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   8601篇
  免费   590篇
  国内免费   731篇
林业   670篇
农学   685篇
基础科学   346篇
  1330篇
综合类   4071篇
农作物   414篇
水产渔业   501篇
畜牧兽医   1153篇
园艺   351篇
植物保护   401篇
  2024年   53篇
  2023年   228篇
  2022年   373篇
  2021年   373篇
  2020年   418篇
  2019年   405篇
  2018年   286篇
  2017年   391篇
  2016年   511篇
  2015年   529篇
  2014年   609篇
  2013年   561篇
  2012年   693篇
  2011年   709篇
  2010年   527篇
  2009年   479篇
  2008年   434篇
  2007年   461篇
  2006年   332篇
  2005年   296篇
  2004年   216篇
  2003年   180篇
  2002年   134篇
  2001年   108篇
  2000年   89篇
  1999年   82篇
  1998年   60篇
  1997年   64篇
  1996年   55篇
  1995年   57篇
  1994年   42篇
  1993年   39篇
  1992年   20篇
  1991年   30篇
  1990年   17篇
  1989年   15篇
  1988年   13篇
  1987年   9篇
  1986年   4篇
  1985年   5篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1962年   2篇
  1956年   3篇
排序方式: 共有9922条查询结果,搜索用时 803 毫秒
961.
利用16个茶叶主产省2 210份茶农调查数据,借助Logit模型分析了影响茶农绿色防控技术采用行为的因素。结果表明,茶农采用绿色防控技术受个人特征、家庭特征、茶园经营特征和组织与技术服务特征4个方面的因素影响,其中组织与技术服务特征因素的影响最大。具体来看,年龄、家庭人口规模和茶园规模对茶农采用绿色防控技术有显著的负向影响;农残限量标准认知、家庭年收入、组织化程度、技术培训和技术交流对茶农采用绿色防控技术有显著的积极影响。了解农残限量标准的茶农采用绿色防控技术的概率约是不了解的2倍;家庭收入每增加1万元,技术采用发生比相对增加2%;加入合作社的茶农采用绿色防控技术的概率是未加入的1.73倍;茶农参加病虫害防治培训次数每增加1次,技术采用发生比提升为原来的150%。受教育程度、打工收入占比、农药价格敏感性等因素在本研究中对茶农绿色防控技术采用的影响不显著。由此,有关政府部门需要通过增强茶农组织化程度,加强农户病虫害防治培训,降低技术使用成本等手段促进农户绿色防控技术的采用,以便实现绿色农业。  相似文献   
962.
为了研究添加芽孢杆菌对池塘中真核微生物群落结构和理化因子的影响,采用高通量测序技术分析了实验组(添加芽孢杆菌池塘)与对照组(普通池塘)水体真核微生物群落结构,同时分析了两组池塘的水体理化指标。结果表明:8、9月实验组池塘水体中TN、NH_4~+-N、NO_3~--N含量显著低于对照组(P0.05)。水体中梅尼小环藻(Cyclotella meneghiniana)、红囊藻(Hedriocystis)、蓝隐藻(Chroomonas)、丝孢酵母属(Trichosporon)和小环藻属(Cyclotella)真核微生物丰度显著高于对照组(P0.05)。实验组池塘水体真核微生物Chao1指数和Shannon指数显著高于对照组(P0.05)。实验结果证实:通过向池塘添加芽孢杆菌,可以改变水体中真核微生物群落的结构,从而实现对池塘理化因子的调节。研究结果对于降低水产养殖尾水对水域环境的污染具有一定的意义。  相似文献   
963.
