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   1062篇
  免费   74篇
  国内免费   12篇
林业   82篇
农学   44篇
基础科学   4篇
  221篇
综合类   126篇
农作物   71篇
水产渔业   110篇
畜牧兽医   388篇
园艺   31篇
植物保护   71篇
  2023年   12篇
  2022年   22篇
  2021年   39篇
  2020年   33篇
  2019年   30篇
  2018年   32篇
  2017年   38篇
  2016年   34篇
  2015年   41篇
  2014年   41篇
  2013年   58篇
  2012年   64篇
  2011年   71篇
  2010年   58篇
  2009年   55篇
  2008年   75篇
  2007年   65篇
  2006年   51篇
  2005年   57篇
  2004年   56篇
  2003年   37篇
  2002年   30篇
  2001年   23篇
  2000年   23篇
  1999年   13篇
  1998年   8篇
  1997年   5篇
  1996年   7篇
  1995年   5篇
  1994年   4篇
  1993年   4篇
  1992年   4篇
  1991年   4篇
  1990年   3篇
  1989年   4篇
  1987年   2篇
  1986年   4篇
  1984年   2篇
  1983年   2篇
  1981年   2篇
  1978年   2篇
  1975年   4篇
  1971年   2篇
  1969年   4篇
  1937年   2篇
  1936年   1篇
  1935年   1篇
  1932年   1篇
  1924年   1篇
  1918年   1篇
排序方式: 共有1148条查询结果,搜索用时 0 毫秒
861.
862.

Background

Toumeyella parvicornis is an invasive soft scale insect native to North America that is rapidly spreading in Italy and France, provoking severe infestations on Pinus pinea L. To date, the control of this pest is entrusted to three endotherapic techniques whose short-term efficacy is partially known. No information on long-term efficacy is currently available, although fundamental. This work aims to report on the long-term effect that abamectin-based insecticides, injected with the three different techniques, have on adult female populations.

Results

The study was carried out in an infested P. pinea forest in the area of Rome, Italy. Results showed that the tested methods had a similar long-term effect, and only in one case there were differences with the untreated control. Multiresidue analysis reported a zero level of abamectin in plant tissues 14 months apart from injection, except for one treatment where pesticide concentration was just above the limit of quantification.

Conclusions

This study represents the first long-term evaluation about endotherapic control strategy against T. parvicornis. In fact, the pest may quickly bring the death and fall of the stone pines, representing a concerning risk for citizens, however, control actions to manage it are still partially known and deserve more in-depth investigations. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.  相似文献   
863.
864.
865.
Maropitant is a neurokinin-1 inhibitor that acts to prevent and treat vomiting by blocking stimuli to the final common pathway in the emetic centre of the brain. The field efficacy and safety of a single oral dose of maropitant were investigated for the prevention of vomiting in dogs with a history of motion sickness resulting from transportation by car in two blinded, placebo-controlled studies. In an exploratory study designed as a two-way crossover trial with 17 dogs, 10 of the dogs given the placebo vomited during a car journey but only three of the dogs vomited under maropitant treatment. In a larger multicentred parallel design study, 69 of 105 dogs treated with the placebo vomited during the journey compared with 15 of 106 dogs treated with maropitant (P < 0.0001).  相似文献   
866.
867.
为了明确耕作方式对东北薄层黑土坡耕地土壤物理性状以及玉米根系垂直分布的影响,该研究以东北薄层黑土坡耕地土壤为研究对象,设置免耕和翻耕2种耕作方式,研究耕作方式对不同坡位土壤水稳性团聚体粒径分布与稳定性、土壤容重、土壤孔隙度、土壤贯入阻力以及玉米根系在垂直方向主要分布深度的影响,并进一步探究各指标间的相互关系.结果表明,...  相似文献   
868.
A commercially available competitive enzyme-linked immunosorbent assay (cELISA, VMRD®) was validated for the detection of Neospora caninum antibodies in the serum of dogs, using as a reference test an indirect fluorescent antibody test (IFAT, Fuller®). A partial verification approach was used. A total of 618 dogs were screened with cELISA and a subset of positive and negative sera (n = 237) were then tested with IFAT. Naïve relative sensitivity (SEnv) and naïve relative specificity (SPnv) of cELISA were calculated and then corrected (SEcorr; SPcorr) for studies with partial validation. Results showed a SEnv of 72% and a SPnv of 89.3%; corrected estimates showed a SEcorr of 47% and a SPcorr of 96%. ROC analysis showed that the cutoff recommended by the manufacturer (30%) corresponded to the highest naïve sensitivity (72%) combined with a good naïve specificity (90%) of cELISA. Corrected estimates of SE and SP for partial verification method revealed that SE of the cELISA is lower and SP is higher than naïve estimates. The results suggest to use this test for confirmation of a clinical suspicion of neosporosis, and to use some techniques for adjustment of misclassification in prevalence and risk-factor studies.  相似文献   
869.
Conservation of apex predators is a key challenge both in marine and terrestrial ecosystems. The white shark is a rare but persistent inhabitant of the Mediterranean Sea and it is currently assessed as “critically endangered” in the region. However, the population trends and dynamics of this species in the area are still unknown. Little is known about white shark distribution, habitat use and population abundance trends, aspects that are critical for conservation and management. In this study, we built the most comprehensive database of white shark occurrence records in the region. We collected 773 different records from different sources and used them to characterize the spatial and temporal patterns of abundance of Mediterranean white sharks between 1860 and 2016. We analysed these data by using generalized additive models and used spatially disaggregated information on human population abundance as a proxy of observation effort. Our results suggest a complex trajectory of population change characterized by a historical increase and a more recent reduction (61%, range 58%–72%) since the second half of the 20th century. In particular, analyses reveal a 52% (range 37%–88%) to 96% (range 92%–100%) overall decline in different Mediterranean sectors and a contraction in spatial distribution. Here, we provide the first reconstruction of abundance trends and offer new hypotheses regarding the drivers of change of white sharks in the Mediterranean. Our approach can be broadly applied to data‐poor contexts to reconstruct change and inform the conservation of endangered top predators in the Mediterranean Sea and other intensely used marine regions.  相似文献   
870.
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