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   6865篇
  免费   554篇
  国内免费   90篇
林业   389篇
农学   511篇
基础科学   88篇
  1077篇
综合类   876篇
农作物   290篇
水产渔业   398篇
畜牧兽医   3083篇
园艺   113篇
植物保护   684篇
  2023年   49篇
  2021年   56篇
  2020年   79篇
  2019年   121篇
  2018年   222篇
  2017年   233篇
  2016年   196篇
  2015年   214篇
  2014年   211篇
  2013年   385篇
  2012年   289篇
  2011年   341篇
  2010年   277篇
  2009年   233篇
  2008年   328篇
  2007年   289篇
  2006年   254篇
  2005年   216篇
  2004年   208篇
  2003年   209篇
  2002年   155篇
  2001年   240篇
  2000年   188篇
  1999年   186篇
  1998年   84篇
  1997年   90篇
  1996年   67篇
  1995年   79篇
  1994年   52篇
  1993年   68篇
  1992年   114篇
  1991年   117篇
  1990年   115篇
  1989年   113篇
  1988年   88篇
  1987年   82篇
  1986年   75篇
  1985年   58篇
  1984年   66篇
  1983年   52篇
  1980年   48篇
  1979年   72篇
  1978年   52篇
  1977年   52篇
  1976年   59篇
  1975年   52篇
  1974年   61篇
  1973年   75篇
  1972年   44篇
  1971年   45篇
排序方式: 共有7509条查询结果,搜索用时 625 毫秒
121.
122.
The paper presents the results of faunistic, ecological and viral investigations concerning phlebotomine sandflies in an endemic focus of visceral leishmaniasis in Yugoslavia. These investigations were carried out in the period from 1969 to 1981.  相似文献   
123.
Samples of blood sera collected from 608 sheep in large farms of the districts of Trebisov, Michalovce, Vranov nad Toplou and Humenné were investigated in hemagglutination-inhibition test for the presence of mosquito-borne viruses Sindbis, West Nile, Tahyna and Calovo. Antibodies to arboviruses Tahyna (11.5%) and Calovo (10.9%) were detected most frequently, while a lower sero-positivity was recorded to the Sindbis (2.3%) and West-Nile (1.0%) viruses. Certain differences were found in the infection rates in the respective districts: the highest frequency of antibodies to Tahyna and Calovo viruses was recorded in sheep of the district of Trebisov and the lowest one in animals of the district of Humenné.  相似文献   
124.
Rhabdovirus-like particles containing nucleoprotein in a helix with eight turns was demonstrated by transmission electron microscopy in subtegumental cells and syncytial layer of tegument in Brachylaimus fuscatus sporocyst. This is the first case of virus infection in trematodes. The possibility of transfer of the virus to intra-molluscan parasitic generations of the trematode is discussed with respect to the peculiarities of the life cycles of the family Brachylaimidae.  相似文献   
125.
Cotton was grown in loess soil, in rows 1 m apart, and drip-lines were placed in the center of every second space between rows at a distance of 50 cm from the plants. Aldicarb was applied as granules (containing 15% a.i.) to the field on two dates (mid-June and mid-July) and incorporated into the soil(a) 25 cm from the plants,i.e., equidistant from the plants and the drip-lines, on both sides of the drip-lines; and(b) 50 cm from the plants,i.e., in the center of the spaçe between the rows, near the drip-line. Measurements of mortality ofBemisia tabaci larvae, and of the accumulation of aldicarb from the late (mid-July) treatment showed that best control of the pest and the highest aldicarb residues were obtained with the late treatment. The pest control effectiveness was found to depend on both date and location of aldicarb application. Early treatment (mid-June) was more effective if applied close (25 cm distance) to the plant stems, whereas late treatment (mid-July) was more effective if applied at a distance of 50 cm from the plant stems.  相似文献   
126.
All North American plum cultivars investigated in Poland for their reaction to plum pox potyvirus appeared to be susceptible, showing severe symptoms on the leaves. Fruits of cvs Valor and Empress were also heavily damaged. Of the Yugoslav cultivars evaluated, Cacanska Najbolja was most tolerant whereas Cacanska Rodna appeared to be most sensitive to PPV.  相似文献   
127.
