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   5628篇
  免费   564篇
  国内免费   386篇
林业   507篇
农学   578篇
基础科学   324篇
  1102篇
综合类   1629篇
农作物   425篇
水产渔业   330篇
畜牧兽医   1145篇
园艺   191篇
植物保护   347篇
  2024年   104篇
  2023年   119篇
  2022年   226篇
  2021年   255篇
  2020年   251篇
  2019年   239篇
  2018年   170篇
  2017年   250篇
  2016年   189篇
  2015年   237篇
  2014年   227篇
  2013年   315篇
  2012年   343篇
  2011年   384篇
  2010年   276篇
  2009年   231篇
  2008年   261篇
  2007年   243篇
  2006年   247篇
  2005年   227篇
  2004年   158篇
  2003年   200篇
  2002年   230篇
  2001年   175篇
  2000年   170篇
  1999年   103篇
  1998年   83篇
  1997年   65篇
  1996年   61篇
  1995年   54篇
  1994年   36篇
  1993年   48篇
  1992年   36篇
  1991年   27篇
  1990年   36篇
  1989年   33篇
  1988年   21篇
  1987年   25篇
  1986年   21篇
  1985年   21篇
  1984年   13篇
  1983年   13篇
  1982年   12篇
  1981年   12篇
  1979年   9篇
  1971年   9篇
  1970年   8篇
  1965年   9篇
  1964年   14篇
  1963年   12篇
排序方式: 共有6578条查询结果,搜索用时 15 毫秒
71.
大豆室内耐冷筛选及其在田间的应用研究   总被引:3,自引:1,他引:3  
本试验把生长箱大豆耐低温萌发筛选与田间早春播研究相结合,验证耐低温发芽的可靠性。在实验室,萌发期表现抗冷的大豆,田间出昔期仍表现抗冷或较抗冷。实验表明,大豆出苗的生物学最低温度平均为7.1℃,所需有效积温136℃。地温的高低直接影响大豆早春出苗的多寡,两者呈密切的正相关。黄、青、黑豆中,以黑豆抵抗早春不良气候条件的能力最强。  相似文献   
72.
农业信息化专业硕士人才培养评价体系构建   总被引:1,自引:0,他引:1  
针对现有农业信息化专业硕士培养评价体系现状及存在的问题进行了分析,从专业人才培养定位出发,针对课程体系、实践创新能力、教学过程监控等方面构建了多元化、特色鲜明的二级评价指标体系。以黑龙江八一农垦大学农业信息化硕士培养为例进行评价,结果表明,学生对课程体系设置、实践创新能力培养、教学组织、管理、考核等的比较认可,同时学生对教学过程监控有更大的期望,需要进一步加强现有培养方案的教学过程监控,调整培养方案,提高农业信息化专业硕士人才培养质量。  相似文献   
73.
Understanding both historic and current fire regimes is indispensable to sustainable forest landscape management. In this paper, we use a spatially explicit landscape simulation model, LANDIS, to simulate historic and current fire regimes in the Great Xing’an Mountains, in northeastern China. We analyzed fire frequency, fire size, fire intensity, and spatial pattern of burnt patches. Our simulated results show that fire frequency under the current fire scenario is lower than under the historic fire scenario; total area burnt is larger with lower fire intensity under the historic fire scenario, and smaller with higher fire intensity under the current fire scenario. We also found most areas were burned by high intensity fires under the current fire scenario, but by low to moderate fires under the historic fire scenario. Burnt patches exhibit a different pattern between the two simulation scenarios. Large patches burnt by high intensity class fires dominate the landscape under the current fire scenario, and under historic fire scenario, patches burnt by low to moderate fire intensity fires have relatively larger size than those burnt by high intensity fires. Based on these simulated results, we suggest that prescribed burning or coarse woody debris reduction should be incorporated into forest management plans in this region, especially on north-facing slopes. Tree planting may be a better management option on these severely burned areas whereas prescribed burning after small area selective cutting, retaining dispersed seed trees, may be a sound forest management alternative in areas except for the severely burned patches.  相似文献   
74.

Purpose

Remediate metal contamination is a fundamental step prior to reclaim oil sands tailing ponds, and copper (Cu(II)) is the most abundant metal in the tailings water or oil sands process-affected water (OSPW). Biochars produced at four pyrolysis conditions were evaluated for sorption of Cu(II) in synthetic OSPW to explore different biochar potentials in removing Cu(II) from the contaminated water.

Materials and methods

Pine sawdust biochars pyrolyzed at 300 and 550 °C with and without steam activation were investigated by batch sorption experiments. Isotherm and kinetic studies were conducted to compare the sorption capacities of the four biochars and to examine potential mechanisms involved.

