全文获取类型
收费全文 | 2265篇 |
免费 | 87篇 |
国内免费 | 7篇 |
专业分类
化学 | 1764篇 |
晶体学 | 25篇 |
力学 | 35篇 |
数学 | 228篇 |
物理学 | 307篇 |
出版年
2023年 | 13篇 |
2022年 | 23篇 |
2021年 | 53篇 |
2020年 | 47篇 |
2019年 | 52篇 |
2018年 | 33篇 |
2017年 | 27篇 |
2016年 | 73篇 |
2015年 | 58篇 |
2014年 | 57篇 |
2013年 | 109篇 |
2012年 | 167篇 |
2011年 | 200篇 |
2010年 | 93篇 |
2009年 | 66篇 |
2008年 | 163篇 |
2007年 | 153篇 |
2006年 | 154篇 |
2005年 | 117篇 |
2004年 | 111篇 |
2003年 | 86篇 |
2002年 | 93篇 |
2001年 | 25篇 |
2000年 | 23篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 20篇 |
1996年 | 22篇 |
1995年 | 24篇 |
1994年 | 17篇 |
1993年 | 24篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1972年 | 7篇 |
排序方式: 共有2359条查询结果,搜索用时 187 毫秒
161.
Zou L Wang J Beleva VJ Kooijman EE Primak SV Risse J Weissflog W Jákli A Mann EK 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2772-2780
A systematic study of five different, symmetric bent-core liquid crystals in Langmuir thin films at the air/water interface is presented. Both the end chains (siloxane vs hydrocarbon) and the core (more or less amphiphilic) are varied, to allow an exploration of different possible layer structures at the interface. The characterization includes systematic surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. The properties of these layers are strongly dependent on the individual type of molecule: the molecules with amphiphilic end chains lie quite flat on the surface, while the molecules with hydrophobic end chains construct multilayer structures. In both cases, the three-dimensional collapse structure is reversible. 相似文献
162.
Beer PD Berry NG Cowley AR Hayes EJ Oates EC Wong WW 《Chemical communications (Cambridge, England)》2003,(19):2408-2409
A novel family of redox-active dinuclear transition metal based cryptands self-assembled from dithiocarbamate ligands has been synthesised; depending upon the nature of the spacer groups these new cryptand systems have been shown to electrochemically recognise the binding of cations or anions. 相似文献
163.
Zelikin AN Trukhanova ES Putnam D Izumrudov VA Litmanovich AA 《Journal of the American Chemical Society》2003,125(45):13693-13699
The physicochemical characteristics of a nonviral gene delivery system will govern its functional bioactivity; however, empiricism dominates the literature in this field, and a significant deficiency of quantitative investigation and evaluation of nonviral gene delivery vehicles remains. Herein, we derive a physical model and experimental method to quantitatively determine the binding constants between a model polycationic nonviral gene delivery vehicle poly-L-histidine (PLH) and calf thymus DNA. The approach has utility to a variety of systems and is not limited to the described polymer model. The interaction of PLH with DNA was monitored by fluorescence quenching of an ethidium bromide probe in the pH range 4 to 8. The interaction increased with pH decrease with the most pronounced change between pH 6 and 7. The obtained pH-dependence of fraction of salt bonds formed between PLH and DNA was used to estimate pK(a) of PLH in the presence of DNA, which equaled 6.24. The interaction of PLH with DNA in the presence of added synthetic polyanions was studied by the same approach and found to be controlled by pH, nature of the charge groups of the polyanion, and its degree of polymerization. In the mixture with sodium poly(styrenesulfonate) the interaction was negligible in the whole studied pH range, whereas in the mixtures with sodium poly(acrylate) (PA) or sodium poly(methacrylate), DNA was able to compete effectively for the binding with PLH. For PA samples with degree of polymerization higher than degree of polymerization of PLH, DP(PA) > DP(PLH), the fraction of polycation bound to DNA was constant regardless of DP(PA.) In contrast, at DP(PA) < DP(PLH), a pronounced increase in the bound fraction was observed. It substantiates the notion that the binding energy of two polymers is mainly controlled by the DP of the shorter component of polyelectrolyte complex. The data on PLH distribution between DNA and added polyanion with different values of DP were treated according to the developed procedure to yield the effective binding constants of PLH with DNA and polyanion-competitor, calculated both per mole of interacting units K(1) and mole of interacting chains K(n). In all cases, K(1) had similar numerical values reflecting common type of interaction stabilizing the complexes, i.e., electrostatics. Slight variation of K(1) yielded in drastic changes in K(n) and alteration of dominance of PLH interaction with DNA or synthetic polyanion. The results of the study can have a high impact in deriving the correlation between the binding constant of a polycation to DNA and its ability to serve as gene delivery vehicle. 相似文献
164.
