全文获取类型
收费全文 | 12176篇 |
免费 | 1530篇 |
国内免费 | 693篇 |
专业分类
电工技术 | 391篇 |
技术理论 | 4篇 |
综合类 | 1001篇 |
化学工业 | 2044篇 |
金属工艺 | 1389篇 |
机械仪表 | 974篇 |
建筑科学 | 1220篇 |
矿业工程 | 608篇 |
能源动力 | 494篇 |
轻工业 | 427篇 |
水利工程 | 694篇 |
石油天然气 | 424篇 |
武器工业 | 526篇 |
无线电 | 341篇 |
一般工业技术 | 2415篇 |
冶金工业 | 689篇 |
原子能技术 | 211篇 |
自动化技术 | 547篇 |
出版年
2024年 | 72篇 |
2023年 | 247篇 |
2022年 | 379篇 |
2021年 | 488篇 |
2020年 | 530篇 |
2019年 | 398篇 |
2018年 | 445篇 |
2017年 | 511篇 |
2016年 | 565篇 |
2015年 | 589篇 |
2014年 | 833篇 |
2013年 | 1031篇 |
2012年 | 853篇 |
2011年 | 963篇 |
2010年 | 700篇 |
2009年 | 618篇 |
2008年 | 611篇 |
2007年 | 685篇 |
2006年 | 636篇 |
2005年 | 520篇 |
2004年 | 433篇 |
2003年 | 349篇 |
2002年 | 296篇 |
2001年 | 293篇 |
2000年 | 255篇 |
1999年 | 209篇 |
1998年 | 163篇 |
1997年 | 130篇 |
1996年 | 131篇 |
1995年 | 100篇 |
1994年 | 101篇 |
1993年 | 57篇 |
1992年 | 45篇 |
1991年 | 36篇 |
1990年 | 41篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1965年 | 1篇 |
1959年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
1.
大坝运行监测易受自然环境和监测条件影响,存在时间和空间上的变异性,监测数据具有不确定性。以云理论的随机性和不确定性分析方法为基础,并与空间数据辐射思想相结合,建立了云滴概率密度分布估计模型,然后导出云概率密度分布函数,依据样本监测数据推求母体空间数据的分布特征,并设计了基于逆向云算法云变换的计算程序。分析陆浑水库1979~1999年测压管监测数据和位移变形数据的云概率密度分布特征和云数字特征,得出了20 a来大坝的数据分布特征和运行状态。监测数据分析结果表明,云概率密度分布估计不仅能有效合理地分析大坝的运行状态,而且能够依据云数字特征来判断监测状态和监测环境的异常变化。
相似文献
2.
Wang Xuegang Yan Fengjie Yan Qian Li Xingeng 《Frontiers of Materials Science in China》2007,1(2):225-227
An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel
pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer
(EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base
metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base
metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the
mechanical properties of the joint are similar around the pipe. 相似文献
3.
In this paper, the test results of liquid injection impact on the performance of new alternative refrigerant mixtures such as: R-410A, R-507, R-407C and R-404A are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various liquid injection ratios. Performance tests were conducted according to the ARI/ASHRAE standards. The performance data demonstrated that as liquid injection ratio increases, compressor head pressure and discharge temperature decrease. This has a positive effect in protecting the compressor. The effect of liquid injection on mixture behaviour varies from one mixture to another depending upon the mixture's composition. Furthermore, liquid injection appears to have a significant influence on R-410A behaviour compared to the other mixtures in question. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
5.
Reinforced concrete slabs are among the most common structural elements. In spite of the large number of slabs designed and built, the effect of their details on their behavior under impact loads are not always appreciated or properly taken into account. This experimental study was aimed at understanding the dynamic behavior of structural concrete slabs under impact loading to improve the state of the art of protective design. This study investigated the effects of different types of slab reinforcements and the applied impact loads on the dynamic response and behavior of reinforced concrete slabs. 相似文献
6.
Hung‐Yee Shu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(3):273-280
Liquid–liquid two‐phase epoxidation from cyclohexene and cyclooctene in aqueous potassium peroxymonosulfate (commercially available as Oxone®) solution was studied as an application in pollution prevention. To avoid potential emissions of volatile organic compounds an aqueous solution was employed to replace the usual chlorinated solvents used in epoxide production. A droplet column reactor and stirred tank reactor were used to investigate two‐phase synthesis of epoxide. An aqueous Oxone® solution was used to oxidize a dispersion of alkene droplets and form epoxide. The study of aqueous epoxidation in both reactors showed that the epoxidation of alkenes can be represented as a first order reaction with respect to alkene. The salting out effect of Oxone® concentration was studied in both reactors and found to be very similar at optimal conditions. In comparing the two reactors, it was found that the droplet column reactor produces larger quantities of product per unit reactor volume for the same reaction time. The objective of this study is to provide an alternative reactor design and synthesis route that can meet pollution prevention goals. Copyright © 2004 Society of Chemical Industry 相似文献
7.
During the day, there are considerable variations in the climatic factors prevailing in these regions. This is especially so during the 24-hour daily cycle of the long, hot and dry summer (mid-May to midOctober). Such climatic conditions have had a considerable impact on the daily living pattern of family life in the same season, particularly in the urban areas. During the same 24-hour cycle, they have compelled the inhabitants to shift their living activities both vertically in section and horizontally in plan; they do this in pursuit of more acceptable, if not, desirable internal thermal environmental ambience. 相似文献
8.
对弹性杆与水下壳体接触冲击问题进行了研究,用有限元法模拟壳体,边界无法模拟无限域流体,通过温面上的耦合条件进行联立求解,文中给出了典型算例,并进行了有关讨论。 相似文献
9.
Quantitative analyses of flow and stage data, remote sensing and geographic information systems analysis, and field studies were used to assess the impact of dams and diversions on the point bar habitat of the Sacramento Valley Tiger Beetle (Cicindela hirticollis abrupta). The reaches of interest include sites of known historic populations of C. h. abrupta along the Sacramento River from approximately 8 km north of Colusa southward to the confluence with the Feather River and along the Feather River between Yuba City and its confluence with the Sacramento River. The results from this study show that construction of two major dams has altered flows such that prolonged and increased flows during summer, fall, and early winter have most likely disrupted life cycles, flooded larvae, drowned overwintering adults and led to high mortality. Additionally, habitat availability has decreased over time because point bars have decreased in number and area causing increased distances between populations and isolation of populations. Moreover, point bar armouring, channel scouring, altered flows, redirected flows through weirs, and lithologic controls have produced a bimodal distribution of mean grain sizes in the Sacramento River in which the more northern bars contain gravel deposits and more southern bars possess fine sands. These conditions negatively alter moisture retention and sediment compaction and, consequently, burrowing conditions needed by this tiger beetle. Additionally, more stabilized flows (reduced variability) and increased fine‐grained deposition have enabled development and encroachment of vegetation onto the sand bars. Finally, human stresses, such as foot traffic and vehicular traffic may have interfered with burrowing, ovipositing, and foraging. The combination of these stress factors has most likely led to a reduction in source populations and, ultimately, the apparent extirpation of the entire metapopulation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
10.