全文获取类型
收费全文 | 433篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
化学 | 277篇 |
晶体学 | 3篇 |
力学 | 8篇 |
数学 | 37篇 |
物理学 | 127篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 29篇 |
2015年 | 17篇 |
2014年 | 15篇 |
2013年 | 42篇 |
2012年 | 38篇 |
2011年 | 25篇 |
2010年 | 23篇 |
2009年 | 19篇 |
2008年 | 13篇 |
2007年 | 26篇 |
2006年 | 12篇 |
2005年 | 16篇 |
2004年 | 10篇 |
2003年 | 17篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 8篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1980年 | 3篇 |
1934年 | 1篇 |
1933年 | 2篇 |
1932年 | 1篇 |
1930年 | 3篇 |
1929年 | 3篇 |
1928年 | 1篇 |
1927年 | 4篇 |
1926年 | 1篇 |
1925年 | 1篇 |
1924年 | 2篇 |
排序方式: 共有452条查询结果,搜索用时 15 毫秒
11.
The design, synthesis and evaluation of a pentacyclic scaffold, CWO-324 to mimic saframycin A is described. CWO-324 is readily synthesized in five steps from 1,4-diacetyl-piperazine-2,5-dione and 2,5-dimethoxybenzaldehyde. CWO-324 was found to scission DNA, binds to bases 69-83(5′-GCAGTCAGG CACCGT-3′) of Hind III/Rsa I from plasmid pBR322 DNA in a foot-printing study and possesses anti-tumor activity. 相似文献
12.
The structures of hydrated 1-hydroxyanthraquinone complexes (1-HAQ), 1-HAQ(H2O)n=1,2, with intramolecular and intermolecular hydrogen bonding interactions were studied using laser spectroscopic methods such as laser induced fluorescence, fluorescence-detected infrared, infrared-visible hole burning, and visible-visible hole burning spectroscopy. In the 1:1 complex 1-HAQ(H2O)1, the water binds to the free carbonyl group of 1-HAQ not associated with intramolecular hydrogen bond. The second water in the 1:2 complex, 1-HAQ(H2O)2, binds to the first water of the 1:1 complex rather than other hydrogen bonding sites of 1-HAQ. A pair of two geometric isomers was produced in a supersonic jet for each of the 1:1 and 1:2 complexes. Both isomers of each complex have the same vibrational spectra in the region of the OH stretching vibration of water, but have different energies for the 0-0 band of vibronic transition due to the asymmetry of the two phenyl rings in 1-HAQ. The 0-0 bands for all four species of 1-HAQ(H2O)n=1,2 were unambiguously assigned by comparing with the results of ab initio calculations, which yielded the structures, vibrational frequencies, and relative energies of the frontier molecular orbitals. 相似文献
13.
The thermodynamics of water incorporation into Fe-doped SrTiO(3) was investigated by thermogravimetric measurements. Changes in valence states of redox-active dopant ions (Fe(3+)/Fe(4+)) with water vapor pressure were taken into account in the defect chemical analysis. The proton solubility was significantly enhanced by the presence of the redox centers. The hydration enthalpies and entropies were -60 kJ mol(-1) and -122 J mol(-1) K(-1). The defect chemical model was applied to describe the water vapor dependence of the electrical conductivity in mixed ionic and electronic conducting Fe-doped SrTiO(3) single crystals. 相似文献
14.
The kinetics of the oxidation of promazine and chlorpromazine by hexaimidazolcobalt(III) were studied in the presence of a
large excess of cobalt(III) and H+ ions using u.v.–vis. spectroscopy ([CoIII] = (1–6) × 10−3 m, [ptz] = (2.5–10) × 10−5 m, [H+] = 0.05–0.8 m, I = 1.0 m (H+, Na+, Cl−), T = 333–353 K, l = 1 cm). In each case, the reversible reaction leads to formation of cobalt(II) species and a stable cationic radical. A
linear dependence of the pseudo-first-order rate constant (kobs) on [CoIII] with a non-zero intercept was established for both phenothiazine derivatives. A marked difference in the observed reaction
rate for promazine and chlorpromazine is associated with the difference in its ability to undergo oxidation and is consistent
with a trend in the redox potential changes for these reductants. The activation parameters for reactions studied were determined.
Mechanistic consequences of all the results are discussed. 相似文献
15.
Andrzej Maączyński Marian Góral Barbara Wiśniewska-Gocłowska Adam Skrzecz David Shaw 《Monatshefte für Chemie / Chemical Monthly》2003,134(5):633-653
Summary. The evaluation of mutual solubility data for systems water with n-alkanes, isoalkanes, and cycloalkanes along the three phase line is reported and a formula for the prediction of solubility
of alkanes in water is developed. Then a cubic equation of state with an added term, which accounts for hydrogen bonding is
used for correlation of liquid–liquid equilibrium data and for prediction of solubility of water in hydrocarbons using alkane
in water solubility data. Comparison of the predicted and experimental solubilities is performed using all accessible experimental
data. With this approach it is possible to predict the solubilities of water in alkanes with good accuracy over the temperature
range up to about 20 K below critical temperature. Solubility of alkanes in water can also be calculated using experimental
data for solubility of water in alkanes but results of these calculations are more sensitive to experimental errors of the
data.
