全文获取类型
收费全文 | 49169篇 |
免费 | 6670篇 |
国内免费 | 3250篇 |
专业分类
电工技术 | 10399篇 |
技术理论 | 1篇 |
综合类 | 4787篇 |
化学工业 | 7559篇 |
金属工艺 | 1580篇 |
机械仪表 | 2072篇 |
建筑科学 | 3803篇 |
矿业工程 | 1851篇 |
能源动力 | 2181篇 |
轻工业 | 1819篇 |
水利工程 | 1685篇 |
石油天然气 | 3946篇 |
武器工业 | 472篇 |
无线电 | 4123篇 |
一般工业技术 | 4215篇 |
冶金工业 | 2351篇 |
原子能技术 | 937篇 |
自动化技术 | 5308篇 |
出版年
2024年 | 278篇 |
2023年 | 792篇 |
2022年 | 1486篇 |
2021年 | 1770篇 |
2020年 | 2065篇 |
2019年 | 1783篇 |
2018年 | 1676篇 |
2017年 | 2014篇 |
2016年 | 2070篇 |
2015年 | 2152篇 |
2014年 | 3200篇 |
2013年 | 3436篇 |
2012年 | 3568篇 |
2011年 | 3717篇 |
2010年 | 2673篇 |
2009年 | 2803篇 |
2008年 | 2677篇 |
2007年 | 3047篇 |
2006年 | 2830篇 |
2005年 | 2311篇 |
2004年 | 2045篇 |
2003年 | 1820篇 |
2002年 | 1495篇 |
2001年 | 1223篇 |
2000年 | 1066篇 |
1999年 | 906篇 |
1998年 | 734篇 |
1997年 | 555篇 |
1996年 | 502篇 |
1995年 | 428篇 |
1994年 | 423篇 |
1993年 | 296篇 |
1992年 | 233篇 |
1991年 | 207篇 |
1990年 | 176篇 |
1989年 | 147篇 |
1988年 | 112篇 |
1987年 | 80篇 |
1986年 | 56篇 |
1985年 | 53篇 |
1984年 | 35篇 |
1983年 | 23篇 |
1982年 | 32篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1959年 | 8篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A method for multi-parameter PDF estimation of random variables 总被引:1,自引:1,他引:0
Guo-Kang Er 《Structural Safety》1998,20(1):25-36
The probability distribution function (PDF) of a random variable Z is approximated with c·eQ(z), where Q(z) is a polynomial function and c is normalizing constant. Based upon the weighted residual method, general linear algebraic equations have been derived for the evaluation of the unknown parameters in the polynomial. Numerical examples are presented and the results show that the PDFs obtained using the proposed method converge to those obtained from Monte Carlo simulation as the number of parameters in the approximate PDF increases. 相似文献
62.
63.
Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased. 相似文献
64.
单元系T—p相图的数学结构 总被引:1,自引:0,他引:1
作者以化学元素的稳定单质为基准,推演出了任意物质M_i(相态Ω)的热力学生成活度{相态Ω)的函数形式:?D_Ω数值的大小体现着相态Ω的热力学相对稳定性.根据集合论原理沿D(稳定性)座标取极大值的方法把物理性质互不连续的各个异相态连结在一起,建立了单元系在T-p面上的优势分布方程(PSDE):■作者以H_2O为实例,计算了T-p相图,与实验相图基本一致. 相似文献
65.
定量电子晶体学硼对Ni3Al的电荷密度分布的影响 总被引:1,自引:0,他引:1
阐述了定量电子晶体学测定晶体电荷密度分布的基本原理和方法,不足之处和改善途径。以硼对Ni3Al的电荷密度分布的影响为实例,介绍了定量电子晶体学在研究晶体电子结构方面的应用前景。 相似文献
66.
67.
68.
Zhen Wang 《Applied Composite Materials》1995,2(4):257-264
A bimodal Weibull distribution function was applied to analyse the strength distribution of glass fibre bundles under tensile impact. The simulation was performed using a one-dimensional damage constitutive model. The results show that there were two concurrent flaw populations in the fracture process. The regression analysis using the bimodal Weibull distribution function was in good agreement with experiment. 相似文献
69.
本文通过对某液压挖掘机工作装置实验样本长度的研究,详细讨论了样本长度的确定方法,重点分析了趋势曲线拟合法,提出了样本长度精度区间分析的方法,并在处理大量实验数据的基础上,从载荷分布及寿命估算的角度做了实际的验证.编制了应用程序,使样本长度确定至寿命估算整个过程程序化. 相似文献
70.
A semi-Markov model is constructed that describes an arbitrarily structured multicomponent technological system and takes
into account its calendar maintenance. Using an aggregation algorithm, approximate values of stationary reliability characteristics
and an optimal term of maintenance work are determined for the system.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 69–86, March–April 2006. 相似文献