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951.
用于近红外光谱仪的平场全息凹面光栅的模拟与设计 总被引:3,自引:0,他引:3
针对近红外光谱分析属于微弱信号与多元信息处理的特点,基于全息凹面光栅理论,采用光学设计软件CODE V,从初始结构出发,利用软件强大的全局优化功能,设计出一种用于近红外光谱仪的平场全息凹面光栅,成功地减小了像 差,解决了宽光谱、窄谱面展宽的矛盾,并充分利用了光谱信息,是一种高效率的分光光学系统结构。利用CODE V软件,不需要求解复杂的高级像差方程,能对结果进行迅速评价,并可在设计中同时兼顾平场和提高分辨率的要求,极大地 提高了工作效率。最后,给出了实例,设计出的全息凹面光栅工作波长范围为900~1700 nm、直径ф=25 mm、F/#=1.5,对设计结果分析表明:在宽度为50 μm缝光源再现情况下,理论分辨率优于6.3 nm。 相似文献
952.
953.
介绍了HL-2A 上基于脉冲步进阶梯调制(PSM)技术的高压电源控制系统的研究。控制系统以数字信号处理+现场可编程门阵列(DSP+FPGA)为架构,控制112 个每秒采样(SPS)模块,按照一定的控制方式使电源输出稳定的电压。DSP 负责数据传输、通讯、控制算法等;FPGA 利用其强大的逻辑功能输出所需的脉冲。通过对程序的编写、仿真和调试,实验结果表明该控制系统的特性达到了设计要求。 相似文献
954.
A data set over space and time is assumed to have a low-rank representation in separated spatial and temporal modes. The problem of evaluating these modes from a temporal series of partial measurements is considered. Each elementary instantaneous measurement captures only a “window” (in space) of the observed data set, but the position of this window varies in time so as to cover the entire region of interest and would allow for a complete measurement would the scene be static. A novel procedure, alternative to the Gappy Proper Orthogonal Decomposition (GPOD) methodology, is introduced. It is a fixed-point iterative procedure where modes are evaluated sequentially. Tested upon very sparse acquisition (1% of measurements being available) and very noisy synthetic data sets (10% noise), the proposed algorithm is shown to outperform two variants of the GPOD algorithm, with much faster convergence, and better reconstruction of the entire data set. 相似文献
955.
956.
《Electrophoresis》2018,39(4):608-615
A sensitive method using CZE‐UV detection has been developed for the determination of five tetracycline antibiotics in human urine samples. To improve the sensitivity of the method, an on‐line preconcentration strategy, named field‐amplified sample injection, has been developed, based on the electrokinetic injection of the sample, which requires only a 1:100 dilution with sample solvent before injection. Under optimum conditions, sensitivity enhancement factors ranged from 450 to 800 for the studied compounds. The applicability of the proposed method was demonstrated by the determination of these antibiotics in spiked urine samples. The limits of quantification were lower than 0.8 mg/L and the precision (intra‐ and inter‐day), expressed as %RSD was below 14%. Recoveries ranged from 92.1 to 96.7%. Thus, the proposed procedure is a simple, fast and efficient strategy which could be used as therapeutic drug monitoring in human urine samples. 相似文献
957.
Summary The dynamic behaviour of a railway system is influenced by the interaction of its three subsystems: the vehicles, the rail
construction itself and the subsoil. In this paper, the subsoil is considered as a linear-elastic layered half-space. Integral
transformations are used for the analysis of this system: Fourier transformation for the time/frequency domain and for the
space/wavenumber domains with respect to the horizontal coordinates. One arrives at an ordinary differential equation for
the vertical direction, by which different layers or continuously changing elastic properties can be taken into account in
an efficient manner. The efficiency of the transformation technique depends substantially on the effort necessary for the
inverse transformation. A substantial reduction of data can be achieved in an error-controlled procedure if a wavelet transformation
is applied as an additional transformation. The calculations are illustrated by solutions of several examples of moving time-dependent
loads, particularly of a train model with four vehicles idealized by moving forces, time depending as if they were passing
a rigid surface with a given roughness.
Received 23 December 1997; accepted for publication 22 July 1998 相似文献
958.
959.
Annealing temperature influence on the degree of inhomogeneity of the Schottky barrier in Ti/4H–SiC contacts
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Tung's model was used to analyze anomalies observed in Ti/Si C Schottky contacts. The degree of the inhomogeneous Schottky barrier after annealing at different temperatures is characterized by the ‘T0anomaly' and the difference(△Φ)between the uniformly high barrier height(Φ0B) and the effective barrier height(Φeff B). Those two parameters of Ti Schottky contacts on 4H–Si C were deduced from I–V measurements in the temperature range of 298 K–503 K. The increase in Schottky barrier(SB) height(ΦB) and decrease in the ideality factor(n) with an increase measurement temperature indicate the presence of an inhomogeneous SB. The degree of inhomogeneity of the Schottky barrier depends on the annealing temperature, and it is at its lowest for 500-°C thermal treatment. The degree of inhomogeneity of the SB could reveal effects of thermal treatments on Schottky contacts in other aspects. 相似文献
960.
ABSTRACTHere we propose a model to understand the influence of structural inhomogeneity on the shear band behaviours of metallic glasses. By considering the inhomogeneous structure and stress concentration, the model predicts that the strain for shear band nucleation in metallic glasses can be variable and far below the theoretical elastic limit. During sliding, the shear band will approach a dynamic equilibrium state of balanced free volume generation and annihilation. By considering the accumulation of irreversible structure change, the shear band will finally develop into fracture. Under fluctuating load, the shear band shows an ‘activate-arrest’ behaviour, which results from a delayed response to the external load change. These results reasonably explain and correlate the physics behind the elastic limit, stick-slip shear band behaviour, implicit shear events, and shear band fracture in metallic glasses. The study can provide another perspective and platform to understand the correlations between structural inhomogeneity and shear band behaviours in metallic glasses, and further explore other shear band related phenomena not only in metallic glasses but also in the class of shear-softened materials. 相似文献