全文获取类型
收费全文 | 175959篇 |
免费 | 13785篇 |
国内免费 | 8892篇 |
专业分类
电工技术 | 5538篇 |
技术理论 | 10篇 |
综合类 | 16627篇 |
化学工业 | 16229篇 |
金属工艺 | 23994篇 |
机械仪表 | 8623篇 |
建筑科学 | 49087篇 |
矿业工程 | 5046篇 |
能源动力 | 3886篇 |
轻工业 | 6131篇 |
水利工程 | 3320篇 |
石油天然气 | 6380篇 |
武器工业 | 1280篇 |
无线电 | 6273篇 |
一般工业技术 | 17616篇 |
冶金工业 | 17802篇 |
原子能技术 | 999篇 |
自动化技术 | 9795篇 |
出版年
2024年 | 568篇 |
2023年 | 2043篇 |
2022年 | 4335篇 |
2021年 | 4809篇 |
2020年 | 5022篇 |
2019年 | 3927篇 |
2018年 | 3522篇 |
2017年 | 5071篇 |
2016年 | 5293篇 |
2015年 | 5957篇 |
2014年 | 12292篇 |
2013年 | 9654篇 |
2012年 | 12418篇 |
2011年 | 13851篇 |
2010年 | 10978篇 |
2009年 | 11542篇 |
2008年 | 9922篇 |
2007年 | 12135篇 |
2006年 | 10573篇 |
2005年 | 9092篇 |
2004年 | 7474篇 |
2003年 | 6623篇 |
2002年 | 5618篇 |
2001年 | 4712篇 |
2000年 | 3993篇 |
1999年 | 3329篇 |
1998年 | 2596篇 |
1997年 | 2282篇 |
1996年 | 1845篇 |
1995年 | 1446篇 |
1994年 | 1318篇 |
1993年 | 922篇 |
1992年 | 801篇 |
1991年 | 610篇 |
1990年 | 491篇 |
1989年 | 368篇 |
1988年 | 266篇 |
1987年 | 155篇 |
1986年 | 105篇 |
1985年 | 111篇 |
1984年 | 80篇 |
1983年 | 80篇 |
1982年 | 89篇 |
1981年 | 38篇 |
1980年 | 108篇 |
1979年 | 19篇 |
1978年 | 13篇 |
1976年 | 10篇 |
1975年 | 16篇 |
1959年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
The current-voltage (I-V) characteristics of metal-oxide-semiconductor (MOS) structures with hafnium oxide as the gate dielectric film were studied. Sharp shifts from a low-voltage ohmic regime to a tunneling conduction were observed in the high-voltage range. The paper demonstrates that this behavior can be described very well with a double-layer dielectric model. Excellent fittings of the experimental curves were obtained and the related key structural and physical parameters were obtained. The model fitting further suggests the optimal annealing conditions for preparing the hafnium oxide films. 相似文献
33.
A series of new o‐phenylenediamine (OPD)/o‐phenetidine (PHT) copolymers with partly phenazine‐like structures has been successfully synthesized at three polymerization temperatures by chemically oxidative polymerization in four different polymerization media. The molecular structures and properties of the resulting OPD/PHT polymers were investigated by IR, UV–vis and high‐resolution 1H NMR spectroscopies, and DSC, in order to ascertain the effect of reaction temperature, comonomer ratio and acid medium. The copolymerization mechanism of OPD with PHT monomers has been proposed. It is found that the statistical OPD/PHT copolymer obtained at a temperature of 118 °C has a higher degree of polymerization than that obtained at 12–17 °C. The OPD content in the copolymers calculated from NMR spectroscopic analysis is higher than that in the feed OPD content, whereas the OPD content calculated from element analysis is slightly lower than the feed OPD content. It can be predicted that denitrogenation takes place in the OPD units during the polymerization process at OPD/PHT molar ratios of 90/10 and 100/0. These OPD/PHT copolymers exhibit a much better solubility than the OPD homopolymer, hence suggesting an incorporation of PHT units into the phenazine structure of the homopolymer. The thermal behavior of the copolymers was also studied. Copyright © 2004 Society of Chemical Industry 相似文献
34.
人类聚居环境学对于居住区规划设计的启示 总被引:1,自引:0,他引:1
以人类聚居环境学的研究方法从若干方面对目前的居住区规划设计进行了一定的探讨,分析规划设计及建设方面目前存在的主要问题,提出以人类聚居环境学为指导的居住区规划设计理念。 相似文献
35.
Periklis E. Ergatis Panagiotis G. Massouros Georgia C. Athanasouli George P. Massouros 《国际能源研究杂志》2003,27(9):795-811
A time‐dependent coefficient of heat transfer is proposed for the computation of thermal power required, so that a room temperature reaches a desired value within a given time. A mathematical formulation of the room heating transient phenomenon is constructed in a dimensionless form. Using an integral approximate solution an analytical expression for this coefficient is provided and it is verified by diagrams adopted by DIN 4701. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
36.
T. Bag 《Information Sciences》2006,176(19):2910-2931
In this paper, definitions of strongly fuzzy convergent sequence, l-fuzzy weakly convergent sequence and l-fuzzy weakly compact set are given in a fuzzy normed linear space. The concepts of fuzzy normal structure, fuzzy non-expansive mapping, uniformly convex fuzzy normed linear space are introduced and fixed point theorems for fuzzy non-expansive mappings are proved. 相似文献
37.
钢纤维聚合物混凝土抗压本构关系 总被引:2,自引:0,他引:2
钢纤维聚合物混凝土是由聚合物混凝土基体和钢纤维共同组成的纤维增强复合材料,它的力学行为不仅依赖于聚合物混凝土基体的行为,而且与钢纤维的掺量、分散特征以及钢纤维的几何尺寸有关,本文将基于损伤力学原理研究在不同纤维掺量下的钢纤维聚合物混凝土的全程压力-应变曲线及其本构模型。 相似文献
38.
39.
Hong Kong is known as a migrant city because its population was sourced from mainland China, and because there has always been outflows of people to overseas countries, especially from the mid-1980s to mid-1990s. Emigration to mainland China has become a significant recent trend. This article discusses this phenomenon in the theoretical contexts of migration and trans-border residential development. It contends that the trend will intensify more quickly than other cross-border movements because the two systems are separated by a political border within one country, and because there are common cultural ties and rapid economic integration. 相似文献
40.