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   1915篇
  免费   10篇
  国内免费   3篇
电工技术   27篇
综合类   1篇
化学工业   128篇
金属工艺   19篇
机械仪表   20篇
建筑科学   25篇
矿业工程   1篇
能源动力   14篇
轻工业   68篇
水利工程   6篇
石油天然气   2篇
无线电   128篇
一般工业技术   137篇
冶金工业   1203篇
原子能技术   4篇
自动化技术   145篇
  2021年   11篇
  2018年   6篇
  2017年   5篇
  2016年   7篇
  2015年   6篇
  2014年   14篇
  2013年   42篇
  2012年   23篇
  2011年   40篇
  2010年   30篇
  2009年   25篇
  2008年   39篇
  2007年   28篇
  2006年   34篇
  2005年   35篇
  2004年   35篇
  2003年   28篇
  2002年   26篇
  2001年   26篇
  2000年   24篇
  1999年   58篇
  1998年   360篇
  1997年   204篇
  1996年   154篇
  1995年   83篇
  1994年   64篇
  1993年   83篇
  1992年   33篇
  1991年   28篇
  1990年   38篇
  1989年   25篇
  1988年   19篇
  1987年   26篇
  1986年   14篇
  1985年   30篇
  1984年   7篇
  1983年   6篇
  1982年   13篇
  1981年   21篇
  1980年   16篇
  1979年   10篇
  1978年   10篇
  1977年   30篇
  1976年   60篇
  1975年   6篇
  1974年   7篇
  1973年   7篇
  1972年   6篇
  1971年   3篇
  1970年   6篇
排序方式: 共有1928条查询结果,搜索用时 15 毫秒
81.
82.
83.
STUDY OBJECTIVES: To compare lung deposition of fenoterol or flunisolide administered from a novel, multidose inhalation device delivering liquid droplets (RESPIMAT; Boehringer Ingelheim Ltd; Bracknell, UK) or from conventional metered-dose inhalers (MDIs) with and without spacers. DESIGN: Two randomized, three-way crossover studies. SETTING: Clinical research laboratory. PARTICIPANTS: Healthy, nonsmoking volunteers. INTERVENTIONS: In one study, radiolabeled aerosols of fenoterol from the RESPIMAT device and from a conventional MDI with or without an Aerochamber spacer (Trudell Medical; London, Ontario Canada). In the second study, radiolabeled aerosols of flunisolide from a RESPIMAT device, from a RESPIMAT device modified by inclusion of a baffle/impactor in the mouthpiece, and from a conventional MDI with an Inhacort spacer (Boehringer Ingelheim; Ingelheim, Germany). MEASUREMENTS AND RESULTS: Assessment of the deposition of fenoterol or flunisolide in the lung and oropharynx using gamma scintigraphy. Safety was assessed based on reported adverse effects and spirometry (FEV1, FVC, and peak expiratory flow rate) to detect any paradoxical bronchoconstriction. The RESPIMAT device delivered significantly more fenoterol to the lungs than either an MDI alone or an MDI with Aerochamber (39.2% vs 11.0% and 9.9% of metered dose, respectively; p<0.01). Oropharyngeal deposition of fenoterol from the new device was lower than that from the MDI (37.1% vs 71.7%, respectively; p<0.01). The RESPIMAT device deposited significantly more flunisolide in the lungs compared with MDI plus spacer (44.6% vs 26.4%, respectively; p<0.01), while resulting in similar oropharyngeal deposition (26.2% vs 31.2%, respectively). Introduction of a baffle into the RESPIMAT system reduced lung deposition of flunisolide to 29.5%, and oropharyngeal deposition to 7.8% (p<0.01). CONCLUSION: The RESPIMAT device may prove to be an effective alternative to MDIs for the administration of inhaled bronchodilators and corticosteroids. The high lung deposition and low oropharyngeal deposition may lead to improved efficacy and tolerability of inhaled medications, especially corticosteroids.  相似文献   
84.
A women aged 36 with a positive family anamnesis for autoimmune endocrine diseases and a history of thyroid diseases, developed major complaints of general malaise, orthostatic hypotension and loss of appetite after the start of a treatment with levothyroxin because of (sub)clinical hypothyroidism. She was found to suffer from primary adrenocortical insufficiency masked by excessive use of liquorice and a lowered metabolism, but which via the suppletion with thyroid hormone had led to an addisonian crisis.  相似文献   
85.
