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   116篇
  免费   9篇
林业   4篇
农学   10篇
基础科学   1篇
  16篇
综合类   5篇
农作物   11篇
水产渔业   5篇
畜牧兽医   62篇
园艺   9篇
植物保护   2篇
  2023年   2篇
  2022年   3篇
  2021年   3篇
  2020年   3篇
  2019年   2篇
  2018年   3篇
  2017年   11篇
  2016年   7篇
  2015年   3篇
  2014年   8篇
  2013年   15篇
  2012年   4篇
  2011年   9篇
  2010年   11篇
  2009年   9篇
  2008年   4篇
  2007年   4篇
  2006年   4篇
  2004年   2篇
  2002年   1篇
  2001年   2篇
  1998年   3篇
  1997年   1篇
  1996年   2篇
  1995年   3篇
  1993年   2篇
  1992年   1篇
  1989年   1篇
  1985年   1篇
  1967年   1篇
排序方式: 共有125条查询结果,搜索用时 15 毫秒
21.
22.
Development of the foetal respiratory system includes both pulmonary growth and maturation. In human medicine, a higher incidence of respiratory distress is reported in newborn males. This study aimed to identify different phases of canine foetal lung maturation throughout pregnancy, to determine the stage of pregnancy in which surfactant production begins and to compare pulmonary development of male and female foetuses. Pregnant bitches (34) were subjected to elective ovariohysterectomy and allocated into four groups, according to the stage of pregnancy: 30–40 days of pregnancy (n = 10), 41–50 days (n = 10), 51–60 days (n = 10) and bitches in the first stage of parturition (n = 4). Foetal lungs were histologically processed and evaluated by optical microscopy. The pseudoglandular phase was identified between the 35th day and 46th day of gestation; the onset of canalicular and saccular periods was observed, respectively, from the 48th day and 60th day of pregnancy. Lungs from foetuses at term were in the saccular phase; thus, the development into the alveolar period occurs in the neonatal period. The histological analyses revealed that respiratory tract development is centrifugal, from upper to lower airways. Therefore, it is possible to identify distinct development periods in different portions of the same organ. In conclusion, the saccular phase of lung development begins around 57 and 60 days of pregnancy, the period in which surfactant production is believed to occur. Male and female foetuses present similar pulmonary development from early pregnancy until parturition.  相似文献   
23.
The results on the biological activities of the in vitro culture of Graphis guimarana, G. nakanishiana and G. schizograpta lichen are reported. The methanolic extracts of natural thalli and their cultures were found to inhibit tyrosinase, xanthine oxidase and to scavenge superoxide.  相似文献   
24.
25.
The objective of this study was to define the patterns of organogenesis and foetal haemodynamics during the normal gestation of healthy agoutis (Dasyprocta prymnolopha) kept in captivity. Thirty pregnant agoutis that ranged in size from small to medium and weighed between 2.5 and 3 kg underwent B‐mode and Doppler ultrasonography for the biometric evaluation of the foetal organs. The foetal aortic blood flow proved to be predominantly systolic, and the measured flow velocity was 78.89 ± 2.95 cm/s, with a maximum pressure gradient of 2.12 ± 0.27 mmHg. The liver was characterized by its large volume, occupying the entire cranial aspect of the abdominal cavity, and it was associated cranially with the diaphragm and caudally with the stomach. The flow velocity in the portal vein was estimated to equal 12.17 ± 2.37 cm/s, with a resistivity index of 0.82 ± 0.05. The gallbladder was centrally located and protruded cranially towards the diaphragm. The spleen was visualized as an elongated structure with tapered cranial and caudal extremities, and the foetal kidneys were visualized bilaterally in the retroperitoneal region, with the right kidney positioned slightly more cranially than the left. The morphological characterization and hemodynamic analysis of the foetal organs of black‐rumped agoutis via B‐mode and Doppler ultrasonography allow determination of the vascular network and of reference values for the blood flow required for perfusing the anatomical elements essential for maintaining the viability of foetuses at different gestational ages.  相似文献   
26.
The aim of this work was to determine the enzymatic activity of phosphofructokinase (PFK), malate dehydrogenase (MDH) and isocitrate dehydrogenase (IDH) in boar spermatozoa and study their participation in bicarbonate‐induced capacitation and follicular fluid‐induced acrosome reaction. Enzymatic activity of these enzymes was determined spectrophotometrically in extracts of boar spermatozoa. Sperm suspensions were incubated in the presence of bicarbonate (40 mM), a well‐known capacitation inducer, or follicular fluid (30%), as an acrosome reaction inducer, and different concentrations of oxoglutarate, oxalomalate and hydroxymalonate, inhibitors of PFK, IDH and MDH, respectively. Capacitation percentages were determined by the fluorescence technique of chlortetracycline (CTC), and true acrosome reaction was determined by trypan blue and differential–interferential contrast, optical microscopy. The activity of PFK in boar spermatozoa enzymatic extracts was 1.70 ± 0.19 U/1010 spermatozoa, the activity of NAD‐ and NADP‐dependent IDH was 0.111 ± 0.005 U/1010 and 2.22 ± 0.14 U/1010 spermatozoa, respectively, and the activity of MDH was 4.24 ± 0.38 U/1010 spermatozoa. The addition of the specific inhibitors of these enzymes prevented sperm capacitation and decreased sperm motility during capacitation and inhibited the acrosome reaction (AR), without affecting the sperm motility during this process. Our results demonstrate the participation of PFK, IDH and MDH in bicarbonate‐induced capacitation and follicular fluid‐induced acrosome reaction in boar spermatozoa, contributing to elucidate the mechanisms that produce energy necessary for these processes in porcine spermatozoa.  相似文献   
27.
(1) To evaluate the cognitive ability of male and female Vanaraja birds, three hundred and sixty 1-d-old sexed chickens were reared under similar conditions in three treatment groups with 4 replicates in each group: 120 females in Treatment 1, 120 males in Treatment 2 and both males and females (60 + 60) as a mixed group in Treatment 3.

