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   1329篇
  免费   70篇
林业   109篇
农学   44篇
  360篇
综合类   33篇
农作物   122篇
水产渔业   130篇
畜牧兽医   468篇
园艺   31篇
植物保护   102篇
  2024年   2篇
  2023年   16篇
  2022年   31篇
  2021年   68篇
  2020年   60篇
  2019年   62篇
  2018年   63篇
  2017年   64篇
  2016年   68篇
  2015年   43篇
  2014年   65篇
  2013年   70篇
  2012年   129篇
  2011年   118篇
  2010年   61篇
  2009年   54篇
  2008年   76篇
  2007年   83篇
  2006年   58篇
  2005年   51篇
  2004年   38篇
  2003年   38篇
  2002年   36篇
  2001年   9篇
  2000年   3篇
  1999年   2篇
  1998年   7篇
  1997年   4篇
  1996年   5篇
  1995年   3篇
  1994年   3篇
  1992年   2篇
  1990年   1篇
  1989年   1篇
  1983年   1篇
  1980年   1篇
  1979年   1篇
  1973年   1篇
  1971年   1篇
排序方式: 共有1399条查询结果,搜索用时 15 毫秒
991.
The objective of this study was to evaluate duodenocecostomy in horses performed through a ventral midline laparotomy and report its influence on body weight, glucose absorption, serum components, and characteristics of jejunum, cecum, and large colon histology. Four horses were submitted to the duodenocecostomy technique through a ventral midline laparotomy with animals in dorsal recumbency under inhalation anesthesia, followed by abdominal exploration. A side-to-side anastomosis was performed between the duodenojejunal flexure and the base of the cecum with two simple continuous suture lines of the serosal and muscular layers. The size of the opening created was approximately 2 cm in diameter. The mucosa layer was not sutured. After 30 days, animals were submitted to a second laparotomy to check the patency of the duodenocaecal fistula. During both laparotomy procedures, excisional biopsies of different segments of the gastrointestinal tract were performed. Information on physical examination findings, results of hematologic and histopathologic evaluations, and oral glucose absorption test were recorded. The horses did not have significant weight loss from baseline, and absorption curve of glucose did not significantly vary from baseline. Only triglycerides had significant alterations. Histologic evaluation of jejunum, cecum, and large colon did not show alterations of intestinal structure and morphology. We concluded that the proposed technique, principally in relation to the fistula size and not suturing the mucosa layer, allowed partial or total occlusion of the fistulae without the necessity of a second surgery and avoided the permanent bypass of ingesta and weight loss.  相似文献   
992.
Non-flying mammal richness and distribution were studied in a landscape matrix consisting of a highly managed agro-silvo-pastoral system dominated by a cork oak woodland (montado) to test the predictions of the Intermediate Disturbance Hypothesis (IDH). Sampling consisted on detection of mammalian signs of presence, along with the use of scent stations and small mammal live-trapping. Results were analyzed using generalized linear models, considering land uses, landscape metrics and grazing intensity and gave support to the predictions of the IDH. Pure forestry and intensive agricultural uses showed lower species richness than the silvopastoral system, whilst landscape heterogeneity and riparian corridors were shown to be most beneficial to mammal species richness, with small mammals being directly and negatively affected by grazing intensity. The increasing use of the montado for raising cattle has led to landscape homogenization by means of grazing and shrub clearance for pasture cultivation and this, combined with incremented stocking rates, constrains species richness. In this landscape context, watercourses assume a relevant role as patches of suitable habitat providing shelter, food, movement corridors and dispersion routes for mammals. Recent options of fencing forest patches with good forest natural regeneration or with a high diversity/density of Mediterranean maquis, and restoring degraded watercourses, both to improve landscape heterogeneity, appear to positively affect the mammal community. This is a current challenge in terms of monitoring and research.  相似文献   
993.
The root of Terminalia macroptera Guill. & Perr. (Combretaceae) is widely used in African traditional medicine to treat various infectious diseases, including stomach-associated diseases. This study investigates the in vitro activity of T. macroptera root extract against reference strains and clinical isolates of H. pylori and attempts to localize the extract bioactivity. T. macroptera hydroethanol (80% V/V) root extract (Tmr) activity was tested against three standard strains and sixty two clinical strains of H. pylori. Tmr liquid-liquid partition fractions were screened against twenty H. pylori strains. Qualitative analysis of Tmr and its fractions was performed by HPLC-UV/DAD. The antibiotic characterization of the H. pylori strains revealed that 20% of the tested clinical isolates were resistant to at least two of the three antibiotics belonging to the main groups of antibiotics used in multi-therapy to eradicate H. pylori infections. In contrast, Tmr showed anti-H. pylori activity against the majority (92%) of the tested strains (MIC(50) and MIC(90)=200 μg/ml). The Tmr water liquid-liquid fraction (Tmr-3) and the precipitate obtained from this fraction (Tmr-5) were the most active tested samples, showing a MIC(50) of 100 μg/ml. The present work proves the in vitro activity of T. macroptera against H. pylori, thus confirming the utility of this traditional medicinal plant to treat stomach complaints due to H. pylori infection. The main compounds of Tmr and of Tmr-3 were the ellagitannins terchebulin and punicalagin. These compounds can be considered as markers of T. macroptera root active extracts against H. pylori.  相似文献   
994.
995.

