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   626篇
  免费   49篇
  国内免费   1篇
林业   10篇
农学   20篇
基础科学   6篇
  53篇
综合类   144篇
农作物   30篇
水产渔业   18篇
畜牧兽医   336篇
园艺   9篇
植物保护   50篇
  2023年   6篇
  2021年   9篇
  2020年   15篇
  2019年   24篇
  2018年   9篇
  2017年   25篇
  2016年   14篇
  2015年   16篇
  2014年   17篇
  2013年   21篇
  2012年   39篇
  2011年   44篇
  2010年   22篇
  2009年   19篇
  2008年   41篇
  2007年   27篇
  2006年   29篇
  2005年   20篇
  2004年   26篇
  2003年   32篇
  2002年   24篇
  2001年   9篇
  2000年   8篇
  1999年   4篇
  1998年   8篇
  1997年   4篇
  1996年   4篇
  1995年   5篇
  1994年   5篇
  1993年   4篇
  1991年   10篇
  1989年   9篇
  1987年   4篇
  1985年   5篇
  1984年   6篇
  1983年   3篇
  1982年   3篇
  1979年   4篇
  1976年   6篇
  1975年   6篇
  1974年   5篇
  1973年   5篇
  1972年   3篇
  1970年   4篇
  1969年   3篇
  1967年   3篇
  1900年   3篇
  1899年   5篇
  1898年   3篇
  1892年   3篇
排序方式: 共有676条查询结果,搜索用时 453 毫秒
271.
A juvenile to young adult, male, great horned owl (Bubo virginianus,GHOW) was presented to the wildlife rehabilitation hospital at Lindsay Wildlife Museum (WRHLWM) due to trauma to the right patagium from barbed wire entanglement. On presentation, both corneas were irregular, dry, and no movement of the third eyelid was noted. A severe corneal enlargement/globoid appearance was the predominant ophthalmic feature. The fundus was normal in both eyes (OU). Over the course of several days, both corneas developed edema combined with further dessication at the ocular surface associated with diffuse dorsal fluorescein stain uptake. Repeated ophthalmic examinations found normal intraocular pressures and an inability to move the third eyelid over the enlarged corneas. The bird was deemed nonreleasable due to severe wing damage and poor prognosis associated with eye abnormalities and was humanely euthanized. Postmortem CT, enucleation, and histopathology were performed to evaluate the ocular anatomical abnormality and confirm the suspected diagnosis of keratoglobus. This GHOW represents the first reported case of presumptive keratoglobus in a raptor.  相似文献   
272.
273.
The early detection and correct identification of polydorid polychaete species is essential as they are often encountered as invasive alien pests in aquaculture facilities or the intertidal where they may modify the ecosystem. Accurate identification is, however, often hampered by high levels of morphological similarity among species. This taxon will therefore benefit from the development of a library of sequences, such as COI barcodes, to aid identification. However, the universal primers for the cytochrome c oxidase I (COI) DNA barcoding marker has failed to consistently amplify this gene for polydorids, greatly hampering the development of such a library. We describe the development of unique PCR primers for the COI gene that work across four genera and nine species of polydorids. We also compared its efficacy with sequence data for mitochondrial cytochrome b and nuclear 18S rRNA, and a concatenated dataset consisting of all three markers. The nuclear 18S rRNA gene showed the least variation both intra- (0.0–1.2%) and interspecifically (0.6–4.3%), and was the most accurate for species identifications among the three markers. Although COI was characterised by higher intraspecific variation compared with Cyt b (0.0–14.5% and 0.0–4.2%, respectively), Cyt b showed considerably higher levels of interspecific variation (16.6–30.2%) compared with COI (2.2–20.7%). Of the two mitochondrial DNA markers, COI was actually less accurate for species identifications, having suggested two species within Boccardia pseudonatrix that was not supported by the other markers. Overall, the concatenated dataset yielded the most consistent intraspecific groupings, suggesting that this is the most accurate means of identifying polydorids using DNA sequence data. Thus, there may not be a quick and easy way to identify these species accurately using only molecular data.  相似文献   
274.
275.
OBJECTIVE: To evaluate the effect of two types of iron pots on haemoglobin (Hb) and serum ferritin (SF) concentrations in young children (6-24 months), adolescent girls (11-15 years) and women of reproductive age (15-44 years), whose households were provided with iron pots for cooking food over a period of 6 months, compared with controls.Design and methodsWe randomly assigned 161 households including 339 individuals from the three subgroups to cast iron pots, blue steel pots or oral iron supplements (control). In the control group, children received micronutrient Sprinklestrade mark, and adolescent girls and women received iron tablets daily for 6 months. We measured Hb, SF and C-reactive protein concentrations at baseline and 6 months, and compared groups using regression models. RESULTS: Anaemia prevalence (Hb < 110 g l-1 in infants, Hb < 120 g l-1 in girls or women) was 47% (cast iron group), 50% (blue steel group) and 50% (control) at baseline. At 6 months, there were no significant differences in Hb concentrations among groups; however, differences in SF concentrations were significant (P < 0.0001) - the control group had higher SF concentrations compared with the groups using iron pots. Also, differences in the prevalence of iron-deficiency anaemia (IDA; anaemia plus SF < 15 mug l-1) were almost significant between cast iron and control groups (P = 0.08), and blue steel and control groups (P = 0.05).ConclusionThere is no evidence that iron cooking pots are effective against IDA. Further research is warranted to determine whether the iron leached from the pots is bioavailable.  相似文献   
276.
277.
Rust caused by Uromyces appendiculatus (Pers., Pers.) Unger is one of the major foliar diseases of common bean (Phaseolus vulgaris) in Uganda. The use of host resistance remains the best option in managing this disease. The objective of this study was to identify sources of broad-spectrum rust resistance in common bean germplasm including landraces, commercial cultivars and introduced genotypes using a combination of phenotypic and genotypic screening with 22 simple sequence repeat (SSR) markers located on chromosome Pv04. A total of 138 genotypes were field screened from 2014 and 2015 using an alpha lattice design. The variance and correlation of disease incidence, area under the disease progression curve (AUDPC) and total grain yield were computed using GenStat. The polymorphism information content of the genotypes was determined, and the association of the markers and the disease resistance traits were analyzed using PowerMarker and TASSEL respectively. Resistance of each genotype was compared to the presence and absence of amplified markers. There were highly significant differences (P < 0.001) among the genotypes for disease incidence, AUDPC and total grain yield and a strong correlation (P < 0.001) between disease incidence and AUDPC in both years. The SSR markers, BARC_PV_SSR04725, bean_ssr_0778 and bean_ssr_2892 were associated (P ≤ 0.05) with rust resistance. Fifteen 15 genotypes which included the landraces Nabufumbo, and Kapchorwa white, and the commercial cultivar NABE 2 were identified as new sources of rust resistance that would be useful in future bean breeding programmes in Uganda.  相似文献   
278.
279.
Sex differences in mathematical reasoning ability: more facts   总被引:2,自引:0,他引:2  
Almost 40,000 selected seventh-grade students from the Middle Atlantic region of the United States took the College Board Scholastic Aptitude Test as part of the Johns Hopkins regional talent search in 1980, 1981, and 1982. A separate nationwide talent search was conducted in which any student under age 13 who was willing to take the test was eligible. The results obtained by both procedures establish that by age 13 a large sex difference in mathematical reasoning ability exists and that it is especially pronounced at the high end of the distribution: among students who scored greater than or equal to 700, boys outnumbered girls 13 to 1. Some hypothesized explanations of such differences were not supported by the data.  相似文献   
280.
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