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191.
We have conducted a systematic study on the effects of post rubbing annealing on the relaxation of rubbing-induced birefringence of polystyrene. It is found that annealing at T0 only affects the relaxation up to T0 + TLag, where TLag is proportional to the logarithm of the annealing time tA. A theoretical model based on the distribution of relaxation times due to the individual birefringence elements is proposed. To remove its contribution to the net birefringence each element must overcome an energy barrier E = (317 + 1.17ξ)×103 J/mol, and therefore must have a characteristic relaxation time τ which depends on temperature T and a barrier height which ranges from 340.4 kJ/mol to 445.7 kJ/mol. The relaxation of birefringence is expressed by the equation NB(T, t) =
N(ξ)e-t/τ(T,ξ)dξ, in which both the relaxation time τ(T,ξ) and the distribution function N(ξ) can be extracted from experimental data. The predictions of the model agree well with all the experimental results presented in this work. The differences and similarities of the relaxation of birefringence with respect to the physical aging of quenched PS are discussed. In particular, similarities in terms of the general temperature lag phenomena are noted. 相似文献
192.
193.
Daniel Conus Mathew Joseph Davar Khoshnevisan Shang-Yuan Shiu 《Probability Theory and Related Fields》2013,156(3-4):483-533
Consider the stochastic heat equation ${\partial_t u = (\varkappa/2)\Delta u+\sigma(u)\dot{F}}$ , where the solution u := u t (x) is indexed by ${(t, x) \in (0, \infty) \times {\bf R}^d}$ , and ${\dot{F}}$ is a centered Gaussian noise that is white in time and has spatially-correlated coordinates. We analyze the large- ${\|x\|}$ fixed-t behavior of the solution u in different regimes, thereby study the effect of noise on the solution in various cases. Among other things, we show that if the spatial correlation function f of the noise is of Riesz type, that is ${f(x)\propto \|x\|^{-\alpha}}$ , then the “fluctuation exponents” of the solution are ${\psi}$ for the spatial variable and ${2\psi-1}$ for the time variable, where ${\psi:=2/(4-\alpha)}$ . Moreover, these exponent relations hold as long as ${\alpha \in (0, d \wedge 2)}$ ; that is precisely when Dalang’s theory [Dalang, Electron J Probab 4:(Paper no. 6):29, 1999] implies the existence of a solution to our stochastic PDE. These findings bolster earlier physical predictions [Kardar et al., Phys Rev Lett 58(20):889–892, 1985; Kardar and Zhang, Phys Rev Lett 58(20):2087–2090, 1987]. 相似文献
194.
Hu GR Chao CS Shiu HW Wang CT Lin WR Hsu YJ Luo MF 《Physical chemistry chemical physics : PCCP》2011,13(8):3281-3290
With a variety of surface probe techniques, we investigated low-temperature decomposition of methanol on Au nanoclusters formed by vapor deposition onto an ordered Al(2)O(3)/NiAl(100) thin film. Upon adsorption of methanol on the Au clusters (with mean diameter 1.5-3.8 nm and height 0.45-0.85 nm) at 110 K, some of the adsorbed methanol dehydrogenates directly into carbon monoxide (CO); the produced hydrogen atoms (H) begin to desorb near 125 K whereas most of the CO desorbs above 240 K. The reaction exhibits a significant dependence on the Au coverage: the produced CO increases in quantity with the Au coverage, reaches a maximum at about 1.0-1.5 ML Au, whereas decreases with further increase of the Au coverage. The coverage-dependence is rationalized partly by an altered number of reactive sites associated with low-coordinated Au in the clusters. At least two kinds of reactive sites for the low-temperature decomposition are distinguished through distinct C-O stretching frequencies (2050 cm(-1) and 2092 cm(-1)) while the produced CO co-adsorbs with H and methanol. 相似文献
195.
