全文获取类型
收费全文 | 3773篇 |
免费 | 105篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 39篇 |
综合类 | 20篇 |
化学工业 | 916篇 |
金属工艺 | 59篇 |
机械仪表 | 63篇 |
建筑科学 | 192篇 |
矿业工程 | 11篇 |
能源动力 | 70篇 |
轻工业 | 276篇 |
水利工程 | 19篇 |
石油天然气 | 6篇 |
无线电 | 230篇 |
一般工业技术 | 593篇 |
冶金工业 | 831篇 |
原子能技术 | 32篇 |
自动化技术 | 523篇 |
出版年
2021年 | 28篇 |
2020年 | 19篇 |
2019年 | 38篇 |
2018年 | 41篇 |
2017年 | 42篇 |
2016年 | 55篇 |
2015年 | 66篇 |
2014年 | 83篇 |
2013年 | 152篇 |
2012年 | 138篇 |
2011年 | 164篇 |
2010年 | 146篇 |
2009年 | 147篇 |
2008年 | 160篇 |
2007年 | 149篇 |
2006年 | 129篇 |
2005年 | 121篇 |
2004年 | 112篇 |
2003年 | 81篇 |
2002年 | 79篇 |
2001年 | 91篇 |
2000年 | 81篇 |
1999年 | 100篇 |
1998年 | 207篇 |
1997年 | 125篇 |
1996年 | 99篇 |
1995年 | 84篇 |
1994年 | 72篇 |
1993年 | 63篇 |
1992年 | 57篇 |
1991年 | 58篇 |
1990年 | 66篇 |
1989年 | 72篇 |
1988年 | 55篇 |
1987年 | 56篇 |
1986年 | 35篇 |
1985年 | 37篇 |
1984年 | 31篇 |
1983年 | 39篇 |
1982年 | 32篇 |
1981年 | 29篇 |
1980年 | 39篇 |
1979年 | 27篇 |
1978年 | 37篇 |
1977年 | 32篇 |
1976年 | 58篇 |
1975年 | 37篇 |
1974年 | 37篇 |
1973年 | 37篇 |
1972年 | 18篇 |
排序方式: 共有3880条查询结果,搜索用时 31 毫秒
31.
A yeast mitochondrial translation initiation codon mutation affecting the gene for cytochrome oxidase subunit III (COX3) was partially suppressed by a spontaneous nuclear mutation. The suppressor mutation also caused cold-sensitive fermentative growth on glucose medium. Suppression and cold sensitivity resulted from inactivation of the gene product of RPS18A, one of two unlinked genes that code the essential cytoplasmic small subunit ribosomal protein termed S18 in yeast. The two S18 genes differ only by 21 silent substitutions in their exons; both are interrupted by a single intron after the 15th codon. Yeast S18 is homologous to the human S11 (70% identical) and the Escherichia coli S17 (35% identical) ribosomal proteins. This highly conserved family of ribosomal proteins has been implicated in maintenance of translational accuracy and is essential for assembly of the small ribosomal subunit. Characterization of the original rps18a-1 missense mutant and rps18a delta and rps18b delta null mutants revealed that levels of suppression, cold sensitivity and paromomycin sensitivity all varied directly with a limitation of small ribosomal subunits. The rps18a-1 mutant was most affected, followed by rps18a delta then rps18b delta. Mitochondrial mutations that decreased COX3 expression without altering the initiation codon were not suppressed. This allele specificity implicates mitochondrial translation in the mechanism of suppression. We could not detect an epitope-tagged variant of S18 in mitochondria. Thus, it appears that suppression of the mitochondrial translation initiation defect is caused indirectly by reduced levels of cytoplasmic small ribosomal subunits, leading to changes in either cytoplasmic translational accuracy or the relative levels of cytoplasmic translation products. 相似文献
32.
Distributed Multirobot Exploration and Mapping 总被引:3,自引:0,他引:3
Fox D. Ko J. Konolige K. Limketkai B. Schulz D. Stewart B. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2006,94(7):1325-1339
Efficient exploration of unknown environments is a fundamental problem in mobile robotics. We present an approach to distributed multirobot mapping and exploration. Our system enables teams of robots to efficiently explore environments from different, unknown locations. In order to ensure consistency when combining their data into shared maps, the robots actively seek to verify their relative locations. Using shared maps, they coordinate their exploration strategies to maximize the efficiency of exploration. This system was evaluated under extremely realistic real-world conditions. An outside evaluation team found the system to be highly efficient and robust. The maps generated by our approach are consistently more accurate than those generated by manually measuring the locations and extensions of rooms and objects. 相似文献
33.
