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   988篇
  免费   30篇
林业   74篇
农学   39篇
基础科学   3篇
  125篇
综合类   300篇
农作物   31篇
水产渔业   67篇
畜牧兽医   324篇
园艺   28篇
植物保护   27篇
  2024年   2篇
  2023年   7篇
  2022年   5篇
  2021年   14篇
  2020年   21篇
  2019年   33篇
  2018年   20篇
  2017年   18篇
  2016年   24篇
  2015年   13篇
  2014年   31篇
  2013年   50篇
  2012年   49篇
  2011年   69篇
  2010年   46篇
  2009年   36篇
  2008年   78篇
  2007年   71篇
  2006年   91篇
  2005年   68篇
  2004年   65篇
  2003年   64篇
  2002年   56篇
  2001年   4篇
  2000年   13篇
  1999年   8篇
  1998年   4篇
  1997年   4篇
  1996年   3篇
  1995年   11篇
  1994年   6篇
  1993年   4篇
  1992年   6篇
  1991年   2篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1983年   4篇
  1981年   2篇
  1980年   1篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1961年   1篇
  1955年   2篇
排序方式: 共有1018条查询结果,搜索用时 250 毫秒
21.
Immunological basis of differences in disease resistance in the chicken   总被引:9,自引:0,他引:9  
Genetic resistance to diseases is a multigenic trait governed mainly by the immune system and its interactions with many physiologic and environmental factors. In the adaptive immunity, T cell and B cell responses, the specific recognition of antigens and interactions between antigen presenting cells, T cells and B cells are crucial. It occurs through a network of mediator proteins such as the molecules of the major histocompatibility complex (MHC), T cell receptors, immunoglobulins and secreted proteins such as the cytokines and antibodies. The diversity of these proteins that mainly is due to an intrinsic polymorphism of the genes causes phenotypic variation in disease resistance. The well-known linkage of MHC polymorphism and Marek's disease resistance difference represents a classic model revealing immunological factors in resistance differences and diversity of mediator molecules. The molecular bases in any resistance variation to infectious pathogens are vaguely understood. This paper presents a review of the major immune mediators involved in resistance and susceptibility to infectious diseases and their functional mechanisms in the chicken. The genetic interaction of disease resistance with production traits and the environment is mentioned.  相似文献   
22.
The purpose of this study was to evaluate the effects on the intraocular pressure (IOP) of lidocaine or diazepam administered intravenously (IV) before induction of anesthesia with propofol-atracurium and orotracheal intubation in normal dogs, as well as the effects on the IOP of lidocaine applied topically to the larynx after induction with propofol-atracurium. We randomly assigned 32 random-source dogs, obtained from municipal pounds, to receive the following: lidocaine, 2 mg/kg IV, with saline, 0.1 mL/kg topically applied to the larynx (LIDOsal); saline, 0.1 mL/kg IV, with lidocaine, 2 mg/kg topically applied to the larynx (SALlido); diazepam (Valium), 0.25 mg/kg IV, with saline, 0.1 mL/kg topically applied to the larynx (VALsal); or saline, 0.1 mL/kg IV, with saline, 0.1 mL/kg topically applied to the larynx (SALsal). We measured arterial pressure directly, by means of an indwelling catheter placed in a peripheral artery. Anesthesia was induced with propofol, 8 mg/kg IV, until loss of jaw tone, followed by atracurium, 0.3 mg/kg IV. We measured the IOP in triplicate in each eye before premedication, before induction, before intubation, and after intubation. After induction, the IOP was significantly increased except in the VALsal group, in which the IOP was significantly lower than in the negative-control group before intubation. After intubation, the IOP was significantly elevated in all the groups compared with the values before induction. Cardiovascular parameters were essentially similar in all the groups, except for a significant increase in blood pressure after intubation in the SALlido group. Thus, propofol-atracurium anesthesia causes an increase in IOP that is blunted by diazepam. However, diazepam does not blunt the increase in IOP observed with intubation.  相似文献   
23.
Progressive multisystemic disease caused by Blastomyces dermatitidis was diagnosed in a 17-year-old Quarter horse broodmare. The mare had been treated unsuccessfully with antibiotics for mastitis 3 months postpartum. The disease progressed to exudative cutaneous lesions affecting the ventrum, pectoral region, and limbs accompanied by weight loss across several months. Yeast bodies were observed in swabs of the cutaneous exudate, suggesting a clinical diagnosis of blastomycosis. Following referral, pleural effusion, cavitated lung lesions, and hyperproteinemia were identified, and the mare was euthanized because of poor prognosis. Necropsy revealed extensive pyogranulomas in the mammary gland, skin, subcutaneous tissues, and lungs, accompanied by thrombi in major blood vessels of the lungs and hind limbs. Histologically, pyogranulomatous inflammation was evident in many tissues, and fungal organisms were seen in sections of mammary gland, skin, subcutis, pericardium, and lung. Blastomyces dermatitidis was cultured from mammary tissue, lungs, lymph node, and an inguinal abscess. Although blastomycosis is endemic in the area of origin of the mare in northwestern Wisconsin, the disease is extremely rare in horses and hence easily misdiagnosed. Unique features of this case included the extent of mammary gland involvement and the presence of thrombi in multiple sites.  相似文献   
24.
