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   4095篇
  免费   114篇
  国内免费   1篇
电工技术   25篇
综合类   3篇
化学工业   612篇
金属工艺   18篇
机械仪表   32篇
建筑科学   202篇
矿业工程   85篇
能源动力   55篇
轻工业   433篇
水利工程   26篇
石油天然气   6篇
无线电   117篇
一般工业技术   428篇
冶金工业   1708篇
原子能技术   9篇
自动化技术   451篇
  2022年   28篇
  2021年   66篇
  2020年   34篇
  2019年   48篇
  2018年   50篇
  2017年   60篇
  2016年   74篇
  2015年   53篇
  2014年   58篇
  2013年   216篇
  2012年   144篇
  2011年   186篇
  2010年   169篇
  2009年   153篇
  2008年   199篇
  2007年   198篇
  2006年   143篇
  2005年   168篇
  2004年   136篇
  2003年   155篇
  2002年   126篇
  2001年   97篇
  2000年   84篇
  1999年   99篇
  1998年   82篇
  1997年   86篇
  1996年   100篇
  1995年   75篇
  1994年   85篇
  1993年   99篇
  1992年   96篇
  1991年   37篇
  1990年   84篇
  1989年   68篇
  1988年   70篇
  1987年   71篇
  1986年   72篇
  1985年   61篇
  1984年   53篇
  1983年   48篇
  1982年   42篇
  1981年   32篇
  1980年   21篇
  1979年   33篇
  1978年   29篇
  1977年   14篇
  1976年   19篇
  1975年   17篇
  1974年   13篇
  1973年   16篇
排序方式: 共有4210条查询结果,搜索用时 344 毫秒
101.
The objectives of this study were to examine varying extraction conditions of Thymus vulgaris L. as related to phenolic content and profiles of the extracts and their antioxidant, antihypertensive and antidiabetic properties. Phenolics were extracted under various conditions pertaining to free and bound phenolics, solvent type and combination of extraction time and temperature, and these extracts were evaluated in terms of their antioxidant activities and inhibitory activities of angiotensin‐converting enzyme (ACE), α‐glucosidase and α‐amylase. The acetone–water solvent mixture (1:1; v/v) produced the extract with the greatest phenolic content, antioxidant activity and inhibitory activities of ACE and α‐glucosidase. The optimal extraction temperature for maximum phenolic content and antioxidant activity associated with methanol extraction was 60 °C, whereas a lower temperature at 40 °C was required to maximise inhibitory activities for ACE, α‐glucosidase and α‐amylase. An inverse relationship was seen between antioxidant and glucosidase inhibitory activities vs. the ACE and α‐amylase inhibitory activities, which suggests the need for extractions to be directed to specific bioactivities of thyme extracts. Generally, the results indicate major differences in phenolic profiles among the tested extraction conditions with thymol as the predominant phenolic seen in most extractions, while gallic acid, rosmarinic acid or diosmin also predominated in other extracts. Extracts with the same predominant phenolic compound and similar phenolic content showed major disparities in their ACE, glucosidase and α‐amylase inhibitory activities, indicating that the major phenolic profiles of thyme extracts may not be necessarily related to the degree of inhibition of ACE, glucosidase and α‐amylase enzymes.  相似文献   
102.
103.
104.
The Mediterranean diet is considered one of the healthiest diets in the world. This is often attributed to low saturated fat consumption, moderate wine consumption, and high vegetable consumption. However, herbs and spices associated with these diets may also play an important role in the quality of this diet. This review summarizes the most recent research regarding the anti-diabetic, anti-inflammatory, anti-hyperlipidemic and anti-hypertensive properties of this collection of culinary species. Additionally, this review briefly summarizes studies performed on lesser known herbs from around the world, with the goal of identifying new culinary species that may be useful in the treatment or prevention of diseases.  相似文献   
105.
106.
107.
108.
The astrocytic endfoot membranes of the healthy blood-brain barrier—contacting the capillary—are covered with a large number of the water channel aquaporin 4 (AQP4). They form orthogonal arrays of particles (OAPs), which consist of AQP4 isoform M1 and M23. Under pathologic conditions, AQP4 is distributed over the whole cell and no or only small OAPs are found. From cell culture experiments, it is known that cells transfected only with AQP4-M1 do not form OAPs or only small ones. We hypothesized that in astrocytomas the situation may be comparable to the in vitro experiments expecting an upregulation of AQP4-M1. Quantitative Real-time PCR (qRT-PCR) of different graded astrocytomas revealed an upregulation of both isoforms AQP4 M1 and M23 in all astrocytomas investigated. In freeze fracture replicas of low-grade malignancy astrocytomas, more OAPs than in high-grade malignancy astrocytomas were found. In vitro, cultured glioma cells did not express AQP4, whereas healthy astrocytes revealed a slight upregulation of both isoforms and only a few OAPs in freeze fracture analysis. Taken together, we found a correlation between the decrease of OAPs and increasing grade of malignancy of astrocytomas but this was not consistent with an upregulation of AQP4-M1 in relation to AQP4 M23.  相似文献   
109.
A pilot study was conducted to determine whether membrane treatment on a side stream of recirculating cooling-tower water could reduce overall water usage and discharge. The treated permeate was returned to the cooling tower while the concentrate was discharged to the sanitary sewer. Flow rates, pressures and water chemistry were monitored. The pilot demonstrated potential substantial water savings. Maximum make-up water and discharge reduction were 16% and 49%, respectively. As high as possible permeate recovery is needed to maximize water conservation. Silica scaling on the membranes limited water savings in this pilot. Development of membranes with a solute-rejection capacity less than the 92% average of the membranes used in the pilot would assist in optimizing water savings. Decreased water outlays compensated for the additional energy used by membrane treatment. Scaling control is critical for economic operation.  相似文献   
110.
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