全文获取类型
收费全文 | 30844篇 |
免费 | 1341篇 |
国内免费 | 137篇 |
专业分类
化学 | 15612篇 |
晶体学 | 243篇 |
力学 | 695篇 |
数学 | 2182篇 |
物理学 | 5756篇 |
无线电 | 7834篇 |
出版年
2024年 | 49篇 |
2023年 | 331篇 |
2022年 | 426篇 |
2021年 | 795篇 |
2020年 | 606篇 |
2019年 | 648篇 |
2018年 | 575篇 |
2017年 | 550篇 |
2016年 | 974篇 |
2015年 | 757篇 |
2014年 | 1132篇 |
2013年 | 1765篇 |
2012年 | 1985篇 |
2011年 | 2175篇 |
2010年 | 1452篇 |
2009年 | 1455篇 |
2008年 | 2041篇 |
2007年 | 1787篇 |
2006年 | 1807篇 |
2005年 | 1594篇 |
2004年 | 1431篇 |
2003年 | 1257篇 |
2002年 | 1124篇 |
2001年 | 752篇 |
2000年 | 688篇 |
1999年 | 539篇 |
1998年 | 393篇 |
1997年 | 359篇 |
1996年 | 385篇 |
1995年 | 265篇 |
1994年 | 257篇 |
1993年 | 266篇 |
1992年 | 211篇 |
1991年 | 179篇 |
1990年 | 168篇 |
1989年 | 131篇 |
1988年 | 104篇 |
1987年 | 90篇 |
1986年 | 57篇 |
1985年 | 89篇 |
1984年 | 62篇 |
1983年 | 56篇 |
1982年 | 70篇 |
1981年 | 71篇 |
1980年 | 39篇 |
1979年 | 49篇 |
1978年 | 49篇 |
1976年 | 41篇 |
1975年 | 38篇 |
1974年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
The photonic quantum ring (PQR) laser is a three dimensional whispering gallery (WG) mode laser and has anomalous quantum wire properties, such as microampere to nanoampere range threshold currents and √T‐dependent thermal red shifts. We observed uniform bottom emissions from a 1‐kb smart pixel chip of a 32×32 InGaAs PQR laser array flip‐chip bonded to a 0.35 µm CMOS‐based PQR laser driver. The PQR‐CMOS smart pixel array, now operating at 30 MHz, will be improved to the GHz frequency range through device and circuit optimization. 相似文献
982.
Using stereo images with ephemeris data from the Korea Multi‐Purpose Satellite‐1 electro‐optical camera (KOMPSAT‐1 EOC), we performed geometric modeling for three‐dimensional (3‐D) positioning and evaluated its accuracy. In the geometric modeling procedures, we used ephemeris data included in the image header file to calculate the orbital parameters, sensor attitudes, and satellite position. An inconsistency between the time information of the ephemeris data and that of the center of the image frame was found, which caused a significant offset in satellite position. This time inconsistency was successfully adjusted. We modeled the actual satellite positions of the left and right images using only two ground control points and then achieved 3‐D positioning using the KOMPSAT‐1 EOC stereo images. The results show that the positioning accuracy was about 12‐17 m root mean square error (RMSE) when 6.6 m resolution EOC stereo images were used along with the ephemeris data and only two ground control points (GCPs). If more accurate ephemeris data are provided in the near future, then a more accurate 3‐D positioning will also be realized using only the EOC stereo images with ephemeris data and without the need for any GCPs. 相似文献
983.
Mi-Ra Yoon Ju-Dong Shin Chang-Hyun Jeong Jun-Mo Jo Oh-Han Kang Sung-Un Kim 《Photonic Network Communications》2004,7(2):161-178
A virtual private network (VPN) over Internet has the benefit of being cost-effective and flexible. However, it has difficulties providing sufficient QoS and adequate transmission capacity for high bandwidth services. Given the increasing demand for high bandwidth Internet and the demand for QoS assurances in a VPN over Internet, IP/generalized multi-protocol label switching (GMPLS) based on a control plane combined with a high-bandwidth, dense-wavelength division multiplexing (DWDM) optical network is seen as a very favorable approach for realizing the future optical VPN (OVPN) over IP/GMPLS over DWDM. Within this architecture, providing QoS guaranteed multimedia services with a differentiated QoS guaranteed protocol framework with QoS recovery is one of the key issues to implement. Therefore, we suggest in this paper optical-label switched path (O-LSP) establishment and its QoS maintenance scheme based on differentiated optical QoS-service (DOQoS) classes. They are the key components for this DOQoS framework in assuring end-to-end QoS in an OVPN over IP/GMPLS over DWDM architecture. 相似文献
984.
In this paper, recent results of Weibull slopes, area scaling factors, and breakdown behaviors observed for both soft breakdown and hard breakdown are discussed. These results would help to shed light on the breakdown mechanism of HfO2 gate dielectrics. The Weibull slope β of the hard breakdown for both the area dependence and the time-to-dielectric-breakdown distribution was found to be β=2, whereas that of the soft breakdown was about 1.4 (EOT=14 Å). We also integrated the time-to-breakdown characteristics of HfO2 under unipolar AC voltage stress on MOS capacitors. The results show that longer lifetime of HfO2 has been observed when compared to constant voltage stress. Higher frequency and lower duty cycle in the AC stress resulted in longer lifetime. As thickness decreases, the amount of lifetime enhancement decreases. The enhancement of unipolar tBD is attributed to less charge trapping during the “on time”, ton and charge detrapping during the off time, toff. It is proposed that time (τin) for charge to be trapped in HfO2 is longer than ton of unipolar stress under high frequency. In addition to experimental results, possible solutions are discussed. 相似文献
985.
