全文获取类型
收费全文 | 25621篇 |
免费 | 1689篇 |
国内免费 | 928篇 |
专业分类
电工技术 | 1267篇 |
综合类 | 1659篇 |
化学工业 | 3526篇 |
金属工艺 | 1302篇 |
机械仪表 | 1666篇 |
建筑科学 | 1720篇 |
矿业工程 | 647篇 |
能源动力 | 770篇 |
轻工业 | 2571篇 |
水利工程 | 453篇 |
石油天然气 | 585篇 |
武器工业 | 244篇 |
无线电 | 2931篇 |
一般工业技术 | 2917篇 |
冶金工业 | 2137篇 |
原子能技术 | 264篇 |
自动化技术 | 3579篇 |
出版年
2024年 | 63篇 |
2023年 | 203篇 |
2022年 | 569篇 |
2021年 | 772篇 |
2020年 | 658篇 |
2019年 | 378篇 |
2018年 | 536篇 |
2017年 | 650篇 |
2016年 | 612篇 |
2015年 | 944篇 |
2014年 | 1326篇 |
2013年 | 1832篇 |
2012年 | 2062篇 |
2011年 | 2219篇 |
2010年 | 2003篇 |
2009年 | 1936篇 |
2008年 | 1852篇 |
2007年 | 1652篇 |
2006年 | 1231篇 |
2005年 | 787篇 |
2004年 | 583篇 |
2003年 | 405篇 |
2002年 | 279篇 |
2001年 | 219篇 |
2000年 | 233篇 |
1999年 | 236篇 |
1998年 | 443篇 |
1997年 | 353篇 |
1996年 | 302篇 |
1995年 | 237篇 |
1994年 | 205篇 |
1993年 | 203篇 |
1992年 | 155篇 |
1991年 | 154篇 |
1990年 | 104篇 |
1989年 | 107篇 |
1988年 | 117篇 |
1987年 | 112篇 |
1986年 | 90篇 |
1985年 | 130篇 |
1984年 | 121篇 |
1983年 | 134篇 |
1982年 | 100篇 |
1981年 | 103篇 |
1980年 | 94篇 |
1979年 | 90篇 |
1978年 | 78篇 |
1977年 | 99篇 |
1976年 | 146篇 |
1975年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
基于直升机目标旋转部件的调制模型,本文针对防空雷达提出了分析直升机信号特征的一种新方法——WVD法,并对直升机目标旋转部件调制回波信号在不同噪声情况下加以仿真分析,结果表明:用WVD分析雷达回波中直升机信号特征是一种非常有效的方法。 相似文献
2.
Thanapalan Murugesan G. S. Venkat Rathnam S. Panduranga Rao P. Gangadhar Rao 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):290-294
In the present study of gas–liquid contactors, mean residence/contact time was calculated from knowledge of superficial velocity and the gas phase hold-up, for various gas rates and impeller geometry and speeds, and compared with values obtained from RTD measurements. A new correlation, involving Flow Number, Froude Number, system geometry and the physical properties, is proposed. This uses the authors data and those available in literature. 相似文献
3.
4.
In this paper, we examine methods of characterizing somatosensory evoked potentials (SEP's) in both the time and frequency domains. We have found that the truncated impulse response (TIR) method produced an accurate time domain model of the SEP signals at model orders greatly reduced from the original state space matrix. The TIR method was valuable for smoothing signals that were slightly corrupted by noise. In this case, the simulated data sequence was close to the original data sequence in the mean squared error sense. For signals that were greatly corrupted by noise, the TIR method was not able to perform as well. Therefore, the TIR method was not a feature extraction method but was valuable for data simulation. In the frequency domain, we have used the autoregressive moving average model (ARMA) to parameterize the SEP signal. An overdetermined set of Yule-Walker equations was created to determine the autoregressive (AR) parameters of the original data with the model order established by the singular value decomposition. From these AR parameters, a residual time series was generated which was used to find the moving average parameters. The resulting ARMA model was used to produce a simulated data sequence. The frequency domain characteristics of the simulated sequence and the corresponding power spectral density of the ARMA filter were very close to the periodogram of the original data sequence. Accurate parameterization was achieved for the SEP waveforms at low filter lengths. 相似文献
5.
吕云霞 《昆明冶金高等专科学校学报》2004,20(2):18-20
埋在粮食筒仓中构件的受力量值的大小是筒仓结构设计中是不容忽视的问题,可作为特种结构土建结构设计人员计算参考. 相似文献
6.
7.
SV Varha OH Reznikov IS Turchyn VM Demchenko OP Potikha PV Sinitsyn LV Tarasenko LV Cha?kovs'ka 《Canadian Metallurgical Quarterly》1994,40(5-6):105-109
The effect exerted by transplantation of the 5 day culture of testicles from newly born piglets on the hypogonadal state of mature X-ray irradiated (3 Gy) rats was studied. It has been found that a month after transplantation (two months after irradiation) the hypogonadal state disappeared for a while, which is confirmed by normalization of the weight of seminal vesicles, content of testosterone and biologically active lutropine, restoration of the reproductive function of rats. No significant changes in steroidogenesis activity have been found, which proves a substituent character of transplantation. The effect disappears three months later but certain restoration of the content of nucleic acids in the testicles is observed. 相似文献
8.
The buckling of plain and discretely stiffened composite axisymmetric shell panels/shells made of repeated sublaminate construction is studied using the finite element method. In repeated sublaminate construction, a full laminate is obtained by repeating a basic sublaminate, which has a smaller number of plies. The optimum design for buckling is obtained by determining the layup sequence of the plies in the sublaminate by ranking, so as to achieve maximum buckling load for a specified thickness. For this purpose, a four-noded 48-dof quadrilateral composite thin shell element, together with fully compatible two-noded 16-dof composite meridional and parallel circle stiffener elements are used. 相似文献
9.
10.
We compared the data from four growth hormone (GH) immunoassays for analyzing 24-h GH profiles in four apparently normal subjects and four obese subjects (508 serum samples). The detection limit was 0.02 microgram/L for one immunochemiluminometric assay (ICMA), 0.1 microgram/L for two IRMAs, and 0.4 microgram/L for one RIA. All GH pulses with a peak ICMA value > 1 microgram/L were detected by each of the other methods. Overall, the correlation coefficient between the values obtained with all four assays exceeded 0.90. However, for GH concentrations < or = 0.25 microgram/L, acceptable concordance (r2 > or = 0.80) was reached only between the ICMA and one IRMA; between the ICMA and the RIA, concordance was acceptable only for GH concentrations > or = 10 micrograms/L. In the normal subjects, the percentage of undetectable values was 0% with the ICMA but 29% with one of the IRMAs; in obese subjects, the corresponding values were 12% and 38%. 相似文献