全文获取类型
收费全文 | 53356篇 |
免费 | 15874篇 |
国内免费 | 784篇 |
专业分类
电工技术 | 1829篇 |
综合类 | 1342篇 |
化学工业 | 19372篇 |
金属工艺 | 1181篇 |
机械仪表 | 1606篇 |
建筑科学 | 2880篇 |
矿业工程 | 411篇 |
能源动力 | 1315篇 |
轻工业 | 8005篇 |
水利工程 | 672篇 |
石油天然气 | 771篇 |
武器工业 | 110篇 |
无线电 | 8947篇 |
一般工业技术 | 13186篇 |
冶金工业 | 1441篇 |
原子能技术 | 160篇 |
自动化技术 | 6786篇 |
出版年
2024年 | 59篇 |
2023年 | 208篇 |
2022年 | 406篇 |
2021年 | 804篇 |
2020年 | 1821篇 |
2019年 | 3478篇 |
2018年 | 3433篇 |
2017年 | 3780篇 |
2016年 | 4196篇 |
2015年 | 4441篇 |
2014年 | 4542篇 |
2013年 | 5746篇 |
2012年 | 3614篇 |
2011年 | 3270篇 |
2010年 | 3516篇 |
2009年 | 3347篇 |
2008年 | 2968篇 |
2007年 | 2779篇 |
2006年 | 2456篇 |
2005年 | 2003篇 |
2004年 | 1908篇 |
2003年 | 2135篇 |
2002年 | 2377篇 |
2001年 | 2068篇 |
2000年 | 1607篇 |
1999年 | 853篇 |
1998年 | 399篇 |
1997年 | 325篇 |
1996年 | 229篇 |
1995年 | 205篇 |
1994年 | 218篇 |
1993年 | 147篇 |
1992年 | 130篇 |
1991年 | 95篇 |
1990年 | 71篇 |
1989年 | 59篇 |
1988年 | 57篇 |
1987年 | 38篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 27篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
气烟囱效应——礁滩相岩性气藏的典型地震响应特征 总被引:14,自引:0,他引:14
品质良好的地震剖面上出现的地震模糊带称为气烟囱,发现和识别气烟囱是寻找大型气藏的有效方法。四川盆地东北部长兴组气藏是礁滩相岩性气藏,礁、滩作为一个独立的岩性体,与周围的地层、岩性结构差异较大,由此在构造应力场中形成力学尖点,从而产生气烟囱效应。已知的黄龙场、普光等气田,其气烟囱普遍存在。点礁通常形成下方的气烟囱,台缘礁通常在上方形成气烟囱;礁滩相在构造运动中控制了断层的发育过程,凸起的礁滩相上方可能发育对冲断层;斜坡较陡的台缘礁可能发育叠置的逆冲断层;礁、滩两侧边缘的断层一般都比较发育。断层发育加强了气烟囱效应。模拟试验验证了地震剖面解释结果。根据气烟囱地震相特征,预测黑池梁存在一个大型气藏。 相似文献
84.
Dong‐Wook Kim 《ETRI Journal》2006,28(1):84-86
This letter presents a small‐sized, high‐power single‐pole double‐throw (SPDT) switch with defected ground structure (DGS) for wireless broadband Internet application. To reduce the circuit size by using a slow‐wave characteristic, the DGS is used for the quarter‐wave (°/4) transmission line of the switch. To secure a high degree of isolation, the switch with DGS is composed of shunt‐connected PIN diodes. It shows an insertion loss of 0.8 dB, an isolation of 50 dB or more, and power capability of at least 50 W at 2.3 GHz. The switch shows very similar performance to the conventional shunt‐type switch, but the circuit size is reduced by about 50% simply with the use of DGS patterns. 相似文献
85.
86.
87.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
88.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
89.
Rongfang Song Shu Hung Leung 《Broadcasting, IEEE Transactions on》2003,49(2):202-210
Conventional direct sequence code division multiple access systems (DS-CDMA) using offset quadrature phase shift key (OQPSK) usually employ a strictly bandlimited partial response square-root raised cosine pulse as the chip waveform. They have the disadvantage of large envelope fluctuation that will incur performance degradation due to the intermodulation and bandwidth enlargement caused by post nonlinear processing. To improve the performance of DS-CDMA systems, the chip waveform and receiver should be properly selected. This paper presents a systematic performance analysis of a matched filter receiver and zero-forcing filter (ZF) receiver for DS-CDMA using a time-limited partial response chip waveform. Nevertheless the systematic performance analysis is applicable to bandlimited chip pulse as well. For the zero-forcing filters, we propose to select the frequency responses that satisfy the first Nyquist criterion. With this class of filters, we can choose the roll-off factor to minimize the total power of multiple access interference and noise power. The zero-forcing filter with proper choice of roll-off factor, referred to as optimum ZF, yields a performance better than the matched filter counterpart. The bit error rate (BER) performance of the optimum ZF with superposed quadrature amplitude modulation signal as the time pulse waveform is evaluated. It is shown that the optimum ZF provides better BER performance than conventional OQPSK and minimum shift keying, and its envelope uniformity is much better than that of OQPSK. 相似文献
90.
Wu-An Kuo TingTing Hwang Wu A.C.-H. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2006,14(1):81-85
This paper presents a novel power-driven multiplication instruction-set design method for application-specific instruction-set processors (ASIPs). Based on a dual-and-configurable-multiplier structure, our proposed method devises a multiplication instruction set for low-power ASIPs. Our method exploits the execution sequences of multiplication instructions and effective bit widths of variables to reduce power consumed by redundant multiplication bits while minimizing the multiplication execution time. Experimental results on a set of DSP programs demonstrate that our proposed method achieves significant power reduction (up to 18.53%) and execution time improvement (up to 10.43%) with 18% area overhead. 相似文献