全文获取类型
收费全文 | 516篇 |
免费 | 37篇 |
国内免费 | 1篇 |
专业分类
林业 | 43篇 |
农学 | 14篇 |
基础科学 | 1篇 |
64篇 | |
综合类 | 94篇 |
农作物 | 16篇 |
水产渔业 | 42篇 |
畜牧兽医 | 235篇 |
园艺 | 11篇 |
植物保护 | 34篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 22篇 |
2020年 | 27篇 |
2019年 | 27篇 |
2018年 | 10篇 |
2017年 | 24篇 |
2016年 | 12篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 27篇 |
2012年 | 34篇 |
2011年 | 44篇 |
2010年 | 19篇 |
2009年 | 15篇 |
2008年 | 35篇 |
2007年 | 36篇 |
2006年 | 28篇 |
2005年 | 32篇 |
2004年 | 21篇 |
2003年 | 20篇 |
2002年 | 18篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1948年 | 1篇 |
1898年 | 2篇 |
排序方式: 共有554条查询结果,搜索用时 740 毫秒
251.
A survey, which included questionnaires for fishermen and the placement of observers onboard fishing vessels, was conducted to assess turtle catch off the Balearic Islands. The survey focused on those fishing vessels whose base port was in the archipelago and, hence, the catch of South-eastern Spain longliners moving in summer to the archipelago was not considered. The fishermen's perception was that the stock of loggerhead turtles is declining in the archipelago and that fishing activities are at least partially responsible for this trend. The observer reports indicated that the figures produced by the interviewees for catch per unit effort (CPUE) were reliable. Therefore, on the basis of these figures we calculated a total catch of 373 (95% CI: 365-308) loggerheads for 2001. Most turtles were caught in lobster trammel nets (196; 95% CI: 269-123) or drifting longlines (102; 95% CI: 111-93). Although the CPUE was much lower for the former, total catch was greater because of a larger fleet. Moreover, most loggerheads caught in lobster trammel nets were found dead when nets were hauled in, while no immediate mortality was observed in individuals caught in drifting longlines. This observation highlights the threat of trammel nets to loggerhead turtle populations. The estimated impact of the catches on the turtle population depends on the origin of the individuals inhabiting the region, which is yet to be established. 相似文献
252.
Galle SA Koot A Soukoulis C Cappellin L Biasioli F Alewijn M van Ruth SM 《Journal of agricultural and food chemistry》2011,59(6):2554-2563
Volatile fingerprints of 30 cumin cheese samples of artisanal farmers' cheese of Leiden with EU Protected Designation of Origin (PDO) and 29 cumin cheese samples of varying commercial Dutch brands without PDO protection were used to develop authentication models. The headspace concentrations of the volatiles, as measured with high sensitivity proton-transfer mass spectrometry, were subsequently subjected to partial least-squares discriminant analysis (PLS-DA). Farmers' cheese of Leiden showed a distinct volatile profile with 27 and 9 out of the 60 predominant ions showing respectively significantly higher and lower concentrations in the headspace of the cheese in comparison to the other cumin cheeses. The PLS-DA prediction models developed classified in cross-validation 96% of the samples of PDO protected, artisanal farmers' cheese of Leiden correctly, against 100% of commercial cumin cheese samples. The characteristic volatile compounds were tentatively identified by PTR-time-of-flight-MS. A consumer test indicated differences in appreciation, overall flavor intensity, creaminess, and firmness between the two cheese groups. The consumers' appreciation of the cumin cheese tested was not influenced by the presence of a name label or PDO trademark. 相似文献
253.
