全文获取类型
收费全文 | 1250篇 |
免费 | 22篇 |
国内免费 | 4篇 |
专业分类
化学 | 907篇 |
晶体学 | 3篇 |
力学 | 23篇 |
数学 | 196篇 |
物理学 | 147篇 |
出版年
2020年 | 10篇 |
2019年 | 11篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 12篇 |
2014年 | 18篇 |
2013年 | 61篇 |
2012年 | 48篇 |
2011年 | 32篇 |
2010年 | 35篇 |
2009年 | 27篇 |
2008年 | 54篇 |
2007年 | 54篇 |
2006年 | 42篇 |
2005年 | 48篇 |
2004年 | 53篇 |
2003年 | 43篇 |
2002年 | 32篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 20篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 15篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1985年 | 25篇 |
1984年 | 23篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 19篇 |
1979年 | 24篇 |
1978年 | 30篇 |
1977年 | 15篇 |
1976年 | 25篇 |
1975年 | 26篇 |
1974年 | 25篇 |
1973年 | 24篇 |
1972年 | 11篇 |
1970年 | 12篇 |
1969年 | 10篇 |
1968年 | 11篇 |
1960年 | 8篇 |
1959年 | 9篇 |
1954年 | 8篇 |
排序方式: 共有1276条查询结果,搜索用时 15 毫秒
51.
Maurice J. Ahsman Bart C. van der Nagel Ron A. Mathot 《Biomedical chromatography : BMC》2010,24(9):969-976
Currently, pharmacokinetic–pharmacodynamic studies of sedatives and analgesics are performed in neonates and children to find suitable dose regimens. As a result, sensitive assays using only small volumes of blood are necessary to determine drug and metabolite concentrations. We developed an ultra‐performance liquid chromatographic method with tandem mass spectrometry detection for quantification of midazolam, 1‐hydroxymidazolam, hydroxymidazolamglucuronide, morphine, morphine‐3‐glucuronide and morphine‐6‐glucuronide in 100 μL of plasma. Cleanup consisted of 96 wells micro‐solid phase extraction, before reversed‐phase chromatographic separation (ultra‐performance liquid chromatography) and selective detection using electrospray ionization tandem mass spectrometry. Separate solid‐phase extraction methods were necessary to quantify morphine, midazolam and their metabolites because of each group's physicochemical properties. Standard curves were linear over a large dynamic range with adequate limits of quantitation. Intra‐ and interrun accuracy and precision were within 85–115% (of nominal concentration using a fresh calibration curve) and 15% (coefficient of variation, CV) respectively. Recoveries were >80% for all analytes, with interbatch CVs (as a measure of matrix effects) of less than 15% over six batches of plasma. Stability in plasma and extracts was sufficient, allowing large autosampler loads. Runtime was 3.00 min per sample for each method. The combination of 96‐well micro‐SPE and UPLC‐MS/MS allows reliable quantification of morphine, midazolam and their major metabolites in 100 μL of plasma. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
52.
Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH)2− over At− in Basic Conditions 下载免费PDF全文
Dumitru‐Claudiu Sergentu Dr. David Teze Dr. Andréa Sabatié‐Gogova Dr. Cyrille Alliot Ning Guo Dr. Fadel Bassal Dr. Isidro Da Silva Prof. Dr. David Deniaud Dr. Rémi Maurice Dr. Julie Champion Dr. Nicolas Galland Dr. Gilles Montavon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):2964-2971
It is generally assumed that astatide (At?) is the predominant astatine species in basic aqueous media. This assumption is questioned in non‐complexing and non‐reductive aqueous solutions by means of high‐pressure anion‐exchange chromatography. Contrary to what is usually believed, astatide is found to be a minor species at pH=11. A different species, which also bears a single negative charge, becomes predominant when the pH is increased beyond 7. Using competition experiments, an equilibrium constant value of 10?6.9 has been determined for the formation of this species from AtO(OH) with the exchange of one proton. The identification of this species, AtO(OH)2?, is achieved through relativistic quantum mechanical calculations, which rule out the significant formation of the AtO2? species, while leading to a hydrolysis constant of AtO(OH) in excellent agreement with experiment when the AtO(OH)2? species is considered. Beyond the completion of the Pourbaix diagram of astatine, this new information is of interest for the development of 211At radiolabeling protocols. 相似文献
53.
