全文获取类型
收费全文 | 26605篇 |
免费 | 1688篇 |
国内免费 | 164篇 |
专业分类
林业 | 2793篇 |
农学 | 1174篇 |
基础科学 | 198篇 |
4268篇 | |
综合类 | 2845篇 |
农作物 | 866篇 |
水产渔业 | 1544篇 |
畜牧兽医 | 12282篇 |
园艺 | 547篇 |
植物保护 | 1940篇 |
出版年
2023年 | 168篇 |
2022年 | 168篇 |
2021年 | 256篇 |
2020年 | 316篇 |
2019年 | 308篇 |
2018年 | 729篇 |
2017年 | 664篇 |
2016年 | 667篇 |
2015年 | 591篇 |
2014年 | 615篇 |
2013年 | 1291篇 |
2012年 | 1110篇 |
2011年 | 1208篇 |
2010年 | 826篇 |
2009年 | 697篇 |
2008年 | 1080篇 |
2007年 | 1173篇 |
2006年 | 1033篇 |
2005年 | 1015篇 |
2004年 | 852篇 |
2003年 | 899篇 |
2002年 | 766篇 |
2001年 | 1068篇 |
2000年 | 1020篇 |
1999年 | 792篇 |
1998年 | 237篇 |
1997年 | 214篇 |
1996年 | 204篇 |
1995年 | 258篇 |
1994年 | 220篇 |
1993年 | 175篇 |
1992年 | 436篇 |
1991年 | 468篇 |
1990年 | 436篇 |
1989年 | 419篇 |
1988年 | 404篇 |
1987年 | 429篇 |
1986年 | 373篇 |
1985年 | 314篇 |
1984年 | 286篇 |
1983年 | 239篇 |
1982年 | 154篇 |
1979年 | 255篇 |
1978年 | 177篇 |
1977年 | 157篇 |
1975年 | 155篇 |
1974年 | 169篇 |
1973年 | 176篇 |
1971年 | 162篇 |
1969年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
Swinepox--skin disease with sporadic occurrence 总被引:1,自引:0,他引:1
Moorkamp L Beineke A Kaim U Diesterbeck U Urstadt S Czerny CP Rüberg H Grosse Beilage E 《DTW. Deutsche tier?rztliche Wochenschrift》2008,115(4):162-166
Swinepox virus infection results in an acute, mild or subclinical course and is characterised by typical poxvirus skin lesions in affected pigs. Additionally, sporadic vertical swinepox virus transmission leads to congenital generalised infection and subsequent abortion or stillbirth. The present report describes the occurrence of epidermal efflorescences in two piglets after intrauterine natural suipoxvirus infection. No clinical abnormalities of the gilt and littermates as well as in other pigs from this herd were present. One of the affected piglets was stillborn and submitted for necropsy, the other animal was alive at birth, but died 3 days later. Histologically, a proliferative to ulcerative dermatitis with epithelial ballooning degeneration and characteristic intracytoplasmatic inclusion bodies was observed. The pathomorphological and histopathological suspected diagnosis of a poxvirus infection was confirmed by electron microscopy. Furthermore, the agent was identified as suipoxvirus by polymerase chain reaction. As demonstrated here, obvious skin lesions in suipoxvirus infection leads to a suspected diagnosis in newborn piglets on macroscopic examination. However, further post mortem examinations, including electron microscopy as well as molecular techniques are essential for the identification of the aetiology and the exclusion of differential diagnoses. Because the disease only affected two pigs there was only a small economic loss. A valid diagnostic plays an important role in advising farmers and for herd health monitoring. 相似文献
64.
Summary Results from a cooperative breeding programme with timothy for the northern areas of Scandinavia are presented. The main aim of the programme was to identify genotypes for synthetic populations that are high yielding, adapted over the whole area and stable over years. A polycross comprising 12 genotypes from each of five sites within the region was formed. The subsequent 60 half-sib families and four reference varieties were then compared under sward conditions at the same sites. The trials lasted for three years and results for total dry matter yields are presented.Significant differences in yield between lines were found. There were also significant two and three factor interactions between lines, sites and years. A new two-step procedure is presented to select the genotypes to make up a synthetic variety. Firstly, a superiority measure (Q-value) is used to select a group of genotypes that are high yielding and stable over sites and years. Secondly, the GxE part of the Q-value is split into two terms. One measures adaptation to predictable environmental conditions. The other one measures stability to unpredictable changes in the environment. A plot of these two measures provides a tool for discarding unstable or poorly adapted genotypes. The statistical properties of the selection parameters are discussed. 相似文献
65.
