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   1519篇
  免费   2篇
化学工业   5篇
金属工艺   1篇
机械仪表   6篇
建筑科学   1篇
轻工业   1篇
无线电   3篇
一般工业技术   7篇
冶金工业   1495篇
自动化技术   2篇
  2023年   1篇
  2021年   1篇
  2019年   1篇
  2015年   1篇
  2014年   1篇
  2013年   2篇
  2011年   1篇
  2010年   1篇
  2009年   1篇
  2008年   1篇
  2007年   2篇
  2006年   2篇
  2005年   2篇
  2004年   2篇
  2003年   6篇
  2002年   2篇
  2001年   1篇
  2000年   3篇
  1999年   50篇
  1998年   544篇
  1997年   283篇
  1996年   159篇
  1995年   94篇
  1994年   62篇
  1993年   108篇
  1992年   11篇
  1991年   14篇
  1990年   12篇
  1989年   10篇
  1988年   10篇
  1987年   7篇
  1986年   13篇
  1985年   10篇
  1983年   4篇
  1982年   3篇
  1981年   2篇
  1980年   11篇
  1978年   6篇
  1977年   24篇
  1976年   52篇
  1960年   1篇
排序方式: 共有1521条查询结果,搜索用时 15 毫秒
71.
Growth indices were examined in 24 identically managed tanks, each containing 120 diploid juvenile rainbow trout (initial mean body weight, 9.3 g) during a 12-week study to examine tank effects associated with tank location in a multi user research facility. Growth indices included mean body weight, feed intake, feed conversion index, and specific growth rate. The null hypothesis that tank effect had no effect on growth over the 12-week period was rejected (P = 0.038), and mean weight in individual tanks differed by as much as 18.7%). During the study it was determined that the proximity of tanks to common-use walkways in the facility could affect growth indices. This was indicated by significant differences in the mean fish weights among blocks of tanks served by different header tanks after 4 (P = 0.001) and 8 (P = 0.024) week. The block containing tanks of fish with the highest them weight was nearest to the 2 common-use walkways in the facility. Fish in this block of tanks, compared with those in other blocks, had significantly greater feed intake but no significant differences in conversion efficiency. Compensatory growth, a well known growth attribute in fishes, diminished the difference in mean weight be tween these blocks of tanks by the end of the study. Comparison of paired ranks within header tank blocks indicated that fish in those located nearest to walkways had higher feeding rates over the 12-week period (P = 0.048), but less efficient feed conversion (P = 0.040) than did fish in matched tanks located farthest from walkways. However, there were no differences in mean weight of fish. Results of this trial document the risks involved in identifying fish in a tank as the experimental unit when treatments are administered to the tank of fish, the latter being the true experimental unit.  相似文献   
72.
The nutritional status of 75 maintenance hemodialysis (MHD) patients was evaluated according to the dietary intake analysis, anthropometric measurements, biochemical and immunological parameters in this study. Furthermore, some possible factors which would affect nutritional status of hemodialysis patients were discussed. The results showed that hemodialysis patients demonstrated a high incidence of malnutrition. The low intake of protein and calorie, metabolic acidosis and inadequate dialysis would worsen the malnutrition while erythropoietin treatment improve the nutritional status of hemodialysis patients. Based on these results, suggestions were proposed for the improvement of nutritional status of MHD.  相似文献   
73.
We have prepared a panel of lipidic ammonium tetrafluoroborate salts that contain trifluoromethyl, trichloromethyl, and methyl groups attached to the headgroup. 19F-NMR analyses of the cationic lipid panel revealed that the differences in electron-withdrawal from the ammonium ion headgroup accounted for differences in ion-pairing. Exchange of the tetrafluoroborate counterion by complexation to DNA-phosphate of a reporter gene enabled us to probe the influence of inductive electron-withdrawal in cationic lipid-mediated DNA transfection. We tested the lipid panel for transfection activity in two cell lines. The results indicate that the inductive effects of electron-withdrawing functionality diminish transfection activity in modest (2-4-fold) increments. The present study suggests that the mechanism whereby poly(alcohol)- or poly(ether)-substituted headgroups improve DNA transfection is not based on electronic activation of the ammonium ion.  相似文献   
74.
