全文获取类型
收费全文 | 576篇 |
免费 | 25篇 |
专业分类
林业 | 13篇 |
农学 | 15篇 |
基础科学 | 5篇 |
79篇 | |
综合类 | 139篇 |
农作物 | 30篇 |
水产渔业 | 21篇 |
畜牧兽医 | 270篇 |
园艺 | 5篇 |
植物保护 | 24篇 |
出版年
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 8篇 |
2014年 | 15篇 |
2013年 | 15篇 |
2012年 | 36篇 |
2011年 | 28篇 |
2010年 | 21篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 29篇 |
2006年 | 17篇 |
2005年 | 27篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1979年 | 4篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1971年 | 5篇 |
1970年 | 9篇 |
1969年 | 7篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1924年 | 8篇 |
排序方式: 共有601条查询结果,搜索用时 15 毫秒
541.
We compared how management approaches affected shade tree diversity, soil properties, and provisioning and carbon sequestration
ecosystem services in three shade coffee cooperatives. Collectively managed cooperatives utilized less diverse shade, and
pruned coffee and shade trees more intensively, than individual farms. Soil properties showed significant differences among
the cooperatives, with the following properties contributing to differentiation: N, pH, P, K, and Ca. Higher tree richness
was associated with higher soil pH, CEC, Ca, and Mg, and lower K. Higher tree densities were associated with lower N, K, and
organic matter. Although we found differences in the incidence of provisioning services (e.g., fruit), all plantations generated
products other than coffee. No differences were observed between C-stocks. The history and institutional arrangements of cooperatives
can influence management approaches, which affect ecosystem properties and services. Our study corroborates that interdisciplinary
investigations are essential to understand the socio-ecological context of tropical shade coffee landscapes. 相似文献
542.
Cary L. Matwichuk DVM MVSc Susan M. Taylor DVM Gregory B. Daniel DVM MS A.A Wilkinson MB Gilbert G. Matte Bpharm PhD E.M. Dudzic MD Cindy L. Shmon DVM DVSc 《Veterinary radiology & ultrasound》2000,41(5):461-469
The purpose of this study was to evaluate the utility of double-phase parathyroid scintigraphy using 99mTc-sestamibi for detecting and localizing hyperfunctioning parathyroid glands in hypercalcemic dogs. Fifteen hypercalcemic dogs that underwent parathyroid scintigraphy were included in this study: 3 dogs with hypercalcemia of malignancy, and 12 dogs with hyperfunctioning parathyroid tissue (parathyroid adenoma or parathyroid hyperplasia). The presence of parathyroid adenoma or parathyroid hyperplasia was documented by histopathologic examination. In 3 dogs with hypercalcemia of malignancy, parathyroid scintigraphy was negative for hyperfunctioning parathyroid tissue and the scans were classified as true negative. Parathyroid scintigraphy correctly identified the presence and location of hyperfunctioning parathyroid tissue in only 1 of 6 dogs with a parathyroid adenoma. False positive and false negative results occurred in dogs with parathyroid adenomas. Parathyroid scintigraphy failed to detect hyperfunctioning parathyroid tissue in 5 of 6 dogs with parathyroid hyperplasia and were classified as false negative. False positive results were obtained in the remaining dog with parathyroid hyperplasia. Sensitivity of parathyroid scintigraphy for detecting and localizing hyperfunctioning parathyroid tissue was 11%, specificity was 50%, and overall accuracy was 27%. Positive and negative predictive value were 25% and 27%, respectively. Sensitivity for detection of parathyroid adenomas was 25%, and sensitivity for detection of hyperplastic glands was 0 %. Results of this study indicate that double-phase parathyroid scintigraphy does not appear to have acceptable accuracy in detecting hyperfunctioning parathyroid glands in dogs. Due to the poor sensitivity and specificity of the technique in dogs, parathyroid scintigraphy is not recommended for definitive identification of abnormal parathyroid glands as the cause of hypercalcemia in dogs. 相似文献
543.
