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51.
52.
R. Catenacci M. Debernardi P.A. Grassi D. Matessi 《Journal of Geometry and Physics》2009,59(10):1363-1378
We first review the definition of superprojective spaces from the functor-of-points perspective. We derive the relation between superprojective spaces and supercosets in the framework of the theory of sheaves. As an application of the geometry of superprojective spaces, we extend Donaldson’s definition of balanced manifolds to supermanifolds and we derive the new conditions of a balanced supermanifold. We apply the construction to superpoints viewed as submanifolds of superprojective spaces. We conclude with a list of open issues and interesting problems that can be addressed in the present context. 相似文献
53.
This paper reports the observations of boiling flow patterns in FC-72, performed during a microgravity experiment, recently
flown aboard of Foton-M2 satellite, in some instances with the additional aid of an electrostatic field to replace the buoyancy
force. The heater consisted of a flat plate, 20 × 20 mm2, directly heated by direct current. Several levels of liquid subcooling (from 20 to 6 K) and heat fluxes up to 200 kW/m2 were tested. A complete counterpart test, carried out on ground before the mission, allowed direct comparison with terrestrial
data. The void fraction in microgravity revealed much larger than in normal gravity condition: this may be attributed to increased
bubble coalescence that hinders vapor condensation in the bulk of the subcooled fluid. In several cases, an oscillatory boiling
behavior was detected, leading to periodical variation of average wall overheating of some degrees. The electric field confirmed
to be very effective, even at low values of applied voltage, in reducing bubble size, thus improving their condensation rate
in the bulk fluid, and in enhancing heat transfer performance, suppressing the boiling oscillations and preventing surface
dryout. 相似文献
54.
Microemulsions are profitably employed in the pharmaceutical field to prepare drug delivery systems release for guest drugs
sparingly soluble in water. In particular, they can be used for topical and transdermal administration in place of ointments
or creams, on condition that their rheological properties are properly modulated. The present work concerns the analysis of
the rheological effects produced by the addition of different amounts of Carbopol 940, a polymer widely used for topical applications,
to an O/W microemulsion containing a lipophilic phase (Labrafac Hydro, 21 wt%) and stabilized by the surfactant (Cremophor
RH40)/co-surfactant (Transcutol) couple. The contribution of the disperse phase is evaluated by comparing the linear and nonlinear
properties of the Carbopol/microemulsion system (CM) with those of the corresponding aqueous Carbopol systems with co-surfactant
(CWT) and without co-surfactant (CW). Four polymer concentrations (0.25%, 0.5%, 1%, and 2%) are taken into consideration.
The linear viscoelastic properties of the microemulsions essentially mirror those of the corresponding aqueous Carbopol systems
when the polymer concentration is sufficiently high (1–2%). In these conditions the oil phase is reasonably hosted within
the meshes of the three-dimensional polymeric gel network and gives only a slight contribution to the connectivity of the
whole system. Similar considerations can be drawn from the flow behavior of the systems examined in the low shear region.
Received: 6 February 2000 Accepted: 13 November 2000 相似文献
55.
Elliptic flow is easy to compute in hydrodynamics. However experimentally it is obtained in an indirect way. The question we address in this paper is how comparable are these two approaches. For both cases, our study is done using the hydrodynamical code
NeXSPheRIO and simulating nuclear collisions at RHIC. 相似文献
56.
Ahlen S Ambrosio M Antolini R Auriemma G Baker R Baldini A Barbarino GC Barish BC Battistoni G Bellotti R Bemporad C Bernardini P Bilokon H Bisi V Bloise C Bussino S Cafagna F Calicchio M Campana P Campana D Carboni M Cecchini S Cei F Chiarella V Chiera C Cobis A Cormack R Corona A Coutu S DeCataldo G Dekhissi H DeMarzo C De Vincenzi M Di Credico A Diehl E Erriquez O Favuzzi C Ficenec D Forti C Foti L Fusco P Giacomelli G Giannini G Giglietto N Giubellino P Grassi M Green P Grillo A Guarino F 《Physical review letters》1992,69(13):1860-1863
57.
