全文获取类型
收费全文 | 145099篇 |
免费 | 1753篇 |
国内免费 | 482篇 |
专业分类
化学 | 68481篇 |
晶体学 | 2035篇 |
力学 | 4956篇 |
综合类 | 5篇 |
数学 | 12105篇 |
物理学 | 39248篇 |
无线电 | 20504篇 |
出版年
2016年 | 1396篇 |
2015年 | 1062篇 |
2014年 | 1476篇 |
2013年 | 5061篇 |
2012年 | 3596篇 |
2011年 | 4598篇 |
2010年 | 3007篇 |
2009年 | 3018篇 |
2008年 | 4557篇 |
2007年 | 4839篇 |
2006年 | 4830篇 |
2005年 | 4764篇 |
2004年 | 4246篇 |
2003年 | 3861篇 |
2002年 | 3790篇 |
2001年 | 4335篇 |
2000年 | 3443篇 |
1999年 | 2865篇 |
1998年 | 2584篇 |
1997年 | 2562篇 |
1996年 | 2462篇 |
1995年 | 2412篇 |
1994年 | 2224篇 |
1993年 | 2223篇 |
1992年 | 2438篇 |
1991年 | 2409篇 |
1990年 | 2295篇 |
1989年 | 2261篇 |
1988年 | 2189篇 |
1987年 | 1948篇 |
1986年 | 1823篇 |
1985年 | 2397篇 |
1984年 | 2498篇 |
1983年 | 2120篇 |
1982年 | 2414篇 |
1981年 | 2199篇 |
1980年 | 2254篇 |
1979年 | 2227篇 |
1978年 | 2338篇 |
1977年 | 2253篇 |
1976年 | 2277篇 |
1975年 | 2204篇 |
1974年 | 2039篇 |
1973年 | 2291篇 |
1972年 | 1409篇 |
1971年 | 1094篇 |
1970年 | 1030篇 |
1969年 | 987篇 |
1968年 | 1138篇 |
1967年 | 1177篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
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
72.
The interaction of isotactic polypropylene with ethylene propylene diene terpolymer in their blends has been investigated by use of differential scanning calorimetry, dynamic mechanical analysis, wide- and small-angle x-ray scattering, and by investigating the nucleation and kinetics of crystallization of the iPP component under the polarization microscope. It is found, that the dispersion of the EPDM component in the iPP matrix is dependent on blend composition and is maximal at 10% EPDM content. An interface layer between the two components is formed by migration of iPP molecules into the EPDM phase. A model for this interface is proposed. 相似文献
73.
The trend in magnetic recording media is towards higher frequencies and larger storage capacities. Base film technology has developed in a manner analogous to corresponding demands on particulate and thin-film media, i.e. in the direction to reduced thickness, smoother surfaces, and very high uniformity. Key elements for the success of polyester films as substrates for all kinds of flexible media are new concepts for pigmentation and surface design. Future digital video recording systems and thin-film media will require new substrates with higher mechanical strength and thermal stability. Trends in base film development including dual-surface films and alternative polymer substrates are discussed. 相似文献
74.
We discuss circuit parameters that limit the precision of basic dynamic current-memory cells. In addition to analyzing current-copying errors caused by the finite output conductances of the current sources and by the clock-feedthrough (CFT) of the feedback switches, we analyze the noise performance of the basic memory cell. To reduce CFT and noise, we propose a novel circuit based on Miller capacitance-enhancement. Measurement results of memory cells integrated in a 1-μm CMOS process confirm the theoretical findings; with our CFT and noise reduction technique based on Miller enhanced capacitance and dummy switches, we achieve a dynamic range of 11 b at clock frequencies greater than 100 kHz 相似文献
75.
76.
77.
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
78.
Steinwandt R. Geiselmann W. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(11):2990-2991
An attack on the public key cryptosystem Polly Cracker is described, that reveals the complete secret key σ ∈ Fq n by means of n (nonadaptively) chosen "fake" ciphertexts 相似文献
79.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
80.
Wang J.R. Racette P. Tiesky M.E. Manning W. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(6):1220-1229
The airborne Millimeter-wave Imaging Radiometer (MIR) measurements conducted over the Midwest region of the continental United States during January/February 1997 and over the Alaska-Arctic region during May 1998 are used to estimate column water vapor W<0.8 g/cm/sup 2/ under a clear sky. On board the same aircraft are two other instruments, the Cloud Lidar System (CLS) and MODerate-resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS), which provide cloud cover information and independent measurements of W, respectively. The MIR-estimated W values are compared and found to be in very good agreement with those measured by rawinsondes at near concurrence. A close correlation is found between the MIR-estimated W and that estimated from the MAS near-IR reflectance ratios. Water surface emissivities at several MIR frequencies are obtained in the process of the W retrieval from several flights over the Midwest lakes. These estimated emissivities compared favorably with values calculated for a calm water surface, which are based on a di-electric permittivity model and MAS-measured surface temperatures. The results from all comparisons strongly demonstrate the soundness of the technique for estimating W. 相似文献