全文获取类型
收费全文 | 298篇 |
免费 | 25篇 |
专业分类
化学 | 172篇 |
晶体学 | 1篇 |
力学 | 7篇 |
数学 | 74篇 |
物理学 | 69篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 26篇 |
2019年 | 32篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 20篇 |
2014年 | 11篇 |
2013年 | 20篇 |
2012年 | 14篇 |
2011年 | 37篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 19篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
排序方式: 共有323条查询结果,搜索用时 15 毫秒
51.
52.
UV‐Free Microfluidic Particle Fabrication at Low Temperature Using ARGET‐ATRP as the Initiator System 下载免费PDF全文
A new way to fabricate monodisperse polymer particles in a microfluidic device without UV‐light and without the need for high temperatures is described in this article. By applying an activator regeneration by electron transfer ‐ atom transfer radical polymerization (ARGET‐ATRP) initiator system in a co‐capillary microfluidic setup and by separating the monomer mixture in an initiator and a catalyst phase, a fast polymerization of the droplets at low temperature without premature curing and thus clogging of the capillaries can be achieved. The influence of the flow rates on the particle sizes and their polydispersity as well as the controlled character of the polymerization are investigated. The particle size is well adjustable, but the reaction is not controlled due to the high radical concentration needed for rapid polymerization. In addition, particles with incorporated UV‐dyes are produced as a proof of concept at low temperature.
53.
van As BA van Buijtenen J Mes T Palmans AR Meijer EW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(29):8325-8332
The well-known dynamic kinetic resolution of secondary alcohols and esters was extended to secondary diols and diesters to afford chiral polyesters. This process is an example of iterative tandem catalysis (ITC), a polymerization method where the concurrent action of two fundamentally different catalysts is required to achieve chain growth. In order to procure chiral polyesters of high enantiomeric excess value (ee) and good molecular weight, the catalysts employed need to be complementary and compatible during the polymerization reaction. We here show that Shvo's catalyst and Novozym 435 fulfil these requirements. The optimal polymerization conditions of 1,1'-(1,3-phenylene) diethanol (1,3-diol) and diisopropyl adipate required 2 mol% Shvo's catalyst and 12 mg Novozym 435 per mmol alcohol group in the presence of 0.5 M 2,4-dimethyl-3-pentanol as the hydrogen donor. With these conditions, chiral polyesters were obtained with peak molecular weights up to 15 kDa, an ee value up to 99% and with 1-3 % ketone end groups. Also with the structural isomer, 1,4-diol, a chiral polyester was obtained, albeit with lower molecular weight (8.3 kDa) and slightly lower ee (94%). Aliphatic secondary diols also resulted in enantio-enriched polymers but at most an ee of 46 % was obtained with molecular weights in the range of 3.3-3.7 kDa. This low ee originates from the intrinsic low enantioselectivity of Novozym 435 for this type of secondary aliphatic diols. The results presented here show that ITC can be applied to procure chiral polyesters with good molecular weight and high ee from optically inactive AA-BB type monomers. 相似文献
54.
Metal-organic networks of CuCN with diimines (L) = pyrazine (Pyz), 2-aminopyrazine (PyzNH(2)), quinoxaline (Qox), phenazine (Phz), 4,4'-bipyridyl (Bpy), pyrimidine (Pym), 2-aminopyrimidine (PymNH(2)), 2,4-diaminopyrimidine (Pym(NH(2))(2)), 2,4,6-triaminopyrimidine (Pym(NH(2))(3)), quinazoline (Qnz), pyridazine (Pdz), and phthalazine (Ptz) were studied. Open reflux reactions produced complexes (CuCN)(2)(L) for L = Qox, Phz, Bpy, PymNH(2), Pym(NH(2))(2), Qnz, and Pdz and (CuCN)(3)(L) complexes for L = Pyz, PyzNH(2), Qox, Bpy, Pym(NH(2))(3), and Pdz. Also produced were (CuCN)(3)(Pyz)(2), (CuCN)(PyzNH(2)), (CuCN)7(Pym)(2), (CuCN)(5)(Qnz)(2) and (CuCN)(5)(Ptz)(2). X-ray structures are presented for (CuCN)(2)(Pdz), (CuCN)(2)(PymNH(2)), and (CuCN)(7)(Pym)(2). Hydrothermal reactions yielded additional X-ray structures of (CuCN)(2)(PyzNH(2)), (CuCN)(3)(Pym(NH(2))(2)), (CuCN)(4)(Qnz), a second (CuCN)(2)(Pdz) phase, (CuCN)(5)(Pdz)2, (CuCN)(2)(Ptz), and (CuCN)(7)(Ptz)2. Structural trends, including cuprophilic interactions and cyano-bridged Cu(2)(CN)(2) dimer formation, are discussed. Particularly short Cu...Cu interactions are noted for the novel 4- and 5-coordinate Cu(2)(CN)(2) dimers. Thermal analyses show that most of the complexes decompose with loss of L around 160-180 degrees C. Luminescence behavior is relatively weak in the products. 相似文献
55.
