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   6464篇
  免费   9篇
  国内免费   2篇
综合类   1篇
化学工业   72篇
金属工艺   8篇
机械仪表   3篇
建筑科学   6篇
能源动力   9篇
轻工业   13篇
石油天然气   1篇
无线电   5篇
一般工业技术   66篇
冶金工业   6265篇
原子能技术   13篇
自动化技术   13篇
  2024年   4篇
  2022年   2篇
  2021年   5篇
  2020年   6篇
  2019年   4篇
  2018年   3篇
  2017年   2篇
  2016年   6篇
  2015年   4篇
  2014年   5篇
  2013年   12篇
  2012年   12篇
  2011年   12篇
  2010年   12篇
  2009年   19篇
  2008年   13篇
  2007年   5篇
  2006年   4篇
  2005年   6篇
  2004年   12篇
  2003年   20篇
  2002年   4篇
  2001年   4篇
  2000年   4篇
  1999年   205篇
  1998年   1988篇
  1997年   1084篇
  1996年   779篇
  1995年   402篇
  1994年   335篇
  1993年   368篇
  1992年   44篇
  1991年   89篇
  1990年   56篇
  1989年   69篇
  1988年   64篇
  1987年   67篇
  1986年   67篇
  1985年   48篇
  1983年   9篇
  1982年   26篇
  1981年   38篇
  1980年   64篇
  1979年   7篇
  1978年   17篇
  1977年   136篇
  1976年   314篇
  1975年   11篇
  1955年   5篇
  1931年   1篇
排序方式: 共有6475条查询结果,搜索用时 15 毫秒
51.
52.
53.
Tibial torsion?     
A longitudinal study evaluating the degree of rotation of the bimalleolar axis of tibia and fibula at birth, 6 month, 12 months and 24 months revealed a gradual statistically significant external rotation from a mean of 4 degrees at birth to a mean of 11 degrees at 24 months. There was no correlation with the sex or race of the child or with the age at which the child began independent walking. It is concluded that this external rotation is a part of normal growth and development of the infants' lower extremities.  相似文献   
54.
The uni-arterial vascularisation of the lateral bilary duct makes it impossible to systematise the arteries which supply the common bile duct. Only the cystic artery is seen at coelio-mesenteric catheterization. The techniques essential for visualisation of the cystic artery are discussed, on the basis of one hundred coelio-mesenteric arteriograms: frequency of demonstration, origin, course, termination, calibre and length. The frequent finding of opacification of the wall of the gall bladder under normal conditions is stressed.  相似文献   
55.
As a step toward defining in molecular terms the sperm-triggered block to polyspermy reaction established by the egg at fertilization, vitelline (VE) and fertilization (FE) envelopes were isolated from eggs of the Sounth African clawed toad Xenopus laevis and some of their physicochemical properties determined. Envelopes were isolated after lysis of the fertilized or unfertilized eggs by sieving techniques; isolated envelopes retained their in situ morphology as determined by electron microscopy. The isolated envelopes had different solubility properties and, in general, VE was more readily dissolved by aqueous solvents than FE, although both could be completely dissolved by detergents or chaotropic agents. Changes in envelope solubility correlated with the progression of the cortical reaction implicating a role for cortical granule material in modifying the solubility properties of the envelope. The VE and FE were composed of protein and carbohydrate with no lipid components detected. As determined by immunodiffusion experiments, the FE contained the same antigens as the VE plus components derived from the cortical granules and the innermost jelly layer, J. The macromolecular composition of the envelopes was determined by sodium dodecyl sulfate gel electrophoresis. The VE contained at least 11 glycoproteins with molecular weights ranging from 125 000 to less than 16 000 with two components (40 000 and 33 000) accounting for almost two-thirds of the total stainable material. The FE contained ten glycoproteins that had the same molecular weights as those in the VE. One glycoprotein component underwent a reduction in molecular weight from 77 000 to 67 500 when the VE was converted to the FE. This molecular weight change was interpreted as the probable result of limited proteolysis. In addition, the FE gel electrophoresis patterns contained macromolecular components derived from the cortical granules and jelly layer, J, consistent with the immunodiffusion experiments. These components were absent when the FE was prepared in the absence of Ca2+, suggesting a role for Ca2+ in binding the VE, cortical granules, and J components together. We concluded that the conversion of the glycoproteinaceous VE to FE at fertilization is caused by interaction of the VE with components from the cortical granules and jelly layer J. These interactions are of both a chemical and physical nature.  相似文献   
56.
