全文获取类型
收费全文 | 8456篇 |
免费 | 582篇 |
国内免费 | 308篇 |
专业分类
电工技术 | 595篇 |
综合类 | 438篇 |
化学工业 | 865篇 |
金属工艺 | 439篇 |
机械仪表 | 355篇 |
建筑科学 | 382篇 |
矿业工程 | 182篇 |
能源动力 | 160篇 |
轻工业 | 768篇 |
水利工程 | 166篇 |
石油天然气 | 195篇 |
武器工业 | 32篇 |
无线电 | 666篇 |
一般工业技术 | 670篇 |
冶金工业 | 2575篇 |
原子能技术 | 81篇 |
自动化技术 | 777篇 |
出版年
2024年 | 30篇 |
2023年 | 89篇 |
2022年 | 225篇 |
2021年 | 242篇 |
2020年 | 192篇 |
2019年 | 142篇 |
2018年 | 150篇 |
2017年 | 169篇 |
2016年 | 168篇 |
2015年 | 244篇 |
2014年 | 305篇 |
2013年 | 391篇 |
2012年 | 430篇 |
2011年 | 389篇 |
2010年 | 414篇 |
2009年 | 394篇 |
2008年 | 458篇 |
2007年 | 394篇 |
2006年 | 355篇 |
2005年 | 259篇 |
2004年 | 240篇 |
2003年 | 173篇 |
2002年 | 174篇 |
2001年 | 153篇 |
2000年 | 129篇 |
1999年 | 118篇 |
1998年 | 538篇 |
1997年 | 372篇 |
1996年 | 260篇 |
1995年 | 147篇 |
1994年 | 140篇 |
1993年 | 155篇 |
1992年 | 67篇 |
1991年 | 62篇 |
1990年 | 73篇 |
1989年 | 54篇 |
1988年 | 73篇 |
1987年 | 68篇 |
1986年 | 50篇 |
1985年 | 39篇 |
1984年 | 37篇 |
1983年 | 43篇 |
1982年 | 41篇 |
1981年 | 40篇 |
1980年 | 65篇 |
1979年 | 39篇 |
1978年 | 36篇 |
1977年 | 96篇 |
1976年 | 203篇 |
1975年 | 35篇 |
排序方式: 共有9346条查询结果,搜索用时 15 毫秒
61.
泾河流域受土壤侵蚀的影响,水土流失较为严重,为对流域水土流失风险评估和防治等提供参考依据,根据1957-2017年泾河流域5个气象站点的日降水资料,运用ArcGIS空间插值、小波分析、R/S分析等方法,分析了该时段降雨量及降雨侵蚀力时空变化规律。结果表明:泾河流域及各气象站点的降雨量与降雨侵蚀力均呈显著正相关关系;泾河流域降雨量与降雨侵蚀力年内分布不均,主要集中在夏季,分别占全年的67.80%和52.86%;泾河流域年均降雨量和降雨侵蚀力分别为496.83 mm和1 481.24 (MJ·mm)/(hm~2·h),年际总体呈波动上升趋势且未来降雨侵蚀力将延续增加趋势,两者均在1996和2009年出现突变点且第一主周期分别为27和17 a;泾河流域降雨量和降雨侵蚀力在空间上均呈从西北到东南递增的趋势。 相似文献
62.
Michael Morris 《Minds and Machines》1992,2(1):85-95
In his response to my Why There Are No Mental Representations, Robert Cummins accused me of having misinterpreted his views, and attempted to undermine a crucial premise of my argument, which claimed that one could only define a semantic type non-semantically by stipulating which tokens should receive a uniform interpretation. I respond to the charge and defend the premise. 相似文献
63.
The influence of Mn content on the ductile-brittle transition in 16 to 36 wt pct Mn steels was investigated and interpreted in light of the evolving microstructure. It was found that when hcp ε martensite is present in the as-quenched condition or forms during deformation, it lowers the toughness. In 25Mn steel, the stress concentrations at e plate intersections result in the formation of planar void sheets along the {111}γ planes. The deformation-induced α’ martensite in 16 to 20 pct Mn alloys enhances the toughness, but leads to a ductile-to-brittle transition at low temperatures that is due to the intrusion of an intergranular fracture mode. Binary alloys with greater than 31 pct Mn also fracture in an intergranular mode at 77 K although the impact energy remains quite high. Auger spectroscopy of the fracture surfaces shows no evidence of significant impurity segregation, which suggests the importance of slip heterogeneity in controlling intergranular fracture in these alloys. 相似文献
64.
