全文获取类型
收费全文 | 269篇 |
免费 | 3篇 |
专业分类
化学 | 164篇 |
力学 | 3篇 |
数学 | 25篇 |
物理学 | 80篇 |
出版年
2020年 | 1篇 |
2019年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 14篇 |
2010年 | 8篇 |
2009年 | 4篇 |
2008年 | 20篇 |
2007年 | 12篇 |
2006年 | 19篇 |
2005年 | 10篇 |
2004年 | 17篇 |
2003年 | 10篇 |
2002年 | 2篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 13篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 9篇 |
1971年 | 6篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1964年 | 1篇 |
1939年 | 3篇 |
1929年 | 1篇 |
1924年 | 2篇 |
排序方式: 共有272条查询结果,搜索用时 15 毫秒
151.
W. E. Dickinson 《Fresenius' Journal of Analytical Chemistry》1924,64(8-9):358
Ohne Zusammenfassung 相似文献
152.
We present observations of sub-micron- to micron-sized particles generated by high fluence (≈2 J/cm2) 248-nm laser ablation of pressed polytetrafluorethylene (PTFE) targets in air at atmospheric pressure. The original target
material was hydrostatically compressed ≈7 μm PTFE powder, sintered at 275 °C. Collected ejecta due to laser irradiation consists
of four basic particle morphologies ranging from small particles 50–200 nm in diameter to larger particles ≈10 μm in diameter.
Many particles formed in air carry electric charge. Using charged electrodes we are able to collect charged particles to determine
relative numbers of ± charge. We observe roughly equal numbers of positively and negatively charged particles except for the
largest particles which were predominantly negative. For a range of particle sizes we are able to measure the sign and magnitude
of this charge with a Millikan-oil-drop technique and determine surface charge densities. The implications of these observations
with respect to pulsed laser deposition of PTFE thin films and coatings are discussed.
Received: 15 January 1999 / Accepted: 18 January 1999 / Published online: 7 April 1999 相似文献
153.
The emulsifying behaviour of glyco-protein complexes of the non-ionic polysaccharide dextran (500 kDa) with whey protein isolate (WPI) have been investigated in systems containing (20 vol.% oil phase) medium-chain triglyceride oil, silicone oil, orange oil, and n-tetradecane under acidic and high electrolyte concentrations. Covalent coupling of protein to polysaccharide is achieved by dry heat treatment of protein+polysaccharide mixtures. Emulsions were made with WPI and whey protein isolate-dextran (WPI-DX) conjugate, and stability was followed by determining changes in average droplet size and extent of serum separation with time, with gum arabic (GA) chosen as reference emulsifier. The results show that the WPI-DX conjugate gives much better stability than the whey protein alone or GA under similar conditions. The improved emulsifying properties of WPI on complexing with dextran is probably due to the enhanced steric stabilization provided by the bulky hydrophilic polysaccharide moiety. 相似文献
154.
Dickinson E 《Journal of colloid and interface science》2011,356(1):196-202
The heteroaggregation behaviour of mixtures of equal-sized particles (type A+type B) exhibiting short-ranged attractive interactions is investigated using the sticky hard-sphere model. The average cluster size is calculated as a function of the total particle volume fraction, the binary mixture composition, and the A-B stickiness interaction parameter τ(AB)(-1). We show that a value of τ(AB)(-1)=10(2), equivalent to an attractive well depth of ~5kT in a realistic continuous pair potential, leads to a state of heteroaggregation just below the gelation threshold of the equimolar mixture of volume fraction 0.1. We discuss the conditions under which the assumptions of this statistical thermodynamic model are satisfied experimentally, with particular reference to recent data on the heteroaggregation behaviour of protein-stabilized emulsions and latex particle dispersions. 相似文献
155.
