全文获取类型
收费全文 | 3036篇 |
免费 | 195篇 |
国内免费 | 4篇 |
专业分类
林业 | 202篇 |
农学 | 70篇 |
基础科学 | 22篇 |
495篇 | |
综合类 | 732篇 |
农作物 | 73篇 |
水产渔业 | 242篇 |
畜牧兽医 | 1087篇 |
园艺 | 90篇 |
植物保护 | 222篇 |
出版年
2024年 | 8篇 |
2023年 | 20篇 |
2022年 | 30篇 |
2021年 | 73篇 |
2020年 | 78篇 |
2019年 | 95篇 |
2018年 | 80篇 |
2017年 | 80篇 |
2016年 | 90篇 |
2015年 | 70篇 |
2014年 | 81篇 |
2013年 | 109篇 |
2012年 | 196篇 |
2011年 | 225篇 |
2010年 | 151篇 |
2009年 | 98篇 |
2008年 | 225篇 |
2007年 | 215篇 |
2006年 | 199篇 |
2005年 | 194篇 |
2004年 | 199篇 |
2003年 | 188篇 |
2002年 | 183篇 |
2001年 | 35篇 |
2000年 | 29篇 |
1999年 | 31篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 18篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1974年 | 9篇 |
1973年 | 4篇 |
1972年 | 5篇 |
排序方式: 共有3235条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
Singleton Megan P. Thode Andrea E. Sánchez Meador Andrew J. Iniguez Jose M. Stevens Jens T. 《Landscape Ecology》2021,36(12):3429-3449
Landscape Ecology - Spatial patterns of high-severity wildfire in forests affect vegetation recovery pathways, watershed dynamics, and wildlife habitat across landscapes. Yet, less is known about... 相似文献
46.
Miriam S Martin Michael D Kleinhenz Lily N Edwards-Callaway Terry E Engle Octavio Guimaraes David W Schafer Shawnee R Montgomery Andrew K Curtis Mikaela M Weeder Devin R Jacobs Johann F Coetzee 《Journal of animal science》2022,100(3)
Hot-iron branding uses thermal injury to permanently identify cattle causing painful tissue damage. The primary objective was to examine the physiological and behavioral effects of oral meloxicam (MEL), compared to a control, administered at the time of hot-iron branding in Angus and Hereford steers and heifers. The secondary objectives were to investigate breed and sex effects on pain biomarkers. A total of 70 yearlings, consisting of 35 heifers and 35 steers (Angus, Hereford, or Angus × Hereford), were enrolled in the study. Animals were blocked by sex, randomized across weight, and assigned to receive MEL (1 mg/kg) or a placebo (CON). Biomarkers were assessed for 48 h after branding and included infrared thermography (IRT), mechanical nociceptive threshold (MNT), accelerometry and a visual analog scale (VAS), and serum cortisol and prostaglandin E2 metabolites (PGEM). Wound healing was assessed for 12 wk. Hair samples to quantify cortisol levels were taken prior to and 30 d post-branding. Responses were analyzed using repeated measures with calf nested in treatment as a random effect, and treatment, time, treatment by time interaction, breed, and sex as fixed effects. There was a treatment by time interaction for PGEM (P < 0.01) with MEL having lower values than CON at 6, 24, and 48 h (MEL: 18.34 ± 3.52, 19.61 ± 3.48, and 22.24 ± 3.48 pg/mL, respectively; CON: 32.57 ± 3.58, 37.00 ± 3.52, and 33.07 ± 3.48 pg/mL; P < 0.01). MEL showed less of a difference in maximum IRT values between the branded (2.27 ± 0.29 °C) and control site (3.15 ± 0.29 °C; P < 0.01). MEL took fewer lying bouts at 0–12 h (4.91 bouts ± 0.56) compared with CON (6.87 bouts ± 0.55; P < 0.01). Compared with Hereford calves, Angus calves exhibited greater serum but lower hair cortisol, greater PGEM, more lying bouts, and less healed wound scores at 3, 4, and 5 wk. Compared with heifers, steers exhibited lower PGEM, lower branding site and ocular IRT, higher MNT, and lower plasma meloxicam levels. Steers spent more time lying, took more lying bouts and had greater VAS pain, and more healed wound scores at 5 wk than heifers. Meloxicam administration at branding reduced branding and control site temperature differences and reduced lying bouts for the first 12 h. Breed and sex effects were observed across many biomarkers. Changes from baseline values for IRT, MNT, lying time, step count, VAS pain, and wound scoring all support that branding cattle is painful. 相似文献
47.
