全文获取类型
收费全文 | 4517篇 |
免费 | 132篇 |
国内免费 | 4篇 |
专业分类
林业 | 2310篇 |
农学 | 53篇 |
基础科学 | 7篇 |
323篇 | |
综合类 | 72篇 |
农作物 | 221篇 |
水产渔业 | 109篇 |
畜牧兽医 | 1294篇 |
园艺 | 57篇 |
植物保护 | 207篇 |
出版年
2021年 | 43篇 |
2020年 | 52篇 |
2018年 | 48篇 |
2017年 | 47篇 |
2015年 | 45篇 |
2014年 | 75篇 |
2013年 | 167篇 |
2012年 | 93篇 |
2011年 | 102篇 |
2010年 | 82篇 |
2009年 | 97篇 |
2008年 | 85篇 |
2007年 | 81篇 |
2006年 | 87篇 |
2005年 | 109篇 |
2004年 | 113篇 |
2003年 | 79篇 |
2002年 | 76篇 |
2001年 | 41篇 |
1997年 | 54篇 |
1996年 | 78篇 |
1995年 | 55篇 |
1994年 | 54篇 |
1993年 | 67篇 |
1992年 | 74篇 |
1991年 | 55篇 |
1990年 | 44篇 |
1989年 | 40篇 |
1988年 | 48篇 |
1987年 | 39篇 |
1986年 | 48篇 |
1984年 | 49篇 |
1983年 | 51篇 |
1982年 | 60篇 |
1981年 | 107篇 |
1980年 | 48篇 |
1979年 | 81篇 |
1978年 | 43篇 |
1953年 | 61篇 |
1938年 | 58篇 |
1937年 | 47篇 |
1936年 | 49篇 |
1935年 | 49篇 |
1934年 | 48篇 |
1933年 | 53篇 |
1932年 | 48篇 |
1930年 | 37篇 |
1927年 | 44篇 |
1926年 | 74篇 |
1925年 | 55篇 |
排序方式: 共有4653条查询结果,搜索用时 15 毫秒
51.
Clinicopathological Phenotype of Autosomal Recessive Cholesterol Deficiency in Holstein Cattle 下载免费PDF全文
52.
Kook PH Boretti FS Hersberger M Glaus TM Reusch CE 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2007,21(3):388-393
BACKGROUND: Measurement of high concentrations of urine catecholamines and metanephrines is useful in diagnosing pheochromocytoma in humans. Stress increases catecholamine excretion in urine. HYPOTHESIS: Stress of a hospital visit increases urinary catecholamine and metanephrine excretion in dogs. ANIMALS: Fourteen clinically normal dogs, 2 dogs with pheochromocytoma. METHODS: Voided urine samples were collected by the owners 7 days before (t-7), during the hospital visit immediately after diagnostic procedures (t0), as well as 1 (t1) and 7 days (t7) after the hospital visit. Urine catecholamine and metanephrine concentrations were measured using high-pressure liquid chromatography and expressed as ratios to urine creatinine concentration. RESULTS: In client-owned dogs epinephrine and norepinephrine ratios at t0 were significantly higher compared with ratios at t7. Metanephrine and normetanephrine ratios at t-7, t0, and t1 did not differ significantly from each other; however, at t7 they were significantly lower compared to values at t-7. In staff-owned dogs no significant differences were detected among the different collecting time points for any variable. Metanephrine and normetanephrine ratios were significantly higher in client-owned dogs compared to staff-owned dogs at t-7, t0, and t1 but not at t7. CONCLUSIONS AND CLINICAL IMPORTANCE: Stress associated with a hospital visit and with the sampling procedure causes increases in urine catecholamine and metanephrine excretion. Urine collection for the diagnosis of pheochromocytoma probably should take place at home after adaptation to the sampling procedure. 相似文献
53.
Claudia TRANQUILLO Lucas Armand WAUTERS Francesca SANTICCHIA Damiano PREATONI Adriano MARTINOLI 《Integrative zoology》2023,18(4):746-761
Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species, which can result in habitat-dependent phenotypic differences among animals living in heterogeneous environments. We studied 3 alpine populations of Eurasian red squirrels (Sciurus vulgaris), 1 living in a marginal high-elevation habitat at the edge of the species’ altitudinal distribution, and 2 occurring in higher-quality habitats. Here, we investigated whether squirrels living in the marginal area differed in 2 morphological parameters (body size and body mass) and/or in the expression of 4 personality traits estimated with an open field test and a mirror image stimulation test (activity, exploration, activity-exploration, and social tendency). Furthermore, we tested whether within-individual variance of the traits (behavioral plasticity) was higher in the edge habitat. Male squirrels in the edge habitat were smaller and weighed less than in the other study areas, while among females, size–habitat relationships were less marked. These sex-specific patterns were explained by a strong association between body mass and reproductive success in female squirrels. Squirrels in the marginal habitat were more active, explorative, and had a more social personality than in the other habitats. However, in contrast to our predictions, behavioral plasticity was smaller in the marginal habitat, but only for the trait exploration. Our results suggest that animals choose the habitat that best fits their personality, and that habitat-related differences in selective pressures may shape animals’ morphology. 相似文献
54.