Forty-nine term infants were prospectively shown to have hypoxic-ischemic encephalopathy (HIE). All infants survived the neonatal period, and all but two infants (seen at 12 months) were followed up to at least 27 months of age. Factors that significantly correlated with outcome included the Sarnat encephalopathy stage and the occurrence of intractable seizures not controlled by phenobarbital sodium alone. There was no association between the one- or five-minute Apgar score, the need for early ventilation, the EEG, the occurrence of seizures, and the subsequent outcome. There was no significant difference in outcome for those infants who received dexamethasone sodium phosphate (n = 29) v those who did not receive the drug (n = 20). A review of 97 term infants with HIE from a regional perinatal program during a one-year period (1979), including 35 of the 49 infants in the present study, did show a significant increase in morbidity and mortality for transported infants.  相似文献   
75.
76.
The mode of inheritance of susceptibility or refractoriness of insect vectors to medically important pathogens such as those causing malaria or filariasis is usually believed to follow normal Mendelian laws and to involve a single pair of alleles. In this report, experiments are described that demonstrate another mode of inheritance of mosquito susceptibility to filarial parasites. Crosses were made between susceptibile and refractory species of the Aedes Scutellaris complex, and the hybrid and backcross progeny were tested for susceptibility to infection by Brugia malayi and Brugia pahangi. The data indicate that inheritance follows a non-Mendelian pattern indicative of extrachromosomal factors inherited through the maternal parent.  相似文献   
77.
78.
79.
Abstract

Towns and cities in India are facing complex problems regarding the provision and maintenance of services and infrastructure in the face of the rapid growth of pupulation, caused both by natural increase and migration. In order to meet such challenges a planner needs to have fairly accurate and up-to-date information, especially about physical structures and related land parameters. A study of their trends generally helps in the understanding of the emerging growth pattern and in formulating policies to guide or redirect it. Recent advances in the field of remote sensing technology and computer based Geographical Information Systems (GIS) provide very useful tools in undertaking such analysis. The results from a study about growth trends of the urban areas in the Bombay Metropolitan Region using multi-date remote sensing data and ARC/INFO GIS package are described here. The period under consideration is from 1968 to 1989. It should be noted that the major growth in the region is confined to Greater Bombay between 1968 to 1975. After the year 1975, a distinct outward growth along the rail corridors is visible. Growth after 1975 is mainly in the Kalyan, Bhiwandi, New Bombay and Panvel areas and in the area around Manori creek (Charkop area). The growth rate is found to be higher after the year 1975 compared to the prior growth rate. The spatial growth trends are examined in relation to the population and the population density has been computed for different periods. Based upon these densities, the extent of land required for urban development for the year 2001 has been calculated. Suitability of land for urbanisation has been carried out based upon physical characteristics of the land and environmental parameters. The priority areas of urban development to meet the additional requirement in 2001 have been identified on the basis of this suitability analysis. A map on a 1:250000 scale has been prepared to show the areas for urbanisation which will meet the demands for the year 2001. This study demonstrates the potential offered by the integration of the tools of remote sensing and GIS for urban and regional planning.  相似文献   
80.
The genes of the trithorax group (trxG) in Drosophila melanogaster are required to maintain the pattern of homeotic gene expression that is established early in embryogenesis by the transient expression of the segmentation genes. The precise role of each of the diverse trxG members and the functional relationships among them are not well understood. Here, we report on the isolation of the trxG gene moira (mor) and its molecular characterization. mor encodes a fruit fly homolog of the human and yeast chromatin-remodeling factors BAF170, BAF155, and SWI3. mor is widely expressed throughout development, and its 170-kDa protein product is present in many embryonic tissues. In vitro, MOR can bind to itself and it interacts with Brahma (BRM), an SWI2-SNF2 homolog, with which it is associated in embryonic nuclear extracts. The leucine zipper motif of MOR is likely to participate in self-oligomerization; the equally conserved SANT domain, for which no function is known, may be required for optimal binding to BRM. MOR thus joins BRM and Snf5-related 1 (SNR1), two known Drosophila SWI-SNF subunits that act as positive regulators of the homeotic genes. These observations provide a molecular explanation for the phenotypic and genetic relationships among several of the trxG genes by suggesting that they encode evolutionarily conserved components of a chromatin-remodeling complex.  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