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   528篇
  免费   14篇
电工技术   7篇
化学工业   96篇
金属工艺   15篇
机械仪表   6篇
建筑科学   32篇
能源动力   25篇
轻工业   70篇
水利工程   3篇
无线电   34篇
一般工业技术   77篇
冶金工业   93篇
原子能技术   5篇
自动化技术   79篇
  2022年   5篇
  2021年   12篇
  2020年   6篇
  2019年   4篇
  2018年   16篇
  2017年   11篇
  2016年   13篇
  2015年   20篇
  2014年   13篇
  2013年   47篇
  2012年   23篇
  2011年   27篇
  2010年   17篇
  2009年   17篇
  2008年   20篇
  2007年   16篇
  2006年   22篇
  2005年   22篇
  2004年   14篇
  2003年   9篇
  2002年   8篇
  2001年   8篇
  2000年   8篇
  1999年   7篇
  1998年   27篇
  1997年   21篇
  1996年   12篇
  1995年   10篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   6篇
  1990年   6篇
  1989年   5篇
  1988年   7篇
  1986年   3篇
  1985年   6篇
  1984年   10篇
  1983年   3篇
  1982年   3篇
  1981年   7篇
  1980年   8篇
  1979年   3篇
  1977年   5篇
  1976年   3篇
  1973年   3篇
  1972年   2篇
  1971年   3篇
  1956年   2篇
  1955年   1篇
排序方式: 共有542条查询结果,搜索用时 18 毫秒
51.
52.
Nine patients with Charcot-Marie-Tooth disease with reduced motor nerve conduction velocity (MNCV), i.e. type 1 (CMT1), demyelinating form, and nine patients with Charcot-Marie-Tooth disease with normal or near-normal MNCV, i.e. type 2 (CMT2), axonal form, were subjected to percutaneous muscle biopsy from the anterior tibial muscle in order to characterize histopathological abnormalities and evaluate differences between the two groups. Data from the biopsies were compared with those from 18 age- and sex-matched healthy controls. Muscle biopsies from the CMT1 patients exhibited angular atrophic fibres that were scattered or in small groups, findings commonly described as neuropathic. Muscle biopsies from the CMT2 patients exhibited atrophic fibres that were rounded or elongated in groups and hypertrophic fibres with central nuclei and fibre splitting. There were also increased amounts of connective tissue, 'whorled fibres', degeneration and signs of regeneration, findings commonly regarded as myopathic. In conclusion, muscle biopsies from patients with CMT1 and CMT2 showed markedly different histopathological abnormalities. Possible underlying mechanisms are discussed.  相似文献   
53.
54.
The wettable cathode is one of the most promising medium-term modifications to the Hall-Héroult process. For implementing this concept, cathode materials of anthracite or semigraphitized carbon matrices with TiB2 (up to 50 wt. %) have been made and evaluated in the laboratory. In this article, the sodium penetration, abrasion resistance, electrical resistivity, and crushing strength are discussed in relation to the cathode performance in aluminum electrolysis.  相似文献   
55.
56.
This report concerns the use of transaxillary thoracotomy for a variety of pulmonary, pleural, and mediastinal conditions in 50 patients. Primary and metastatic carcinomas, pneumothoraces, and benign lesions such as bronchogenic cysts and neurogenic tumors can be identified, evaluated, and treated with confidence. Reduced postoperative pain and morbidity, rapid return of arm and shoulder movements, reduced hospital stay, and excellent cosmetic result are among the advantages of this approach when compared with the usual posterolateral thoracotomy.  相似文献   
57.
    
Summary The authors report the results of their investigations concerning the variations in the stock of Capercaillies. Communications about long-distance migrations of Capercaillies lack certain proofs and will probably not prove right.The period of decrease ofTetraonidae depends essentially upon the lacking capacity of rejuvenescence. In SwedenToxoplasmose was stated as the cause of death with 30% of 400 pieces of investigated animals. This illness appears only in the South of the 62nd degree of latitude; the mortality of young birds will probably have to be attributed to this kind of illness. In the case of chicken, however, Toxoplasmose proved never to be the cause of death; here investigations showed a direct relation between chicken mortality and unfavorable weather conditions. Capercaillie chicken are lacking a satisfactory ability to regulate their body temperatures up to the age of 18 days. The weather being cool the chicken want additional warmth provided by the hen, which may cause the risk that they take up an insufficient quantity of food. At periods of unfavorable weather this is the reason why many chicken die because of under-nourishment.
Résumé Les auteurs se rapportent sur le résultat de leurs recherches relatives aux variations dans l'état des coqs de bruyère (Tétraonidae). Les informations données sur les migrations à grande distance des grand Tetras sont dépourvues des fondements positifs et sont non-authentiques.La période de récule qui fut observée chez les coqs de bruyère (Tétraonidae) dépend avant tout d'une capacité insuffisante de rajeunissement. La Toxoplasmose fut reconnue en Suéde sur 30% de 400 coqs de bruyère (Tetraonidae) comme cause de mort. La maladie ne fut que constaté qu'au sud du 62ième degré de latitude et on doit certainement reconduire la mortalité des jeunes oiseaux sur cette maladie. Par contre on n'a jamais pû constater, que la Toxoplasmose fut la cause de la mort chez les poussins; ici il fut établi qu'il y avait une relation directe entre la mortalité des poussins et une température défavorable. Jusqu'à l'age de 18 jours les poussins des coq de bruyères sont incapable de régulariser leurs température corporelles. Aux temps frais elles doivent en plus être chauffés par la poule, de quoi peut venir une risque d'une absorption insuffisante de nourriture. Beaucoup des poussins meurent à la suite de cette sous-alimentation aux temps défavorables.
  相似文献   
58.
59.
60.
BACKGROUND: Many consumers perceive organic foods as more nutritious than conventional foods. However, the existing evidence is insufficient to support or refute this belief. The purpose of the present study was to investigate the effect of three different model cultivation systems on selected major and trace element contents of dried foodstuffs (carrots, kale, peas, potatoes and apples) grown in two consecutive years, as well as mineral retention determined in 36 rats (second generation in a multi‐generation study) fed diets based on these foodstuffs from one year. RESULTS: Overall, there was no evident trend towards differences in element content of foodstuffs or diets due to the use of different cultivation systems, and differences between harvest years exceeded those seen between cultivation methods. Also, no significant differences in the retention of elements in rats fed diets derived from different cultivation systems were seen, since higher intake resulted in correspondingly higher excretion. CONCLUSION: This study does not support the belief that organically grown foodstuffs generally contain more major and trace elements than conventionally grown foodstuffs, nor does there appear to be an effect on the bioavailability of major and trace minerals in rats. Copyright © 2008 Society of Chemical Industry  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