全文获取类型
收费全文 | 274篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 156篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 17篇 |
物理学 | 98篇 |
出版年
2023年 | 1篇 |
2022年 | 12篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 19篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 16篇 |
2012年 | 19篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 20篇 |
2007年 | 16篇 |
2006年 | 9篇 |
2005年 | 20篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1973年 | 2篇 |
1962年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
1937年 | 2篇 |
排序方式: 共有280条查询结果,搜索用时 62 毫秒
151.
Tariq M. Butt Noomen Ben El Hadj Anke Skrobek Willem J. Ravensberg Chengshu Wang Catherine M. Lange Alain Vey Umi‐Kulsoom Shah Ed Dudley 《Rapid communications in mass spectrometry : RCM》2009,23(10):1426-1434
Mass spectrometry was applied to the identification of the destruxins (dtxs), cyclic peptides that are commonly produced by the fungal insect‐pathogen, Metarhizium anisopliae. The aim of the study was to optimise a methodology in order to firstly determine whether these compounds were present in other species and to determine the effect of differing growth conditions upon the dtx content detected. Matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐ToF‐MS) was initially used to analyse the dtxs, but limitations were indicated. Nano‐scale high‐performance liquid chromatography/electrospray ionisation mass spectrometry (HPLC/ESI‐MS) and automated ‘data‐dependent’ tandem mass spectrometric (MS/MS) analysis were also applied, utilising characteristic neutral losses during fragmentation to confirm the presence of the dtxs. This latter approach distinguished the dtx E and B isoforms by retention time and diagnostic neutral losses during fragmentation allowing extraction of the destruxin data from a complex dataset. This process revealed the presence of a number of dtxs in the fungal species Lecanicillium longisporum, a species previously not known to produce dtxs, and dtx production in this species was shown to be significantly higher in aerated cultures compared with still cultures. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
152.
Nguyen TH Steinbock LJ Butt HJ Helm M Berger R 《Journal of the American Chemical Society》2011,133(7):2025-2027
The rupture force of a split (bipartite) aptamer that forms binding pockets for adenosine monophosphate (AMP) was measured by atomic force spectroscopy. Changes in the rupture force were observed in the presence of AMP, while this effect was absent when mutant aptamers or inosine were used. Thus, changes in the rupture force were a direct consequence of specific binding of AMP to the split aptamer. The split aptamer concept allowed the detection of nonlabeled AMP and enabled us to determine the dissociation constant on a single-molecule level. 相似文献
153.
de Viguerie L Keller R Jonas U Berger R Clark CG Klein CO Geue T Müllen K Butt HJ Vlassopoulos D 《Langmuir : the ACS journal of surfaces and colloids》2011,27(14):8776-8786
Semifluorinated alkanes (C(n)F(2n+1)C(m)H(2m+1)), short FnHm display local phase separation of mutually incompatible hydrocarbon and fluorocarbon chain moieties, which has been utilized as a structure-forming motif in supramolecular architectures. The packing of semifluorinated alkanes, nominally based on dodecyl subunits, such as perfluoro(dodecyl)dodecane (F12H12) and perfluoro(dodecyl)eicosane (F12H20), as well as a core extended analogue, 1,4-dibromo-2-((perfluoroundecyl)methoxy)-5-(dodecyloxy)benzene) (F11H1-core-H12), was studied at the air/water interface. Langmuir monolayers were investigated by means of neutron reflectivity directly at the air/water interface and scanning force microscopy after transfer to silicon wafers. Narrowly disperse surface micelles formed in all three cases; however, they were found to bear different morphologies with respect to molecular orientation and assembly dimensionality, which gives rise to different hierarchical aggregate topologies. For F12H12, micelles of ca. 30 nm in diameter, composed of several circular or "spherical cap" substructures, were observed and a monolayer model with the fluorocarbon block oriented toward air is proposed. F12H20 molecules formed larger (ca. 50 nm diameter) hexagonally shaped surface micelles that were hexagonally, densely packed, besides more elongated but tightly interlocked wormlike structures. Conversely, F11H1-core-H12 films organized into linear rows of elongated surface micelles with comparable width, but an average length of ca. 400 nm, apparently formed by antiparallel molecular packing. 相似文献
154.
