全文获取类型
收费全文 | 289篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
化学 | 226篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 34篇 |
物理学 | 46篇 |
出版年
2022年 | 11篇 |
2021年 | 21篇 |
2020年 | 16篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 9篇 |
2013年 | 9篇 |
2012年 | 10篇 |
2011年 | 20篇 |
2010年 | 8篇 |
2009年 | 10篇 |
2008年 | 18篇 |
2007年 | 11篇 |
2006年 | 15篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 10篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有309条查询结果,搜索用时 15 毫秒
301.
302.
303.
Walczak RJ Nelson ME Priestley ND 《Journal of the American Chemical Society》2001,123(42):10415-10416
304.
Sylwia Bajkacz Paulina Adamczewska Klaudia Kokoszka Elbieta Kycia-Socka Adam Sochacki Ewa Felis 《Molecules (Basel, Switzerland)》2020,25(23)
The increase in the production and consumption of pharmaceuticals increases their presence in the global environment, which may result in direct threats to living organisms. For this reason, there is a need for new methods to analyze drugs in environmental samples. Here, a new procedure for separating and determining selected drugs (diclofenac, ibuprofen, and carbamazepine) from bottom sediment and water samples was developed. Drugs were determined by ultra-high performance liquid chromatography coupled with an ultraviolet detector (UHPLC-UV). In this work, a universal and single-step sample treatment, based on supramolecular solvents (SUPRAS), was proposed to isolate selected anticonvulsants and nonsteroidal anti-inflammatory drugs (NSAIDs) from sediment samples. The following parameters were experimentally selected: composition of the supramolecular solvent (composition THF:H2O (v/v), amount of decanoic acid), volume of extractant, sample mass, extraction time, centrifugation time, and centrifugation speed. Finally, the developed procedure was validated. A Speedisk procedure was also developed to extract selected drugs from water samples. The recovery of analytes using the SUPRAS procedure was in the range of 88.8–115%, while the recoveries of the Speedisk solid-phase extraction procedure ranged from 81.0–106%. The effectiveness of the sorption of the tested drugs by sediment was also examined. 相似文献
305.
Aleksandr Savateev Nadezda V. Tarakina Volker Strauss Tanveer Hussain Katharina ten Brummelhuis Jos Manuel Snchez Vadillo Yevheniia Markushyna Stefano Mazzanti Alexander P. Tyutyunnik Ralf Walczak Martin Oschatz Dirk M. Guldi Amir Karton Markus Antonietti 《Angewandte Chemie (International ed. in English)》2020,59(35):15061-15068
Polymeric carbon nitride materials have been used in numerous light‐to‐energy conversion applications ranging from photocatalysis to optoelectronics. For a new application and modelling, we first refined the crystal structure of potassium poly(heptazine imide) (K‐PHI)—a benchmark carbon nitride material in photocatalysis—by means of X‐ray powder diffraction and transmission electron microscopy. Using the crystal structure of K‐PHI, periodic DFT calculations were performed to calculate the density‐of‐states (DOS) and localize intra band states (IBS). IBS were found to be responsible for the enhanced K‐PHI absorption in the near IR region, to serve as electron traps, and to be useful in energy transfer reactions. Once excited with visible light, carbon nitrides, in addition to the direct recombination, can also undergo singlet–triplet intersystem crossing. We utilized the K‐PHI centered triplet excited states to trigger a cascade of energy transfer reactions and, in turn, to sensitize, for example, singlet oxygen (1O2) as a starting point to synthesis up to 25 different N‐rich heterocycles. 相似文献
306.
Adam Bartoszek Rémi Langevin Paweł G. Walczak 《Bulletin of the Brazilian Mathematical Society》2011,42(2):301-320
Canal surfaces defined as envelopes of 1-parameter families of spheres, can be characterized by the vanishing of one of the conformal principal
curvatures. We distinguish special canals which are characterized by the fact that the non-vanishing conformal principal curvature is constant along the characteristic
circles and show that they are conformally equivalent to either surfaces of revolution, or to cones over plane curves, or
to cylinders over plane curves, so they are isothermic. 相似文献
307.
Distribution and behavior of some radionuclides associated with the Trinity nuclear test 总被引:1,自引:0,他引:1
Jeremy J. Bellucci Christine Wallace Elizabeth C. Koeman Antonio Simonetti Peter C. Burns Jeremy Kieser Eli Port Terri Walczak 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(3):2049-2057
The activities of 133Ba, 137Cs, 152Eu, 154Eu, 155Eu, 239Pu, and 241Am were determined by gamma spectroscopy on the largest sample set (n = 49) of bulk trinitite to date. The range in activity for all isotopes is large. For example, the activity of 241Am (normalized to the time of detonation) ranges between 1 and 42 Bq/g. Comparison of activities for isotopes derived from the device, 241Am versus 137Cs, 155Eu, and 239Pu, indicate positive trends. Correlations were not observed between the activities of the soil-derived activation products 152Eu and 154Eu and the radioisotopes from the device. The calculated ratio of fission products (155Eu/137Cs) is 0.012 ± .006 (1σ, n = 3), which is lower than predicted for the thermal neutron-induced fission of 239Pu (~0.03). This discrepancy may be attributed to the spontaneous fission of the natural U tamper resulting in mixing between fission products from 239Pu and 235U. The spatial distribution of the trinitite samples relative to ground zero has been modeled based on the activity of 152Eu. The calculated distances do not correlate with any of the activities for the radioisotopes investigated here, and suggest a relatively homogeneous distribution. However, trinitite samples with the highest activities for 137Cs, 239Pu, and 241Am yield the shortest calculated distances of 50–60 m away from ground zero. 相似文献
308.
I. Stanimirova K. Michalik Z. Drzazga H. Trzeciak P.D. Wentzell B. Walczak 《Analytica chimica acta》2011,(1):1
The goal of the present study is to assess the effects of anticancer treatment with cyclophosphamide and cytarabine during pregnancy on the mineralization of mandible bones in 7-, 14- and 28-day-old rats. Each bone sample was described by its X-ray fluorescence spectrum characterizing the mineral composition. The data collected are multivariate in nature and their structure is difficult to visualize and interpret directly. Therefore, methods like analysis of variance–principal component analysis (ANOVA–PCA) and ANOVA–simultaneous component analysis (ASCA), which are suitable for the analysis of highly correlated spectral data and are able to incorporate information about the underlined experimental design, are greatly valued. In this study, the ASCA methodology adapted for unbalanced data was used to investigate the impact of the anticancer drug treatment during pregnancy on the mineralization of the mandible bones of newborn rats and to examine any changes in the mineralization of the bones over time.The results showed that treatment with cyclophosphamide and cytarabine during pregnancy induces a decrease in the K and Zn levels in the mandible bones of newborns. This suppresses the development of mandible bones in rats in the early stages (up to 14 days) of formation. An interesting observation was that the levels of essential minerals like K, Mg, Na and Ca vary considerably in the different regions of the mandible bones. 相似文献
309.
L.Rempulska Z.Walczak 《分析论及其应用》2004,20(1):1-15
In this paper we give theorems on the degree of approximation of functions of one and two variables by certain operators of the Szasz-Mirakyan type. 相似文献