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   588篇
  免费   22篇
  国内免费   3篇
林业   87篇
农学   31篇
基础科学   1篇
  37篇
综合类   17篇
农作物   18篇
水产渔业   67篇
畜牧兽医   280篇
园艺   11篇
植物保护   64篇
  2023年   2篇
  2022年   6篇
  2021年   29篇
  2020年   6篇
  2019年   8篇
  2018年   13篇
  2017年   10篇
  2016年   17篇
  2015年   21篇
  2014年   18篇
  2013年   19篇
  2012年   20篇
  2011年   36篇
  2010年   21篇
  2009年   26篇
  2008年   37篇
  2007年   38篇
  2006年   50篇
  2005年   37篇
  2004年   29篇
  2003年   31篇
  2002年   20篇
  2001年   13篇
  2000年   15篇
  1999年   4篇
  1998年   7篇
  1997年   3篇
  1996年   5篇
  1995年   1篇
  1994年   2篇
  1993年   3篇
  1992年   7篇
  1991年   7篇
  1990年   7篇
  1989年   7篇
  1988年   4篇
  1987年   4篇
  1986年   6篇
  1985年   4篇
  1984年   6篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1979年   4篇
  1978年   2篇
  1976年   1篇
  1972年   1篇
  1969年   1篇
  1967年   1篇
排序方式: 共有613条查询结果,搜索用时 15 毫秒
1.
2.
3.
DNA from 111 ticks collected by flagging in Tokachi district, Eastern Hokkaido, Japan were examined for infection with Rickettsia and Ehrlichia, by PCR and sequencing methodology. For Rickettsia, analysis of the partial sequence of the citrate synthase gene was successfully performed on 11 DNA samples from I. persulcatus, and 7 of them showed 99.8% identical with Rickettsia helvetica while the other 4 showed 99.8% identical with ;Candidatus Rickettsia tarasevichiae'. For Ehrlichia, a partial sequence of the 16S rRNA gene detected from I. persulcatus was 100% identical with that from Ehrlichia muris, and another DNA sample from I. ovatus showed 99.8% identical with Ehrlichia species detected from I. ovatus. The results suggest that the pathogens detected here might be distributed in this area.  相似文献   
4.
ABSTRACT:   Experimental insemination was performed using artificially produced low-motility sperm. A mathematical model was applied to the results of the insemination in order to clarify the relationship between sperm motility, the density of sperm and the fertilization rate of eggs. In the model, the probability of fertilization by individual spermatozoa was a function of sperm density in the insemination solution. The results showed that the probability of fertilization clearly decreased with increased sperm density, and the maximum possible fertilizing rate by increasing the sperm density was constrained by the proportion of motile sperm (% motility). The model was also applied to the results of insemination tests of cryopreserved sperm in order to evaluate the fertilizing capacity of cryopreserved sperm. It was proven that cryopreserved sperm needed a higher density to obtain the maximum fertilization rate compared with fresh sperm, and it was anticipated that the ratio of the motile inseminated cryopreserved sperm should be more than 5.0% to achieve an egg fertilization rate greater than 90%.  相似文献   
5.
An eleven-year-old female pug was referred to Yamaguchi University Animal Hospital for evaluation of anemia and thrombocytopenia. The cytological examination of the peripheral blood showed some giant monocytic lineage blast cells. A few granulocytes and platelets had dysplastic features. On day 7, in addition to increasing the monocytic lineage cells, the dysplastic features of the blood had also increased compared to the initial examination. We performed bone marrow aspiration upon her death. The bone marrow revealed dysplastic features in all three hematopoietic cell lines, and an increase in the monocytic cell line. Based on the features of the bone marrow and the peripheral blood, this case was confirmed to be myelodysplastic syndrome--Chronic myelomonocytic leukaemia (MDS-CMML).  相似文献   
6.
We investigated endometrial expression of trophinin mRNA and protein, homophilic cell adhesion molecules, during the estrous cycle of gilts. An immunopositive reaction for trophinin was observed in the luminal and glandular epithelia of the endometrium at all stages of the estrous cycle, but not in endometrial stromal cells or the myometrium. A partial coding sequence of porcine trophinin was similar to sequences in humans and mice, with homologies of 75% and 70%, respectively. As in humans and mice, the trophinin gene is expressed in the endometrium. Trophinin, however, is expressed in the endometrium of the pig throughout the estrous cycle, higher expression levels were observed at some points of the luteal phase, as in humans. These findings suggest that regulation of trophinin gene expression in the pig is different from that in mice, but similar to that in humans. Furthermore, the present results suggest that the pig might be a suitable model for studying the physiological importance of trophinin in early pregnancy in humans.  相似文献   
7.
