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   242篇
  免费   12篇
电工技术   3篇
化学工业   51篇
金属工艺   2篇
机械仪表   2篇
建筑科学   8篇
能源动力   14篇
轻工业   42篇
无线电   39篇
一般工业技术   17篇
冶金工业   57篇
自动化技术   19篇
  2023年   2篇
  2022年   3篇
  2021年   11篇
  2020年   12篇
  2019年   8篇
  2018年   12篇
  2017年   8篇
  2016年   7篇
  2015年   2篇
  2014年   9篇
  2013年   10篇
  2012年   7篇
  2011年   7篇
  2010年   7篇
  2009年   11篇
  2008年   5篇
  2007年   6篇
  2006年   10篇
  2005年   1篇
  2004年   4篇
  2003年   2篇
  2002年   4篇
  2001年   2篇
  2000年   3篇
  1999年   2篇
  1998年   26篇
  1997年   14篇
  1996年   4篇
  1995年   6篇
  1994年   7篇
  1993年   7篇
  1991年   1篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1986年   4篇
  1985年   2篇
  1983年   5篇
  1982年   3篇
  1981年   3篇
  1979年   2篇
  1978年   2篇
  1977年   1篇
  1976年   5篇
排序方式: 共有254条查询结果,搜索用时 31 毫秒
61.
62.
A new, easily implementable technique for mode-field radius measurement is described. It is based on a dynamical filtering and the detection of two harmonics of the fibre output radiation. The results are presented and discussed.  相似文献   
63.
The aim of this study was to evaluate the effect of transdermal clonidine on hemodynamic and metabolic parameters in patients who have elevated blood pressure and non-insulin-dependent diabetes mellitus (NIDDM). After a 2-week run in placebo period, 20 NIDDM patients who had diastolic blood pressure in the range of 90 to 105 mm Hg underwent a randomized, single blind, placebo controlled, cross-over study of 4 week treatment with clonidine (transdermal patch 2.5 mg/week) or placebo (inactive patch). Compared with placebo, clonidine significantly reduced systolic (153 +/- 6 v 163 +/- 8) and diastolic (88 +/- 2 v 98 +/- 3.5 mm Hg, P = .001) blood pressure, left ventricular mass (94 +/- 11 v 99 +/- 12 g/m2, P < .01) and fasting glucose levels. Total glucose disposal (glucose clamp) was 6.5 +/- 1.5 with placebo and 7.1 +/- 1.6 mg/kg/min with clonidine (P < .01). Oxidative glucose disposal (indirect calorimetry) was also greater after clonidine. Plasma glucose, insulin, and C-peptide responses following oral glucose (75 g) were significantly lower after clonidine, as well as urinary albumin excretion. Transdermal clonidine is effective in reducing blood pressure in hypertensive NIDDM patients and is well tolerated. It may be useful to reduce the cardiovascular impact of hypertension in diabetes mellitus.  相似文献   
64.
This paper looks at how articulators can be of value in everyday NHS practice. A variation on the conventional classification of articulators is suggested with advice provided for the practitioner who wants to enhance his or her restorative work without immediately investing in high cost equipment. It is argued that rather than prolong chairside time, for specific types of treatment the use of an appropriate articulator and facebow can not only enhance the quality of the completed restoration, but also save on chairside time.  相似文献   
65.
66.
Epidemiologic studies have provided evidence of an inverse relation between coronary artery disease and antioxidant intake, and vitamin E supplementation in particular. The oxidative-modification hypothesis implies that reduced atherosclerosis is a result of the production of LDL that is resistant to oxidation, but linking the reduced oxidation of LDL to a reduction in atherosclerosis has been problematic. Several important additional mechanisms may underlie the role of antioxidants in preventing the clinical manifestations of coronary artery disease (Fig. 2). Specifically, there is evidence that plaque stability, vasomotor function, and the tendency to thrombosis are subject to modification by specific antioxidants. For example, cellular antioxidants inhibit monocyte adhesion, protect against the cytotoxic effects of oxidized LDL, and inhibit platelet activation. Furthermore, cellular antioxidants protect against the endothelial dysfunction associated with atherosclerosis by preserving endothelium-derived nitric oxide activity. We speculate that these mechanisms have an important role in the benefits of antioxidants.  相似文献   
67.
