全文获取类型
收费全文 | 69331篇 |
免费 | 15275篇 |
国内免费 | 4556篇 |
专业分类
化学 | 56071篇 |
晶体学 | 671篇 |
力学 | 1756篇 |
综合类 | 233篇 |
数学 | 4131篇 |
物理学 | 9971篇 |
无线电 | 16329篇 |
出版年
2024年 | 58篇 |
2023年 | 648篇 |
2022年 | 763篇 |
2021年 | 1323篇 |
2020年 | 2694篇 |
2019年 | 4017篇 |
2018年 | 2187篇 |
2017年 | 1817篇 |
2016年 | 4993篇 |
2015年 | 5139篇 |
2014年 | 5365篇 |
2013年 | 6428篇 |
2012年 | 5738篇 |
2011年 | 5044篇 |
2010年 | 4969篇 |
2009年 | 4858篇 |
2008年 | 4630篇 |
2007年 | 3719篇 |
2006年 | 3341篇 |
2005年 | 3358篇 |
2004年 | 2756篇 |
2003年 | 2519篇 |
2002年 | 3238篇 |
2001年 | 2261篇 |
2000年 | 2096篇 |
1999年 | 1042篇 |
1998年 | 621篇 |
1997年 | 526篇 |
1996年 | 486篇 |
1995年 | 441篇 |
1994年 | 330篇 |
1993年 | 285篇 |
1992年 | 270篇 |
1991年 | 238篇 |
1990年 | 184篇 |
1989年 | 140篇 |
1988年 | 130篇 |
1987年 | 82篇 |
1986年 | 82篇 |
1985年 | 87篇 |
1984年 | 52篇 |
1983年 | 45篇 |
1982年 | 39篇 |
1981年 | 28篇 |
1980年 | 16篇 |
1979年 | 16篇 |
1977年 | 8篇 |
1971年 | 8篇 |
1970年 | 9篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 771 毫秒
91.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
92.
93.
A route to synthesize ZSM‐5 crystals with a bimodal micro/mesoscopic pore system has been developed in this study; the successful incorporation of the mesopores within the ZSM‐5 structure was performed using tetrapropylammonium hydroxide (TPAOH)‐impregnated mesoporous materials containing carbon nanotubes in the pores, which were encapsulated in the ZSM‐5 crystals during a solid rearrangement process within the framework. Such mesoporous ZSM‐5 zeolites can be readily obtained as powders, thin films, or monoliths. 相似文献
94.
The multihop optical network is the most appropriate solution to satisfy the increasing applications of Internet services. This paper extends the regular Kautz graph to one with multiple layers in order to produce more architectural variations. The connectivity between adjacent layers utilizes the systematic connection patterns of a regular Kautz graph. A routing algorithm based on its property is presented. Optical passive star (OPS) couplers are adopted to implement our new topologies. Three scheduling criteria that can solve the contention problem in the intermediate nodes are evaluated and compared in terms of their capability to improve the accessibility. 相似文献
95.
Jin Tae Kim Keun Byoung Yoon Choon-Gi Choi 《Photonics Technology Letters, IEEE》2004,16(7):1664-1666
A novel fabrication process using a hot embossing technique has been developed for micromechanical passive alignment of polymer planar lightwave circuit (PLC) devices. With only one step of embossing, single-mode waveguide straight channels and micropedestals for passive aligning are simultaneously defined on a polymer thin film with an accuracy of /spl plusmn/0.5 /spl mu/m. This process reduces the steps for fabricating alignment structures. A fabricated polymer PLC chip and fibers are combined on a v-grooved silicon optical bench (SiOB) in a flip-chip manner. The process provides a coupling loss as low as 0.67 dB per coupling face and a cost-effective packaging solution for various polymer PLC devices. 相似文献
96.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
97.
T. Choi J.‐H. Jang C.K. Ullal M.C. LeMieux V.V. Tsukruk E.L. Thomas 《Advanced functional materials》2006,16(10)
The probing of the micromechanical properties within a two‐dimensional polymer structure with sixfold symmetry fabricated via interference lithography reveals a nonuniform spatial distribution in the elastic modulus “imprinted” with an interference pattern in work reported by Tsukruk, Thomas, and co‐workers on p. 1324. The image prepared by M. Lemieux and T. Gorishnyy shows how the interference pattern is formed by three laser beams and is transferred to the solid polymer structure. The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern. 相似文献
98.
99.
Woo‐Seok Cheong 《ETRI Journal》2003,25(6):503-509
Selective epitaxial growth (SEG) of silicon has attracted considerable attention for its good electrical properties and advantages in building microstructures in high‐density devices. However, SEG problems, such as an unclear process window, selectivity loss, and nonuniformity have often made application difficult. In our study, we derived processing diagrams for SEG from thermodynamics on gas‐phase reactions so that we could predict the SEG process zone for low pressure chemical vapor deposition. In addition, with the help of both the concept of the effective supersaturation ratio and three kinds of E‐beam patterns, we evaluated and controlled selectivity loss and nonuniformity in SEG, which is affected by the loading effect. To optimize the SEG process, we propose two practical methods: One deals with cleaning the wafer, and the other involves inserting dummy active patterns into the wide insulator to prevent the silicon from nucleating. 相似文献
100.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献