全文获取类型
收费全文 | 225806篇 |
免费 | 2224篇 |
国内免费 | 709篇 |
专业分类
化学 | 107881篇 |
晶体学 | 3292篇 |
力学 | 7820篇 |
综合类 | 4篇 |
数学 | 18400篇 |
物理学 | 60276篇 |
无线电 | 31066篇 |
出版年
2016年 | 2506篇 |
2015年 | 1802篇 |
2014年 | 2638篇 |
2013年 | 8316篇 |
2012年 | 5582篇 |
2011年 | 6976篇 |
2010年 | 4938篇 |
2009年 | 5174篇 |
2008年 | 7055篇 |
2007年 | 7542篇 |
2006年 | 7326篇 |
2005年 | 6747篇 |
2004年 | 6194篇 |
2003年 | 5584篇 |
2002年 | 5502篇 |
2001年 | 7032篇 |
2000年 | 5590篇 |
1999年 | 4580篇 |
1998年 | 3800篇 |
1997年 | 3833篇 |
1996年 | 3736篇 |
1995年 | 3459篇 |
1994年 | 3332篇 |
1993年 | 3215篇 |
1992年 | 3721篇 |
1991年 | 3607篇 |
1990年 | 3419篇 |
1989年 | 3445篇 |
1988年 | 3294篇 |
1987年 | 2935篇 |
1986年 | 2762篇 |
1985年 | 3645篇 |
1984年 | 3657篇 |
1983年 | 3077篇 |
1982年 | 3213篇 |
1981年 | 3149篇 |
1980年 | 3009篇 |
1979年 | 3116篇 |
1978年 | 3364篇 |
1977年 | 3144篇 |
1976年 | 3112篇 |
1975年 | 2933篇 |
1974年 | 2881篇 |
1973年 | 2901篇 |
1972年 | 1901篇 |
1971年 | 1608篇 |
1968年 | 2042篇 |
1967年 | 2215篇 |
1966年 | 2021篇 |
1965年 | 1583篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Kang-Ngee Chia Hea Joung Kim Lansing S. Mangione-Smith W.H. Villasensor J. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》1998,6(3):364-371
Under the Mojave configurable computing project, we have developed a system for achieving high performance on an automatic target recognition (ATR) application through the use of configurable computing technology. The ATR system studied here involves real-time image acquisition from a synthetic aperture radar (SAR). SAR images exhibit statistical properties which can be used to improve system performance. In this paper, the Mojave configurable computing system uses field programmable gate arrays (FPGA's) to implement highly specialized circuits while retaining the flexibility of programmable components. A controller sequences through a set of specialized circuits in response to real-time events. Computer-aided design (CAD) tools have been developed to support the automatic generation of these specialized circuits. The resulting configurable computing system achieves a significant performance advantage over the existing solution, which is based on application specific integrated circuit (ASIC) technology 相似文献
42.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
43.
Modeling ion implantation of HgCdTe 总被引:2,自引:0,他引:2
H. G. Robinson D. H. Mao B. L. Williams S. Holander-Gleixner J. E. Yu C. R. Helms 《Journal of Electronic Materials》1996,25(8):1336-1340
Ion implantation of boron is used to create n on p photodiodes in vacancy-doped mercury cadmium telluride (MC.T). The junction
is formed by Hg interstitials from the implant damage region diffusing into the MC.T and annihilating Hg vacancies. The resultant
doping profile is n+/n-/p, where the n+ region is near the surface and roughly coincides with the implant damage, the n- region is where Hg vacancies have been annihilated revealing a residual grown-in donor, and the p region remains doped by
Hg vacancy double acceptors. We have recently developed a new process modeling tool for simulating junction formation in MC.T
by ion implantation. The interstitial source in the damage region is represented by stored interstitials whose distribution
depends on the implant dose. These interstitials are released into the bulk at a constant, user defined rate. Once released,
they diffuse away from the damage region and annihilate any Hg vacancies they encounter. In this paper, we present results
of simulations using this tool and show how it can be used to quantitatively analyze the effects of variations in processing
conditions, including implant dose, annealing temperature, and doping background. 相似文献
44.
Croon J.A. Rosmeulen M. Decoutere S. Sansen W. Maes H.E. 《Solid-State Circuits, IEEE Journal of》2002,37(8):1056-1064
In this paper, a physics-based mismatch model is presented. It is demonstrated on a 0.18-/spl mu/m technology that a simple mismatch model can still be used to characterize deep-submicron technologies. The accuracy of the model is examined and found to be within 20% in the strong inversion region. Bulk bias dependence is modeled in a physical way. To extract the mismatch parameters, a weighted fit is introduced. It is shown that the width and length dependence of the mismatch parameters is given by the Pelgrom model. 相似文献
45.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration 相似文献
46.
Fahmy H.I. Develekos G. Douligeris C. 《Selected Areas in Communications, IEEE Journal on》1997,15(2):226-237
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies 相似文献
47.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
48.
Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(√(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel 相似文献
49.
Sugawara F. Aoki K. Yamaguchi H. Sasaki K. Sasaki T. Fujisaki H. 《Electron Device Letters, IEEE》1997,18(10):483-485
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor 相似文献
50.
Watanabe H. Komori J. Higashitani K. Sekine M. Koyama H. 《Semiconductor Manufacturing, IEEE Transactions on》1997,10(2):228-232
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices 相似文献