In 1999, the Grain for Green Project was implemented by the Chinese government. Since then, the vegetation of Zuli River Basin, a semi-arid river basin of the Chinese Loess Plateau, has been greatly changed. Clearly understanding the impact of natural and artificial factors on vegetation change is important for policy making and ecosystem management. In this study, spatio-temporal variations in vegetation cover in Chinese Zuli River Basin during 1999–2016 were investigated using Landsat normalized difference vegetation index (NDVI) data. Analyses of several indicators, including changes in NDVI in different slopes and land use changes and the relationships between climatic factors and NDVI change, were presented to quantitatively evaluate the effects of agriculture, climate, and policy on NDVI change. The NDVI in the Zuli River Basin increased during the study period, and the main contributors to this change were forest in 1999–2011, cropland, abandoned farmland, and grassland in 2009–2016, and land with slopes ≤ 15°. Land with slope > 15°, where the “Project” was implemented, slightly contributed to the increase in regional NDVI. In 1999–2011, the project (?98.16%) combined with climate change (?68.18%) showed negative effects on the increase in NDVI in the Zuli River Basin, but agriculture (22.28%) played a positive role in increasing this index. In 2009–2016 and 1999–2016, the project (38.45% and 35.25%, respectively), the project combined with climate change (49.83% and 46.30%, respectively), agriculture (18.61% and 23.30%, respectively), promoted increases in NDVI in the basin.  相似文献   
964.
研究了塑料大棚内的光照强度、气温、地温、CO2浓度及氮肥施量5个环境因子5水平的处理组合对春季早熟苋菜栽培营养品质与外观品质的影响。结果表明,苋菜体内硝酸盐含量由低到高的次序为AB>C>D>E,其中VC含量后4者比处理A分别减少了11.7%,18.4%,31.3%和32.4%,在处理A、B内,随氮肥水平提高VC含量增加,其余处理氮水平间变化不大。花青素含量分别减少了18.6%,23.5%,39.2%和52.9%,在各处理内随氮水平提高而增加,变化幅度较大。不同处理粗纤维和还原糖含量变化呈现相同趋势:B>A>C>D>E,但不同氮水平间变化趋势两者相反。光照强度显著或极显著地影响各品质指标的变化,是春季大棚早熟苋菜栽培能否获得优质的首要因子。综合评判各环境因子组合,B组(0网1膜,平均光强17 800 lx,地温21.2℃,气温23.5℃和CO2浓度1 500μmol/mol)在施氮水平为N5(300 kg/hm2)时,可以实现苋菜的优质栽培。  相似文献   
965.
966.
BACKGROUND: No reliable tool to predict outcome of acute kidney injury (AKI) exists. HYPOTHESIS: A statistically derived scoring system can accurately predict outcome in dogs with AKI managed with hemodialysis. ANIMALS: One hundred and eighty-two client-owned dogs with AKI. METHODS: Logistic regression analyses were performed initially on clinical variables available on the 1st day of hospitalization for relevance to outcome. Variables with P< or = .1 were considered for further analyses. Continuous variables outside the reference range were divided into quartiles to yield quartile-specific odds ratios (ORs) for survival. Models were developed by incorporating weighting factors assigned to each quartile based on the OR, using either the integer value of the OR (Model A) or the exact OR (Models B or C, when the etiology was known). A predictive score for each model was calculated for each dog by summing all weighting factors. In Model D, actual values for continuous variables were used in a logistic regression model. Receiver-operating curve analyses were performed to assess sensitivities, specificities, and optimal cutoff points for all models. RESULTS: Higher scores were associated with decreased probability of survival (P < .001). Models A, B, C, and D correctly classified outcomes in 81, 83, 87, and 76% of cases, respectively, and optimal sensitivities/specificities were 77/85, 81/85, 83/90 and 92/61%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The models allowed outcome prediction that corresponded with actual outcome in our cohort. However, each model should be validated further in independent cohorts. The models may also be useful to assess AKI severity.  相似文献   
967.