The performance of insect-resistant transgenic poplar trees (Populusnigra) expressing a Cry1Ac gene from Bacillus thuringiensis subsp. Kurstaki HD-1 against poplar defoliators was evaluated in the field at the Manas Forest Station in Xinjiang Uygur
Autonomous Region during1994–1997. The results showed that the average percentage of highly damaged leaves on the transgenic
trees was 10% while that on the control trees in nearby plantations reached 80–90%. The average number of pupae per m2 of soil at 20cm depth in transgenic poplar plantation was 18 which was only 20% of that found in the non-transgenic control
field. The number of pupae and the leaf-damage on transgenic trees described above are all far below the threshold set for
chemical protection measures. The non-transformed poplar trees grown in the same plantation with the transgenic trees were
also protected indicating that cross protection occurred between these two kinds of trees. Insect-resistant transgenic poplar
trees have a potential application value in afforestation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
66.
1. The objective of this study was to evaluate whether the oligosaccharide stachyose enhances gastrointestinal tract health by fermentation and proliferation of desirable bacteria species and thus affects growth performance and nutrient digestibility in broilers. 2. A total of 432 1-d-old male Arbor Acres (AA) broilers were randomly allocated to one of 6 treatments, with 12 replicate pens per treatment and 6 birds per pen. Chicks were fed a maize-hamlet protein 300 (HP300) basal diet with 0, 4.0, 8.0, 12.0 or 16.0 g/kg stachyose. A sixth diet contained no HP300 but soybean meal (SBM) and provided 8.7 g/kg stachyose and 3.1 g/kg raffinose. The duration of the study was 42 d. 3. Stachyose contents above 12.0 g/kg depressed group body weights, average daily gain and feed/gain but not feed intake during the whole experimental period. Broiler growth decreased linearly and quadratically with increasing stachyose content. No differences were detected between diets supplemented with 12.0 g/kg stachyose and SBM. 4. Nutrient digestibility tended to decrease but not significantly with increasing stachyose. 5. Stachyose content had no significant positive effects on caecal pH, microflora population and the resulting short-chain fatty acid (SCFA) metabolites during the 42 d experiment, with only butyrate differing significantly in the initial period. 相似文献
67.
68.
The entire dog population of Hanoveranian Scenthounds registered since the foundation of the kennel club Hirschmann in the year 1894 was analysed for the development of the inbreeding and relationship coefficient and the contribution of Hanoveranian Scenthound population of foreign countries. The analyses were performed using all available pedigree information. In the history, the breeding of the Hanoveranian Scenthound was difficult because of the low number of breeding dogs which was additionally reduced during World War I and II. The mean coefficient of inbreeding of the entire German population was 6.35%. From 1950 to 1990, the mean coefficient of inbreeding increased from 8.3% to 9.7%. In the birth years from 1990 to 2002, the mean coefficient of inbreeding decreased slightly to 9.2%. The rates of inbreeding decreased since 1950. For the last 8 generations the increase of the coefficients of inbreeding per generation was 0.71%. The mean degree of relationship of the entire population was 7.17%, whereby values higher than 75% were found. Gene contributions of 8 other European stud books for the Hanoveranian Scenthound could be found in the German population. Hereby, the Austrian Hanoveranian Scenthounds had the largest impact on the German population with 24.4%. The proportion of genes from the German stud book amounted to 67%. 相似文献
69.
In Schleswig-Holstein, F.R.G., two typical soil associations from loamy boulder marl and loamy pleistocene sands were mapped and ecologically characterized in order to show the necessity of an adequate classification of Colluvic Cumulic Anthrosols (Colluvisols). More than 50% of the original soils have been altered by erosion. The depth of the colluvic wM horizon ranges between 10 cm and more than 100 cm. The amounts of soil organic matter and plant available nutrients are much higher in the Colluvisols than in the haplic soils. Soil classification does not deal with all these aspects with regard to mapping of colluvic soils. In the German soil classification adequate and ecologically significant definitions and instructions of the nomenclature of colluvic soils are not available. Therefore, a proposal is presented to classify colluvic soils. In addition the threshold value of 0.6% soil organic matter in sandy parent material is too low in order to distinguish a Bv from a M horizon; 1.0% would be a more acceptable value. It would be necessary to investigate yield on erodic, non-erodic and colluvic soils in order to determine the effect of erosion and accumulation on crop yield. 相似文献
70.
Cao Honghe Wang Yachun Chen Youchun Y. Zhang L. Ferretti 《中国农业科学》2000,(1):120-124
Five microsatellites, IDVGA-2, IDVGA-27, IDVGA-46, IDVGA-55 and TGLA-44,were analyzed for polymorphisms in beef cattle. The number of alleles and polymorphism information content (PIC) values were 12/0. 82, 5/0. 58, 8/0. 70, 6/0. 57 and 11/0. 86 respectively. Each microstellite was typed on a half-sib family in order to verify the segregation of the alleles. 相似文献