Demographic changes have shaped the nation's past and will continue to shape its future. During the first half of the 1990s, the U.S. population grew, on average, by 2.7 million people each year, reaching 262.8 million in 1995. Population growth is projected to continue for the next 50 years, although at a slower rate. The forecast is for more than 390 million Americans by the year 2050. As the U.S. population grows, it will increasingly become more diverse along many socioeconomic dimensions. This increasing diversity will represent an historic shift in America's racial and ethnic composition with long-range implications for how we view racial issues, how we define racial categories and how the political landscape will be refashioned. By the middle of the 21st century the "minority" population will almost equal the size of the non-Hispanic white population. The minority population grew 14 percent during the first half of the 1990s compared with a 3 percent growth in the non-Hispanic white population. But even within the minority population, growth rates varied. Between 1990 and 1995, the Asian population grew 23 percent, the Hispanic population 20 percent and the African American population increased their numbers by 8 percent. Hispanics are projected to outnumber African Americans within the next 15 years. In part, these demographic changes are shifting because of U.S. immigration policies. Until the early 1960s, immigrants to the United States were primarily of white, European stock. Nowadays, Europeans account for about 20 percent of the immigrants. Three-quarters of legal immigrants in the mid-1990s now come from Latin America, the Caribbean and Asia. The increasing racial and ethnic diversity in the United States will create both challenges and opportunities for U.S. schools and businesses in the future. The magnitude of these numbers and their geographic location will be important factors to consider as we prepare for the 21st century.  相似文献   
68.
This paper proposes a methodological approach for the multi-objective optimization of steel towers made from prefabricated cylindrical stacks that are typically used in the oil and gas sector. The goal is to support engineers in designing economical products while meeting structural requirements. The multi-objective optimization approach involves the minimization of the weights and costs related to the manufacturing and assembly phases. The method is based on three optimization levels. The first is used in the preliminary design phase when a company receives a request for proposal. Here, minimal information on the order is available, and the time available to formulate an offer is limited. Thus, parametric cost models and simplified 1-D geometries are used in the optimization loop performed by genetic algorithms. The second phase, the embodiment design phase, starts when an offer becomes an order based on the results of the first stage. Simplified shell geometries and advanced parametric cost models are used in the optimization loop, which present a restricted problem domain. In the last phase involving detailed design, a full 3-D computer-aided design model is generated, and specific finite-element method simulations are performed. The cost estimations, given the high levels of detail considered, are analytic and are performed using dedicated software.  相似文献   
69.
The influence of different factors (submerged and/or solid‐state fermentation, pediococci strain, lupine variety and protein isolation process) on the protein digestibility, total phenolic compounds (TPC) content and radical scavenging activity of Lupinus luteus and angustifolius wholemeal and protein isolates was evaluated. As safety factor, biogenic amines (Bas) formation was analysed. The Pediococcus pentosaceus strains No. 8, No. 9 and No. 10 are suitable starters for lupine wholemeal fermentation and both applied processes (fermentation and protein isolation) increase protein digestibility (by 10%). Higher TPC content in fermented wholemeal can be obtained, compare to isolates. In SMF isolates by 58.3%, 68.2%, 95.6%, 76.6%, lower content of phenylethylamine, putrescine, cadaverine and histamine, respectively was found. The highest protein digestibility and the lowest BAs content using submerged fermentation with pediococcus No. 8 in lupine variety Vilnius protein isolates can be obtained and this technology for high‐quality lupine proteins preparation can be recommended.  相似文献   
70.
The irradiation of four Italian white wines with a visible light comparable to that encountered in the market place showed a modification in the amount of aliphatic esters in the wines. Aliphatic esters are responsible for fruity aromas in wines. The first wine studied was the Gewürztraminer, a white wine from Alto Adige (Northern Italy). The amounts of the esters presents in the wine decreased. All the curves follow a pseudo-first-order kinetics. This behaviour can be explained assuming a photooxidation process catalysed by riboflavin. When Arneis Blangè was irradiated, ethyl acetate showed an increase after one day of irradiation; its content then decreased and after five days' irradiation its concentration reached a maximum. Conversely, the concentration of other aliphatic esters decreased after one day's irradiation and then increased progressively to reach a maximum after five days' irradiation. The same behaviour was observed with Pecorino wine. In this case, the concentration of the aliphatic esters decreased until the second day of irradiation but increased after five days' irradiation. In the case of the irradiation of Lighea Zibibbo all the esters showed an increase in concentration after one day of irradiation. The concentration decreased after two days' irradiation, and then increased to reach a maximum after seven days of irradiation. The increase in the amount of esters in some wines and, by contrast, the decrease in the same compounds in Gewürztraminer can be explained by considering that, during the irradiation, the pH of Gewürztraminer did not change, while the pH of Arneis Blangè changed following a curve similar to that showed by the concentration of esters. The pH change can be explained assuming the presence of a photocatalytic process induced by the presence of metals in the wines and influencing the amount of tartaric acid.  相似文献   
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