars are characterized by a good adaptability to the local environmental conditions and represent a valuable source of genetic variability, as well as an important source of the gene pool for further breeding programs. Additionally, they show a higher phenolic content and a stronger antioxidant activity, in comparison to commercial cultivars. Therefore, they are more likely to be used as a functional food. The subjects of this study were seventeen samples of fruits and leaves from autochthonous apple cultivars, five international standard cultivars, and six resistant apple cultivars. The phenolic profile was determined using ultra-high performance liquid chromatography (UHPLC), coupled with a diode array detector and a TSQ Quantum Access Max triple-quadrupole mass spectrometer. A total of twenty compounds were quantified in the samples. Most of the analyzed phenolics were detected in higher amounts in the peel, compared to the mesocarp. The results of the multivariate analysis of variance (MANOVA) indicate that 5-O-caffeoylquinic acid is present in the highest amount in the mesocarp, while in the peel and leaves, quercetin-glycosides were detected in the highest amount. According to the MANOVA: phloretin, phlorizin, 5-O-caffeoylquinic acid, kaempferol, and p-coumaric acid are present in significantly higher levels in the autochthonous cultivars, compared to the standard and resistant ones (in both fruits and leaves). Therefore, these compounds can be used as chemical tracers of the apple varietal origin. 相似文献
7.
Postbiotics are health-promoting microbial metabolites delivered as a functional food or a food supplement. They either directly influence signaling pathways of the body or indirectly manipulate metabolism and the composition of intestinal microflora. Cancer is the second leading cause of death worldwide and even though the prognosis of patients is improving, it is still poor in the substantial part of the cases. The preventable nature of cancer and the importance of a complex multi-level approach in anticancer therapy motivate the search for novel avenues of establishing the anticancer environment in the human body. This review summarizes the principal findings demonstrating the usefulness of both natural and synthetic sources of postbotics in the prevention and therapy of cancer. Specifically, the effects of crude cell-free supernatants, the short-chain fatty acid butyrate, lactic acid, hydrogen sulfide, and β-glucans are described. Contradictory roles of postbiotics in healthy and tumor tissues are highlighted. In conclusion, the application of postbiotics is an efficient complementary strategy to combat cancer. 相似文献
8.
9.
10.