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   14850篇
  免费   312篇
  国内免费   152篇
电工技术   169篇
综合类   6篇
化学工业   1406篇
金属工艺   510篇
机械仪表   150篇
建筑科学   261篇
矿业工程   1篇
能源动力   162篇
轻工业   404篇
水利工程   62篇
石油天然气   22篇
无线电   731篇
一般工业技术   1071篇
冶金工业   680篇
原子能技术   123篇
自动化技术   9556篇
  2023年   51篇
  2022年   150篇
  2021年   184篇
  2020年   123篇
  2019年   128篇
  2018年   158篇
  2017年   145篇
  2016年   150篇
  2015年   151篇
  2014年   385篇
  2013年   462篇
  2012年   1051篇
  2011年   3416篇
  2010年   1390篇
  2009年   1284篇
  2008年   950篇
  2007年   825篇
  2006年   621篇
  2005年   699篇
  2004年   655篇
  2003年   703篇
  2002年   377篇
  2001年   69篇
  2000年   70篇
  1999年   91篇
  1998年   211篇
  1997年   114篇
  1996年   82篇
  1995年   36篇
  1994年   37篇
  1993年   35篇
  1992年   38篇
  1991年   28篇
  1990年   28篇
  1989年   27篇
  1988年   38篇
  1987年   23篇
  1986年   38篇
  1985年   34篇
  1984年   42篇
  1983年   26篇
  1982年   19篇
  1981年   18篇
  1980年   17篇
  1979年   15篇
  1977年   12篇
  1976年   25篇
  1974年   12篇
  1973年   11篇
  1972年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Soybean oil hydrogenation alters the linolenic acid molecule to prevent the oil from becoming rancid, however, health reports have indicated trans-fat caused by hydrogenation, is not generally regarded as safe. Typical soybeans contain approximately 80 g kg−1 to 120 g kg−1 linolenic acid and 240 g kg−1 of oleic acid. In an effort to accommodate the need for high-quality oil, the United Soybean Board introduced an industry standard for a high oleic acid greater than 750 g kg−1 and linolenic acid less than 30 g kg−1 oil. By combing mutations in the soybean plant at four loci, FAD2-1A and FAD2-1B, oleate desaturase genes and FAD3A and FAD3C, linoleate desaturase genes, and seed oil will not require hydrogenation to prevent oxidation and produce high-quality oil. In 2017 and 2018, a study comparing four near-isogenic lines across multiple Tennessee locations was performed to identify agronomic traits associated with mutations in FAD3A and FAD3C loci, while holding FAD2-1A and FAD2-1B constant in the mutant (high oleic) state. Soybean lines were assessed for yield and oil quality based on mutations at FAD2-1 and FAD3 loci. Variations of wild-type and mutant genotypes were compared at FAD3A and FAD3C loci. Analysis using a generalized linear mixed model in SAS 9.4, indicated no yield drag or other negative agronomic traits associated with the high oleic and low linolenic acid genotype. All four mutations of fad2-1A, fad2-1B, fad3A, and fad3C were determined as necessary to produce a soybean with the new industry standard (>750 g kg−1 oleic and <30 g kg−1 linolenic acid) in a maturity group-IV-Late cultivar for Tennessee growers.  相似文献   
2.
Under normal physiological conditions the brain primarily utilizes glucose for ATP generation. However, in situations where glucose is sparse, e.g., during prolonged fasting, ketone bodies become an important energy source for the brain. The brain’s utilization of ketones seems to depend mainly on the concentration in the blood, thus many dietary approaches such as ketogenic diets, ingestion of ketogenic medium-chain fatty acids or exogenous ketones, facilitate significant changes in the brain’s metabolism. Therefore, these approaches may ameliorate the energy crisis in neurodegenerative diseases, which are characterized by a deterioration of the brain’s glucose metabolism, providing a therapeutic advantage in these diseases. Most clinical studies examining the neuroprotective role of ketone bodies have been conducted in patients with Alzheimer’s disease, where brain imaging studies support the notion of enhancing brain energy metabolism with ketones. Likewise, a few studies show modest functional improvements in patients with Parkinson’s disease and cognitive benefits in patients with—or at risk of—Alzheimer’s disease after ketogenic interventions. Here, we summarize current knowledge on how ketogenic interventions support brain metabolism and discuss the therapeutic role of ketones in neurodegenerative disease, emphasizing clinical data.  相似文献   
3.
4.
d -Glycero-d -manno-heptose-1β,7-bisphosphate (HBP) and d -glycero-d -manno-heptose-1β-phosphate (H1P) are bacterial metabolites that were recently shown to stimulate inflammatory responses in host cells through the activation of the TIFA-dependent NF-κB pathway. To better understand structure-based activity in relation to this process, a family of nonhydrolyzable phosphonate analogues of HBP and H1P was synthesized. The inflammation modulation by which these molecules induce the TIFA-NF-κB signal axis was evaluated in vivo at a low-nanomolar concentration (6 nM) and compared to that of the natural metabolites. Our data showed that three phosphonate analogues had similar stimulatory activity to HBP, whereas two phosphonates antagonized HBP-induced TIFA-NF-κB signaling. These results open new horizons for the design of pro-inflammatory and innate immune modulators that could be used as vaccine adjuvant.  相似文献   
5.
6.
This work investigates emulsion templating to synthesize hexadecane oil/geopolymer composites. In a system with hexadecane as the internal (dispersed) phase and an alkali activated continuous phase without added surfactant, adding aluminosilicate clay particles does not increase resistance against creaming or coalescence, while adding a surfactant (L35 or CTAB) stabilizes the solid-liquid interface. Infrared studies and rheological studies of the associated geopolymerization determined that the presence of the organic phase or surfactant has no significant effect on the geopolymerization kinetics, as determined by the change in time of the Si-O-T IR stretching frequency and the rheological moduli involved during the process. The stabilization of the organic template is reminiscent of Pickering emulsion even though we employ a much greater amount of inorganic material for geopolymer formation. Although the addition of surfactant has a significant effect on the behavior of the paste, the percolation of the network remains unmodified, highlighting the fact that the phenomenon is not dependent on viscosity. Finally, rheological measurements were used to obtain the mass fractal dimension of the as-made gel network, which is able to differentiate the interfacial effect between surfactant molecules with a slightly denser interphase when a cationic surfactant is used.  相似文献   
7.
8.
9.
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