全文获取类型
收费全文 | 153288篇 |
免费 | 13624篇 |
国内免费 | 8006篇 |
专业分类
电工技术 | 7113篇 |
技术理论 | 8篇 |
综合类 | 14274篇 |
化学工业 | 24886篇 |
金属工艺 | 4847篇 |
机械仪表 | 5179篇 |
建筑科学 | 22404篇 |
矿业工程 | 7876篇 |
能源动力 | 8203篇 |
轻工业 | 9829篇 |
水利工程 | 20650篇 |
石油天然气 | 11502篇 |
武器工业 | 900篇 |
无线电 | 9153篇 |
一般工业技术 | 12551篇 |
冶金工业 | 6944篇 |
原子能技术 | 2523篇 |
自动化技术 | 6076篇 |
出版年
2024年 | 567篇 |
2023年 | 1970篇 |
2022年 | 3713篇 |
2021年 | 4444篇 |
2020年 | 4915篇 |
2019年 | 4232篇 |
2018年 | 3945篇 |
2017年 | 4984篇 |
2016年 | 5350篇 |
2015年 | 5449篇 |
2014年 | 9078篇 |
2013年 | 9410篇 |
2012年 | 11215篇 |
2011年 | 11512篇 |
2010年 | 8614篇 |
2009年 | 8869篇 |
2008年 | 8066篇 |
2007年 | 10299篇 |
2006年 | 9485篇 |
2005年 | 8304篇 |
2004年 | 6688篇 |
2003年 | 6024篇 |
2002年 | 5231篇 |
2001年 | 4205篇 |
2000年 | 3602篇 |
1999年 | 2830篇 |
1998年 | 2114篇 |
1997年 | 1854篇 |
1996年 | 1487篇 |
1995年 | 1325篇 |
1994年 | 1059篇 |
1993年 | 808篇 |
1992年 | 664篇 |
1991年 | 520篇 |
1990年 | 409篇 |
1989年 | 389篇 |
1988年 | 255篇 |
1987年 | 215篇 |
1986年 | 157篇 |
1985年 | 150篇 |
1984年 | 137篇 |
1983年 | 83篇 |
1982年 | 54篇 |
1981年 | 35篇 |
1980年 | 43篇 |
1979年 | 48篇 |
1977年 | 11篇 |
1975年 | 8篇 |
1959年 | 12篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Cognitive Operations in the Generation Effect on a Recall Test: Role of Aging and Divided Attention.
Generation effect (generated words are better memorized than read words) of anagrams, rhymes, and associates of target words was examined in young, elderly, and very old subjects. Experiments 1 and 2 showed that only young subjects benefit from the generation effect in a free-recall test when the rule is of a phonological nature. Experiments 3, 4, and 5 showed that the generation effect of rhymes was due to a resources-dependent self-initiated process. Experiments 4 and 5 showed that in a divided-attention situation, generation effect of rhymes is not significant in young subjects, but that the generation effect of semantic associates remains significant for both groups (Experiment 5). The results are discussed within the environmental support framework and the transfer-appropriate processing framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
63.
Alleviation Effect of Lanthanum on Cadmium Stress in Seedling Hydroponic Culture of Kidney Bean and Corn 总被引:4,自引:0,他引:4
Since1970s,rare earths(RE)have been exten-sively used as micro-fertilizers for crops in China.Ithas already been proved that REcani mprove the pro-duction and quality of crops.However,there havebeen a fewinvestigations about using RE as regulatorin pollution ecology.For example,An et al[1]studiedthe effects of O3on wheat growth and the protectiveeffect of RE.Yan and Zhou et al[2,3]discussed theprotective effect of RE on plants under acid rainstress.Jia et al[4]and Hu et al[5]reported th… 相似文献
64.
建(构)筑物机械拆除方法综述 总被引:1,自引:0,他引:1
介绍了几种常用的建(构)筑物机械拆除方法,对其工作原理、特点、应用条件及局限性加以分析和说明。 相似文献
65.
G. Lange 《Materialwissenschaft und Werkstofftechnik》2003,34(1):80-85
Failures by notch induced fatigue fractures Notches produce local stress concentrations and promote the formation of fatigue cracks. Characteristic types of notches as a result of design, manufacturing and operation are presented and remedial measures are discussed. Examples demonstrate the effect of different kinds of notches on various components. 相似文献
66.
本文通过对立式旋风水膜除尘器除尘性能的模型试验,揭示了几个主要参数对其除尘性能的影响,确定了合理的取值范围,对该种除尘器的设计和应用提供了依据。 相似文献
67.
Poly(L-ornithine)s having various azo-contents in the side chains were synthesized by the water-soluble carbodiimide procedure. The photochemical properties of the polypeptides poly[Nδ-p-(phenylazo)benzoyl-L-ornithine] (PPABLO) containing 3–77 mol% azobenzene were investigated by absorption and circular dichroism spectroscopy in hexafluoro-2-propanol (HFIP) or water, and in HFIP-water or methanol-water solvent mixtures. The photochromism of the dichroic bands of the PPABLOs containing 20–77 mol% azobenzene in the visible and ultraviolet wavelength regions was found to be mostly reversible as a function of irradiation time at different wavelengths due to the photostationary state (above 80% trans-cis photoisomerization) of the azo aromatic moieties. The PPABLO containing 3.2 mol% azobenzene in water exhibited conformational changes from random coil to helix by the addition of methanol or sodium dodecyl sulphate (SDS). The photo-induced conformational change was observed in HFIP-water-SDS solvent mixtures, while no conformational change was seen in water and HFIP-water solvent mixtures. 相似文献
68.
一、引言从束流动力学的观点出发,对于粒子束在直线加速器中的运动,有两种主要的分析方法,也即粒子轨迹跟踪法及考察束流包络运动的方法。前者是通过解单粒子运动方程,跟踪大量的单粒子运动轨迹而后进行分析;后者则是通过解束流的包络线方程,根据束流包络的变化来进 相似文献
69.
70.
Phase separation during polymerization was studied in a model system consisting of a diepoxide based on diglycidyl ether of bisphenol A (DGEBA), variable amounts of ethylenediamine (EDA) and the mass of castor oil (CO) necessary to obtain a mass fraction equal to 0-15 in a final system where the stoichiometric ratio of amine to epoxy equivalents, r, was equal to 1. A two-step polymerization process was performed by curing first a system with r = 0-5, during variable times before phase separation, and then carrying the system to r = 1. Thermodynamic analysis of samples with different r values led to a linear relationship between the Flory-Huggins interaction parameter and r. The concentration (P) and average size (D?) of dispersed-phase particles followed opposite trends, i.e. P increased while D? decreased, when either r was increased or the time of curing in the first step of a two-step process was decreased. This was explained by assuming that the competition between nucleation and growth was determined by the viscosity at the cloud point, ηcp. Low values of ηcp favoured growth over nucleation and led to fewer but larger particles. 相似文献