全文获取类型
收费全文 | 64684篇 |
免费 | 4618篇 |
国内免费 | 4334篇 |
专业分类
电工技术 | 2842篇 |
技术理论 | 1篇 |
综合类 | 3413篇 |
化学工业 | 18833篇 |
金属工艺 | 10034篇 |
机械仪表 | 2168篇 |
建筑科学 | 3713篇 |
矿业工程 | 898篇 |
能源动力 | 1763篇 |
轻工业 | 2534篇 |
水利工程 | 182篇 |
石油天然气 | 2051篇 |
武器工业 | 605篇 |
无线电 | 5780篇 |
一般工业技术 | 9569篇 |
冶金工业 | 3394篇 |
原子能技术 | 1094篇 |
自动化技术 | 4762篇 |
出版年
2024年 | 172篇 |
2023年 | 954篇 |
2022年 | 1778篇 |
2021年 | 2163篇 |
2020年 | 1821篇 |
2019年 | 1590篇 |
2018年 | 1394篇 |
2017年 | 1830篇 |
2016年 | 2165篇 |
2015年 | 2233篇 |
2014年 | 3042篇 |
2013年 | 3466篇 |
2012年 | 3779篇 |
2011年 | 4709篇 |
2010年 | 3588篇 |
2009年 | 4222篇 |
2008年 | 3477篇 |
2007年 | 4286篇 |
2006年 | 3996篇 |
2005年 | 3175篇 |
2004年 | 2754篇 |
2003年 | 2664篇 |
2002年 | 2319篇 |
2001年 | 1911篇 |
2000年 | 1731篇 |
1999年 | 1418篇 |
1998年 | 1067篇 |
1997年 | 871篇 |
1996年 | 778篇 |
1995年 | 569篇 |
1994年 | 478篇 |
1993年 | 424篇 |
1992年 | 374篇 |
1991年 | 279篇 |
1990年 | 257篇 |
1989年 | 193篇 |
1988年 | 143篇 |
1987年 | 133篇 |
1986年 | 153篇 |
1985年 | 148篇 |
1984年 | 121篇 |
1983年 | 107篇 |
1982年 | 98篇 |
1981年 | 107篇 |
1980年 | 96篇 |
1978年 | 94篇 |
1977年 | 98篇 |
1976年 | 111篇 |
1975年 | 112篇 |
1974年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
Walter Soares Leal Antônio Ricardo Panizzi Cintia Carla Niva 《Journal of chemical ecology》1994,20(5):1209-1216
The alarm pheromone system ofLeptoglossus zonatus (Dallas) adults was shown to be composed of hexyl acetate, hexanol, hexanal, and hexanoic acid. Single components tested in the field elicited dispersive behavior of over 70% of adults. 2-(E)-Hexenal, found in the secretion of nymphs, but not in the exudates of adults, was also active against adults. In addition, first-instar nymphs responded to the four components of the alarm pheromone of adults as well as to 2-(E)-hexenal, a component of their own alarm pheromone system. Adults and nymphs possess different alarm pheromone systems, which are not specific to their own life stage. That hemipteran alarm pheromone systems are not species-specific was supported by the fact that both adult and nymphL. zonatus responded to butanoic acid, an alarm pheromone of Alydidae, which was not found in this Coreidae species. 相似文献
992.
徐维正 《精细与专用化学品》2002,10(2):17-18
俄罗斯轮胎工业研究院对俄轮胎稳定剂(稳定剂1)和P(稳定剂2)在俄轻、重型轮胎中的试用及与国外稳定剂产品Wingstay100、SPPD、6PPD、IPPD的配合使用进行了研究。结果表明,由于轻型轮胎的胎侧比重型胎胎侧薄1倍多,稳定剂损耗更快,因此在轻型胎胶中稳定剂1的用量一般比重型胎多50%-100%;稳定剂1与稳定剂2配合使用可提高侧胶耐磨损和抗破裂的稳定性;IPPD/SPPD/稳定剂2配合的稳定剂体系使胎侧胶耐热老化和抗疲劳的稳定性最好。 相似文献
993.
994.