57.
Some reaction parameters were tested in the hydrolysis of casein by papain, in order to prepare hydrolysates with high oligopeptide contents, for either dietetic or pharmaceutical purposes. Five casein hydrolysates were prepared and then fractionated by size‐exclusion HPLC. The rapid correct fraction area method was used for quantifying peptides and free amino acids. Among the five reaction conditions tested, three produced similar peptide profiles. However, the use of a temperature of 37°C and an E:S ratio of 2% is probably the most economical condition for use in large‐scale manufacture. With the aim of masking the bitterness of these preparations, a new method, based on the encapsulation in lipospheres, was used. Also, second derivative spectrophotometry was used for the first time to measure the extent of encapsulation of protein hydrolysates, which changed from 50% to 83%. Moreover, the efficiency of this system was evaluated by analysing other parameters, which showed a reduction of hydrophobicity and bitterness of all samples, as well as good chemical stability during 60 days of storage under refrigeration. The electron microscopical analysis of liposheres showed an average size around 5.0 ± 1.0 µm. Copyright © 2004 Society of Chemical Industry  相似文献   
58.
59.
The study of cooperative ligand binding among the four subunits of haemoglobin has played a central role in the understanding of allosteric transitions in a large number of enzymes. Haem iron out-of-plane motion has been suggested to be the trigger for the cooperative transition of haemoglobin. To function as a trigger in a dynamic sense, haem-iron doming must be the first conformational change to occur following ligand dissociation. Here we present the first direct demonstration that haem-iron doming occurs on the same time scale as the breaking of the iron-ligand bond, thus establishing haem-iron doming as the primary event which lead to the R-->T transition in haemoglobin.  相似文献   
60.
BACKGROUND: The increase in frequency of peanut allergy and fatal cases have been reported. OBJECTIVES: The objective of this study is to document the severity of food allergy to peanuts by evaluating the reactive dose of peanuts and to search for the role of peanut oil. METHODS: This study is carried out on the basis of 142 observations collected according to the same diagnostic methodology in two allergy centres in France. Skin-prick-tests were performed with peanut powder, peanut oil and peanut oil proteinic extract. Labial provocation tests were performed on 121 patients. The reactive dose of peanuts and the role of peanut oil were determined by standardized oral provocation tests in 50 and 62 patients respectively. The data are computerized and the data bank includes 509 food allergic patients. RESULTS: Allergy to peanuts represents 28% of food allergies and occurs under 1 year of age in 46% of cases, under 15 years of age in 93%. The clinical features were atopic dermatitis (40%), angioedema (37%), asthma (14%), anaphylactic shock (6%) and digestive symptoms (1.4%). The specific IgE were class 3 or higher in 80% of cases. The total reactive dose was less than 100 mg in 25% of cases, from 100 mg to 1 g in 62.5%. All patients reacted to a dose of less than 7.1 g. The threshold of peanut reactivity was lower than the threshold of egg reactivity. An allergy to peanut oil was demonstrated in 14 patients. CONCLUSION: The severity of peanut allergy and the early onset of the occurrence of this allergy is documented. The role of residual allergenic proteins in peanut oil is established by positive skin-prick tests to proteic extracts from peanut oil and by double-blind placebo-controlled challenges to peanut oil. The increased consumption of allergens in the form of peanut oil and fats can contribute to the occurrence or persistence of symptoms and may be suspected to increase the risk of sensitisation.  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