Adult sows have a more developed gastro-intestinal system than young growing pigs resulting in a superior capacity to digest fibrous components. The main objective of this study was to describe the capacity of sows and growing pigs to digest the fibre components in concentrated low dietary fibre (DF) diet and two high DF diets similar in DF but with contrasting DF solubility. Six sows and four growing pigs were fitted with a simple T-cannula at the terminal ileum. Each balance experiment consisted of a 7-day initial period followed by a 3-day collection of faeces and a 2 or 3-day collection of ileal digesta for growing pigs and adult sows, respectively. When feeding diets with high proportions of soluble non-starch polysaccharides (NSP), the difference in fermentation capacity between growing pigs and adult sows was small. The adult sows showed a higher fermentative capacity, evidenced by a higher fermentation and a higher methane production, when high fibre diet with high amount of insoluble fibre was fed.  相似文献   
25.
Sustainable development requires, among other things, that development projects not result in the degradation of natural resources for outdoor recreation. There has been a rapid increase in knowledge regarding the importance of the external environment to our health and well-being. Stress is reduced significantly when people are exposed to health-promoting nature and landscape values. Many people are actively choosing to reduce their stress. Doctors today prescribe outdoor walks in peaceful environments for the same purpose. A high level of traffic noise increases stress. This paper discusses the application of silent values in an infrastructure development project, the extension of Sturup Airport, east of Malmö, Sweden and Copenhagen, Denmark. Through estimating the change in noise resulting from the development, it is possible to integrate mitigating and compensating measures in the planning process discussions. Such measures can be negotiated as conditions for authorization of the project. The airport is situated in an area rich in nature values for recreation. The airport expansion will mean both new noise impacting "silent" areas and increasing noise levels in already noise-affected areas. In this study, we have taken a positive stand on the silent areas, mostly agriculture land, where compensation measures could be taken, thus balancing the loss of silent nature values for recreation. Silent areas that will not be affected are suitable and feassible for compensation measures thus can be called compensation areas. In this way the development of new recreational areas, preferably designed as urban forests, are critical preconditions for the negotiations for the airport extension. The conclusion is that urban forest investments for health and well-being can be an important part of strategic decisions in spatial planning. As preconditions for a permit, the development and financing of new urban forests and green areas can be part of the total development plan. This is an issue of global interest, as many countries are in a process of rapid urbanization, and urban greening and urban forestry have an important role to play in the process of promoting quality of life and improving environmental quality.  相似文献   
26.
In mehrjährigen Feldversuchen (1990–1995) in Nordostdeutschland wurde der Einfluß selektierter assoziativer Rhizosphärenbakterien auf den Ertrag und die Nährstoffaufnahme bei Mais untersucht.

Der Trockenmasse‐ und Kolbenertrag zur Siloreife bzw. der Samenertrag wurde durch die Bakterienstämme Pseudomonas fluorescens (PsIA12), Agrobacterium rhizogenes (A1A4), Rhizobium trifolii (R39) und z.T. durch Stenotrophomonas maltophilia (PsIB2) in den Jahren 1990 bis 1995 auf lehmigen Sandböden wiederholt signifikant, auf sandigem Lehm zum Teil signifikant erhöht. Maissorten können unterschiedlich auf die Bakterieninokulation reagieren. Die Bakterien stimulierten insbesondere bei Jungpflanzen die Wurzelentwicklung und die Nährstoffaufnahme (N, P, K) aus dem Boden. Sie bildeten Phytohormone (Auxine und z.T. Cytokinine) und überlebten, auch unter Feldbedingungen, im Rhizosphärenraum von Mais während der gesamten Vegetation.  相似文献   
27.
28.
29.
ABSTRACT

Forest productivity is a crucial variable in forest planning, usually expressed as site index (SI). In Nordic commercial forest inventories, SI is commonly estimated by a combination of aerial image interpretation, field assessment and information obtained from previous inventories. Airborne laser scanning (ALS) and digital aerial photogrammetry (DAP) data can alternatively be used for SI estimation, however the economic utilities of the inventory methods have not been compared. We compared seven methods of SI estimation in a cost-plus-loss analysis, by which we added the expected economic losses due to sub-optimal treatment decisions to the inventory costs. The methods comprised direct and indirect estimation from combinations of ALS, DAP and stand register data, and manual interpretation from aerial imagery supported by field assessment and information from previous inventories (conventional practices). The choice of method had great impact on both the accuracy and the economic value of the produced estimates. Direct methods using bitemporal ALS and DAP data gave the best accuracy and the smallest total cost. DAP was a suitable and low-cost data source for SI estimation. Estimation from single-date ALS and DAP data and age obtained from the stand register provided practical alternatives when applied to even-aged stands.  相似文献   
30.
A 56 year old Quercus petraea × Q. robur F1-hybrid was back-crossed to both parental species. Pollen mixes were applied and paternity assigned to offspring based on microsatellite markers. The studied Q. petraea × Q. robur hybrid proved highly fertile and back-crossed well with both Q. robur and Q. petraea with slight but not significant preference for Q. robur. The results do not support the hypothesis about highly unidirectional gene flow between Q. robur and Q. petraea towards Q. robur as the observed back-crossing ability of the hybrid opens a route for nuclear gene flow from Q. robur to Q. petraea. However, Q. petraea × Q. robur hybrids may be rare in nature and the results do not tell us if the (probably more common) reciprocal hybrid also back-crosses easily to Q. petraea.  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