A review on the geographic distribution, vectors and hosts of Bhanja virus (Bunyaviridae) is based on reports about: isolations of the virus; antibody surveys. Bhanja virus has been isolated in 15 countries of Asia, Africa and Europe, and antibodies against it have been detected in 15 additional countries. Vector range includes ticks of the family Ixodidae (subfam. Amblyomminae; not subfam. Ixodinae): 13 species of 6 genera (Haemaphysalis, Dermacentor, Hyalomma, Amblyomma, Rhipicephalus and Boophilus) yielded the virus. Bhanja virus has only rarely been isolated from vertebrates (Atelerix, Xerus, Ovis, Bos; possibly bats), though antibodies have been detected frequently in a wide range of mammals (Ruminantia being the major hosts), in several species of birds (Passeriformes, Galliformes) and even reptiles (Ophisaurus apodus). Natural foci of the Bhanja virus infections are of the boskematic type (sensu Rosicky), associated closely with pastures of domestic ruminants infested by ticks in the regions of tropical, subtropical and partly temperate climatic zones.  相似文献   
128.
Two pairs of hitherto unknown multiciliate sensory endings have been demonstrated in free-swimming cercariae of Echinostoma revolutum using transmission and scanning electron microscopy. This type of receptor consists of a bundle of 36--40 short, conically projecting cilia ensheathed by a collar formed by a circular evagination of tegument in shape of a cup. The cilia projecting from the centre of a widened nerve fibre, filled with electron-lucid vesicles, possess a well developed basal body and do not contain a ciliary rootlet. The function of this receptor is discussed.  相似文献   
129.
Seeds of Johnsongrass [Sorghum halepense (L.) Pers.] germinated to higher percentages (20–30% higher) when incubated at 28 and 35° C than at 10 or 22° C. After-ripening was accelerated by dry storage of these seeds at 50°C. Seeds pre-chilled at 6°C for 2–4 weeks followed by incubation at 28°C germinated 40–60%. Light effects on germination were related to incubation temperatures; inhibitory at 22°C; no response at 28°C; and stimulatory at 35°C. Effects of gibberellin A3 (GA3) also varied depending on incubation temperature, sodium hypochlorite (NaOCl) immersion and light conditions. Immersion of dry seeds in either 700 mM NaOCl, 900 mM H2O2 or concentrated H2SO4 before incubation in water was effective in breaking dormancy. This result suggests the modes of action of H2SO4 in the termination of dormancy may be similar to those of NaOCl and H2SO4 as previously suggested by Hsiao & Quick (1984), that is by modification or scarification of the hull or seed coat membranes, and also by the supply of additional oxygen to the seed.  相似文献   
130.
Our objective was to examine the distribution of enterocyte digestive enzyme activity along the crypt-villus and longitudinal axes of the small intestine in formula-fed neonatal pigs between the ages of 14 and 18 d. The distended intestinal sac method was used to isolate 12 sequential fractions (F1 through F12) of epithelial cells. Enterocyte migration rate was measured in the proximal and distal intestine using in vivo bromodeoxyuridine labeling. Specific activities of representative villus cell marker enzymes of alkaline phosphatase, aminopeptidase N, sucrase, and lactase increased 6- to 17-fold from F12 (crypt cells) to F1 (villus cells), whereas the crypt cell marker [3H]thymidine incorporation increased 8- to 18-fold from F1 (villus cells) to F12 (crypt cells). Enterocyte migration rate was similar (3.2 vs 3.0 microm/h), whereas the villus height (547.4 vs 908.5 microm) and enterocyte life span (4.7 vs 10.2 d) were markedly lower (P < 0.05) in the proximal than in the distal segments, respectively. In general, the specific activities of all enzymes were lowest in the crypt fractions (F9 through F12) but increased markedly (ranging from 8- to 17-fold) from F12 to F1. The activity of aminopeptidase N was higher and that of sucrase was lower in the distal than in the proximal segment. The activities of the remaining enzymes were similar in the proximal and the distal segments. Our results suggest that the enterocyte life span in the distal small intestine is approximately twice as long as in the proximal small intestine. However, despite the difference in life span, the patterns of enzyme activities along the crypt-villus axis were generally similar in the proximal and the distal regions.  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