全文获取类型
收费全文 | 248959篇 |
免费 | 1665篇 |
国内免费 | 265篇 |
专业分类
电工技术 | 4039篇 |
综合类 | 91篇 |
化学工业 | 40321篇 |
金属工艺 | 15143篇 |
机械仪表 | 10061篇 |
建筑科学 | 4175篇 |
矿业工程 | 3759篇 |
能源动力 | 3872篇 |
轻工业 | 9696篇 |
水利工程 | 4087篇 |
石油天然气 | 13006篇 |
武器工业 | 28篇 |
无线电 | 20186篇 |
一般工业技术 | 62746篇 |
冶金工业 | 32130篇 |
原子能技术 | 11134篇 |
自动化技术 | 16415篇 |
出版年
2021年 | 2754篇 |
2019年 | 2730篇 |
2018年 | 5428篇 |
2017年 | 5709篇 |
2016年 | 6044篇 |
2015年 | 3051篇 |
2014年 | 5322篇 |
2013年 | 10079篇 |
2012年 | 7303篇 |
2011年 | 8926篇 |
2010年 | 7293篇 |
2009年 | 8103篇 |
2008年 | 8171篇 |
2007年 | 7855篇 |
2006年 | 6356篇 |
2005年 | 5561篇 |
2004年 | 5478篇 |
2003年 | 5299篇 |
2002年 | 5132篇 |
2001年 | 4947篇 |
2000年 | 4937篇 |
1999年 | 4252篇 |
1998年 | 7172篇 |
1997年 | 5831篇 |
1996年 | 4420篇 |
1995年 | 3653篇 |
1994年 | 3422篇 |
1993年 | 3623篇 |
1992年 | 3214篇 |
1991年 | 3359篇 |
1990年 | 3481篇 |
1989年 | 3369篇 |
1988年 | 3267篇 |
1987年 | 3260篇 |
1986年 | 3156篇 |
1985年 | 3314篇 |
1984年 | 3252篇 |
1983年 | 3146篇 |
1982年 | 2993篇 |
1981年 | 3045篇 |
1980年 | 3071篇 |
1979年 | 3257篇 |
1978年 | 3490篇 |
1977年 | 3460篇 |
1976年 | 3911篇 |
1975年 | 3209篇 |
1974年 | 3293篇 |
1973年 | 3341篇 |
1972年 | 2987篇 |
1971年 | 2754篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Markov decision processes (MDPs) may involve three types of delays. First, state information, rather than being available instantaneously, may arrive with a delay (observation delay). Second, an action may take effect at a later decision stage rather than immediately (action delay). Third, the cost induced by an action may be collected after a number of stages (cost delay). We de rive two results, one for constant and one for random delays, for reducing an MDP with delays to an MDP without delays, which differs only in the size of the state space. The results are based on the intuition that costs may be collected asynchronously, i.e., at a stage other than the one in which they are induced, as long as they are discounted properly. 相似文献
993.
We study the resistance of stainless steels with different contents of nitrogen after plasma-arc remelting to hydrogen degradation. The dependence of the mechanical properties of steels on the content of nitrogen is quite complicated, which is explained by changes in the phase composition. In the analyzed collection of steels (Kh18AN9, Kh20AN15, Kh18AG10, and Kh18AG15), Kh18AG15 steel has the best combination of the characteristics of strength and plasticity in hydrogen. 相似文献
994.
We focus on problems suited to the current evaluation infrastructure. The current limitation and trends in evaluation techniques are troublesome and could noticeably slow the rate of computer system innovation. New research has been recommended to help and make quantitative evaluations of computer systems manageable. We support research in the areas of simulation frameworks, benchmarking methodologies, analytic methods, and validation techniques. 相似文献
995.
Astadjov D.N. Isaev A.A. Petrash G.G. Ponomarev I.V. Sabotinov N.V. Vuchkov N.K. 《Quantum Electronics, IEEE Journal of》1992,28(10):1966-1969
Populations of CuI ground state, resonance, and metastable levels have been measured in CuBr laser with and without hydrogen additives. Temporal evolution and spatial distribution populations have been studied during the excitation pulse and also during the interpulse period of time. Addition of hydrogen results in a smaller rate of resonance and metastable levels excitation and smaller depopulation of the ground state during the excitation pulse. Repopulation of the ground state after the excitation pulse with hydrogen is much faster. CuBr molecules have been detected only in the periphery of the active zone. The density of the CuBr molecules had no noticeable change either during the excitation pulse or in the interpulse period 相似文献
996.
A novel approach to the derivation of Bažant’s size effect law is presented. Contrarily to the original Lagrangian derivation
which hinged on energetic consideration, a Newtonian approach based on local stress intensity factors is presented. Through
this approach, it is shown that Bažant’s size effect law is the first (and dominant) term in a series expansion for the nominal
stress. Furthermore, analytical expressions forB are derived for selected specimen geometries. 相似文献
997.
998.
999.
V. I. Evenko 《Chemical and Petroleum Engineering》1995,31(1):13-20
Translated from Khimicheskoe i Neftyannoe Mashinostroenie, No. 1, pp. 7–12, January, 1995. 相似文献
1000.
V. V. Skryabin 《Journal of Engineering Physics and Thermophysics》1991,60(3):307-309
It is proposed to calculate the maximum discharge velocity of a chemically neutral real gas out of a Laval nozzle with consideration given to the latent heat of vapor formation of the substance in the expansion of the gas within the nozzle to total condensation, as well as to calculate the parameters which correspond to the saturation line. An equation has been derived to determine the maximum velocity of the discharge gas from an energy point of view.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 3, pp. 391–393, March, 1991. 相似文献