Sarah A. Slaughter Andrew D. Eitzer Sara E. Tolliver Sarah N. Holman Sara A. Colopy Seamus E. Hoey Samantha J. Loeber 《The Canadian veterinary journal. La revue veterinaire canadienne》2022,63(5):515
A 14-week-old male unilaterally cryptorchid Clumber spaniel was presented for acute lethargy. Physical examination revealed abdominal pain, and a single testis was palpated in the scrotum. Abdominal ultrasound and computed tomography (CT) revealed a poorly vascularized, ovoid structure immediately caudal to the left kidney with scant regional peritoneal effusion. Left intra-abdominal testicular torsion was confirmed at surgery, and routine cryptorchidectomy was performed. The patient recovered uneventfully from anesthesia and surgery.Key clinical message:The most common CT characteristics of testicular torsion were present in this case and correlated well with sonographic findings to allow for rapid, accurate diagnosis and surgical planning of unilateral, non-neoplastic, intra-abdominal cryptorchid testicular torsion in a juvenile dog. Contrast enhanced CT facilitated accurate localization of the undescended testis and evaluation of testicular perfusion and may be a useful alternative to ultrasound for diagnosing testicular torsion, especially in indeterminate cases. 相似文献
48.
The lipid content and fatty acid composition in the edible meat of twenty-nine species of wild and cultured freshwater and marine fish and shrimps were investigated. Both the lipid content and fatty acid composition of the species were specified due to their unique food habits and trophic levels. Most of the marine fish demonstrated higher lipid content than the freshwater fish, whereas shrimps had the lowest lipid content. All the marine fish and shrimps had much higher total n-3 PUFA than n-6 PUFA, while most of the freshwater fish and shrimps demonstrated much lower total n-3 PUFA than n-6 PUFA. This may be the biggest difference in fatty acid composition between marine and freshwater species. The cultured freshwater fish demonstrated higher percentages of total PUFA, total n-3 PUFA, and EPA + DHA than the wild freshwater fish. Two freshwater fish, including bighead carp and silver carp, are comparable to the marine fish as sources of n-3 PUFA. 相似文献
49.
Andrew C. Sherfy John S. Tyner Youngil Kim 《Communications in Soil Science and Plant Analysis》2016,47(3):305-312
A multifunctional heat pulse probe (MFHPP) can measure soil thermal and hydraulic properties. Though its successful implementation has been documented, previous studies have reported some limitations. One specific cause of the limitations is the absorption of the generated heat pulse within the probe itself, which creates error in the measurements. The objective of this study was to develop and evaluate a new calibration method to account for measurement error due to heat loss to the probe. A MFHPP was constructed and tested in six soil types using both a traditional method and the newly developed calibration method. The new calibration utilizes heat pulse response curves from real soils with thermal conductivities similar to that of the MFHPP rather than the traditional agar-stabilized water solution. This new approach significantly reduced average measurement errors from 9.1% to 2.4% for heat capacity and 13.5% to 4.5% for volumetric water content. 相似文献
50.
Tredoux A de Villiers A Májek P Lynen F Crouch A Sandra P 《Journal of agricultural and food chemistry》2008,56(12):4286-4296
A simple method for the analysis of major wine volatiles and semivolatiles by stir bar sorptive extraction in combination with thermal desorption and gas chromatography-mass spectrometry (SBSE-TD-GC-MS) was developed. Significant experimental parameters such as extraction time, temperature, salt addition, pH, and thermal desorption parameters were optimized to provide a sensitive and robust analytical method. The method provided good repeatability (%RSD < 10%) for 38 major wine volatile compounds, including alcohols, acids, esters, phenols, aldehydes, ketones, and lactones. Quantitative data for 62 South African red and white wines were used to study the suitability of major volatile data for the differentiation of wine samples according to grape variety or cultivar. Principal component analysis (PCA) and cluster analysis (CA) showed that most of the variation in volatile composition between wine samples could be ascribed to differences in wine age, wood contact, and fermentation practices. Despite the contribution of these factors, discriminant analysis (DA) was successfully applied to the classification of red and white wine samples according to cultivar. 相似文献