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   3701篇
  免费   257篇
  国内免费   96篇
电工技术   192篇
综合类   188篇
化学工业   748篇
金属工艺   170篇
机械仪表   171篇
建筑科学   210篇
矿业工程   70篇
能源动力   90篇
轻工业   495篇
水利工程   66篇
石油天然气   188篇
武器工业   20篇
无线电   351篇
一般工业技术   419篇
冶金工业   145篇
原子能技术   27篇
自动化技术   504篇
  2025年   27篇
  2024年   110篇
  2023年   96篇
  2022年   184篇
  2021年   262篇
  2020年   183篇
  2019年   137篇
  2018年   153篇
  2017年   159篇
  2016年   136篇
  2015年   172篇
  2014年   228篇
  2013年   223篇
  2012年   257篇
  2011年   264篇
  2010年   238篇
  2009年   203篇
  2008年   191篇
  2007年   175篇
  2006年   148篇
  2005年   114篇
  2004年   81篇
  2003年   62篇
  2002年   39篇
  2001年   45篇
  2000年   36篇
  1999年   24篇
  1998年   18篇
  1997年   21篇
  1996年   12篇
  1995年   15篇
  1994年   10篇
  1993年   6篇
  1992年   6篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1970年   1篇
  1969年   1篇
  1959年   1篇
排序方式: 共有4054条查询结果,搜索用时 0 毫秒
91.
通过分析水库加固处理前后大坝测压管水位和渗漏量的变化,评价大坝加固处理的质量和效果,表明社上水库大坝加固处理措施合理,且效果良好,质量较高,为大坝加固处理效果评价探索了一种简单、有效的方法.  相似文献   
92.
径流周期识别是径流模拟预测的依据。基于功率谱和极大熵谱分析原理,进行了陕北地区12个测站的年径流序列的周期识别。结果表明:最大熵谱分析具有高分辨率的周期识别的特点,陕北地区的年径流一般具有2-4年、11年左右和18-24年的水文周期。对于年径流序列长度大于35年的测站,功率谱分析和最大熵谱分析的分析结果一致,但是对于序列长度小于35年的序列,功率谱分析表现出分辨率低的不足;最大熵谱分析具有分辨率高的特点,提取的主要周期符合实际。  相似文献   
93.
Goat dairy products are considered as a suitable alternative to cow milk products for some special categories of consumers (infants, old, and convalescent people). In the present research, a study on the lipid fraction of commercial goat milk and cheese samples purchased from Umbrian market was carried out. Particular attention has been paid to evaluating conjugated linoleic acid (CLA) content and determining some interesting nutritional indexes. The results of goat milk samples showed that saturated, monounsaturated and polyunsaturated fatty acid contents were on average 71.2, 23.4, and 3.8 %, respectively. CLA content (cis-9, trans-11 isomer) was on average 11.5 mg/100 g in milk. Considerable variability was observed for n6/n3 ratio that varied from 2.7 to 10.6 in the considered goat milk samples. With regard to goat cheese samples CLA concentration was on average 118.8 mg/100 g in fresh cheese and 217.7 mg/100 g in semi-hard cheese, and the difference was not significant. Interestingly, α-linolenic acid content was higher and n6/n3 ratio was lower in semi-hard with respect to fresh cheese samples (p < 0.05).  相似文献   
94.
通过聚丙烯酰胺(PAM)的霍夫曼反应得到的聚乙烯胺(PVAm)与淀粉共混制备PVAm/淀粉复合物。在中性造纸条件下,PVAm/淀粉复合物对再生浆具有显著的助滤和纸张增强作用。当添加量为0.5%(对绝干浆)时,样品SF-1502的纸张干抗张强度增加33.3%,湿抗张强度提高2倍,打浆度降低41.3%。  相似文献   
95.
通过分子生物学手段即根系差异蛋白质组学分析不同养地方式处理对烤烟生长的影响。结果表明,共有39个蛋白质表达丰度发生明显变化,LC-MS/MS成功鉴定24个差异蛋白质点。经生物信息学分析,其中22个蛋白质的功能得到鉴定,其中2个与香气有关的蛋白,转酮醇酶、GDP-甘露糖-3’,5’-表异构酶(GME),这两个蛋白在稻草回田上调表达,有助于烟草品质提高,而紫云英处理下调表达,不利于品质提高。还鉴定到涉及多种信号转导、物质运输、蛋白质代谢、能量代谢等途径的蛋白,均对烟草生长发育起重要作用,这些酶在稻草回田处理和紫云英回田处理上调表达,促进烟草的生长,而在冬闲处理下调表达,生长较弱。研究结果显示,稻草回田有利于烟草的生长,有利于提高烟草产量和品质且经济效益较好。  相似文献   
96.
Soil and water conservation ecological compensation can be simply defined as a monetary payment to offset the environmental loss. An illustration is given in this study describing the payment compensation to water resource conservation and soil losses in Erlongshan reservoir catchment, China. A semi-distributed hydrological SWAT model was applied to establish compensation standard considering six scenarios of land use changes by combined application of remote sensing and geographic information systems. Cost-benefit analysis (CBA) method is applied to evaluate the function of soil and water conservation, of which marginal opportunity cost and market value methods have been explored calculate the cost and benefit of water and soil conservation ecological function from provider and beneficiaries. Finally the ecological compensation of soil and water conservation for different land-use scenarios is calculated incorporating benefit apportion coefficient. The results provide an economically evaluated and market-oriented standard for the study of eco-compensation of environmental services and will be of great benefit to the implementation of soil and water conservation at a mesoscale catchment scale.  相似文献   
97.
    
