全文获取类型
收费全文 | 2690篇 |
免费 | 16篇 |
国内免费 | 13篇 |
专业分类
化学 | 1791篇 |
晶体学 | 6篇 |
力学 | 26篇 |
数学 | 540篇 |
物理学 | 356篇 |
出版年
2016年 | 23篇 |
2015年 | 17篇 |
2014年 | 35篇 |
2013年 | 79篇 |
2012年 | 66篇 |
2011年 | 63篇 |
2010年 | 50篇 |
2009年 | 39篇 |
2008年 | 63篇 |
2007年 | 61篇 |
2006年 | 76篇 |
2005年 | 69篇 |
2004年 | 64篇 |
2003年 | 51篇 |
2002年 | 48篇 |
2001年 | 21篇 |
2000年 | 36篇 |
1999年 | 37篇 |
1998年 | 27篇 |
1997年 | 37篇 |
1996年 | 55篇 |
1995年 | 41篇 |
1994年 | 38篇 |
1993年 | 49篇 |
1992年 | 42篇 |
1991年 | 40篇 |
1990年 | 31篇 |
1989年 | 31篇 |
1988年 | 23篇 |
1987年 | 30篇 |
1986年 | 37篇 |
1985年 | 58篇 |
1984年 | 32篇 |
1983年 | 35篇 |
1982年 | 45篇 |
1981年 | 37篇 |
1980年 | 58篇 |
1979年 | 54篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1976年 | 48篇 |
1975年 | 31篇 |
1974年 | 34篇 |
1973年 | 38篇 |
1972年 | 26篇 |
1971年 | 24篇 |
1970年 | 27篇 |
1967年 | 17篇 |
1930年 | 18篇 |
1929年 | 15篇 |
排序方式: 共有2719条查询结果,搜索用时 31 毫秒
961.
Flow‐coated, two‐dimensional polymer ribbon structures undergo a shape‐transformation into a three‐dimensional helix upon their release into a solution. Driven by surface forces and due to geometric asymmetry, the helix radius and spring constant depend upon the ribbon cross‐section dimensions, surface energy, and material elastic modulus. Such spring‐like microhelices offer multiple functionalities combined with mechanical stretching and shape recovery. Fabricating such microhelices requires a sequence of processing steps, beginning with flow‐coating of ribbons on a substrate, followed by etching of a “scum layer” to allow for an independent release into a solution, upon which shape‐transformation occurs. During the deposition‐etch‐release sequence, various control parameters influence the nanoribbon size and geometry, hence the helix properties. The experimental study presented here focuses on the influence of meniscus height, substrate velocity, substrate surface energy, and etch time on nanoribbon size (height and width), scum layer thickness, and helix radius. The results show that meniscus height and contact angle dictate flux toward the meniscus edge and volume available for spatial assembly, allowing control over the aspect ratio of ribbons. We vary the aspect ratio by two orders of magnitude, while maintaining geometric asymmetry needed for helix shape‐transformation. We provide robust scaling for the nanoribbon size and geometry and report the advantages and disadvantages of different parameters, in the control of polymer nanoribbon and helix fabrication. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1270–1278 相似文献
962.
Meister A Bastrop M Koschoreck S Garamus VM Sinemus T Hempel G Drescher S Dobner B Richtering W Huber K Blume A 《Langmuir : the ACS journal of surfaces and colloids》2007,23(14):7715-7723
The formation of temperature-, concentration-, and pH-responsive hydrogels composed of the symmetric long-chain bolaamphiphile dotriacontane-1,1'-diyl bis[[2-(dimethylammonio)ethyl]phosphate] (Me(2)PE-C32-Me(2)PE) was investigated by rheological, scattering, and spectroscopic techniques. At pH 5, this bolaamphiphile is known to form a dense network of helically structured nanofibers (K?hler et al. Soft Matter 2006, 2, 77-86). Rheological measurements and dynamic light scattering were used to describe the macroscopic behavior of the hydrogels. Small-angle neutron scattering (SANS) and time-resolved static light scattering were applied to get information about the morphology of the self-assembled aggregates. Finally, solid-state 31P NMR spectroscopy was used to gain insight into the mobility of the bolaamphiphile molecules within the fiber aggregates. In comparison with the previously examined trimethylammonio analogue PC-C32-PC, which forms temperature-dependent hydrogels, Me(2)PE-C32-Me(2)PE exhibits additional concentration- and pH-dependent gelling properties. The significantly higher stability of the Me(2)PE-C32-Me(2)PE hydrogel is supported by the SANS data, which indicate the presence of fiber aggregates up to 50 degrees C. 相似文献
963.
964.
965.
966.
Roger W. Richardson proved that any parabolic subgroup of a complex semisimple Lie group admits an open dense orbit in the nilradical of its corresponding parabolic subalgebra. In the case of complex symmetric spaces we show that there exist some large classes of parabolic subgroups for which the analogous statement which fails in general, is true. Our main contribution is the extension of a theorem of Peter E. Trapa (in 2005) to real semisimple exceptional Lie groups.
967.
968.
The thermodynamical properties (equilibrium constants K, association enthalpies -ΔH, and association entropies -ΔS) and selected spectroscopic parameters (ΔνOH/νOH and ΔνOD/νOD of the associate band) of hydrogen bonded systems, formed by tertiary amines and benzyl alcohol or isopropanol as well as their O-deuteriated analogous species, have been obtained by ir measurements. In all cases the values of KH/KD were found lower than unity, but ΔHH/ΔHD higher than unity. 相似文献
969.
Alfred Gieren 《Fresenius' Journal of Analytical Chemistry》1985,320(7):689
970.
As main theorem we show that any duality in the projective geometry associated to a vector space is induced by a non-degenerate sesquilinear form on this space. In particular, any polarity is induced by a non-degenerate orthosymmetric sesquilinear form.Supported by a grant from the Swiss National Founds for Scientific Research. 相似文献