Ahlen S Ambrosio M Antolini R Auriemma G Baldini A Bam BB Barbarino GC Barish BC Battistoni G Bellotti R Bemporad C Bernardini P Bilokon H Bisi V Bloise C Bussino S Cafagna F Calicchio M Campana P Campana D Carboni M Cecchini S Cei F Chiarella V Chiera C Cobis A Cormack R Corona A Coutu S DeCataldo G DeMarzo C De Vincenzi M Di Credico A Diehl E Erriquez O Favuzzi C Ficenec D Forti C Foti L Fusco P Giacomelli G Giannini G Giglietto N Giubellino P Grassi M Green P Grillo A Guarino F Gustavino C 《Physical review D: Particles and fields》1992,46(3):895-902
58.
Metal hydride complexes find widespread application in catalysis and their properties are often understood on the basis of the available crystal structures. However, some catalytically relevant metal hydrides are only spontaneously formed in situ, cannot be isolated in large quantities or crystallised and their structure is therefore ill defined. One such example is the paramagnetic Ti(iii)-hydride involved in homogeneous Ziegler–Natta catalysis, formed upon activation of CpTi(iv)Cl3 with modified methylalumoxane (MMAO). In this contribution, through a combined use of electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopies we identify the nature of the ligands, their bonding interaction and the extent of the spin distribution. From the data, an atomistic and electronic model is proposed, which supports the presence of a self-assembled ion pair between a cationic terminal Ti-hydride and an aluminate anion, with a hydrodynamic radius of ca. 16 Å.Catalytically competent titanium-hydrides are reactive and difficult to isolate. We use EPR spectroscopy to define the electronic and geometrical structures as well as dynamics of an open-shell Ti-H active in syndiospecific olefin polymerization. 相似文献
59.
Bandini AL Banditelli G Grassi M Ponti A 《Dalton transactions (Cambridge, England : 2003)》2004,(13):2027-2035
The dynamic behaviour of the binuclear mu-hydrido mu-carbonyl cations with chelating diphosphines, [Pt2(P-P)2(mu-H)(mu-CO)]+ [P-P = dppe, 1, dppp, 2, and dppb, 3] have been investigated by multinuclear (1H, 31P and 195Pt) variable temperature NMR spectroscopy. The 195Pt and 1H results are consistent with intramolecular mutual exchange of the P atoms with respect to the bridging ligands in all of the complexes 1-3. A detailed dynamical analysis carried out on complexes 2 and 3 shows that the dynamical process exchanges the P atoms within a single diphosphino ligand, and excludes the simultaneous P atom exchange in both ligands. The bite of the diphosphino ligands affects the rate of this process in the order 3 > 2 > 1. The process follows an activation law with deltaH++ = 67 and 60 kJ mol(-1) for 2 and 3, respectively, so that P-Pt bond breaking should not be involved. The positive activation entropy (17-19 J K(-1) mol(-1)) hints at a mechanism where the intermediate(s) have a less ordered structure than that of the stable complex. In accordance with the NMR results, two reactivity experiments provided further evidence of the intramolecular nature of the observed dynamics and exclude any equilibration path via Pt-P and/or Pt-Pt bond breaking. On these grounds, a mechanism involving rotation about a Pt-Pt bond could be proposed. 相似文献
60.
Carbon-13 NMR spin-lattice relaxation times (T1) were measured for morphine, oxymorphone, nalorphine, naloxone and naltrexone as hydrochloride salts in 2H2O solution. The data refer to the molecules in the N-equatorial configuration. The experimental T1 values were interpreted using a model of anisotropic reorientation of a rigid body with superimposed internal motions of the flexible N-methyl, N-methyl-allyl and N-methyl-cyclopropyl fragments. The calculated internal motional rates were found to markedly decrease on passing from agonists to mixed (nalorphine) and pure (naloxone, naltrexone) antagonists. For these latter the observed trend of the internal flexibility about N---C and C---C bonds of the N-substituents is discussed in terms of a correlation with their relative antagonistic potencies. In fact, such an evidence of decreasing internal conformational dynamics in the order nalorphine, naloxone, naltrexone, appeared interestingly in line with the “two-state” model of opiate receptor operation mode proposed by Snyder. 相似文献