全文获取类型
收费全文 | 4020篇 |
免费 | 88篇 |
国内免费 | 14篇 |
专业分类
化学 | 2286篇 |
晶体学 | 29篇 |
力学 | 122篇 |
综合类 | 1篇 |
数学 | 645篇 |
物理学 | 1039篇 |
出版年
2022年 | 34篇 |
2021年 | 46篇 |
2020年 | 51篇 |
2019年 | 50篇 |
2018年 | 64篇 |
2017年 | 60篇 |
2016年 | 104篇 |
2015年 | 84篇 |
2014年 | 101篇 |
2013年 | 184篇 |
2012年 | 194篇 |
2011年 | 219篇 |
2010年 | 142篇 |
2009年 | 120篇 |
2008年 | 221篇 |
2007年 | 190篇 |
2006年 | 185篇 |
2005年 | 207篇 |
2004年 | 160篇 |
2003年 | 125篇 |
2002年 | 101篇 |
2001年 | 80篇 |
2000年 | 54篇 |
1999年 | 49篇 |
1998年 | 39篇 |
1997年 | 44篇 |
1996年 | 61篇 |
1995年 | 39篇 |
1994年 | 30篇 |
1993年 | 34篇 |
1992年 | 34篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 33篇 |
1988年 | 34篇 |
1986年 | 36篇 |
1985年 | 57篇 |
1984年 | 55篇 |
1983年 | 35篇 |
1982年 | 46篇 |
1981年 | 36篇 |
1980年 | 53篇 |
1979年 | 39篇 |
1978年 | 49篇 |
1977年 | 35篇 |
1976年 | 38篇 |
1975年 | 31篇 |
1974年 | 28篇 |
1973年 | 28篇 |
1971年 | 25篇 |
排序方式: 共有4122条查询结果,搜索用时 0 毫秒
141.
The reflection spectra of Ge-Si alloys have been measured at room temperature in the photon energy range 2–5 eV. The curve giving the dependence of the energy of the first characteristic peak in the reflection spectrum on the composition of the alloy shows a break at about 79 at. per cent of Si. The consequences of this observation for the band structure are discussed. 相似文献
142.
A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery.Despite being less condu... 相似文献
143.
α-n-amylcinnamaldehyde (jasminaldehyde) was obtained with 82 % yield by solid-liquid phase transfer catalysis without solvent within 3 days at room temperature. By use of domestic microwave irradiation, the same yield was obtained within 1 minute at a power of 600 W. 相似文献
144.
Pirita Rämänen Paavo A. Penttilä Kirsi Svedström Sirkka Liisa Maunu Ritva Serimaa 《Cellulose (London, England)》2012,19(3):901-912
Cellulose whiskers were prepared from wood- and cotton-based microcrystalline cellulose and dried by two methods: freeze-drying
or air-drying. The effect of drying method on the properties and structure of the whiskers were studied. Furthermore, the
influence of the source of cellulose on the nanoscale structure was investigated. Drying method was observed to slightly influence
the thermal stability of cellulose whiskers, whereas the char residue varied significantly depending on the drying process
performed. Small- and wide-angle X-ray scattering and solid state nuclear magnetic resonance spectroscopy were used to examine
the crystallinity and nanoscale structure of the dried whiskers. It was observed that the crystal structure and crystallinity
of cellulose whiskers remained during all treatments, whereas their nanoscale structure was significantly influenced by drying
method, neutralization, and source of cellulose. Relationships between thermal behavior and nanoscale structure were reported
and discussed. 相似文献
145.
146.
Hanna Hedström Henrik Ramebäck Christian Ekberg 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(2):847-852
Co-precipitation of radium, barium and strontium is an important process in many contexts, such as uranium mining, oil extraction and in the safety assessment of a final repository for used nuclear fuel. Co-precipitation to a solid solution is possible since radium, barium and strontium act as chemical analogues. In this work the co-precipitation of radium, barium and strontium was studied and the kinetic behavior of the co-precipitation process was investigated. It was shown that radium, barium and strontium co-precipitate congruently and that the precipitation followed an Arrhenius behavior and the Arrhenius parameters for the systems was determined. When studying the differences of the Arrhenius constants by using a student m>t m> test (95 % confidence interval) it was observed that the only significant difference in the activation energy, m>E m> a, is between radium and barium and between radium and strontium respectively, the pure strontium having the larger activation energy in comparison. This is most likely coupled to the metal ion size; since the hydration waters are more strongly bound, which leads to them having a slower exchange rate, which in turn effects the rate of co-precipitation to the metal these reactions will be slower. 相似文献
147.
148.
The effect of the ionic strength on the properties of a carboxymethylated nanofibrillated cellulose (NFC) system was investigated through rheological studies. It was shown that homogenization of pulp suspensions containing a high amount of a monovalent electrolyte leads to the production of NFC systems displaying a lower magnitude in the rheological response as compared with systems prepared at lower ionic strengths conditions. It was further shown that increasing the ionic strength of NFC suspensions after their manufacturing also results in a lowering of the rheological response. The decreased rheological response in the former case was postulated to be caused by a lowering of the delamination deficiency of the homogenization process, due to decreased swelling of the carboxymethylated pulp, caused by the screening of the charges. In the latter case (post-addition of the electrolyte), the lowering of the rheological response was postulated to be due to the compression of the electrostatic double layer, when the electrostatic repulsion between the charged fibrils diminished in the presence of the electrolyte. 相似文献
149.
д. A. князеß Е. В. добuэιса Т. д казmснзз 《Isotopes in environmental and health studies》2013,49(4):130-133
Es werden Aufbau, Arbeitsweise und Eigenschaften einer Apparatur beschrieben, mit der natiürliche Tritium-Aktivitäten in Oberflächen- und Grundwässern gemessen werden können. Diese Messungen erfolgen in 4 Arbitsschritten: elektrolytische Anreicherung der natiärlichen Tritium-Konzentrationen, Messung des Anreicherungsfaktors mit einem Flüssigkeitsszintillationszähler, Synthese von Äthan aus dem angereicherten Probenwasser und tritiumfreiem Acetylen, Messung des Probentritiums in Äthan mit einem Proportionalzähler. Die untcre Nachweisgrenze (Meβzeit 48 Studnden, statistischer Fehler 50%) beträgt 1 T.E. 相似文献
150.
Asymmetric synthesis of 1,3-oxathiolan-5-one derivatives through dynamic covalent kinetic resolution
The asymmetric synthesis of 1,3-oxathiolan-5-one derivatives through an enzyme-catalyzed, dynamic covalent kinetic resolution strategy is presented. Dynamic hemithioacetal formation combined with intramolecular, lipase-catalyzed lactonization resulted in good conversions with moderate to good enantiomeric excess (ee) for the final products. The process was evaluated for different lipase preparations, solvents, bases, and reaction temperatures, where lipase B from m>Candida antarctica m> (CAL-B) proved most efficient. The substrate scope was furthermore explored for a range of aldehyde structures, together with the potential access to nucleoside analog inhibitor core structures. 相似文献