Chromosome compositions of seven lines, derived from hybrids between a wheat cultivar and the wheat-Thinopyrum intermedium addition line Z6, with barley yellow dwarf virus (BYDV) resistance, were determined by genomic in situ hybridization, cytogenetic and SSR assays. The results showed that line N522 was a disomic addition line, lines N420 and N439 were 2Ai-2(2B) chromosome substitution lines, lines N431 and N452 were 2Ai-2(2D) chromosome substitution lines, line N523 was a 2Ai-2S(2D) ditelosomic substitution line, and line N530 was a double ditelosomic line with the mitotic chromosome number of 2n = 40 + 4t. One pair of telosomes in line N530 lacked several proximal SSR markers of chromosome 2AS, but possessed certain terminal markers, which were consistent with an acrocentric structure, and the other pair of chromosome arms were presumably 2Ai-2S telosomes with BYDV-resistance. These wheat-Th. intermedium lines provide useful genetic resources for developing alien chromosome translocation lines.  相似文献   
8.
In this study,effects of temperature,light and their interactions on allelopathic effects and the functional traits specific leaf area(SLA)and stem mass fraction(SMF)of different allelopathic potential rice accessions at different growth stages were analyzed.The main results were as follows:Allelopathic responses to temperature and light varied with different allelopathic potential rice accessions at different growth stages.With the rise of temperature and the extension of photoperiod,allelopathic effect increased firstly and then decreased at 2–3 leaf stage,but increased constantly at the 4–5 and 7–8 leaf stages in strong allelopathic rice accessions[O.longistaminata,F1(O.longistaminata×RD23),F2(RL159 and RL169)].Temperature had significant impact on allelopathic effect without considering light factors,but light showed little effect on rice allelopathy at the same temperature conditions.The greatest allelopathic effect was attained with moderate temperature and long photoperiod at 2–3 leaf stage in strong allelopathic rice accessions,but all the rice accessions showed weak allelopathic effects at the low temperature condition(15oC/10oC),and the influence of different factors on allelopathy followed a general trend as temperatureleaf stagelight,indicating that among the multiple factors impacting rice allelopathy,temperature was the main factor.Allelopathic characteristics of F1 and F2 to various temperature and light were similar to O.longistaminata,showing that allelopathic genes from wild rice can be expressed in its descendants.Temperature and light also had significant effects on SLA and SMF,and rice allelopathy was closely correlative to SLA in strong allelopathic rice accessions at the 4–5 and 7–8 leaf stages,but there was no correlation between rice allelopathy and SMF at different growth stages.These results suggested that rice adjust the relationship between allelopathy and SLA and adapt to the varied environments,and that high temperature and long photoperiod can enhance rice allelopathic activity.  相似文献   
9.
The present study was aimed to determine the allelopathic potential of mango (Mangifera indica L.) leaves and to identify allelopathic substances in the leaves. The aqueous methanol extracts of mango leaves inhibited seedling growth of garden cress, radish, rapeseed, foxtail fescue and crabgrass, and the inhibitory effects increased with the increasing extract concentration, suggesting that mango leaves may contain allelopathic substances. The extract was then purified by several chromatographic runs through a bioassay-directed fractionation, and an growth inhibitory substance was isolated and identified by spectral data as methyl-3,4,5-trihydroxybenzoate (methyl gallate). Methyl gallate at the concentration of 10 mM inhibited 98.6% and 99.8% of root and shoot growth of garden cress relative to the control, respectively, and 94.4% and 49.3% of those of foxtail fescue, respectively. The concentrations of methyl gallate required for 50% growth inhibition (I50) on garden cress roots and shoots were 3.9 and 3.3 mM, and those on foxtail fescue roots and shoots were 1.5 and 9.5 mM, respectively. It is the first report of an allelopathic substance in mango leaves and allelopathic activity of methyl gallate. Therefore, the mango leaves may have potential as a soil additive material for the weed management options.  相似文献   
10.
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