A dielectric model comprising band gap transitions and free electron excitations (Drude model) is successfully applied to simulate transmittance spectra of ZnO films doped with 0.5%, 1% and 2% Al. The Drude formula contains a frequency-dependent damping term in order to get a good fit in the visible spectral region. Useful physical parameters obtained from the fit are electron density and mobility within the grains, film thickness, band gap and refractive index. The optically determined film thickness agrees with that obtained with the stylus method within 2%. The optically determined electronic parameters are compared with those obtained by electrical measurements. Contrary to thin In2O3:Sn films, the Drude mobility inside the grains is similar to the direct current Hall mobility indicating more perfect film growth without forming pronounced grain boundaries. Maximum value is 35 cm2/V s. The effective electron mass is estimated to be about 0.6 of the free electron mass. The refractive index at 550 nm decreases with increasing electron density. 相似文献
34.
Dieter Ullmann 《NTM》2006,14(1):1-8
A lot of publications on the acoustics of theatres and churches were published around the turn of the 18th to the 19th century.The
authors were architects who were interested in acoustical problems. Chladni was the first physicist who published on the acoustics
of rooms, he introduced the term “reverberation” into this field. His publications on this subject are reviewed. They have
been the basis for the great progress of room acoustics since 1900.
Zum 250. Geburtstag des Gelehrten 相似文献
Zum 250. Geburtstag des Gelehrten 相似文献
35.
Slab casting for hot rolled steel and strip casting using the twin roll casting (TRC) method are compared in terms of inclusions evolution. There are differences of the processes, mainly the use of casting flux in CC of slabs, or pool shapes and sizes in terms of TRC, particularly when roll diameters vary. The inclusion evolution of alumina in a low carbon steel grade was estimated. By modelling particle growth rate, coagulation and deposition, an ‘agglomeration index’ was created to describe the probability of clogging in the SEN. Similarly the growth of secondary alumina precipitation during cooling of the melt in the pool by Stokes collision and turbulent collision was estimated in terms of forming large particles which are able to float‐up. Influences of melt superheat or caster size were taken into account. 相似文献
36.
Reinhold Kleiner Dieter Koelle John Clarke 《Journal of Low Temperature Physics》2007,149(5-6):230-260
We investigate the characteristics and noise performance of rf Superconducting Quantum Interference Devices (SQUIDs) by solving
the corresponding Langevin equations numerically and optimizing the model parameters with respect to noise energy. After introducing
the basic concepts of the numerical simulations, we give a detailed discussion of the performance of the SQUID as a function
of all relevant parameters. The best performance is obtained in the crossover region between the dispersive and dissipative
regimes, characterized by an inductance parameter β′
L
≡2π
LI
0/Φ
0≈1; L is the loop inductance, I
0 the critical current of the Josephson junction, and Φ
0 the flux quantum. In this regime, the lowest (intrinsic) values of noise energy are a factor of about 2 above previous estimates
based on analytical approaches. However, several other analytical predictions, such as the inverse proportionality of the
noise energy on the tank circuit quality factor and the square of the coupling coefficient between the tank circuit and the
SQUID loop, could not be well reproduced. The optimized intrinsic noise energy of the rf SQUID is superior to that of the
dc SQUID at all temperatures. Although for technologically achievable parameters this advantage shrinks, particularly at low
thermal fluctuation levels, we give examples for realistic parameters that lead to a noise energy comparable to that of the
dc SQUID even in this regime.
相似文献
37.
Alexander Babich Konstantinos Mavrommatis Dieter Senk Heinrich Wilhelm Gudenau 《国际钢铁研究》2004,75(7):428-432
This contribution deals with advanced educational technologies needed to equip customers from higher education institutions, research and industry with efficient tools supporting their work and operating new skills‐training methods. The challenges are reducing the training costs, improving quality and increasing the number of graduates in engineering departments. The concept of a Virtual Lab based on the combination of various teaching methods and tools is presented. Principles of mathematisation in metallurgical education and training are discussed. An example of online course designed in the form of Virtual Lab is demonstrated. 相似文献
38.
Market for FRP grows in the power industry 总被引:2,自引:0,他引:2
Debbie Fox 《Reinforced Plastics》2008,52(9):40-43
39.
40.