全文获取类型
收费全文 | 533篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 429篇 |
晶体学 | 2篇 |
力学 | 10篇 |
数学 | 70篇 |
物理学 | 40篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 28篇 |
2012年 | 20篇 |
2011年 | 46篇 |
2010年 | 22篇 |
2009年 | 21篇 |
2008年 | 30篇 |
2007年 | 23篇 |
2006年 | 24篇 |
2005年 | 20篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1978年 | 3篇 |
1974年 | 5篇 |
1970年 | 5篇 |
1968年 | 2篇 |
1914年 | 1篇 |
1913年 | 3篇 |
1911年 | 1篇 |
1909年 | 1篇 |
排序方式: 共有551条查询结果,搜索用时 15 毫秒
101.
Among others, two main objectives of modern vehicle design are road friendliness and ride comfort. Both aspects are strongly related since the dynamical tire forces depend on the vertical acceleration of the vehicle. In order to investigate the influence of design and operation parameters, different car models are considered which move with constant velocity on a rippled road. First, a linear half car model is examined and the influence of different design parameters is discussed. Second, nonlinear suspensions with Coulomb friction due to sealings as well as with bilinear shock absorbers are taken into account. The vertical dynamics of the vehicle model and the dynamic tire forces between vehicle and road are calculated using analytical methods. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
102.
Model reduction in aerodynamic applications usually makes use of Proper Orthogonal Decomposition (POD). In this work a POD-based method, called Missing Point Estimation (MPE), will be applied to steady state flows with variation of the flow parameter angle of attack. The basic idea of MPE is to select a subset of the computational grid points (control volumes) and limit the governing equations to these. Subsequently, the remaining equations are projected onto the POD subspace. This approach has the advantage that the nonlinear right hand side of the governing equations has to be evaluated only for some selected points (control volumes) which makes the MPE faster than classical Galerkin projection. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
103.
104.
Mass spectrometric approaches for the identification of anthracycline analogs produced by actinobacteria
下载免费PDF全文
![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Anelize Bauermeister Tiago Domingues Zucchi Luiz Alberto Beraldo Moraes 《Journal of mass spectrometry : JMS》2016,51(6):437-445
Anthracyclines are a well‐known chemical class produced by actinobacteria used effectively in cancer treatment; however, these compounds are usually produced in few amounts because of being toxic against their producers. In this work, we successfully explored the mass spectrometry versatility to detect 18 anthracyclines in microbial crude extract. From collision‐induced dissociation and nuclear magnetic resonance spectra, we proposed structures for five new and identified three more anthracyclines already described in the literature, nocardicyclins A and B and nothramicin. One new compound 8 (4‐[4‐(dimethylamino)‐5‐hydroxy‐4,6‐dimethyloxan‐2‐yl]oxy‐2,5,7,12‐tetrahydroxy‐3,10‐dimethoxy‐2‐methyl‐3,4‐dihydrotetracene‐1,6,11‐trione) was isolated and had its structure confirmed by 1H nuclear magnetic resonance. The anthracyclines identified in this work show an interesting aminoglycoside, poorly found in natural products, 3‐methyl‐rhodosamine and derivatives. This fact encouraged to develop a focused method to identify compounds with aminoglycosides (rhodosamine, m/z 158; 3‐methyl‐rhodosamine, m/z 172; 4′‐O‐acethyl‐3‐C‐methyl‐rhodosamine, m/z 214). This method allowed the detection of four more anthracyclines. This focused method can also be applied in the search of these aminoglycosides in other microbial crude extracts. Additionally, it was observed that nocardicyclin A, nothramicin and compound 8 were able to interact to DNA through a DNA‐binding study by mass spectrometry, showing its potential as anticancer drugs. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
105.
Brückner R Haller H Ellwanger M Riedel S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(18):5741-5747
Polychloride monoanions stabilized by quaternary ammonium salts are investigated using Raman spectroscopy and state-of-the-art quantum-chemical calculations. A regular V-shaped pentachloride is characterized for the [N(Me)(4)][Cl(5)] salt, whereas a hockey-stick-like structure is tentatively assigned for [N(Et)(4)][Cl(2)???Cl(3)(-)]. Increasing the size of the cation to the quaternary ammonium salts [NPr(4)](+) and [NBu(4)](+) leads to the formation of the [Cl(3)](-) anion. The latter is found to be a pale yellow liquid at about 40 °C, whereas all the other compounds exist as powders. Further to these observations, the novel [Cl(9)](-) anion is characterized by low-temperature Raman spectroscopy in conjunction with quantum-chemical calculations. 相似文献
106.
