全文获取类型
收费全文 | 438篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 375篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 28篇 |
物理学 | 46篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 26篇 |
2012年 | 24篇 |
2011年 | 19篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 18篇 |
2007年 | 21篇 |
2006年 | 23篇 |
2005年 | 37篇 |
2004年 | 32篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有454条查询结果,搜索用时 46 毫秒
81.
Itoh Y Ezawa A Kikuchi K Tsuruta Y Niwa T 《Analytical and bioanalytical chemistry》2012,403(7):1841-1850
Cardiovascular disease (CVD) is prevalent in patients with chronic kidney disease (CKD). In hemodialysis (HD) patients, some protein-bound uremic toxins are considered to be associated with CVD. However, it is not yet known which uremic toxins are important in terms of endothelial toxicity. Serum samples were obtained from 45 HD patients before and after HD. Total and free serum concentrations of indoxyl sulfate, indoxyl glucuronide, indoleacetic acid, p-cresyl sulfate, p-cresyl glucuronide, phenyl sulfate, phenyl glucuronide, phenylacetic acid, phenylacetyl glutamine, hippuric acid, 4-ethylphenyl sulfate, and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF) were simultaneously measured by liquid chromatography/electrospray ionization-mass spectrometry/mass spectrometry (LC/ESI-MS/MS). The effects of these solutes at their pre-HD mean and maximum serum concentrations on reactive oxygen species (ROS) production in human umbilical vein endothelial cells (HUVEC) were measured with a ROS probe. Serum levels of 11 of the solutes (all except 4-ethylphenyl sulfate) were significantly increased in HD patients compared to healthy subjects. All 12 solutes showed changes in their protein-binding ratios. In particular, indoxyl sulfate, p-cresyl sulfate, CMPF, and 4-ethylphenyl sulfate showed high protein-binding ratios (>95 %) and low reduction rates by HD (<35 %). Indoxyl sulfate at its mean and maximum pre-HD serum concentrations-even with 4 % albumin-stimulated ROS production in HUVEC most intensely, followed by CMPF. In conclusion, the serum levels of 11 protein-bound uremic toxins were increased in HD patients. Indoxyl sulfate, p-cresyl sulfate, and CMPF could not be removed efficiently by HD due to their high protein-binding ratios. Indoxyl sulfate most intensely induced endothelial ROS production, followed by CMPF. 相似文献
82.
83.
Dr. Hayato Fukuda Yuko Nishiyama Shiina Nakamura Yutaro Ohno Prof. Dr. Tadashi Eguchi Prof. Dr. Yoshiharu Iwabuchi Prof. Dr. Takeo Usui Prof. Dr. Naoki Kanoh 《化学:亚洲杂志》2012,7(12):2872-2881
We have developed two syntheses of vicenistatin and its analogues. Our first‐generation strategy included the rapid and sequential assembly of the macrocyclic lactam by using an intermolecular Horner–Wadsworth–Emmons reaction between the C3–C13 fragment and the C1–C2, C14–C19 fragment, followed by an intramolecular Stille coupling reaction. The second‐generation strategy utilized a ring‐closing metathesis of a hexaene intermediate to generate the desired 20‐membered macrolactam. This second‐generation strategy made it possible to prepare synthetic analogues of vicenistatin, including the C20‐ and/or C23‐demethyl analogues. Evaluation of the cytotoxic effect of these analogues indicated the importance of the fixed conformation of aglycon for determining the biological activity of the vicenistatins. 相似文献
84.
85.
Yoshiharu Nishiyama Glenn P. Johnson Alfred D. French 《Cellulose (London, England)》2012,19(2):319-336
Powder and fiber diffraction patterns were calculated for model cellulose crystallites with chains 20 glucose units long.
Model sizes ranged from four chains to 169 chains, based on cellulose Iβ coordinates. They were subjected to various combinations
of energy minimization and molecular dynamics (MD) in water. Disorder induced by MD and one or two layers of water had small
effects on the relative intensities, except that together they reduced the low-angle scattering that was otherwise severe
enough to shift the 1 [`1] \bar {1} 0 peak. Other shifts in the calculated peaks occurred because the empirical force field used for MD and minimization caused
the models to have small discrepancies with the experimental intermolecular distances. Twisting and other disorder induced
by minimization or MD increased the breadth of peaks by about 0.2–0.3° 2-θ. Patterns were compared with experimental results.