Pollution impacts on bird population density and species diversity at four non-ferrous smelter sites
Tapio Eeva Eugen Belskii Alex S. Gilyazov Mikhail V. Kozlov 《Biological conservation》2012,150(1):33-41
Non-ferrous smelters pose a potential hazard for breeding bird populations, but comprehensive analyses of the impacts on bird population densities around smelter sites are currently lacking. We measured with point counts bird population densities around four smelter sites in Russia (Monchegorsk, Karabash and Revda) and Finland (Harjavalta) to explore the relationships between bird population density/species diversity and exposure level quantified by the potentially bioavailable copper concentrations in forest litter. Total bird densities, bird biomasses and species diversities decreased in the vicinity of all three Russian smelters. In Harjavalta, there were no pollution-related trends in total bird density or biomass, although species diversity (species number and Shannon’s index) decreased towards the pollution source. In general, the four smelters showed negative effects on bird populations in decreasing order of impact as follows: Monchegorsk > Karabash > Revda > Harjavalta, reflecting the amount of current and past emissions and consequent habitat change at each site. Our results suggest that around copper–nickel and copper smelters the pollution impact on bird diversity is accelerated when the litter copper level exceeds 1000 μg/g. However, even though bird densities and diversities reflected the exposure levels in our study, they were not associated with litter copper concentrations in a strictly dose-dependent manner, indicating that copper itself is not a primary cause for the changes in bird communities, but rather the combined effect of multiple pollutants on birds and especially on the resources necessary for breeding, such as food and suitable habitat. 相似文献
254.
255.
Debra Taylor DVM MS Alex Sperandeo Thomas Passler Anne Wooldridge Rhodes Bell Adam Cooner Leah Guidry Hannah Matz-Creel Ivy Ramey Pete Ramey 《Journal of Equine Veterinary Science》2014
A specific method of rehabilitation was used to manage obese horses with laminitis, and clinical outcome was evaluated after 5 to 20 months. Clinical data from 14 similar laminitis cases were statistically analyzed to evaluate response to rehabilitation. Data were analyzed using repeated measures or logistic regression methodologies. Each horse presented as obese and laminitic with no history of a systemic inflammatory disease. The rehabilitation method emphasized a mineral-balanced, low nonstructural carbohydrate diet; daily exercise; hoof trimming that minimized hoof wall loading; and sole protection in the form of rubber hoof boots and/or hoof casts. Distal phalanx alignment within the hoof capsule was significantly improved, and hoof wall thickness was significantly decreased (P < .0001) following treatment. Solar depth was significantly increased (P < .0015). Reduction of palmar angle measurements was detected in acutely and chronically affected horses. This treatment effect was statistically greater for horses with chronic laminitis than for horses with acute laminitis (P interaction < .0001). Horses were 5.5 times more likely to be sound post-treatment than before treatment. Daily exercise, dietary modification, and removal of ground reaction force from the hoof wall were foci of the rehabilitation program. Hoof care and husbandry as applied to these horses may be an effective method of rehabilitation of horses from obesity-associated laminitis. 相似文献
256.
OBJECTIVE: The objective of the study was to determine the effects of systemic 0.5% tropicamide on intraocular pressure (IOP), pupillary diameter (PD), blood pressure, and heart rate (HR) in normal felines with normotensive eyes. PROCEDURES: Intraocular pressure, PD, systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP), and HR were measured in 18 clinically healthy cats. Each of the previously mentioned parameters was measured every 30 min during the trial period. At T(60), each cat was treated with one to two drops of 0.5% tropicamide ophthalmic solution placed on the dorsal aspect of the tongue. Changes in SBP, DBP, MBP, and HR were evaluated using one-way repeated measures analysis of variance, with time as the repeated factor. IOP and PD were evaluated using two-way repeated measures analysis of variance, with time and side (OD vs. OS) as the repeated factors. P values less than or equal to 0.05 were considered statistically significant. RESULTS: After lingual tropicamide administration, the mean PD at T(60) was 3.53 mm OD and 3.53 mm OS. The mean PD at T(90) was 6.36 mm OD and 6.31 mm OS. The mean PD at T(120) was 8.25 mm OD and 8.19 mm OS. This change in PD from T(60), T(90), and T(120) was statistically significant, demonstrating a linear increase in PD over time after tropicamide application on the tongue (P<0.0001). There was no statistically significant difference in PD when comparing the right to the left pupils (P=0.10). The mean IOP at T(60) was 14 mmHg OD and 12.94 mmHg OS. The mean IOP at T(90) was 14.5 mmHg OD and 14.23 mmHg OS. The mean IOP at T(120) was 14.94 mmHg OD and 14.89 mmHg OS. This change in IOP from T(60), T(90), and T(120) was statistically significant, demonstrating a linear increase in IOP over time after tropicamide application on the tongue (P=0.034). There was no statistically significant difference in IOP when comparing the right eye to the left eye (P=0.28). There were no statistically significant differences in SBP, DBP, MBP, and HR values over time for the duration of the study. CONCLUSIONS: We conclude that although lingual application of tropicamide appears to result in systemic absorption, causing significant pupillary dilation and elevations in IOP, systemic effects on SBP, DBP, MBP, and HR were not observed. 相似文献
257.
