全文获取类型
收费全文 | 490篇 |
免费 | 10篇 |
专业分类
化学 | 247篇 |
晶体学 | 4篇 |
力学 | 30篇 |
数学 | 36篇 |
物理学 | 183篇 |
出版年
2021年 | 4篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 19篇 |
2012年 | 14篇 |
2011年 | 14篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 22篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 16篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1972年 | 4篇 |
1971年 | 7篇 |
1970年 | 3篇 |
1968年 | 3篇 |
排序方式: 共有500条查询结果,搜索用时 15 毫秒
91.
92.
In a proteomic approach using 2-DE, the changes in protein expression patterns in wing imaginal discs induced by hormone treatment have been studied. Here we show the response of butterfly imaginal wing disc tissue taken from late fifth instar larvae of the African-Mocker swallowtail Papilio dardanus (Lepidoptera) to the insect hormones 20-hydroxyecdysone (20-HE) and juvenile hormone (JH). The tissues were cultured in the presence of one hormone or a combination of both and their protein expression was compared to the pattern obtained from untreated wing discs. All the treatments resulted in changes in the expression pattern distinct from the uninduced control, indicating a distinct protein regulation induced by the hormones. The treatment with both of the hormones, which are known to have antagonistic physiological effects, did show a unique pattern, presumably the result, in part, of synergistic effects on protein expression mediated by the combined effects of both the hormones. The extent of the interaction between JH and 20-HE indicates a complex molecular regulation, far beyond a simple antagonistic effect. 相似文献
93.
Protection of lithium metal surfaces using chlorosilanes 总被引:1,自引:0,他引:1
Marchioni F Star K Menke E Buffeteau T Servant L Dunn B Wudl F 《Langmuir : the ACS journal of surfaces and colloids》2007,23(23):11597-11602
In this paper, we present a new approach for protecting metallic lithium surfaces based on a reaction between the thin native layer of lithium hydroxide present on the surface and various chlorosilane derivatives. The chemical composition of the resulting layer and the chemistry involved in layer formation were analyzed by polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray analysis (EDX). Spectroscopy shows the disappearance of surface hydroxide groups and the appearance of silicon and chloride on the lithium surface. Differential scanning calorimetry (DSC) and electrochemical impedance spectroscopy (EIS) show that this surface treatment protects the lithium from certain gas-phase reactions and is ionically conductive. 相似文献
94.
The thermal decomposition of sodium ethyl xanthate (SEX) was used to compare the techniques of pyrolysis-gas chromatography-mass
spectrometry (py-GC-MS), thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), and TG-MS.
In the py-GC-MS analysis, SEX was pyrolysed at 400°C in an inert atmosphere. Major gases evolved were carbon disulfide, diethyl
sulfide, ethanol, and carbonyl sulfide. The TG of SEX exhibited a sharp mass loss at 201°C (42.3%) and a gradual mass loss
at 217-325°C (20.8 %). The MS spectra of the evolved gases were complex due to overlapping of molecular, isotope, and fragment
ion signals. Using the MS in selected ion monitoring mode, the major gases evolved were found to be carbon disulfide and carbonyl
sulfide. The FTIR spectra of the evolved gases displayed vibrational frequencies due to alkanes, carbonyls, carbonyl sulfide,
and carbon disulfide.
From the analyses it was concluded that py-GC-MS provided unambiguous gas identification. Interpretation of the MS results
was reliant on the py-GC-MS results, and the FTIR data was limited to identifying gases with very characteristic vibration
frequencies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
95.
Marcus Weck Alex R. Dunn Kozo Matsumoto Geoffrey W. Coates Emil B. Lobkovsky Robert H. Grubbs 《Angewandte Chemie (International ed. in English)》1999,38(18):2741-2745
A stabilization of the liquid-crystalline mesophase and thus an enlarged temperature range of the mesogenic phase is achieved by adding perfluorotriphenylene to a chiral liquid-crystalline triphenylene. This mesophase is based on 1:1 perfluoroarene–arene interactions (see picture). In a polymer with triphenylenes as mesogens in the side chains, the addition of perfluorotriphenylene led to crystallization. 相似文献
96.
Sameer Bargir Steve Dunn Bruce Jefferson Simon Parsons 《Applied Surface Science》2009,255(9):4873-4879
We have studied a series of solids using contact angle measurements; stainless steel, gold, aluminium, titanium nitride and PTFE that are frequently used in domestic water environments. It was found the influence of electron-donor (γ−) and electron-acceptor (γ+) free energies on material scaling rate was dominated by water wetting angles, providing materials exhibit an average roughness below 100 nm. The γ− component had the greatest influence on theoretical adhesion, while γLW, (Lifshitz-van der Waals) γ+ and γAB (acid-base) had little effect. From the materials analysed, amorphous carbon coatings were least adhesive, while ‘kettle coating’ and highly roughened steel the most adhesive. The size and distribution of asperities also influenced the polar free energies and subsequent adhesion due to fluctuations in the wetting angle. The results obtained indicate works of adhesion can be used as a complementary technique with Lewis acid-base theory to deliver useful information about the propensity of scale to deposit on solids. 相似文献
97.
98.
99.
Li-Ming?Lo Candace?S.-J.?TsaiEmail author William?A.?Heitbrink Kevin?H.?Dunn Jennifer?Topmiller Michael?Ellenbecker 《Journal of nanoparticle research》2017,19(8):293
This site study was conducted in a chemical laboratory to evaluate nanomaterial emissions from 20–30-nm-diameter bundles of single-walled carbon nanotubes (CNTs) during product development activities. Direct-reading instruments were used to monitor the tasks in real time, and airborne particles were collected using various methods to characterize released nanomaterials using electron microscopy and elemental carbon (EC) analyses. CNT clusters and a few high-aspect-ratio particles were identified as being released from some activities. The EC concentration (0.87 μg/m3) at the source of probe sonication was found to be higher than other activities including weighing, mixing, centrifugation, coating, and cutting. Various sampling methods all indicated different levels of CNTs from the activities; however, the sonication process was found to release the highest amounts of CNTs. It can be cautiously concluded that the task of probe sonication possibly released nanomaterials into the laboratory and posed a risk of surface contamination. Based on these results, the sonication of CNT suspension should be covered or conducted inside a ventilated enclosure with proper filtration or a glovebox to minimize the potential of exposure. 相似文献
100.
A planar, trivalent phosphorus compound is shown to undergo reversible two-electron redox cycling (P(III)/P(V)) enabling its use as catalyst for a transfer hydrogenation reaction. The trivalent phosphorus compound activates ammonia-borane to furnish a 10-P-5 dihydridophosphorane, which in turn is shown to transfer hydrogen cleanly to azobenzene, yielding diphenylhydrazine and regenerating the initial trivalent phosphorus species. This result constitutes a rare example of two-electron redox catalysis at a main group compound and suggests broader potential for this nonmetal platform to support bond-modifying redox catalysis of the type dominated by transition metal catalysts. 相似文献