65.
Leonard S. Haynes Graham H. Morris 《International Journal of Machine Tools and Manufacture》1988,28(3)
Experience has proved that exploiting robots for assembly tasks is much more difficult than manufacturing engineers had expected and many attempts at implementing robotic assembly have failed. Our research has led us to believe that a formal approach to specifying the steps required for assembly would be of great benefit in developing the required software for a specific task, and in adaptively controlling and monitoring the execution of robotic assembly steps. The US National Bureau of Standards has developed a formal system, called ABC (for Assembly By Constraints) for specifying the steps required for assembly. The system is based on the reduction in the degrees of freedom of objects as they are assembled. Using this basic concept, we have developed 14 primitive operations which can be used to completely specify assembly steps for a large class of problems. This paper initially outlines the historical development of the system, then describes two pieces of software developed to allow easy definition of assembly tasks using the ABC system, and finally presents two practical examples. 相似文献
66.
Calculated hardenability for improved consistency of properties in heat treatable engineering steels
W. T. Cook P. F. Morris L Woollard 《Journal of Materials Engineering and Performance》1997,6(4):443-448
Hardenability is one of the most important parameters controlling the heat treated properties of engineering steels. It affects
the consistency of response for microstructure, hardness, strength, toughness, and dimensional change (distortion). This study
illustrates that a major benefit of controlling hardenability is improving the consistency of dimensional distortion resulting
from heat treatment. To facilitate the supply of steels to hardenability limits, especially restricted hardenability, a new
technique was developed for the prediction of Jominy hardenability from chemical composition. The technique, termed the “Database
Method,” uses measured Jominy hardenability and chemical composition data, contained in a database, to calculate the hardenability
for a query composition. Using up to ten known steels, selected from the database with compositions closely matching that
of the query steel, a small adjustment is made to the measured hardenability of each known steel allowing for the small difference
in composition between the query and chosen steel. The final calculated result for the query steel is taken as the average
of the various estimates. The basis of the Database Method is explained, and the advantages are illustrated for selecting
engineering grades. 相似文献
67.
68.
Dale A. Creaser Philip G. Harrison M. A. Morris B. A. Wolfindale 《Catalysis Letters》1994,23(1-2):13-24
X-ray photoelectron spectroscopy has been used to examine the nature of the oxide overlayers on a passivated cerium metal foil as a function of a variety of oxidation and reduction treatments. Oxidation of a clean uncontaminated cerium(III) oxide surface is facile at room temperature and produces non-stoichiometric ceria (CeO2–x) at oxygen doses as low as 10 L. At higher doses the overlayer thickens, and after a dose of 160 L the layer depth exceeds the Ce 3d photoelectron attenuation distance of about 20 Å. High pressure treatment of the foil in oxygen (0.5 bar at RT and 473 K) produces CeO2 in a high degree of crystallographic order such that O 1s photoelectron intensities are increased above that expected from a randomly oriented powder. An attempt to reduce the CeO2 layer formed by controlled oxidation with CO (633 K, 14 h, 0.6 bar) results in the formation of a carbonated surface layer. Results following attempts to reoxidise this layer are discussed. 相似文献
69.
介绍了如何提高甲醇触媒的活性及寿命,进一步降低电耗。文中对“精脱硫新工艺”的研发及设备的选取作了详细的论述。 相似文献
70.
S. G. Morris P. Magidman S. F. Herb 《Journal of the American Oil Chemists' Society》1972,49(9):505-507
A study was made of the noncatalytic hydrogenation of acetylenic bonds in fatty esters tocis double bonds using various metals in different solvent systems. The best results were obtained with 15% propanol in water
using iron. The yields ofcis double bonds for the nonconjugated diynoate and monoynoate ranged from 90% to 99% and for the conjugated diynoate the yields
ranged from 56% to 77%. In the reduction of methyl santalbate to a conjugated diene, the yields were ca. 85%.
Presented at the AOCS Meeting, New Orleans, April 1970.
E. Market. Nutr. Res. Div., ARS, USDA. 相似文献