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101.
Mohamed K. Watfa Samir Selman Hovig Denkilkian 《International Journal of Communication Systems》2010,23(4):485-506
As over 70% of the earth's surface is covered by water, it is desirable to deploy underwater sensor networks (UWSNs) to support oceanic research. UWSNs use acoustic waves and are characterized by long and variable propagation delays, intermittent connectivity, limited bandwidth and low bit rates. Energy savings have always been the primary concern in wireless sensor network protocols; however, there are applications where the latency and throughput are prioritized over energy efficiency and are so significant that the application would not be able to satisfy its requirements without them. Although existing duty‐cycle MAC protocols are power efficient, they introduce significant end‐to‐end delivery latency, provide poor throughput and are not suitable for the challenging environment of a UWSN. In this paper, we utilize CDMA as the underlying multiple access technique, due to its resilience to multi‐path and Doppler's effects prevalent in underwater environments. We propose UW‐MAC, a CDMA‐based power‐controlled medium access protocol that uses both transmitter‐based and receiver‐based CDMA inside a formed cluster, and uses a TDMA schedule to make the cluster heads communicate with the base station. Our MAC algorithm targets the latency and throughput needs in addition to its ability to increase the overall network lifetime. We discuss the design of UW‐MAC, and provide a head‐to‐head comparison with other protocols through extensive simulations focusing on the performance in terms of latency, throughput, and energy consumption. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
102.
一种水下主动探测系统的模拟预处理机设计 总被引:2,自引:1,他引:1
模拟预处理机是水下主动探测系统的关键部件。针对水下主动探测系统的应用,设计了一种模拟预处理机.该电路采用分级放大结构,并使用两级滤波器对信号进行滤波处理,在达到对信号放大倍数要求的同时避免了放大器自激.采用噪声性能好的AD867X系列芯片有效抑制了电路噪声对信号的影响。分析了该模拟预处理机的工作原理,给出了电路结构图,选择了芯片,调试检测结果表明,电路工作正常,性能指标达到要求。 相似文献
103.
一种激光扫描水下成像系统的衰减长度值研究 总被引:1,自引:1,他引:0
简述了水下目标激光成像方法和优点。并描述了一种水下连续蓝绿激光点扫描,微光增强CCD面成像实验系统。分析了该系统的物理模型和计算公式。验证:处于对比度极限模式工作时。在水质及目标确定条件下,该值也许可成为判断系统优劣的依据。 相似文献
104.
The one-dimensional ballistic aggregation process is considered when the initial mass density or the initial particle velocities vanish outside of a finite or semi-infinite interval. In all cases, we compute the mass distributions in closed analytical form and study their long time asymptotics. The relevant length scales are found different (of the order t, t
2/3, t
1/2) if, at the initial time, particles occupy a finite (or semi-infinite) interval and if a finite (or infinite) number of them are set into motion. 相似文献
105.
Curing kinetics of anisotropic conductive adhesive film 总被引:1,自引:0,他引:1
Polymer-based conductive-adhesive materials have become widely used in many electronic packaging interconnect applications,
such as chip-on-glass, chip-on-flex, etc. Among all the conductive-adhesive materials, anisotropic conductive adhesive film
(ACF) is an attractive interconnect material because of its fine pitch capability. Anisotropic conductive-adhesive film is
a thermosetting, epoxy matrix impregnated with a small amount of electrically conductive particles. During component assembly,
the epoxy resin is cured to provide mechanical connection, and the conducting medium provides electrical connection in the
z direction. The thermal cure process is critical to develop the ultimate electrical and mechanical properties of the ACF.
In this paper, the curing reaction of ACF was studied with a differential scanning calorimeter (DSC) under isothermal conditions
in the range of 120–180°C. An autocatalyzed kinetic model was used to describe the curing reaction. The rate constant and
the reaction orders were determined and used to predict the progress of the curing reaction. A good agreement is found between
the proposed kinetic model and the experimental reaction-rate data. The reaction-rate constants were correlated with the isothermal
temperature by the Arrhenius equation. The glass-transition temperature also has been studied as a function of cure degree
and moisture absorption. 相似文献
106.
107.
V. I. Boyarintsev A. K. Lednev A. S. Prudnikov A. S. Savin E.O. Savina 《Fluid Dynamics》2004,39(6):972-978
The data of a laboratory experiment to observe the small perturbations of a free surface by a thin hydrofoil profile moving horizontally in water are presented and compared with the calculation results obtained for a hydrofoil modeled by a system of distributed sources and sinks within the framework of the small-wave approximation.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 145–152.Original Russian Text Copyright – 2004 by Boyarintsev, Lednev, Prudnikov, Savin, and Savina. 相似文献
108.
对角切片谱法分析信号中相位耦合的频率分量 总被引:1,自引:0,他引:1
给出了三阶累积量对角切片谱的性质,分析了水中目标辐射信号的特点,并将3阶累积量对角切片谱法应用于提取水下目标辐射信号中相位耦合的频率分量。以水下某目标辐射噪声的实测数据为例,进行了仿真研究。结果表明,该方法在提取水下运动目标辐射信号中的参加相位耦合的频率分量和相位耦合产生的频率分量、抑制环境噪声和非耦合的频率分量等方面的性能优于自相关谱法。 相似文献
109.
There has been a steadily increasing interest in using electrically conductive adhesives as interconnecting materials in electronics
manufacturing. In this paper, several anisotropic conductive adhesive (ACA) pastes were formulated, which consist of diglycidyl
ether of bisphenol F or diglycidyl ether of bisphenol A as polymer matrix, imidazoles as curing agents, and different sizes
of silver (Ag) powders or gold (Au)-coated polymer spheres as conductive particles. The effects of ACA resin and different
curing agents, as well as different conductive particles, on flexible substrate of the flip-chip joint were studied. The results
show that the size and type of different conductive particles have very limited influence on an ACA flip-chip joint. The ACA
resin as well as the curing agent can affect the reliability of the joint. The same results can be applied for the failure
analysis of ACA flip-chip technology. 相似文献
110.
Anisotropic conductive adhesive film (ACF) can be preheated by microwave (MW) radiation in order to reduce the bonding time
for flip-chip technology. Due to sluggish and nonuniform curing kinetics at the beginning of the curing reaction, thermal
curing of epoxy is more time consuming. Therefore, MW radiation may be more effective, due to its uniform heating rate during
the cycle. In this paper, MW preheating (for 1–4 sec) of ACF prior to final bonding has been applied to determine the electrical
and mechanical performance of the bond. Powers of 80 and 240 W MW were used to study the effect of the MW preheating. A final
bonding time of 6–7 sec can be used for flip chip on flex bonding instead of 10–15 sec (standard time for flip chip bonding)
for MW preheating time and power used in this study. The contact resistance (as low as 0.01) is low in these samples, whereas
the standard resistance is 0.017 ohm (bonded at 180°C for 10 sec without prior MW preheating). The shear forces at breakage
were satisfactory (0.167–0.183 KN) for the samples bonded for 6–7 sec with MW preheating. This is very close and even higher
than the standard sample (0.173 KN). For MW preheating power of 80 W and sweeping time of 2 sec, final bonding at 6 sec can
also be used because of its low contact resistance (0.019 ohm). Scanning electron microscope (SEM) investigation of microjoints
and fracture surface shows uneven distribution of conductive particles and thick bond lines in samples bonded for 5 sec (with
MW preheating). Samples treated with MW radiation (80 W and 2–3 sec time) serve as evidence that well-distributed particles
along with thin bond lines cause low contact resistance and high joint strength. 相似文献