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   21262篇
  免费   1217篇
  国内免费   17篇
电工技术   138篇
综合类   12篇
化学工业   4285篇
金属工艺   430篇
机械仪表   424篇
建筑科学   579篇
矿业工程   56篇
能源动力   440篇
轻工业   4016篇
水利工程   229篇
石油天然气   77篇
武器工业   2篇
无线电   912篇
一般工业技术   3512篇
冶金工业   4479篇
原子能技术   80篇
自动化技术   2825篇
  2024年   50篇
  2023年   181篇
  2022年   225篇
  2021年   560篇
  2020年   498篇
  2019年   547篇
  2018年   972篇
  2017年   918篇
  2016年   947篇
  2015年   759篇
  2014年   956篇
  2013年   1807篇
  2012年   1338篇
  2011年   1087篇
  2010年   954篇
  2009年   887篇
  2008年   863篇
  2007年   808篇
  2006年   510篇
  2005年   382篇
  2004年   411篇
  2003年   369篇
  2002年   333篇
  2001年   222篇
  2000年   211篇
  1999年   275篇
  1998年   1483篇
  1997年   956篇
  1996年   596篇
  1995年   314篇
  1994年   254篇
  1993年   293篇
  1992年   97篇
  1991年   85篇
  1990年   88篇
  1989年   81篇
  1988年   84篇
  1987年   71篇
  1986年   73篇
  1985年   99篇
  1984年   71篇
  1983年   67篇
  1982年   69篇
  1981年   83篇
  1980年   71篇
  1979年   39篇
  1978年   31篇
  1977年   106篇
  1976年   199篇
  1974年   22篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
46.
Decision making with a fuzzy ontology   总被引:2,自引:2,他引:0  
Knowledge mobilisation is a transition from the prevailing knowledge management technology that has been widely used in industry for the last 20?years to a new methodology and some innovative methods for knowledge representation, formation and development and for knowledge retrieval and distribution. Knowledge mobilisation aims at coming to terms with some of the problems of knowledge management and at the same time to introduce new theory, new methods and new technology. More precisely, this paper presents an outline of a fuzzy ontology as an enhanced version of classical ontology and demonstrates some advantages for practical decision making. We show that a number of soft computing techniques, e.g. aggregation functions and interval valued fuzzy numbers, will support effective and practical decision making on the basis of the fuzzy ontology. We demonstrate the knowledge mobilisation methods with the construction of a support system for finding the best available wine for a number of wine drinking occasions using a fuzzy wine ontology and fuzzy reasoning methods; the support system has been implemented for a Nokia N900 smart phone.  相似文献   
47.
Granados  M. López  Galisteo  F. Cabello  Lambrou  P. S.  Alifanti  M.  Mariscal  R.  Gurbani  A.  Sanz  J.  Sobrados  I.  Efstathiou  A. M.  Fierro  J. L. G. 《Topics in Catalysis》2007,42(1-4):443-447
The chemical nature of P-containing species of varying concentration present in CeO2 after impregnation with (NH4)2HPO4 and calcination at 1273 K, and their effects on the oxygen storage and release (OSR) properties of ceria are reported for the first time. The samples were characterized by different techniques and the results were compared with those recently reported on the same samples but calcined at 873 K. When P-containing ceria solids were calcined at 1273 K, CePO4 (monazite) was the predominant P-containing species on the surface of ceria, confirming previous studies that showed that monazite exists for those samples in which the surface P loading (P atoms per nm−2) is larger than 5.5. For lower surface P concentrations, isolated orthophosphate units are present at the surface and within the subsurface region of the solid. Severe sintering of CeO2 after calcination at 1273 K resulted in P concentrations >5.5 P atoms·nm−2 in all samples. Isolated PO4 units that could initially be present in the samples calcined at 873 K nucleated and CePO4 was formed when samples were calcined at 1273 K. OSR properties of CeO2 deteriorated progressively when P loading increased due to the presence of larger crystals of the very stable Ce(III) phase of CePO4 at the surface of the P-containing ceria solids.  相似文献   
48.
49.
Two approaches in the care of malnourished children were evaluated in order to ascertain both their medical and economical effectiveness. One was a group of 745 children under an ambulatory nutritional rehabilitation program that included health care, supplementary foods and nutrition education; a second group of 420 children attended Day Care Centers (8 hours a day and five days per week) where they received a balanced diet, psychomotor stimulation according to age, and health care. The evolution of nutritional status was followed up and plotted against the NCHS/WHO weight-for-height tables. The rate of recovery was unsatisfactory; below 50% in mild cases of malnutrition, and even less in the more severe cases. The average length of time for attaining normality was longer for moderate malnutrition and for the ambulatory program. When the calculation included a correction for the probability of recovery for each system, the advantage of the Day Care Centers became even more evident: the mean length of time for recovery was 33.2% less than the ambulatory program. The social cost per child, per day, was substantially lower in the ambulatory program. The integral calculus of social cost per child, per day, and the corrected mean time for recovery provided the social cost-effectiveness of nutritional recovery. This figure was clearly adventageous for the ambulatory program for all ages and degrees of malnutrition, exception made for moderately malnourished children below two years of age. In this case, the Day Care Centers appeared to be the most effective therapeutic alternative. This type of analysis is a contribution to the evaluation of medico-social programs for the recuperation of malnutrition. The advantage lies in the fact that it allows an optimization in the allocation of resources, when the previous step is the choice of best therapeutic alternative based upon the patient's age and nutritional status.  相似文献   
50.
Enhancement of the basic properties of the X zeolite with FAU framework has been carried out during synthesis, without further treatment such as ion-exchange or impregnation. Control of the washing stage enables retention of the optimum amount of alkaline hydroxides, which increases the basic catalytic activity of X zeolite in the alkylation of toluene. This alkaline hydroxides neither affect the FAU framework nor the silicon/aluminium molar ratio of the X zeolite. The optimum (Na + K)/Al molar ratio of the improved catalyst was 1.06 corresponding to a washing volume of 200 mL. This X zeolite presented better catalytic activity than a cesium-zeolite prepared by ion-exchange. The presence of hydroxysodalite impurity in the X zeolite increased the amount of impregnated alkaline hydroxides but not the catalytic activity. The present study shows that it is possible to increase the basic properties of the X zeolite directly in the synthesis process.  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