MUHAMMAD Danish SABA Akbar MUHAMMAD Nawaz Tahir MUHAMMAD Naeem Ahmed RABIA Ayub Butt MUHAMMAD Asam Raza MUHAMMAD Ashfaq 《结构化学》2018,(6)
Using a bidentate ligand, a Schiff base 4-({[(Z)-(2-hydroxyphenyl)methyldene]amino}methyl)cyclohexanecarboxylic acid, complex I(ML2, where M = Cd(Ⅱ)) was synthesized and characterized by IR spectroscopy and X-ray crystallography. It crystallizes in monoclinic system, space group C2/c, M_r = 685.04, 0.34 mm × 0.26 mm × 0.14 mm, a = 54.050(3), b = 6.1220(3), c = 9.5081(5) ?, β = 90.229(2)°, Z = 4, C_(30) H_(40) CdN_2 O_9 and V = 3146.2(3) ?~3. Complex I was screened for its bactericidal activity against four bacterial strains Chromohalobactersalexigens, Chromohalobacterisraelensis, Halomonashalofila and Halomonassalina and fungicidal activity against Aspergillusnigerand Aspergillusflavus. Antimicrobial activity results showed that the synthesized complex displayed good anti-fungal activity against two fungal strains. It was found to be inactive against four different bacterial strains analyzed and was negative for bactericidal effect. 相似文献
155.
Farshchi-Tabrizi M Kappl M Cheng Y Gutmann J Butt HJ 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2171-2184
In this study we measured the adhesion forces between atomic force microscope (AFM) tips or particles attached to AFM cantilevers and different solid samples. Smooth and homogeneous surfaces such as mica, silicon wafers, or highly oriented pyrolytic graphite, and more rough and heterogeneous surfaces such as iron particles or patterns of TiO2 nanoparticles on silicon were used. In the first part, we addressed the well-known issue that AFM adhesion experiments show wide distributions of adhesion forces rather than a single value. Our experiments show that variations in adhesion forces comprise fast (i.e., from one force curve to the next) random fluctuations and slower fluctuations, which occur over tens or hundreds of consecutive measurements. Slow fluctuations are not likely to be the result of variations in external factors such as lateral position, temperature, humidity, and so forth because those were kept constant. Even if two solid bodies are brought into contact under precisely the same conditions (same place, load, direction, etc.) the result of such a measurement will often not be the same as that of the previous contact. The measurement itself will induce structural changes in the contact region, which can change the value for the next adhesion force measurement. In the second part, we studied the influence of humidity on the adhesion of nanocontacts. Humidity was adjusted relatively fast to minimize tip wear during one experiment. For hydrophobic surfaces, no signification change in adhesion force with humidity was observed. Adhesion force versus humidity curves recorded with hydrophilic surfaces either showed a maximum or continuously increased. We demonstrate that the results can be interpreted with simple continuum theory of the meniscus force. The meniscus force is calculated based on a model that includes surface roughness and takes into account different AFM tip (or particle) shapes by a two-sphere model. Experimental and theoretical results show that the precise contact geometry has a critical influence on the humidity dependence of the adhesion force. Changes in tip geometry on the sub-10-nm length scale can completely change adhesion force versus humidity curves. Our model can also explain the differences between earlier AFM studies, where different dependencies of the adhesion force on humidity were observed. 相似文献
156.
Ferric iron, even in the presence of comparatively large amounts of phosphate, can be determined by titrating with the disodium salt of ethylenediaminetetraacetic acid (Versenate, Complexone III), using ammonium thiocyanate as indicator and extracting the red ferric thiocyanate into amyl alcohol, provided the pH is controlled at 2.0—2.4 at the end-point. The method has been successfully used for the determination of iron in phosphate-containing deposits from steam boilers. 相似文献
157.
