全文获取类型
收费全文 | 128442篇 |
免费 | 3696篇 |
国内免费 | 2293篇 |
专业分类
电工技术 | 3351篇 |
技术理论 | 3篇 |
综合类 | 1797篇 |
化学工业 | 14784篇 |
金属工艺 | 7127篇 |
机械仪表 | 4794篇 |
建筑科学 | 4330篇 |
矿业工程 | 893篇 |
能源动力 | 3621篇 |
轻工业 | 7707篇 |
水利工程 | 1119篇 |
石油天然气 | 2100篇 |
武器工业 | 221篇 |
无线电 | 18907篇 |
一般工业技术 | 24934篇 |
冶金工业 | 26301篇 |
原子能技术 | 1634篇 |
自动化技术 | 10808篇 |
出版年
2023年 | 633篇 |
2022年 | 1183篇 |
2021年 | 1782篇 |
2020年 | 1362篇 |
2019年 | 1310篇 |
2018年 | 1880篇 |
2017年 | 1892篇 |
2016年 | 1892篇 |
2015年 | 1878篇 |
2014年 | 2658篇 |
2013年 | 6095篇 |
2012年 | 4166篇 |
2011年 | 5527篇 |
2010年 | 4656篇 |
2009年 | 5155篇 |
2008年 | 5272篇 |
2007年 | 5486篇 |
2006年 | 5047篇 |
2005年 | 4603篇 |
2004年 | 4037篇 |
2003年 | 3793篇 |
2002年 | 3455篇 |
2001年 | 3584篇 |
2000年 | 3426篇 |
1999年 | 3796篇 |
1998年 | 10031篇 |
1997年 | 6635篇 |
1996年 | 5247篇 |
1995年 | 3539篇 |
1994年 | 3101篇 |
1993年 | 2966篇 |
1992年 | 1830篇 |
1991年 | 1724篇 |
1990年 | 1604篇 |
1989年 | 1409篇 |
1988年 | 1239篇 |
1987年 | 899篇 |
1986年 | 919篇 |
1985年 | 930篇 |
1984年 | 819篇 |
1983年 | 709篇 |
1982年 | 709篇 |
1981年 | 688篇 |
1980年 | 575篇 |
1979年 | 477篇 |
1978年 | 415篇 |
1977年 | 533篇 |
1976年 | 958篇 |
1975年 | 299篇 |
1974年 | 276篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Juan Ding Yong He Shenhe Fu Xiangsheng Xie Haowen Liang Jianying Zhou 《Journal of the Society for Information Display》2022,30(2):159-167
Illumination is essential for modern life as colorful world is perceived by human visionary system. Display technology has been developing rapidly in recent decades, and the basic principle is related to the way that the image is illuminated and light is emanated. Traditional illumination is provided by different types of light sources, and the display image is visible in large viewing space until the emanating light decays to zero. This work proposes and demonstrates a novel illumination scheme for a display in which the displaying images are visible only in specific spatial regions. The directional backlight ensures the image propagating to specific direction while imaging visibility can be controlled to terminate abruptly at certain distance from the display screen while exerting no influence to nearby regions. The working principle for such an illumination scheme is the use of the modulated coherent directional backlight through an axicon lens. It is shown that the illumination scheme can robustly deliver carried image information to the designated viewing region. This new illumination scheme has many advantages over conventional illumination, including its usage for personal display, very lower energy consumption, as well as minimizing light hazard pollution. 相似文献
12.
Ava Kwong Cecilia Y. S. Ho Vivian Y. Shin Chun Hang Au Tsun Leung Chan Edmond S. K. Ma 《International journal of molecular sciences》2021,22(2)
The germline carrier of the BRCA1 pathogenic mutation has been well proven to confer an increased risk of breast and ovarian cancer. Despite BRCA1 biallelic pathogenic mutations being extremely rare, they have been reported to be embryonically lethal or to cause Fanconi anemia (FA). Here we describe a patient who was a 48-year-old female identified with biallelic pathogenic mutations of the BRCA1 gene, with no or very subtle FA-features. She was diagnosed with ovarian cancer and breast cancer at the ages of 43 and 44 and had a strong family history of breast and gynecological cancers. 相似文献
13.
Ting Cui Ling Xu Feng Ding Ahmed Alsaedi Tasawar Hayat 《International Journal of Adaptive Control and Signal Processing》2020,34(11):1658-1676
Parameter estimation plays an important role in the field of system control. This article is concerned with the parameter estimation methods for multivariable systems in the state-space form. For the sake of solving the identification complexity caused by a large number of parameters in multivariable systems, we decompose the original multivariable system into some subsystems containing fewer parameters and study identification algorithms to estimate the parameters of each subsystem. By taking the maximum likelihood criterion function as the fitness function of the differential evolution algorithm, we present a maximum likelihood-based differential evolution (ML-DE) algorithm for parameter estimation. To improve the parameter estimation accuracy, we introduce the adaptive mutation factor and the adaptive crossover factor into the ML-DE algorithm and propose a maximum likelihood-based adaptive differential evolution algorithm. The simulation study indicates the efficiency of the proposed algorithms. 相似文献
14.
15.
16.
J. Cochard P. Léonide J. Borgomano Y. Guglielmi G. Massonnat J-P. Rolando L. Marié A. Pasquier 《Journal of Petroleum Geology》2020,43(1):75-94
Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation. 相似文献
17.
18.
19.
20.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献