Corresponding author: E-mail: macz@ichf.edu.pl
Received August 5, 2002; accepted (revised) September 13, 2002
Published online March 13, 2003
RID="a"
ID="a" Dedicated to Prof. Dr. H. Gamsj?ger on the occasion of his 70th birthday anniversary 相似文献
16.
Differencies between the mechanism ofn-hexane and benzene adsorption on active carbon were investigated on the ground of kinetic measurements. As it has been stated, the kinetic measurements show fundamental differencies between the mechanism of adsorption in spite of analogy existing in the state of adsorption equilibrium. Within the range investigated, only the adsorption ofn-hexane follows the model of volume filling of micropores. Existence of those differencies is also confirmed by measurements of effective diffusion coefficient values as well as changes of activation energy of the diffusion—adsorption process.
Anwendung kinetischer Untersuchungen zur Interpretation des Adsorptionsverhaltens vonn-Hexan und Benzol an Aktivkohle
Zusammenfassung Mittels kinetischer Messungen untersuchte man die Unterschiede im Mechanismus des Adsorptionsverlaufes vonn-Hexan und Benzol an Aktivkohle. Man stellte fest, daß trotz der Analogie im Adsorptionsgleichgewichtszustand die kinetischen Messungen auf prinzipielle Unterschiede im Adsorptionsmechanismus hinweisen. Im untersuchten Bereich verläuft nur die Adsorption vonn-Hexane nach dem Modell der Mikroporenvolumenausfüllung. Die auftretenden Unterschiede wurden auch durch die Berechnungen der Werte der effektiven Diffusionskoeffizienten sowie Änderungen der Aktivierungsenergie des Diffusions-Adsorptionsprozesses bestätigt.相似文献
17.
Rhodium(II)-catalyzed reactions of cyclic diazodicarbonyl compounds with a variety of halides have been examined. With acid halides, β-acyloxy α-haloenones are produced in good yields. With benzyl halides, β-benzyloxy α-haloenones are obtained in good yields. Reactions with methylene halides yield β-halomethoxy α-haloenones in good yields, whereas reactions with ethyl halides and ethylene dihalides result in β-hydroxy α-haloenones in high yields. These reactions provide a useful and rapid entry to β-substituted α-haloenones. The mechanistic pathway for the formation of these products has been also described in terms of halonium ylides. 相似文献
18.
微波-气相-热压法分解高纯铂的研究 总被引:1,自引:0,他引:1
本文研究了微波气相热压法新技术分解高纯铂在密闭的聚四氟乙烯高压罐中,以微波瞬间加热混合酸产生的高压、纯净蒸气分解金属铂,此法避免了酸中杂质的沾污以制备供高纯铂分析的试液,提高了痕量杂质分析的准确度和降低检测限 相似文献
19.
The direct reaction of iron pentacarbonyl with diethylamidocyclohexadiene gave three isomeric tricarbonyliron complexes, 1, 2 and 3. Only 1 isomerized to give 2 under acidic conditions, whereas 3 remained unchanged. The chemical properties of the tricarbonyl(amidocyclohexadiene)iron complexes differed from those of the tricarbonyl(carboxycyclohexadiene)iron complexes. Complex 3 which underwent no hydride abstraction with triphenylmethyl hexafluorophosphate, has an exo stereochemistry. 相似文献
20.
Development of hollow fiber‐supported liquid‐phase microextraction and HPLC‐DAD method for the determination of pyrethroid metabolites in human and rat urine
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wielgomas Bartosz Wiśniewski Marcin Czarnowski Wojciech 《Biomedical chromatography : BMC》2014,28(5):708-716
A simple hollow fiber liquid‐phase microextraction method for the determination of synthetic pyrethroid metabolites, 3‐phenoxybenzoic acid and 4‐hydroxy‐3‐phenoxybenzoic acid, in human and rat urine was developed and validated. A polypropylene hollow fiber tightly fitted onto a Nylon rod and impregnated with organic solvent served as a disposable extraction device. Desorption of analytes was carried out in NaOH solution, analyzed further by gradient HPLC and diode array detection method. Important factors were identified using Taguchi OA16 (45) orthogonal array design and further optimized using univariate approach. The optimum method performance was observed when 1 mL of urine hydrolyzed with 0.2 mL of concentrated HCl was further supplemented with 100 mg of NaCl and extracted for 120 min into dihexyl ether immobilized in the pores of the hollow fiber. Metabolites were desorbed into 0.1 mL of 0.1 M NaOH for another 120 min. Limits of detection and quantitation of 15 and 50 ng/mL were obtained for both analytes. Relative standard deviations of 1.6–12.6% over the linear range (50–10,000 ng/mL, r > 0.9906) were observed. Intra‐ and inter‐day accuracies of the method ranged from 98.3 to 109.5% and from 93.3 to 110.9%, respectively. The optimized method was applied to the analysis of real urine samples collected from rats exposed orally to cypermethrin. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献