首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   16562篇
  免费   1431篇
  国内免费   773篇
电工技术   435篇
综合类   1220篇
化学工业   6630篇
金属工艺   1370篇
机械仪表   462篇
建筑科学   879篇
矿业工程   459篇
能源动力   273篇
轻工业   2179篇
水利工程   201篇
石油天然气   1663篇
武器工业   230篇
无线电   609篇
一般工业技术   1257篇
冶金工业   471篇
原子能技术   71篇
自动化技术   357篇
  2024年   28篇
  2023年   178篇
  2022年   380篇
  2021年   435篇
  2020年   434篇
  2019年   333篇
  2018年   317篇
  2017年   414篇
  2016年   454篇
  2015年   450篇
  2014年   728篇
  2013年   831篇
  2012年   1090篇
  2011年   1139篇
  2010年   899篇
  2009年   958篇
  2008年   846篇
  2007年   1183篇
  2006年   1197篇
  2005年   1076篇
  2004年   879篇
  2003年   781篇
  2002年   687篇
  2001年   594篇
  2000年   525篇
  1999年   394篇
  1998年   318篇
  1997年   251篇
  1996年   196篇
  1995年   170篇
  1994年   138篇
  1993年   89篇
  1992年   114篇
  1991年   50篇
  1990年   47篇
  1989年   41篇
  1988年   22篇
  1987年   16篇
  1986年   11篇
  1985年   9篇
  1984年   11篇
  1983年   10篇
  1982年   8篇
  1981年   7篇
  1980年   2篇
  1979年   7篇
  1978年   3篇
  1977年   6篇
  1976年   4篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
Flesh colour, which is affected by cultivars and browning, can largely impact consumer acceptance in fresh-cut apples. The study profiled phenolic metabolites from apple flesh of twenty-three cultivars by widely targeted metabolomics. Comparison among white- and yellow-fleshed cultivars showed fifteen phenolics, mainly quercetin 3-O-glucoside, hyperoside, hesperetin 5-O-glucoside and cymaroside, in white-fleshed apples were significantly higher than those in yellow-fleshed apples. It may indicate a metabolite basis of yellow and white flesh colour, and better potential nutrition in white-fleshed apples. In addition, ten phenolic metabolites including five cyanidin glycosides showed significant differences between the highest and the lowest browning groups, indicating them may be crucial in browning of fresh-cut apple. This work elucidates the differences of phenolic profiles among apple cultivars with different flesh colour and provides useful data to evaluate the suitability of apple for fresh-cut processing.  相似文献   
2.
The table-like magnetocaloric effect is significant for the magnetic refrigeration applications above 20 K based on the Ericsson cycle. Herein, we prepared a series of Nd6Fe13Pd1–xCux (x = 0.05, 0.1, 0.15) compounds by the arc-melting method. These compounds show the single crystalline phase in the tetragonal Nd6Fe13Si-type structure with the space group I4/mcm. A magnetic phase transition from ferromagnetism to antiferromagnetism and a metamagnetic transition from the antiferromagnetic state to the ferromagnetic state are observed in each of the compounds. The compounds exhibit table-like magnetocaloric effects with large refrigerant capacities. A constant ΔSM in a temperature span of 40 K in the Nd6Fe13Pd0.85Cu0.15 compound are observed. For a field change of 0–5 T, the peak values of –ΔSM for the Nd6Fe13Pd0.95Cu0.05, Nd6Fe13Pd0.90Cu0.10, and Nd6Fe13Pd0.85Cu0.15 compounds are estimated to be 4.8, 4.6 and 4.4 J/(kg·K) with corresponding refrigerant capacity values of 323, 331 and 316 J/kg, respectively. The obtained table-like magnetocaloric effects with large refrigerant capacities as well as fairly small thermal and magnetic hysteresis deem these series of compounds good candidates for single-phase magnetic refrigeration based on the Ericsson cycle.  相似文献   
3.
Macrophages act as immune scavengers and are important cell types in the homeostasis of various tissues. Given the multiple roles of macrophages, these cells can also be found as tissue resident macrophages tightly integrated into a variety of tissues in which they fulfill crucial and organ-specific functions. The lung harbors at least two macrophage populations: interstitial and alveolar macrophages, which occupy different niches and functions. In this review, we provide the latest insights into the multiple roles of alveolar macrophages while unraveling the distinct factors which can influence the ontogeny and function of these cells. Furthermore, we will highlight pulmonary diseases, which are associated with dysfunctional macrophages, concentrating on congenital diseases as well as pulmonary infections and impairment of immunological pathways. Moreover, we will provide an overview about different treatment approaches targeting macrophage dysfunction. Improved knowledge of the role of macrophages in the onset of pulmonary diseases may provide the basis for new pharmacological and/or cell-based immunotherapies and will extend our understanding to other macrophage-related disorders.  相似文献   
4.