Kinins lower blood pressure but the stimuli leading to kinin generation and their origin are less well known. We administered angiotensin II in graded infusion doses to patients with primary hypertension and normotensive controls to study the effects of on circulating kallikreins. Angiotensin II infusion did not significantly alter plasma prekallikrein or tissue kallikrein levels and the plasma levels and their changes did not correlate with blood pressure levels or changes. In the normotensive group prekallikrein levels and renin activity correlated negatively with urinary sodium and chloride excretion during basal conditions and partially during the infusion. U-tissue kallikrein concentration increased in the normotensive group. Thus, acute elevation of blood pressure induced by angiotensin II does not activate the circulating kallikrein-kinin systems. Data rather indicate that the circulating kallikrein-kinin systems may be related to alterations in volume and sodium balance and that these mechanisms may be altered in primary hypertension.  相似文献   
86.
87.
Focal nodular hyperplasia of the liver in a 3 year old child has been successfully treated by ligation of the hepatic artery branches supplying the lesion. The prominence of the abnormal vasculature in the lesion and its possible aetiological involvement is stressed. Because of the risks of partial hepatectomy, hepatic artery ligation is suggested as the treatment of choice for focal nodular hyperplasia.  相似文献   
88.
Efforts have been made to establish the chemical constitution of water-blown polyurethane foams. Specific reagents have been used to indicate the presence of biuret or allophanate linkages. Partial hydrolysis techniques have been used to degrade foams selectively and hence isolate parts of the chain network. These methods yield information which is not satisfactorily obtained from the examination of undegraded polymer and which is not available after total degradation. It has been shown that polyureatype linkages are present in the chain network of both polyester and polyether foams.  相似文献   
89.
Suspended solids were collected from 105 streams on the Canadian side of the Great Lakes during snow melt and spring flow between 1974 and 1977. Analyses were performed for organochlorine and organophosphorus insecticides and three industrial chemicals. All streams sampled contained suspended solids that were contaminated with DDT, its metabolites, and polychlorinated biphenyl (PCB). The highest mean concentrations of ΣDDT (356 μg/kg) occurred in 1974 from streams draining the Niagara Peninsula and entering Lake Ontario; these were correlated to areas of high use on fruit in the past. The highest loadings by lake section, however, were along the north shore of Lake Erie involving a very much larger delivery of suspended solids. The highest concentrations of PCB were on suspended solids entering Lake Ontario in 1974 along the northern (191 μg/kg) and southwestern (172 μg/kg) shore and were associated with the high urban-industrial activity in the megalopolis of Hamilton-Burlington-Oakville-Mississauga-Toronto. However, the highest loadings occurred along Lake St. Clair where two large rivers, the Thames and Sydenham, discharge a much larger volume of suspended solids. The highest individual concentrations of HEOD (dieldrin) were found on suspended solids in two streams entering along the southwestern shoreline of Lake Ontario. However, the highest mean residues on solids for all streams was in waters entering Lake Erie (3 μg/kg) and the highest loadings were into Lake St. Clair. Endosulfan, chlordane, and heptachlor epoxide were detected in some streams entering all five lakes. No aldrin, endrin, mirex, heptachlor, or organophosphorus insecticides were detected.  相似文献   
90.
Enzymes of the Krebs-Henseleit urea-cycle were localized by means of differential centrifugation and fractional tissue extraction in rat liver and in human liver. Argininosuccinatlyase (ASAL) and Argininosuccinatsynthetase (ASAS) represent enzymes of the soluble cytoplasmic fraction. Ornithine-ketoacid-transaminase(OKT), carbamyl-phosphate-synthetase (CPS) and ornithine-carbamyl-transferase (OCT) are localized in the mitochondrial and nuclei fractions of the liver cell. Most of the arginase activity is bound to subcellular structures (probably to nuclei). A small portion of arginase-activity was found in the soluble cytoplasmatic fraction. The enzymes of the Krebs-Henseleit urea-cycle are equally distributed in rat liver and in human liver. Differences in the subcellular localisation of (mitochondrial) enzymes in human liver could be attributed to mitochondrial breakage during tissue preparation and do not represent in-vivo conditions.  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