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   35篇
  国内免费   23篇
林业   120篇
农学   11篇
基础科学   18篇
  186篇
综合类   84篇
农作物   4篇
水产渔业   23篇
畜牧兽医   80篇
园艺   3篇
植物保护   18篇
  2024年   1篇
  2023年   10篇
  2022年   4篇
  2021年   8篇
  2020年   7篇
  2019年   12篇
  2018年   8篇
  2017年   18篇
  2016年   17篇
  2015年   14篇
  2014年   16篇
  2013年   26篇
  2012年   18篇
  2011年   19篇
  2010年   31篇
  2009年   35篇
  2008年   40篇
  2007年   40篇
  2006年   43篇
  2005年   41篇
  2004年   32篇
  2003年   28篇
  2002年   22篇
  2001年   10篇
  2000年   12篇
  1999年   7篇
  1998年   8篇
  1997年   2篇
  1996年   4篇
  1995年   4篇
  1994年   3篇
  1992年   2篇
  1990年   1篇
  1989年   1篇
  1988年   3篇
排序方式: 共有547条查询结果,搜索用时 328 毫秒
441.
以攀枝花视野区为例,研究了基于GIS的干热河谷区植被恢复适宜性评价及分区方法.在干热河谷植被恢复适宜性评价及分区中,主要考虑对植被类型及植物生长影响较大的海拔高度、坡向、坡度、岩土类型、土层厚度等因素,并采用专家评分法给各影响因子权重和适宜性评价赋值.经过GIS的数据处理、空间分析、模型建立及运算,得到植被恢复适应性评价图,再经过分类、合并,将攀枝花市视野区划分为适宜区、较适宜区、较不适宜区、不适宜区、极不适宜区,得到植被恢复分区图.  相似文献   
442.
浅论水土保持生态建设中的生态自然修复   总被引:4,自引:1,他引:4  
在任何自然环境下都会有相应的植物来生存 ,逐步形成植物群落 ,并由低级向高级逐步演替 ;环境对生长的植物进行适应性选择 ,适应该环境条件的植物能够繁衍、演替 ,不适应的就被淘汰 ,这是生态自然修复的理论基础。水土保持林草植被建设就是一个人工植物群落的形成过程 ,必须注意生态自然修复与人工治理相结合 ,包括以下几个步骤 :一是裸地成因及类型分析 ,二是植物种的选择 ,三是适时加大人工干预力度 ,促进进展演替。  相似文献   
443.
在野外调查与室内分析的基础上,对黄土丘陵区典型草原带植被自然恢复过程中土壤水稳性团聚体及其主要影响因子的演变规律进行了研究,并用典范相关分析法对二者的相互关系进行了定量分析。结果表明:随着植被演替,土壤中大粒级水稳性团聚体含量逐步增加,〉5mm粒级团聚体在土壤团粒结构中占主导地位,含量占50%~80%。其次是5~2mm含量,占到10%~15%左右。土壤全氮与有机质含量对〉5mm与1~0.5mm两个粒级团聚体影响较大。全量铝、全量铁、物理性粘粒对2~1mm与0.5~0.25mm两个粒级团聚体影响较大。全铝、全铁、全氮、有机质是影响土壤团聚体的主要因子群,其次为粘粒、物理性粘粒。主要作用因子可划分为综合物理因子(物理性粘粒,粘粒)、综合化学因子(全氮,有机质)、综合矿质因子(铁、铝氧化物)。  相似文献   
444.
Rehabilitation project of the Dabanshan highland road tunnel   总被引:1,自引:0,他引:1  
The rehabilitation project of road tunnel in highland area and cold region is an important and worthy exploring research field. The development of the defects of crack in the liner, water leakage, structural deterioration and frost defects for Dabanshan road tunnel are studied. After an insight into the cause and development of tunnel defects, the water leakage and frost damage are considered as the root of defect, so restoration of drainage system and the reinstallation of cold prevention system are the focuses of the rehabilitation project. For consideration of safety, cover arch is installed for the tunnel structure enforcement as well. Results indicate measures in Dabanshan road tunnel rehabilitation project are effective for road tunnel of high altitude and tunnel in cold region.  相似文献   
445.
Reasons for performing study: It is considered that specific exercises to strengthen limb musculature would be helpful. Objective: To describe swing phase kinematic and kinetic changes in the hindlimbs of trotting horses in response to the addition of leg weights to the hind pasterns. Methods: Six horses were prepared by placing reflective skin markers on the hindlimbs, the withers and fore hooves. Horses were evaluated at trot for 6 trials with and without leg weights (700 g) attached around the pasterns, with the 2 conditions applied in random order. The markers were tracked to determine peak heights of the flight arc of the hind hooves and swing phase joint angulations. Inverse dynamic analysis was used to calculate positive and negative work done across each joint in the first and second halves of the swing phase. Comparisons between conditions were made using paired t tests (normally distributed data) or the Wilcoxon rank‐sum test (non‐normally distributed data). Results: Peak height of the flight arc of the hind hooves was significantly higher with leg weights as a result of increased flexions of the stifle, tarsal and metatarsophalangeal joints. Increased positive (concentric) work was performed by the hip and tarsal musculature to protract and raise the limb in early swing, then to retract and lower the limb in late swing. Increased negative (eccentric) work was performed across the stifle and metatarsophalangeal joints to control their movements in response to increases in inertia and momentum due to the weights. Conclusions: The addition of weight to the hind pasterns stimulates increased muscular activity across all the hindlimb joints from the hip to the metatarsophalangeal joint. Clinical significance: The addition of weight to the hind pasterns may have therapeutic applications in activating and strengthening the hindlimb musculature. This is particularly relevant in the hip region, which appears more sensitive and responsive to the effect of weights than to tactile stimulation alone.  相似文献   
446.
