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   6561篇
  免费   947篇
  国内免费   152篇
电工技术   97篇
综合类   319篇
化学工业   2374篇
金属工艺   197篇
机械仪表   99篇
建筑科学   275篇
矿业工程   116篇
能源动力   207篇
轻工业   1734篇
水利工程   73篇
石油天然气   196篇
武器工业   8篇
无线电   531篇
一般工业技术   987篇
冶金工业   151篇
原子能技术   88篇
自动化技术   208篇
  2024年   3篇
  2023年   108篇
  2022年   104篇
  2021年   207篇
  2020年   251篇
  2019年   257篇
  2018年   260篇
  2017年   319篇
  2016年   254篇
  2015年   329篇
  2014年   402篇
  2013年   515篇
  2012年   428篇
  2011年   507篇
  2010年   397篇
  2009年   387篇
  2008年   348篇
  2007年   423篇
  2006年   327篇
  2005年   292篇
  2004年   240篇
  2003年   243篇
  2002年   192篇
  2001年   109篇
  2000年   100篇
  1999年   83篇
  1998年   65篇
  1997年   58篇
  1996年   53篇
  1995年   55篇
  1994年   42篇
  1993年   44篇
  1992年   50篇
  1991年   43篇
  1990年   32篇
  1989年   24篇
  1988年   21篇
  1987年   18篇
  1986年   9篇
  1985年   23篇
  1984年   15篇
  1983年   6篇
  1982年   3篇
  1981年   2篇
  1980年   7篇
  1979年   2篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有7660条查询结果,搜索用时 15 毫秒
1.
新疆奎屯河流域是我国大陆第一个地方性砷中毒的区域,然而在人类活动与自然条件下,对该区地下水砷超标的原因未得到清楚的解释。通过2017年在研究区采集地表水、地下水样品51组,分析了主、微量元素组分;2019年在典型的高砷区钻井2个孔,采集沉积物样品44组,分析了粒径、化学成分。结果表明,研究区地下水砷浓度范围为10~887 μg/L,平均为55.8μg/L,沉积物中砷最高为28.41 mg/kg,砷超标(As≥10 μg/L)较为严重。周边山区分布的菱铁矿、砷酸钙、砷酸锰等矿物,为该区地下水砷含量超标提供了物质来源;强烈的蒸发浓缩作用与岩石风化作用使得地下水中的砷浓度进一步升高;高pH值、低Eh的地下水化学环境,造成砷酸盐从矿物表面解吸附聚集在地下水中;沉积物中Fe、Mn氧化物矿物和黏土矿物的还原过程使与之共存的砷被释放,也是该区地下水中砷超标的原因。  相似文献   
2.
王鹏 《中国酿造》2022,41(4):199-203
该试验以无花果、仙人掌果为原料制备果酒,并研究复合果酒的最优发酵工艺。通过单因素试验及响应面试验,探讨了酵母接种量、发酵温度、初始pH值、初始糖度、发酵时间对无花果-仙人掌果酒发酵产酒精量的影响。结果表明,最佳发酵条件为仙人掌果∶无花果=1∶2,酵母接种量0.04%,发酵温度25 ℃,初始pH值3.40,初始糖度20 °Bx,发酵时间7 d,在此优化条件下,制得无花果-仙人掌果酒的酒精度为11.01%vol,感官评分为97分,总花青素含量为50.68 mg/100 mL。果酒鲜艳紫红,酒体清澈,具有浓郁的果香和醇厚的口感。  相似文献   
3.
扩展青霉 (Penicillium expansum)和指状青霉(Penicillium digitatum)是两种典型采后致病菌,其中扩展青霉能够引起苹果、梨、猕猴桃、樱桃等水果的采后贮藏期腐烂,指状青霉则是引起柑橘类水果采后及贮藏期间腐烂的主要致病菌之一。为明确两株青霉菌生长及产酸的适宜环境条件,本试验对不同营养、温度、pH值、光照等条件下青霉菌的生长情况进行了研究。结果表明,在实验给定的条件下,最适宜扩展青霉生长和产酸的培养基为马铃薯葡萄糖琼脂培养基,温度分别为25℃和20℃,pH分别为4和10,均为黑暗环境;最适宜指状青霉生长和产酸的培养基为马铃薯葡萄糖琼脂培养基,温度均为20℃,pH分别为4和8,均为黑暗环境。这为后续对两株菌株产酸及致病性的探究提供科学依据。  相似文献   
4.
Proximal tubular (PT) acidosis, which alkalinizes the urinary filtrate, together with Ca2+ supersaturation in PT can induce luminal calcium phosphate (CaP) crystal formation. While such CaP crystals are known to act as a nidus for CaP/calcium oxalate (CaOx) mixed stone formation, the regulation of PT luminal Ca2+ concentration ([Ca2+]) under elevated pH and/or high [Ca2+] conditions are unknown. Since we found that transient receptor potential canonical 3 (TRPC3) knockout (KO; -/-) mice could produce mild hypercalciuria with CaP urine crystals, we alkalinized the tubular pH in TRPC3-/- mice by oral acetazolamide (0.08%) to develop mixed urinary crystals akin to clinical signs of calcium nephrolithiasis (CaNL). Our ratiometric (λ340/380) intracellular [Ca2+] measurements reveal that such alkalization not only upsurges Ca2+ influx into PT cells, but the mode of Ca2+ entry switches from receptor-operated to store-operated pathway. Electrophysiological experiments show enhanced bicarbonate related current activity in treated PT cells which may determine the stone-forming phenotypes (CaP or CaP/CaOx). Moreover, such alkalization promotes reactive oxygen species generation, and upregulation of calcification, inflammation, fibrosis, and apoptosis in PT cells, which were exacerbated in absence of TRPC3. Altogether, the pH-induced alteration of the Ca2+ signaling signature in PT cells from TRPC3 ablated mice exacerbated the pathophysiology of mixed urinary stone formation, which may aid in uncovering the downstream mechanism of CaNL.  相似文献   
5.
