全文获取类型
收费全文 | 3720篇 |
免费 | 122篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 216篇 |
综合类 | 4篇 |
化学工业 | 885篇 |
金属工艺 | 72篇 |
机械仪表 | 92篇 |
建筑科学 | 89篇 |
能源动力 | 148篇 |
轻工业 | 401篇 |
水利工程 | 11篇 |
石油天然气 | 1篇 |
无线电 | 314篇 |
一般工业技术 | 639篇 |
冶金工业 | 432篇 |
原子能技术 | 177篇 |
自动化技术 | 375篇 |
出版年
2023年 | 26篇 |
2022年 | 55篇 |
2021年 | 92篇 |
2020年 | 32篇 |
2019年 | 43篇 |
2018年 | 90篇 |
2017年 | 67篇 |
2016年 | 116篇 |
2015年 | 63篇 |
2014年 | 111篇 |
2013年 | 214篇 |
2012年 | 169篇 |
2011年 | 214篇 |
2010年 | 146篇 |
2009年 | 189篇 |
2008年 | 204篇 |
2007年 | 165篇 |
2006年 | 146篇 |
2005年 | 135篇 |
2004年 | 126篇 |
2003年 | 118篇 |
2002年 | 111篇 |
2001年 | 96篇 |
2000年 | 53篇 |
1999年 | 88篇 |
1998年 | 215篇 |
1997年 | 120篇 |
1996年 | 84篇 |
1995年 | 67篇 |
1994年 | 61篇 |
1993年 | 55篇 |
1992年 | 31篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 25篇 |
1986年 | 32篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 19篇 |
1976年 | 26篇 |
1973年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有3856条查询结果,搜索用时 15 毫秒
81.
82.
A quantum-inspired evolutionary algorithm (QEA) is proposed as a stochastic algorithm to perform combinatorial optimization
problems. The QEA is evolutionary computation that uses quantum bits and superposition states in quantum computation. Although
the QEA is a coarse-grained parallel algorithm, it involves many parameters that must be adjusted manually. This paper proposes
a new method, named pair swap, which exchanges each best solution information between two individuals instead of migration
in the QEA. Experimental results show that our proposed method is a simpler algorithm and can find a high quality solution
in the 0-1 knapsack problem.
This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January
25–27, 2007 相似文献
83.
Makoto Sakamoto Kaoru Kajisa Naoko Tomozoe Takao Ito Hiroshi Furutani Michio Kono Satoshi Ikeda 《Artificial Life and Robotics》2008,13(1):61-64
In 1997, C.R. Dyer and A. Rosenfeld introduced an acceptor on a two-dimensional pattern (or tape), called the pyramid cellular acceptor, and demonstrated that many useful recognition tasks are executed by pyramid cellular acceptors in time proportional to the
logarithm of the diameter of the input. They also introduced a bottom-up pyramid cellular acceptor which is a restricted version of the pyramid cellular acceptor, and proposed some interesting open problems of the bottom-up
pyramid cellular acceptors. On the other hand, we think that the study of threedimensional automata has been meaningful as
the computational model of three-dimensional information processing such as computer vision, robotics, and so forth. In this
paper, we investigate about bottom-up pyramid cellular acceptors with three-dimensional layers, and show their some accepting
powers.
This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January
31–February 2, 2008 相似文献
84.
Given a digraph (or an undirected graph) G=(V,E) with a set V of vertices v with nonnegative real costs w(v), and a set E of edges and a positive integer k, we deal with the problem of finding a minimum cost subset SV such that, for each vertex vV−S, there are k vertex-disjoint paths from S to v. In this paper, we show that the problem can be solved by a greedy algorithm in
time in a digraph (or in
time in an undirected graph), where n=|V| and m=|E|. Based on this, given a digraph and two integers k and ℓ, we also give a polynomial time algorithm for finding a minimum cost subset SV such that for each vertex vV−S, there are k vertex-disjoint paths from S to v as well as ℓ vertex-disjoint paths from v to S. 相似文献
85.
Tetsu Ando Hirokazu Ohsawa Tadahiro Ueno Hideki Kishi Yutaka Okamura Satoshi Hashimoto 《Journal of chemical ecology》1993,19(4):787-798
Although several sex pheromones of the family Geometridae have been characterized, investigations on Japanese species are limited. In order to obtain more information, screening using known sex pheromones and their analogs was carried out. The (Z,Z,Z)-3,6,9-triunsaturated and (Z,Z)-6,9-diunsaturated hydrocarbons with straight C19-C21 chains were synthesized by the Grignard coupling reaction as a key step starting from linolenic and linoleic acids, respectively. Oxidation of the homoconjugated trienes withm-chloroperoxybenzoic acid yielded a 111 mixture of three monoepoxy derivatives that could be separated by silica gel chromatography. The chemical structure of each positional isomer was confirmed using two-dimensional NMR techniques and MS measurements, which enabled characteristic fragment ions from the isomers to be identified. Field tests using lures incorporating only one of the above six hydrocarbons or nine epoxides were carried out in a forest in Tokyo. Consequently, attraction of male moths of 14 geometrid species in addition to four species in another family, the Noctuidae, was observed. It was concluded that hydrocarbons with a homoconjugated polyene system and the monoepoxy derivatives are important components of sex pheromones produced by Japanese lepidopterous insects, particularly the geometrid moths. 相似文献
86.
