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   3706篇
  免费   256篇
  国内免费   7篇
电工技术   62篇
综合类   2篇
化学工业   956篇
金属工艺   86篇
机械仪表   84篇
建筑科学   111篇
矿业工程   5篇
能源动力   117篇
轻工业   379篇
水利工程   23篇
石油天然气   23篇
无线电   372篇
一般工业技术   623篇
冶金工业   499篇
原子能技术   35篇
自动化技术   592篇
  2023年   31篇
  2022年   97篇
  2021年   132篇
  2020年   86篇
  2019年   100篇
  2018年   114篇
  2017年   128篇
  2016年   132篇
  2015年   110篇
  2014年   168篇
  2013年   229篇
  2012年   177篇
  2011年   266篇
  2010年   151篇
  2009年   181篇
  2008年   170篇
  2007年   185篇
  2006年   137篇
  2005年   106篇
  2004年   111篇
  2003年   92篇
  2002年   83篇
  2001年   58篇
  2000年   57篇
  1999年   67篇
  1998年   159篇
  1997年   106篇
  1996年   79篇
  1995年   56篇
  1994年   41篇
  1993年   47篇
  1992年   35篇
  1991年   24篇
  1990年   18篇
  1989年   20篇
  1988年   20篇
  1987年   25篇
  1986年   14篇
  1985年   17篇
  1984年   17篇
  1983年   14篇
  1982年   13篇
  1981年   16篇
  1980年   14篇
  1979年   9篇
  1978年   7篇
  1977年   8篇
  1976年   15篇
  1972年   5篇
  1965年   4篇
排序方式: 共有3969条查询结果,搜索用时 15 毫秒
51.
Here we apply the so-called Horace method for zero-dimensional schemes to error-correcting codes on complete intersections. In particular, we obtain sharper estimates on the minimum distance.  相似文献   
52.
The relationship between manometric and pH-metric data was studied in a group of 50 patients with symptoms of gastroesophageal reflux. Using a multiple regression analysis, we found that the total percentage of reflux was significantly correlated to the infradiaphragmatic length and resting pressure of the lower esophageal sphincter and also to the mean amplitude of the contractile waves of the distal esophagus, thus revealing the important role of these factors in the antireflux mechanism. When the patients were divided into groups according to their manometric characteristics and the values of the various pH-metric parameters between these groups compared using a one-way analysis of variance, we found that the amplitude of the contractile waves and the percentage of deglutitions without response were related not only to the total percentage of reflux but also to the number of reflux episodes of greater than 5 min duration and to the duration of the longest episode. This shows that prolonged exposure of the esophageal mucosa to the refluxed material may be due, in part, to an alteration in the capacity for esophageal clearing.  相似文献   
53.
54.
55.
56.
ThreeHypselodoris species,H. villafranca, H. cantabrica, and H. tricolor, have been studied in order to further investigate the defensive strategies of Chromodorididae mollusks from Iberian coasts. All animals possess large amounts of furanosesquiterpenoids, probably derived from their diet of sponges. The products are transferred and stored in specific sites of the mantle (mantle dermal formations, MDFs) to be used as chemical deterrents against predators. Chemical analysis of CantabrianHypselodoris species has led to the characterization of eight sesquiterpenoids. Among these, six have been found previously in both sponges and nudibranchs, while two are new natural products.Hypselodoris species cooccurring in the same area contained comparable mixtures of sesquiterpenoids. However, two populations ofH. cantabrica from different sites of the Cantabrian sea showed different metabolic patterns. All sesquiterpenoids induce feeding deterrence inCarassius auratus and two are also toxic toGambusia affinis.  相似文献   
57.
The kaolinite-mullite reaction series in single crystal kaolinite has been characterized by transmission electron microscopy. The exotherm observed at 980° C is attributed to the formation of a spinel phase. Mullite crystallites have also been observed with the spinel phase and both phases have a composition near that of 32 mullite. Subsequent heat treatment leads to the growth of mullite crystallites on the original kaolinite plates with the c-axis perpendicular to the plate.  相似文献   
58.
Vehicular sensor networks are an emerging network paradigm, suitable for various applications in vehicular environment making use of vehicles’ sensors as data sources and Inter-Vehicle Communication systems for the transmissions. We present a solution, based on vehicular sensor networks, for gathering data from a certain geographic area while satisfying with a specific delay bound. The method leverages the time interval during which the query is active in order to make the gathering process efficient, properly alternating data muling and multi-hop forwarding strategies like in delay-bounded routing protocols. Simulations show that our proposed solution succeeds in performing efficient data gathering outperforming other solutions.  相似文献   
59.
In Part 1 and Part 2 of this paper the preparation of linear polyethylene (PE)-carbon black processed composites with conducting electrical properties was examined by means of elongation flow injection moulding. Mould geometry was optimized in the form of oriented double-armed bars so as to give enhanced mechanical properties combined with a high degree of electrical homogeneity. The present paper deals with composites using a high molecular weight PE matrix. It is shown that the injection-moulded composite material exhibits not only a lower percolation threshold, c, than the conventionally pressure-moulded isotropic sample, but also conductivities two to three orders of magnitude larger than the latter. The radial and axial conductivity profiles, for concentrations well above c, are discussed in the light of the molecular orientation variations across the bars as determined by birefringence. A segregation of primary filler particles, during flow-induced orientation, into axial channels has been shown to explain the enhancement of conductivity detected in the injected mouldings. In addition, for filler concentrations near 7%, -profile analysis indicates the development of a uniform conductive-stiff inner cylinder, several millimetres wide, homogeneously extending along the full length of the injected material.  相似文献   
60.
Bilirubin toxicity to the central nervous system (CNS) is responsible for severe and permanent neurologic damage, resulting in hearing loss, cognitive, and movement impairment. Timely and effective management of severe neonatal hyperbilirubinemia by phototherapy or exchange transfusion is crucial for avoiding permanent neurological consequences, but these therapies are not always possible, particularly in low-income countries. To explore alternative options, we investigated a pharmaceutical approach focused on protecting the CNS from pigment toxicity, independently from serum bilirubin level. To this goal, we tested the ability of curcumin, a nutraceutical already used with relevant results in animal models as well as in clinics in other diseases, in the Gunn rat, the spontaneous model of neonatal hyperbilirubinemia. Curcumin treatment fully abolished the landmark cerebellar hypoplasia of Gunn rat, restoring the histological features, and reverting the behavioral abnormalities present in the hyperbilirubinemic rat. The protection was mediated by a multi-target action on the main bilirubin-induced pathological mechanism ongoing CNS damage (inflammation, redox imbalance, and glutamate neurotoxicity). If confirmed by independent studies, the result suggests the potential of curcumin as an alternative/complementary approach to bilirubin-induced brain damage in the clinical scenario.  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