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   1051篇
  免费   78篇
  国内免费   1篇
林业   47篇
农学   34篇
基础科学   4篇
  115篇
综合类   269篇
农作物   55篇
水产渔业   50篇
畜牧兽医   488篇
园艺   10篇
植物保护   58篇
  2023年   10篇
  2022年   9篇
  2021年   13篇
  2020年   24篇
  2019年   30篇
  2018年   21篇
  2017年   28篇
  2016年   24篇
  2015年   20篇
  2014年   30篇
  2013年   47篇
  2012年   46篇
  2011年   51篇
  2010年   32篇
  2009年   26篇
  2008年   52篇
  2007年   50篇
  2006年   32篇
  2005年   43篇
  2004年   40篇
  2003年   50篇
  2002年   35篇
  2001年   28篇
  2000年   23篇
  1999年   18篇
  1998年   11篇
  1997年   12篇
  1996年   21篇
  1995年   9篇
  1994年   6篇
  1993年   10篇
  1992年   14篇
  1991年   12篇
  1990年   7篇
  1989年   14篇
  1988年   14篇
  1987年   14篇
  1986年   9篇
  1985年   13篇
  1984年   7篇
  1983年   13篇
  1981年   6篇
  1980年   5篇
  1979年   14篇
  1975年   11篇
  1974年   7篇
  1972年   5篇
  1970年   7篇
  1969年   7篇
  1968年   7篇
排序方式: 共有1130条查询结果,搜索用时 15 毫秒
991.
The use of lime and phosphates in reclaiming heather moorland was investigated in two experiments.
Large initial dressings of hme resulted in a rapid rise in pH. An initial dressing of 9 tons CaCO3/ac resulted in a more rapid rise to pH 6 than did 6 tons/ac and the soil was maintained above pH 6 for a longer period. Three annual dressings of 3 tons/ac gave a slower rise in pH and a longer period above pH 6. Split treatments, half before and half after the first ploughing, gave no long–term advantage where a programme of pioneer cropping was being followed.
Basic slag and North African phosphate were as effective as superphosphate for root crops at low pH values. Basic slag was as effective as superphosphate for grassland establishment and gave a greater rise in soil phosphate. North African phosphate was virtually worthless as a source of phosphate for establishing grasses and clovers, and gave a negligible rise in soil phosphate.
Given adequate supphes of lime and phosphate, frequent small apphcations of N over the first 2 or 3 years are vital to the success of a reclamation programme under the conditions described.  相似文献   
992.
993.
994.
Generalized linear mixed models for spatial processes are widely used in applied statistics. In many applications of the spatial generalized linear mixed model (SGLMM), the goal is to obtain inference about regression coefficients while achieving optimal predictive ability. When implementing the SGLMM, multicollinearity among covariates and the spatial random effects can make computation challenging and influence inference. We present a Bayesian group lasso prior with a single tuning parameter that can be chosen to optimize predictive ability of the SGLMM and jointly regularize the regression coefficients and spatial random effect. We implement the group lasso SGLMM using efficient Markov chain Monte Carlo (MCMC) algorithms and demonstrate how multicollinearity among covariates and the spatial random effect can be monitored as a derived quantity. To test our method, we compared several parameterizations of the SGLMM using simulated data and two examples from plant ecology and disease ecology. In all examples, problematic levels multicollinearity occurred and influenced sampling efficiency and inference. We found that the group lasso prior resulted in roughly twice the effective sample size for MCMC samples of regression coefficients and can have higher and less variable predictive accuracy based on out-of-sample data when compared to the standard SGLMM.Supplementary materials accompanying this paper appear online.  相似文献   
995.
New Forests - Forest managers are increasingly planting non-native tree species that are adapted to anticipated future conditions such as increased droughts. This work quantified individual tree...  相似文献   
996.
Understanding large‐scale migratory behaviours, local movement patterns and population connectivity are critical to determining the natural processes and anthropogenic stressors that influence population dynamics and for developing effective conservation plans. Atlantic tarpon occur over a broad geographic range in the Atlantic Ocean where they support valuable subsistence, commercial and recreational fisheries. From 2001 through 2018, we deployed 292 satellite telemetry tags on Atlantic tarpon in coastal waters off three continents to document: (a) seasonal migrations and regional population connectivity; (b) freshwater and estuarine habitat utilization; (c) spawning locations; and (d) shark predation across the south‐eastern United States, Gulf of Mexico and northern Caribbean Sea. These results showed that some mature tarpon make long seasonal migrations over thousands of kilometres crossing state and national jurisdictional borders. Others showed more local movements and habitat use. The tag data also revealed potential spawning locations consistent with those inferred in other studies from observations of early life stage tarpon leptocephalus larvae. Our analyses indicated that shark predation mortality on released tarpon is higher than previously estimated, especially at ocean passes, river mouths and inlets to bays. To date, there has been no formal stock assessment of Atlantic tarpon, and regional fishery management plans do not exist. Our findings will provide critical input to these important efforts and assist the multinational community in the development of a stock‐wide management information system to support informed decision‐making for sustaining Atlantic tarpon fisheries.  相似文献   
997.
