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181.
M. Thambidurai N. Muthukumarasamy Dhayalan Velauthapillai S. Agilan R. Balasundaraprabhu 《Journal of Electronic Materials》2012,41(4):665-672
In the present work, a systematic study has been carried out to understand the influence of cobalt (Co) doping on various
properties of CdS nanoparticles. CdS and Co-doped CdS quantum dots have been prepared at room temperature using a chemical
precipitation method without using catalysts, capping agents, or surfactants. X-ray diffraction reveals that both undoped
and Co-doped CdS nanoparticles exhibit hexagonal structure without any impurity phase, and the lattice constants of CdS nanoparticles
are observed to decrease slightly with increasing cobalt concentration. High-resolution transmission electron microscopy (HRTEM)
shows that the particle size of CdS and 5.02% Co-doped CdS nanoparticles is in the range of 2 nm to 4 nm. The Raman spectra
of Co-doped CdS nanoparticles exhibit a red-shift compared with that of bulk CdS, which may be attributed to optical phonon
confinement. The optical absorption spectra of Co-doped CdS nanoparticles also exhibit a red-shift with respect to that of
CdS nanoparticles. The electrical conductivity of CdS and Co-doped CdS nanoparticles is found to increase with increasing
temperature and cobalt concentration. 相似文献
182.
Dimitrios J. Vergados Dimitrios D. Vergados Maria Koutsogiannaki 《Wireless Personal Communications》2012,62(3):687-713
Many scheduling techniques have been developed to solve the problem of sharing the common channel to multiple stations. TDMA
has been increasingly used as a scheduling technique in ad-hoc networks. The current trend for QoS capable applications led
to the deployment of numerous routing schemes that use TDMA. These schemes try to solve the problem of distributing the available
slots among the wireless nodes and at the same time, to find paths within the network that fulfill some QoS related limitations,
such as end-to-end delay. The exact way the slots are distributed among the transmitting nodes has an impact on the end-to-end
delay and other performance parameters of the network, such as capacity. Therefore, the efficiency of the scheduling algorithms
is closely related to the network topologies. In this paper, we propose two new end-to-end TDMA scheduling algorithms that
try to enhance the network capacity by increasing the number of concurrent connections established in the network, without
causing additional end-to-end delay. We study the efficiency of the proposed algorithms, when applied on various random topologies,
and compare them in terms of end-to-end delay and network capacity. 相似文献
183.
Kazuyuki Uno Takahisa Jitsuno Tetsuya Akitsu 《Journal of Infrared, Millimeter and Terahertz Waves》2012,33(5):485-490
We have developed a longitudinally excited CO2 laser without a high-voltage switch. The laser produces a short laser pulse similar to those from TEA and Q-switched CO2 lasers. This system, which is the simplest short-pulse CO2 laser yet constructed, includes a pulsed power supply, a high-speed step-up transformer, a storage capacitor, and a laser
tube. At high pressure (4.2 kPa and above), a rapid discharge produces a short laser pulse with a sharp spike pulse. In mixed
gas (CO2: N2: He = 1: 1: 2) at a pressure of 9.0 kPa, the laser pulse contains a spike pulse of 218 ns and has a pulse tail length of
16.7 μs. 相似文献
184.
S. C. Chan Z. Y. Zhu K. T. Ng C. Wang S. Zhang Z. G. Zhang Zhongfu Ye H. Y. Shum 《Journal of Signal Processing Systems》2012,67(3):305-316
Image-based rendering (IBR) is an promising technology for rendering photo-realistic views of scenes from a collection of
densely sampled images or videos. It provides a framework for developing revolutionary virtual reality and immersive viewing
systems. While there has been considerable progress recently in the capturing, storage and transmission of image-based representations,
most multiple camera systems are designed to be stationary and hence their ability to cope with moving objects and dynamic
environment is somewhat limited. This paper studies the design and construction of a movable image-based rendering system
based on a class of dynamic representations called plenoptic videos, its associated video processing algorithms and an application
to multiview audio-visual conferencing. It is constructed by mounting a linear array of 8 video cameras on an electrically
controllable wheel chair and its motion is controllable manually or remotely through wireless LAN by means of additional hardware
circuitry. We also developed a real-time object tracking algorithm and utilize the motion information computed to adjust continuously
the azimuth or rotation angle of the movable IBR system in order to cope with a given moving object in a large environment.
Due to imperfection in tracking and mechanical vibration encountered in movable systems, the videos may appear very shaky
and a new video stabilization technique is proposed to overcome this problem. The usefulness of the system is illustrated
by means of a multiview conferencing application using a multiview TV display. Through this pilot study, we hope to disseminate
useful experience for the design and construction of movable IBR systems with improved viewing freedom and ability to cope
with moving object in a large environment. 相似文献
185.