以富氮羧酸类分子2,2'-(3,3'-偶氮-双(1H-1,2,4-三唑-5基))二乙酸(H2DTDA)与氢氧化锶八水合物为原料,在水热条件下制备了一种金属有机框架(MOF)结构的新型红色烟火着色剂[Sr_2(DTDA)(H_2O)_6]_n(1);采用傅里叶变换红外光谱(FT-IR)、X射线单晶衍射(XRD)、粉末X射线单晶衍射(PXRD)和元素分析等对化合物结构进行了表征;采用热重法(TG)-差示扫描量热法(DSC)、BAM标准法测试了化合物1的热性能和感度性能;设计了烟火剂配方,对化合物1应用于红色烟火着色剂的可行性进行分析。结果表明,化合物1是一种具有二维空间结构的MOF材料,其层状结构之间存在丰富的氢键作用;放大合成的水热实验同样可以得到高纯度的化合物1;撞击感度为80 J,摩擦感度 360 N;化合物1可作为红色着色剂应用于烟火剂配方中。  相似文献   
5.
The production of macrofungi (mushrooms) as well as their economic value have been steadily increasing globally. The use of functional foods, dietary supplements, and traditional medicines derived from macrofungi is increasing as they have numerous health benefits as well as abundant nutrients. Macrofungi are diverse with complex and highly varied growth conditions and bioactive constituents, most macrofungal resources have not yet been fully explored and applicated, leading to an urgent need for appropriate strategies to address the problem. Increasing attention has been paid to the macrofungal cultivation and application, in particular, potential prebiotics. Herein, the present review comprehensively summarizes recent progress in the cultivation, newly identified bioactive constituents, and their effects on gut microbiota as well as the potential ways in which they affect human health. Moreover, the macrofungal food development is discussed to improve food nutritional value and change the quality characteristics of food. Finally, the review addresses consumer safety concerns and the prospective genetic manipulation of macrofungi. We hope that this review can provide a comprehensive research reference for ensuring the safety and efficacy, along with maximizing the value and profitability of macrofungi production.  相似文献   
6.
7.
8.
A series of polyethylene glycol-linked Gemini fatty alcohol phosphate surfactants (GFAP) were prepared with long chain n-alkanol (C = 8, 12, 16, 18), polyethylene glycol (PEG-200, PEG-400, PEG-600, PEG-800, PEG-1000) and phosphorus oxychloride (POCl3). The structure of the prepared surfactants was characterized by Fourier transform infrared spectrometer (FT-IR). The surfactants were employed for the modification of chrome-tanned leather. The morphological changes of chrome-tanned leather and modified chrome-tanned leather were observed by scanning electron microscopy (SEM). The relationship between the alkyl chain length and molecular weight of the PEG and the hydrophobicity, softness, mechanical strength of modified chrome-tanned leather was also discussed. The experimental results showed that the mechanical strength and softness of modified chrome-tanned leather were enhanced with an increase of alkyl chain length, while the hydrophobicity, mechanical strength and softness were decreased with an increase of molecular weight of the PEG. The hydrophobicity, mechanical strength and softness of modified chrome-tanned leather were optimized for an alkyl chain length of 16. Therefore, 16–200 Gemini phosphate surfactants with an alkyl chain length of 16 and a PEG molecular weight of 200 have a good comprehensive modification effect on Chrome-tanned leather, the tensile strength, tear strength and softness of modified chrome-tanned leather are 57.07 N mm−2, 79.49 N mm−1, 9.73 mm, respectively.  相似文献   
9.
李翔  张继伟  吴柏志 《橡胶科技》2020,18(1):0031-0033
研究抗硫化返原剂PK900在全地形轮胎胎面胶中的应用。结果表明:在全地形轮胎胎面胶中添加抗硫化返原剂PK900,胶料硫化速度变化不大,抗硫化返原性能提高,在过硫条件下硫化胶可保持较好的物理性能;成品轮胎的耐久性能提高,使用寿命延长。  相似文献   
10.
梁星星  张永旺  王斌  朱保宁  曹辉 《化工进展》2020,39(6):2487-2494
生物质热电厂焚烧废弃物的主要成分是草木灰,其产生量大、密度小。大量草木灰不经处理会造成环境污染问题。本文首先分析草木灰的化学成分,确定草木灰的肥料特征,通过添加NH4H2PO4使草木灰的pH达到国家复合肥的相关标准。选用聚天冬氨酸(30%水溶液)作为复合肥的黏结剂,应用于草木灰复合肥的成形造粒,以增加其抗压强度和肥效。研究不同烘干时间、烘干温度、聚天冬氨酸添加量对草木灰复合肥抗压强度的影响规律,通过分析植物的形态及生理指标,进而研究草木灰复合肥的肥效。结果表明:最佳烘干条件为10h、140℃,聚天冬氨酸对草木灰的抗压强度有明显的增强作用,并且草木灰与聚天冬氨酸的复配比为6g∶1mL时肥效最好。此方法解决了元素循环中断、草木灰环境污染,在运输过程中草木灰复合肥易碎,纯草木灰肥效低等问题。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号