Sang-Wan Ryu Sung-Bock Kim Jae-Sik Sim Yong-Duck Chung Jong-Hyun Lee Jeha Kim 《Microelectronics Journal》2004,35(2):203-206
We integrated a μ-heater array with a multi-wavelength laser array for accurate control of the channel spacing. A μ-heater array was formed on a 4-channel laser array with asymmetric sampled gratings. The lasers showed threshold current of 9-13 mA and slope efficiency of around 0.21 W/A. High side mode suppression ratio over 44 dB was observed as well. With the μ-heaters, all the laser wavelengths were precisely controlled simultaneously. The laser wavelength was red shifted with the μ-heater and the tuning efficiency was 3.3 nm/W. However, thermal crosstalk between neighboring channels was observed and it was measured to be 1.1 nm/W. 相似文献
986.
Tae-Wook Kim Nathan Cernetic Yan Gao Sukang Bae Sanghyun Lee Hong Ma Hongzheng Chen Alex K.-Y. Jen 《Organic Electronics》2014,15(11):2775-2782
Low voltage organic field effect memory transistors are demonstrated by adapting a hybrid gate dielectric and a solution processed graphene oxide charge trap layer. The hybrid gate dielectric is composed of aluminum oxide (AlOx) and [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) plays an important role of both preventing leakage current from gate electrode and providing an appropriate surface energy to allow for uniform spin-casting of graphene oxide (GO). The hybrid gate dielectric has a breakdown voltage greater than 6 V and capacitance of 0.47 μF/cm2. Graphene oxide charge trap layer is spin-cast on top of the hybrid dielectric and has a resulting thickness of approximately 9 nm. The final device structure is Au/Pentacene/PMMA/GO/PhO-19-PA/AlOx/Al. The memory transistors clearly showed a large hysteresis with a memory window of around 2 V under an applied gate bias from 4 V to −5 V. The stored charge within the graphene oxide charge trap layer was measured to be 2.9 × 1012 cm−2. The low voltage memory transistor operated well under constant applied gate voltage and time with varying programming times (pulse duration) and voltage pulses (pulse amplitude). In addition, the drain current (Ids) after programming and erasing remained in their pristine state after 104 s and are expected to be retained for more than one year. 相似文献
987.
Tandem organic light-emitting devices (OLEDs) were fabricated with a hybrid organic charge generation layer (CGL) composed of bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) doped 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene (TPBi), 1,3-bis(cabazol-9-yl)benzene (mCP), and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) in an attempt to enhance their current efficiency. While the operating voltage of the tandem OLEDs with a hybrid structure composed of BEDT-TTF-doped TPBi, mCP, and a HAT-CN CGL at 10 mA/cm2 was 1 V lower than that of the tandem OLEDs with a typical CGL composed of BEDT-TTF-doped TPBi and a HAT-CN, the corresponding the current efficiency of the tandem OLEDs with a hybrid CGL at 10 mA/cm2 was 2.9 cd/A higher than that of the tandem OLEDs with a typical CGL. The increase in the current efficiency and the decrease in the operating voltage of the tandem OLEDs with the hybrid CGL were attributed to enhanced electron injection due to the insertion of the mCP layer into the hybrid CGL. 相似文献
988.
Seok Hun Kang In Gyoo Kim Bit-Na Kim Ji Hwan Sul Young Sun Kim In-Kyu You 《ETRI Journal》2018,40(2):275-282
Flash reduction of graphene oxide is an efficient method for producing high quality reduced graphene oxide under room temperature ambient conditions without the use of hazardous reducing agents (such as hydrazine and hydrogen iodide). The entire process is fast, low-cost, and suitable for large-scale fabrication, which makes it an attractive process for industrial manufacturing. Herein, we present a simple fabrication method for a flexible in-plane graphene micro-supercapacitor using flash light irradiation. All carbon-based, monolithic supercapacitors with in-plane geometry can be fabricated with simple flash irradiation, which occurs in only a few milliseconds. The thinness of the fabricated device makes it highly flexible and thus useful for a variety of applications, including portable and wearable electronics. The rapid flash reduction process creates a porous graphene structure with high surface area and good electrical conductivity, which ultimately results in high specific capacitance (36.90 mF cm−2) and good cyclic stability up to 8,000 cycles. 相似文献
989.
Batteries: In Situ Formation of Conductive Metal Sulfide Domain in Metal Oxide Matrix: An Efficient Way to Improve the Electrochemical Activity of Semiconducting Metal Oxide (Adv. Funct. Mater. 31/2015) 下载免费PDF全文
In Young Kim Jiyoon Seo Seung Mi Oh Sharad B. Patil Seong‐Ju Hwang 《Advanced functional materials》2015,25(31):4921-4921
990.
Delay‐ or Disruption‐Tolerant Networking (DTN) is a communications approach that is utilized in easily disrupted or delayed networks. Examples of such networks are often found in heterogeneous networks, mobile or extreme terrestrial networks, and planned networks in space. In this paper, we examine the metropolitan bus network as a research target of DTN for a public transport network. We analyze the metropolitan bus network through spatial and temporal modeling using an existing Bus Information System (BIS) database. On the basis of the results of our analysis, we propose and design an appropriate DTN routing scheme called Hybrid Position‐based DTN Routing. This scheme uses position‐based routing instead of address‐based routing by soliciting infrastructural help from nearby Access Points for the real‐time BIS location service. We simulated our scheme using a WLAN for the wideband DTN communication and evaluated it by comparing it with traditional Ad hoc flooding, Epidemic routing, and strategic protocol steps in our own algorithm. The results indicate that our scheme achieves reasonably high performance in terms of packet delivery ratio, latency, and resource usage. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献