Background

Astaxanthin (ASTA) is a fat-soluble xanthophyll with powerful antioxidant functions. It is extracted from e.g. salmon, an important food source for certain human populations known to have a reduced risk of tumor development. It is possible that ASTA plays a role in cancer chemoprevention in such populations. The purpose of this study was to investigate the effects of dietary ASTA on chemically induced mammary tumorigenesis using N-methyl-N-nitroso-urea (MNU) in immature Wistar rats.

Methods

Thirty-six 37 days old juvenile female Wistar rats were at random allocated to 4 groups of which Groups 1 and 2 received a single dose of 55 mg MNU/kg body weight. The effects of ASTA was evaluated by giving rats of Groups 2 and 4 a dose of 50 mg ASTA/kg/day for the entire duration of the study. Group 3 rats received feed added alimentary oil.Necropsy and histopathological examinations were carried out on each rat 14 months after the administration of MNU. Haematological values and antioxidative status were determined. Oxidative stress was evaluated by monitoring superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in hepatic tissue. Lipid peroxidation and carbonylation of proteins was determined in protein extracts from the liver.

Results

Tumor development occurred only in rats of Groups 1 and 2, i.e. MNU exposed animals. Frequency of tumor development in general and average number of tumors per animal were insignificant between these two groups. Mammary gland tumors developed in equal frequencies in Group 1 and 2 rats, respectively. Although only rather few tumors were found in the mammary glands, a substantial number of other tumors were found in Group 1 and 2 rats, but at equal rates.Biochemical analyses showed significant higher levels of GPx, malondialdehyde and dinitrophenylhydrazine in Group 1 rats that for rats in all other groups thus indicating protective effects of ASTA on MNU induced hepatic oxidative stress.