Generating information for aquaculture development: The art and science of economic policy modelling
Gilbert Sylvia 《Aquaculture Economics & Management (Blackwell Science)》2013,17(1-2):87-98
Abstract The rapid growth of aquaculture and concerns about economic and ecological ‘sustainability’ have focused attention on industry externalities. Developing institutions which ‘sustain’ aquaculture will require skills in the ‘art and science’ of public policy modelling. Analysis of existing approaches demonstrates that no single modelling paradigm is ‘best’ for all aquaculture policy situations. Modelling approaches other than cost‐benefit including multiobjective analysis may be more appropriate if the objective of the modeller is to improve the effectiveness of the policy process itself. A review of the relatively small but growing literature on aquaculture policy models reveals a wide range of issues and approaches. In general, economic models have focused on the single objective of maximizing efficiency; in contrast, models used in actual aquacultural policy and planning focus on controlling environmental pollution. The findings suggest that economic models have not yet played a significant role in aquacultural policy development. This raises concerns that myopic views of ‘sustainability’ will result in institutions which do not promote socially efficient aquacultural industry growth. 相似文献
544.
Mohamed Omar El-Magsodi Peter Bossier Patrick Sorgeloos Gilbert Van Stappen 《Aquaculture International》2014,22(5):1515-1532
Nauplii hatching from Artemia cysts are crucial in larviculture nutrition. Artemia cysts may be exposed to repeated hydration/dehydration (H/D) cycles pre-harvesting or during processing and storage. To observe the effect of these cycles on cyst quality, Artemia franciscana cysts were exposed to a comprehensive set of various H/D treatments, differing in the number of cycles (1, 2, or 3) and the duration of the freshwater hydration period (2 or 4 h). Cyst quality was assessed using the criteria of immediate relevance for aquaculture use, such as hatching percentage directly after H/D treatment and after ?18 °C storage up to 1 month, longevity of axenically hatched starved nauplii, cyst and naupliar energy content, and (for the most extreme H/D treatment) cyst and naupliar fatty acid and vitamin C content. Repeated H/D cycles resulted in significantly (P < 0.05) decreased cyst hatching, reduced starved naupliar longevity and individual energy content, loss in vitamin C and fatty acid content, and moreover a close correlation between these parameters as a function of progressive H/D treatments. This is of immediate relevance for aquaculture nutrition, as commercial Artemia cysts may have gone through an unknown sequence of H/D cycles in nature or in the processing line, which affects the nutritional quality of the nauplii used in larviculture operations. 相似文献
545.
BZ Yang CY Yang RC Li GS Qin XF Zhang CY Pang MT Chen FX Huang Z Li HY Zheng YJ Huang XW Liang 《Reproduction in domestic animals》2010,45(5):e21-e25
The aim of this study was to explore the feasibility of cryopreservation of inter‐subspecies cloned embryos in buffalo. In our experiment, river buffalo ear fibroblast nucleus was fused into swamp buffalo oocyte cytoplasm. The blastocyst formation rate for nuclear transfer of freshly thawed cells was not different from those of growing cells, confluent or serum‐starved cells. A total of 122 cloned blastocysts derived from cryopreserved fibroblasts were cryopreserved and thawed, 37 were survived, the cryosurvival rate was 30.3%. The survived blastocysts were transferred into 15 recipient buffalos. Five of the recipients established pregnancy, but four of them aborted on day 53, 59, 145 and 179 of gestation respectively. One cross‐bred buffalo (Murrah × Swamp buffalo (2n = 49) received three embryos delivered a 40.5 kg female calf by natural delivery on day 320 of gestation. Up to now (13‐month old), the cloned calf has been growing well with no abnormity observed. These results demonstrated that cryopreservation of inter‐subspecies cloned embryos is feasible to produce buffalo offspring. 相似文献
546.