In particular, the calculated fiber patterns revealed a potential for a larger number of experimental diffraction spots to
be found for cellulose from some higher plants when crystallites are well-oriented. Either that, or further understanding
of those structures is needed. One major use for patterns calculated from models is testing of various proposals for microfibril
organization. 相似文献
86.
A nitroxyl-radical-catalyzed oxidation of alcohols using diisopropyl azodicarboxylate (DIAD) as the terminal oxidant is reported. A variety of primary and secondary alcohols including aliphatic, benzylic, and allylic alcohols are efficiently oxidized to their corresponding aldehydes and ketones without overoxidation to carboxylic acid. 1,2-Diols are oxidized to hydroxyl ketones or diketones depending on the amount of DIAD used. 相似文献
87.
Railway companies are encouraged to install platform screen doors (PSDs) for safety reason in Japan. The PSDs might affect train noises in stations, but the effects are not well understood. The aim of the present study is to clarify the effects of PSDs on acoustic characteristics. PSDs can be principally classified by two types, i.e., mobile full-height (MFH) and mobile half-height (MHH). Train noises were recorded in ground and underground train stations with MFH, MHH and without PSDs. The noises were evaluated by noise level, the maximum peak of the interaural cross-correlation function (IACC), and the width of the first decay (WΦ(0)) of the autocorrelation function. Noise level emitted by trains was reduced by PSDs in both aboveground and underground stations. IACC was decreased by PSDs in both ground and underground stations, suggesting that PSDs made train noises more diffused. WΦ(0) was decreased by PSDs in both ground and underground stations, which means that the train noises in station with PSDs have higher spectral centroid, suggesting that the PSDs blocked the lower frequency components of train noises. 相似文献
88.
Annals of the Institute of Statistical Mathematics - Recently, it is becoming more active to apply appropriate statistical methods dealing with missing data in clinical trials. Under not missing at... 相似文献
89.
Jun'ichiro Miura Masaru Yamada Yoshiharu Nakamura 《Fresenius' Journal of Analytical Chemistry》1985,321(6):575-577
Summary A selective preconcentration technique for copper using the kerateine gel is described. The gel is prepared by partial oxidation of kerateine which is obtained by reducing the disulphide bonds of wool fiber. Copper is selectively adsorbed on the gel at pH 3.5. It is eluted with 3 M hydrochloric acid and is determined by atomic-absorption spectrometry. This method has been applied to the determination of copper in river water.
Selektive Anreicherung von Kupfer aus wäßriger Lösung mit Hilfe von Keratein-Gel
Zusammenfassung Ein selektives Anreicherungsverfahren für Kupfer mit Hilfe von Keratein-Gel wurde ausgearbeitet. Das Gel wird durch teilweise Oxidation von Keratein hergestellt, das aus Wollfaser durch Reduktion der Disulfidbindungen gewonnen wird. Kupfer wird bei pH 3,5 selektiv an diesem Gel adsorbiert und kann mit 3 M Salzsäure eluiert werden. Die Bestimmung erfolgt mit Hilfe der AAS. Das Verfahren kann zur Kupferbestimmung in Flußwasser angewendet werden.相似文献
90.
Chuzo Tanaka M.D. Shoji Naruse M.D. Yoshiharu Horikawa M.D. Kimiyoshi Hirakawa M.D. Kazuo Yoshizaki M.D. Hiroyasu Nishikawa M.D. 《Magnetic resonance imaging》1986,4(6):503-508
Proton nuclear magnetic resonance (NMR) spectra were successfully measured in human brain tumor tissues and experimental rat brain tumors. The investigation was performed on clinical materials which consisted of tissue from one normal brain and 36 brain tumors. Normal rat brain tissue and rat glioma implanted in the brain were also analysed. NMR measurements were carried out at the resonance frequency of 99.54 MHz. The proton NMR spectrum of the normal brain consisted of one broad component and eight superimposed sharp peaks. The sharp peaks obtained from the brain tumors varied from those of the normal brain. A decrease in the signal intensity from N-acetyl aspartate was the most common finding in all tumors. Spectral patterns were similar within the same histological types, but varied among the different types. Therefore, 1H-NMR spectra might indicate the metabolism characteristic of each tumor type which would be invaluable for clinical differential dagnosis of brain tumors. 相似文献