Multicast is a scalable solution for group communications. In order to offer security for multicast applications, a group
key has to be changed whenever a member joins or leaves the group. This incurs 1-affects-n problem, which is a constraint on scalability. Decentralized approaches solve the scalability problem by dividing a group
into several subgroups that use independent group keys. These approaches, however, introduce new challenges: problem of trusting
third party and inefficiency of data delivery. Proxy encryption is a good approach to solve the problem of trusting third
party. In this paper, we propose a novel secure multicast scheme using the proxy cryptography. The proposed scheme provides
not only scalability but also data transmission efficiency by dynamic subgrouping of group members while intermediate data-relaying
third parties are not required to be trusted. 相似文献
186.
Fritz Keilmann Sergiu Amarie 《Journal of Infrared, Millimeter and Terahertz Waves》2012,33(5):479-484
We describe a coherent mid-infrared continuum source with 700 cm-1 usable bandwidth, readily tuned within 600–2500 cm-1 (4–17 μm) and thus covering much of the infrared "fingerprint" molecular vibration region. It is based on nonlinear frequency
conversion in GaSe using a compact commercial 100-fs-pulsed Er fiber laser system providing two amplified near-infrared beams,
one of them broadened by a nonlinear optical fiber. The resulting collimated mid-infrared continuum beam of 1 mW quasi-cw
power represents a coherent infrared frequency comb with zero carrier-envelope phase, containing about 500,000 modes that
are exact multiples of the pulse repetition rate of 40 MHz. The beam's diffraction-limited performance enables long-distance
spectroscopic probing as well as maximal focusability for classical and ultraresolving near-field microscopies. Applications
are foreseen also in studies of transient chemical phenomena even at ultrafast pump-probe scale, and in high-resolution gas
spectroscopy for e.g. breath analysis. 相似文献
187.
In this paper, we present a CAD technique to design low-power and low phase noise integrated frequency synthesizers. This
technique introduces a key parameter, Phase Noise per Unit Power, which correlates phase noise and power among all the sub-circuits
in the frequency synthesizer. By correlating the performance of all the independent circuits together, sophisticated synthesizer
design and optimization can be significantly simplified. We demonstrate a 1.8 GHz frequency synthesizer design in a 0.18 μm
CMOS process achieving −132 dBc/Hz phase noise at 100 kHz offset with less than 4.3 mW power consumption. 相似文献
188.
The increased usage of directional methods of communications has prompted research into leveraging directionality in every layer of the network stack. In this paper, we explore the use of directionality in layer 3 to facilitate routing in highly mobile environments. We introduce Mobile Orthogonal Rendezvous Routing Protocol (MORRP) for mobile ad-hoc networks (MANETs). MORRP is a lightweight, but scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space embedding, node localization, and mobility. This relaxation is done by introducing a novel concept called the directional routing table (DRT) which maps a set-of-IDs to each interface direction to provide probabilistic routing information based on interface direction. We show that MORRP achieves connectivity with high probability even in highly mobile environments while maintaining only probabilistic information about destinations. Additionally, we compare MORRP with various proactive, reactive, and position-based routing protocols using single omni-directional interfaces and multiple directional interfaces and show that MORRP gains over 10–14 × additional goodput vs. traditional protocols and 15–20% additional goodput vs. traditional protocols using multiple interfaces. MORRP scales well without imposing DHT-like graph structures (eg: trees, rings, torus etc). We also show that high connectivity can be achieved without the need to frequently disseminate node position resulting increased scalability even in highly mobile environments. 相似文献
189.
Cooperative energy spectrum sensing has been proved effective to detect the spectrum holes in Cognitive Radio (CR). However, its performance may suffer from the noise uncertainty, which is portrayed by the SNR wall in some literatures. In this paper we analyze the spectrum sensing performance under noise uncertainty and find an alternative approach to obtain the SNR wall. Then the average SNR wall is proposed to illustrate the statistically average impact of noise uncertainty. In addition, the cooperative sensing performance under noise uncertainty with AND rule is discussed. Analyses and numerical results show that cooperative sensing can significantly improve the sensing performance under the condition of noise uncertainty. 相似文献
190.
Osnat Keren 《Journal of Electronic Testing》2010,26(3):337-353
The paper deals with context-oriented codes for concurrent error detection. We consider a fault model for which, in the presence of a fault, the values on the circuit’s output are arbitrary. This model allows one to design an error detection code without analyzing sensitive parts or error cones in the synthesized circuit. Conventional coding schemes are based on a one-to-one mapping between an original output vector (information word) and a codeword. In this paper, we introduce a different approach, which we call one-to-many coding. In one-to-many code, each codeword comprises a predefined set of words. The functional unit is referred to as an encoder enabling each activation to map an information word to a different word. This flexible mapping system results in a lower implementation cost of the functional unit and its checker. 相似文献