Humans and animals seek appropriate solutions to novel problems through trial-and-error (TE) actions and observation of their outcomes. Once an individual has obtained the knowledge (rule) to solve a problem, knowledge-based (KB) actions may be applied in a stereotypical manner. Solutions can thus be based on TE or KB actions. To characterize this learning process at the behavioral level, we developed a new cognitive task for a laboratory monkey (Macaca fuscata) to perform. In this task, a search array consisting of six elements of different colors was presented, one of which was the behaviorally relevant target. The target color was changed unpredictably with no instruction or signal, requiring the monkey to use a TE search strategy to find the target color. We found that once the monkey identified the relevant color by chance after a color change, correct performance increased in a step-like manner and at the same time, other response properties (reaction time and color-choice tendency) also changed discontinuously. These step-like alternations in behavioral performance may be attributed to the subject’s switching between TE and KB search strategies in the two phases. The present study has therefore provided behavioral evidence for the timing and manner of switching between search strategies during the process of updating knowledge. 相似文献
87.
Periodic flooding alters riverine vegetation community composition; moderate flood disturbance maintains communities at an early seral stage, whereas severe floods may remove entire communities. After disturbance, plants may recolonize riverbeds from refugia.Here, we investigated the morphological characteristics of refugia where riverine plants survived large floods. At three sites, plant communities growing on cobble-bars were surveyed, and the hydraulic characteristics of each site were analyzed. The populations of an indicator plant, Anaphalis margaritacea sub-species yedoensis (Franch. et Savat.) were assessed after major floods in 2004 and 2009. At each survey, the particle size and bed composition were measured, and the critical shear-stress required to move particles at each site was calculated. A one-dimensional flow and the average and local shear-stress at ten different discharges, including that of the largest flood were calculated. The results demonstrate that the A. margaritacea community is maintained at locations where the local shear-stress at peak discharge in large-floods does not exceed a critical value. These conditions were achieved in locations with particular morphological characteristics, where the river is not constrained by levees and is restricted by a downstream narrow-pass; in this reach river width increases with discharge thus limiting the increase in water depth with increasing discharge and allowing the establishment of refugia where plant species may survive large floods.Flooding and reestablishment from refugia maintain a characteristic riverbed community in equilibrium. 相似文献
88.
粒子网格混合方法模拟液滴夹带起始点 总被引:1,自引:0,他引:1
环状流动的特性对反应堆事故工况分析具有重要意义,本研究基于粒子网格混合方法对这一现象中的液滴夹带起始点问题进行了数值分析,利用网格求解流场,利用粒子模拟液膜及液滴的运动,探讨了气水流动大密度比情况下,不同流动方向,不同流体粘度,不同液膜厚度下的液滴夹带所需的临界气相流速,结果同经典关系式进行了对比,吻合良好.这一方法对于反应堆事故中的两相流动研究具有参考意义. 相似文献
89.
Full analysis of triglycerides of natural fats and oils has been investigated by the combination of argentation high performance
liquid chromatography (HPLC) with nonaqueous reversed phase (NARP) HPLC. An infrared detector was used in argentation HPLC,
because it indicated molar responsibility to all triglycerides. After peak trapping with argentation HPLC, each triglyceride
fraction was analyzed with NARP chromatography using the glyceride-selective post-column reactor detector. The results of
the analyses of triglycerides of palm oil and cocoa butter by the proposed method agreed well with those reported earlier. 相似文献
90.
The potential protection of Picea glehnii seedlings from damping-off by seed-epiphytic Penicillium species was investigated. We studied the chemical response of seed-epiphytic Penicillium species (Pen. cyaneum, Pen. damascenum, and Pen. implicatum) to Pythium vexans, a damping-off fungus, in vitro. Penicillium species were cultured singly or cocultured with Pyt. vexans for 14 or 18 d, and mycelial growth, pH of culture filtrate, antifungal activity of the culture filtrate against Pyt. vexans, and the amount of antifungal compound produced by each Penicillium species, were examined. The filtrate of both the single culture of Penicillium and the coculture of Penicillium and Pyt. vexans showed antifungal activity against Pyt. vexans. In a coculture with Pyt. vexans, Pen. cyaneum produced an antifungal compound (patulin) as in the single culture. Pen. damascenum cocultured with Pyt. vexans produced an antifungal compound (citrinin), as it did in the single culture and in larger amounts on day 10. Pen. implicatum produced two antifungal compounds, frequentin and palitantin, and the ratio of frequentin (with higher antifungal activity than palitantin) to palitantin was higher in the coculture with Pyt. vexans than in the single culture. Our results indicate that these Penicillium species have the ability to produce antifungal compounds and to keep antifungal activity under competitive condition with Pyt. vexans. The chemical response of these Penicillium species to Pyt. vexans may contribute to protect P. glehnii seedlings from damage by Pyt. vexans. 相似文献