Background: Endocarditis is a rare heart condition with variable clinical expressions in equids. Risk factors for this disease are incompletely understood. Objective: Describe risk factors for endocarditis in equids. Animals: One hundred and fifty‐three equids admitted to Liège University, 9 diagnosed with endocarditis and 144 free from endocarditis but admitted to the hospital with a differential diagnosis including this disease. Methods: Retrospective case‐control study. Results: Equids with endocarditis were significantly younger (mean age = 4.84 ± 5.74 years) than control equids (mean age = 10.8 ± 7.73 years) (P= .01). No sex or breed predisposition was observed. Animals with hyperthermia (odds ratio [OR] = 24.4; confidence interval [CI] = 1.40–428), synovial distension (OR = 13.4; CI = 3.00–59.8), lameness (OR = 6.52; CI = 1.63–26.1), hyperglobulinemia (OR = 26.4; CI = 3.03–229), hypoalbuminemia (OR = 11.4; CI = 1.34–96.8), hyperfibrinogenemia (OR = 9.81; CI = 1.16–82.7), or leukocytosis (OR = 7.12; CI = 1.40–36.4) presented a significantly higher risk of having endocarditis than control horses. The presence of two of the clinical signs mentioned above significantly increased the probability of a diagnosis of endocarditis (P≤ .05). Conclusions and Clinical Importance: Age is associated with equine endocarditis. The diagnostic value of certain clinical signs and abnormalities in blood parameters in this disease are described.  相似文献   
968.
大肠杆菌O157:H7是一种感染剂量低,致病性强,临床上无特效治疗药物的新型肠道致病菌,在世界范围内多次爆发流行,已构成严重的公共卫生问题。对大肠杆菌O157:H7的基本生物学特征,从非生物因素(包括传染源、气候等因素)和生物因素两个方面综述了影响大肠杆菌O157:H7传播的环境因子,最后从病原菌的监测诊断技术、废弃物堆肥处理、加强食品以及饮水安全管理等方面提出了控制大肠杆菌O157:H7的对策,最终为大肠杆菌O157:H7的疫病生态学研究提供了理论基础和参考依据。  相似文献   
969.
Research in control of tick-borne diseases and trypanosomosis, and their vectors, namely, ticks and tsetse flies respectively, has been on going for decades. However, very little attention has been paid to the socio-economic factors that are likely to influence the outcome of the interventions in the control of these diseases. Thus, this study was designed to investigate these factors, mainly the intra-household factors influencing decision-making in the control of Vector-borne diseases in the pastoralist areas of Uganda. These factors included: indigenous technical knowledge, household economic factors, and gender. Both qualitative and quantitative methods were used in the collection and analysis of data. The tools used for data collection included among others, participatory learning and action (PLA), and Case studies. The findings included the following: In pastoralist households, a big proportion of the household budget was allocated to vector-borne diseases control. In the male-headed households, men dominated decision-making on vector-borne diseases control, although the goals and priorities of men and women in these households were not the same. Also, vector-borne disease control was predominantly by use of modern veterinary drugs, and pastoralists treated sick cattle by themselves even in situations where there were veterinary personnel.  相似文献   
970.
The objective of the present study was to describe the prevalence and risk factors associated with cryptosporidiosis in buffalo calves in Middle Egypt. During one year, 458 fecal samples were collected from buffalo calves less than 3 month age in 55 small scale herds and examined for the presence of Cryptosporidium oocysts. Data describing age, gender, season, and herd management practices were gathered to assess potential risk factors. Fecal examination showed that 14.19% of the examined calves were positive for Cryptosporidium spp. Calves at 1-15 days were at the highest risk (P < 0.001), and a significant relationship between season and infection (P < 0.05) was recorded. A significant association between infection and hygiene (P < 0.001), type of floor (P < 0.01) and source of water (P < 0.01) was also recorded. Statistical analysis concerning the clinical signs and fecal characteristics revealed a significant association with fecal consistency (P < 0.001), presence of blood (P < 0.01) and mucous (P < 0.01). Moreover, a significant association was found between infection and the desire for suckling (P < 0.05) and tenesmus (P < 0.05). The results of the present study demonstrated the strong relation between infections by Cryptosporidium spp. and diarrhea in buffalo calves.  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