Abramowski A Acero F Aharonian F Akhperjanian AG Anton G Barnacka A de Almeida UB Bazer-Bachi AR Becherini Y Becker J Behera B Bernlöhr K Bochow A Boisson C Bolmont J Bordas P Borrel V Brucker J Brun F Brun P Bulik T Büsching I Carrigan S Casanova S Cerruti M Chadwick PM Charbonnier A Chaves RC Cheesebrough A Chounet LM Clapson AC Coignet G Conrad J Dalton M Daniel MK Davids ID Degrange B Deil C Dickinson HJ Djannati-Ataï A Domainko W Drury LO Dubois F Dubus G Dyks J Dyrda M Egberts K Eger P 《Physical review letters》2011,106(16):161301
A search for a very-high-energy (VHE; ≥100 GeV) γ-ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance r~45-150 pc from the Galactic center. The background-subtracted γ-ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) γ-ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual γ-ray flux. Assuming conventional Navarro-Frenk-White and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section (σv) as a function of the DM particle mass. These are among the best reported so far for this energy range and in particular differ only little between the chosen density profile parametrizations. In particular, for the DM particle mass of ~1 TeV, values for (σv) above 3×10(-25) cm(3)?s(-1) are excluded for the Einasto density profile. 相似文献
156.
The set of polynomials that are nonnegative over a subset of the nonnegative orthant (we call them set-semidefinite) have many uses in optimization. A common example of this type set is the set of copositive matrices, where we are effectively considering nonnegativity over the entire nonnegative orthant and are restricted to homogeneous polynomials of degree two. Lasserre (SIAM J. Optim., 21(3):864–885, 2011) has previously considered a method using moments in order to provide an outer approximation to this set, for nonnegativity over a general subset of the real space. In this paper, we shall show that, in the special case of considering nonnegativity over a subset of the nonnegative orthant, we can provide a new outer approximation hierarchy. This is based on restricting moment matrices to be completely positive, and it is at least as good as Lasserre’s method. This can then be relaxed to give tractable approximations that are still at least as good as Lasserre’s method. In doing this, we also provide interesting new insights into the use of moments in constructing these approximations. 相似文献
157.
Zero-valent iron nanoparticles are effective remediators of uranium from solution. It is postulated that the improved core
crystallinity and the migration of impurity phases to the nanoparticle surfaces induced by annealing may improve their corrosion
resistance and reactive lifespan. The ability of annealed and non-annealed Fe and FeNi nanoparticles to remediate a U-contaminated
effluent from AWE, Aldermaston was investigated. Nanoparticles (of diameter typically between 0 and 100 nm) were introduced
to the effluent and allowed to react for 7 days during which the liquid and nanoparticulate solids were periodically sampled.
In all the systems, the maximum U-uptake occurred within 1 h of introduction, with variable efficiency. The Fe nanoparticles
removed 98% of the total U from solution, resulting in a final U-concentration of <4 μg/L. A rapid release of Fe into solution
was recorded early in the reaction period: attributed to limited partial dissolution of the nanoparticles. Annealing the Fe
nanoparticles did not affect their efficiency but the dissolution of Fe was significantly reduced and X-ray Photoelectron
Spectroscopy indicated slower progressive oxidation. The performance of the FeNi nanoparticles was significantly improved
by annealing, with U-uptake increasing from 50 to 94%. Although the dissolution of Ni was completely inhibited by annealing,
the Fe dissolution increased compared to that observed for the non-annealed FeNi nanoparticles, in contrast to behaviour exhibited
by Fe-annealed nanoparticles. In all the systems, U was reduced to U(IV) and retained on the surfaces of the nanoparticulate
solids for up to 48 h; the U-stability was not affected by annealing the Fe or the FeNi nanoparticles before use. 相似文献
158.
159.
Xing Zhang Demetria M. Dickinson Lei Lin Matthew Suflita Sultan Baytas Robert J. Linhardt 《Tetrahedron letters》2019,60(13):911-915
Heparan sulfate tetrasaccharide 2 was efficiently prepared in seven steps through chemoenzymatic synthesis. A monosaccharide 5, N-acetyl-α-d-glucosamine- O-methylglycoside (GlcNAc-OMe), was successfully used as an acceptor in a heparosan synthase (pmHS2)-catalyzed glycosylation reaction. This avoided the multi-step synthesis of a more complex disaccharide acceptor 3, greatly simplifying the route to tetrasaccharide target 2. This approach provides a critical tetrasaccharide intermediate for subsequent chemoenzymatic transformation to fondaparinux and its analogues. 相似文献
160.