全文获取类型
收费全文 | 299414篇 |
免费 | 1950篇 |
国内免费 | 317篇 |
专业分类
电工技术 | 4933篇 |
综合类 | 176篇 |
化学工业 | 46617篇 |
金属工艺 | 20185篇 |
机械仪表 | 12782篇 |
建筑科学 | 5187篇 |
矿业工程 | 4159篇 |
能源动力 | 4461篇 |
轻工业 | 10841篇 |
水利工程 | 4837篇 |
石油天然气 | 13582篇 |
武器工业 | 28篇 |
无线电 | 24865篇 |
一般工业技术 | 75953篇 |
冶金工业 | 35797篇 |
原子能技术 | 11627篇 |
自动化技术 | 25651篇 |
出版年
2021年 | 2753篇 |
2019年 | 2730篇 |
2018年 | 11108篇 |
2017年 | 11571篇 |
2016年 | 9576篇 |
2015年 | 3393篇 |
2014年 | 5400篇 |
2013年 | 10125篇 |
2012年 | 9110篇 |
2011年 | 14480篇 |
2010年 | 12770篇 |
2009年 | 12355篇 |
2008年 | 12724篇 |
2007年 | 13865篇 |
2006年 | 6401篇 |
2005年 | 7754篇 |
2004年 | 6914篇 |
2003年 | 6659篇 |
2002年 | 5699篇 |
2001年 | 5008篇 |
2000年 | 5076篇 |
1999年 | 4271篇 |
1998年 | 7177篇 |
1997年 | 5834篇 |
1996年 | 4436篇 |
1995年 | 3663篇 |
1994年 | 3450篇 |
1993年 | 3647篇 |
1992年 | 3231篇 |
1991年 | 3380篇 |
1990年 | 3481篇 |
1989年 | 3371篇 |
1988年 | 3274篇 |
1987年 | 3261篇 |
1986年 | 3158篇 |
1985年 | 3315篇 |
1984年 | 3253篇 |
1983年 | 3146篇 |
1982年 | 2994篇 |
1981年 | 3047篇 |
1980年 | 3073篇 |
1979年 | 3257篇 |
1978年 | 3490篇 |
1977年 | 3463篇 |
1976年 | 3915篇 |
1975年 | 3209篇 |
1974年 | 3294篇 |
1973年 | 3341篇 |
1972年 | 2989篇 |
1971年 | 2756篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
V. H. Novyts’kyi V. P. Havrylyuk D. D. Panasenko M. O. Kal’chuk V. Ya. Khoruzhyi 《Materials Science》2006,42(6):799-807
The positive influence of lead (2.5%) on the original structure of a cast composite of the Fe-Cr-Cu-C-Ti system, its wear
rate, friction coefficient, and the formation of secondary structures is established under the conditions of dry friction
and friction with boundary lubrication.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 73–80, November–December, 2006. 相似文献
992.
993.
The emission and conductivity characteristics of oxide cathodes depend largely on the activation process. In this paper, the electrical properties of new type of oxide cathodes for cathode ray tube (CRT) application, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes. The influence of the activation process over different durations has been investigated. A temperature of T=1425 K was chosen to be higher than the optimum cathode activation temperature (T=1200 K), and the other temperature of T=1125 K was lower than that. The electron activation energy (E) was found to vary in the range from 0.58 to 2.28 eV for cathodes activated at the higher temperature regime, and from 1.08 to 1.9 eV for those activated at the lower temperature regime. Scanning electron microscopy (SEM) and electron diffraction X-ray (EDX) analyses show a structural phase transformation in the oxide material that was activated at 1125 K for a period of 1-12 hours. The SEM mapping shows a large contamination of Ba in the top layer of oxide material. The activator agents tungsten and aluminum are found to penetrate into the BaO/spl bsol/SrO layer in two different ways. 相似文献
994.
The safe operation of VVéR reactors has been discussed throughout the entire design process, taking account of the normative
documentation, including the international requirements (IAEA, EUR). After the first domestic normative document “Basic principles
for securing the safety of nuclear power plants” was approved in 1973, work began on the reconstruction of the first-generation
VVéR-440 power-generating units. The measures taken to increase safety concerned all types of reactors VVéR-440 and-1000.
Information on implementing these measures is presented.
__________
Translated from Atomnaya énergiya, Vol. 101, No. 2, pp. 87–93, August, 2006. 相似文献
995.
V. P. Vasilevskii M. N. Mikhailov A. A. Petrov M. I. Rozhdestvenskii Yu. M. Cherkashov 《Atomic Energy》2006,100(4):295-301
The basic stages and directions of upgrading and reconstruction of the power-generating units of nuclear power plants with
RBMK reactors over a period of 20 yr since the Chernobyl accident are reflected in this paper. The greatest amount of work
was done in 1986–1990 on all units with RBMK-1000 and-1500 reactors which were operating at that time in the USSR. The purpose
of the upgrade was to improve the neutron-physical characteristics of the reactor cores, increase the response speed of the
safety and control system and decrease the positive effect of water outflow from the cooling loop of this system, increase
the flow capacity of the systems performing emergency discharge of the steam-gas mixture from the reactor, and improve the
basic operating documentation.
