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971.
In this paper we apply the reciprocal theorem[1] to further research on the bending problem of the cantilever rectangular plate under a concentrated load acting at any of its points. This method is even simpler and more general. 相似文献
972.
在超晶格样品(GaAs)4/(AlAs)2的一级共振拉曼光谱的界面模的观察中,四个界面模在XX和XY两种偏振态中均能被观察到,这与传统的选择定则相矛盾。这是因为传统的理论假设电子波函数是完全限制在势阱当中,而在超薄系统中例如在GaAs势阱中的电子波函数会穿透到AlAs势垒中,从而得到新的结果。这表明传统的理论在被应用到超薄系统或超小系统时需要进行一定的修正。 相似文献
973.
H.-K. Zhao J. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):513-524
The time-dependent transport through an ultrasmall quantum dot coupling to two electron reservoirs is investigated. The quantum
dot is perturbed by a quantum microwave field (QMF) through gate. The tunneling current formulae are obtained by taking expectation
values over coherent state (CS), and SU(1,1) CS. We derive the transport formulae at low temperature by employing the nonequilibrium
Green function technique. The currents exhibit coherent behaviors which are strongly associated with the applied QMF. The
time-dependent currents appear compound effects of resonant tunneling and time-oscillating evolution. The time-averaged current
and differential conductance are calculated, which manifest photon-assisted behaviors. Numerical calculations reveal the similar
properties as those in classical microwave field (CMF) perturbed system for the situations concerning CS and squeezed vacuum
SU(1,1) CS. But for other squeezed SU(1,1) CS, the tunneling behavior is quite different from the system perturbed by a single
CMF through gate. Due to the quantum signal perturbation, the measurable quantities fluctuate fiercely.
Received 28 May 1998 相似文献
974.
F.N. Braun H. Yokoyama 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):377-379
Capillary waves and director fluctuations reduce the surface tension of a non-anchoring unbound nematic surface by comparable
amounts. These are relatively small effects in three dimensions, but in two dimensions they become more significant. We examine
the conditions in two dimensions under which they dominate explicitly within the framework of a model of the Maier-Saupe type.
We find that for reasonable physical parameters of the model the onset of the fluctuation dominated regime generally preempts
the nematic-isotropic transition. We conclude that processes which are sensitive to line tension, such as Ostwald ripening
during two-dimensional liquid-gas phase separation, are much more strongly coupled to anisotropic molecular interactions and
associated nematic ordering than in three dimensions.
Received 10 February 1999 and Received in final form 29 March 1999 相似文献
975.
C. Blanc M. Kléman 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):53-60
In the quasi-ternary CPCl/brine/hexanol lyotropic system, the interface of the lamellar and L3 sponge phases displays a phenomenon of epitaxy: the layers of the lamellar phase tend to make a constant non-trivial angle
with the interface. Thin samples of lamellar phase embedded in the sponge phase are thus submitted to oblique anchoring conditions
and defects are created in the lamellar phase in order to satisfy the bulk lamellar ordering and the boundary conditions.
We have studied small droplets of lamellar phase in the sponge phase. They do not exhibit the classic defects (focal conic domains) but wall defects, which appear in order to satisfy the smectic elasticity and the boundary
conditions. Moreover we show through experiments in controlled geometry that, even in the presence of focal conic domains,
wall defects control the size and periodicity of the textures which are observed at the interface.
Received 4 November 1998 相似文献
976.
Interfacial rheological properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The
interfacial viscosity, the non-Newtonian flow behavior and the activation energy of viscous flow were determined as a function
of shear rate, alkali concentration and aging time. The fundamental conclusion of the experimental results is that the interfacial
viscosity drastically decreases in the presence of alkaline materials and the change under favorable conditions may exceed
3 or 4 orders of magnitude. Simultaneously, the sodium hydroxide effectively suppresses the non-Newtonian flow behavior of
the interfacial layer. The experimental observations are explained by simultaneous chemical processes taking place in the
boundary layer. The present data may help to elucidate the formation, stability and breaking of alkali-containing oil-water
emulsions and they provide additional information for better understanding of the displacement mechanism and for the formulation
of alkaline flooding as a potential chemically enhanced oil-recovery method.