Dr. Vincent Maurice Dr. Guylhaine Clavel Prof. Markus Antonietti Dr. Cristina Giordano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11624-11630
Porous TiNxOy‐based particles were synthesized by an aerosol spray process. At first, the starting sol solution containing the metal precursor and the nitrogen source is sprayed to form an aerosol that is subsequently pyrolysed at different temperatures. The obtained dried particles are an amorphous coordination “polymer” rich in carbon and nitrogen. These “glassy” particles are finally thermally treated at 800 °C, promoting the crystallization of the particles and the release of a major part of the carbon. As the particles keep their original shape, carbon loss and density increase during the crystallization step and lead to the development of an accessible pore structure. The process was analyzed and extended to the synthesis of other metal nitrides, such as VN and W2N, thereby showing its general validity for the production of functional nanocrystalline nitride ceramics with high porosity still occupying a relatively small volume, and otherwise not easily accessible. 相似文献
54.
55.
Pascal Tola Alain Retournard Jeannette Dexpert-Ghys Marc Lemonnier Maurice Pagel José Goulon 《Chemical physics》1983,78(3):339-345
The realization of a XEOL (X-ray-excited optical luminescence) spectrometer is reported. The aim of the present paper is to show that a comparison between UV-excited emission spectra and XEOL spectra can be helpful in the assignment of some weak transitions for multiple site rare-earth compounds. The case of c-Y2O3 doped with Eu3+ cations is considered in some detail, as in the XEOL spectrum three lines to be assigned to transitions occurring at the centrosymmetrical Eu3+ (C3i) site are strongly enhanced. Additional site-selective UV-excited emission spectra are also reported supporting the present discussion. 相似文献
56.
The polymer-bound quinone2 has been prepared and used in column form with organic solvents for the convenient preparation of other quinones. In contrast to the solution reaction hydrocyanation of this quinone by the Thiele-Meisenheimer reaction did not yield a useful proportion of polymer-bound dicyanohydroquinone but instead gave a mixture of products including much monocyanohydroquinone. Helferich and Bodenbender's 2,3-dicyanocyclohexan-1, 4-dione is in fact wholly the di-enol and is a likely intermediate in the hydrocyanation of benzoquinone, being oxidised by the latter to 2,3-dicyanocyclohex-2-ene-1, 4-dione which tautomerises to the observed product, 2,3-dicyanohydroquinone. A lower accessibility to polymer-bound reactants as compared with those in solution is implied by these results. 相似文献
57.
Hugues dOrchymont Maurice P. Goeldner Jean-Fran?ois Biellmann 《Tetrahedron letters》1982,23(16):1727-1730
Beside the Wittig rearrangement and the migration of the cyclooctyl radical to the para position, the title carbanion gives rise to an elimination in a syn process. 相似文献
58.
59.
Thomas A. Elwood Kenneth H. Dudley Joan M. Tesarek Peter F. Rogerson Maurice M. Bursey 《Journal of mass spectrometry : JMS》1970,3(7):841-861
Several alkylhydroxynaphthoquinones and chemically related cyclic compounds were subjected to mass spectrometric investigation. Fragmentation pathways were elucidated by use of metastable ions, relative intensities of normal ions and accurate mass measurement. In these series, differences in the spectra of 1,2- and 1,4-naphthoquinones are slight. Evidence for ring expansion in ions from furans is suggested. 相似文献
60.
The C5H5+ fragment ion bound in many EI spectra is determined not to be cyclopentadienyl cation by CID-MIKE spectrometry. 相似文献