Conclusions

Supplementation with ASTA did not reduce tumorigenesis induced by MNU in Wistar rats. However, supplementation with ASTA seemed to have anti-inflammatory effects.  相似文献   
996.
Genetic diversity and relationships between local cultivars and wild olive trees from three important Spanish olive-growing regions, Andalusia (South), Catalonia and Valencia (from Eastern Mediterranean Coastal area), were studied by means of eight SSR loci. Distinct allelic composition and heterozygosity levels were found in wild olive populations and cultivars. The observed patterns of genetic variation revealed: a) the independent clustering of Andalusian wild olives in a separate gene pool, b) the belonging of wild populations and most cultivars from Catalonia to another gene pool, c) the joined clustering of Andalusian and a set of Valencian cultivars in a third gene pool, and d) clustering of wild individuals from Valencia to the three different gene pools. These results suggest that wild populations of Andalusia may represent true oleasters, the ones from Catalonia may be feral forms derived from cultivar seed spreading, while the population of Valencia seems to be the most admixed one. The significant differentiation between Andalusian and most Catalonian cultivars is indicating an independent selection of olive cultivars in the two regions. The detection of a certain wild genetic background in some Catalonian and Valencian cultivars and the similarity found between wild and cultivated forms may suggest the use of local wild trees in olive domestication. The proposed scenario for the development of olive cultivars in Andalusia includes an empirical selection of outstanding local wild genotypes followed by various generations of crosses and various replanting campaigns, as well as possible introductions of ancestral cultivars. Therefore, our findings would lead us to support the hypothesis that the current diversity found in Spanish olive cultivars may be regionally differentiated and due to both, autochthonous and allochthonous origin. The information obtained in this work gives insights into the genetic resources of the main olive producing country, demonstrating that wild olive populations and local cultivars both represent potential sources of useful variability for olive breeding programs.  相似文献   
997.
998.
About one-fifth of all bananas harvested become culls that are normally disposed of improperly. However, ripe banana pulp contains significant amounts of fibre and polyphenol compounds as well as a high content of simple sugars (61.06 g/100 g), making it suitable for sucrose replacement in bakery products. This work studied the feasibility of incorporating ripe banana flour (20 and 40% of replacement) in cake formulation. Physical, nutritional and sensory attributes of sponge and layer cakes were evaluated. The inclusion of ripe banana flour generally led to an increased batter consistency that hindered cake expansion, resulting in a slightly lower specific volume and higher hardness. This effect was minimised in layer cakes where differences in volume were only evident with the higher level of replacement. The lower volume and higher hardness contributed to the decline of the acceptability observed in the sensory test. Unlike physical attributes, the banana flour inclusion significantly improved the nutritional properties of the cakes, bringing about an enhancement in dietary fibre, polyphenols and antioxidant capacity (up to a three-fold improvement in antioxidant capacity performance). Therefore, results showed that sugar replacement by ripe banana flour enhanced the nutritional properties of cakes, but attention should be paid to its inclusion level.  相似文献   
999.
1000.

Objectives

To describe an ultrasound-guided thoracic paravertebral block and determine the distribution after injection of two volumes of methylene blue in dog cadavers.

Study design

Prospective experimental cadaveric study.

Animals

Twelve dog cadavers weighing 11 ± 3 kg.

Methods

Ultrasound-guided injections aimed at the fifth thoracic (T5) paravertebral space were performed in randomized order using 0.1 or 0.3 mL kg–1 dye solution (six dogs for each volume). Anatomic dissections determined dye spread characteristics, including the presence and degree of staining of spinal nerves, and the presence of intercostal and sympathetic trunk spread. Staining of mediastinum, epidural, intrapleural and contralateral thoracic paravertebral space was recorded.

Results

There was no significant difference in dye distribution between groups. The use of anatomic landmarks resulted in the inaccurate identification of the T5 paravertebral space. The T4, T5 and T6 paravertebral spaces were injected in four, five and three of 12 dogs, respectively. Complete staining of the spinal nerve of the thoracic paravertebral space injected was observed in 11 of 12 dogs, and partial staining in one dog in the low-volume group. Multisegmental distribution was demonstrated with staining of contiguous spinal nerves in one dog in the high-volume group, and multiple segments of intercostal (three dogs) and sympathetic trunk (four dogs) spread in both groups. No mediastinal, epidural, intrapleural or contralateral thoracic paravertebral space staining was observed.

Conclusions and clinical relevance

Ultrasound-guided injection at the thoracic paravertebral space resulted in staining of the spinal nerve in all dogs. However, T5 paravertebral space was not accurately identified using anatomic landmarks. Dye distribution was not significantly different between the two groups; therefore, the use of the lower-volume and multiple-site injections would be potentially necessary in clinical cases to achieve ipsilateral blockade of the thoracic wall.  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