全文获取类型
收费全文 | 89486篇 |
免费 | 5205篇 |
国内免费 | 783篇 |
专业分类
林业 | 3961篇 |
农学 | 2757篇 |
基础科学 | 747篇 |
10785篇 | |
综合类 | 16798篇 |
农作物 | 3544篇 |
水产渔业 | 4264篇 |
畜牧兽医 | 45804篇 |
园艺 | 1324篇 |
植物保护 | 5490篇 |
出版年
2021年 | 727篇 |
2020年 | 810篇 |
2019年 | 996篇 |
2018年 | 1501篇 |
2017年 | 1754篇 |
2016年 | 1564篇 |
2015年 | 1546篇 |
2014年 | 1696篇 |
2013年 | 3062篇 |
2012年 | 3300篇 |
2011年 | 3760篇 |
2010年 | 2391篇 |
2009年 | 2244篇 |
2008年 | 3161篇 |
2007年 | 3014篇 |
2006年 | 2724篇 |
2005年 | 3520篇 |
2004年 | 3082篇 |
2003年 | 2877篇 |
2002年 | 2345篇 |
2001年 | 2598篇 |
2000年 | 2559篇 |
1999年 | 2063篇 |
1998年 | 802篇 |
1997年 | 715篇 |
1995年 | 751篇 |
1992年 | 1607篇 |
1991年 | 1834篇 |
1990年 | 1777篇 |
1989年 | 1710篇 |
1988年 | 1613篇 |
1987年 | 1620篇 |
1986年 | 1697篇 |
1985年 | 1490篇 |
1984年 | 1270篇 |
1983年 | 1087篇 |
1979年 | 1176篇 |
1978年 | 913篇 |
1977年 | 749篇 |
1976年 | 778篇 |
1975年 | 862篇 |
1974年 | 1114篇 |
1973年 | 1092篇 |
1972年 | 1072篇 |
1971年 | 986篇 |
1970年 | 931篇 |
1969年 | 896篇 |
1968年 | 753篇 |
1967年 | 816篇 |
1966年 | 753篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Validation of the accuracy of household reporting of subsistence fishing catch and effort: a Fijian case study 总被引:1,自引:0,他引:1
Abstract The accuracy of household reporting of subsistence fishing catch and effort and seafood consumption on the Fijian island of Ono-i-Lau was studied. A creel survey was carried out concurrently to validate the household survey data. Reported estimates of fishing participation, effort, and fish consumption were not significantly different to the creel survey estimates. Householder's appeared to overestimate the number of fish from the most abundant family Lethrinidae, and underestimate rarer fish. However, there was no significant difference between the reported and observed contribution of the majority of finfish families and invertebrate taxa. The reported and observed catch rate estimates were not significantly different, indicating that Ono-i-Lau villagers are relatively accurate in their estimation of the number and size of fish from recalled catches. 相似文献
92.
M E Olson C J Hannigan P F Gaviller L A Fulton 《The Canadian veterinary journal. La revue veterinaire canadienne》2001,42(11):865-868
Dogs (n = 13), which had failed to be cured of giardiosis following chemotherapeutic measures, were treated with a Giardia vaccine (2-3 injections). Clinical signs resolved between 16 and 42 days postvaccination and cessation of fecal cyst shedding was between 21 and 70 days. Vaccination is a potential method of treating giardiosis in dogs. 相似文献
93.
Fireblight disease, caused by Erwinia amylovora was first detected in Bulgaria on quince in the region of Plovdiv in 1989. The disease was initially localized in that area but, during 1995/1997, due to favourable climate conditions, it became epidemic. Infected trees were grubbed out and destroyed. The main hosts are quince and pear (over 40% of affected trees), then apple, medlar and Cotoneaster. Containment measures undertaken by the Bulgarian NPPO are laid down in the Plant Protection Law, in Phytosanitary Regulation no. 1 for phytosanitary control, and in Phytosanitary Regulation no. 5 of 1996 (amended 1997) for containment of fireblight. Phytosanitary control is mainly focused on fruit‐tree nurseries and on the distribution of healthy plants for planting. In 2003, 41 protected zones and 29 protected sectors within infested areas have been established. 相似文献
94.
L S Pelan-Mattocks B A Pesch M E Kehrli 《American journal of veterinary research》2001,62(11):1740-1744
OBJECTIVE: To develop an efficient and reliable method that accurately differentiates bovine lymphocytes from monocytes in leukograms. SAMPLE POPULATION: Blood samples from 30 healthy cows and 1 calf with bovine leukocyte adhesion deficiency. PROCEDURE: Flow cytometric analysis of intracellular complexity and CD45 expression on bovine leukocytes was compared with results for conventional light microscopy methods. Verification of leukocyte subpopulations determined by intracellular complexity and CD45 expression was conducted, using 2-color phenotypic analysis with selected monoclonal antibodies. RESULTS: The CD45 and side-scatter properties of bovine leukocytes clearly differentiated cell types, including neutrophils, eosinophils, monocytes, and lymphocytes. CONCLUSIONS AND CLINICAL RELEVANCE: This is a rapid assay that is simple to use. More importantly, it is more accurate than the conventional method that involves the use of blood slides and light microscopy, because of the ability of the assay to readily distinguish bovine monocytes and lymphocytes. Rapid preparation of samples and short analysis times allow for efficient and reliable examination of a large number of samples, and the task of viewing slides by light microscopy is eliminated. The labor-savings benefit of this procedure is most apparent in research environments that require frequent processing of batches of blood samples. 相似文献
95.
Genetic diversity within and among 20 herbicide-resistant (HR) and 16 herbicide-susceptible (HS) Avena fatua multi-field populations was determined using 82 polymorphic loci resulting from two intersimple sequence repeat (ISSR) primers and one long-primer random amplified polymorphic DNA (LP-RAPD) primer. Collections from the Red River Valley of North Dakota and Minnesota, sampled in 1964 and 2000, represented A. fatua populations before and after intensive exposure to herbicides. A 1995 collection from south-west North Dakota represented A. fatua exposed to low herbicide selection. Despite differences in years of herbicide exposure among collections, both HR and HS populations from every collection maintained nearly similar levels of ISSR and RAPD diversity. Genetic differentiation among populations (GST) varied from 11% to 13% among HR populations and from 9% to 16% among HS populations, indicating that 84–91% of total variation remained within HS or within HR populations. Minimal difference in gene diversity between HR and HS is consistent with multiple origins of resistance, where HR A. fatua most likely evolved from diverse founding individuals. 相似文献
96.
97.
98.
99.
100.
E C?té 《Veterinary Clinics of North America: Small Animal Practice》2001,31(6):1129-45, v
Severe heart disease may cause hypotension and hypoperfusion, and ultimately circulation may cease altogether. These two clinical syndromes are cardiogenic shock and cardiac arrest, respectively. This review summarizes the causes and clinical features of each, and describes the treatment options available to clinicians managing patients in cardiogenic shock. 相似文献