全文获取类型
收费全文 | 21137篇 |
免费 | 2977篇 |
国内免费 | 2076篇 |
专业分类
电工技术 | 3129篇 |
技术理论 | 3篇 |
综合类 | 2545篇 |
化学工业 | 2806篇 |
金属工艺 | 758篇 |
机械仪表 | 1009篇 |
建筑科学 | 1575篇 |
矿业工程 | 592篇 |
能源动力 | 715篇 |
轻工业 | 774篇 |
水利工程 | 483篇 |
石油天然气 | 717篇 |
武器工业 | 247篇 |
无线电 | 2502篇 |
一般工业技术 | 2439篇 |
冶金工业 | 767篇 |
原子能技术 | 311篇 |
自动化技术 | 4818篇 |
出版年
2024年 | 142篇 |
2023年 | 383篇 |
2022年 | 518篇 |
2021年 | 639篇 |
2020年 | 823篇 |
2019年 | 818篇 |
2018年 | 711篇 |
2017年 | 847篇 |
2016年 | 905篇 |
2015年 | 892篇 |
2014年 | 1219篇 |
2013年 | 1384篇 |
2012年 | 1331篇 |
2011年 | 1471篇 |
2010年 | 1084篇 |
2009年 | 1074篇 |
2008年 | 1169篇 |
2007年 | 1278篇 |
2006年 | 1305篇 |
2005年 | 1101篇 |
2004年 | 962篇 |
2003年 | 847篇 |
2002年 | 791篇 |
2001年 | 666篇 |
2000年 | 596篇 |
1999年 | 557篇 |
1998年 | 386篇 |
1997年 | 365篇 |
1996年 | 316篇 |
1995年 | 273篇 |
1994年 | 266篇 |
1993年 | 232篇 |
1992年 | 174篇 |
1991年 | 120篇 |
1990年 | 115篇 |
1989年 | 74篇 |
1988年 | 66篇 |
1987年 | 37篇 |
1986年 | 35篇 |
1985年 | 21篇 |
1984年 | 32篇 |
1983年 | 27篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1960年 | 5篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
Antti Valmari 《International Journal on Software Tools for Technology Transfer (STTT)》2006,8(3):180-194
This article discusses observations made when the state space of the 2 × 2 × 2 Rubik’s cube was constructed with various programs
based on various data structures, gives theoretical explanations for the observations, and uses them to develop more memory-efficient
data structures. The cube has 3,674,160 reachable states. The fastest program runs in 20 s and uses 11.1 million bytes of
memory for the state set structure. It uses a 31-bit representation of the state and also stores the rotation through which
each state was first found. Its memory consumption is remarkably small, considering that 3,674,160 × 31 bits is about 14.2
million bytes. Getting below this number was made possible by sharing common parts of states. Obviously, it is not possible
to reduce memory consumption without limit. We derive an information-theoretic hard average lower bound of 6.07 million bytes
that applies in this setting. We introduce a general-purpose variant of the data structure and end up with 8.9 million bytes
and 48 s. We also discuss the performance of BDDs and perfect state packing in this application. 相似文献
123.
Calcining of the mixture of BaCO3 and TiO2 with a ratio 1:4 at different temperatures was carried out to synthesize BaTi4O9 powders. Phase evolution of the samples was studied using the differential thermal analysis (DTA) and X-ray diffractometry
(XRD). Both techniques confirmed that the formation of BaTi4O9 started around 1000 °C. The XRD peaks showed that BaTi4O9 was most pronounced at 1250 °C. X-ray line broadening methods were employed to study the variation of particle size and microstrain
of the BaTi4O9 powders. The Voigt function in a single line and the pseudo-Voigt function in the variance methods were used in our case.
We found that both functions resulted in the same trends, i.e., the particle size increased with the temperature with the
biggest size of 180 and 160 nm, whilst the microstrain yielded the opposite trend with the lowest values of 6.2 × 10–3 and 1.1 × 10–3. The scanning electron microscopy (SEM) study revealed the size of the large particles formed, due to agglomeration, to be
about 0.5–1.9 μm. Furthermore, it was shown that irregular shapes of BaTi4O9 powders necked to each other appeared at 1000 °C and grew into ellipse and rod shapes at 1250 °C.
Electronic Publication 相似文献
124.
喻尧全 《石油化工管理干部学院学报》2002,(2):1-3
剖析国有企业党风廉政建设中的突出问题。提出“推进国有企业党风廉政建设运用市场经济原则经营运作是重要途径;加强对企业经营管理者的监督管理是关键;完善法人治理结构、建立企业内部权力制衡机制是重要基础”的观点。 相似文献
125.
实施ISO14000标准促进中国企业可持续发展 总被引:6,自引:0,他引:6
阐述ISO14000标准与国有企业可持续发展的关系。企业按ISO14000建立环境管理体系是企业可持续发展的重要方面,具有战略意义。企业施行ISO14000标准的效能显著,但目前实行IS O14000的企业相对较少。分析了企业施行ISO14000标准存在的困难,提出了建立环境管理体系的几点建议。 相似文献
126.
127.
128.
129.
130.
The objective of this work is to simulate the gas flow across a concrete wall of a nuclear power plant internal enclosure. In the laboratory, permeability measurements are generally made on cylindrical samples (15 cm diameter×5 cm height: ∅ 15×5 cm) with a steady-state experiment. To be able to predict structural behaviour, we studied size effect and steady-state time with a modified CEMBUREAU permeability test. A statistical approach showed that there is no size effect on concrete permeability. Laboratory results found on cylindrical samples can be applied to tests in situ, where concrete specimens are thicker. A model based on the mass balance relation provided times to reach steady state and reproduced experimental flow kinetics for uniform water content across specimens. 相似文献