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   1509篇
  免费   137篇
林业   124篇
农学   40篇
基础科学   2篇
  283篇
综合类   103篇
农作物   74篇
水产渔业   140篇
畜牧兽医   718篇
园艺   39篇
植物保护   123篇
  2024年   8篇
  2023年   18篇
  2022年   31篇
  2021年   69篇
  2020年   66篇
  2019年   63篇
  2018年   70篇
  2017年   60篇
  2016年   71篇
  2015年   53篇
  2014年   77篇
  2013年   71篇
  2012年   117篇
  2011年   147篇
  2010年   69篇
  2009年   67篇
  2008年   95篇
  2007年   80篇
  2006年   77篇
  2005年   76篇
  2004年   61篇
  2003年   54篇
  2002年   46篇
  2001年   13篇
  2000年   4篇
  1999年   9篇
  1998年   2篇
  1997年   9篇
  1996年   5篇
  1995年   7篇
  1994年   6篇
  1993年   3篇
  1992年   3篇
  1991年   3篇
  1988年   3篇
  1986年   4篇
  1984年   3篇
  1983年   3篇
  1981年   1篇
  1979年   3篇
  1978年   1篇
  1976年   1篇
  1973年   3篇
  1969年   1篇
  1966年   1篇
  1962年   1篇
  1961年   1篇
  1959年   1篇
  1958年   3篇
  1955年   1篇
排序方式: 共有1646条查询结果,搜索用时 15 毫秒
51.
164 total hip prostheses of different manufacturers were implanted over an 8-year period. Clinical records were evaluated with a complication rate of 29.0% (42 of 145 joints) or 31.7% (39 of 123 dogs). The complications encountered in dogs that received the modular hip prosthesis (Biomécanique, Bretigny-sur-orge, France) amounted to 16.3% (15 of 92), dogs that received a fixed head prosthesis (5 different manufactures) had 39% complications (28 of 72). Although the complication rate was influenced by different surgeons (n = 5) with different system predelictions and a different learning curve it was obvious that luxations (n = 6 of 10) and stem fractures (n = 5) more often occurred with the fixed head prosthesis systems. These stem fractures might be due to implant material failure or due to improper cementation followed by fatigue material failure. Femur fracture or infection were encountered with both prosthesis systems.  相似文献   
52.
53.
ObjectiveTo determine if a nerve stimulation test (NST) could act as a monitoring technique to confirm sacrococcygeal epidural needle placement in cats.Study designProspective experimental trial in a clinical setting.AnimalsTwenty-four adult cats, scheduled for a therapeutic procedure where epidural anesthesia was indicated.MethodsUnder general anesthesia, an insulated needle was inserted through the S3-Cd1 intervertebral space guided by the application of a fixed electrical current (0.7 mA) until a motor response was obtained. The NST was considered positive when the epidural nerve stimulation produced a motor response of the muscles of the tail, whereas it was considered negative when no motor response was evoked. In the NST positive cases, 0.3 mL kg−1 of 0.5% bupivacaine was administrated before needle withdrawal. Ten minutes after injection, epidural blockade was confirmed by the loss of perineal (anal), and pelvic limbs reflexes (patellar and withdrawal).ResultsThe use of a fixed electrical stimulation current of 0.7 mA resulted in correct prediction of sacrococcygeal epidural injection, corroborated by post bupivacaine loss of perineal and pelvic limb reflexes, in 95.8% of the cases.Conclusion and clinical relevanceThis study demonstrates the feasibility of using, in a clinical setting, an electrical stimulation test as an objective and in real-time method to confirm sacrococcygeal epidural needle placement in cats.  相似文献   
54.
NURSING CARE: The term nursing care means different things to different people. The authors of these AAFP and ISFM Feline-Friendly Nursing Care Guidelines define nursing care as any interaction between the cat and the veterinary team (veterinarian, technician or nurse, receptionist or other support staff) in the clinic, or between the cat and its owner at home, that promotes wellness or recovery from illness or injury and addresses the patient's physical and emotional wellbeing. Nursing care also helps the sick or convalescing cat engage in activities that it would be unable to perform without help. GUIDELINES RATIONALE: The purpose of the Guidelines is to help all members of the veterinary team understand the basic concepts of nursing care, both in the clinic and at home. This includes methods for keeping the patient warm, comfortable, well nourished, clean and groomed. The Guidelines provide numerous practical tips gleaned from the authors' many years of clinical experience and encourage veterinary team members to look at feline nursing care in ways they previously may not have considered. OVERARCHING GOAL: The primary goal of feline-friendly nursing care is to make the cat feel safe and secure throughout its medical experience.  相似文献   
55.
