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   2554篇
  免费   163篇
  国内免费   3篇
林业   194篇
农学   103篇
基础科学   5篇
  622篇
综合类   151篇
农作物   188篇
水产渔业   140篇
畜牧兽医   1083篇
园艺   57篇
植物保护   177篇
  2024年   3篇
  2023年   28篇
  2022年   54篇
  2021年   123篇
  2020年   121篇
  2019年   140篇
  2018年   109篇
  2017年   96篇
  2016年   112篇
  2015年   89篇
  2014年   101篇
  2013年   167篇
  2012年   206篇
  2011年   220篇
  2010年   122篇
  2009年   91篇
  2008年   162篇
  2007年   141篇
  2006年   121篇
  2005年   118篇
  2004年   82篇
  2003年   83篇
  2002年   56篇
  2001年   20篇
  2000年   14篇
  1999年   13篇
  1998年   7篇
  1997年   7篇
  1996年   11篇
  1995年   8篇
  1994年   7篇
  1993年   8篇
  1992年   7篇
  1991年   7篇
  1990年   8篇
  1989年   2篇
  1986年   4篇
  1985年   8篇
  1984年   6篇
  1983年   4篇
  1982年   2篇
  1981年   2篇
  1980年   5篇
  1978年   3篇
  1977年   3篇
  1973年   3篇
  1972年   2篇
  1967年   2篇
  1966年   2篇
  1955年   1篇
排序方式: 共有2720条查询结果,搜索用时 15 毫秒
91.
Objective Canine leishmaniosis is a disease characterized by the wide distribution of the parasite throughout the tissues of the host. The purpose of this study was to describe the presence of Leishmania spp. and associated inflammation in ocular‐associated muscles of dogs with patent leishmaniosis. Procedures Smooth muscles (iris dilator muscle, iris sphincter muscle, ciliary muscle, Müller muscle, smooth muscle of the periorbita and smooth muscle of the nictitating membrane) and striated muscles (orbicularis oculi muscle, obliquus dorsalis muscle and dorsal rectus muscle) were evaluated. Routine staining with hematoxylin and eosin and immunohistochemistry to detect Leishmania spp. were performed on tissue sections. Results Granulomatous inflammation was seen surrounding muscular fibers and was composed mainly of macrophages with scattered lymphocytes and plasma cells. This infiltrate could be seen in 52/473 (10.99%) samples of smooth muscle and 36/142 (25.35%) samples of striated muscle. Parasites were detected in 43/473 (9.09%) samples of smooth muscle and in 28/142 (19.71%) samples of striated muscle. Conclusions To the authors’ knowledge, this is the first report assessing the presence of Leishmania spp. and associated infiltrate in intraocular, extraocular and adnexal smooth and striated muscles. The inflammation present in those muscles could contribute to clinical signs already described, such as blepharitis, uveitis, and orbital cellulitis.  相似文献   
92.
Anna German 《Phytoparasitica》1985,13(3-4):209-213
A 5-minute contact of nursing mothers of the Levant vole,Microtus guentheri, with paper impregnated with a DES suspension in soybean oil (125 μg/cm2 ) caused sterilization of 60% of the newborn female offspring. A 1-hour contact was sufficient to sterilize more than 90% of them. When the DES concentration was decreased to 1 μg/cm2 only 44% of the newborn female offspring were sterile although their nursing mothers had been exposed to contact with the treated paper for a period of 2 hours. The concentration of 0.1 μg/cm2 was totally ineffective in causing sterilization. Treatment of nesting material with DES offers a promising means of reproductive suppression in Levant voles.  相似文献   
93.
Post-harvest apple treatment with 1-methylcyclopropene (1-MCP) was previously found to inhibit fruit ripening but also to inhibit the production of volatile compounds that contribute to apple flavor. The first objective of this study was to determine if consumers could distinguish 1-MCP treated and untreated Gala apples [Malus sylvestris L. (Mill.) var. domestica Borkh. Mansf.] following long-term storage. Chemical analysis showed 1-MCP treated fruit had reduced flavor volatiles compared to untreated fruit. Consumer difference tests showed they could distinguish between 1-MCP treated and untreated fruit. A second objective was to compare consumers’ acceptance for 1-MCP treated to untreated apples. Both 1-MCP treated and untreated apples received high overall liking scores that were not significantly different. Equal numbers of consumers indicated preference for 1-MCP treated and untreated fruit and there was no difference in purchase intent. However, subsets of consumers who eat Gala, Fuji or Red Delicious apples showed preference for untreated over 1-MCP treated fruit compared to consumers who do not eat these varieties.  相似文献   
94.
95.
In Argentina, the Yungas forests are among the ecosystems most affected by human activity, with loss of biodiversity. To assess the mycorrhizal status in these ecosystems, the roots of 41 native plant species belonging to 25 families were collected throughout the year from two sites of the Yungas forests. Roots were washed and stained to study the presence of arbuscular mycorrhizas (AM). Morphological types of arbuscular mycorrhizas (Arum and Paris-type) and colonization patterns were identified and photographed. All plants presented AM colonization. The AM colonization patterns varied from single intracellular aseptate hyphae, coils, appresoria, to vesicles and/or arbuscules. Among the species studied, the Paris-type colonization showed to be dominant. Results confirmed that AM hosts are predominant in the Yungas of South American forests.  相似文献   
96.
