全文获取类型
收费全文 | 706篇 |
免费 | 12篇 |
专业分类
化学 | 421篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 37篇 |
物理学 | 253篇 |
出版年
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 26篇 |
2012年 | 23篇 |
2011年 | 19篇 |
2010年 | 20篇 |
2009年 | 8篇 |
2008年 | 19篇 |
2007年 | 25篇 |
2006年 | 30篇 |
2005年 | 38篇 |
2004年 | 20篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 14篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 11篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 13篇 |
1973年 | 26篇 |
1972年 | 10篇 |
1971年 | 12篇 |
1970年 | 5篇 |
1969年 | 10篇 |
1968年 | 9篇 |
1967年 | 10篇 |
1925年 | 5篇 |
排序方式: 共有718条查询结果,搜索用时 31 毫秒
91.
Two-component bottle-brush polymers, where flexible side chains containing N = 20, 35 and 50 effective monomers are grafted alternatingly to a rigid backbone, are studied by Molecular Dynamics simulations,
varying the grafting density s \sigma and the solvent quality. Whereas for poor solvents and large enough s \sigma the molecular brush is a cylindrical object with monomers of different type occupying locally the two different halves of
the cylinder, for intermediate values of s \sigma an axially inhomogeneous structure of “pearl-necklace” type is formed, where microphase separation between monomers of different
type within a cluster takes place. These “pearls” have a strongly non-spherical ellipsoidal shape, due to the fact that several
side chains cluster together in one “pearl”. We discuss the resulting structures in detail and we present a comparison with
the single-component bottle-brush case. 相似文献
92.
David M. Berube Christopher L. Cummings Jordan H. Frith Andrew R. Binder Robert Oldendick 《Journal of nanoparticle research》2011,13(8):3089-3099
Over the last decade social scientific researchers have examined how the public perceives risks associated with nanotechnology.
The body of literature that has emerged has been methodologically diverse. The findings have confirmed that some publics perceive
nanotechnology as riskier than others, experts feel nanotechnology is less risky than the public does, and despite risks the
public is optimistic about nanotechnology development. However, the extant literature on nanotechnology and risk suffers from
sometimes widely divergent findings and has failed to provide a detailed picture of how the public actually feels about nanotechnology
risks when compared to other risks. This study addresses the deficiencies in the literature by providing a comparative approach
to gauging nanotechnology risks. The findings show that the public does not fear nanotechnology compared to other risks. Out
of 24 risks presented to the participants, nanotechnology ranked 19th in terms of overall risk and 20th in terms of “high
risk.” 相似文献
93.
The molecular order within the hydrophobic core of membranes of the diene lipid di-tetradecadienoylphosphatidylcholine was studied by means of infrared spectroscopy on multibilayer assemblies which orient macroscopically on the surface of an attenuated total reflection crystal. The relative humidity and temperature were used as variable parameters to demonstrate that there were profound differences in the melting transition of lipids possessing predominantly cis and trans diene groups. The cis isomer undergoes the phase transition at a vapor pressure which is increased by 0.15 GPa when compared with that of the trans isomer. The methylene wagging band progression gives no indication of differences between the acyl chain conformation of the cis and trans forms in the gel state. The frequencies of a number of absorption bands of the diene groups reveal that these moieties are predominantly in the s-trans conformation to accommodate a favorable packing within the bilayer. The linear dichroism of selected in-plane and out-of-plane vibrations of the diene groups gives indications of the biaxial ordering of these moieties. We present the basic equations for the quantitative analysis of IR dichroism data of lamellar structures in terms of transverse and longitudinal molecular order parameters. It turns out that the planes of the rigid diene groups orient preferentially in a perpendicular direction with respect to the bilayer surface and parallel to each other forming in this way a layer of well-aligned diene groups in the bilayer center. This finding is confirmed by the results of X-ray measurements. We suggest that the partial interdigitation of the diene groups of the sn-1 acyl chains promotes the formation of the inverse HII phase and/or enables the formation of covalent bonds between both the monolayers upon polymerization of diene lipids. 相似文献
94.