Van Emmerik TJ Sandström DE Antzutkin ON Angove MJ Johnson BB 《Langmuir : the ACS journal of surfaces and colloids》2007,23(6):3205-3213
Sorption of phosphate onto gibbsite (gamma-Al(OH)3) and kaolinite has been studied by both macroscopic and 31P solid-state NMR measurements. Together these measurements indicate that phosphate is sorbed by a combination of surface complexation and surface precipitation with the relative amounts of these phases depending on pH and phosphate concentration. At low pH and high phosphate concentrations sorption is dominated by the presence of both amorphous and crystalline precipitate phases. The similarity between the single-pulse and CP/MAS NMR spectra suggests that the precipitate phases form a thin layer on the surface of the particles in close contact with protons from surface hydroxyl groups or coordinated water molecules. While the crystalline phase is only evident on samples below pH 7, amorphous AlPO4 was found at all pH and phosphate concentrations studied. As pH was increased the fraction of phosphate sorbed as an inner-sphere complex increased, becoming the dominant surface species by pH 8. Comparison of sorption and NMR results suggests that the inner-sphere complexes form by monodentate coordination to singly coordinated Al-OH sites on the edges of the gibbsite and kaolinite crystals. Outer-sphere phosphate complexes, which are readily desorbed, are also present at high pH. 相似文献
56.
Montassar Khalil Alexis Hocquigny Mathieu Berchel Tristan Montier Paul-Alain Jaffrs 《Molecules (Basel, Switzerland)》2021,26(24)
A convergent synthesis of cationic amphiphilic compounds is reported here with the use of the phosphonodithioester–amine coupling (PAC) reaction. This versatile reaction occurs at room temperature without any catalyst, allowing binding of the lipid moiety to a polar head group. This strategy is illustrated with the use of two lipid units featuring either two oleyl chains or two-branched saturated lipid chains. The final cationic amphiphiles were evaluated as carriers for plasmid DNA delivery in four cell lines (A549, Calu3, CFBE and 16HBE) and were compared to standards (BSV36 and KLN47). These new amphiphilic derivatives, which were formulated with DOPE or DOPE-cholesterol as helper lipids, feature high transfection efficacies when associated with DOPE. The highest transfection efficacies were observed in the four cell lines at low charge ratios (CR = 0.7, 1 or 2). At these CRs, no toxic effects were detected. Altogether, this new synthesis scheme using the PAC reaction opens up new possibilities for investigating the effects of lipid or polar head groups on transfection efficacies. 相似文献
57.
Tristan A. Geervliet Ionela Gavrila Giuseppe Iasilli Francesco Picchioni Andrea Pucci 《化学:亚洲杂志》2019,14(6):877-883
This study reports for the first time the use of bio‐based alternatives for PMMA as host matrix for luminescent solar concentrators (LSCs). Notably, two types of renewable polyesters were synthesized in varying molar ratios via a two‐step melt‐polycondensation reaction with dibutyl tin oxide as catalyst. The first is a homopolymer of diethyl 2,3:4,5‐di‐O‐methylene galactarate (GxMe) and isosorbide (IGPn), and the second is a random copolymer of GxMe with 1,3‐propanediol and dimethyl terephthalate (GTPn). The two polyesters were found to be optically transparent, totally amorphous with a Tg higher than 45 °C and temperature resistance comparable to PMMA. Lumogen Red (LR) and an aggregation‐induced emission (AIE) fluorophore, TPETPAFN, were utilized as fluorophores and the derived thin polymer films (25 μm) were found highly homogeneous, especially for those prepared from GTPn, possibly due to the presence of compatibilizing terephthalate units in the matrix composition and the higher molecular weight. The spectroscopic characterization and the optical efficiency determination (ηopt) evidenced LSCs performances similar or superior to those collected from LR/PMMA thin films. Noteworthy, ηopt of 7.7 % and 7.1 % were recorded for the GTPn‐based matrix containing LR and TPETPAFN, respectively, thus definitely supporting the bio‐based polyesters as renewable and highly fluorophore‐compatible matrices for high‐performance LSCs. 相似文献
58.
A new algorithm for the removal of additive uncorrelated Gaussian noise from a digital image is presented. The algorithm is based on a data driven methodology for the adaptive thresholding of wavelet coefficients. This methodology is derived from higher order statistics of the residual image, and requires no a priori estimate of the level of noise contamination of an image. 相似文献
59.
Charrière F Marian A Montfort F Kuehn J Colomb T Cuche E Marquet P Depeursinge C 《Optics letters》2006,31(2):178-180
For what we believe to be the first time, digital holographic microscopy is applied to perform optical diffraction tomography of a pollen grain. Transmission phase images with nanometric axial accuracy are numerically reconstructed from holograms acquired for different orientations of the rotating sample; then the three-dimensional refractive index spatial distribution is computed by inverse radon transform. A precision of 0.01 for the refractive index estimation and a spatial resolution in the micrometer range are demonstrated. 相似文献
60.
A quantum system \({\mathcal S}\) undergoing continuous time measurement is usually described by a jump-diffusion stochastic differential equation. Such an equation is called a quantum filtering equation (or quantum stochastic master equation) and its solution is called a quantum filter (or quantum trajectory). This solution describes the evolution of the state of \({\mathcal S}\) . In the context of quantum non demolition measurement, we investigate the large time behavior of this solution. It is rigorously shown that, for large time, this solution behaves as if a direct Von Neumann measurement has been performed at time 0. In particular the solution converges to a random pure state which can be directly linked to the wave packet reduction postulate. Using the theory of Girsanov transformation, we obtain the explicit rate of convergence towards this random state. The problem of state estimation (used in experiment) is also investigated. 相似文献