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   11582篇
  免费   534篇
  国内免费   174篇
电工技术   283篇
综合类   248篇
化学工业   2227篇
金属工艺   206篇
机械仪表   284篇
建筑科学   679篇
矿业工程   176篇
能源动力   282篇
轻工业   1098篇
水利工程   174篇
石油天然气   124篇
武器工业   37篇
无线电   1049篇
一般工业技术   1596篇
冶金工业   2281篇
原子能技术   226篇
自动化技术   1320篇
  2022年   123篇
  2021年   256篇
  2020年   190篇
  2019年   183篇
  2018年   195篇
  2017年   209篇
  2016年   221篇
  2015年   229篇
  2014年   359篇
  2013年   674篇
  2012年   537篇
  2011年   642篇
  2010年   538篇
  2009年   524篇
  2008年   542篇
  2007年   528篇
  2006年   460篇
  2005年   412篇
  2004年   334篇
  2003年   335篇
  2002年   295篇
  2001年   221篇
  2000年   191篇
  1999年   203篇
  1998年   177篇
  1997年   158篇
  1996年   141篇
  1995年   164篇
  1994年   158篇
  1993年   143篇
  1992年   147篇
  1991年   104篇
  1990年   118篇
  1989年   127篇
  1988年   129篇
  1987年   120篇
  1986年   122篇
  1985年   147篇
  1984年   137篇
  1983年   121篇
  1982年   132篇
  1981年   126篇
  1980年   93篇
  1979年   126篇
  1978年   124篇
  1977年   109篇
  1976年   94篇
  1975年   84篇
  1974年   94篇
  1973年   101篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
The β-Carotene (BC), an important precursor of vitamin A (VA), possesses antioxidant activity but is fat-soluble and has low bioavailability. In previous in-vitro assays evaluating antioxidant and 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) free radical scavenging, both BC and VA showed a strong ability to scavenge radicals and protected cells from oxidative stress. Here, we used artificially simulated gastrointestinal digestion and Caco-2 cell absorption models to evaluate the bioavailability of the BC during gastrointestinal digestion and absorption using high-performance liquid chromatography (HPLC) analysis. We observed high absorptive and transfer rates of BC and detected retinol metabolites (Vitamin A). Therefore, BC can be detected in the acidic gastrointestinal environment using HPLC. Optimised method provided better separation of BC and VA in the column, improving the accuracy of the test results.  相似文献   
2.
The sensitivity of a monitoring scheme depends on many factors including the variance of the charting statistic which is very important in the computation of the control limits. This paper discusses the computation of the variance of the recently proposed hybrid homogeneously weighted moving average (HHWMA) X¯ scheme which was based on an incorrect assumption. The correct variance is used to evaluate the run-length characteristics of the HHWMA X¯ scheme. It is observed that the incorrect variance has a significant impact on the sensitivity (or performance) of the HHWMA X¯ scheme.  相似文献   
3.
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic...  相似文献   
4.
5.
Yogurt preserves and enhances nutritional value of milk. In this study, we have compared several strains to determine the physicochemical, sensory, rheological and aroma characteristics of different yogurts. We used Lactobacillus gasseri LGZ 1029 (LG), commercial probiotic L. rhamnosus (LGG) and traditional fermentation strains Streptococcus thermophilus and L. bulgaricus (SL). Results showed that the flavour and texture characteristics of mixed-strain yogurts were obviously better than in single-strain yogurts. Addition of LG increased pseudoplastic behaviour, as shown by Herschel–Bulkley model analysis of rheological behaviour. The LG + SL group also had both the highest viscosity consistency index and thickening ability. In addition, a total of 57 volatile compounds were detected in yogurts and the fermentation with the addition of LG was mainly affected by ketones. Our study suggested that a yogurt with new attributes can be produced by using LGZ 1029.  相似文献   
6.
International Journal of Computer Vision - Expressive representations for characterizing face appearances are essential for accurate face detection. Due to different poses, scales, illumination,...  相似文献   
7.
The electrochemical water splitting to produce H2 in high efficiency with earth-abundant-metal catalysts remains a challenge. Here, we describe a simple “cyclic voltammetry + ageing” protocol at room temperature to activate Ni electrode (AC-Ni/NF) for hydrogen evolution reaction (HER), by which Ni/Ni(OH)2 heterostructure is formed at the surface. In situ Raman spectroscopy reveals the gradual growth of Ni/Ni(OH)2 heterostructure during the first 30 min of the aging treatment and combined with polarization measurements, it suggests a positive relation between the Ni/Ni(OH)2 amount and HER performance of the electrode. The obtained AC-Ni/NF catalyst, with plentiful Ni–Ni(OH)2 interfaces, exhibits remarkable performance towards HER, with the low overpotential of only 30 mV at a H2-evolving current density of 10 mA/cm2 and 153 mV at 100 mA/cm2, as well as a small Tafel slope of 46.8 mV/dec in 1 M KOH electrolyte at ambient temperature. The excellent HER performance of the AC-Ni/NF could be maintained for at least 24 h without obvious decay. Ex situ experiments and in situ electrochemical-Raman spectroscopy along with density functional theory (DFT) calculations reveal that Ni/Ni(OH)2 heterostructure, although partially reduced, can still persist during HER catalysis and it is the Ni–Ni(OH)2 interface reducing the energy barrier of H1 adsorption thus promoting the HER performance.  相似文献   
8.
A sizable part (~2%) of the human genome encodes for proteases. They are involved in many physiological processes, such as development, reproduction and inflammation, but also play a role in pathology. Mast cells (MC) contain a variety of MC specific proteases, the expression of which may differ between various MC subtypes. Amongst these proteases, chymase represents up to 25% of the total proteins in the MC and is released from cytoplasmic granules upon activation. Once secreted, it cleaves the targets in the local tissue environment, but may also act in lymph nodes infiltrated by MC, or systemically, when reaching the circulation during an inflammatory response. MC have been recognized as important components in the development of kidney disease. Based on this observation, MC chymase has gained interest following the discovery that it contributes to the angiotensin-converting enzyme’s independent generation of angiotensin II, an important inflammatory mediator in the development of kidney disease. Hence, progress regarding its role has been made based on studies using inhibitors but also on mice deficient in MC protease 4 (mMCP-4), the functional murine counterpart of human chymase. In this review, we discuss the role and actions of chymase in kidney disease. While initially believed to contribute to pathogenesis, the accumulated data favor a more subtle view, indicating that chymase may also have beneficial actions.  相似文献   
9.
Lithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes.  相似文献   
10.
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