M. Ryan Smith DVM DACVECC Virginie A. Wurlod MS Dr vet med DACVECC DECVECC Chin-Chi Liu MS MApStat PhD 《Journal of Veterinary Emergency and Critical Care》2023,33(6):648-655
Objective
To describe hemostatic derangements associated with canine anaphylaxis and to assess for association with syndrome severity.Design
Prospective observational study.Setting
University teaching hospital.Animals
Twenty-seven client-owned dogs, recruited from November 2018 to January 2022, diagnosed with anaphylaxis of varying severity were included. Study inclusion required presentation <6 hours after initiation of clinical signs, no medications or history of illness within the prior 2 weeks, lack of comorbidities expected to affect hemostasis, and lack of a disease state that could alternatively explain the clinical presentation.Interventions
Blood samples were collected within the first hour of presentation for CBC, serum biochemistry, prothrombin time (PT), activated partial thromboplastin time (aPTT), and viscoelastic coagulation testing for use with a cartridge-based point-of-care device.Measurements and main results
Clotting time and clot formation time were prolonged, alpha angle and maximum clot firmness were decreased, PT and aPTT were prolonged, and platelet counts were lower in severe cases compared to mild and moderate cases. There were no differences for any parameter between mild and moderate cases. The presence or absence of abdominal effusion was not associated with hemostatic status.Conclusions
Global hemostatic derangements consistent with hypocoagulability are a prominent feature of severe anaphylaxis in dogs and should be considered for routine evaluation. 相似文献55.
56.
57.
Dr. Keit T. Ingram 《Agricultural Water Management》1992,20(4):341-342
58.
即使是最有进取心的养猪生产者也会忽视水质对猪生产性能的影响。尽管水质检验表明猪场水质仍在可接受的范围内,但水管内积聚起的水藻、细 相似文献
59.
Table grape quality and firmness are key parameters for Chile's export, given distances from the main markets. As a consequence, calcium (Ca) fertilization has become a standard practice in the country, although its effects have not been fully evaluated. The objectives in this study were to investigate the effects of calcium fertilization on table grape nutrition and quality. A two-year field trial was conducted in central Chile, using grapevines (Vitis vinifera) cv. ‘Thompson seedless’, grown on an overhead trellis system. Calcium (CaCl2) application treatments included foliar, soil, foliar plus soil, and a control without Ca fertilization. Calcium and other nutrients concentration were determined afterwards in soil, leaves, and berries. Also, yield and some fruit quality parameters were evaluated. Calcium application method did not have an effect on soil, leaf or fruit Ca content, neither on yield and berry sugar concentration, with levels being similar to the control treatment. Additionally, in treatments where CaCl2 was applied to soil, chlorides concentration in soil, leaves, and berries were higher. Also, berries were larger, more turgent, with lower dry matter and larger cells. In the second season, in these same treatments, berry firmness at harvest was higher, but this effect disappeared after the storage simulation period. These results question the validity that Ca applications might improve table grape postharvest quality for growing conditions similar to the ones in this experiment. The temporal changes in berry quality parameters were attributed to higher Cl soil content and the associated plant osmoregulatory mechanisms. 相似文献
60.
Dr Uwe Schindler Joerg Steidl Lothar Mueller 《Archives of Agronomy and Soil Science》2013,59(1):63-73
Abstract The influence of regional soil distribution and land use on discharge formation in the “Stettiner Haff” catchment (8,456 km2) was investigated. The model ABIMO was used to calculate mean discharge for a long period (1961 – 1990) in consideration of regional differences in hydrological site conditions and soil heterogeneity. The highest discharge was found on settlement areas (276 mm a?1), on devastated plots (319 mm a?1) and on the non-hydromorphic agriculturally used sandy soils (214 mm a?1). Due to their small size these sub-areas were found to influence regional discharge for a limited extent only. On loam and clay soils only about 100 mm a?1 of discharge was formed. However, this share proved to be most important for the height of regional discharge because of the high area proportion in the region. Mineral soils of comparable parent material produce lower discharge under hydromorphic conditions than under non-hydromorphic conditions. With increasing clay content of the soils these differences decreased. The agriculturally used areas were found to be most important for the region's water discharge. They accounted for 83% of the discharge, i.e. they originated 119 mm a?1 on average. At forest sites, the discharge height was about 52 mm a?1. Sites close to groundwater table (groundwater level <1 m) proved to act as depletive areas. 相似文献