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   569篇
  免费   38篇
林业   45篇
农学   13篇
基础科学   9篇
  100篇
综合类   106篇
农作物   27篇
水产渔业   36篇
畜牧兽医   210篇
园艺   18篇
植物保护   43篇
  2023年   5篇
  2022年   8篇
  2021年   13篇
  2020年   21篇
  2019年   12篇
  2018年   25篇
  2017年   26篇
  2016年   30篇
  2015年   12篇
  2014年   15篇
  2013年   23篇
  2012年   38篇
  2011年   48篇
  2010年   16篇
  2009年   19篇
  2008年   32篇
  2007年   21篇
  2006年   18篇
  2005年   19篇
  2004年   20篇
  2003年   18篇
  2002年   21篇
  2001年   6篇
  2000年   17篇
  1999年   4篇
  1994年   4篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1989年   7篇
  1988年   9篇
  1987年   5篇
  1983年   5篇
  1982年   3篇
  1979年   5篇
  1978年   4篇
  1973年   3篇
  1972年   5篇
  1971年   4篇
  1970年   2篇
  1969年   2篇
  1967年   2篇
  1966年   3篇
  1965年   2篇
  1954年   3篇
  1953年   2篇
  1952年   3篇
  1943年   2篇
  1940年   2篇
  1901年   2篇
排序方式: 共有607条查询结果,搜索用时 15 毫秒
21.
An epidemiological investigation of an outbreak of intestinal atresia in Israeli Holstein-Friesian newborn calves showed a linkage with rectal palpation for early pregnancy diagnosis, performed less than 42 days after insemination. The odds of an exposed calf, i.e., one born to a dam that was diagnosed by early palpation as having intestinal atresia were 119.7 times higher than one born in normal control herds (95% CI; 7.4-1946.3). A total of 682 calves-at-risk was recorded from mid-1998 to mid-2000 and a total of 47 calves (6.9%) were born with intestinal atresia during this period. Two forms of intestinal atresia were recognized at post-mortem: atresia coli and atresia ilei.  相似文献   
22.
The influence of three diets, comprising dam's milk (DM) from the same farm, commercial milk replacer with (CMRL) or without 3.2% lactose (CMR), on the duration and intensity of Candida glabrata shedding in the faeces of preweaned calves following experimental oral infection was examined. Shedding of other potential enteric pathogens was also monitored. The duration and intensity of C. glabrata shedding in DM-fed calves were reduced significantly compared with the calves fed the two diets based on milk replacers. Consequently, feeding calves with DM might disrupt the infective cycle, resulting in the yeast's elimination from a farm. In the CMR and CMRL groups, the periods of intensive shedding of C. glabrata and rotavirus overlapped but no diarrhoea was associated with the shedding of either microorganism. There was no evidence that lactose diminished colonization in vivo.  相似文献   
23.
ABSTRACT The syndrome "basses richesses" of sugar beet (SBR) was first observed in 1991 in Burgundy, France. A cixiid planthopper, Pentastiridius beieri, has been proved to be involved in the transmission to sugar beet of a stolbur phytoplasma, which could be detected in some affected plants. In 2000, periwinkle and sugar beet exposed to field-collected cixiids developed symptoms similar to SBR on sugar beet. Use of 4'-6-diamidino-2-phenylindole (DAPI) staining and transmission electron microscopy confirmed the presence of phytoplasma in some of the plants, which were also positive for this pathogen in a polymerase chain reaction (PCR) analysis. A phloem-restricted gram-negative bacteria was seen in all other plants with symptoms but PCR-negative for phytoplasma. Three primer pairs reported as diagnostic for phloem-limited bacteria were tested but only primers specific for 'Candidatus Phlomobacter fragariae' gave a positive signal, which related to the presence of DAPI-stained bacteria-like objects in diseased plants. Although phytoplasma and bacterium-like organisms were associated with the same macroscopic symptoms on sugar beet, histochemical analysis of phloem cells showed that phytoplasma were associated with cell necrosis and cell wall lignification, while bacteria were associated with these same abnormalities as well as deposit of phenolic compounds in the lumen of phloem cells.  相似文献   
24.
