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   489篇
  免费   52篇
  2021年   2篇
  2020年   2篇
  2019年   5篇
  2018年   6篇
  2017年   4篇
  2016年   7篇
  2015年   11篇
  2014年   15篇
  2013年   11篇
  2012年   8篇
  2011年   13篇
  2010年   12篇
  2009年   8篇
  2008年   14篇
  2007年   11篇
  2006年   12篇
  2005年   15篇
  2004年   11篇
  2003年   9篇
  2002年   13篇
  2001年   12篇
  2000年   18篇
  1999年   16篇
  1998年   10篇
  1997年   10篇
  1996年   14篇
  1995年   6篇
  1994年   13篇
  1993年   13篇
  1992年   31篇
  1991年   29篇
  1990年   22篇
  1989年   24篇
  1988年   23篇
  1987年   12篇
  1986年   10篇
  1985年   12篇
  1984年   10篇
  1983年   4篇
  1982年   4篇
  1981年   8篇
  1980年   4篇
  1979年   13篇
  1978年   2篇
  1977年   6篇
  1976年   6篇
  1975年   4篇
  1974年   5篇
  1970年   3篇
  1969年   2篇
排序方式: 共有541条查询结果,搜索用时 15 毫秒
91.
92.
This study aimed to analyze the impact of winter weather conditions on young children’s behavior and affective states by examining a group of 61 children attending day-care centers in Florence (Italy). Participants were 33 males, 28 females and their 11 teachers. The mean age of the children at the beginning of the observation period was 24.1 months. The day-care teachers observed the children’s behavioral and emotional states during the morning before their sleeping time and filled in a questionnaire for each baby five times over a winter period of 3 weeks. Air temperature, relative humidity, air pressure and solar radiation data were collected every 15 min from a weather station located in the city center of Florence. At the same time, air temperature and relative humidity data were collected in the classroom and in the garden of each day-care center. We used multilevel linear models to evaluate the extent to which children’s emotional and behavioral states could be predicted by weather conditions, controlling for child characteristics (gender and age). The data showed that relative humidity and solar radiation were the main predictors of the children’s emotional and behavioral states. The outdoor humidity had a significant positive effect on frustration, sadness and aggression; solar radiation had a significant negative effect only on sadness, suggesting that a sunny winter day makes children more cheerful. The results are discussed in term of implications for parents and teachers to improve children’s ecological environment.  相似文献   
93.
Justine J.-L., Lambert A. and Mattei X. 1985. Spermatozoon ultrastructure and phylogenetic relationships in the monogeneans (Platyhelminthes). International Journal for Parasitology15: 601–608. New observations reported in this study together with bibliographical data allow comparisons of spermatozoon ultrastructure in 28 genera of monogeneans, belonging to 19 families. The authors propose to compare and classify monogenean spermatozoa using two simple ultrastructural characteristics: (a) the number of axonemes, 1 or 2, (b) the presence or absence of cortical microtubules. These traits make it possible to group monogenean spermatozoa in four patterns. Pattern 1 (2 axonemes plus microtubules) is characteristic of the polyopisthocotyleans (9 families). The three other patterns are found in the monopisthocotyleans. Pattern 2 (2 axonemes without microtubules) is found in the Capsalidae and Dionchidae, which seem closely related, and also in the Udonellidae, Gyrodactylidae and Euzetrema. Pattern 3 (1 axoneme plus 1 altered axoneme plus microtubules) is found in the Monocotylidae and Loimoidae. Pattern 4 (1 axoneme without microtubules) is found in the Amphibdellatidae, Ancyrocephalidae, Calceostomatidae and Diplectanidae. A phylogeny of the monogeneans is drawn from the data of comparative spermatology; this scheme coincides in many points with the phylogeny of Lambert (1980) which was based on the study of chaetotaxy and ciliated cells of the oncomiracidium.  相似文献   
94.
In the process of generating transgenic mice, inserted foreign DNA can cause insertional inactivation of the flanking genetic locus and simultaneously provide a molecular tag for localizing and cloning the inactivated gene. We describe the case of an insertional mutation leading, in animals homozygous for the insertion, to severe anaemia that was lethal within a few days after birth. The haemolytic anaemia and microspherocytosis of the red cells strongly suggested membrane abnormalities of the erythrocytes. Byin situ localization of the integration site, protein analysis of the red cell membranes, northern and Southern blot analyses, we were able to demonstrate that the integrated transgene had affected the α-spectrin gene locus.  相似文献   
95.
We present a 5-year-old boy with developmental delay, severe microcephaly and preaxial polydactyly. These features are very similar to those previously described by Howard and Young (1) in their princeps report.  相似文献   
96.
Plasma lipids and apoprotein A and B levels were measured in 63 children, of both sexes, in the age range 11-14 years. The children have been subjected to a blood drawing after a 12 hour fast at least. Statistical analysis proves that total cholesterol (TC) is positively correlated with triglycerides (TG), HDL cholesterol (HDL) with apolipoproteins A (Apo A), apolipoproteins A (Apo A) with apoproteins B (Apo B). In the end we confirm the utility of determining plasma lipids and apoproteins to estimate lipidic risk for atherosclerosis in pediatric age.  相似文献   
97.
98.
Despite progress in treating B‐cell precursor acute lymphoblastic leukemia (BCP‐ALL), disease recurrence remains the main cause of treatment failure. New strategies to improve therapeutic outcomes are needed, particularly in high‐risk relapsed patients. Che‐1/AATF (Che‐1) is an RNA polymerase II‐binding protein involved in proliferation and tumor survival, but its role in hematological malignancies has not been clarified. Here, we show that Che‐1 is overexpressed in pediatric BCP‐ALL during disease onset and at relapse, and that its depletion inhibits the proliferation of BCP‐ALL cells. Furthermore, we report that c‐Myc regulates Che‐1 expression by direct binding to its promoter and describe a strict correlation between Che‐1 expression and c‐Myc expression. RNA‐seq analyses upon Che‐1 or c‐Myc depletion reveal a strong overlap of the respective controlled pathways. Genomewide ChIP‐seq experiments suggest that Che‐1 acts as a downstream effector of c‐Myc. These results identify the pivotal role of Che‐1 in the control of BCP‐ALL proliferation and present the protein as a possible therapeutic target in children with relapsed BCP‐ALL.  相似文献   
99.

