全文获取类型
收费全文 | 5033篇 |
免费 | 700篇 |
国内免费 | 1302篇 |
专业分类
化学 | 5906篇 |
晶体学 | 66篇 |
力学 | 51篇 |
综合类 | 32篇 |
数学 | 13篇 |
物理学 | 967篇 |
出版年
2024年 | 11篇 |
2023年 | 65篇 |
2022年 | 157篇 |
2021年 | 172篇 |
2020年 | 248篇 |
2019年 | 177篇 |
2018年 | 170篇 |
2017年 | 191篇 |
2016年 | 281篇 |
2015年 | 273篇 |
2014年 | 309篇 |
2013年 | 461篇 |
2012年 | 367篇 |
2011年 | 362篇 |
2010年 | 315篇 |
2009年 | 347篇 |
2008年 | 322篇 |
2007年 | 361篇 |
2006年 | 340篇 |
2005年 | 291篇 |
2004年 | 323篇 |
2003年 | 241篇 |
2002年 | 202篇 |
2001年 | 169篇 |
2000年 | 130篇 |
1999年 | 111篇 |
1998年 | 129篇 |
1997年 | 99篇 |
1996年 | 82篇 |
1995年 | 79篇 |
1994年 | 54篇 |
1993年 | 43篇 |
1992年 | 31篇 |
1991年 | 25篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1972年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有7035条查询结果,搜索用时 31 毫秒
951.
952.
In this paper, a new highly sensitive potentiometric pH electrode is proposed based on the solid-state PbO2 film electrodeposited on carbon ceramic electrode (CCE). Two different crystal structures of PbO2, α and β were examined and the similar results were obtained. Moreover, the experimental results obtained for the proposed
pH sensor and a conventional glass pH electrode were in good agreement. The electromotive force (emf) signal between the pH-sensitive
PbO2-coated CCE and SCE reference electrode was linear over the pH range of 1.5–12.5. Near-Nernstian slopes of −64.82 and −57.85 mV/pH
unit were obtained for α- and β-PbO2 electrodes, respectively. The interferences of some mono-valence and multi-valence ions on potentiometric response of the
sensor were studied. The proposed pH sensor displayed high ion selectivity with respect to K+, Na+, Ca2+, and Li+, with log values around −12 and has a working lifetime of about 30 days. Key parameters important for the pH sensor performance, including
kind of PbO2 film, selectivity, response time, stability, and reproducibility, have been characterized. The proposed electrode showed
a good efficiency for direct pH-metry after calibration and pH-metric titrations without calibration step. The response time
was about 1 s in acidic medium and less than 30 s in alkaline solutions. The pH values of complex matrix samples such as fruit
juices measured by the proposed sensor and a conventional glass pH electrode were in good agreement. 相似文献
953.
954.
955.
Robertson N 《Angewandte Chemie (International ed. in English)》2008,47(6):1012-1014
956.
Huan Wang 《Tetrahedron》2008,64(2):314-318
Electrochemical carboxylation of cinnamate esters has been carried out by cathodic reduction of CC bond in an undivided cell equipped with Mg sacrificial anode and using MeCN saturated with CO2 as solvent. The yields and the ratio of mono- and dicarboxylic acids are strongly affected by various factors: cathodic material, current, charge, and temperature. The highest yield (78.9%) was obtained starting from ethyl cinnamate. Cyclic voltammograms have been measured and reaction pathways have been proposed. 相似文献
957.
Devdutt Chaturvedi Nisha Mishra Virendra Mishra 《Monatshefte für Chemie / Chemical Monthly》2008,139(3):267-270
Summary. A Mitsunobu-based protocol has been developed for the synthesis of symmetrically and unsymmetrically substituted ureas from a variety
of primary and secondary amines using gaseous carbon dioxide, in good to excellent yields. This protocol is mild and efficient
compared to other reported methods. 相似文献
958.
Zhongze Ma 《Tetrahedron letters》2008,49(11):1782-1785
To unambiguously confirm the actual product in autoxidation of salvinorin A under basic conditions, deacetyl-1,10-didehydrosalvinorin G was synthesized from salvinorin C via intermediate salvinorin H. Furthermore, oxidation of salvinorin D with manganese dioxide gave salvinorin G in good yield. 相似文献
959.
Heterostructures of TiO2 with a biscyanine dye were obtained, and their photocatalytic activity in the reduction of methylene blue was investigated.
The results from analysis of the spectral parameters showed that the decrease of activity with increase of the dye content
results from weakening of its interaction with the semiconductor.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 79–82, March–April, 2008. 相似文献
960.
The catalytic efficiency of Fe(+) ion over the CO(2) decomposition in the gas phase has been extensively investigated with the help of electronic structure calculation methods. Potential-energy profiles for the activation process Fe(+) + CO(2) --> CO + FeO(+) along two rival potential reaction paths, namely the insertion and addition pathways, originating from the end-on kappa(1)-O and kappa(2)-O,O coordination modes of CO(2) with the metal ion, respectively, have been explored by DFT calculations. For each pathway the potential energy surfaces of the high-spin sextet (S = 5/2) and the intermediate-spin quartet (S = 3/2) spin-states have been explored. The complete energy reaction profile calculated by a combination of ab initio and density functional theory (DFT) computational techniques reveals a two-state reactivity, involving two spin inversions, for the decomposition process and accounts well for the experimentally observed inertness of bare Fe(+) ions towards CO(2) activation. Furthermore, the coordination of up to three extra ancillary NH(3) ligands with the Fe(+) metal ion has been explored and the geometric and energetic reaction profiles of the CO(2) activation processes Fe(+) + n x NH(3) + CO(2) --> [Fe(NH(3))(n)(CO(2))](+) --> [Fe(NH(3))(n)(O)(CO)](+) --> CO + [Fe(O)(NH(3))(n)](+) (n = 1, 2 or 3) have thoroughly been scrutinized for both the insertion and the addition mechanisms. Inter alia, the geometries and energies of the various states of the [Fe(NH(3))(n)(CO(2))](+) and [Fe(NH(3))(n)(O)(CO)](+) complexes are explored and compared. Finally, a detailed analysis of the coordination modes of CO(2) in the cationic [Fe(NH(3))(n)(CO(2))](+) (n = 0, 1, 2 and 3) complexes is presented. 相似文献