全文获取类型
收费全文 | 3575篇 |
免费 | 592篇 |
国内免费 | 195篇 |
专业分类
电工技术 | 209篇 |
技术理论 | 2篇 |
综合类 | 454篇 |
化学工业 | 309篇 |
金属工艺 | 44篇 |
机械仪表 | 108篇 |
建筑科学 | 881篇 |
矿业工程 | 219篇 |
能源动力 | 63篇 |
轻工业 | 304篇 |
水利工程 | 307篇 |
石油天然气 | 165篇 |
武器工业 | 38篇 |
无线电 | 280篇 |
一般工业技术 | 191篇 |
冶金工业 | 377篇 |
原子能技术 | 14篇 |
自动化技术 | 397篇 |
出版年
2024年 | 14篇 |
2023年 | 84篇 |
2022年 | 189篇 |
2021年 | 269篇 |
2020年 | 201篇 |
2019年 | 143篇 |
2018年 | 168篇 |
2017年 | 169篇 |
2016年 | 158篇 |
2015年 | 160篇 |
2014年 | 274篇 |
2013年 | 198篇 |
2012年 | 254篇 |
2011年 | 271篇 |
2010年 | 223篇 |
2009年 | 220篇 |
2008年 | 199篇 |
2007年 | 224篇 |
2006年 | 184篇 |
2005年 | 144篇 |
2004年 | 119篇 |
2003年 | 95篇 |
2002年 | 100篇 |
2001年 | 54篇 |
2000年 | 44篇 |
1999年 | 19篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 24篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1974年 | 3篇 |
1968年 | 3篇 |
1964年 | 1篇 |
1961年 | 3篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有4362条查询结果,搜索用时 140 毫秒
11.
新中国早期产品品牌的命名和设计,在政治内容、审美趣味与商业企图之间获得了平衡。构建了易于被大众接受,群众喜闻乐见,紧随时代潮流的命名和设计范式。其中,以烟标最为典型,散发出鲜明的视觉特色和独有魅力,给人们留下诸多的回忆。为新中国立国建国、经济建设、航天国防、友好和平和文化生活等方面信息的传播和价值观的塑造,作出了不可忽视的贡献,也为现代产品品牌的命名和设计提供了早期的范式参考。 相似文献
12.
为克服三乙醇胺早强剂对水泥抗折强度和后期强度的影响,合成了马来酸三乙醇胺酯,并通过背散射电子成像(BSE)和BET分析,研究了马来酸三乙醇胺酯对水泥水化程度、C-S-H含量和水泥水化28 d分形维数的影响。结果表明:马来酸三乙醇胺酯可促进水泥水化尤其是水泥中硅酸盐相的水化;复掺马来酸三乙醇胺酯和聚羧酸减水剂,可显著提高水泥水化产物中C-S-H的含量;三乙醇胺降低了水泥石28 d的分形维数,马来酸三乙醇胺酯单掺及与聚羧酸减水剂复掺则使水泥石28 d的分形维数提高。由此可见,马来酸三乙醇胺酯作为增强型水泥早强剂具有广阔的应用前景。 相似文献
13.
14.
Ultrafine,fine, and black carbon particle concentrations in California child‐care facilities 下载免费PDF全文
F. W. Gaspar R. Maddalena J. Williams R. Castorina Z.‐M. Wang K. Kumagai T. E. McKone A. Bradman 《Indoor air》2018,28(1):102-111
Although many U.S. children spend time in child care, little information exists on exposures to airborne particulate matter (PM) in this environment, even though PM may be associated with asthma and other respiratory illness, which is a key concern for young children. To address this data gap, we measured ultrafine particles (UFP), PM2.5, PM10, and black carbon in 40 California child‐care facilities and examined associations with potential determinants. We also tested a low‐cost optical particle measuring device (Dylos monitor). Median (interquartile range) concentrations for indoor UFP, gravimetric PM2.5, real‐time PM2.5, gravimetric PM10, and black carbon over the course of a child‐care day were 14 000 (11 000‐29 000) particles/cm3, 15 (9.6‐21) μg/m3, 15 (11‐23) μg/m3, 48 (33‐73) μg/m3, and 0.43 (0.25‐0.65) ng/m3, respectively. Indoor black carbon concentrations were inversely associated with air exchange rate (Spearman's rho = ?.36) and positively associated with the sum of all Gaussian‐adjusted traffic volume within a one‐kilometer radius (Spearman's rho = .45) (P‐values <.05). Finally, the Dylos may be a valid low‐cost alternative to monitor PM levels indoors in future studies. Overall, results indicate the need for additional studies examining particle levels, potential health risks, and mitigation strategies in child‐care facilities. 相似文献
15.
