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   1625篇
  免费   41篇
电工技术   78篇
综合类   1篇
化学工业   412篇
金属工艺   27篇
机械仪表   19篇
建筑科学   62篇
矿业工程   5篇
能源动力   22篇
轻工业   284篇
水利工程   9篇
石油天然气   8篇
无线电   102篇
一般工业技术   223篇
冶金工业   292篇
原子能技术   7篇
自动化技术   115篇
  2022年   16篇
  2021年   22篇
  2020年   25篇
  2018年   22篇
  2017年   27篇
  2016年   27篇
  2015年   17篇
  2014年   34篇
  2013年   52篇
  2012年   41篇
  2011年   82篇
  2010年   33篇
  2009年   44篇
  2008年   59篇
  2007年   54篇
  2006年   41篇
  2005年   45篇
  2004年   29篇
  2003年   34篇
  2002年   35篇
  2001年   21篇
  2000年   26篇
  1999年   24篇
  1998年   48篇
  1997年   36篇
  1996年   38篇
  1995年   29篇
  1994年   28篇
  1993年   21篇
  1992年   26篇
  1991年   17篇
  1990年   21篇
  1989年   20篇
  1988年   19篇
  1987年   21篇
  1985年   19篇
  1984年   16篇
  1983年   13篇
  1982年   16篇
  1981年   16篇
  1979年   14篇
  1978年   13篇
  1977年   14篇
  1976年   19篇
  1975年   13篇
  1974年   22篇
  1973年   17篇
  1971年   18篇
  1970年   19篇
  1966年   22篇
排序方式: 共有1666条查询结果,搜索用时 11 毫秒
131.
Legionella-contaminated hot water systems and moist sanitary areas in six hospitals were sampled for amoebae by following a standardized collection protocol. Genus identifications and temperature tolerance determinations were made. Amoebae identified as Hartmannella vermiformis (65%), Echinamoebae spp. (15%), Saccamoebae spp. (12%), and Vahlkampfia spp. (9%) were detected in 29 of 56 (52%) hot water samples. Twenty-three of 49 (47%) swabs obtained from moist areas were amoeba positive. The following genera were identified: Acanthamoeba (22%), Naegleria (22%), Vahlkampfia (20%), Hartmannella (15%), and Vanella (7%). The temperature tolerance of amoebae from hot water systems was strikingly different from that of amoebae from moist areas. At 44 degrees C on agar, 59% of amoebic isolates sampled from hot water systems showed growth. The corresponding value for isolates from moist areas was only 17%. Six Acanthamoeba isolates from the moist areas were considered potential pathogens. Four Hartmannella and two Saccamoeba isolates from hot water could be cultured at 53 degrees C.  相似文献   
132.
The reactivity of sera of 96 individuals infected with human T-cell leukemia virus type I (HTLV-I) was tested against various synthetic peptides corresponding to the gp46 immunodominant antigenic domains: residues 86-107, 175-199, and 239-261. The frequency of reactive sera was higher for 175-199 (93%) than for 239-261 (78%) or 86-107 (24%) with some variations in geographical regions and in diseases. The region 239-261 was extensively analyzed and five (linear or conformational) epitopes were found. The reactivity of sera toward functional or immunodominant domains may depend on the sequence of the infecting virus, and the role of three frequent substitutions (asparagine by tyrosine, proline by serine, and serine by proline or leucine at positions 93, 192, and 250 respectively) was established. Finally, the role of the genetic background of the host may condition the humoral immune response as individuals infected by HTLV-Is harboring the same predicted gp46 peptide sequence may recognize one, several, or all regions examined.  相似文献   
133.
134.
Discusses the role of psychology in educational practice. It is suggested that psychological research and theory can help (1) policy makers and administrators improve schools as organizations, (2) teachers develop more effective strategies for motivating and stimulating learning, and (3) learners construct meaning and develop new skills throughout their lives. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
135.