Received: 6 April 1998 Accepted: 18 August 1998 相似文献
977.
J Snchez-Gonzlez M.A Cabrerizo-Vlchez M.J Glvez-Ruiz 《Colloids and surfaces. B, Biointerfaces》1999,12(3-6):123-138
The interactions between lipids (cholesterol, distearoylphosphatidylcholine, distearoylphosphatidylethanolamine and sphingomyelin) and the γ-globulin protein have been analyzed using the monolayer technique at the air–liquid interface. The analysis has been carried out using both state equations and an adequate thermodynamic formulation for the surface pressure (π)–molecular area (a) isotherms. Different parameters as the virial coefficients, have been estimated. For the uncharged lipid monolayers, the interactions between the molecules are of an attractive nature, at medium and long distance, and of a steric repulsive nature at short distance. At low surface pressures the lipid molecules form small domains. The net force between γ-Globulin molecules in the monolayers has been found to be attractive. Finally, it can be concluded that when the lipid monolayers are uncharged, there is practically no interaction between the protein and lipid molecules at the mentioned interface. 相似文献
978.
Ma Rosario Rodrguez Nio Cecilio Carrera Snchez Juan M.Rodrguez Patino 《Colloids and surfaces. B, Biointerfaces》1999,12(3-6):161-173
Casein is well known to be a good protein emulsifier and β-casein is the major component of casein and commercial sodium caseinate. This work studies the behaviour of β-casein at the interface. The interfacial characteristics (structure and stability) of β-casein spread films have been examined at the air–water interface in a Langmuir-type film balance, as a function of temperature (5–40°C) and aqueous phase pH (pH 5 and 7). From surface pressure–area isotherms (π–A isotherms) as a function of temperature we can draw a phase diagram. β-Casein spread films present two structures and the collapse phase. That is, there is a critical surface pressure and a surface concentration at which the film properties change significantly. This transition depends on the temperature and the aqueous phase pH. The film structure was observed to be more condensed and β-casein interfacial density was higher at pH 5. β-Casein films were stable at surface pressures lower than equilibrium surface pressure. In fact, no hysteresis was observed in π–A isotherms after continuous compression-expansion cycles or over time. The relative area relaxation at constant surface pressure (10 or 20 mN m−1) and the surface pressure relaxation at constant area near the monolayer collapse, can be fitted by two exponential equations. The characteristic relaxation times in β-casein films can be associated with conformation–organization changes, hydrophilic group hydration and/or surface rheology, as a function of pH. 相似文献
979.
Degradation of the residual strength of a glass-fiber-reinforced polyester composite of a lay-up typical of the wind rotor
blade material is studied at low-cycle fatigue. A gradual reduction of the residual strength is observed as expected for GRP,
accompanied by an increasing scatter of strength. The residual strength model based on the strength-life equal rank assumption
yields an accurate approximation of experimental data. The strength reduction at a stress level corresponding to high-cycle
fatigue (N>10
6 cycles) appears to correlate well with the test results at higher stress levels, which indicates that the strength degradation
at the design stress level can be evaluated using low-cycle tests. Assuming that the parameters of the strength degradation
model do not depend on the applied stress level, the residual strength data obtained in low stress level tests of comparatively
short duration can be used to estimate the average fatigue life at the same stress thus reducing the total test time.
Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 5, pp. 595–604, September–October, 1999. 相似文献
980.
复合材料的力学性能参数比金属材料呈现出更大的分散性。本文提出采用加权线性响应面法对复合材料单钉连接结构进行可靠性分析。采用三维有限元模型进行复合材料单钉连接的确定性渐进失效分析。单向铺层的力学性能参数和强度参数均考虑为输入随机变量,用于可靠性分析。详细研究了不同失效准则和不同刚度退化方法的影响。结果表明,Olmedo-Santiuste失效准则与Camanho-Matthews刚度退化方法的组合能够给出与试验均值最接近的强度分析结果。另外,还仔细研究了响应面参数f的影响。结果表明,取f=1的线性加权响应面能够为复合材料单钉连接可靠性分析提供较好的统计特性逼近值。 相似文献