Mylonakis ME Koutinas AF Leontides LS 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2006,35(3):311-314
BACKGROUND: Bone marrow mastocytosis has been reported rarely in naturally occurring canine monocytic ehrlichiosis (CME). OBJECTIVES: The aims of the present study were to estimate the prevalence and magnitude of bone marrow mastocytosis in a case series of dogs with natural CME and to assess the association, if any, between mastocytosis and the clinical severity of the disease. METHODS: Seventy-six dogs with confirmed CME (Ehrlichia canis) were included in the study. Affected dogs were allocated into group A (n = 51) without bone marrow hypoplasia and group B (n = 25) with bone marrow hypoplasia. Twenty clinically healthy Beagles not previously exposed to E canis served as controls (group C). The main inclusion criteria for group A were documentation of normocellular to hypercellular bone marrow and complete clinical cure following a 4-week treatment with doxycycline, while those for group B were bone marrow hypoplasia and lack of response to doxycycline. Bone marrow aspirate smears from all 96 dogs were Giemsa-stained and examined for the presence of mast cells, which were calculated as a percentage of 1,000 nucleated cells (NCs). The prevalence of mastocytosis was compared among the 3 groups by the Pearson's chi-square test. RESULTS: Bone marrow mastocytosis (>0.1% of NCs) was found in 5 (20%) dogs in group B (range, 0.5-2.5% of NCs; median, 1% of NCs). One dog in each of groups A and C had 0.1% mast cells in the marrow. The prevalence of bone marrow mastocytosis in dogs in group B was significantly higher (P = .004) than in groups A and C. CONCLUSION: Bone marrow mastocytosis can be seen in a substantial number of dogs with E canis-induced myelosuppression. 相似文献
258.
259.
260.
Increased use of forest resources and a shrinking forestland base threaten the sustainability of forest genetic resources
and highlight the importance of conservation and sustainable management of these resources. As forest trees are normally the
keystone species of forest ecosystems, their continued existence is essential for many floral and faunal associations of these
ecosystems. Major concepts, challenges and opportunities for conservation of forest genetic resources are briefly discussed
in this paper. The major challenges include population decline and population structure changes due to forest removal and
conversion of forest land to other uses,forest fragmentation, forestry practices, climate change, disease conditions,introduced
pests, atmospheric pollution, and introgressive hybridization. Developing scientifically sound conservation strategies, maintaining
minimum viable population sizes, and deployment of genetically engineered organisms represent other important challenges in
conservation. The usefulness of various biochemical and molecular genetic markers, adaptive traits, and genetic diversity
measures for developing conservation strategies for in situ and ex situ genetic resource conservation are also discussed. Major opportunities for conservation of forest genetic resources include:
use of molecular genetic markers and adaptive traits for developing conservation strategies; in situ conservation through natural reserves,protected areas, and sustainable forest management practices; ex situ conservation through germplasm banks, common garden archives, seed banks, DNA banks, and tissue culture and cryopreservation;
incorporation of disease, pest, and stress tolerance traits through genetic transformation;plantation forestry; and ecological
restoration of rare or declining tree species and populations. Forest genetic resource conservation and resource use should
be considered complementary rather than contradictory to each other.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献