Considering that a series of complex issues such as environmental problems, sustainable development, animal welfare, and human health are on a global scale, the development of vegetable protein-based meat substitutes provides a potential solution to the disparity between meat consumption demand and supply. The research and development of vegetable protein-based meat substitutes have become a major commercial activity, and the market is expanding to meet the growing consumer demand. Soy protein isolates (SPI) are often used as a raw material for vegetable meat substitutes because of their potential to form fiber structures. Although significant initial success has been achieved, it is still a challenge to explain how the composition and aggregation of SPI influence gel properties and the mechanism(s) involved. This article reviews the latest research about SPI. The relationship between the composition, aggregation, and gelation properties of SPI is based on a through literature search. It focused on the application of SPI in heat- and cold-induced gels, given the diversified market demands. The research on cold gel has helped expand the market. The methods to improve the properties of SPI gels, including physical, chemical, and biological properties, are reviewed to provide insights on its role in the properties of SPI gels. To achieve environmentally friendly and efficient ways for the food industry to use SPI gel properties, the research prospects and development trends of the gel properties of SPI are summarized. New developments and practical applications in the production technology, such as for ultrasound, microwave and high pressure, are reviewed. The potential and challenges for practical applications of cold plasma technology for SPI gel properties are also discussed. There is a need to transfer the laboratory technology to actual food production efficiently and safely.  相似文献   
6.
为有效解决膜过滤过程中由于膜污染加剧而导致分离效率下降的问题,提出引入微纳米气泡工艺,研究了pH值为3.0、6.0和10.0时微纳米气泡(MNBs)对超滤过程的影响,通过扫描电镜和聚焦离子束电子束双束显微镜分析了膜表面污染。实验结果表明pH值为3.0、6.0和10.0时鼓入MNBs后超滤归一化通量分别为0.96、1.19和1.14。pH值为3.0时鼓入MNBs对腐植酸(HA)截留率无明显增强,pH值为6.0和10.0时鼓入MNBs后截留率分别提高了12.7%和10.0%。超滤膜表面滤饼层厚度随pH值增大而减小,鼓入MNBs后滤饼层疏松多孔,有效减弱了归一化通量下降。  相似文献   
7.
在小试条件下,以石英砂为载体,利用表面负载的铁锰复合氧化膜研究了地表水和地下水催化氧化去除锰的效果差异。结果表明,保持相同的操作条件,地表水中锰去除率(20%)远不及地下水(40%)。通过对比水质参数,认为该差异可能主要取决于水中pH和碱度。将地表水pH提高至和地下水相同,去除效果未见大幅提升;而将碱度提高至和地下水相同时去除效果有较大改善,锰去除率由20%提高至40%,认为碱度含量的不同是导致不同水源水中锰去除效果差异的主要原因。进而在提高碱度至120 mg/L的基础上改变其他运行条件,以寻求保持活性氧化膜去除地表水中锰的有效方法。发现降低进水锰浓度、滤速,增加滤层厚度均有助于提高去除效率,几乎可达到与地下水相同去除率。  相似文献   
8.
The study was carried out in four districts, that is, Gujranwala, Gujarat, Narowal and Sialkot of Punjab, Pakistan. The sampling was carried out randomly in different seasons from the water bodies especially from wastewater. Twenty-one species belonging to Euglenophycota were identified using light microscopy and scanning electron microscopy from which 04 species belong to genus Phacus, 02 species belonging to Trachelomonas and Euglena based on light microscopy. It was observed that Euglena was the most diverse genus and it is supposed to be the indicator species of the polluted water. It was observed that E. oblonga was found in maximum pH range, that is, 7.0–11.0. Similarly, E. brevicaudatus was found in maximum EC, that is, 169 ± 1.5 ms/cm these outcomes indicated that for internal examination along with LM, SEM was necessary for correct identification of algal sample up to specie level.  相似文献   
9.
10.
Stability of milk drinks could be improved by adding high methoxyl pectin. In this work, effect of the modified high methoxyl pectin (MHMP) on the fermented milk beverage (FMB) was investigated by the characteristics of adsorption, viscosity, rheological properties, particle size, zeta-potential (ζ-potential), microstructure, and phase behavior. The low concentration of MHMP (<0.2%, w/v) and final pH (<4.0) might easily cause the instability among the particles inducing from the bridging flocculation. The FMB system obviously had a good stability as the adding of 0.4% MHMP. Meanwhile, the particle size had a slight downward trend with decreasing the value of pH. The increase of MHMP concentration could increase the properties of viscosity and ζ-potential. However, the ζ-potential of the system had a decreasing trend by reducing the pH of the FMB with the same concentration of MHMP. The microstructure of the FMB was thick and dense compared with the sample without MHMP. As the concentration of MHMP was above 0.4%, the FMB system presented the uniform dispersion and only slight stratification water occurred for the phase behavior. Besides, it was also indicated that most part of MHMP was not adsorbed onto the casein micelles but was involved in a network with MHMP/casein complexes in the FMB.  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