全文获取类型
收费全文 | 27646篇 |
免费 | 1733篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 449篇 |
综合类 | 73篇 |
化学工业 | 6436篇 |
金属工艺 | 776篇 |
机械仪表 | 671篇 |
建筑科学 | 1357篇 |
矿业工程 | 152篇 |
能源动力 | 659篇 |
轻工业 | 3405篇 |
水利工程 | 210篇 |
石油天然气 | 44篇 |
武器工业 | 1篇 |
无线电 | 1755篇 |
一般工业技术 | 6803篇 |
冶金工业 | 1487篇 |
原子能技术 | 261篇 |
自动化技术 | 4860篇 |
出版年
2023年 | 354篇 |
2022年 | 392篇 |
2021年 | 738篇 |
2020年 | 556篇 |
2019年 | 509篇 |
2018年 | 947篇 |
2017年 | 955篇 |
2016年 | 1115篇 |
2015年 | 941篇 |
2014年 | 1145篇 |
2013年 | 2169篇 |
2012年 | 1513篇 |
2011年 | 1777篇 |
2010年 | 1463篇 |
2009年 | 1388篇 |
2008年 | 1444篇 |
2007年 | 1381篇 |
2006年 | 1034篇 |
2005年 | 825篇 |
2004年 | 653篇 |
2003年 | 661篇 |
2002年 | 623篇 |
2001年 | 487篇 |
2000年 | 430篇 |
1999年 | 342篇 |
1998年 | 484篇 |
1997年 | 397篇 |
1996年 | 316篇 |
1995年 | 282篇 |
1994年 | 240篇 |
1993年 | 226篇 |
1992年 | 177篇 |
1991年 | 134篇 |
1990年 | 126篇 |
1989年 | 114篇 |
1988年 | 113篇 |
1987年 | 102篇 |
1986年 | 81篇 |
1985年 | 177篇 |
1984年 | 213篇 |
1983年 | 125篇 |
1982年 | 131篇 |
1981年 | 167篇 |
1980年 | 123篇 |
1979年 | 110篇 |
1978年 | 105篇 |
1977年 | 112篇 |
1976年 | 136篇 |
1975年 | 105篇 |
1973年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Ashraf A. Aly Tamer El Malah Esam A. Ishak Stefan Bräse 《Journal of Sulfur Chemistry》2016,37(2):141-147
Dithiacarbamates reacted with malononitrile dimer to give 1,4-dihydropyridine-2-thiols. The structures of the obtained products were proven by IR, mass, and NMR spectra and elemental analyses. The reaction mechanism is also discussed. 相似文献
992.
993.
Stefan Schachner Shengli Jin Dietmar Gruber Harald Harmuth 《Journal of the European Ceramic Society》2019,39(14):4384-4393
During operation, thermomechanical stresses occur in refractory linings. Under elevated stress and temperatures, these ceramics experience primary creep, which can further proceed to the secondary and tertiary creep stages. This necessitates a characterization of their three-stage creep behavior. Hence, two advanced uniaxial tensile and compressive creep testing devices are utilized. The Norton-Bailey creep equations and an inverse identification procedure are applied for the evaluation of the creep curves. To account for the full three-stage creep behavior in thermomechanical modelling activities, a creep-stage transition criterion is identified and subsequently implemented together with the Norton-Bailey creep-strain rate representations in a new developed creep model. The finite element simulation results from different creep testing procedures are in accordance with the corresponding experimental results of a magnesia-chromite refractory ceramic. The study also reveals the temperature-dependent asymmetrical creep behavior of the material in terms of the creep-strain rates and critical creep strains. 相似文献
994.
995.
996.
Christian Sandström Henrik Berglund Mats Magnusson 《Creativity & Innovation Management》2014,23(4):472-483
The literature on disruptive innovation has convincingly explained why many established firms encounter problems under conditions of discontinuous change. Incumbents fail to invest in new technologies that are not demanded by their existing customers. This argument is grounded in resource dependency theory and the associated assumption that existing customers control a firm's internal resource allocation processes. While the problem of disruptive innovation has been convincingly explained, there is still a need for managerial solutions. We argue that a key reason why such solutions are lacking can be found in the asymmetric assumptions made in the original theory of disruptive innovation. Specifically, we identify two related forms of asymmetry. First, the focal (incumbent) firm is treated as a collection of heterogeneous actors with different preferences, incentives and competencies, whereas firms in the surrounding environment are treated as if they contained no such heterogeneity. Second, the theory of disruptive innovation describes incumbents as controlled by their environment, but has failed to recognize that the environment can also be influenced. In this paper we argue that a more symmetric theory of disruptive innovation – i.e. one that treats all similar entities in the same way – opens up for a range of interesting managerial solutions. 相似文献
997.
Anshu Tyagi Florian Döring Hans-Ulrich Krebs Astrid Pundt 《International Journal of Hydrogen Energy》2017,42(35):22575-22582
The influence of a thin polycarbonate de-adhesion layer on the hydrogen concentration is studied on 30 nm vanadium films deposited on glass substrates, using electrochemical hydrogenography in an optical microscopy and scanning tunneling microscopy. It is shown that the optical reflection provides information about the de-adhesion morphology (buckles) while the optical transmission signal gives information about concentration and film thickness changes. Artificially patterned samples allow simultaneous studying adhered and de-adhered film parts, for similar mean concentrations. The optical data clearly show a different hydrogen behavior of the two parts. Data interpretation suggests higher local hydrogen content in the adhered film parts than for the detached films parts. Strong changes in the optical transmission of the adhered film parts can be attributed to strong morphological changes at the film surface. These changes are mainly attributed to grain sliding processes in the vanadium film. 相似文献
998.
This article analyzes the challenges of supporting continual changes of context information in Internet-of-Things applications. These applications require a constant flow of continuously changing information from sensor based sources in order to ensure a high quality-of-experience. However, an uncontrolled flow between sources and sinks on a global scale wastes resources, such as computational power, communication bandwidth, and battery time. In response to these challenges we present a general approach which focuses on four layers where we provide a proposed solution to each layer. We have realized the general model into a proof-of-concept implementation running on devices with limited resources, where we can moderate the information exchange based on relevance and sought after quality-of-experience by the applications. In conclusion, we evaluate our solution and present a summary of our experiences regarding the impact of continuously changing information on the Internet-of-Things. 相似文献
999.
1000.