全文获取类型
收费全文 | 62725篇 |
免费 | 2872篇 |
国内免费 | 42篇 |
专业分类
林业 | 2529篇 |
农学 | 1649篇 |
基础科学 | 429篇 |
6173篇 | |
综合类 | 14796篇 |
农作物 | 2468篇 |
水产渔业 | 2360篇 |
畜牧兽医 | 31162篇 |
园艺 | 643篇 |
植物保护 | 3430篇 |
出版年
2017年 | 556篇 |
2016年 | 537篇 |
2014年 | 542篇 |
2013年 | 1863篇 |
2012年 | 1209篇 |
2011年 | 1438篇 |
2010年 | 921篇 |
2009年 | 880篇 |
2008年 | 1428篇 |
2007年 | 1392篇 |
2006年 | 1373篇 |
2005年 | 1390篇 |
2004年 | 1320篇 |
2003年 | 1392篇 |
2002年 | 1359篇 |
2001年 | 1496篇 |
2000年 | 1478篇 |
1999年 | 1209篇 |
1998年 | 535篇 |
1997年 | 545篇 |
1995年 | 603篇 |
1994年 | 576篇 |
1993年 | 567篇 |
1992年 | 1314篇 |
1991年 | 1401篇 |
1990年 | 1460篇 |
1989年 | 1493篇 |
1988年 | 1405篇 |
1987年 | 1362篇 |
1986年 | 1408篇 |
1985年 | 1378篇 |
1984年 | 1153篇 |
1983年 | 1007篇 |
1982年 | 724篇 |
1981年 | 690篇 |
1980年 | 648篇 |
1979年 | 1131篇 |
1978年 | 921篇 |
1977年 | 822篇 |
1976年 | 771篇 |
1975年 | 863篇 |
1974年 | 1129篇 |
1973年 | 1063篇 |
1972年 | 1133篇 |
1971年 | 1081篇 |
1970年 | 1023篇 |
1969年 | 876篇 |
1968年 | 712篇 |
1967年 | 844篇 |
1966年 | 693篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
961.
Dilated cardiomyopathy is the usual cause of congestive heart failure in the dobermann pinscher and was the presumptive diagnosis in an eight-year-old female dobermann pinscher presented for dyspnoea and syncope. This was supported by thoracic radiography and electrocardiographic evidence of ventricular tachycardia. An echocardiogram revealed a left atrial tumour as the principal cause of cardiac failure. Pathological examination confirmed that the tumour was a large aortic body carcinoma in an unusual location. Multifocal myocardial infarctions were also found. This unusual case demonstrates the importance of a complete cardiological examination as part of a diagnostic work up and confirms the necessity of echocardiography as one of the examination methods. 相似文献
962.
963.
964.
Evaluating methods for identifying large mammal road crossing locations: black bears as a case study
Landscape Ecology - Roads have several negative effects on large mammals including restricting movements, isolating populations, and mortality due to vehicle collisions. Where large mammals... 相似文献
965.
Landscape Ecology - Habitat fragmentation can exacerbate the negative effects of habitat loss for some species. Mitigating fragmentation is difficult, however, because population responses depend... 相似文献
966.
Michelle T. Hulin Robert W. Jackson Richard J. Harrison John W. Mansfield 《Plant pathology》2020,69(6):962-978
Bacterial canker disease is a major limiting factor in the growing of cherry and other Prunus species worldwide. At least five distinct clades within the bacterial species complex Pseudomonas syringae are known to be causal agents of the disease. The different pathogens commonly coexist in the field. Reducing canker is a challenging prospect as the efficacy of chemical controls and host resistance may vary against each of the diverse clades involved. Genomic analysis has revealed that the pathogens use a variable repertoire of virulence factors to cause the disease. Significantly, strains of P. syringae pv. syringae possess more genes for toxin biosynthesis and fewer encoding type III effector proteins. There is also a shared pool of key effector genes present on mobile elements such as plasmids and prophages that may have roles in virulence. By contrast, there is evidence that absence or truncation of certain effector genes, such as hopAB, is characteristic of cherry pathogens. Here we highlight how recent research, underpinned by the earlier epidemiological studies, is allowing significant progress in our understanding of the canker pathogens. This fundamental knowledge, combined with emerging insights into host genetics, provides the groundwork for development of precise control measures and informed approaches to breed for disease resistance. 相似文献
967.
