全文获取类型
收费全文 | 653篇 |
免费 | 15篇 |
国内免费 | 3篇 |
专业分类
化学 | 479篇 |
晶体学 | 2篇 |
力学 | 12篇 |
数学 | 89篇 |
物理学 | 89篇 |
出版年
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 20篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 41篇 |
2012年 | 38篇 |
2011年 | 36篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 32篇 |
2007年 | 29篇 |
2006年 | 36篇 |
2005年 | 35篇 |
2004年 | 31篇 |
2003年 | 26篇 |
2002年 | 16篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1968年 | 5篇 |
1966年 | 4篇 |
排序方式: 共有671条查询结果,搜索用时 15 毫秒
31.
3,3′-Thiobispyridine is prepared by reaction of pyridine-3-thiol with 3-bromopyridine. The base peak in the mass spectrum of 3,3′-thiobispyridine is due to the molecular ion which fragments by loss of H, HCN and CS as well as by central bond rupture. The 1,1′-dimethyl diquaternary salt of 3,3′-thiobispyridine is reduced polarographically by a one electron transfer not involving hydrogen to an unstable radical cation at a potential (Eo) of −0.72 V in the pH range 7.4–11.2. 相似文献
32.
Sylvia Marhold Ernst Koller Isabella Meyer Otto S. Wolfbeis 《Fresenius' Journal of Analytical Chemistry》1990,336(2):111-113
Summary A new fluorimetric assay for cationic surfactants is based on their capability of quenching the fluorescence of 8-octadecyloxypyrene-1,3,6-trisulfonate (PTS-18). It is specific for cationic surfactants which can be determined in the 40–400 g concentration range. The method is considered to be advantageous over former methods in that it only requires addition of the sample solution to the fluorophore solution, followed by measurement of fluorescence intensity of the probe. This is in contrast to existing methods where the detergent/dye ion pair has to be extracted before measurement. 相似文献
33.
34.
M. E. Vol'pin Yu. N. Novikov V. A. Postnikov V. B. Shur B. Bayerl L. Kaden M. Wahren L. M. Dmitrienko R. A. Stukan A. V. Nefed'ev 《无机化学与普通化学杂志》1977,428(1):231-236
Investigations on the Catalysis of Ammonia Synthesis and Nitrogen Isotope Exchange by Lamellar Compounds of Graphite with Iron, Ruthenium, and Osmium The catalytic activity of transition metal potassium-graphite lamellar compounds for the synthesis of ammonia from the elements and the catalysis of the equilibration by isotope exchange of the isotopic nitrogen molecules are shown to correlate. Connections between the state of metal in the catalyst exist with iron as metal which is shown by Mössbauer spectroscopy and the catalytic activity in relation to the potassium content. 相似文献
35.
36.
Vinck E Van Doorslaer S Dewilde S Moens L 《Journal of the American Chemical Society》2004,126(14):4516-4517
Human neuroglobin (hNgb) and human cytoglobin (hCygb), two recently discovered members of the vertebrate globin family, are known to be able to form an intramolecular disulfide bridge. Using electron paramagnetic resonance (EPR), we show that formation of a disulfide bridge in ferric hNgb causes a considerable change in the heme pocket structure, whereas this is not so clear for ferric hCygb. The structural results can be related nicely to earlier histidine and dioxygen affinity studies of the ferrous proteins. 相似文献
37.
38.
Background
Although previous studies suggest that postural control requires attention and other cognitive resources, the central mechanisms responsible for this relationship remain unclear. To address this issue, we examined the effects of altered attention on cortical activity and postural responses following mechanical perturbations to upright stance. We hypothesized that cortical activity would be attenuated but not delayed when mechanical perturbations were applied during a concurrent performance of a cognitive task (i.e. when attention was directed away from the perturbation). We also hypothesized that these cortical changes would be accompanied by alterations in the postural response, as evidenced by increases in the magnitude of anteroposterior (AP) centre of pressure (COP) peak displacements and tibialis anterior (TA) muscle activity. Healthy young adults (n = 7) were instructed to continuously track (cognitive task) or not track (control task) a randomly moving visual target using a hand-held joystick. During each of these conditions, unpredictable translations of a moving floor evoked cortical and postural responses. Scalp-recorded cortical activity, COP, and TA electromyographic (EMG) measures were collected. 相似文献39.
An all-solid-state internal reference system for pH glass electrodes employing polypyrrole (PPy)-Nafion® composites is described. pH sensors based on this reference system are characterised at 23±3°C. The observed characteristics of the resulting all-solid-state sensors, i.e. slope and linearity of the calibration plot, response behaviour, and signal stability, are very promising, and the differences with respect to the parameters of conventional liquid filled sensors are negligible. The values of the zero potential point, which differ from those of conventional pH glass electrodes, could be controlled within limits via the composition of the PPy-Nafion composite.The excellent sensor performance observed seems to be the consequence of a reversible charge transfer between the ion-conducting membrane, the mixed conducting PPy-Nafion interlayer, and the metal wire. A first discussion of the mechanism of this charge transfer is given. 相似文献
40.
Sylvia Pulmannová 《International Journal of Theoretical Physics》2003,42(7):1413-1423
A noncommutative version of generalized Sasaki projections in pseudoeffect algebras is introduced. It is proved that an ideal in a pseudoeffect algebra is Riesz if and only if it is closed under the right and left Sasaki projections. In lattice ordered pseudoeffect algebras, it is shown that generalized Sasaki projections are one-element sets, and their explicit form is found. It is shown that if a supremum of a normal Riesz ideal in a lattice ordered pseudoeffect algebra exists, it is a central element. These results extend those obtained recently by Avallone and Vitolo for effect algebras. 相似文献