The subsequent stages of the upgrading and reconstruction concerned mainly the first-generation power-generating units (Nos.
1 and 2 units of the Leningrad and Kursk nuclear power plants). These works were performed to make the power-generating units
conform to the requirements of the modern normative documents on safety and allow for the possibility of these units to remain
in operation after the nominal 30-yr service life has been exhausted.
__________
Translated from Atomnaya énergiya, Vol. 100, No. 4, pp. 312–320, April, 2006. 相似文献
996.
McIntyre H. Wendell D. Lin K.J. Kaushik P. Seshadri S. Wang A. Sundararaman V. Ping Wang Song Kim Hsu W.-J. Hee-Choul Park Levinsky G. Jiejun Lu Chirania M. Heald R. Lazar P. Dharmasena S. 《Solid-State Circuits, IEEE Journal of》2005,40(1):52-59
A 4-MB L2 data cache was implemented for a 64-bit 1.6-GHz SPARC(r) RISC microprocessor. Static sense amplifiers were used in the SRAM arrays and for global data repeaters, resulting in robust and flexible timing operation. Elimination of the global clock grid over the SRAM array saves power, enabled by combining the clock information with array select signals. Redundancy was implemented flexibly, with shift circuits outside the main data array for area efficiency. The chip integrates 315 million transistors and uses an 8-metal-layer 90-nm CMOS process. 相似文献
997.
DREAM (dynamic reflective asynchronous middleware) is a software framework for building asynchronous middleware from components, which we can assemble statically or dynamically (at deployment time or at runtime). DREAM's component library and set of tools lets us build, configure, and deploy middleware that implements various asynchronous communication paradigms, including message-passing, event-reaction, and publish-subscribe. We show how to use our framework to dynamically control resource consumption and concurrency. The performance of dynamically configurable MOMs built with the DREAM framework compares favorably to monolithic, functionally equivalent middleware 相似文献
998.
Study of direct and indirect naphtha recycling to a resid FCC unit for maximum propylene production 总被引:2,自引:0,他引:2
To satisfy the increasing propylene demand, direct and indirect naphtha recycling schemes around an existing resid fluid catalytic cracking (FCC) unit were investigated. To this aim, light cracked naphtha (LCN), heavy cracked naphtha (HCN) and a PolyNaphtha (PN) oligomerisation product were cracked under a wide range of operating conditions over a commercial Y zeolite based equilibrium catalyst. Experimental data were acquired in three different units: a fixed bed bench scale unit, a fixed fluidised bed unit and an adiabatic circulating fluidised bed pilot plant. It was shown that FCC naphthas require high operating severities to crack, and that even then their conversion remains relatively moderate. Hence, direct recycling to the main riser does not seem a viable pathway to increase propylene product. Feeding FCC naphthas to a second reaction zone operating at high severity allows to increase the propylene yield in a significant manner. Increasing conversion, however, not only leads to higher LPG and propylene yields, but also results in very high dry gas yields. An alternative scheme was proposed, in which the olefinic C4 and C5 fractions are converted into a naphtha fraction through oligomerisation in a dedicated unit before being recracked in the secondary riser. As the highly olefinic oligomerised effluent mainly consist of dimerised and trimerised butenes and pentenes, this feed is more easily cracked and high conversions can be achieved. This indirect interconversion of butenes and pentenes into propylene therefore effectively allows to convert these butenes and pentenes into propylene, resulting in a significant increase in propylene yield. Each of the three main naphtha recycle options (directly to the main riser, directly to a secondary riser or indirectly via a light olefin oligomerisation unit) have been analysed and compared to a base case. In the evaluation of each of these schemes, all heat balance effects, both on the riser and the regenerator side, have been accounted for. The proposed process scheme with an indirect recycle via an oligomerisation unit enhances the already inherent flexibility of the FCC unit. The naphtha recycle can be turned on or off, the second reaction zone can be used to crack naphtha or to crack resid feed to maximise throughput, while the effluent of the oligomerisation unit can be recycled to the FCC unit for propylene production or hydrogenated and sent to gasoline and kerosene pool. 相似文献
999.
The effect of nucleator additives on the surface relief and the degree of crystallization of material intended for the dentine and enamel layers of artificial denture is considered. It is established that hydroxyapatite additive is optimal for producing the required relief in the prime and dentine layers. 相似文献
1000.
The operating principles of automated control system for glass-melting furnaces and drums for drying sand and dolomite are described.__________Translated from Steklo i Keramika, No. 4, pp. 20 – 22, April, 2005. 相似文献