X. Y. Wang C. W. Zhang W. T. Huang J. Yue J. J. Dou L. Y. Wang Q. Wang Y. Q. Cheng 《Plant pathology》2020,69(1):149-158
Efforts to control viral diseases of grapevine include the production of certified material and development of virus-resistant transgenic grapevines. However, effective antiviral agents, once the viruses have infected the plants, are still lacking. This study shows that a crude garlic extract has significant antiviral activity against grapevine viruses. Replication of grapevine leafroll-associated virus 2 (GLRaV-2) was obviously inhibited in grapevine cv. Cabernet Sauvignon calli treated with diluted (1:100) garlic extract. The relative RNA levels of GLRaV-2 and grapevine fleck virus (GFkV) in cv. Summer Black grapevine in in vitro-grown plantlets 10 days after treatment with diluted (1:100) garlic extract were about 22% and 20%, respectively, of that in controls. The viral RNA accumulation of GLRaV-2, GFkV, grapevine virus A (GVA), grapevine fanleaf virus (GFLV) and grapevine rupestris stem pitting-associated virus (GRSPaV) in field-grown grapevine cv. Centennial Seedless plants sprayed with diluted (1:100) garlic extract were about 31–40%, 26–38%, 18–31%, 17–42% and 15–18%, respectively, of that in controls. Moreover, the garlic extract treatment led to a significant decrease in viral RNA accumulation of GLRaV-3, GLRaV-2, GVA, GFkV, GFLV, GRSPaV and grapevine Pinot Gris virus in pot-grown grapevine cv. Shine Muscat plants, and viral disease symptoms in these plants were obviously attenuated. In addition, this extract significantly induced expression of pathogenesis-related protein genes and stimulated activity of antioxidant enzymes in grapevines. Taken together, these results indicate that the crude garlic extract acts as a significant inhibitor against a broad range of grapevine viruses. 相似文献
968.
Root rot symptoms were observed in fields of alfalfa in Chifeng city, Inner Mongolia, China in 2016. Disease incidences of seven alfalfa varieties planted in 2014 ranged from 56% to 95%, while incidence of Gongnong No. 1 planted in 2016 was 8%, 31% and 76% in 2016, 2017 and 2018, respectively. Paraphoma isolates were consistently recovered from black necrotic root tissues of diseased plants with a frequency of 77.1%. Based on morphological characters and phylogenetic analysis of rDNA internal transcribed spacer (ITS), elongation factor 1-α (EF1-α) and β-tubulin (TUB), this fungus was identified as Paraphoma radicina. Glasshouse pathogenicity experiments showed that P. radicina significantly reduced above- and below-ground biomass of alfalfa plants 2 months after inoculation. Paraphoma radicina infected 70% of the plants inoculated with a root dip in conidia, and these symptoms were consistent with the symptoms in the field. Paraphoma radicina was successfully reisolated from disease roots of the inoculated alfalfa plants. This is the first report of P. radicina as the causal agent of alfalfa root rot in China. 相似文献
969.
Johannes Trini Hans Peter Maurer Sigrid Weissmann Tobias Würschum 《Plant Breeding》2020,139(5):906-915
Accurate hybrid prediction and knowledge about the relative contribution of general (GCA) and specific combining ability (SCA) are of utmost importance for efficient hybrid breeding. We therefore evaluated 91 triticale single-cross hybrids in field trials at seven environments for plant height, heading time, fresh biomass, dry matter content and dry biomass. Fresh and dry biomass showed the highest proportion (23%) of variance due to SCA. Prediction accuracies based on GCA were slightly higher than based on mid-parent values. Utilizing parental kinship information yielded the highest prediction accuracies when both parental lines have been tested in other hybrid combinations, but still moderate-to-low prediction accuracies for two untested parents. Thus, hybrid prediction for biomass traits in triticale is currently promising based on mid-parent values as emphasized by our simulation study, but can be expected to shift to GCA-based prediction with an increasing importance of GCA due to selection in hybrid breeding. Moreover, the performance of potential hybrids between newly developed lines can be predicted with moderate accuracy using genomic relationship information. 相似文献
970.
Precision Agriculture - An accurate and robust strawberry flower representation and detection scheme is a key step to enable the reliable forecasting of fruit yield for use in precision... 相似文献