Two separate studies tested the hypothesis that plasma low-density lipoprotein cholesterol (LDL-C) can be decreased by conjugated linoleic acid (CLA) by depressing hepatic acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity. In the first experiment, 3 groups of 6 early-weaned piglets were fed low-fat diets containing either 1.5% CLA, 1.5% corn oil or 1.5% beef tallow; fat provided 8% of the energy intake. In the second experiment, 4 groups of 6 early-weaned piglets were fed high-fat diets containing either 15% beef tallow, 12% beef tallow plus 3% CLA, 15% corn oil, or 12% corn oil plus 3% CLA; fat provided 29% of energy intake. Cholesterol was balanced across diets in both experiments. In pigs fed the low-fat diets, all dietary fats increased LDL-C and triacylglycerols and decreased high-density lipoprotein cholesterol (HDL-C) and very low-density lipoprotein cholesterol (VLDL-C). LDL-C was the same in pigs fed low-fat tallow or low-fat CLA diets. However, ACAT activity was nearly 80% higher in pigs fed the low-fat tallow diet than in pigs fed the low-fat CLA diets. All high-fat diets increased LDL-C, HDL-C and triacylglycerols equally with no effect on VLDL-C. There were no unique fatty acid effects of the high-fat diets on ACAT activity. We conclude that supplemental fats had differential effects on hepatic ACAT activity and LDL-C, but only in pigs fed low-fat diets. 相似文献
547.
Mohamed Omar El-Magsodi Kartik Baruah Parisa Norouzitallab Peter Bossier Patrick Sorgeloos Gilbert Van Stappen 《Aquaculture International》2016,24(2):429-439
The brine shrimp Artemia franciscana is an important live feed for fish and shellfish larviculture. Cysts of Artemia are naturally found in a wide variety of harsh environments worldwide where they are exposed to different changing environmental conditions. Artemia cysts are also exposed to different hydration/dehydration (H/D) conditions during the post-harvest processing period in the Artemia processing industry. In this study, cysts of two strains of A. franciscana originating from two different geographical locations—one a natural population from Great Salt Lake (GSL), Utah, USA, and the other cultured in the Vinh Chau (VC) salt ponds, Vietnam—where they experience different environmental factors, were exposed to successive hydration/dehydration (H/D) cycles with the aim of determining the effects of these conditions on the stress (i.e., induction of Hsp70) and functional (i.e., resistance toward abiotic and pathogenic biotic factors) responses of the emerged nauplii. Our results showed that a short period of H/D of the cysts did not appear to have a deleterious effect on the emerged nauplii of both strains, as was evidenced by the absence of significant difference in the survival of nauplii emerged from the control and treated cysts, upon challenge with a thermal stressor or with pathogenic Vibrio campbellii. A limited exposure to H/D treatment even leads to the induction of enhanced thermotolerance in GSL nauplii. In essence, these observations add some insights to our current understanding of stress responses in Artemia under the described experimental conditions. In addition, the impact of H/D cycles associated with stress response should be taken into consideration when Artemia is considered as a model organism for future research and applications. 相似文献
548.
GH Miller JW Magee BJ Johnson ML Fogel NA Spooner MT McCulloch LK Ayliffe 《Science (New York, N.Y.)》1999,283(5399):205-208
More than 85 percent of Australian terrestrial genera with a body mass exceeding 44 kilograms became extinct in the Late Pleistocene. Although most were marsupials, the list includes the large, flightless mihirung Genyornis newtoni. More than 700 dates onGenyornis eggshells from three different climate regions document the continuous presence of Genyornis from more than 100,000 years ago until their sudden disappearance 50,000 years ago, about the same time that humans arrived in Australia. Simultaneous extinction of Genyornis at all sites during an interval of modest climate change implies that human impact, not climate, was responsible. 相似文献
549.
Effects of diet, salinity, and consumption of endogenous reserves on the growth, survival and swim bladder inflation of European sea-bass larvae were studied. Primary inflation of the swim bladder occurs in 7-day-old larvae. Inflation is synchronized with the absorption of endogenous reserves. The kinetics of the consumption of these reserves varies with the diets tested, and is the slowest at higher salinity (28.7 and 37.7‰). Best results were obtained with larvae fed on Artemia nauplii. Larvae raised at lower salinity (19.7 and 10.7‰) had the highest proportion of inflated swim bladders. Larvae raised at 28.7‰ salinity had the best survival rate, while those raised at 38.7‰ had the best growth rate. Larval mortality was associated with inappropriate functioning of the swim bladder. Larvae exposed to decreasing salinity during rearing showed very high survival rates and normal swim bladder inflation. 相似文献
550.