A series of neutral Ir(III)‐based heteroleptic complexes with a formula of [Ir(η2‐(C∧N))2(η2‐(S∧S))] ((C∧N)‐ = ppy‐, (S∧S)‐ = Et2NCS2‐ ( 2a ), MeOCS2‐ ( 2b ), EtOCS2‐ ( 2c ), iPrOCS2‐ ( 2d ); (C∧N)‐ = tpy‐, (S∧S) = Et2NCS2‐ ( 3a ), MeOCS2‐ ( 3b ), EtOCS2‐ ( 3c ), iPrOCS2‐ ( 3d ); (C∧N)‐ = epb‐ , (S∧S)‐ = Et2NCS2‐ ( 4a ), MeOCS2‐ ( 4a ), EtOCS2‐ ( 4a ); ppyH = 2‐phenylpyridine; tpyH = 2‐(4′‐tolyl)pyridine; epbH = ethyl 4‐(2′‐pyridyl)benzate) was synthesized and characterized. The crystal structure of complex 2d was also determined. The electron‐releasing substituents on (C∧N)‐ or (S∧S)‐ blueshift λmax values. 相似文献
196.
"Turn-on" FRET-based luminescent probes containing iridium(III) complexes for the detection of Cys and Hcy have been designed and synthesized. The relationship between the steric bulk of the probe and the corresponding emission intensity enhancement towards detection of Cys and Hcy has been studied. 相似文献
197.
A proper edge coloring of a graph G is called adjacent vertex-distinguishing acyclic edge coloring if there is no 2-colored cycle in G and the coloring set of edges incident with u is not equal to the coloring set of edges incident with v, where uv ∈ E(G). The adjacent vertex distinguishing acyclic edge chromatic number of G, denoted by x′
Aa
(G), is the minimal number of colors in an adjacent vertex distinguishing acyclic edge coloring of G. If a graph G has an adjacent vertex distinguishing acyclic edge coloring, then G is called adjacent vertex distinguishing acyclic. In this paper, we obtain adjacent vertex-distinguishing acyclic edge coloring
of some graphs and put forward some conjectures. 相似文献
198.
Back Cover: Antagonizing STAT3 Dimerization with a Rhodium(III) Complex (Angew. Chem. Int. Ed. 35/2014) 下载免费PDF全文
199.
Ultrafast Spectroscopy Studies on Thickness Dependence of Acoustic Phonon Modes in Silver Nanoprisms
Time-resolved transient absorption technique is used to investigate the thickness dependence of acoustic phonon modes of silver nanoprisms with two thicknesses, 7.8 ± 1.2 and 8.5 ± 0.69 nm, and a similar bisector length of 31.4 ∼ 31.6 nm. Coherent acoustic phonon signals are observed. A new acoustic phonon frequency within 7.81 cm−1 ∼ 11.7 cm−1 is found and this phonon mode is associated with the thickness of the nanoprism. Another phonon frequency between 1.95 cm−1 and 1.71 cm−1 is also observed, and its origin can be associated with the bisector length of the nanoprism. 相似文献
200.
Bo-Yuan Shiu 《Tetrahedron》2008,64(27):6221-6229
Several cobalt-containing bulky monodentate phosphines (μ-PPh2CH2PPh2)Co2(CO)4(μ,η-(tBu)2PCC(C6H4R)) (4a: R=H; 4b: R=p-F; 4cp: R=p-CF3; 4cm: R=m-CF3; 4d: R=p-OMe) were prepared from the reactions of (tBu)2PCC(R-C6H4) (2a: R=H; 2b: R=p-F; 2cp: R=p-CF3; 2cm: R=m-CF3; 2d: R=p-OMe) with Co2(CO)6(μ-PPh2CH2PPh2) 3. Further reactions of 4a, 4b, 4cp, 4cm, and 4d with Pd(OAc)2 yielded unique palladium complexes (μ-PPh2CH2PPh2)Co2(CO)4(μ,η-(tBu)2PCC(C6H3R)-κC1)Pd(μ-OAc) (5a: R=H; 5b: R=p-F; 5cp: R=p-CF3; 5cm: R=m-CF3; 5d: R=p-OMe, respectively). The strong electron-withdrawing substituents, -F and -CF3, assist the ortho-metalation process during the formation of 5b, 5cp, and 5cm. The more positively charged palladium center in 5b (or 5cp, 5cm) enhances the probability for PhB(OH)3− to attack the metal center and the rate of reduction thereafter. DFT studies on the charges of these palladium centers support this assumption. The enhancement of the reaction rates of the Suzuki-Miyaura cross-coupling reactions using 5b, 5cp, and 5cm is thereby attributed to this effect. 相似文献