Polyester polyurethane cationomers are prepared using polyester polyol of molecular weight 2000 as soft segments, N-methyl diethanolamine as chain extender, glycolic acid as quaternization agent, methyl ethyl ketone as solvent, and 4,4'-diphenylenemethylene diisocyanate (MDI) as diisocyanate. Properties of the films cast from solutions and emulsions are studied by infrared spectroscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, and tensile-elongation testing. Ionization can cause phase separation and produces increased cohesion in the hard domains. The dispersion process can be divided into three stages involving a separation of hard segment aggregates due to adsorption of water on their surface, water entering into hard segment microionic lattics, and finally a rearrangement of agglomerates to form microspheres. The dispersion can disrupt the order in the hard domains and an increased phase separation. 相似文献
995.
铝锆炭滑板在浇铸钙处理钢时的化学侵蚀 总被引:1,自引:0,他引:1
利用扫描电镜对抗钙处理钢液侵蚀试验后的铝锆炭残样进行了显微结构观察 ,并分析了铝锆炭滑板在钙处理钢液中的化学侵蚀机理。结果表明 :高温下 ,钙处理钢液中的Ca及CaO会与滑板中的Al2 O3 、SiO2 发生反应 ,生成低熔点的 12CaO·7SiO2 (1392℃ )和 2CaO·SiO2 ·Al2 O3 (15 39℃ )等物质 ,这些低熔物被钢水冲刷掉 ,使得滑板表层的Al2O3 和SiO2 含量迅速降低 ,从而导致了滑板的损毁。 相似文献
996.
997.
本文以对氯苯酚(4-cP)、对硝基苯酚(4-NP)和罗丹明B(RhB)为模型有机物(以4-CP和4-NP为小分子模型有机物,以RhB为大分子模型有机物),分别研究了185nmUV对水中这3种模型有机物的降解规律、性能和效果.研究结果表明,185nmUV直接对水中4-CP、4-NP和RhB有很好的降解效果.研究内容包括:185nmUV降解模型有机物的浓度、TOC(Totalorganic carbon)浓度、185nmUV降解模型有机物过程中溶液pH及电导率变化、以及降解模型有机物过程中产生的无机离子等几个方面. 相似文献
998.
The presence of dissolved cations such as Al and Zn in alkaline electrolyte (6 M KOH) suppresses the -nickel hydroxide transformation. The uptake of Al (10 mol%) and Zn (30 mol%) exhibited by the active material likely stabilizes the -phase. Dissolved Al is deleterious to the performance of the nickel hydroxide electrode, whereas, dissolved Zn enhances the specific discharge capacity of nickel hydroxide by approximately 25% showing that the mode of metal uptake is different in the two cases. 相似文献
999.
We investigated cues that mediate the aggregation behavior of immature pentatomid bugs by using nymphs of six different pentatomid bug species (Nezara viridula, Acrosternum hilare, Chlorochroa ligata, Chlorochroa sayi, Thyanta pallidovirens, and Euschistus conspersus). When first instars of any two species were put together in a Petri dish, they readily formed heterospecific aggregations similar to their natural conspecific aggregations. The chemical profiles of first and second instar nymphs of each species were determined by solvent extraction with pentane, followed by GC-MS analysis. Immature bugs of the different species had some compounds in common, and some that were more species specific. Within a species, there were distinct differences in the profiles of compounds extracted from first and second instars. Bugs did not aggregate around untreated polysulfone beads (1 mm diam) that were glued together in groups approximating bug egg masses, suggesting that tactile cues alone were insufficient to induce aggregation. Furthermore, when tested over a range of doses, groups of polysulfone beads treated with crude whole-body extracts of bugs did not induce or maintain aggregations. However, first instar N. viridula nymphs did respond to beads treated with two of the three major components of bug extracts. 4-Oxo-(E)-2-decenal induced significant aggregations at two doses, whereas tridecane, the major component in extracts from all six species, did not, and (E)-2-decenal was repellent. The repellence of (E)-2-decenal may explain why we and previous researchers were unable to induce aggregations of first instar N. viridula using whole-body extracts. 相似文献
1000.