全文获取类型
收费全文 | 16426篇 |
免费 | 1371篇 |
国内免费 | 944篇 |
专业分类
电工技术 | 1067篇 |
综合类 | 1337篇 |
化学工业 | 1526篇 |
金属工艺 | 964篇 |
机械仪表 | 907篇 |
建筑科学 | 2794篇 |
矿业工程 | 322篇 |
能源动力 | 2051篇 |
轻工业 | 1018篇 |
水利工程 | 86篇 |
石油天然气 | 408篇 |
武器工业 | 92篇 |
无线电 | 699篇 |
一般工业技术 | 1262篇 |
冶金工业 | 1326篇 |
原子能技术 | 349篇 |
自动化技术 | 2533篇 |
出版年
2024年 | 86篇 |
2023年 | 265篇 |
2022年 | 447篇 |
2021年 | 555篇 |
2020年 | 573篇 |
2019年 | 446篇 |
2018年 | 406篇 |
2017年 | 486篇 |
2016年 | 549篇 |
2015年 | 598篇 |
2014年 | 1041篇 |
2013年 | 1078篇 |
2012年 | 1077篇 |
2011年 | 1177篇 |
2010年 | 1009篇 |
2009年 | 871篇 |
2008年 | 763篇 |
2007年 | 1025篇 |
2006年 | 911篇 |
2005年 | 887篇 |
2004年 | 717篇 |
2003年 | 676篇 |
2002年 | 639篇 |
2001年 | 520篇 |
2000年 | 373篇 |
1999年 | 306篇 |
1998年 | 239篇 |
1997年 | 208篇 |
1996年 | 153篇 |
1995年 | 137篇 |
1994年 | 81篇 |
1993年 | 90篇 |
1992年 | 76篇 |
1991年 | 56篇 |
1990年 | 63篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1973年 | 1篇 |
1959年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
21.
Higher heating values (HHVs) of fatty acids (C4–C18) were measured and correlated using linear least square regression analysis. Equations were developed for the estimation of the HHVs of saturated fatty acids from their molecular weight (Mw), density (DN) and carbon number (CN). These equations are HHV = 0.0518 Mw + 29.76, HHV = −93.4 DN + 122.67 and HHV = 0.7271 CN + 31.419 with R2 values of 0.9895, 0.9798, and 0.9895, respectively. The correlations may be used for HHV estimation of mixtures of fatty acids developed from vegetable oils. 相似文献
22.
介绍了热水采暖系统运行及调整的注意事项,分析了立支管阀门、集气罐的作用,提出了使热水采暖系统的调节和集排气操作达到理想程度的有效措施,以实现良好的供暖效果。 相似文献
23.
Gijsbert Erkens Jeroen Janssen 《International Journal of Computer-Supported Collaborative Learning》2008,3(4):447-470
Although protocol analysis can be an important tool for researchers to investigate the process of collaboration and communication,
the use of this method of analysis can be time consuming. Hence, an automatic coding procedure for coding dialogue acts was
developed. This procedure helps to determine the communicative function of messages in online discussions by recognizing discourse
markers and cue phrases in the utterances. Five main communicative functions are distinguished: argumentative, responsive, informative, elicitative, and imperative. A total of 29 different dialogue acts are specified and recognized automatically in collaboration protocols. The reliability
of the automatic coding procedure was determined by comparing automatically coded dialogue acts to hand-coded dialogue acts
by a human rater. The validity of the automatic coding procedure was examined using three different types of analyses. First,
an examination of group differences was used (dialogue acts used by female versus male students). Ideally, the coding procedure
should be able to distinguish between groups who are likely to communicate differently. Second, to examine the validity of
the automatic coding procedure through examination of experimental intervention, the results of the automatic coding procedure
of students, with access to a tool that visualizes the degree of participation of each student, were compared to students
who did not have access to this tool. Finally, the validity of the automatic coding procedure of dialogue acts was examined
using correlation analyses. Results of the automatic coding procedure of dialogue acts of utterances (form) were related to
results of a manual coding procedure of the collaborative activities to which the utterances refer (content). The analyses
presented in this paper indicate promising results concerning the reliability and validity of the automatic coding procedure
for dialogue acts. However, limitations of the procedure were also found and discussed. 相似文献
24.
碳化硅加热元件的电性能和使用 总被引:2,自引:0,他引:2
本文介绍碳化硅加热元件的电特性、表面负荷以及工作气氛对它的影响,并对它设计和使用要点举例予以说明。 相似文献
25.
06NiCuCrMoNb钢高温加热时表层铜的行为 总被引:2,自引:2,他引:0
将06NiCuCrMoNb钢试样在不同的加热温度保温不同时间后,观察并分析试样表层的形貌和成分。结果表明,在一定条件下铜会扩散进入表层奥氏体晶界,得到沿奥氏体晶界分布的富铜相,并在热变形加工时导致热脆。试验得到了沿奥氏体晶界分布的富铜相与加热温度和保温时间的关系。 相似文献
26.
Jane Pitcher 《Urban Policy and Research》2006,24(1):67-82
This article explores the role of qualitative and collaborative methods when undertaking evaluation research into local community safety partnerships and neighbourhood strategies. It draws on recent examples of research and evaluation studies of regeneration and community safety programmes in a number of cities and towns in England. The discussion is set against the background of the major changes in policy relating to crime and community safety, particularly the introduction of Crime and Disorder Partnerships and their engagement with local communities. The value of qualitative methods in exploring some key questions is discussed, particularly within a collaborative approach to policy research. 相似文献
27.
本文详细论述了我公司自主开发的自润滑料垫的结构设计和技术特点,分析了这种料垫的优缺点,对其应用前景进行了展望。 相似文献
28.
Waste-to-energy based greenhouse heating: exploring viability conditions through optimisation models
An optimisation approach is proposed in order to assess the technical and economic feasibility of a renewable-energy-based greenhouse in North-Eastern Italy. A floor heating system that can exploit a low-temperature heat flow coming from the condenser of a waste-to-energy plant is chosen for the greenhouse and designed developing a non-linear optimisation model, solved by a genetic algorithm. In order to determine under what conditions the combination of a floor-heating-based greenhouse with a waste-to-energy plant can be profitable, a mixed integer optimisation model is introduced to allow selection of the minimum cost fuel solution as a function of different design variables of the greenhouse, such as indoor temperature settings and floor area. The ranges within which the renewable energy solution can lead to significant savings in comparison to traditional fossil fuel are identified both from the point of view of costs and of environmental impact. Furthermore, the sales prices for waste heat that would make investment in the renewable energy solution attractive for potential entrepreneurs are given. 相似文献
29.
利用平板型热管纺丝装置对普通高速纺丝机进行技术改造,并一步法生产出充分结晶的PET纤维(FCY)。该纤维可直接用于织造,调节热管温度、热管安装位置可获得满足后道工序不同需要的FCY。 相似文献
30.
中国先进研究堆冷中子源核发热和冷中子增益研究 总被引:3,自引:3,他引:0
为准确计算和研究中国先进研究堆(CARR)冷中子源装置氢系统的核发热和冷中子增益,建立了一整套计算方法。对参考堆的验证计算证明了该方法的正确性和有效性。对影响CARR冷中子源核发热和冷中子增益的各种因素(如慢化剂、冷包材料、冷包形状等)进行了计算和优化选择。结果表明:在核发热量较小的条件下获得了较好的冷中子增益。 相似文献