全文获取类型
收费全文 | 38224篇 |
免费 | 3249篇 |
国内免费 | 1728篇 |
专业分类
电工技术 | 2212篇 |
技术理论 | 1篇 |
综合类 | 2581篇 |
化学工业 | 6257篇 |
金属工艺 | 2161篇 |
机械仪表 | 2144篇 |
建筑科学 | 2857篇 |
矿业工程 | 958篇 |
能源动力 | 1301篇 |
轻工业 | 2474篇 |
水利工程 | 600篇 |
石油天然气 | 1952篇 |
武器工业 | 315篇 |
无线电 | 4791篇 |
一般工业技术 | 4511篇 |
冶金工业 | 1979篇 |
原子能技术 | 420篇 |
自动化技术 | 5687篇 |
出版年
2024年 | 134篇 |
2023年 | 566篇 |
2022年 | 1013篇 |
2021年 | 1463篇 |
2020年 | 1051篇 |
2019年 | 1014篇 |
2018年 | 1043篇 |
2017年 | 1196篇 |
2016年 | 1116篇 |
2015年 | 1451篇 |
2014年 | 1850篇 |
2013年 | 2321篇 |
2012年 | 2370篇 |
2011年 | 2569篇 |
2010年 | 2269篇 |
2009年 | 2251篇 |
2008年 | 2186篇 |
2007年 | 2043篇 |
2006年 | 2094篇 |
2005年 | 1769篇 |
2004年 | 1446篇 |
2003年 | 1511篇 |
2002年 | 1776篇 |
2001年 | 1328篇 |
2000年 | 897篇 |
1999年 | 835篇 |
1998年 | 670篇 |
1997年 | 569篇 |
1996年 | 523篇 |
1995年 | 403篇 |
1994年 | 326篇 |
1993年 | 228篇 |
1992年 | 195篇 |
1991年 | 141篇 |
1990年 | 108篇 |
1989年 | 76篇 |
1988年 | 94篇 |
1987年 | 53篇 |
1986年 | 50篇 |
1985年 | 28篇 |
1984年 | 35篇 |
1983年 | 21篇 |
1982年 | 29篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 19篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
采动覆岩中关键层运动对围岩支承压力分布的影响 总被引:5,自引:2,他引:3
运用数值模拟方法,主要分析了关键层的破断、关键层相对位置及采深等对围岩支承压力的影响;同时,研究了采空区支承压力的分布规律.研究结果对采场围岩的控制提供了一定的理论依据. 相似文献
42.
聚苯乙烯(PS)在苯溶液中与溴代丁二酰亚胺(NBS)反应,经分离提纯得到了固体溴代聚苯乙烯(PSB)。将所得PSB溶于苯并与低分子量的聚二甲基硅氧烷硅醇锂(PDMSOLi)反应,经分离提纯得到固体的溴代聚苯乙烯接枝聚二甲基硅氧烷(PSB-g-PDMSO),所得PSB-g-PDMSO的结构经^1H-NMR、IR及TEM表征。 相似文献
43.
In the design process of the photocatalytic oxidation (PCO) reactor using TiO2-coated foam nickels, the optimum of catalyst film thickness, light intensity and flow velocity were considered. A model was developed to study the effect of catalyst film thickness on photocatalytic degradation of formaldehyde by a TiO2-coated foam nickel at continuous flow mode. In this model, external mass transfer and internal molecule diffusion-reaction were considered. A first-order kinetics equation was used to account for the photocatalytic reaction. Two exponential equations were employed to describe the distribution of light intensities in foam nickels and catalyst films, respectively. Validated with experimental data, the model can be used to predict the optimal thickness of catalyst films. A method for determining appropriate light intensities was proposed and discussed. The appropriate light intensity can be obtained by giving a margin, regarded as an excess coefficient, to the light intensity calculated based on the assumption of complete use of excited electron–hole pairs. The excess coefficient needs to be determined experimentally. In addition, the optimal flow velocity of PCO reactors could be consistent with the required one by changing the windward area of foam nickels. Based on the theoretical analyses, a novel PCO reactor containing 15 parallel-connected cells was designed. Each reaction cell was composed of an UV lamp and a TiO2-coated tubular foam nickel. The performance of the reactor was tested by degrading gaseous formaldehyde at an indoor concentration level. The results showed that the reactor had low pressure loss and good degradation capability. 相似文献
44.
