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991.
We have developed a fetal movement monitoring system based on small displacement measurement of internal tissues. When ultrasonic pulses are transmitted to the fetus, the reflected ultrasonic waves which have a Doppler frequency shift due to the fetal movements are detected by using an ultrasonic pulsed Doppler technique. In this paper, we propose a displacement measurement method for internal tissues which is based on the Doppler signal digital detection technique. In the method, the received ultrasonic RF signals are sampled with a sampling frequency of four times higher than the centre frequency of the ultrasonic waves; the Doppler frequency shift signals are derived using digital signal processing. From the detected signals, the internal displacements are estimated using the arc-tangent method. The basic algorithm of the detection method has already been used in the area of blood flow sensing, however, we apply the algorithm to the displacement measurement of internal tissues. The comparison between the proposed method and the conventional method is presented. The fetal movement quantitative monitoring system based on the method which has been constructed is shown. 相似文献
992.
本文给出了具有功能性反应函数为 x的捕食系统x=γx-δ x y-αx2 ,y=-sy+β x y-εy2的全局相图 .得到了两种群持续共存和捕食者种群必将灭绝的条件 .讨论了此系统唯一正平衡点的 Hopf分支 ,并证明了该点可以成为二阶不稳定细焦点 ,从而得到该系统有出现至少三个极限环的可能 . 相似文献
993.
994.
Francesca Biagini Yaozhong Hu Bernt
ksendal Agns Sulem 《Stochastic Processes and their Applications》2002,100(1-2):233-253
We prove a stochastic maximum principle for controlled processes X(t)=X(u)(t) of the formwhere B(H)(t) is m-dimensional fractional Brownian motion with Hurst parameter
. As an application we solve a problem about minimal variance hedging in an incomplete market driven by fractional Brownian motion. 相似文献
dX(t)=b(t,X(t),u(t)) dt+σ(t,X(t),u(t)) dB(H)(t),
995.
RESTRICTED FLOWS OF A HIERARCHYOF INTEGRABLE DISCRETE SYSTEMS 总被引:1,自引:0,他引:1
曾云波 《应用数学学报(英文版)》1998,14(2):176-184
1.IntroductionTherestrictedflowsofsolitonhierarchyhavebeenextensivelystudied(see,forexample,[1--7]).Theapproachforconstructingrestrictedflowsofsolitonhierarchycanalsobeappliedtoobtainrestrictedflows(discretemaps)ofahierarchyofdiscreteintegrablesystems(nonlineardifferential-differenceequations)IS,9].TheserestrictedflowshavetheformofLagrangeequationsandthereforecanmodelphysicallyinterestingprocesses.Wesupposethatthehierarchyofdiscreteintegrablesystems(DIS)isassociatedwithadiscreteisospectralp… 相似文献
996.
Zhiyi P. Zhang 《Fiber and Integrated Optics》2003,22(6):357-371
Computer simulation was used to understand the adhesive-based coupling of optical fibers to planar waveguides with a view to adhesive development. Satisfactory coupling performance could be achieved with facet-angled fibers and waveguides, regardless of the adhesive's index and optical loss. A high-temperature epoxy adhesive was developed for coupling applications based on the simulation. The adhesive is able to achieve a material-related loss of -0.05 dB and a back-reflection loss of less than -50 dB in the coupling. In addition, the adhesive has excellent mechanical and thermal properties and can easily meet the Telcordia standard GR1221 while withstanding high temperatures and high optical power. 相似文献
997.
本文用几何光学基本定律对两种不同外形发光管的光学性能作了一般性的分析和探讨。通过具体的计算,从等效发光点、可被利用光能、聚光性能和使用场合等方面对它们进行了比较,用以指导光路设计,并提出了改进建议 相似文献
998.
Anatoliy Malyarenko 《Journal of Theoretical Probability》2008,21(2):459-475
We derive a series expansion for the multiparameter fractional Brownian motion. The derived expansion is proven to be rate
optimal.
This work is supported in part by the Foundation for Knowledge and Competence Development and Sparbanksstiftelsen Nya. 相似文献
999.
在证券的价格过程是几何布朗运动的前提下,建立了最优投资组合的多目标规划模型,使得投资收益最大和投资风险最小,并利用线性加权和法求得有效解.最后用实例进行分析. 相似文献
1000.
Let B denote a separable Banach space with norm ‖⋅‖, and let μ be a probability measure on B for which linear functionals have mean zero and finite variance. Then there is a Hilbert space H
μ
determined by the covariance of μ such that H
μ
⊆B. Furthermore, for all ε>0 and x in the B-norm closure of H
μ
, there is a unique point, T
ε
(x), with minimum H
μ
-norm in the B-norm ball of radius ε>0 and center x. If X is a random variable in B with law μ, then in a variety of settings we obtain the central limit theorem (CLT) for T
ε
(X) and certain modifications of such a quantity, even when X itself fails the CLT. The motivation for the use of the mapping T
ε
(⋅) comes from the large deviation rates for the Gaussian measure γ determined by the covariance of X whenever γ exists. However, this is only motivation, and our results apply even when this Gaussian law fails to exist.
Research partially supported by NSA Grant H98230-06-1-0053. 相似文献