OBJECTIVES: The purpose of this study was to check the precision of the Dr?ger vaporizer model 19.3 when filled with three different preparations of isoflurane. METHODS: Six Dr?ger vaporizers model 19.3 calibrated with forene were filled with forene (Abbott), isoflurane (Lilly) and isoflurane (Pharmacia); gas output was measured by infrared absorption (Irina, Dr?ger) at vaporizer settings of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 and 5.0 vol%, starting with a fresh gas flow of 2 1/min followed by 4, 6 and 12 1/min. Thus each of the three isoflurane preparations was checked in six different vaporizers and with four different fresh gas flows. RESULTS: Within the concentration range used in clinical practice there was no significant difference in the delivery of the three isoflurane preparations. Each of the six vaporizers produced a controllable and predictable concentration of the three preparations. CONCLUSION: Vaporizers of Dr?ger type 19.n calibrated with forene deliver the same predictable concentration of the volatile anaesthetic when filled with isoflurane from Lilly or isoflurane from Pharmacia instead of forene and may be used without impairment in patient safety. In addition, no specific calibration with one of the new isoflurane preparations is required.  相似文献   
136.
Reports an error in "The meaning(s) of conditionals: Conditional probabilities, mental models, and personal utilities" by Klaus Oberauer and Oliver Wilhelm (Journal of Experimental Psychology: Learning, Memory, and Cognition, 2003[Jul], Vol 29[4], 680-693). On page 684, Table 4, all correlations should have been identified as having a p2003-06626-018.) Five experiments were conducted to test the hypothesis that people understand conditional statements ("if p then q") as indicating a high conditional probability P(q|p). Participants estimated the probability that a given conditional is true (Experiments 1A, 1B, and 3) or judged whether a conditional was true or false (Experiments 2 and 4) given information about the frequencies of the relevant truth table cases. Judgments were strongly influenced by the ratio of pq to p?q cases, supporting the conditional probability account. In Experiments 1A, 1B, and 3, judgments were also affected by the frequency of pq cases, consistent with a version of mental model theory. Experiments 3 and 4 extended the results to thematic conditionals and showed that the pragmatic utility associated with believing a statement also affected the degree of belief in conditionals but not in logically equivalent quantified statements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
137.
A short overview of the emerging field ubiquitous computing is given. It is argued, that this technology, characterized as highly distributed and interactive, requires a shift of focus from the traditional view of computer science as a domain of computable functions and turing machines (TM) to a cybernetic view of energy–signal–control cycles. This is accompanied by a reconsideration of interface-technology and the derivation of a new type of locally controlled signal to energy transformation based on the continuity of energy flow. It is shown how the concept of hyper-bonds could serve some requirements in this new field. Some applications in mixed reality and mechatronics are given and further perspectives for human–machine collaboration, human skills, and knowledge are presented.  相似文献   
138.
The amphibian pronephros is fated to die during early development. Pronephric cells undergo apoptosis and their function is replaced by the mesonephros, which becomes the functional kidney of the adult frog. Tadpoles of the northern leopard frog, Rana pipiens, were inoculated with a Lucké tumour herpesvirus (LTV) preparation. Most of the animals developed typical Lucké renal carcinomas at metamorphosis. Fewer developed carcinomas of the pronephric cell type. A pronephric carcinoma, rescued from apoptosis by the herpesvirus, was harvested from a post-metamorphic frog. The tumour was judged to be pronephric by its anatomical location (in the anterior part of the body) and because both mesonephric kidneys were intact and tumour-free upon removal of the tumour mass. A tumour fragment was fixed for histological examination, which confirmed that the tissue was a renal carcinoma. A further fragment was subjected to short-term culture in order to produce metaphase cells for cytogenetical analysis. Based upon silverstained nucleolar organizing region numbers, 14 of 15 metaphase cells were estimated to have the diploid number (2N = 26) of chromosomes and a karyotype was constructed which did not appear to differ from that of normal cells. A single cell was estimated to be tetraploid (4N = 52). This is the first report of chromosomes of a pronephric Lucké carcinoma. LTV replicates only in tumour tissue maintained in the cold. Because the frog in this study had been maintained in the laboratory at 22 degrees C for about 10 months, no viruses would have been detectable with electron microscopy. However, the presence of Lucké herpesvirus DNA was detected in tumour homogenates by polymerase chain reaction amplification of a 1.2 kbp Hind III restriction fragment of the LTV DNA. The presence of LTV DNA provided assurance that the rescued pronephric tumour was indeed a Lucké carcinoma.  相似文献   
139.
Thermobalance hydropyrolysis experiments are carried out on a highly volatile coal sample and its main macerals, vitrinite and exinite. The results are discussed according to the characterization of the tars using ultrasound solvent extractions, extrography, liquid chromatography, capillary gas chromatography and mass spectrometry.  相似文献   
140.
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