The concept of “blue growth,” which aims to promote the growth of ocean economies while holistically managing marine socioecological systems, is emerging within national and international marine policy. The concept is often promoted as being novel; however, we show that historical analogies exist that can provide insights for contemporary planning and implementation of blue growth. Using a case‐study approach based on expert knowledge, we identified 20 historical fisheries or aquaculture examples from 13 countries, spanning the last 40–800 years, that we contend embody blue growth concepts. This is the first time, to our knowledge, that blue growth has been investigated across such broad spatial and temporal scales. The past societies managed to balance exploitation with equitable access, ecological integrity and/or economic growth for varying periods of time. Four main trajectories existed that led to the success or failure of blue growth. Success was linked to equitable rather than open access, innovation and management that was responsive, holistic and based on scientific knowledge and monitoring. The inability to achieve or maintain blue growth resulted from failures to address limits to industry growth and/or anticipate the impacts of adverse extrinsic events and drivers (e.g. changes in international markets, war), the prioritization of short‐term gains over long‐term sustainability, and loss of supporting systems. Fourteen cross‐cutting lessons and 10 recommendations were derived that can improve understanding and implementation of blue growth. Despite the contemporary literature broadly supporting our findings, these recommendations are not adequately addressed by agendas seeking to realize blue growth.  相似文献   
998.
Temperature is considered as an important environmental factor, and the increasing water temperature resulting from global warming is a great concern. The present study was conducted to examine the effects of elevated water temperature on growth, hemato‐biochemical parameters in Nile tilapia, Oreochromis niloticus acclimatized to three temperatures (31°C, 34°C and 37°C) for 60 days. Additionally, erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) tests were assayed using peripheral erythrocytes after exposure to the three temperatures. Fish were sacrificed on days 7, 15, 30 and 60 of exposure. Growth performances viz., weight gain, % weight gain and specific growth rate (SGR) showed decreasing tendency at 34°C but significantly declined at 37°C compared to 31°C. The abundance of haemoglobin (Hb) and red blood cells (RBCs) significantly decreased in response to temperature increases, while white blood cells (WBCs) displayed the opposite response. At days 7 and 15, blood glucose levels significantly increased in response to the temperature increase, while at days 30 and 60 glucose declined. Frequencies of ECA and ENA were significantly enhanced at the highest temperature throughout the experimental period. Dissolved oxygen decreased and free CO2 increased significantly with increasing temperature throughout the study period. The present study revealed that temperatures higher than 34°C may be hazardous to O. niloticus.  相似文献   
999.
Immunohistochemistry plays an important part in the diagnosis of some viral diseases. Demonstration of viral antigen in a lesion is an important contribution to diagnosis, either at the time of investigation or retrospectively. At the CSIRO Australian Animal Health Laboratory, the most frequent use of immunohistochemistry has been in the diagnosis of the important avian diseases, highly pathogenic avian influenza and Newcastle disease. The technology took key roles in the diagnoses of Hendra virus infections, and, later, an immunoperoxidase test gave the first indication of the existence of Australian bat lyssavirus. The test can often confirm that a virus isolated in an animal is the actual virus causing disease and not a coincidental isolation. Good examples of that in some more new diseases were the association of Wallal virus with blindness in kangaroos, and of the new porcine Menangle virus in natural and experimental cerebral disease in foetal piglets.  相似文献   
1000.
Antibiotics applied to the skin must be formulated in a base that is nonirritant and nontoxic. They may have a narrow or fairly wide spectrum of activity but should produce no local reaction or sensitization; the commensal flora should not be affected unduly. Three antibiotics that have been used topically in humans and animals are fusidic acid, mupirocin and bacitracin, all of which have a narrow antibacterial spectrum. When applied to intact skin, fusidic acid penetrates more rapidly than other antibiotics. Clinically, the frequency of staphylococcal resistance to it and to mupirocin has remained low. Fusidic acid and mupirocin have been recommended for the treatment of acute staphylococcal skin lesions. However, the use of topical antibiotics for the treatment of chronic or recurring dermatitis and surgical or infected wounds may be inappropriate because of possible development of resistance and sensitization. Topical use of bacitracin may produce treatment failure and sensitization.  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