全文获取类型
收费全文 | 130143篇 |
免费 | 6088篇 |
国内免费 | 3935篇 |
专业分类
电工技术 | 5160篇 |
综合类 | 6531篇 |
化学工业 | 17903篇 |
金属工艺 | 7463篇 |
机械仪表 | 6375篇 |
建筑科学 | 5931篇 |
矿业工程 | 1917篇 |
能源动力 | 2609篇 |
轻工业 | 6647篇 |
水利工程 | 2350篇 |
石油天然气 | 2321篇 |
武器工业 | 772篇 |
无线电 | 15162篇 |
一般工业技术 | 21003篇 |
冶金工业 | 4214篇 |
原子能技术 | 948篇 |
自动化技术 | 32860篇 |
出版年
2024年 | 184篇 |
2023年 | 588篇 |
2022年 | 1227篇 |
2021年 | 1857篇 |
2020年 | 1428篇 |
2019年 | 1155篇 |
2018年 | 15598篇 |
2017年 | 14722篇 |
2016年 | 11218篇 |
2015年 | 2669篇 |
2014年 | 2733篇 |
2013年 | 3304篇 |
2012年 | 6569篇 |
2011年 | 13034篇 |
2010年 | 11819篇 |
2009年 | 9005篇 |
2008年 | 10120篇 |
2007年 | 10965篇 |
2006年 | 3125篇 |
2005年 | 3648篇 |
2004年 | 3019篇 |
2003年 | 2874篇 |
2002年 | 2305篇 |
2001年 | 1677篇 |
2000年 | 1305篇 |
1999年 | 821篇 |
1998年 | 512篇 |
1997年 | 394篇 |
1996年 | 387篇 |
1995年 | 276篇 |
1994年 | 215篇 |
1993年 | 195篇 |
1992年 | 165篇 |
1991年 | 111篇 |
1990年 | 89篇 |
1989年 | 58篇 |
1988年 | 58篇 |
1986年 | 29篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1960年 | 30篇 |
1959年 | 40篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
962.
环氧树脂质量对紫外光固化涂料性能的影响 总被引:4,自引:1,他引:4
介绍了紫外光(UV)固化涂料基本组成,双酚A环氧树脂质量对环氧丙烯酸酯的合成及对UV涂料性能的影响。 相似文献
963.
肾缺血再灌注细胞内钙水平与氧化应激损伤研究 总被引:5,自引:0,他引:5
目的 观察肾细胞中游离钙([Ca~(2+)]i)及氧自由基在缺血再灌注损伤过程中的改变情况,探讨二者在再灌注肾损伤中发生作用机制。方法 摘除Wistar大鼠左肾,钳夹右侧肾蒂,建立急性缺血再灌注肾损伤模型,应用Fura-2/AM荧光指示剂测定缺血再灌注大鼠肾细胞内[Ca~(2+)]i浓度的变化,同时测定谷胱甘肽过氧化物酶(GSH-Px)活性、超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量。结果 缺血再灌注不同时期肾细胞内[Ca~(2+)]i浓度均有不同程度增高,与对照组相比差异有显著意义,各实验组SOD活力水平降低,与对照组相比差异有显著意义,MDA生成高于对照组,GSH-Px在再灌注早期活力减弱,明显低于对照组,晚期活力基本恢复。结论 1.缺血再灌注不同时期大鼠肾细胞内[Ca~(2+)]i超载和不同程度的氧化侵袭,在缺血再灌注肾损伤病理过程中起重要作用;2.再灌注时间与肾细胞内[Ca~(2+)]i超载呈正相关,提示再灌注损伤通过不同机制加重细胞钙超载。 相似文献
964.
965.