OBJECTIVE: To compare cutaneous and mucosal mycoflora in cats infected with FIV or FeLV with that in noninfected cats. ANIMALS: 85 client-owned cats; 24 seropositive for FIV, 10 seropositive for FeLV, 1 seropositive for both viruses, and 50 seronegative for both viruses. PROCEDURE: Cutaneous specimens were obtained from the coat and external acoustic meatus (ear canal) and mucosal specimens from the oropharynx and rectum. Fungi were isolated from specimens, using Sabouraud dextrose agar incubated at 27 or 37 C for cutaneous and mucosal specimens, respectively. RESULTS: Fungal colonies were cultured from at least 1 specimen from 83 of 85 (97.6%) cats. The most common fungal isolates were Aspergillus spp (cultured from 59.3% of all specimens), Penicillium spp (50.0%), Cladosporium spp (44.2%), Scopulariopsis spp (41.8%), and lipophilic yeasts of the genus Malassezia (31.4%). A greater diversity of fungal genera was isolated from retrovirus-infected cats, and Malassezia spp were more commonly recovered from these cats, compared with noninfected cats. Candida albicans, Cryptococcus neoformans, and dermatophytes (eg, Microsporum canis) were rarely isolated from any cat. Significant differences in frequency of isolation of C. neoformans and dermatophytes were not found between infected and noninfected cats. CONCLUSIONS AND CLINICAL RELEVANCE: Cats infected with FIV or FeLV may have a greater diversity of cutaneous and mucosal mycoflora than noninfected cats. However, infected cats may be no more likely than noninfected cats to expose humans to zoonotic fungi such as C. albicans, C. neoformans, and M. canis.  相似文献   
25.
An adult male black-necked swan (Cygnus melanocoryphus) was evaluated for a routine physical examination and West Nile virus vaccination. Nine days later, the swan was hospitalized for weakness, dehydration, tremors, and leukocytosis. Gradual clinical improvement was seen over a 2-wk course of supportive care. However, the animal became acutely weak and was found dead. Histopathology revealed severe granulomatous pneumonia and air sacculitis with dissemination to the liver, spleen, intestine, and coelom. Mycobacterial infection was confirmed by identification of acid-fast bacilli within tissue sections and by polymerase chain reaction. Concurrent West Nile virus infection was identified in sections of brain by using immunohistochemistry.  相似文献   
26.
The effect of an application of pST- and beta-agonists on the fattening-capacity and carcass-composition of the pig is evaluated by means of data available in literature. American stress-resistant cross-bred pigs show a stronger reaction on pST in their fattening-capacity than European breeds. Obviously, this has derived from genetic differences. Feed-utilization, meat-gain, and reduction of lipid content in the case of European breeds are, nevertheless, subject to a pronounced improvement through pST and beta-agonists. Further positive aspects are the decrease of the N-excretion in urine and no, resp. only minor influence on the quality of meat. A negative aspect of the meat with regard to consumers' acceptance is the fact that the mentioned substances belong to the group of hormones.  相似文献   
27.
A silvopastoral agroforestry system involving sheep is an important silvicultural issue. We examined the factors that affect the continuation or discontinuation of sheep vegetation management (SVM) in British Columbia. A questionnaire was used to conduct interviews with a randomly selected sample of contractors and farmers who were involved in SVM in British Columbia (BC). Based on a stepwise discriminant analysis, we found that the profitability of SVM, and the practitioners' commitment (number of ewes owned by the farmer or contractor), experience (number of years the farmer or contractor has practiced SVM on public lands in BC) and trust or confidence (number of years the farmer or contractor has consistently worked for the landlord) contributed to the farmer's or contractor's continuation or discontinuation of SVM practice. The factors we defined seemed to be validated (corroborated) by a complex of determinants voiced by various experts concerning the relationship between SVM and the forestry economy in BC, the scale of sheep farming in BC, the relative absence of an agricultural infrastructure to support sheep farming in BC, and the continuity of SVM from year to year. Further investigation into these factors and others is required to advance our understanding of SVM in British Columbia. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
28.
Fine roots and ectomycorrhizal root tips were sampled in a Norway spruce (Picea abies (L.) Karst.) stand in the eastern part of the Belgian Ardennes. The cellular and partly subcellular localizations of aluminum and lead were identified by the micro-analytical laser microprobe mass analysis (LAMMA) technique. In fine roots with secondary structure, localization of aluminum was limited to the peripheral cell layers. Lead was found in the outer layers, and also in the primary phloem. Aluminum penetrated the mycorrhizal mantle, but lead was seldom detected in ectomycorrhizae.  相似文献   
29.
Antimicrobial flavonoids from the stem bark of Erythrina burttii   总被引:1,自引:0,他引:1  
The chloroform extract of the stem bark of Erythrina burttii showed antifungal and antibacterial activities using the disk diffusion method. Flavonoids were identified as the active principles. Activities were observed against fungi and Gram(+) bacteria, but the Gram(-) bacteria Escherichia coli was resistant.  相似文献   
30.
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