全文获取类型
收费全文 | 260895篇 |
免费 | 7669篇 |
国内免费 | 3490篇 |
专业分类
电工技术 | 7619篇 |
技术理论 | 2篇 |
综合类 | 4230篇 |
化学工业 | 37334篇 |
金属工艺 | 11160篇 |
机械仪表 | 9506篇 |
建筑科学 | 8715篇 |
矿业工程 | 2883篇 |
能源动力 | 6333篇 |
轻工业 | 18347篇 |
水利工程 | 2764篇 |
石油天然气 | 6755篇 |
武器工业 | 531篇 |
无线电 | 34866篇 |
一般工业技术 | 44941篇 |
冶金工业 | 48376篇 |
原子能技术 | 4188篇 |
自动化技术 | 23504篇 |
出版年
2023年 | 1418篇 |
2022年 | 2552篇 |
2021年 | 3825篇 |
2020年 | 2894篇 |
2019年 | 3029篇 |
2018年 | 4033篇 |
2017年 | 4203篇 |
2016年 | 4062篇 |
2015年 | 3951篇 |
2014年 | 5618篇 |
2013年 | 11539篇 |
2012年 | 8481篇 |
2011年 | 10520篇 |
2010年 | 8581篇 |
2009年 | 9262篇 |
2008年 | 9498篇 |
2007年 | 9454篇 |
2006年 | 9271篇 |
2005年 | 8313篇 |
2004年 | 7344篇 |
2003年 | 6868篇 |
2002年 | 6465篇 |
2001年 | 6734篇 |
2000年 | 6457篇 |
1999年 | 7133篇 |
1998年 | 17093篇 |
1997年 | 11559篇 |
1996年 | 9057篇 |
1995年 | 6716篇 |
1994年 | 5830篇 |
1993年 | 5581篇 |
1992年 | 3803篇 |
1991年 | 3617篇 |
1990年 | 3471篇 |
1989年 | 3245篇 |
1988年 | 2962篇 |
1987年 | 2354篇 |
1986年 | 2398篇 |
1985年 | 2664篇 |
1984年 | 2342篇 |
1983年 | 2083篇 |
1982年 | 1929篇 |
1981年 | 2059篇 |
1980年 | 1811篇 |
1979年 | 1668篇 |
1978年 | 1663篇 |
1977年 | 2026篇 |
1976年 | 2714篇 |
1975年 | 1431篇 |
1974年 | 1371篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
A hybrid furnace, which allows the simultaneous application of microwave and radiant energy, has been used to investigate the sintering of partially stabilized zirconia (doped with 3 mol % yttria). Microwave-enhanced sintering is clearly demonstrated with densification occurring at a lower temperature when a high-frequency electric field is applied. By considering the variation of electric field strength with furnace temperature, this enhancement is shown to be non-thermal in nature, being dependent on the electric field strength and not the power density (heating) of the microwaves. This dependence on electric field is consistent with an additional driving force term in the equation which describes the diffusion of vacancies through the material during sintering. 相似文献
942.
The fatigue test is a time-consuming experiment. The accelerated fatigue testing technique is a dream for all researchers. In our laboratory, a vibratory fatigue testing machine was built, which works at 20 kHz for R = −1 and permits to carry out tests at cryogenic temperature. This is an automatic machine controlled by a PC computer. By using this apparatus, it is easy to save time by 400 to 500 times and a lot of liquid air (nitrogen or helium).
A titanium alloy, Ti6A14V (TA6V PQ french mark), was tested in liquid nitrogen (77 K) with this machine for S---N curve. At the same time, other fatigue tests were performed in SEP (Société Européenne de Propulsion) in conventional fatigue for the same material and the same conditions except the frequency. The comparison shows that the results are coherent. 相似文献
943.
A broadband power meter calibration system based on a newly constructed coaxial calorimeter has been developed in the frequency region 10 MHz-40 GHz. The RF power is measured as the difference of DC power supplied to the calorimeter built-in heater in the RF load, when RF is turned off and on, holding an isothermal control between the RF load and a temperature reference. To minimize the error due to the adiabatic coaxial waveguide, we devised a new method utilizing its output port as a test port. The evaluations showed a calibration uncertainty of (0.28-2.2)% expressed by one standard deviation at the 1 mW level in the full band 相似文献
944.
International scientific collaboration is very sensitive to political and economic changes in a country or a geopolitical region. Collaboration in research is reflected by the corresponding coauthorship of the published results which can be analysed with the help of bibliometric methods. Based on data from theScience Citation Index (SCI), the change of annual international coauthorship patterns ofBulgaria, Czechoslovakia, Hungary, Poland andRomania have been analysed for the periods 1981–1985 and 1984–1993, respectively. It is shown that international collaboration was not developing similarly in the countries under study. Whilst scientific communities of Hungary and Poland have already been opening in the early 80s, the international collaboration of the other East-European countries was still dominated by COMECON relations till 1989. As expected, since 1990 an increasing scientific collaboration with highly developed countries can be observed in all five countries. At the same time, scientific collaboration with the former communist countries shows a clear decline. The great share of international co-authorship links is some countries reflect various tendencies part of which are interpreted with the help of a cardiologic model. 相似文献
945.
946.
The photoconductive properties of a carotenoid polyene,β-Apo-8′ carotenal in polycrystalline form has been studied. The growth of the photocurrent shows an overshoot in the growth-time
curve before steady state value is attained. This behaviour of photocurrent is proposed to be due to higher value of recombination
coefficient than trapping coefficient. From the temperature dependence study it is observed that the steady state photocurrent,
at first increases with increase of temperature, attains a maximum at a particular temperatureT
max and then decreases with temperature. TheT
max value agrees with the temperature above and below which steady state photocurrent is attained differently. Monomolecular
and bimolecular recombination processes at two temperature regimes are proposed to account for the observed behaviour. The
dependence of photocurrent with excitation light intensity and wavelength study provide information on the carrier generation
processes. The fast decay of photocurrent have been observed at different temperatures and from this study the decay constant
is calculated and it is found to be temperature independent. 相似文献
947.
Hydrogen is the lightest element in nature, and so, its detection and quantitative analysis is difficult by the conventional
methods utilized for other elements. In the recent years the technique of elastic recoil detection analysis (ERD) using 1–2
MeV He+ beam has been developed to quantitatively and simultaneously analyze hydrogen and its isotopes in solids. Such a facility
has been set up using the 2 MeV Van-de-Graaff accelerator at IIT Kanpur. It facilitates H and D analysis in a material up
to a depth of ∼ 1μm with a detection sensitivity of 0·1 at.% and depth resolution of about 300 ?. The application potential of this setup is
illustrated by presenting the results of measurements performed on Al:H:D systems prepared by plasma source ion implantation
and highT
c YBCO pellets exposed to humid atmosphere. 相似文献
948.
The effect of a realistic residual stress field on the predicted initiation of brittle and ductile fracture in a pressure and axially loaded circumferentially cracked pipe is examined using finite element analysis, micromechanical models of fracture initiation, andJ-Q theory. The study confirms that residual stresses contribute to the driving force and reduce fracture loads early in the loading history. In addition, results show that the residual stresses severely alter theJ-value (i.e., fracture toughness) predicted for the onset of brittle fracture. The reason for this decrease is found to be the increase in constraint generated by the residual stress field. In contrast, the effect of residual stresses on the ductile fracture initiation toughness is shown to be negligible. kw]Key words kw]residual stress kw]fracture initiation kw]micromechanics 相似文献
949.
950.