全文获取类型
收费全文 | 10571篇 |
免费 | 1389篇 |
国内免费 | 620篇 |
专业分类
电工技术 | 519篇 |
技术理论 | 1篇 |
综合类 | 1125篇 |
化学工业 | 1368篇 |
金属工艺 | 327篇 |
机械仪表 | 855篇 |
建筑科学 | 1509篇 |
矿业工程 | 258篇 |
能源动力 | 651篇 |
轻工业 | 661篇 |
水利工程 | 376篇 |
石油天然气 | 581篇 |
武器工业 | 184篇 |
无线电 | 602篇 |
一般工业技术 | 1259篇 |
冶金工业 | 611篇 |
原子能技术 | 291篇 |
自动化技术 | 1402篇 |
出版年
2024年 | 142篇 |
2023年 | 147篇 |
2022年 | 268篇 |
2021年 | 306篇 |
2020年 | 332篇 |
2019年 | 332篇 |
2018年 | 323篇 |
2017年 | 359篇 |
2016年 | 447篇 |
2015年 | 464篇 |
2014年 | 683篇 |
2013年 | 911篇 |
2012年 | 890篇 |
2011年 | 931篇 |
2010年 | 642篇 |
2009年 | 666篇 |
2008年 | 611篇 |
2007年 | 700篇 |
2006年 | 560篇 |
2005年 | 535篇 |
2004年 | 399篇 |
2003年 | 317篇 |
2002年 | 259篇 |
2001年 | 245篇 |
2000年 | 213篇 |
1999年 | 118篇 |
1998年 | 105篇 |
1997年 | 94篇 |
1996年 | 75篇 |
1995年 | 52篇 |
1994年 | 47篇 |
1993年 | 38篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1984年 | 11篇 |
1979年 | 11篇 |
1966年 | 10篇 |
1965年 | 13篇 |
1964年 | 17篇 |
1963年 | 12篇 |
1959年 | 14篇 |
1957年 | 15篇 |
1956年 | 11篇 |
1955年 | 15篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Kraut Robert; Olson Judith; Banaji Mahzarin; Bruckman Amy; Cohen Jeffrey; Couper Mick 《Canadian Metallurgical Quarterly》2004,59(2):105
As the Internet has changed communication, commerce, and the distribution of information, so too it is changing psychological research. Psychologists can observe new or rare phenomena online and can do research on traditional psychological topics more efficiently, enabling them to expand the scale and scope of their research. Yet these opportunities entail risk both to research quality and to human subjects. Internet research is inherently no more risky than traditional observational, survey, or experimental methods. Yet the risks and safeguards against them will differ from those characterizing traditional research and will themselves change over time. This article describes some benefits and challenges of conducting psychological research via the Internet and offers recommendations to both researchers and institutional review boards for dealing with them. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
32.
33.
Cheng-Rong Yu Manoj Kumar Yadav Minkyung Kang Yingyos Jittayasothorn Lijin Dong Charles E. Egwuagu 《International journal of molecular sciences》2022,23(15)
Interleukin-27 is constitutively secreted by microglia in the retina or brain, and upregulation of IL-27 during neuroinflammation suppresses encephalomyelitis and autoimmune uveitis. However, while IL-35 is structurally and functionally similar to IL-27, the intrinsic roles of IL-35 in CNS tissues are unknown. Thus, we generated IL-35/YFP-knock-in reporter mice (p35-KI) and demonstrated that photoreceptor neurons constitutively secrete IL-35, which might protect the retina from persistent low-grade inflammation that can impair photoreceptor functions. Furthermore, the p35-KI mouse, which is hemizygous at the il12a locus, develops more severe uveitis because of reduced IL-35 expression. Interestingly, onset and exacerbation of uveitis in p35-KI mice caused by extravasation of proinflammatory Th1/Th17 lymphocytes into the retina were preceded by a dramatic decrease of IL-35, attributable to massive death of photoreceptor cells. Thus, while inflammation-induced death of photoreceptors and loss of protective effects of IL-35 exacerbated uveitis, our data also suggest that constitutive production of IL-35 in the retina might have housekeeping functions that promote sterilization immunity in the neuroretina and maintain ocular immune privilege. 相似文献
34.