以类蛋黄酱体系为研究对象,运用Turbiscan、流变仪、粒度仪、显微镜研究在pH 3条件下橄榄油与椰子油不同比例复配(10∶ 0、9∶ 1、8∶ 2、7∶ 3)的混油基对于乳清分离蛋白-蛋黄卵磷脂稳定的乳液体系流变性质及冻融稳定性的影响。结果表明:随着椰子油比例增加,乳液黏度增加,弹性模量增加,橄榄油与椰子油质量比7∶ 3复配混油基制得的乳液具有最大的黏度和最高的弹性模量;所有乳液在4~40 ℃弹性模量下降,说明乳液在贮存、冷藏运输过程中内部结构完整,乳液具有良好的稳定性;蛋黄卵磷脂能够提高含椰子油(饱和脂肪酸含量高)乳液的冻融稳定性,并且椰子油比例越大(饱和程度越高),冻融稳定性提高效果越好;乳液冻融稳定性从高到低依次为橄榄油与椰子油质量比为7∶ 3>8∶ 2>9∶ 1>10∶ 0。 相似文献
16.
针对矿山深部开采过程中易发生地压动力灾害的问题,基于微震监测技术,结合矿山实际特点建立岩体稳定性监测系统。优化台网设计,通过定点爆破的方法进行波速校正,最终建立了定位误差在10m,灵敏度在-2.2的监测台网。对监测数据进行波形拾取,分析微震事件时空演化特征,圈定潜在危险区域,并对潜在危险区域围岩变形损伤进行分析。最终总结出微震事件大幅度上升且处于较高水平、空间分布高度集聚、能量指数突然下降而累计视体积迅速上升的动力灾害预警前兆。研究结果可为深部开采岩体稳定性监测提供参考。 相似文献
17.
制备了沥青混凝土样品,并进行了不同次数的盐冻融干湿循环试验。在此基础上,测试了沥青混凝土的高温车辙深度、动稳定度和低温抗弯拉强度,得到了车辙深度、动稳定度和抗弯拉强度随盐冻融干湿循环次和盐浓度的变化规律,研究了盐冻融与干湿作用下沥青混凝土的高低温力学性能。研究结果表明:(1)沥青混凝土60min车辙深度随盐浓度的增加和冻融循环次数的增多而呈线性增长的趋势;(2)沥青混凝土的抗高温变形能力随盐冻融干湿循环次数的增多而逐渐弱化;(3)沥青混凝土的抗弯拉强度经历9次和15次盐冻融干湿循环后分别下降22%~26.4%和42.6%~51.5%;(4)冻融干湿循环次数一定时,沥青混凝土的抗弯拉强度随盐浓度的增加而缓慢下降,并且当盐浓度达到12%时,沥青混凝土的抗弯拉强度减小就很不明显。 相似文献
18.
19.
《Journal of dairy science》2021,104(12):12472-12485
The objective of this study was to evaluate the effects of oral administration of fiber from the first week of life on the growth and hindgut environment of preweaning calves. Twenty newborn female Holstein calves were divided into 2 groups as control and treatment. Calves in both groups were reared under the same feeding program except for oral fiber administration. Timothy hay and psyllium were mixed at a 50-to-6 ratio as a treatment diet for oral fiber administration. Calves in the treatment group were orally administered 50 g of fiber daily from 3 to 7 d of age and 100 g of fiber from 8 d of age until weaning. Feed intake and occurrence of diarrhea were recorded daily, and body weight (BW) was recorded weekly for the individual calf. Fresh feces were collected from calves at 7, 21, 35, 49, and 56 d of age to analyze fermentation parameters and microbiota to characterize the hindgut environment. Higher fiber intake in the treatment group due to oral administration of timothy and psyllium did not affect the starter intake and achieved higher BW at 21 d of age. The fecal pH, total volatile fatty acid, lactate, and ammonia nitrogen concentrations were not affected by oral fiber administration; meanwhile, the molar proportion of propionate was higher in the treatment group at 7 d of age. The difference in fecal microbiota in the calves subjected to the oral administration of fiber was observed within 21 d of life; Lactobacillus spp. and Prevotella spp. showed higher abundance, whereas that of Clostridium perfringens was decreased. These higher abundances of beneficial bacteria and lower abundance of pathogenic bacteria during early life may partly explain the higher BW of calves in the treatment group at 21 d of age. Furthermore, no adverse effect was observed for the BW and health status in the treatment group throughout the preweaning period. Therefore, early fiber feeding via oral administration potentially contributes to improving the hindgut environment in newborn calves, which leads to better growth of calves during the early stage of life. 相似文献
20.
Minjie Cao Jing Wang Ailing Cao David Shiuan Rongfa Guan Luyun Cai Yanbo Wang 《International Journal of Food Science & Technology》2019,54(5):1642-1650
Recrystallisation often occurs in the freeze-thaw cycles and results in poor food quality. This study was undertaken to analyse the effects of recrystallisation on the changes of protein conformation and moisture migration within red seabream fillets after the freeze-thaw cycles. The UV second-derivative spectroscopy, intrinsic fluorescence measurement and Raman spectroscopy were employed to evaluate the protein conformational changes. The Low-field NMR spectra analysis was used to evaluate moisture migration. The results indicated that the freeze-thaw cycles altered the secondary and tertiary structure of proteins. It was noticed that interactions between water and protein molecules were decreased gradually and eventually induced the thermal instability of the myosin molecules. The immobilised water content declined and the free water content increased. There were significant destructions in fillet muscle microstructure. These observations unambiguously reflect how the recrystallisations affect the protein conformation and moisture migration patterns of red seabream fillets during freeze-thaw cycles. 相似文献