Ryan Guterman Bradley M. Berven T. Chris Corkery Heng‐Yong Nie Mike Idacavage Elizabeth R. Gillies Paul J. Ragogna 《Journal of polymer science. Part A, Polymer chemistry》2013,51(13):2782-2792
An array of highly fluorinated polymerizable phosphonium salts (HFPPS) were synthesized from PH3 and utilized in UV‐curable formulations. Inclusion of these salts at very low loading (0.1–1 wt %) into hexanediol diacrylate (HDDA) resulted in hydrophobic surfaces. The water repellency was achieved with short C4F9 fluorocarbon appendages in the monomer as opposed to the bioaccumulative C8F17 appended polymers. The physical properties of these new monomers were also characterized. The molecular architecture of the monomers had a pronounced effect on both their physical properties along with the degree of hydrophobicity imparted in the polymer. Salts utilizing the bis(trifluoromethylsulfonyl)imide anion displayed excellent compatibility with HDDA, while the chloride salts were insoluble. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) confirmed the presence of the HFPPS at the surface of the polymer coating. For the first time this demonstrates how these salts may be used to functionalize the surface of a UV‐cured film with ionic species. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2782–2792 相似文献
165.
Hong Li Sahas Rathi Elizabeth S. Sterner Hui Zhao Shaw Ling Hsu Patrick Theato Yongming Zhang E. Bryan Coughlin 《Journal of polymer science. Part A, Polymer chemistry》2013,51(20):4309-4316
The synthesis and characterization of a photocleavable block copolymer containing an ortho‐nitrobenzyl (ONB) linker between poly(methyl methacrylate) and poly(d ‐lactide) blocks is presented here. The block copolymers were synthesized via atom transfer radical polymerization (ATRP) of MMA followed by ring‐opening polymerization (ROP) of d ‐Lactide and ROP of d ‐lactide followed by ATRP of MMA from a difunctional photoresponsive ONB initiator, respectively. The challenges and limitations during synthesis of the photocleavable block copolymers using the difunctional photoresponsive ONB initiator are discussed. The photocleavage of the copolymers occurs under mild conditions by simple irradiation with 302 nm wavelength UV light (Relative intensity at 7.6 cm: 1500 μW/cm2) for several hours. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4309–4316 相似文献
166.
Kumaranand Palaniappan Nadia Hundt Prakash Sista Hien Nguyen Jing Hao Mahesh P. Bhatt Yun‐Yue Han Elizabeth A. Schmiedel Elena E. Sheina Michael C. Biewer Mihaela C. Stefan 《Journal of polymer science. Part A, Polymer chemistry》2011,49(8):1802-1808
Poly(3‐hexylthiophene)‐b‐poly(4‐vinylpyridine) diblock copolymer was synthesized by RAFT polymerization of 4‐vinyl pyridine using a trithiocarbonate‐terminated poly(3‐hexylthiophene) macro‐RAFT agent. The optoelectronic properties and the morphology of the block copolymer blends with CdSe quantum dots were investigated. UV‐vis and fluorescence experiments were performed to prove the charge transfer between CdSe and poly(3‐hexylthiophene)‐b‐poly(4‐vinylpyridine) diblock copolymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
167.
168.
Jeanine Giarolla Daniela G. Rando Kerly F.M. Pasqualoto Márcio H. Zaim Elizabeth I. Ferreira 《Journal of Molecular Structure》2010,939(1-3):133-138
Molecular modeling methodologies were applied to perform preliminary studies concerning the release of active agents from potentially antichagasic and antileishmanial dendrimer prodrugs. The dendrimer was designed having myo-inositol as a core, l-malic acid as a spacer group, and hydroxymethylnitrofurazone (NFOH), 3-hydroxyflavone or quercetin, as active compounds. Each dendrimer presented a particular behavior concerning to the following investigated properties: spatial hindrance, map of electrostatic potential (MEP), and the lowest unoccupied molecular orbital energy (ELUMO). Additionally, the findings suggested that the carbonyl group next to the active agent seems to be the most promising ester breaking point. 相似文献
169.
170.
We prove that when q is any odd prime power, the distance-2 graph on the set of vertices at maximal distance D from any fixed vertex of the Hemmeter graph HemD(q) is isomorphic to the graph QuadD-1(q) of quadratic forms on . 相似文献