Dipl. Chem. Robin Brückner Dipl. Chem. Heike Haller Mathias Ellwanger Dr. Sebastian Riedel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(18):5741-5747
Polychloride monoanions stabilized by quaternary ammonium salts are investigated using Raman spectroscopy and state‐of‐the‐art quantum‐chemical calculations. A regular V‐shaped pentachloride is characterized for the [N(Me)4][Cl5] salt, whereas a hockey‐stick‐like structure is tentatively assigned for [N(Et)4][Cl2???Cl3?]. Increasing the size of the cation to the quaternary ammonium salts [NPr4]+ and [NBu4]+ leads to the formation of the [Cl3]? anion. The latter is found to be a pale yellow liquid at about 40 °C, whereas all the other compounds exist as powders. Further to these observations, the novel [Cl9]? anion is characterized by low‐temperature Raman spectroscopy in conjunction with quantum‐chemical calculations. 相似文献
107.
Junichi Kinoshita Yoshihisa Ikeda Yuji Takeda Misaki Ueno Yoji Kawasaki Yoshiaki Matsuba Atsushi Heike 《Optical Review》2012,19(6):427-431
The speckle contrast of blue light emission out of high-brightness white lamps using phosphors excited by InGaN/GaN blue laser diodes is evaluated as a measure of coherence. As a result, speckle contrast of as low as 1.7%, the same level as a blue light emitting diode, is obtained. This implies that the original blue laser light can be converted into incoherent light through lamp structures without any dynamic mechanisms. This unique speckle-free performance is considered to be realized by multiple scattering inside the lamp structure, the multi-longitudinal mode operation of the blue laser diodes, and the use of multiple laser diodes. Such almost-incoherent white lamps can be applied for general lighting without any nuisance of speckle noise and should be categorized as lamps rather than lasers in terms of laser safety regulation. 相似文献
108.
Binary Al?CTi, Al?CZr and Al?CZn oxides, prepared by the sol?Cgel method were used as supports of catalytic systems. The catalysts were prepared by impregnation of these supports with the low cost Co or Ni nitrate salts and subsequent calcination at 700?°C. Catalysts have been characterized by SBET, XRD and TPR techniques. The catalysts were tested in ethanol partial oxidation using a fixed-bed quartz reactor at atmospheric pressure and temperature at 600?°C. In test reactions a constant feed composition was used with O2/EtOH molar ratio of 0.75 in nitrogen balance. The catalytic performance of the systems depends on type of support and type of promoter. Hydrogen and CO are the predominant products beside some by-products in different quantities (CO2, methane, ethylene, acetaldehyde, acetone, acetic acid). The Co and Ni catalysts supported on AlZn binary oxide showed the highest selectivity to hydrogen and to carbon monoxide with full ethanol conversion. Selectivity of hydrogen follows the order of Co(Ni)AlZn?>?Co(Ni)AlTi?>?Co(Ni)AlZr. The best performance was obtained by NiAlZn catalyst with 89?% hydrogen selectivity. 相似文献
109.
Molten salt hydrates proved to be alternative solvents to cellulose. Toinvestigate the reasons for this dissolving ability, information about thesolvent–cellulose interactions is essential. As well as 13CHR NMR, 7Li NMR was used to obtain further insight into thisproblem.After comparing several molten salt hydrates, the 7Li NMR spectrarevealed a smaller shielding of the lithium cation for not dissolving than fordissolving and swelling cellulose systems. In most solvent systems theshieldingat the 7Li nuclei increases with the cellulose concentration. 2D7Li-1H HOESY NMR was successfully applied to verify thepresence of cellobiose, used as a model compound for cellulose, in the firstco-ordination sphere of the lithium cation. 相似文献
110.
Christian Leischner Markus Burkard Anja Michel Susanne Berchtold Heike Niessner Luigi Marongiu Christian Busch Jan Frank Ulrich M. Lauer Sascha Venturelli 《Molecules (Basel, Switzerland)》2021,26(18)
Resveratrol, a natural plant phytoalexin, is produced in response to fungal infection or− UV irradiation. It exists as an isomeric pair with cis- and trans-conformation. Whereas multiple physiological effects of the trans-form, including a pronounced anti-tumoral activity, are nowadays elucidated, much less knowledge exists concerning the cis-isomer. In our work, we analyzed the antiproliferative and cytotoxic properties of cis-resveratrol in four different human tumor entities in direct comparison to trans-resveratrol. We used human cell lines as tumor models for hepatocellular carcinoma (HCC; HepG2, Hep3B), colon carcinoma (HCT-116, HCT-116/p53(−/−)), pancreatic carcinoma (Capan-2, MiaPaCa-2), and renal cell carcinoma (A498, SN12C). Increased cytotoxicity in all investigated tumor cells was observed for the trans-isomer. To verify possible effects of the tumor suppressor p53 on resveratrol-induced cell death, we used wild type and p53-deleted or -mutated cell lines for every tested tumor entity. Applying viability and cytotoxicity assays, we demonstrated a differential, dose-dependent sensitivity towards cis- or trans-resveratrol among the respective tumor types. 相似文献