全文获取类型
收费全文 | 287篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
化学 | 192篇 |
力学 | 2篇 |
数学 | 37篇 |
物理学 | 65篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 4篇 |
2013年 | 8篇 |
2012年 | 14篇 |
2011年 | 22篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 16篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1942年 | 2篇 |
1940年 | 2篇 |
1935年 | 1篇 |
1934年 | 1篇 |
1933年 | 1篇 |
1931年 | 1篇 |
1929年 | 1篇 |
1924年 | 1篇 |
排序方式: 共有296条查询结果,搜索用时 0 毫秒
41.
Gesinski MR Van Orden LJ Rychnovsky SD 《Synlett : accounts and rapid communications in synthetic organic chemistry》2008,2008(3):363-366
The Mukaiyama aldol-Prins (MAP) cyclization of acetals stereoselectively provided substituted tetrahydropyrans. The scope of the reaction has been expanded to include other electrophiles, including ketals and α-acetoxy ethers. Finally, a double MAP cyclization with orthoformates is described. 相似文献
42.
The purpose of this study was to further develop and validate the Teaching Science as Inquiry (TSI) Instrument, an instrument designed to measure the self‐efficacy beliefs of preservice teachers in regards to the teaching of science as inquiry. Based on the validation processes and the associated data analysis, the TSI demonstrates continued content and construct validity with high internal reliability when used with prospective elementary science teachers. 相似文献
43.
44.
David E. Knowles Lori Nixon Erin R. Campbell Douglas W. Later Bruce E. Richter 《Fresenius' Journal of Analytical Chemistry》1988,330(3):225-228
Summary Polymers can be difficult to fully characterize by conventional chromatographic methods [i.e., gas chromatography (GC), high performance liquid chromatography (HPLC) and size exclusion chromatography (SEC)] due to temperature instability, detector incompatibility, nonvolatility, molecular weight considerations or insufficient chromatographic efficiency. Capillary supercritical fluid chromatography (SFC) offers several advantages for polymer analysis. Complex distributions can be resolved, low temperatures can be used and individual oligomers can be detected, allowing differences in molecular weight distributions to be quantitatively and qualitatively measured. In this paper, results will be shown for the analysis of various types of polymers demonstrating how changes in chromatographic parameters affect the analysis
Industrielle Anwendungen der Chromatographie mit überkritischen fluiden Phasen: Polymeranalyse相似文献
45.
46.
D. Lenoir R. M. Frank F. Cordt A. Gieren und V. Lamm 《Fresenius' Journal of Analytical Chemistry》1980,304(4):283
Ohne Zusammenfassung
X-ray structural analysis of trans-1-Ethyl-2-(1-ethyl-2-adamantylidene)-adamantane. Comparison with force field calculations相似文献
47.
Tobias Lamm 《Calculus of Variations and Partial Differential Equations》2006,27(2):125-157
Let be a compact Riemannian surface and let be a compact Riemannian manifold, both without boundary, and assume that N is isometrically embedded into some ℝ
l
. We consider a sequence of critical points of the functional with uniformly bounded energy. We show that this sequence converges weakly in and strongly away from finitely many points to a smooth harmonic map. One can perform a blow-up to show that there separate at most finitely many non-trivial harmonic two-spheres at these finitely many points. Finally we prove the so called energy identity for this approximation in the case that ↪ ℝ
l
.
Mathematics Subject Classification (2000) 58E20, 35J60, 53C43 相似文献
48.
The effect of masker-frequency variability on the detection performance of 7-9 month-old infants and adults was examined. Listeners detected a 300-ms 1000-Hz pure tone masked by: (1) A random-frequency two-tone complex; (2) a fixed-frequency two-tone complex; or (3) a broadband noise. Maskers repeated at 300-ms intervals throughout testing at 60 dB SPL. The signal was presented simultaneously with one presentation of the masker. Thresholds were determined adaptively using an observer-based method. Infants' thresholds were higher than adults' in all conditions, but infants' and adults' thresholds changed with masker condition in qualitatively similar ways. The fixed two-tone complex produced masking for both age groups, but more masking for infants than for adults. For infants and adults, the random two-tone complex produced more masking than broadband noise, but the difference was greater for infants than for adults. For infants and adults, the random two-tone complex produced more masking than the fixed two-tone complex, and the difference between these conditions was similar for both age groups. These results suggest that infants are more susceptible to informational masking than adults in the absence of spectral variability. Whether infants are more susceptible to the effects of masker-frequency variability than adults remains to be clarified. 相似文献
49.
Larson JW Yantz GR Zhong Q Charnas R D'Antoni CM Gallo MV Gillis KA Neely LA Phillips KM Wong GG Gullans SR Gilmanshin R 《Lab on a chip》2006,6(9):1187-1199
High-throughput stretching and monitoring of single DNA molecules in continuous elongational flow offers compelling advantages for biotechnology applications such as DNA mapping. However, the polymer dynamics in common microfluidic implementations are typically complicated by shear interactions. These effects were investigated by observation of fluorescently labeled 185 kb bacterial artificial chromosomes in sudden mixed shear and elongational microflows generated in funneled microfluidic channels. The extension of individual free DNA molecules was studied as a function of accumulated fluid strain and strain rate. Under constant or gradually changing strain rate conditions, stretching by the sudden elongational component proceeded as previously described for an ideal elongational flow (T. T. Perkins, D. E. Smith and S. Chu, Science, 1997, 276, 2016): first, increased accumulated fluid strain and increased strain rate produced higher stretching efficiencies, despite the complications of shear interactions; and second, the results were consistent with unstretched molecules predominantly in hairpin conformations. More abrupt strain rate profiles did not deliver a uniform population of highly extended molecules, highlighting the importance of balance between shear and elongational components in the microfluidic environment for DNA stretching applications. DNA sizing with up to 10% resolution was demonstrated. Overall, the device delivered 1000 stretched DNA molecules per minute in a method compatible with diffraction-limited optical sequence motif mapping and without requiring laborious chemical modifications of the DNA or the chip surface. Thus, the method is especially well suited for genetic characterization of DNA mixtures such as in pathogen fingerprinting amidst high levels of background DNA. 相似文献
50.
Conditionally on the ABC conjecture, we apply work of Granville to show that a hyperelliptic curve of genus at least three has infinitely many quadratic twists that violate the Hasse Principle iff it has no -rational hyperelliptic branch points. 相似文献