全文获取类型
收费全文 | 729篇 |
免费 | 32篇 |
国内免费 | 10篇 |
专业分类
化学 | 493篇 |
晶体学 | 19篇 |
力学 | 12篇 |
数学 | 173篇 |
物理学 | 74篇 |
出版年
2023年 | 2篇 |
2022年 | 30篇 |
2021年 | 38篇 |
2020年 | 22篇 |
2019年 | 11篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 29篇 |
2015年 | 34篇 |
2014年 | 30篇 |
2013年 | 44篇 |
2012年 | 38篇 |
2011年 | 55篇 |
2010年 | 34篇 |
2009年 | 36篇 |
2008年 | 37篇 |
2007年 | 40篇 |
2006年 | 29篇 |
2005年 | 22篇 |
2004年 | 29篇 |
2003年 | 28篇 |
2002年 | 25篇 |
2001年 | 17篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 2篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
排序方式: 共有771条查询结果,搜索用时 15 毫秒
71.
72.
This paper explores the connection between homeomorphisms of the unit circle, codimension-1 measured laminations on closed surfaces, and free actions of surface groups on IR-trees. 相似文献
73.
In this paper, we give sufficient conditions for the existence of (pseudo) weakly conformal and conformal families of measures for fibred systems. We describe a general construction principle for these families, modelled on the one developed by Denker and Urbanski for conformal measures. For those systems that are fibrewise local homeomorphisms, the constructed families are (pseudo) conformal. If a system is, moreover, weakly topologically exact along fibres, then each measure in the associated family is supported on the whole fibre where it is naturally defined. 相似文献
74.
Dr. Harindranath Kadavath Dr. Mariusz Jaremko Dr. Łukasz Jaremko Dr. Jacek Biernat Prof. Dr. Eckhard Mandelkow Prof. Dr. Markus Zweckstetter 《Angewandte Chemie (International ed. in English)》2015,54(35):10347-10351
Microtubules are regulated by microtubule‐associated proteins. However, little is known about the structure of microtubule‐associated proteins in complex with microtubules. Herein we show that the microtubule‐associated protein Tau, which is intrinsically disordered in solution, locally folds into a stable structure upon binding to microtubules. While Tau is highly flexible in solution and adopts a β‐sheet structure in amyloid fibrils, in complex with microtubules the conserved hexapeptides at the beginning of the Tau repeats two and three convert into a hairpin conformation. Thus, binding to microtubules stabilizes a unique conformation in Tau. 相似文献
75.
Influence of the soft segment length on the properties of water‐cured poly(carbonate‐urethane‐urea)s
下载免费PDF全文
![点击此处可从《先进技术聚合物》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Magdalena M. Mazurek Karolina Tomczyk Monika Auguścik Joanna Ryszkowska Gabriel Rokicki 《先进技术聚合物》2015,26(1):57-67
Poly(carbonate‐urethane‐urea)s (PCUU) based on oligocarbonate diols (Mn ≈ 2000) with different length of the hydrocarbon chain as soft segments were synthesized and investigated. Carbonate oligomerols were obtained in a two‐step method from dimethyl carbonate (DMC) and linear α,ω‐diols (1,4‐butanediol, 1,5‐pentanediol, 1,6‐hexanediol, 1,9‐nonanediol, 1,10‐dekanediol and 1,12‐dodecanediol). Oligo(trimethylene carbonate) diol was synthesized using ring‐opening polymerization of trimethylence carbonate. PCUUs were obtained by prepolymer method using isophorone diisocyanate (IPDI) and water as a chain extender. Changes in polymers properties with increase of methylene group number between carbonate linkages were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), tensile strength and hardness measurements. The thermal stability was also analyzed by means of thermogravimetric analysis (TGA). Based on FTIR analysis influence of methylene groups number between carbonate linkages on phase separation and concentration of allophanate and biuret groups in the samples were investigated. The obtained poly(carbonate‐urethane‐urea)s exhibited very good mechanical properties. Tensile strength and elongation at break were 40 MPa and 400–600%, respectively, depending on the oligocarbonate used. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
76.
We propose a new optimal control model of product goodwill in a segmented market where the state variable behaviour is described by a partial differential equation of the Lotka–Sharp–McKendrick type. In order to maximize the sum of discounted profits over a finite time horizon, we control the marketing communication activities which influence the state equation and the boundary condition. Moreover, we introduce the mathematical representation of heterogeneous electronic word of mouth. Based on the semigroup approach, we prove the existence and uniqueness of optimal controls. Using a maximum principle, we describe a numerical algorithm to find the optimal solution. Finally, we examine several examples on the optimal goodwill model and discover two types of marketing strategies. 相似文献
77.