Results and discussion

For all the biochars, Langmuir and pseudo-second order models were the best-fit for isotherm and kinetic studies, respectively. According to the Langmuir parameters, the maximum adsorption capacities of the biochars produced at 550 °C were around 2.5 mg Cu(II)?g?1, which were 30-folds higher than those produced at 300 °C. However, steam activation did not cause any significant difference in the biochars’ sorption performance. The kinetic study suggested that chemisorption involving valence forces was the limiting factor of the sorption. In addition, ion exchange and precipitation were likely the primary mechanisms for Cu(II) sorption which outweigh complexation with functional groups on the biochars’ surface.

Conclusions

Pine sawdust biochar produced at 550 °C without steam activation could be utilized as a sustainable and cost-effective material to remove Cu(II) from the OSPW.
  相似文献   
75.
76.
77.
The objective of this study was to evaluate the pharmacokinetic properties and adverse effect profile of single‐dose oral bosentan, a dual endothelin receptor antagonist, in healthy cats. Pharmacokinetic parameters were determined following a single mean ± SD oral dose of 3.2 ± 0.6 mg/kg of bosentan in 6 adult cats. Blood was collected for quantification of bosentan via high‐performance liquid chromatography with ultraviolet detection. Blood and urine were evaluated for CBC, plasma biochemical profile, and urinalysis, and repeat physical examinations were performed to evaluate for adverse effects. The mean terminal half‐life of bosentan was 20.4 ± 17.2 h. The mean peak plasma concentration was 0.49 ± 0.24 g/mL, and the mean time to maximum plasma concentration was 6.8 ± 8.6 h. The area under the curve was 5.14 ± 3.81 h·μg/mL. Oral bosentan tablets were absorbed in cats, and no clinically important adverse events were noted. Further evaluation of repeat dosing, investigation into the in vivo efficacy of decreasing endothelin‐1 concentrations in cats, as well as safety in conjunction with other medications is warranted.  相似文献   
78.
For investigating the feasibility of using disperse dyes as an immunoassay chromogenic marker, a disperse dye, DADISPERSE NAVY BLUE SP, was selected in analyzing antibody against infectious bursal disease virus (anti-IBDV). With the color intensity revealed in the disperse dye immunochromatographic test (DICT) strip as the objective function, the optimal dyeing conditions were found as follows: dye concentration absorbance (at lambda(max)=587nm)=3, pH 7, 50 degrees C, for 10min. Under these conditions, the resultant dyed-antibody (rabbit anti-chicken) can produce an optimal color intensity reading of 55,054 on the strip. For performing qualitative immunoassay, chicken sera samples taken from different farms were used for the anti-IBDV titre assessment. The results of DICT strips showed very high sensitivity and specificity as compared to that analyzed by FlockChek enzyme linked immunosorbent assay (F-ELISA) kits. For quantitative immunoassay, it was found that the color intensity measured with DICT was linearly correlated to that of F-ELISA titre (r(2)=0.9687). Therefore, DICT was further applied to the detection of chicken anti-IBDV sera under vaccination in the farms. The average titres of the sampling groups exhibited a strong agreement to that of F-ELISA. Accordingly, the DICT method developed in this study, shown to be reliable, cheap and simple in both qualitative and quantitative immunoassays, is particularly suitable for point-of-need testing (PONT) in agricultural applications.  相似文献   
79.
针对江苏省稻作区水资源、土壤、气候的特点 ,选择浅湿灌溉、浅湿调控灌溉、控制灌溉、水稻旱作灌溉等 4种技术因地制宜进行推广。在灌溉过程中 ,建立和完善了一整套的组织措施和技术措施 ,形成了江苏省水稻节水灌溉技术推广模式 ,取得了显著的效果 ,丰富了水稻节水灌溉技术推广的内容  相似文献   
80.
Canine hyperadrenocorticism (HAC) is one of the most common causes of general osteopenia. In this study, quantitative computed tomography (QCT) was used to compare the bone mineral densities (BMD) between 39 normal dogs and 8 dogs with HAC (6 pituitary-dependent hyperadrenocorticism [PDH]; pituitary dependent hyperadrenocorticism, 2 adrenal hyperadrenocorticism [ADH]; adrenal dependent hyperadrenocorticism) diagnosed through hormonal assay. A computed tomogaraphy scan of the 12th thoracic to 7th lumbar vertebra was performed and the region of interest was drawn in each trabecular and cortical bone. Mean Hounsfield unit values were converted to equivalent BMD with bone-density phantom by linear regression analysis. The converted mean trabecular BMDs were significantly lower than those of normal dogs. ADH dogs showed significantly lower BMDs at cortical bone than normal dogs. Mean trabecular BMDs of dogs with PDH using QCT were significantly lower than those of normal dogs, and both mean trabecular and cortical BMDs in dogs with ADH were significantly lower than those of normal dogs. Taken together, these findings indicate that QCT is useful to assess BMD in dogs with HAC.  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