Synthesis and characterization of polymer linked copper(I) bis(N‐heterocyclic carbene) mechanocatalysts
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Philipp Michael Shima Khazraee Sheidaee Mehr Wolfgang H. Binder 《Journal of polymer science. Part A, Polymer chemistry》2017,55(23):3893-3907
In this paper, the synthesis and characterization of a series of latent polymeric bis(N‐heterocyclic carbene) (NHC) copper(I) complexes is reported, which can be activated for the copper(I)‐catalyzed azide/alkyne cycloaddition (CuAAC) via ultrasound. To prove the influence of chain length and nature of the polymer towards the activation, poly(isobutylene) (PIB), poly(styrene) (PS) and poly(tetrahydrofuran) (PTHF) are synthesized via living polymerization techniques (LCCP, ATRP, CROP) obtaining different chain lengths (from 2500 to 9000 g/mol), followed by quaternization with N‐methylimidazole, generating the corresponding N‐methylimidazolium‐telechelic polymers. The deprotonation of these macroligands via strong bases like sodium tert‐butoxide (NaOtBu) or potassium hexamethyldisilazide (KHMDS) yields the free N‐heterocyclic carbenes (NHCs), which are used to coordinate to tetrakis(acetonitrile)copper(I) hexafluorophosphate, forming the final polymer‐based mono‐ and bis(N‐methylimidazole‐2‐ylidene) copper(I)X complexes. The structural proof of these complexes is accomplished via 1H‐NMR spectroscopy, MALDI‐TOF‐MS and GPC‐techniques. The activation of the copper(I) biscarbene catalysts by ultrasound is studied by GPC, revealing the cleavage of one shielding NHC‐ligand. The initial catalytic latency and the via ultrasound introduced catalytic activation is successfully demonstrated monitoring a CuAAC “click” reaction of benzyl azide and phenylacetylene by in situ 1H‐NMR spectroscopy introducing thus “click” conversions up to 97%. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3893–3907 相似文献
95.
Paul Barbic Leo Binder Susanne Voß Ferdinand Hofer Werner Grogger 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):465-472
Summary. Thin-film electrodes allow the manufacturing of flat batteries of variable design. Their electric performance is better than
that of customary cells because of a larger contact area between anode and cathode and better utilization of the electrochemically
active materials. Bipolar thin-film electrodes for the rechargeable alkaline zinc/manganese dioxide system were assembled
using graphite-filled plastics (high-density polyethylene and polyisobutylene). In a different approach, extremely thin electrodes
were obtained using 25 μm thick foils made of non-conductive micro-porous polypropylene. The electroactive materials were
electrolytically deposited into the pores of the previously metallized foil, providing the required conductive connection
through the plastic matrix by themselves. Cycle behavior, cumulated capacities, and energies of batteries with up to two bipolar
units were measured. At this early stage of development, batteries based on graphite-filled polymer foils showed better results
with regard to storage capacity per unit area and to cycle life. Prototypes based on micro-porous polypropylene suffered from
the relatively small fraction of pore volume available for the deposition of active material (about 38%) and from current
collector corrosion.
Received May 30, 2000. Accepted December 18, 2000 相似文献
96.
97.
98.
We study the problem ofsurfacedirected spinodal decomposition, viz., the dynamical interplay of wetting and phase separation at surfaces. In particular, we focus on the kinetics of wetting-layer
growth in a semi-infinite geometry for arbitrary surface potentials and mixture compositions. We also present representative
results for phase separation in confined geometries, e.g., cylindrical pores, thin films, etc. 相似文献
99.
Summary The unmixing transition of both symmetrical polymer blends AB (i.e. chain lengthsN
A=N
B=N) and asymmetrical ones (N
B/N
A=2,3) is studied by large-scale Monte Carlo simulations of the bond fluctuation model. Combination of semi-grand-canonical
simulation techniques, ?histogram reweighting? and finitesize scaling allows an accurate location of the coexistence curve
in the critical region. The variation of the critical temperature with chain length (N) is studied and compared to theoretical predictions. For the symmetrical case, use of chain lengths up toN=512 allows a rough estimation of crossover scaling functions for the crossover from Ising to mean-field exponents. The order-disorder
transitions in melts of both symmetric (compositionf=N
A/(N
A+N
B)=1/2) and asymmetric (f=3/4) block copolymers is studied for very short chains (16≤N≤60). The interplay between structure and chain configuration is emphasized. Qualitative evidence for ?dumbell formation?
of chains and vacancy enrichment in A-B-interfaces and near hard walls is presented.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
100.