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991.
The function of an expander is to obstruct the noise signal transmitted by the pulser so that it does not pass into the transducer or receive electronics, where it can produce undesirable ring-down in an ultrasound imaging application. The most common type is a diode-based expander, which is essentially a simple diode-pair, is widely used in pulse-echo measurements and imaging applications because of its simple architecture. However, diode-based expanders may degrade the performance of ultrasonic transducers and electronic components on the receiving and transmitting sides of the ultrasound systems, respectively. Since they are non-linear devices, they cause excessive signal attenuation and noise at higher frequencies and voltages. In this paper, a new type of expander that utilizes power MOSFET components, which we call a power MOSFET-based expander, is introduced and evaluated for use in high frequency ultrasound imaging systems. The performance of a power MOSFET-based expander was evaluated relative to a diode-based expander by comparing the noise figure (NF), insertion loss (IL), total harmonic distortion (THD), response time (RT), electrical impedance (EI) and dynamic power consumption (DPC). The results showed that the power MOSFET-based expander provided better NF (0.76 dB), IL (−0.3 dB) and THD (−62.9 dB), and faster RT (82 ns) than did the diode-based expander (NF (2.6 dB), IL (−1.4 dB), THD (−56.0 dB) and RT (119 ns)) at 70 MHz. The −6 dB bandwidth and the peak-to-peak voltage of the echo signal received by the transducer using the power MOSFET-based expander improved by 17.4% and 240% compared to the diode-based expander, respectively. The new power MOSFET-based expander was shown to yield lower NF, IL and THD, faster RT and lower ring down than the diode-based expander at the expense of higher dynamic power consumption. 相似文献
992.
A novel linear ultrasonic motor based on in-plane longitudinal and bending mode vibration is presented in this paper. The stator of the motor is composed of a metal plate and eight piezoelectric ceramic patches. There are four long holes in the plate, designed for consideration of the longitudinal and bending mode coupling. The corresponding model is developed to optimize the mechanical and electrical coupling of the stator, which causes an ellipse motion at the contact tip of the stator when the composite vibrations with longitudinal and bending are excited. Its harmonic and transient responses are simulated and inspected. A prototype based on the model is fabricated and used to conduct experiments. Results show that the amplitude of the stator’s contact tips is significantly increased, which helps to amplify the driving force and speed of the motor. It is therefore feasible to implement effective linear movement using the developed prototype. 相似文献
993.
A process variability control chart 总被引:1,自引:0,他引:1
In this study a Shewhart type control chart namely the V
t
chart, is proposed for improved monitoring of the process variability of a quality characteristic of interest Y. The proposed control chart is based on the ratio type estimator of the variance using a single auxiliary variable X. It is assumed that (Y, X) follows a bivariate normal distribution. The design structure of the V
t
chart is developed for Phase-I quality control and its comparison is made with those of the S
2 chart (a well-known Shewhart control chart) and the V
r
chart (a Shewhart type control chart proposed by Riaz (Comput Stat, 2008a) used for the same purpose. It is observed that
the proposed V
t
chart outperforms the S
2 and V
r
charts, in terms of discriminatory power, for detecting moderate to large shifts in the process variability. It is observed
that the performance of the V
t
chart keeps improving with an increase in |ρ
yx
| , where ρ
yx
is the correlation between Y and X. 相似文献
994.
幂格与商格的关系的注记 总被引:3,自引:3,他引:0
研究了分配格上的幂格,给出了格的相对凸子格的概念,得到了分配格上的幂格的一个充要条件,建立了幂格与商格的联系. 相似文献
995.
Higher order multi-point methods are advantageous to solve scalar nonlinear equations because of their speed of convergence.
The approximate solution is usually obtained in a few steps, thus saving time and computational effort. In this work, we study
the Power Spectrum of the Fourier Transforms of the errors of a well-known family of multi-step Newton method. Firstly, by
two numerical examples we observe that as the order p of the methods increases, the Power Spectrum of Low Frequency modes of successive approximations decreases and the Power
Spectrum of the High Frequency modes increases until they become almost equal when p become large. We prove this point analytically by showing that the Power spectrum of the Fourier Transforms of the errors
of the methods from the error equation is independent of the frequency and the Amplitude of the Power Spectrum tends to zero
as p tends to infinity. From there, we attempt to find the best method of this family. We also compare the family with two other
families of higher order multistep methods, in terms of order, efficiency index and Amplitude of Power Spectrum. Finally,
we conduct more numerical experiments to find the best method of the 3 families.
The work of the first author is partly supported by Tertiary Education Commission and University of Mauritius. 相似文献
996.
In this paper, we consider power control for the uplink of a direct-sequence code-division multiple-access data network. In
the uplink, the purpose of power control is for each user to transmit enough power so that it can achieve the required quality
of service without causing unnecessary interference to other users in the system. One method that has been very successful
in solving this purpose for power control is the game-theoretic approach. The problem for power control is modified as a Nash
equilibrium problem in which each user can choose its transmit power in order to maximize its own utility, and a Nash equilibrium
is an ideal solution of the power-control game. We present a noncooperative power-control game in which each user can choose
the transmit power in a way that it gets the sufficient signal-to-interference-plus-noise ratio and maximizes its own utility.
To ensure the existence of a solution, we also propose the variational inequality problem which is connected with the proposed
game. On a linear receiver, we deal with the matched filter receiver. Next we present a new ergodic algorithm for the proposed
power control because the existing iterative algorithms can not be applied effectively to the proposed power control. We also
present convergence analysis for the proposed algorithm. In addition, applying the proposed algorithm to the proposed power
control, we provide numerical examples for the transmit power, the signal-to-interference-plus-noise ratio and so on. Numerical
results for the proposed algorithm shall show that as compared with the existing power-control game and its method, all users
in the network can enjoy the sufficient signal-to-interference-plus-noise ratio and achieve the required quality of service.
相似文献
997.
In this paper, discrete Fourier transform (DFT) and continuous wavelet transform (CWT) are used to predict the protein structure.
Hydrophobicity plays a key role in the form of protein structure. The amino acid sequence is first mapped into hydrophobicity
sequence, and then process it by DFT and CWT so that power spectral density is gained. The results show that continuous wavelet
transform can extract the features of protein structure effectively and availably and has a tremendous development foreground. 相似文献
998.
999.
The Hermite rank appears in limit theorems involving long memory. We show that a Hermite rank higher than one is unstable when the data is slightly perturbed by transformations such as shift and scaling. We carry out a “near higher order rank analysis” to illustrate how the limit theorems are affected by a shift perturbation that is decreasing in size. We also consider the case where the deterministic shift is replaced by centering with respect to the sample mean. The paper is a companion of Bai and Taqqu (2017) which discusses the instability of the Hermite rank in the statistical context. 相似文献
1000.
The Banzhaf power index was introduced in cooperative game theory to measure the real power of players in a game. The Banzhaf interaction index was then proposed to measure the interaction degree inside coalitions of players. It was shown that the power and interaction indexes can be obtained as solutions of a standard least squares approximation problem for pseudo-Boolean functions. Considering certain weighted versions of this approximation problem, we define a class of weighted interaction indexes that generalize the Banzhaf interaction index. We show that these indexes define a subclass of the family of probabilistic interaction indexes and study their most important properties. Finally, we give an interpretation of the Banzhaf and Shapley interaction indexes as centers of mass of this subclass of interaction indexes. 相似文献