全文获取类型
收费全文 | 31065篇 |
免费 | 3113篇 |
国内免费 | 1395篇 |
专业分类
电工技术 | 1661篇 |
综合类 | 2041篇 |
化学工业 | 5830篇 |
金属工艺 | 1496篇 |
机械仪表 | 1439篇 |
建筑科学 | 1924篇 |
矿业工程 | 690篇 |
能源动力 | 839篇 |
轻工业 | 4307篇 |
水利工程 | 675篇 |
石油天然气 | 1014篇 |
武器工业 | 197篇 |
无线电 | 3283篇 |
一般工业技术 | 3689篇 |
冶金工业 | 1152篇 |
原子能技术 | 281篇 |
自动化技术 | 5055篇 |
出版年
2024年 | 140篇 |
2023年 | 475篇 |
2022年 | 1125篇 |
2021年 | 1406篇 |
2020年 | 1117篇 |
2019年 | 926篇 |
2018年 | 1016篇 |
2017年 | 1131篇 |
2016年 | 1075篇 |
2015年 | 1462篇 |
2014年 | 1878篇 |
2013年 | 2377篇 |
2012年 | 2568篇 |
2011年 | 2734篇 |
2010年 | 2330篇 |
2009年 | 2239篇 |
2008年 | 2067篇 |
2007年 | 1928篇 |
2006年 | 1620篇 |
2005年 | 1273篇 |
2004年 | 847篇 |
2003年 | 663篇 |
2002年 | 558篇 |
2001年 | 417篇 |
2000年 | 361篇 |
1999年 | 305篇 |
1998年 | 255篇 |
1997年 | 215篇 |
1996年 | 168篇 |
1995年 | 141篇 |
1994年 | 112篇 |
1993年 | 106篇 |
1992年 | 65篇 |
1991年 | 69篇 |
1990年 | 52篇 |
1989年 | 42篇 |
1988年 | 40篇 |
1987年 | 31篇 |
1986年 | 25篇 |
1985年 | 29篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1972年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Chun-Yuan Huang Tzu-Min Ou Shu-Ting Chou Meng-Chyi Wu Shih-Yen Lin Jim-Yong Chi 《Nanotechnology, IEEE Transactions on》2007,6(6):589-594
In this paper, we report that low-density InAs/GaAs quantum dots (QDs) can be formed by postgrowth annealing the samples with 1.5-monolayer (ML) InAs coverage, which is thinner than the critical layer thickness for the Stranski-Krastanov growth. The annealing procedure was performed immediately after the deposition of the InAs layer. The effects of annealing time and annealing temperature on the dot density, dot size, and optical characteristics of the QDs were investigated. The optimum annealing conditions to obtain low-density QDs are longer than 60 s and higher than 500degC . Meanwhile, no luminescence can be observed for the wetting-layer, which may suggest that the postgrowth annealing will make the wetting layer thinner and thus reduce the effects of wetting layer on carrier relaxation and recombination. On the other hand, we observe that a decrease of the PL intensity at the annealing conditions of 60 s and 515degC , which is possibly due to the increasing surface dislocations resulted from the In adatom desorption at higher annealing temperature. 相似文献
32.
O'Driscoll Michael P.; Poelmans Steven; Spector Paul E.; Kalliath Thomas; Allen Tammy D.; Cooper Cary L.; Sanchez Juan I. 《Canadian Metallurgical Quarterly》2003,10(4):326
This study examined organizational family-responsive policies, perceptions of the organization as family supportive, and supervisor support as issues that may be salient to the experience of conflict between paid employment (work) and family roles. Data were collected from 355 managerial personnel in New Zealand. Although work-family conflict and psychological strain were strongly linked, the availability of organizational policies had no significant association with levels of conflict or strain, whereas policy usage was related only to work-to-family interference and not to family-to-work interference. On the other hand, perceptions of the organization as family supportive and supervisor support for work-family balance displayed significant relationships with key variables, highlighting the importance of these variables for interventions designed to ameliorate the negative impact of work-family conflict on managerial well-being. Implications for the effective implementation of family-responsive interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
33.