On the Long Time Behavior of Infinitely Extended Systems of Particles Interacting via Kac Potentials
We analyze the long time behavior of an infinitely extended system of particles in one dimension, evolving according to the Newton laws and interacting via a non-negative superstable Kac potential
(x)=(x), (0, 1]. We first prove that the velocity of a particle grows at most linearly in time, with rate of order . We next study the motion of a fast particle interacting with a background of slow particles, and we prove that its velocity remains almost unchanged for a very long time (at least proportional to
–1 times the velocity itself). Finally we shortly discuss the so called Vlasov limit, when time and space are scaled by a factor . 相似文献
158.
We investigate the time evolution of a model system of interacting particles moving in a d-dimensional torus. The microscopic dynamics is first order in time with velocities set equal to the negative gradient of a potential energy term plus independent Brownian motions: is the sum of pair potentials, V(r)+
d
J(r); the second term has the form of a Kac potential with inverse range . Using diffusive hydrodynamic scaling (spatial scale
–1, temporal scale
–2) we obtain, in the limit 0, a diffusive-type integrodifferential equation describing the time evolution of the macroscopic density profile. 相似文献
159.
Dudley E Wang C Skrobek A Newton RP Butt TM 《Rapid communications in mass spectrometry : RCM》2004,18(21):2577-2586
Destruxins are of current interest as bioactive agents. They are cyclic hexadepsipeptides produced by fungi, the most common destruxins, A, B and E, differing in the structure of a side chain. Before they can be widely used, the potential risk of destruxins and their metabolites entering the human food chain must to be assessed; thus, knowledge of the structures of their degradation products is essential. Here we report a study aimed at identifying, by tandem mass spectrometry and accurate mass analysis, the products resulting from thermally and temporally induced degradation of destruxin E. The degradation products fell into two groups: those with relatively simple modifications of the side chain and those involving much more complex rearrangements. The structures of most of the degradation products were deduced from the MS data, with the major product being destruxin E diol: significantly, this compound had previously been reported to have only been produced as a metabolic product of enzyme action rather than as a simple degradation product as demonstrated here. 相似文献
160.
Paolo Buttà Emanuele Caglioti Carlo Marchioro 《Communications in Mathematical Physics》2003,233(3):545-569
We study the time evolution of a charged particle moving in a medium under the action of a constant electric field E. In the framework of fully Hamiltonian models, we discuss conditions on the particle/medium interaction which are necessary for the particle to reach a finite limit
velocity. We first consider the case when the charged particle is confined in an unbounded tube of ℝ3. The electric field E is directed along the symmetry axis of the tube and the particle also interacts with an infinitely many particle system.
The background system initial conditions are chosen in a set which is typical for any reasonable thermodynamic (equilibrium
or non-equilibrium) state. We prove that, for large E and bounded interactions between the charged particle and the background, the velocity v(t) of the charged particle does not reach a finite limit velocity, but it increases to infinite as: |v(t)−Et|≤C
0
(1+t), where C
0
is a constant independent of E. As a corollary we obtain that, if the initial conditions of the background system are distributed according to any Gibbs
state, then the average velocity of the charged particle diverges as time goes to infinite. This result is obtained for E large enough in comparison with the mean energy of the Gibbs state. We next study the one-dimensional case, in which the
estimates can be improved. We finally discuss, at an heuristic level, the existence of a finite limit velocity for unbounded interactions, and give some suggestions about the case of small electric fields.
Received: 7 March 2002 / Accepted: 23 September 2002 Published online: 8 January 2003
RID="*"
ID="*" Work partially supported by the GNFM-INDAM and the Italian Ministry of the University.
Communicated by J.L. Lebowitz 相似文献