薄板坯连铸连轧工艺对铌微合金化高强度钢组织和性能的影响 总被引:1,自引:0,他引:1
首先建立薄板坯连铸连轧工艺的试验室模拟技术,并运用该模拟技术,研究薄板坯连铸连轧工艺(CSP)和传统板坯再加热工艺(TRP)两种工艺对铌微合金化高强度钢的显微组织和力学性能的影响。研究结果表明:CSP钢的晶粒细化效果不如TRP钢,两者的平均铁素体晶粒尺寸分别为8.17μm和6.30μm。在CSP试验钢板中铌的析出量较大,特别是在铁素体中细小颗粒的铌的析出物较多,沉淀强化效果较强。CSP试验钢的σ0.5和σb分别较TRP工艺低约40MPa和约25MPa,同时其低温冲击韧性较好,FATT温度较低。 相似文献
45.
Peter Su Adrian Gerlich Motomichi Yamamoto Thomas H. North 《Journal of Materials Science》2007,42(24):9954-9965
The formation of local melted films during friction stir spot welding of as-cast AZ91D and thixomolded AZ91 material is investigated.
The average temperatures close to the tip of the rotating pin vary from 438 to 454 °C during the dwell period in friction
stir spot welding. These measured temperature values are higher than the melting temperature of α-Mg + Mg17Al12 eutectic (437 °C). It is suggested that the temperature in the stir zone during the dwell period is determined by the relative
proportions of α-Mg and (α-Mg + Mg17Al12) eutectic material, which are incorporated during friction stir spot welding. Based on the stir zone temperature measurements
and a detailed examination of material located at the root of the pin thread it is suggested that material is moved downwards
via the pin thread and into the stir zone during the dwell period in friction stir spot welding. Evidence of local melted
film formation is observed in the stir zone of AZ91 spot welds. It is suggested that melted films are retained since their
dissolution rate is much slower in the high temperature stir zone than it is when melted films is formed in the stir zone
during Al 7075-T6 friction stir spot welding. The spontaneous melting temperature, solute diffusion rate and the thermodynamic
driving force for droplet dissolution are much higher during Al 7075-T6 friction stir spot welding. 相似文献
46.
不同粒度松散煤体的氧扩散特性实验研究 总被引:1,自引:0,他引:1
以自行研制的煤对氧扩散特性测试装置为实验手段,在常温环境条件下测试了不同粒度松散煤体对氧的自由扩散特性.实验结果表明:煤样粒度的变化对取气腔氧浓度流出曲线的影响表现出2个极限值,煤样粒度在20~100目之间时,取气腔氧气浓度梯度随煤样粒度的增大而增大;当煤样粒度<20目或>100目时,煤样粒度的再变化对氧浓度流出曲线的影响则微乎其微;取气腔氧浓度曲线流形基本符合指数曲线的变化规律. 相似文献
47.
合成2,4-二叔丁基苯酚工业试验 总被引:2,自引:0,他引:2
以离子交换树脂为催化剂,苯酚和甲基叔丁基醚为原料合成2,4-二叔丁基苯酚(简称2,4酚),合成产物经过滤再经间歇真空精馏精制提纯,得到高纯度的2,4酚成品。成品精馏后釜中残液在酸性白土催化剂的作用下通过歧化反应生成对叔丁基苯酚,再经精馏提纯得到成品对叔丁基苯酚。通过工艺优化,使2,4酚、对叔丁基苯酚形成联产生产工艺,降低了生产原料消耗和成本。 相似文献
48.
An alternative method to compute the component fractions in the geometrical optical model: visual computing method 总被引:1,自引:0,他引:1
Hong-Bo Su Ren-Hua Zhang Xin-Zhai Tang Xiao-Min Sun Zhi-Lin Zhu Zhao-Liang Li 《Geoscience and Remote Sensing, IEEE Transactions on》2003,41(3):719-724
A method called visual computing was used to solve angular four-components' proportions and directional vegetation cover fraction for discrete canopies and continuous row-planted plants. It proved effective to predict the angular characteristics on pixel scale. The method could be an alternative way to a classical solution of geometrical optical models. A visual computing method would be effective especially when the canopies' spatial distribution and shapes were irregular and could not be described statistically. 相似文献
49.
50.
脉冲电镀最佳参数之探索和优化 总被引:3,自引:0,他引:3
本文利用正交实验法对脉冲电镀各控制参数进行试验,对影响分散能力、镀层可靠性及外观质量的各种因素进行探讨,寻找影响外观质量的显著因子并加以控制,同时进一步优化脉冲电镀的工艺参数。 相似文献