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   237篇
  免费   7篇
电工技术   2篇
化学工业   47篇
金属工艺   2篇
机械仪表   6篇
建筑科学   7篇
能源动力   6篇
轻工业   36篇
水利工程   1篇
石油天然气   1篇
无线电   17篇
一般工业技术   38篇
冶金工业   31篇
原子能技术   1篇
自动化技术   49篇
  2022年   10篇
  2021年   7篇
  2020年   6篇
  2019年   5篇
  2018年   5篇
  2017年   9篇
  2016年   7篇
  2015年   6篇
  2014年   6篇
  2013年   13篇
  2012年   22篇
  2011年   17篇
  2010年   15篇
  2009年   11篇
  2008年   10篇
  2007年   12篇
  2006年   6篇
  2005年   6篇
  2004年   5篇
  2003年   4篇
  2002年   3篇
  2001年   4篇
  2000年   3篇
  1999年   3篇
  1998年   8篇
  1997年   5篇
  1996年   9篇
  1995年   6篇
  1994年   2篇
  1993年   3篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1987年   2篇
  1983年   1篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1969年   1篇
  1968年   2篇
  1967年   2篇
  1966年   1篇
排序方式: 共有244条查询结果,搜索用时 15 毫秒
41.
Although Trifolium pratense (Red Clover) is considered to be one of the leading crops for livestock grazing, it could also be used as a potential source of bioactive compounds in phytopharmacy. The aim of this study was to investigate the phenolic content and its biological activity at the growth phases (30 cm, 50 cm, and bud) of this plant. The phenolic compounds in methanolic extracts of T. pratense leaves at three growth stages, obtained by Microwave Assisted Extraction, were quantified using the HPLC-ESI-MS/MS technique, and their antioxidant and antimicrobial activity were assessed. Isoflavonoids, genistein, and daidzein, as well as other phenols, p-hydroxybenzoic and caffeic acids, kaempferol 3-O-glucoside, quercetin 3-O-glucoside, and hyperoside were found in all the extracts, but the content of these compounds was the highest in the extract of the plant at the lowest growth stage (30 cm, vegetative). Therefore, this extract showed the best antioxidant potential and it was most effective against bacterial strains such as Escherichia coli and Enterobacter aerogenes. These results indicated that red clover has potential health benefits, and that growth phase contributes to its biological activity. The extract of red clover at the growth stage of 30 cm is a great source of bioactive compounds and could be used in phytotherapy and nutrition.  相似文献   
42.
Several formulas for preterm infants contain medium-chain triglycerides (MCT) to enhance fat absorption. Although fat absorption with MCT was slightly higher in several studies in preterm infants, a beneficial effect on growth has only been reported in one publication. We hypothesized that when part of the fat blend of preterm formula is substituted by MCT oil, this might lead to a different metabolic pattern in which, due to the preferential oxidation of MCT, an increase in lipogenesis from glucose could lead to an increase in metabolic rate. To study the impact of MCT on glucose metabolism, 18 preterm infants were randomized to receive either an MCT or an LCT formula containing 38- and 6%-by-weight medium-chain fatty acids, respectively, in their fat blend. At 4 wk of age, the metabolic rate, substrate utilization, glucose kinetics, and oxidation were measured by indirect respiratory calorimetry in combination with a constant-rate oral infusion of [U-13C]glucose. The "true" rate of appearance of glucose (Ra "true") was measured from the dilution of the uniformly labeled (m + 6) species of infused tracer, whereas "apparent" rate of appearance of glucose (Ra "apparent") was measured from the dilution of infused tracer C (carbon). The latter was measured by an on-line combustion method using a gas chromatograph-isotope ratio mass spectrometer. At a carbohydrate intake of 8.4 mg.kg-1.min-1, total utilization of carbohydrate was equal in both groups at 7.6 mg.kg-1.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
43.
The role of a target's orthographic neighborhood in visual word recognition was investigated in 2 lexical decision experiments. In both experiments, some stimuli had 1 letter delayed relative to the presentation of the rest of the stimulus. Exp 1 showed that delaying a letter position, which yielded a potentially competitive neighbor, was more costly to target recognition than delaying a position that yielded no neighbors. This effect was strongest when one of these neighbors was of higher frequency than the target itself. Additionally, the effect was reduced for words with a high friendly-to-unfriendly-neighbor ratio (friendly neighbors being those words containing the delayed letter). In Exp 2 the difficulty of the word–nonword discrimination was manipulated by varying the density of the nonwords' neighborhoods. Only when the nonwords had many neighbors at several positions did the word responses show neighborhood competition effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
44.
The maximal aortic diameter is the only clinically applied predictor of abdominal aortic aneurysm (AAA) progression and indicator for surgical repair. Circulating biomarkers resulting from AAA pathogenesis are attractive candidates for the diagnosis and prognosis of aneurysmal disease. Due to the reported role of interleukin 33 in AAA development, we investigated the corresponding circulating receptor molecules of soluble suppression of tumorigenesis 2 (sST2) in AAA patients regarding their marker potential in diagnosis and prognosis. We conducted a single-center retrospective cohort study in a diagnostic setting, measuring the circulating serum sST2 protein levels of 47 AAA patients under surveillance, matched with 25 peripheral artery disease (PAD) patients and 25 healthy controls. In a prognostic setting, we analyzed the longitudinal monitoring data of 50 monitored AAA patients. Slow versus fast AAA progression was defined as a <2 or ≥2 mm increase in AAA diameter over 6 months and a <4 or ≥4 mm increase over 12 months. Additionally, the association of circulating serum sST2 and AAA growth was investigated using a specifically tailored log-linear mixed model. Serum sST2 concentrations were significantly increased in AAA patients compared with healthy individuals: the median of AAA patient cohort was 112.72 ng/mL (p = 0.025) and that of AAA patient cohort 2 was 14.32 ng/mL (p = 0.039) versus healthy controls (8.82 ng/mL). Likewise, PAD patients showed significantly elevated sST2 protein levels compared with healthy controls (the median was 12.10 ng/mL; p = 0.048) but similar concentrations to AAA patients. Additionally, sST2 protein levels were found to be unsuited to identifying fast AAA progression over short-term periods of 6 or 12 months, which was confirmed by a log-linear mixed model. In conclusion, the significantly elevated protein levels of sST2 detected in patients with vascular disease may be useful in the early diagnosis of AAA but cannot distinguish between AAA and PAD or predict AAA progression.  相似文献   
45.
