全文获取类型
收费全文 | 6563篇 |
免费 | 1308篇 |
国内免费 | 1126篇 |
学科分类
工业技术 | 8997篇 |
出版年
2024年 | 17篇 |
2023年 | 98篇 |
2022年 | 215篇 |
2021年 | 196篇 |
2020年 | 291篇 |
2019年 | 231篇 |
2018年 | 201篇 |
2017年 | 323篇 |
2016年 | 333篇 |
2015年 | 356篇 |
2014年 | 488篇 |
2013年 | 510篇 |
2012年 | 596篇 |
2011年 | 675篇 |
2010年 | 515篇 |
2009年 | 518篇 |
2008年 | 584篇 |
2007年 | 620篇 |
2006年 | 452篇 |
2005年 | 385篇 |
2004年 | 251篇 |
2003年 | 242篇 |
2002年 | 149篇 |
2001年 | 151篇 |
2000年 | 99篇 |
1999年 | 76篇 |
1998年 | 95篇 |
1997年 | 50篇 |
1996年 | 39篇 |
1995年 | 37篇 |
1994年 | 30篇 |
1993年 | 38篇 |
1992年 | 23篇 |
1991年 | 23篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1963年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有8997条查询结果,搜索用时 21 毫秒
31.
在介绍推进波作用下底泥起动特点的基础上,将上层水体作为粘性流体,底泥作为粘弹性体,推导了推进波作用下泥床面剪应力的表达式,并根据试验结果,给出了推进波作用下底泥起动时的床面剪应力与底泥流变参数的关系。 相似文献
32.
提出了一种相似度的新定义,使双极WAT模型的实现更加简洁明了。增加一个阈值使系统能判别非存储模式或因其信息量过低而无法鉴定的输入模式,阈值的大小与要求的容错能力有关。双极相似度及阈值通过光学方法实现。阈值的光学实现使系统仍具有照明不变性。通过电路实现取及WTA网络的迭代运算。 相似文献
33.
The Research of ST-OFDM in Physical Layer of IEEE 802.16a 总被引:1,自引:0,他引:1
JU Mei-yan ZHU Qi FENG Guang-zeng Department of Communication Engineering Nanjing University of Posts Telecommunications Nanjing P.R.China 《中国邮电高校学报(英文版)》2004,11(4)
This paper briefly introduces one of the three physical layer implementations of IEEE 802.16a~[1],WirelessMAN-OFDM PHY.Based on the implementation,the combination of Orthogonal Frequency Division Multiplexing(OFDM)and Space-Time Coding(STC)which is briefly called ST-OFDM in IEEE 802.16a,is investigated under thechannel provided in Ref.[2].Especially,this paper is focused on the influence of the optimal decision threshold on the sys-tern Bit-Error-Rate(BER)performance based on unequal probabilities of sources.The simulations show that when Signal-Noise-Ratio(SNR)is low the optimal decision threshold is obviously superior to the usual one;when SNR is high to someextent,such as 10 dB for 4QAM and 16 dB for 16QAM,we can use the usual decision threshold instead of the optimal 相似文献
34.
35.
36.
37.
汽车侧倾稳定性的动态仿真(一) --数学模型的建立 总被引:1,自引:0,他引:1
本文通过对独立悬架和非独立悬架侧倾运动特性的分析并结合采用已有的轮胎力学模型,建立了反映独立悬架和非独立悬架侧倾运动特性的数学模型。在此基础上,根据汽车侧倾时悬挂质量对前后悬架的力和力矩作用来组合前后悬架,我们得到了双轴汽车在稳态转向时侧倾运动的数学模型。通过组合不同的前后悬架,这个数学模型可以反映各种悬架配置的双轴汽车。它主要是针对汽车进行稳态转向时的侧倾情况,考虑了汽车的结构参数、惯性参数以及悬架、轮胎的柔性形变对汽车侧倾运动特性和抗侧翻能力的影响。它可以用来计算一定横向加速度下汽车的侧倾反应和轮胎的载荷变化,也可以用来计算一辆确定的汽车在保持侧倾稳定性的前提下所能达到的最大横向加速度,还可以用来分析各项参数对汽车侧倾稳定性的影响。 相似文献
38.
Yeon Seok Kim 《Polymer》2008,49(2):570-578
Monodispersed copolymer emulsions with different glass transition temperatures were synthesized to investigate the effect of room temperature polymer matrix modulus on the electrical properties of carbon black (CB) filled segregated network composites. The emulsion with the highest modulus at room temperature produced composites with the lowest percolation threshold. The threshold for a composite made from a copolymer latex containing an equal ratio of butyl acrylate and methyl methacrylate (BA5) is 1.5 vol%, while the percolation threshold for the much lower modulus BA7 (7:3 BA/MMA ratio) is 4.93 vol%. The microstructure of each composite shows significant differences in the level of CB dispersion within the polymer matrix. Higher modulus polymer particles push the CB more efficiently into the interstitial space between them, resulting in a lower percolation threshold. This modulus effect was confirmed by increasing the drying temperature, where the moduli of latexes (BA5, BA5.5, and BA6) were more similar and the percolation thresholds for three composites also become closer to one another. 相似文献
39.
S Davis H Leirs H Viljugrein N Chr Stenseth L De Bruyn N Klassovskiy V Ageyev M Begon 《Journal of the Royal Society Interface》2007,4(15):649-657
Plague surveillance programmes established in Kazakhstan, Central Asia, during the previous century, have generated large plague archives that have been used to parameterize an abundance threshold model for sylvatic plague in great gerbil (Rhombomys opimus) populations. Here, we assess the model using additional data from the same archives. Throughout the focus, population levels above the threshold were a necessary condition for an epizootic to occur. However, there were large numbers of occasions when an epizootic was not observed even though great gerbils were, and had been, abundant. We examine six hypotheses that could explain the resulting false positive predictions, namely (i) including end-of-outbreak data erroneously lowers the estimated threshold, (ii) too few gerbils were tested, (iii) plague becomes locally extinct, (iv) the abundance of fleas was too low, (v) the climate was unfavourable, and (vi) a high proportion of gerbils were resistant. Of these, separate thresholds, fleas and climate received some support but accounted for few false positives and can be disregarded as serious omissions from the model. Small sample size and local extinction received strong support and can account for most of the false positives. Host resistance received no support here but should be subject to more direct experimental testing. 相似文献
40.
TAN Zuo-wen 《通讯和计算机》2007,4(5):40-46
Signcryption is a public key or asymmetric cryptographic method that provides simultaneously both message confidentiality and integrity at a lower computational and communication cost. This paper presents a (t, n) threshold proxy signcryption scheme in which no less than t proxy agents in the proxy group can produce the signcryption cryptogram. combines the functionality of threshold proxy signing and encryption. The proposed scheme combines the functionality of both threshold proxy signing and encryption, and provides fair protection for the sender and the proxy agents. This scheme is secure against attack of public key substitution. It also satisfies security properties such as confidentiality and authenticity. 相似文献