Background

Emphysematous pyometra is a rare canine disease characterized by gas-forming bacteria infecting the uterus and causing an accumulation of both gas and infectious exudate in the uterine lumen. While radiological features of emphysematous pyometra have been previously described in dogs, the ultrasonographic appearance has not been reported.

Case presentation

A 7-year-old intact female Labrador Retriever was presented because of a 1 day history of vomiting, anorexia, mild polyuria/polydipsia and signs of fatigue. On physical examination the dog had a swollen vulva with a sparse amount of yellow discharge. Lateral and ventrodorsal radiographs showed a dilated predominantly gas-filled tubular structure located in the mid and cranial abdomen traversing from left to right and ending dorsally at the level of the 12th thoracic vertebra. A small intestinal ileus was initially suspected. Following the radiographic examination, abdominal ultrasound was performed. In the left mid and caudal abdomen there were two thin-walled gas-containing tubular structures. One had the typical layered appearance of an intestinal wall and represented the descending colon. The second structure had a similar thickness but homogenously hypoechoic wall and contained gas and echogenic fluid in the lumen. By use of several positional changes of the dog aiming to alter the location of the intraluminal gas, the second structure was traced to the right ovary cranially and the uterine body caudally, confirming that the structure was the right uterine horn. A final diagnosis of emphysematous pyometra was made.

Conclusion

Ultrasound can be used as a non-invasive diagnostic method to differentiate between small intestinal ileus and emphysematous pyometra.
  相似文献   
100.
Abstract The structure of the secondary egg envelope of seven species of Cyprinodontidae belonging to the genus Epiplatys was observed by transmission and scanning electron microscopy. The transverse structure of the secondary envelope examined by transmission electron microscopy is a constant feature in all the species studied and represents a good criterion for identification. In contrast, the surface structure of the secondary envelope when observed by scanning electron microscopy exhibits a great diversity of form. It is possible to distinguish each of the seven different species by the pattern of ornamentation, the width of the polygons and the size of the granules comprising them on the secondary egg envelope.  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