Bleeding tendency, a prominent feature of patients with Gaucher disease (GD), is associated with abnormal platelet function. Brain-derived neurotrophic factor (BDNF) is a protein with neuroprotective potential stored in alpha granules of circulating platelets. Here we studied BDNF levels in 50 patients with type I GD (GD1) and their correlation with platelet activity and bleeding tendency. Flow cytometry was used to test unstimulated and stimulated measurement of platelet surface-activated expression of αIIbβ3 integrin, P-selectin and lysosomal-associated membrane protein (LAMP3/CD63). Serum and plasma BDNF levels were quantified using ELISA. The bleeding history was recorded by a bleeding questionnaire. Serum BDNF levels were positively correlated with platelet count and moderately correlated with unstimulated and stimulated platelet P-selectin expression. Patients with more than one bleeding manifestation were shown to have lower serum BDNF levels, albeit similar platelet count. Plasma BDNF levels were significantly elevated in splenectomized patients and showed a moderate positive correlation with stimulated platelet CD63 expression. These observations demonstrate the first association between BDNF levels in the peripheral blood with platelet dysfunction and increased bleeding manifestation. The role of measuring serum BDNF for assessing platelet alpha degranulation defects and bleeding risk in patients with GD and the general population needs further study.  相似文献   
46.
Soybean (Glycine max) is an economically important crop which is very susceptible to salt stress. Tolerance to Na2SO4 stress was evaluated in soybean plants overexpressing or suppressing the phytoglobin GmPgb1. Salt stress depressed several gas exchange parameters, including the photosynthetic rate, caused leaf damage, and reduced the water content and dry weights. Lower expression of respiratory burst oxidase homologs (RBOHB and D), as well as enhanced antioxidant activity, resulting from GmPgb1 overexpression, limited ROS-induced damage in salt-stressed leaf tissue. The leaves also exhibited higher activities of the H2O2-quenching enzymes, catalase (CAT) and ascorbate peroxidase (APX), as well as enhanced levels of ascorbic acid. Relative to WT and GmPgb1-suppressing plants, overexpression of GmPgb1 attenuated the accumulation of foliar Na+ and exhibited a lower Na+/K+ ratio. These changes were attributed to the induction of the Na+ efflux transporter SALT OVERLY SENSITIVE 1 (SOS1) limiting Na+ intake and transport and the inward rectifying K+ channel POTASSIUM TRANSPORTER 1 (AKT1) required for the maintenance of the Na+/K+ balance.  相似文献   
47.
Temporal Constraint Satisfaction Problems (TCSP) is a well-known approach for representing and processing temporal knowledge. Important properties of the knowledge can be inferred by computing the minimal networks of TCSPs. Consistency and feasible values are immediately obtained; computing solutions can be assisted. Yet, in general, computing the minimal network of a disjunctive TCSP is intractable. The minimal network approach requires computation of the full network in order to answer a query. In this paper we characterize TCSPs for which subsets of the minimal network can be computed without having to compute the whole network. The partial computation is enabled by decomposition of the problem into a tree of sub-problems that share at most pairs of time points. Such decompositions are termed sim/2-tree decompositions. For TCSPs that have sim/2-tree decompositions, minimal constraints of input propositions can be computed by independent computations of the minimal networks of the sub-problems at most twice. It is also shown that the sim/2-tree characterization is a minimal set of conditions. The sim/2-tree decomposition extends former results about decomposition of a TCSP into bi-connected components. An algorithm for identifying a sim/2-tree decomposition of a TCSP is provided as well. Finally, the sim/2-tree decomposition is generalized in an inductive manner, which enables components of a decomposition to be further decomposed. For that purpose a model of Structured Temporal Constraint Satisfaction Problems (STCSP(n), 0 ⩽ n), where STCSP(0) is simply TCSP, STCSP(1) is a set of STCSP(0)s, and in general, STCSP(n) for 1 ⩽ n is a set of STCSP(n − 1)s, is introduced. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
48.
Media Use and Perceptions of Welfare   总被引:1,自引:0,他引:1  
This study examines public perceptions of the characteristics of a typical welfare recipient and of welfare programs, and how these perceptions reflect differences in individuals' media use. The evidence shows that contextually poor, event-centered, and personalized media content use, represented by exposure and attention to television cable news, and entertainment shows, works in the direction of introducing typical biases in welfare perceptions: perception of welfare recipients as non-White, female, of younger age, and of higher federal spending on welfare programs. In contrast, watching more thematic television stories about welfare and poverty, as well as reading public affairs content in newspapers, has overall positive effects on the accuracy of perceptions of welfare. In turn, perceptions of welfare recipients and welfare programs affect individual's support for welfare programs.  相似文献   
49.
50.
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