全文获取类型
收费全文 | 857篇 |
免费 | 47篇 |
专业分类
电工技术 | 6篇 |
综合类 | 1篇 |
化学工业 | 199篇 |
金属工艺 | 8篇 |
机械仪表 | 26篇 |
建筑科学 | 72篇 |
矿业工程 | 2篇 |
能源动力 | 31篇 |
轻工业 | 71篇 |
水利工程 | 4篇 |
石油天然气 | 1篇 |
无线电 | 75篇 |
一般工业技术 | 176篇 |
冶金工业 | 123篇 |
原子能技术 | 4篇 |
自动化技术 | 105篇 |
出版年
2023年 | 12篇 |
2022年 | 17篇 |
2021年 | 33篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 31篇 |
2017年 | 18篇 |
2016年 | 23篇 |
2015年 | 15篇 |
2014年 | 27篇 |
2013年 | 37篇 |
2012年 | 55篇 |
2011年 | 61篇 |
2010年 | 35篇 |
2009年 | 33篇 |
2008年 | 32篇 |
2007年 | 31篇 |
2006年 | 35篇 |
2005年 | 41篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 18篇 |
1998年 | 35篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1977年 | 5篇 |
1976年 | 17篇 |
1974年 | 3篇 |
1972年 | 4篇 |
1969年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有904条查询结果,搜索用时 15 毫秒
1.
The mode of interaction between muramyl dipeptide (MDP), a compound with immunopharmacological activities, and 5-hydroxtryptamine (5-HT, serotonin) was studied in isolated nerve-smooth muscle preparations of the carp stomach. Application of exogenous 5-HT evoked direct smooth muscle contractions; electric neurogenic stimulation evoked twitches due to release of 5-HT from nerve endings. Contractions evoked by a high concentration of 5-HT (3-30 microM) were resistant to atropine and potentiated in the presence of MDP. Isamoltan (5-HTID antagonist) decreased the amplitude of contractions, whereas ketanserin (5-HT2 antagonist) and MDL 72,222 (5-HT3 antagonist) had no effect. The addition of low concentrations (0.1-1.5 microM) of 5-HT did not contract the preparation but caused a decrease in the amplitude of neurogenic twitches, which might be due to the presynaptic inhibition of serotonin release. This effect of 5-HT was not changed by isamoltan or ketanserin, but it was largely reduced in the presence of 5-HT3 antagonists tropisetron and MDL 72,222. This inhibitory effect of 5-HT on twitch amplitude was potentiated by MDP. The interaction of MDP with the serotonergic system thus involved not only potentiation of the postsynaptic effect of higher 5-HT concentrations, which might have been mediated via the 5-HT1 subsystem, but also presynaptic inhibition. MDP enhancement of 5-HT's inhibitory effect, mediated via 5-HT3 receptors, might represent a new feature in mutual 5-HT-MDP interactions. 相似文献
2.
Summary The synthesis of di-(4-formylphenyloxyethyl) poly(oxyethylene) and the corresponding oxime derivative are described. Kinetic aspects of the reaction of the dichloro telechelic with 4-hydroxy benzaldehyde are investigated and discussed. 相似文献
3.
4.
Unilateral spatial neglect declines when participants reach to grip the center of long metal rods compared with when they point to the perceived center, suggesting that visuomotor control systems are less affected by neglect than other representational systems (I. H. Robertson, D. Nico, & B. Hood, 1995). In this study, 16 participants with unilateral left neglect actually picked up rods, and we predicted short-term improvements in neglect because of induced conflict between a phenomenally symmetrical visual world on the one hand and a proprioceptively conveyed rightward-biased world on the other. With participants serving as their own controls, significant short-term improvements in neglect were found on 2 out of 4 neglect tasks after participants experienced proprioceptive feedback discrepant from the judgments they made on the basis of visual information alone. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
6.
This work is concerned with the efficient design of a reverse logistics network using an extended version of models currently found in the literature. Those traditional, basic models are formulated as mixed integer linear programs (MILP-model) and determine which facilities to open that minimize the investment, processing, transportation, disposal and penalty costs while supply, demand and capacity constraints are satisfied. However, we show that they can be improved when they are combined with a queueing model because it enables to account for (1) some dynamic aspects like lead time and inventory positions, and (2) the higher degree of uncertainty inherent to reverse logistics. Since this extension introduces nonlinear relationships, the problem is defined as a mixed integer nonlinear program (MINLP-model). Due to this additional complexity, the MINLP-model is presented for a single product-single-level network. Several examples are solved with a genetic algorithm based on the technique of differential evolution. 相似文献
7.
Nico Calavita 《Cities》1985,2(2):106-110
In 1284 the Florence Commune started building the last set of walls that were to surround the city until the second half of the 19th century. In response to the strong demographic and economic expansion of the 13th century, the new walls would have to contain a space commensurate with the present and future grandeur of the Commune.1 When completed in 1333, the walls circled the city for 8.5 kilometres and contained 73 towers, 15 doors and an area five times that included in the previous walls. 相似文献
8.
9.
R. K. Bayer T. A. Ezquerra H. G. Zachmann F. J. Baltá Calleja J. Martinez Salazar W. Meins R. E. Diekow P. Wiegel 《Journal of Materials Science》1988,23(2):475-480
In Part 1 and Part 2 of this paper the preparation of linear polyethylene (PE)-carbon black processed composites with conducting electrical properties was examined by means of elongation flow injection moulding. Mould geometry was optimized in the form of oriented double-armed bars so as to give enhanced mechanical properties combined with a high degree of electrical homogeneity. The present paper deals with composites using a high molecular weight PE matrix. It is shown that the injection-moulded composite material exhibits not only a lower percolation threshold, c, than the conventionally pressure-moulded isotropic sample, but also conductivities two to three orders of magnitude larger than the latter. The radial and axial conductivity profiles, for concentrations well above c, are discussed in the light of the molecular orientation variations across the bars as determined by birefringence. A segregation of primary filler particles, during flow-induced orientation, into axial channels has been shown to explain the enhancement of conductivity detected in the injected mouldings. In addition, for filler concentrations near 7%, -profile analysis indicates the development of a uniform conductive-stiff inner cylinder, several millimetres wide, homogeneously extending along the full length of the injected material. 相似文献
10.
The evolution of the amorphous structure of starch was characterized during the drying process by real‐time X‐ray wide‐angle scattering. The X‐ray diffractograms of injection‐molded starch show two superposed, rather broad, scattering maxima indicative of noncrystalline structures. The location of the two peaks has been associated to disordered starch single helices. A third maximum that arises upon drying the material in vacuum is associated to the scattering emerging from regions containing double helices. A model for the starch network is proposed, assuming a primary and a secondary component. The wider, temperature stable component appearing first, is correlated to the entanglement network of the melt. The narrower network component, which is created later, at lower temperature (secondary network), is explained by the formation of double helix regions that densify the wider primary network. The secondary network is increased strongly by the drying process. X‐ray experiments performed during the penetration of water, provoking a higher molecular mobility, reveal a better‐packed helical structure that becomes the precursor of a double helix crystalline formation. When temperature increases, the secondary network is dissolved and water molecules arrange themselves in better‐organized crystals as strongly bound crystal water. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1880–1886, 2006 相似文献