Predatory bacteria remain molecularly enigmatic, despite their presence in many microbial communities. Here we report the complete genome of Bdellovibrio bacteriovorus HD100, a predatory Gram-negative bacterium that invades and consumes other Gram-negative bacteria. Its surprisingly large genome shows no evidence of recent gene transfer from its prey. A plethora of paralogous gene families coding for enzymes, such as hydrolases and transporters, are used throughout the life cycle of B. bacteriovorus for prey entry, prey killing, and the uptake of complex molecules.  相似文献   
56.
Despite the importance of mucilage for soil–plant relations, little is known about the effect of soil drying on mucilage exudation. We introduce a method to collect mucilage from maize growing in wet and dry soils. Mucilage was collected from brace roots. The amount of mucilage exuded did not change with soil water content and transpiration rate. Mucilage exuded in dry soils had a higher degree of hydrophobicity, suggesting that the wetting properties of mucilage change in response to soil drying.  相似文献   
57.
Mountain forests are traditionally used for cattle grazing during the dry season in southern Bolivia. To evaluate browsing intensity and damage to young trees and shrubs, a forest grazing area was monitored for about 3 months in both 2006 and 2007. Three similar paddocks of about 3 ha each, consisting of grassland and forest in a ratio of about 1:3 were stocked with 0.9, 1.6 and 2.6 tropical livestock units per ha (equivalents of 250 kg of body weight), reflecting low, medium and high stocking densities. Six 5 m × 5 m plots were mapped out within each paddock in 2006. Three additional plots per paddock were added in 2007. Within plots, the individuals of 18 woody species were coded and evaluated weekly for intensity of browsing. Intensity was quantified using five-scale categories reflecting the proportions of plant tissue removed (0 = no browsing, 1 = 1–25%, 2 = 26–50%, 3 = 51–75% and 4 = 76–100%). Across all plant species, the average category of browsing intensity, as determined in the post-grazing evaluation, was affected (P < 0.001) by stocking density. Browsing intensity increased in an approximately linear manner from 1.58 to 2.18 and 2.77 with low, medium and high stocking density, respectively. There was no significant difference between years. Most woody species followed the same general response pattern to stocking density, although some species were only noticeably browsed at high stocking density while a few others were intensively browsed at all stocking densities. The onset of browsing on woody species was observed only after some weeks had passed, indicating that herbaceous plants were preferred as a forage resource. The proportion of fatally damaged individuals, as assessed about 8 months after grazing in 2006, were 10.6%, 8.6% and 11.4% for low, medium and high stocking density, respectively. The percentage of completely browsed individuals increased with stocking density, but 80% of those plant individuals recovered following a resting period of 8 months. However, although most woody species recovered from browsing and fatal damage was infrequent, long-term changes in woody plant species composition and structure caused by grazing cannot be excluded. High stocking density in particular may reduce the vigour of heavily browsed species.  相似文献   
58.
In separate experiments conducted in 2007 and 2008, growth and accumulation of selected caffeic acid derivatives (CADs; i.e., caftaric acid, chlorogenic acid, echinacoside, caffeic acid, cynarin, p-coumaric acid, ferulic acid and cichoric acid) were determined in Echinacea angustifolia DC. var. angustifolia seedlings grown in hydroponic culture (floating raft system) at a density of 122 plant m−2 (at planting). Plants were harvested 11 (2007) or 16 (2008) weeks after transplanting (i.e., 15 or 20 weeks after sowing). In both years, plants grew vigorously and at harvest approximately half of the plants under observation had developed one to three inflorescences. In 2008, the root yield (2940 kg ha−1) harvested in nearly eight months from two consecutive hydroponic cultures was within the yield reported in the literature for field cultivations lasting two to four years. None of the selected CADs was found in the leaves, while the inflorescences (stem and capitulum) contained only caftaric acid and echinacoside at concentrations higher than the detection limits (0.05 mg g−1 dry weight). Echinacoside, cynarin and chlorogenic acid were found in root tissues at concentrations ranging from 0.36 to 5.25 mg g−1 dry weight. In all plant samples, echinacoside, which is the marker compound for E. angustifolia material, did not reach the minimum quality standard (10 mg g−1 dry weight) for the production of standardized extract. We concluded that short-cycle, high-density greenhouse hydroponic culture stimulates plant growth and root production in E. angustifolia, but it does not ensure sufficient CADs accumulation in dried roots.  相似文献   
59.
60.
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