全文获取类型
收费全文 | 575813篇 |
免费 | 6938篇 |
国内免费 | 1016篇 |
专业分类
电工技术 | 10582篇 |
综合类 | 474篇 |
化学工业 | 92240篇 |
金属工艺 | 23435篇 |
机械仪表 | 18765篇 |
建筑科学 | 12982篇 |
矿业工程 | 4334篇 |
能源动力 | 14634篇 |
轻工业 | 47543篇 |
水利工程 | 7027篇 |
石油天然气 | 14980篇 |
武器工业 | 39篇 |
无线电 | 60972篇 |
一般工业技术 | 117895篇 |
冶金工业 | 95953篇 |
原子能技术 | 14703篇 |
自动化技术 | 47209篇 |
出版年
2021年 | 5787篇 |
2020年 | 4258篇 |
2019年 | 5530篇 |
2018年 | 9622篇 |
2017年 | 9804篇 |
2016年 | 10320篇 |
2015年 | 6400篇 |
2014年 | 10716篇 |
2013年 | 26997篇 |
2012年 | 16631篇 |
2011年 | 21789篇 |
2010年 | 17447篇 |
2009年 | 19264篇 |
2008年 | 19532篇 |
2007年 | 19205篇 |
2006年 | 16623篇 |
2005年 | 14990篇 |
2004年 | 14254篇 |
2003年 | 13885篇 |
2002年 | 13441篇 |
2001年 | 12957篇 |
2000年 | 12432篇 |
1999年 | 12079篇 |
1998年 | 27700篇 |
1997年 | 20095篇 |
1996年 | 15688篇 |
1995年 | 12059篇 |
1994年 | 10914篇 |
1993年 | 10660篇 |
1992年 | 8365篇 |
1991年 | 8130篇 |
1990年 | 8008篇 |
1989年 | 7783篇 |
1988年 | 7498篇 |
1987年 | 6759篇 |
1986年 | 6549篇 |
1985年 | 7412篇 |
1984年 | 6724篇 |
1983年 | 6453篇 |
1982年 | 5794篇 |
1981年 | 5919篇 |
1980年 | 5646篇 |
1979年 | 5759篇 |
1978年 | 5675篇 |
1977年 | 6185篇 |
1976年 | 7692篇 |
1975年 | 5116篇 |
1974年 | 4912篇 |
1973年 | 4991篇 |
1972年 | 4281篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
851.
A precoding scheme for noise whitening on intersymbol interference (ISI) channels is presented. This scheme is compatible with trellis-coded modulation and, unlike Tomlinson precoding, allows constellation shaping. It can be used with almost any shaping scheme, including the optimal SVQ shaping, as opposed to trellis precoding, which can only be used with trellis shaping. The implementation complexity of this scheme is minimal-only three times that of the noise prediction filter, hence effective noise whitening can be achieved by using a high-order predictor 相似文献
852.
R. H. Howell P. A. Sterne M. J. Fluss J. H. Kaiser K. Kitazawa H. Kojima 《Journal of Superconductivity and Novel Magnetism》1994,7(1):169-173
High-statistics (>4 × 108 counts), room-temperature measurements of the electron-positron momentum density of La2?x Sr x CuO4 have been performed for samples with Sr concentrations of x=0.0, 0.1, 0.13, and 0.2. These spectra have been analyzed in conjunction with theoretical calculations of the electron-positron momentum density. The metallic samples show features consistent with the presence of a Fermi surface, but its evolution with increasing Sr concentration does not follow the predictions of band theory. These results may indicate the effects of electron-electron correlation on the electron momentum distribution in the Cu-O plane. 相似文献
853.
ST O'Sullivan GT McGreal A Lyons L Burke JG Geoghegan MP Brady 《Canadian Metallurgical Quarterly》1994,47(9):851-852
A case of histologically confirmed Paget's disease of the breast in a 72 year old man, without underlying breast carcinoma, is reported. This report raises questions about the pathogenesis of this condition and suggests that Paget's disease is an independent, intraepidermal carcinoma rather than a direct extension of intraductal carcinoma of the breast to the nipple and areola. 相似文献
854.
We evaluated the effect of 4-(2-benzylphenoxy)-N-methylbutylamine hydrochloride (bifemelane hydrochloride) on superoxide production by human neutrophils using an MCLA-dependent chemiluminescence assay. Bifemelane hydrochloride dose-dependently inhibited superoxide production by neutrophils stimulated with phorbol myristate acetate, opsonized zymosan, or N-formyl-methionyl-leucyl-phenylalanine, while it had no effect on superoxide production by a hypoxanthine-xanthine oxidase system. These results indicate that bifemelane hydrochloride does not have a scavenging effect, but has an inhibitory effect on superoxide generation by neutrophils. Although this drug is commonly used for treating chronic cerebral infarction, it may also have a protective effect on acute ischemia/reperfusion injury. 相似文献
855.
856.
A wideband low-noise pseudomorphic HEMT MMIC variable-gain amplifier has been designed and fabricated. The amplifier has a nominal gain of 13 dB across the band 2-20 GHz, with gain flatness better than ±0.4 dB. The noise figure is less than 3 dB across the band 6-16 GHz. An on-chip temperature-sensing diode is used to provide a linear temperature correction which has been used to reduce the gain variation of the amplifier by a factor of 2 across the temperature range -50°C to +95°C 相似文献
857.
The effect of spreading code length on the BER performance of an asynchronous DS-CDMA system is studied by means of Monte Carlo simulation. The probability of the crosscorrelation value between segments of long sequences is also discussed. Results indicate that the system performance with very long codes is ~1 dB worse compared to that of short CDMA codes 相似文献
858.
Yayla G. Krishnamoorthy A.V. Marsden G.C. Esener S.C. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1994,82(11):1749-1762
We report the implementation of a prototype three-dimensional (3D) optoelectronic neural network that combines free-space optical interconnects with silicon-VLSI-based optoelectronic circuits. The prototype system consists of a 16-node input, 4-neuron hidden, and a single-neuron output layer, where the denser input-to-hidden-layer connections are optical. The input layer uses PLZT light modulators to generate optical outputs which are distributed over an optoelectronic neural network chip through space-invariant holographic optical interconnects. Optical interconnections provide negligible fan-out delay and allow compact, purely on-chip electronic H-tree type fan-in structure. The small prototype system achieves a measured 8-bit electronic fan-in precision and a calculated maximum speed of 640 million interconnections per second. The system was tested using synaptic weights learned off system and was shown to distinguish any vertical line from any horizontal one in an image of 4×4 pixels. New, more efficient light detector and small-area analog synapse circuits and denser optoelectronic neuron layouts are proposed to scale up the system. A high-speed, feed-forward optoelectronic synapse implementation density of up to 104/cm2 seems feasible using new synapse design. A scaling analysis of the system shows that the optically interconnected neural network implementation can provide higher fan-in speed and lower power consumption characteristics than a purely electronic, crossbar-based neural network implementation 相似文献
859.
860.