Zacher D Yusenko K Bétard A Henke S Molon M Ladnorg T Shekhah O Schüpbach B de los Arcos T Krasnopolski M Meilikhov M Winter J Terfort A Wöll C Fischer RA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(5):1448-1455
The progressive liquid-phase layer-by-layer (LbL) growth of anisotropic multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P)(0.5)] (M: Cu(2+), Zn(2+); L: dicarboxylate linker; P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers (SAMs) on gold substrates as templates. It was found that the deposition of smooth, highly crystalline, and oriented multilayer films of these PCPs depends on the conditions at the early growth cycles. In the case of a two-step process with an equimolar mixture of L and P, growth along the [001] direction is strongly preferred. However, employing a three-step scheme with full separation of all components allows deposition along the [100] direction on carboxyl-terminated SAMs. Interestingly, the growth of additional layers on top of previously grown oriented seeding layers proved to be insensitive to the particular growth scheme and full retention of the initial orientation, either along the [001] or [100] direction, was observed. This homo- and heteroepitaxial LbL growth allows full control over the orientation and the layer sequence, including introduction of functionalized linkers and pillars. 相似文献
78.
A comparison of SPE cartridges produced in authors laboratory containing silica modified by addition of three functional moieties with standard C-18 and SDVB cartridges was made in terms of their applicability for the isolation of flavor compounds. Compounds found in wine and grapes were used for model mixture, which was spiked into a grape juice. Functionalized phases for SPE were prepared modifying silica gel with alkoxysilanes with different functional groups: (3-(phenylamino)-propyltrimethoxysilane, octyltriethoxysilane and octadecyl-silane. The functionalization was carried out by the dry method, which resulted 5, 10 and 20 weight parts of initial support. Functionalized phases were characterized using FT-IR, elemental analysis and NMR.Performance for new phases compared to “standard” ones (C-18 and SDVB (styrene–divinylbenzene) varied, depending on the group or type of analyzed compound. They were more efficient in extraction of methyl anthranilate and vanilins. For extraction of terpenes, C-6 alcohols, isoprenoids, benzene derivatives and phenols their efficiency was comparable to that of C-18.Functionalized laboratory-made mixed phases are suitable for extraction of flavor compounds from grape juice. They are suitable for extraction of compounds belonging to different chemical classes with the efficiency comparable to C-18 and SDVB phases. The production of such functionalized phases can be easily performed in the laboratory, at a very low cost, comparing to C-18 or SDVB cartridges. This makes the proposed functionalized phases an interesting alternative, in sample preparation for analysis and particularly in preparative/flash chromatography. 相似文献
79.
Maślanka A Krzek J Stolarczyk M Walczak M Głogowska A 《Journal of AOAC International》2011,94(6):1791-1799
Stability of clonazepam, diazepam, haloperidol, and doxepin was determined in acidic solutions. In addition, determination of the kinetic and thermodynamic properties of this stability was carried out. Reaction rate constants (k), half-life times (t(0.1) and t(0.5)), and activation energy (Ea) were estimated for the drugs, which differed in polarity expressed with log P values. It was observed that estimated Ea values increased from 42.13 to 125.03 kJ/mol with an increase of lipophilicity (log P) beginning from the most hydrophilic drug (clonazepam, 2.70 log P) to the most lipophilic drug (doxepin, 4.10 log P). All degradation products were studied using an HPLC/electrospray ionization-MS technique in the positive ionization mode. 相似文献
80.
Molon M Bollermann T Gemel C Schaumann J Fischer RA 《Dalton transactions (Cambridge, England : 2003)》2011,40(40):10769-10774
Treatment of [Mo(N(2))(PMe(3))(5)] with two equivalents GaCp* (Cp* = η(5)-C(5)(CH(3))(5)) leads to the formation of cis-[Mo(GaCp*)(2)(PMe(3))(4)] (1), while AlCp* did not react with this precursor. In addition, [Ni(GaCp*)(2)(PPh(3))(2)] (2a), [Ni(AlCp*)(2)(PPh(3))(2)] (2b), [Ni(GaCp*)(2)(PCy(3))(2)] (3a), [Ni(GaCp*)(2)(PMe(3))(2)] (3b), [Ni(GaCp*)(3)(PCy(3))] (4) and [Ni(GaCp*)(PMe(3))(3)] (5) have been prepared in high yields by a direct synthesis from [Ni(COD)(2)] and stoichiometric amounts of the ligands PR(3) and ECp* (E = Al, Ga), respectively. All compounds have been fully characterized by (1)H, (13)C, and (31)P NMR spectroscopy, elemental analysis and single crystal X-ray diffraction studies. 相似文献