The main purpose of this study was to investigate the variability of the fibril angle of tracheids in earlywood of Norway spruce (Picea abies L. Karst.). Polarization confocal microscopy was chosen and compared with the method utilizing the orientation of soft rot cavities. There was a significant correlation between the soft rot and polarization confocal microscopy methods, which showed the same trend of high fibril angles in the first part of the earlywood followed by a decrease toward the end of earlywood. This declining trend was less pronounced in annual rings containing compression wood. Moreover, large variations in fibril angle occurred between neighboring tracheids. The investigation also emphasized the differences between X-ray diffraction and microscopic methods, as the large variation seen by the latter methods is not seen by the X-ray diffraction approach because of its large area of measurement. No correlation was found between fiber morphology (i.e., average length, width, density) and the average fibril angle in the investigated annual rings.  相似文献   
97.
ABSTRACT

A natural holm oak forest was selectively thinned to test thinning as a tool to reduce tree mortality, increase productivity, and reverse the recent regression of the dominant species (Quercus ilex) induced by climate change. Thinning increased aboveground productivity and reduced stem mortality in this Mediterranean forest during four years just after thinning, contributing to the maintenance of forest functioning under changing climatic conditions. Q. ilex was the only species positively affected by the thinning: stem growth increased for all stem sizes, and mortality was significantly lower in thinned plots. On the contrary, mortality rates of Phillyrea latifolia and Arbutus unedo were not significantly lower. Stem growth increased for P. latifolia only in the smallest stem-size class. Our results highlight the suitability of selective thinning for improving the forest productivity and ensuring the conservation of Mediterranean coppices. Other benefits of selective thinning, such as a decrease in the risk of fire dispersion and an increase in the water supply for human populations, are also discussed.  相似文献   
98.
Zusammenfassung Es wird gezeigt, da? es m?glich ist, durch die Anwendung subletaler Konzentrationen des Insektizids DTHP, d. h. durch eine allgemeine Schw?chung des Organismus erwachsener Rüsselk?fer (Hylobius abietis L.), eine geeignete Disposition dieses Sch?dlings zur Infektion durch den parasitischen PilzBeauveria bassiana (Bals-Criv.) Vuill. herbeizuführen. Die K?fer, die in Fangrinden oder Fallen an Kiefern? stchen — welche in ein kombiniertes Pr?parat einer 0,05% DTHP-Suspension (Organophosphorverbindung vom Dipterex-Typ, technischer Block 0,0-Dimethyl-2,2,2-trichlor-1-hydroxy?thyl-phosphonat) mit 0,1% Sporen vonBeauveria bassiana getaucht worden waren — konzentriert wurden, nahmen keine Nahrung mehr auf und starben allm?hlich ab. Wie die histologischen Untersuchungen gezeigt haben, wurden Erkrankung und Tod der K?fer durch den genannten parasitischen Pilz herbeigeführt. Obwohl nur zwei Vergleichsfl?chen zur Verfügung standen, ist aus dem obengesagten klar, da? bei der Anwendung des kombinierten Pr?parates mit einer gewissen selektiven Wirkung gerechnet werden kann: W?hrend an der nur mit 1% DTHP behandelten Versuchsfl?che ungef?hr 2,5% nützlicher Insekten unter den get?teten K?fern festgestellt wurden (vor allem Laufk?fer der GattungPterostichus), betrug der Prozentsatz der get?teten nützlichen Insekten bei der Anwendung des kombinierten Pr?parates (DTHPBeauveria bassiana-Sporen) nur 0,25%. Die angeführten Versuche bewiesen die Anwendbarkeit der Kombination von Insektiziden — in subletalen Dosen oder Konzentrationen — mit Sporen parasitischer Pilze.  相似文献   
99.
The present study was carried out to elucidate the drought growth responses of Quercus ilex L., Phillyrea latifolia L., Arbutus unedo L., and other accompanying woody species of the Mediterranean holm oak forest. We submitted holm oak forest stands in Prades mountains (NE Spain) to a 2-year experimental drought. We reduced soil water availability about 15% by plastic strips and funnels that partially excluded rain throughfall and by ditch interception of water runoff. Mean stem diameter increment showed a great variation depending on the species. A. unedo had larger growth rates than Q. ilex and P. latifolia, but it was also the species that experimented the highest growth reduction in the drought plots (77%), suggesting a higher drought sensitivity than Q. ilex (55%) and P. latifolia (no drought effect). The growth reduction was specially marked in the larger trees. Aboveground stand biomass increment, estimated from stem diameter by allometric relationships, was 1.9 Mg ha−1 per year in the control plots. The 15% reduction in the upper soil moisture produced 42% reduction in this biomass increment. In the drier conditions predicted in this Mediterranean area in the frame of climate change, an important reduction of growth rates can be hence expected, accompanied by a gain of dominance of drought-tolerant species such as P. latifolia in detriment of more mesic species such as Q. ilex.  相似文献   
100.
Shoot growth and dieback were compared among progenies of nursery-grown seedlings of Nothofagus obliqua belonging to seven progenies of the same provenance (Quila-Quina, Argentina). First-year shoots consisted of one growth unit (GU) and second-year shoots of one or two GUs. The probability of development of two GU was similar for all progenies. Progenies were different in terms of shoot size, terminal bud abscission, the extent of shoot dieback after shoot extension and the node of origin of the relay shoot on the first shoot. Plants with a second-year shoot consisting of two GUs had a thicker stem and more nodes than those with single-GU shoots. The selection of N. obliqua seed trees based on architectural traits suitable for forestry development at specific sites must contemplate variability among progenies and their probabilities of successful development under different conditions.  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