全文获取类型
收费全文 | 8646篇 |
免费 | 699篇 |
国内免费 | 486篇 |
专业分类
电工技术 | 145篇 |
综合类 | 809篇 |
化学工业 | 1353篇 |
金属工艺 | 130篇 |
机械仪表 | 161篇 |
建筑科学 | 494篇 |
矿业工程 | 198篇 |
能源动力 | 522篇 |
轻工业 | 361篇 |
水利工程 | 183篇 |
石油天然气 | 548篇 |
武器工业 | 26篇 |
无线电 | 1374篇 |
一般工业技术 | 837篇 |
冶金工业 | 327篇 |
原子能技术 | 60篇 |
自动化技术 | 2303篇 |
出版年
2024年 | 34篇 |
2023年 | 106篇 |
2022年 | 159篇 |
2021年 | 287篇 |
2020年 | 354篇 |
2019年 | 202篇 |
2018年 | 233篇 |
2017年 | 295篇 |
2016年 | 341篇 |
2015年 | 301篇 |
2014年 | 465篇 |
2013年 | 598篇 |
2012年 | 504篇 |
2011年 | 586篇 |
2010年 | 492篇 |
2009年 | 558篇 |
2008年 | 483篇 |
2007年 | 595篇 |
2006年 | 553篇 |
2005年 | 481篇 |
2004年 | 374篇 |
2003年 | 387篇 |
2002年 | 266篇 |
2001年 | 217篇 |
2000年 | 172篇 |
1999年 | 152篇 |
1998年 | 127篇 |
1997年 | 86篇 |
1996年 | 83篇 |
1995年 | 68篇 |
1994年 | 61篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1977年 | 2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9831条查询结果,搜索用时 15 毫秒
11.
Electrodeposition of conducting polyaniline (Pani) was made under potentiostatic condition at pH 1.0 in different electrolyte media (H2SO4 and HClO4) in the absence and presence of two organic dopants, disodium salts of naphthalene-1,5-disulphonic acid (NSA) and of catechol-3,5-disulphonic acid (CSA). The rate and yield of Pani deposition were dependent on the acid medium and the dopant employed. NSA in H2SO4 caused an increase in rate and yield but CSA decrease when compared to the rate and yield of H2SO4 alone. In HClO4 medium, both the dopants showed a decrease. With regard to DC electrical conductivity, both the dopants exhibited an enhancement in H2SO4 medium but NSA a decline in HClO4. Characterisation of the electrosynthesised polymer samples by various instrumental techniques (cyclic voltammetric: CV, FTIR, UV-Visible: UV-Vis, EPR, XRD, TGA and DTG methods) revealed that between the two acid media, H2SO4 was the better one. Further, it enlightened the role of two organic dopants in relation to the acid media. The advantageous role of NSA in H2SO4 had origin on its molecular characteristics such as non-polarity, larger π-electron cloud etc., while CSA could not perform such a role because of its easily oxidisable hydroxyl groups. In HClO4, however, both the dopants could play only an unfavourable role owing to its greater polarity and oxidizing power than H2SO4. 相似文献
12.
13.
管壳式换热器流场三维数值模拟 总被引:16,自引:0,他引:16
采用多孔介质方法 ,在PHOENICS 3 3程序的基础上建立了换热器的三维流动计算模型。引入体积穿透率、表面穿透率、分布阻力等来描述换热器内的管束。模型通过计算Halle等[1] 的实验工况来进行验证 ,并尝试用于计算 2 0 0MW低温供热堆主换热器内的流场 相似文献
14.
Yilmaz Muslu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1991,51(4):449-460
A dispersed flow model previously developed to study substrate utilization in unsaturated media was experimentally verified and its practical application was considered. For this purpose, measurements were made using tap water and a synthetic feed solution. The importance of the change in fluid regime as regards to the simultaneous transport and reaction within biological filters were demonstrated. The effect of drop formation and the breakage of liquid jets inside the filters on substrate utilization was also shown. 相似文献
15.
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
16.
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
17.
18.
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
19.
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
20.
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