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991.
为揭示甲烷/煤尘复合爆炸火焰的传播机理,利用气粉两相混合爆炸实验系统,在低于甲烷爆炸下限条件下,采用高速摄影机记录火焰传播图像,通过热电偶采集火焰温度,研究了煤尘种类以及甲烷体积分数对甲烷/煤尘复合火焰传播特性的影响。结果表明:挥发分是衡量煤尘燃烧特性的主导因素;随着煤尘挥发分的升高,燃烧反应增强,火焰传播速度升高,火焰温度升高;挥发分含量差异较小时,水分含量越低,燃烧反应越剧烈;在相同条件下,焦煤的燃烧反应强度最高,其次为长焰煤,最后为褐煤;随着甲烷体积分数的增加,煤尘颗粒的燃烧可由释放挥发分的扩散燃烧转变为气相预混燃烧,燃烧反应增强,火焰传播速度和火焰温度显著升高;热辐射和热对流作用促进煤尘颗粒热解,释放挥发分进行燃烧反应,维持复合火焰的持续传播;随着混合体系中甲烷体积分数的增加,混合爆炸机制由粉尘驱动型爆炸转为气体驱动型爆炸,燃烧反应增强;甲烷/煤尘复合爆炸火焰可由未燃区、预热区、气相燃烧区、多相燃烧区和焦炭燃烧区5部分组成,湍流扰动导致燃烧介质空间分布存在差异,使得燃烧区无规则交错分布。 相似文献
992.
Notional Defined Contribution (NDC) pension schemes are defined contribution plans which are pay-as-you-go financed. From a design viewpoint, the countries where NDCs have been implemented cannot guarantee sustainability due to the choice of notional return paid to the contributions and the indexation rate paid to pensions. We study how the scheme should be designed to achieve liquidity and solvency with a limited set of assumptions in a continuous overlapping generations model that increases traceability of the results. The adequacy and actuarial fairness are also jointly studied in the numerical example for the population of Belgium. We find that the proposed indexation and notional rate act as automatic balancing mechanisms that ensure sustainability and actuarial fairness. However, the effect on pension adequacy depends on the generosity of the annuity scheme at retirement. 相似文献
993.
Ijaz-ur-Rahman 《Il Nuovo Cimento D》1988,10(10):1135-1141
Summary Analytical expressions for the electrical conductivity and thermoelectric power are calculated for thin metal films containing
ionized impurities that affect the value and the energy dependence of the electron relaxation time. The electrical conductivity
decreases, whereas the thermoelectric power increases on addition of such impurities. For pure lattice scattering there is
no size effect in the thermoelectric power.
To speed up publication, the author of this paper has agreed to not receive the proofs for correction. 相似文献
994.
R. Zeyher A. Greco 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):473-485
The feasibility of a perturbation expansion for Green's functions of the t-J model directly in terms of X-operators is demonstrated using the Baym-Kadanoff functional method. As an application we derive explicit expressions for
the kernel of the linearized equation for the superconducting order parameter in leading order of a 1/N expansion. The linearized equation is solved numerically on a square lattice taking instantaneous and retarded contributions
into account. Classifying the order parameter according to irreducible representations of the point group C4v of the square lattice and according to even or odd parity in frequency we find that a reasonably strong instability occurs
only for even frequency pairing with d-wavelike symmetry. The corresponding transition temperature Tc is where t is the nearest-neighbor hopping integral. The underlying effective interaction consists of an attractive, instantaneous term
and a retarded term due to charge and spin fluctuations. The latter is weakly attractive at low frequencies below ,strongly repulsive up to and attractive towards even higher energies. Tc increases with decreasing doping until a d-wavelike bond-order wave instability is encountered near optimal doping at for J=0.3. Tc is essentially linear in J and rather insensitive to an additional second-nearest neighbor hopping integral t'. A rather striking property of Tc is that it is hardly affected by the soft mode associated with the bond-order wave instability or by the Van Hove singularity
in the case with second-nearest neighbor hopping. This unique feature reflects the fact that the solution of the gap equation
involves momenta far away from the Fermi surface (due to the instantaneous term) and many frequencies (due to the retarded
term) so that singular properties in momentum or frequency are averaged out very effectively.
Received: 16 June 1998 / Accepted: 14 July 1998 相似文献
995.
R. Bonin C. Serpico G. Bertotti I. D. Mayergoyz M. d'Aquino 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):435-445
An analytical approach is presented for the study of
magnetization dynamics driven by spin-polarized currents. Two cases
are considered: (i) magnetic layers with in-plane uniaxial
anisotropy; (ii) magnetic layers with uniaxial anisotropy and
applied field perpendicular to the layer plane. Theoretical
predictions are obtained for the existence of stationary modes and
self-oscillations of magnetization by solving the deterministic
Landau-Lifshitz-Gilbert equation with Slonczewski spin-torque term.
Thermal fluctuations are studied by deriving the corresponding
Fokker-Planck equation for the magnetization probability
distribution. Analytical procedures to estimate the effective
potential barrier separating self-oscillatory regimes and/or
stationary modes are proposed. 相似文献
996.
论述铅中毒的生化基础 总被引:6,自引:1,他引:5
张景泰 《广东微量元素科学》1998,5(4):11-12
铅中毒的生化机理是铅与细胞,细胞器官,以及蛋白质的巯基结合,影响其生物功能。受铅干扰最大的代谢环节是抑制血色素及细胞合成。 相似文献
997.
G. Michałek B. R. Bułka 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):411-419
Conductance and other physical quantities are calculated in double quantum dots (DQD) connected in series in the limit of
coherent tunnelling using a Green's function technique. The inter-dot Coulomb repulsion and the exchange interaction are studied
by means of the Kotliar and Ruckenstein slave-boson mean-field approach. The crossover from the atomic to the molecular limit
is analyzed in order to show how the conductance in the model depends on the competition between the level broadening (dot-lead
coupling) and the dot-dot transmission. The double Kondo effect
was found in the gate voltage characteristics of the conductance in the atomic limit. In the case, when each dot accommodates
one electron, the Kondo resonant states are formed between dots and their adjacent leads and transport is dominated by hopping
between these two resonances. In the molecular limit the conductance vanishes for sufficiently low gate voltages, which means
the Kondo effect disappeared. For small dot-lead coupling the transport characteristics are very sensitive on the influence
of the inter-dot Coulomb repulsion and the position of the local energy level. The
resonance region is widened with increase of the inter-dot Coulomb interactions while the exchange interaction has opposite
influence. 相似文献
998.
999.
1000.
《Electroanalysis》2005,17(11):979-984
This paper presents the identification by GC/MS of the products obtained after the total reduction of picloram and clopyralid on a mercury pool electrode. The products found in the strongly acidic media reduction of picloram are 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarboxaldehyde, 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarbinol and 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxylic acid; at pH 3–4 the first compound is substituted by 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxaldehyde. For clopyralid 3,6‐dichloro‐2‐pyridinecarbinol was detected. Under the light of such products the overall reduction processes are discussed showing the partial reductive cleavage of chlorine atoms in both cases. 相似文献