《Fusion Engineering and Design》2014,89(7-8):932-936
Measurement and calculations of long-lived gamma-emitting radionuclide activity forming in the fission reactor fast neutron field were done, for some ITER construction steels. The activation was conducted in fast neutron irradiation channel of the MARIA research fission reactor (Poland). The dimensions of steel samples were 10 mm × 10 mm × 1 mm and mass was approximately 0.8 g. The neutron flux density was measured by means of activation foil method and unfolding technique; fraction of neutrons above 1 keV was 95%. The activation lasted 242 h and cooling took 100 days; the mean neutron flux density was 2.9E12 n/(cm2 s) (neutrons above 500 keV are 53% of total) whereas total fluency 2.53E18 cm−2. The activity measurements were done by means of gamma-ray spectrometry. Activity calculations were done by means of FISPACT-II code using the activation libraries EAF-2010 and TENDL-2011 and experimentally determined neutron flux. Measured activity of long-lived gamma emitting radionuclides was, in average, about 6.3 MBq/g 100 days after activation; the dominant radionuclides were 58Co and 54Mn (about 81% and 14% of total activity respectively). The C/E ratio differs for particular radionuclides and is in the range 0.86–0.92 for 51Cr, 0.93–1.21 for 54Mn, 0.77–0.98 for 57Co, 0.91–1.21 for 58Co, 1.17–1.27 for 59Fe, and 1.75–2.44 for 60Co. 相似文献
35.
Rabah Djedjig Salah-Eddine OuldboukhitineRafik Belarbi Emmanuel Bozonnet 《International Communications in Heat and Mass Transfer》2012
This paper describes a dynamic model of transient heat and mass transfer across a green roof component. The thermal behavior of the green roof layers is modeled and coupled to the water balance in the substrate that is determined accounting for evapotranspiration. The water balance variations over time directly impact the physical properties of the substrate and the evapotranspiration intensity. This thermal and hydric model incorporates wind speed effects within the foliage through a new calculation of the resistance to heat and mass transfer within the leaf canopy. The developed model is validated with experimental data from a one-tenth-scale green roof located at the University of La Rochelle. A comparison between the numerical and the experimental results demonstrates the accuracy of the model for predicting the substrate temperature and water content variations. The heat and mass transfer mechanisms through green roofs are analyzed and explained using the modeled energy balances, and parametric studies of green roof behavior are presented. A surface temperature difference of up to 25 °C was found among green roofs with a dry growing medium or a saturated growing medium. Furthermore, the thermal inertia effects, which are usually simplified or neglected, are taken into account and shown to affect the temperature and flux results. This study highlights the importance of a coupled evapotranspiration process model for the accurate assessment of the passive cooling effect of green roofs. 相似文献
36.
37.
国内外相关研究均显示同轴双向回转可有效降低钻具振动和提高破岩效率,但双向回转相对传统单向回转的钻进效率的提升水平研究较少。据此,本文建立双向回转钻头以及单向回转钻头与岩石相互作用的有限元模型,以破岩比功作为评价指标量化比较分析了2种钻头的破岩效率。通过定义双向钻头内外壁尺寸差、内外钻头的间隙、内钻头壁厚与双向钻头内外壁尺寸差之比、内外钻头转速比和内外钻头底部高度差5种核心参数,并设计正交试验完成了仿真分析。结果显示,内外钻头高度差与内外钻头间隙对于破岩比功影响比较小,内外钻头尺寸差、内外钻头转速比和内钻头壁厚与双向钻头内外尺寸差之比对破岩比功影响显著。 相似文献
38.
评述了首次实现星问光学连接的欧洲空间局(ESA)的SILEX计划的检测与验证方法,相信对我国星间光通信技术的研究与发展具有一定的促进作用。 相似文献
39.
Anoire Ben Jdidia Alain Bellacicco Taissir Hentati Maher Barkallah Mohamed Taoufik Khabou Alain Rivier 《中国工程学刊》2019,42(5):377-384
The accurate evaluation of electrical energy demanded by a CNC toolpath during a machining process is essential to determine its efficiency. Actually, the dynamic behavior of cutting forces seems to be neglected by investigators despite its influence on the consumed cutting energy during a face milling operation. This paper aims to investigate the effect of dynamic behavior of the machining system in order to take into account the dynamic response of the cutting forces on the axis feed power prediction. A dynamic cutting power model is developed in order to predict the consumed cutting energy. A parametric study is performed in order to show the impact of cutting conditions on the consumed energy values. The numerical results are compared to experimental ones. 相似文献
40.
When using a model to predict the behavior of a physical system of interest, engineers must be confident that, under the conditions
of interest, the model is an adequate representation of the system. The process of building this confidence is called model
validation. It requires that engineers have knowledge about the system and conditions of interest, properties of the model
and their own tolerance for uncertainty in the predictions. To reduce time and costs, engineers often reuse preexisting models
that other engineers have developed. However, if the user lacks critical parts of this knowledge, model validation can be
as time consuming and costly as developing a similar model from scratch. In this article, we describe a general process for
performing model validation for reused behavioral models that overcomes this problem by relying on the formalization and exchange
of knowledge. We identify the critical elements of this knowledge, discuss how to represent it and demonstrate the overall
process on a simple engineering example.
相似文献
Christiaan J. J. ParedisEmail: |