(2) To assess learning ability, the birds were trained in T- and Y-mazes and tested at 3-week intervals in 4 test schedules (21, 42, 63 and 84 d). The birds were put into tonic immobility (TI) in each test schedule.

(3) In each maze test, the latency to find the feed was regarded as a successful completion of the task. In the TI-test, the time taken to stabilise on a plane surface after swinging in the hanging cradle for 20–25 s was recorded.

(4) The results indicated that male birds appeared to be cognitively superior to females in terms of learning and cognitive evolution in all the mazes, but by d 84, the females performed as well as the males. With increasing age, spatial memory gathering and processing improved. In the TI-test, the effect of sex or grouping system had no significant effect on the performance of birds at the various ages.  相似文献   

28.
The objectives of this work were to determine the site of persistence of lumpy skin disease virus (LSDV) in bulls shedding the virus in semen for a period longer than 28 days, to determine if the virus is present in all fractions of semen and to study lesions that developed in the genital tract. Six serologically negative postpubertal bulls were experimentally infected with a virulent field isolate of LSDV. The polymerase chain reaction (PCR) was performed on sheath washes, vesicular fluid, supernatant and cell‐rich fractions of semen from day 10 to day 26 postinfection (p.i.). Bulls that were positive by PCR on the whole semen sample collected on day 28 p.i. were slaughtered and tissue samples from their genital tracts submitted for histopathological evaluation, immunoperoxidase staining, virus isolation and PCR. Two of the bulls developed severe lumpy skin disease (LSD) and were found to be shedding viral DNA in their semen on day 28 p.i. Viral DNA was identified in all semen fractions from all bulls, but mostly from the cell‐rich fraction and from the severely affected bulls. The PCR assay was positive on postmortem samples of testes and epididymides from the two severely affected bulls. Virus could be recovered from the testes of these two bulls and from the epididymis of one of them. Immunoperoxidase staining was positive for LSDV staining in sections of testes and epididymides exhibiting necrosis. This study suggests that the testis and epididymis are sites of persistence of LSDV in bulls shedding virus in semen for prolonged periods and revealed that viral DNA is present in all fractions of the ejaculate.  相似文献   
29.
Lipopolysaccharides (LPS), the outer membrane of the Gram-negative bacteria, are reported to stimulate the immunity of different vertebrates including fish. However, their potency and spectrum of actions often differ among different bacteria. In this study, effect of crude LPS, derived from three species of smooth Gram-negative bacterial fish pathogens viz. Edwardsiella tarda, Escherichia coli, and Pseudomonas fluorescens, on certain innate immune parameters of Indian major carp, Labeo rohita was studied. L. rohita yearlings, when injected intraperitoneally with crude LPS extracted from these bacteria showed little variations in different innate immune parameters. Furthermore, LPS injected fish were protected against a virulent E. tarda challenge. Although, no significant difference (p>0.05) in most of the immune parameters were found with LPS of different bacteria, the E. coli LPS injected fish elucidated high resistivity during challenge study. Hence, there could be some variations in LPS with respect to the bacterial type which needs to be further explored.  相似文献   
30.
Starch has been the most popular and economic size material. Synthetic binders have also been developed to be used as size material to improve weaving loom efficiency. Some synthetic size materials have got restrictions in use mainly because of ecological reasons. In the recent years, many modifications have come up in the starch as a sizing agent. Different modification can give different properties, which can be suited for a particular application. In the present study, for comparative analysis of different varieties of natural starch, modified starch and synthetic size material have been evaluated and mechanical properties like cohesion power, adhesion power, abrasion resistance, bending rigidity etc. were studied. PVA shows best properties among all size material. Among modified starch, starch ester shows better properties.  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