Yi Zhang Bin Li Pinggen Rao Ming Lü Jianqing Wu 《Journal of the American Ceramic Society》2007,90(5):1615-1618
The leucite crystallization kinetics from a hydrothermally derived precursor seeded with nano-crystalline leucite was investigated by X-ray diffraction and non-isothermal differential thermal analysis. The nano-crystalline leucite was prepared by high-energy milling of high-purity leucite powder and the leucite precursor was prepared by the hydrothermal method of silica sol, aluminum nitrate, and potassium nitrate. After the seeds were introduced, the crystallization temperature of the precursor was lowered by 100°C and the transition phase kalsilite did not appear during the crystallization process. When the seeded precursor was heat treated at 700°C, a small amount of cubic leucite was stabilized to room temperature. The seeded precursor showed an exothermic peak between 800° and 920°C under different heating rates. The activation energy for the growth of leucite from the seeded precursor was 256(SD9) kJ/mol. 相似文献
966.
967.
Yuan‐Hsiang Yu Chien‐Chih Jen Hsiu‐Ying Huang Pei‐Chi Wu Chao‐Cheng Huang Jui‐Ming Yeh 《应用聚合物科学杂志》2004,91(6):3438-3446
A series of heterocyclically conjugated polymer–clay nanocomposite (PCN) materials that consisted of organic poly(3‐hexylthiophene) (P3HT) and inorganic montmorillonite (MMT) clay platelets were prepared by in situ oxidative polymerization with FeCl3 as an oxidant. The as‐synthesized PCN materials were characterized by Fourier transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (WAXRD), and transmission electron microscopy (TEM). The effects of the material composition on the anticorrosion, gas barrier, thermal stability, flammability, mechanical strength, and electrical conductivity properties of the P3HT and PCN materials were studied by electrochemical corrosion measurements, gas‐permeability analysis (GPA), thermogrametric analysis (TGA), limiting oxygen index (LOI) measurements, dynamic mechanical analysis (DMA), and a four‐point probe technique, respectively. The molecular weights of extracted and bulk P3HT were determined by gel permeation chromatography (GPC) with THF as an eluant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3438–3446, 2004 相似文献
968.
Francisco Salmerón-Miranda Birgitta Båth Henrik Eckersten Johannes Forkman Maria Wivstad 《Nutrient Cycling in Agroecosystems》2007,79(2):125-139
The main objective of this field study was to estimate the total plant uptake of soil mineral N in maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) grown in crop rotations under different N content in Nicaragua. Secondary objectives were to estimate the fraction of
the measured soil mineral N content taken up in this way, and to determine how the measured N in plant aboveground parts was
related to the total mineral N uptake. A large variation in N content was obtained by using data from fertilisation experiments.
Plant total N uptake was estimated as the residual N in a mass balance calculation of soil mineral N. Mineral N content in
the top 0–0.3 m soil layer in the field cultivations and in tubes isolated from root uptake, and N content in aboveground
plant parts were measured every 30 days. Estimated plant total uptake of soil mineral N varied considerably (2.5–14 g N m−2 30 day−1) over periods and N treatments. The range of variation was similar for maize and bean. The fraction of the soil mineral N
that was taken up by the plant daily varied more in maize (about 0.03–0.12 day−1) than in bean (about 0.05–0.08 day−1). Our results suggest that monthly changes in N in aboveground plant parts were linearly related to plant total N uptake
during the same period. Aboveground plant N constituted between about 55% and 80% of total uptake of soil mineral N in maize
depending on period within season, whereas for bean it was more constant and smaller (about 40%). 相似文献
969.
970.
山东东华水泥有限公司是隶属于淄博矿业集团有限责任公司的子公司,东华水泥5000t/d新型干法水泥熟料线是淄矿建设“煤、电、材”产业链的建材板块龙头项目,第一条5000t/d水泥熟料生产线已于2005年2月投产,目前生产稳定,产品质量优良。配套200万吨粉磨站于2005年11月顺利投产。东华公司根据本公司的实际情况,结合国家资源综合利用的产业政策,委托天津水泥工业设计院设计,利用5000t/d水泥熟料生产线的余热配套一座纯低温余热电站(同时对2号5000t/d水泥熟料生产线配套余热电站进行规划)。 相似文献