IrrigationRehab is intended to produce an understanding of irrigation system rehabilitation by simulating the many tasks and problems likely to be encountered during a rehabilitation effort. Using theRehab software and the accompanying slide set, participants are challenged to formulate a rehabilitation plan considering changes that have occurred in a community since its irrigation system was constructed. African and Asian versions are available.  相似文献   
447.
黄河干流大型自流灌区节水潜力分析   总被引:1,自引:0,他引:1  
黄河灌区年均用水量占黄河用水总量的90%左右。受经济条件、灌区设施、管理手段等多种因素制约,灌溉水浪费严重,灌溉水利用水平较低,一般不足0.5,更加剧了黄河水资源短缺的矛盾。根据黄河灌区用水现状,提出了节水潜力的概念和节水潜力的分析计算方法,对黄河干流大型自流灌区的节水潜力进行了分析。  相似文献   
448.
449.
Baylisascaris procyonis, the raccoon roundworm, is a zoonotic ascarid of importance to human and animal health. Wildlife rehabilitators who care for raccoons may be at an increased risk for exposure to the parasite, especially if proper precautions are not taken. In a wider effort to evaluate awareness regarding B. procyonis in the wildlife rehabilitation community, an online survey (38–39 questions) including questions about B. procyonis knowledge and attitudes was developed and administered to wildlife rehabilitators. To assess precautions taken among raccoon rehabilitators, participants who rehabilitated raccoons (n = 447) answered additional questions about use of personal protective equipment (PPE) and infection control practices (ICPs). Reported use of gloves was variable, but hand hygiene was generally consistent. Masks and gowns were seldom used. Part‐time or infrequent volunteers and rehabilitators located in the Central, Midwest and Southeast were significantly less likely to report consistent use of PPE. A total knowledge score from the survey was used to predict the likelihood of reporting the use of particular ICPs/PPE. Knowledge score had a highly significant but small effect on the likelihood of prophylactic use of anthelmintics, anthelmintics use for B. procyonis specifically, cleaning appropriately, and using species‐dedicated housing. Risk factor analysis was performed on data from a prior serologic survey to evaluate factors associated with exposure to B. procyonis and inconsistent handwashing after contact with live raccoons and their faeces; practising rehabilitation in B. procyonis hyperendemic regions and practising rehabilitation in the western region were significant risk factors for being seropositive. These data further demonstrate that correct PPE/ICPs are critical in mitigating the risk of B. procyonis exposure among raccoon rehabilitators and among other captive species.  相似文献   
450.
Wildlife rehabilitators are at risk of zoonotic diseases because they often have prolonged contact with many species of wildlife and their bodily fluids. Raccoon roundworm (Baylisascaris procyonis) is a common zoonotic parasite of raccoons that has the potential to cause severe or fatal neurologic disease in a broad variety of hosts if the eggs within raccoon faeces are ingested. We administered an online survey to wildlife rehabilitators to assess their knowledge regarding aspects of transmission, biology and disease caused by B. procyonis, and also to evaluate attitudes towards wildlife diseases and B. procyonis as an occupational hazard. Knowledge was assessed using multiple choice and true–false questions; attitudes were measured using Likert‐type items. A total of 659 complete or near‐complete responses (missing fewer than three knowledge or attitudes items and/or non‐response to some demographic fields) were collected. The median knowledge score was 7/14 questions correct (range: 0–14 correct). Generally, individuals with higher levels of education and rehabilitation experience, veterinary professionals and those who are members of professional wildlife rehabilitation groups scored above the median significantly more often (p < .01). Significantly more rehabilitators who were located in the south‐east and those with part‐time or infrequent commitments scored below the median overall knowledge score. There was general agreement that B. procyonis is a health risk of rehabilitators and that measures should be taken to control transmission to people and animals. Some factors explaining differences in attitudes include setting of rehabilitation (home versus animal care facility), veterinary profession, region, membership in a wildlife rehabilitation group and rehabilitation of raccoons. Findings emphasize the importance of awareness and mentorship to inform rehabilitators on the potential risks of B. procyonis and other potential zoonoses within captive wildlife settings, and the important role of professional wildlife rehabilitator groups in disseminating educational materials.  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