全文获取类型
收费全文 | 228篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 137篇 |
力学 | 2篇 |
数学 | 10篇 |
物理学 | 90篇 |
出版年
2023年 | 7篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 13篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 16篇 |
2002年 | 4篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有239条查询结果,搜索用时 17 毫秒
201.
A. Afaq Azmat Iqbal Amin Ur Rahman Naveed Khan Fazal-e- Aleem M. Mushraf Ansari 《Brazilian Journal of Physics》2016,46(5):489-495
Photodetachment of negative ions near surfaces is of great interest in view of its fundamental significance and technological applications. We reinvestigate the dynamics of photoelectrons in H? photodetachment near a partially reflecting spherical surface by the semiclassical closed-orbit theory. Reflection parameter R and curvature K is used to observe inelastic and spherical effects of the surface, respectively. The classical action is evaluated from the photodetached electron trajectories incident normally at the surface, arising simultaneously from the source and its image. The derived analytical formula of photodetachment cross section correctly recovers the results of reflective spherical surface published recently based on theoretical imaging method. 相似文献
202.
Urh Černigoj Jana Vidič Ana Ferjančič Urša Sinur Klemen Božič Nina Mencin Anže Martinčič Celjar Pete Gagnon Aleš Štrancar 《Electrophoresis》2021,42(24):2619-2625
Elution of strong and weak anion exchangers with sodium chloride gradients is commonly employed for analysis of sample mixtures containing different isomers of plasmid DNA. Gradient elution of a weak anion exchanger (diethylaminoethyl) in the presence of guanidine hydrochloride (Gdn) roughly doubles resolution between open-circular (oc) and supercoiled (sc) isomers. It also improves resolution among sc, linear, and multimeric/aggregated forms. Sharper elution peaks with less tailing increase sensitivity about 30%. However, elution with an exclusively Gdn gradient to 900 mM causes more than 10% loss of plasmid. Elution with a sodium chloride gradient while maintaining Gdn at a level concentration of 300 mM achieves close to 100% recovery of sc plasmid while maintaining the separation improvements achieved by exclusively Gdn elution. Corresponding improvements in separation performance are not observed on a strong (quaternary amine) anion exchanger. Other chaotropic salts do not produce a favorable result on either exchanger, nor does the inclusion of surfactants or EDTA. Selectivity of the diethylaminoethyl-Gdn method is orthogonal to electrophoresis, but with better quantification than agarose electrophoresis, better quantitative accuracy than CE, and resolution approaching CE. 相似文献
203.
V. F. Ur’yash A. E. Gruzdeva A. V. Ur’yash A. A. Silkin N. Yu. Kokurina 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(7):1097-1102
The radioprotective properties of a substance from pine shoots prepared by supercritical fluid extraction with carbon dioxide
were studied for a model of an experimental bone-marrow radiation sickness form. Experiments were performed for white nonlinear
mice. The CO2 extract of pine shoots was shown to possess radioprotective properties. The extract was subjected to pre-clinical tests for
Wistar line male rats with respect to its antiatherogenic and antioxidative action in the creation of experimental hyperlipemia. 相似文献
204.
205.
Urh Černigoj Urška Lavrenčič Štangar Polonca Trebše Mohamed Sarakha 《Journal of photochemistry and photobiology. A, Chemistry》2009,201(2-3):142-150
Many types of supported photocatalytic TiO2 continue to be the subject of extensive development worldwide. Besides industrial production and practical use of the new photocatalytic materials, there is an increasing need for a simple and reliable procedure for characterization of photocatalytic activities of newly developed materials. The aim of our work was to develop a method for the determination of quantum yields of supported photocatalysts by employing an aqueous solution of a model organic compound and different thin TiO2 films. Additionally, also a newly defined parameter, the so-called mass efficiency, was introduced as an advantageous way of defining the photocatalytic activities. Coumarin (CM) was found to be an appropriate candidate for being a probe molecule when the photocatalytic degradation mainly occurs via the HO radical-mediated mechanism. An advantage of using CM is easy determination of highly fluorescent 7-hydroxycoumarin (7OHC). Different TiO2 films were deposited via sol–gel methods on soda-lime glass slides that were precovered with a thin SiO2 film, and via the sedimentation process from aqueous suspensions. Aqueous solutions of CM were irradiated using 365 nm radiation in the presence of titania films. Although Degussa P25 films showed approximately four times higher degradation rates compared to the sol–gel processed, its quantum yield was not more than 2.5 times higher. This could be explained by higher absorbance of Degussa P25 films per amount of the catalyst compared to sol–gel films. Since no information on the absorption characteristics of the material per unit of mass of the catalyst is included within the calculation of quantum yield, mass efficiency is suggested for the evaluation of photocatalytic properties of the coatings. It is evident from the present study that it is obligatory to evaluate the photocatalytic efficiencies of different area densities of the same photocatalyst in order to properly characterize the material's efficiency. 相似文献
206.
207.
Javid Hussain Najeeb Ur Rehman Hidayat Hussain Liaqat Ali Ahmed Al‐Harrasi Viqar Uddin Ahmad 《Helvetica chimica acta》2011,94(11):2106-2110
The structure elucidation of two new phthalate derivatives named nepethalates A ( 1 ) and B ( 2 ) is reported. Both of these secondary metabolites were isolated from the MeOH extract of Nepeta clarkei. HR‐EI‐MS, IR and UV absorption spectrometry, and NMR experiments including COSY, HMQC, and HMBC were used for the determination of the structures and complete 1H‐ and 13C‐NMR assignments. 相似文献
208.
Hussain J Begum N Hussain H Khan FU Rehman NU Al-Harrasi A Ali L 《Natural product communications》2012,7(5):615-616
Phytochemical investigation of Ajuga bracteosa Wall ex Benth. (Labiatae) resulted in the isolation of a new phenolic compound, ajuganane (1) and three known compounds, 3,4'-dihydroxy-3,6,7-trimethoxyflavone, 7-hydroxy-3,6,3',4'-tetramethoxyflavone and ursolic acid. The structure of the new compound was elucidated by detailed spectroscopic (1H, 13C NMR, COSY, HMQC, HMBC), and HR-EI-MS analysis. 相似文献
209.
The efficiency and selectivity of Cu‐catalyzed allylic acetoxylation of alkene in different solvent systems is improved by the presence of different metallic salts in the reaction medium. The methodology is particularly well employed for the direct allylic acetoxylation of Δ5‐steroids at 7‐position, for which the resulting acetoxylated product obtained was exclusively α‐isomer. Excellent yield was achieved (up to 90%) under optimized conditions, while significantly reducing the costs and environmental hazards and increasing the yield as compared to the other previously reported methods. 相似文献
210.
V. F. Ur’yash V. N. Larina N. Yu. Kokurina A. V. Bakulin E. A. Kashtanov V. P. Varlamov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(1):1-8
Standard enthalpies of combustion and formation were studied, along with the enthalpy of interaction of chitin and chitosan
of different origins with water. The concentration of the water phase solution in chitin and chitosan saturated at 273 K was
determined by calorimetry from the enthalpy of melting of the water excess phase. The dependence of these properties on the
source, molecular mass, and degree of ordering of polysaccharides was demonstrated. 相似文献