马娟 《湖南冶金职业技术学院学报》2003,(4)
通过例句讲解了until的用法,辨析了until与till、before的异同,并列举了高中英语和大学英语部分课文及习题中的例句。 相似文献
34.
ChenluSONG WenjianWENG KuiCHENG HaiboQU PiyiDU GeSHEN GaorongHAN JuanYANC JoseM.F.Ferreira 《材料科学技术学报》2003,19(5):495-499
Fluorapatite/hydroxyapatite solid solution has better biological properties than other apatites, especially used as films or coatings. In this work, sol-gel preparation and in vitro behavior of fluorapatite/hydroxyapatite solid solution films on titanium alloy were investigated. Ca(NO3)2-4H20 and PO(OH)x(OEt)3-x were selected as precursors, and hexafluorophosphoric acid (HPFo) was used as a fluorine containing reagent. The Ca and P precursors were mixed with HPFo to keep the Ca/P molar ratio 1.67. The mixtures refluxed for 12 h were used as dipping sols for the preparation of the films. The phase of the films obtained at 600℃ was apatite. The F contents in the films increased with the concentrations of HPF6 in the dipping sols. The solid solution films were shown to have better stability than hydroxyapatite films, and a reasonably good bioactivity in the in vitro evaluation. 相似文献
35.
Chia‐Yin Chen Yu‐Chi Cheng Shau‐Wei Tsai 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2002,77(6):699-705
A lipase‐catalyzed enantioselective hydrolysis process under in situ racemization of the remaining (R)‐thioetser substrate with trioctylamine as the catalyst was developed for the production of (S)‐fenoprofen from (R,S)‐fenoprofen 2,2,2‐trifluoroethyl thioester in isooctane. Detailed investigations of trioctylamine concentration on the enzyme activation and the kinetic behavior of the thioester in racemization and enzymatic reactions were conducted, in which good agreement between the experimental data and theoretical results was observed. © 2002 Society of Chemical Industry 相似文献
36.
1 诚信对兖矿资本运营的贡献1.1 在兖矿股票发行方面 1988年4月兖矿煤业在纽约、香港打响了上市的第一炮,这次兖州煤业全球发行8.2亿股,发行总收入折合人民币2.58亿元。可是当时的背景是亚洲金融危机爆发所带来的负面影响尚未完全消除,世界各地失信现象屡屡发生。活力28集团股份有限公司股票上市申报时虚增利润1667.7万元,上市后三年虚增利润21124.3万元,1998年公司在配股时公开披露国家股股东荆州市国资局以现金2320万元认购 相似文献
37.
In this work, we present a novel process to produce plasticized PVC articles. Plasticized PVC dispersion resin (dry blend) was extruded and poured into a hot mold. The mold was transferred to a rotomolding machine, where the final geometry was obtained. Formulations using commercial PVC suspension resin and three different types of plasticizers were prepared under different processing conditions. The physical appearance of the articles and the tensile properties of the materials were evaluated. 相似文献
38.
节理岩体的代表单元集合体模型及弹性参数预测 总被引:8,自引:0,他引:8
本文明确提出了节理岩体“代表单元集合体”的概念和模型,通过对节理岩体的“代表单元集合体”进行数值模拟,研究了节理岩体的“代表单元集合体”的变形特性,建立了节理岩体的弹性模型,提出了预测节理岩体宏观等效弹性参数的计算机模拟方法,并将其应用于岩体工程稳定性分析中。 相似文献
39.
40.
V. Recarte R. B. Pérez-Sáez J. San Juan E. H. Bocanegra M. L. Nó 《Metallurgical and Materials Transactions A》2002,33(8):2581-2591
The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration
range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases as a function
of alloy concentration has been determined. It is found that when the aluminum content increases, the transformation changes
from β
3 ⇒ β′3 to β
3 ⇒ γ′3, with an intermediate concentration range where both martensites coexist due to a β
3 ⇒ γ′3+β′3 transformation. On the other hand, an increase of nickel content stabilizes the martensite β′3, changing from a mixed β
3 ⇒ γ′3 + β′3 to a single β
3 ⇒ β′3 transformation. Furthermore, linear relationships between M
s
and Al and Ni concentrations have been obtained for all types of martensitic phases. 相似文献