Transition metal catalysts are widely used in the 2e− ORR due to their cost-effectiveness. However, they often encounter issues related to low activity. Defect engineering are used on developing highly active catalysts, which can effectively modify active sites and promote electron transfer. Here, carbon-coated Ni3S2 (Ni3S2@C), where the additional sulfur vacancies (VS) is prepared induced by the carbon layer is coupled with active nickel sites. Through in situ and ex situ experiments combined with DFT calculations, it is demonstrated that the carbon layer can regulate the quantity of VS in Ni3S2. Materials with a higher concentration of VS exhibit enhanced 2e− ORR activity and higher H2O2 selectivity. In situ Raman spectroscopy confirms that Ni serves as the key active site in this catalyst. DFT calculations indicate that the OOH binding energy (ΔG) decreases with an increase in the number of VS, favoring the protonation of *OOH to generate H2O2. Upon performance testing, the average H2O2 selectivity is 92.3%, with the highest yield reaching up to 3860 mmol gcat−1 h−1. It is noteworthy that Ni3S2@C exhibits high stability, with only a slight decrease in 2e− pathway selectivity after 5000 cycles of ADT.  相似文献   
98.
    
The spin‐gapless semiconductors (SGSs) are a new class of zero‐gap materials which have fully spin polarized electrons and holes. They bridge the zero‐gap materials and the half‐metals. The band structures of the SGSs can have two types of energy dispersion: Dirac linear dispersion and parabolic dispersion. The Dirac‐type SGSs exhibit fully spin polarized Dirac cones, and offer a platform for massless and fully spin polarized spintronics as well as dissipationless edge states via the quantum anomalous Hall effect. With fascinating spin and charge states, they hold great potential for spintronics. There have been tremendous efforts worldwide to find suitable candidates for SGSs. In particular, there is an increasing interest in searching for Dirac type SGSs. In the past decade, a large number of Dirac or parabolic type SGSs have been predicted by density functional theory, and some parabolic SGSs have been experimentally demonstrated. The SGSs hold great potential for spintronics, electronics, and optoelectronics with high speed and low‐energy consumption. Here, both the Dirac and the parabolic types of SGSs in different material systems are reviewed and the concepts of the SGS, novel spin and charge states, and the potential applications of SGSs in next‐generation spintronic devices are outlined.  相似文献   
99.
    
Hepatocellular carcinoma (HCC) is the third leading cause of cancer‐related death worldwide. The prognosis of HCC remains very poor; thus, an effective treatment remains urgent. Herein, a type of nanomedicine is developed by conjugating Fe@Fe3O4 nanoparticles with ginsenoside Rg3 (NpRg3), which achieves an excellent coupling effect. In the dimethylnitrosamine‐induced HCC model, NpRg3 application significantly prolongs the survival of HCC mice. Further research indicates that NpRg3 application significantly inhibits HCC development and eliminates HCC metastasis to the lung. Notably, NpRg3 application delays HCC‐induced ileocecal morphology and gut microbial alterations more than 12 weeks during HCC progression. NpRg3 administration elevates the abundance of Bacteroidetes and Verrucomicrobia, but decreases Firmicutes. Twenty‐nine predicted microbial gene functions are enriched, while seven gene functions are reduced after NpRg3 administration. Moreover, the metabolomics profile presents a significant progression during HCC development, but NpRg3 administration corrects tumor‐dominant metabolomics. NpRg3 administration decreases 3‐indolepropionic acid and urea, but elevates free fatty acids. Importantly, NpRg3 application remodels the unbalanced correlation networks between gut microbiota and metabolism during HCC therapy. In conclusion, nanoparticle conjugation of ginsenoside Rg3 inhibits HCC development and metastasis via the remodeling of unbalanced gut microbiota and metabolism in vivo, providing an antitumor therapy strategy.  相似文献   
100.
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