全文获取类型
收费全文 | 8022篇 |
免费 | 685篇 |
国内免费 | 451篇 |
专业分类
电工技术 | 140篇 |
综合类 | 788篇 |
化学工业 | 1323篇 |
金属工艺 | 112篇 |
机械仪表 | 143篇 |
建筑科学 | 452篇 |
矿业工程 | 187篇 |
能源动力 | 514篇 |
轻工业 | 359篇 |
水利工程 | 143篇 |
石油天然气 | 541篇 |
武器工业 | 24篇 |
无线电 | 1256篇 |
一般工业技术 | 820篇 |
冶金工业 | 298篇 |
原子能技术 | 59篇 |
自动化技术 | 1999篇 |
出版年
2024年 | 34篇 |
2023年 | 101篇 |
2022年 | 156篇 |
2021年 | 283篇 |
2020年 | 346篇 |
2019年 | 197篇 |
2018年 | 224篇 |
2017年 | 278篇 |
2016年 | 323篇 |
2015年 | 287篇 |
2014年 | 442篇 |
2013年 | 569篇 |
2012年 | 473篇 |
2011年 | 539篇 |
2010年 | 461篇 |
2009年 | 511篇 |
2008年 | 440篇 |
2007年 | 543篇 |
2006年 | 514篇 |
2005年 | 443篇 |
2004年 | 334篇 |
2003年 | 349篇 |
2002年 | 248篇 |
2001年 | 200篇 |
2000年 | 153篇 |
1999年 | 144篇 |
1998年 | 117篇 |
1997年 | 75篇 |
1996年 | 76篇 |
1995年 | 62篇 |
1994年 | 53篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1965年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有9158条查询结果,搜索用时 0 毫秒
21.
VTI介质中弹性参数地震反演方法 总被引:2,自引:2,他引:0
根据地震波在具有垂直对称轴的横向各向同性(VTI)介质中的运动学特征,应用传播时间反演方法,进行了水平层状VTI介质的地层弹性参数反演方法研究。在VTI介质中,P-P波的传播时间曲线不再是双曲线,尤其在长排列情况下,已不能用二项泰勒展式精确地反演P-P波的传播时间,用三项泰勒展式则可以达到更高精度;P-SV波的传播时间也可用三项泰勒展式表达,在中等及短排列长度时可达到一定精神。对P-P波、P-SV波的传播时间进行三项泰勒展开时,它们的系数中包含了地震波的各向异性信息及垂直速度信息,中以为地震波的弹性参数反演提供提供基础,模试验分析及江苏油田某地区的二维多波资料实际反演结果表明,在最大炮间距为1.5倍地层埋深时,可以很精确地得到三项泰勒展式的系数,应用这些系数能精确反演地层弹性参数,包括P波、S波的垂直速度和各向异性参数。图4表1参5(杜丽英摘) 相似文献
22.
数据广播是现阶段一种新的文化传媒体系,随着数字电视的不断发展完善,数据广播在信息产业飞速发展的今天,逐渐成为新时期信息传播的主要媒介方式,阐述数据广播在当今社会信息领域的存在形态、发展方向以及如何合理、高效地运营这样一种增值业务。 相似文献
23.
应用分层取样法测试了滤以的截污量。通过滤柱实验,2能够更好地分析研究石英砂均质滤料层截留浊质物的变化规律。 相似文献
24.
羰基铁类随机混合吸波材料等效电磁参数的计算 总被引:3,自引:0,他引:3
本文为计及多重散射偶极子间的相互作用,引入参量εh和μh,导得一组公式。它不仅能计算铁氧体类也能计算羰基铁类的随机混合吸波材料的等效电磁参数,均与实验结果吻合良好。 相似文献
25.
26.
Summary In flow through porous media, solutions of poly(ethylene oxide) (PEO) exhibit extension thickening, whereas hydroxypropyl
guar (HPG) solutions are shear-thinning at high concentrations. The results show that the extension-thickening exhibited by
PEO solutions becomes less critical with increasing flow rate as the concentration of HPG in the solution is increased. At
high concentrations of HPG, the presence of PEO inhibits the shear-thinning behaviour, without increasing the apparent viscosity
of the solution. The presence of HPG reduces the rate and extent of degradation of PEO in the flowing solution. 相似文献
27.
A new functional perturbation method (FPM) for calculating the probabilistic response of stochastically heterogeneous, linear elastic structures is developed. The method is based on treating the governing differential operator as well as the unknown displacement function as a functional of material modulus field. By executing a functional perturbation around the homogeneous case, a set of successive differential equations is obtained and solved, from which the average and variance of any local parameter (displacements, stresses, strains) can be found. For a linear problem, the equations to be solved in each approximation order differ from the one for the homogeneous case by a pseudo external loading (right hand side) part only. Thus, only the Green function for the homogeneous case is needed for an analytical solution of the corresponding heterogeneous problem. A one dimensional stochastically heterogeneous rod embedded in a uniform shear resistant elastic medium is solved as an example. The statistical variance of displacements and stresses are found analytically, including the edge regions. Morphological (grain size) and material (modulus) effects on the stochastic response are demonstrated. The above results are essential for estimating the stochastic features of local stress concentrations, which are the source for many strength-related macro properties of materials. Extensive usage of generalized functions (Dirac operator and its derivatives) is needed for the analysis. 相似文献
28.
超临界流体中的酶催化 总被引:3,自引:0,他引:3
与其他非水相酶催化介质相比 ,超临界流体有其独特的优越性。阐述了超临界流体的概念、对超临界流体的选择原则以及在超临界流体中酶催化的各种影响因素 ,还讨论了在此类流体中酶催化的应用和发展前景 相似文献
29.
This article reviews research on the implementation of media-rating systems, parents' use and evaluation of them, and the impact of ratings on children. Although half or more of parents report using media-rating systems, understanding of various components of the systems is low, particularly for television ratings. A meta-analysis of national polls shows that parents overwhelmingly prefer that ratings specify content, rather than giving age recommendations. A second meta-analysis, of experiments testing the effects of ratings on children's interest in programs, shows that ratings indicating restricted or controversial content have a deterrent effect for children under age 8 but that, by age 11 and especially for boys, the ratings show a small enticement effect. This effect occurs for both age-based and content-based ratings. Implications for policymakers and parents are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
The gasification reaction of fir charcoal with CO2 was studied by isothermal thermogravimetric analysis under kinetic control. The derived reaction rate (r=dX/dt) as a function of the converted carbon mass (X) was compared with random pore model predictions and found to be much higher at elevated conversion levels than predicted by theory. Similar enhanced reaction rate behaviour was evidenced after removing the natural alkali catalyst from the charcoal by acid washing, suggesting that with untreated charcoal the late reaction rate contribution stems from both, catalytic and additional structure effects. Literature attributes the unpredicted late reaction rate behaviour to the disintegration of the porous char particle into small fragments, which, in line with percolation theory predictions, seems to occur only after a critical conversion level has been reached. However, our gasification data reveal a gradual rise in the charcoal reactivity thereafter, suggesting a breaking up (embrittlement) of the solid phase accompanied by the exposure of fresh surface area from fracturing. The original random pore model derivation given by Bhatia and Perlmutter is extended to account also for these peculiarities and the resulting kinetic relation described our reaction rate data well over the entire conversion range. 相似文献