全文获取类型
收费全文 | 16666篇 |
免费 | 458篇 |
国内免费 | 28篇 |
专业分类
林业 | 1302篇 |
农学 | 463篇 |
基础科学 | 131篇 |
2482篇 | |
综合类 | 1941篇 |
农作物 | 863篇 |
水产渔业 | 1281篇 |
畜牧兽医 | 6955篇 |
园艺 | 469篇 |
植物保护 | 1265篇 |
出版年
2022年 | 103篇 |
2021年 | 159篇 |
2020年 | 216篇 |
2019年 | 217篇 |
2018年 | 319篇 |
2017年 | 398篇 |
2016年 | 377篇 |
2015年 | 411篇 |
2014年 | 445篇 |
2013年 | 605篇 |
2012年 | 983篇 |
2011年 | 1003篇 |
2010年 | 472篇 |
2009年 | 423篇 |
2008年 | 695篇 |
2007年 | 658篇 |
2006年 | 631篇 |
2005年 | 1326篇 |
2004年 | 1251篇 |
2003年 | 1009篇 |
2002年 | 613篇 |
2001年 | 228篇 |
2000年 | 123篇 |
1999年 | 240篇 |
1998年 | 87篇 |
1992年 | 174篇 |
1991年 | 194篇 |
1990年 | 225篇 |
1989年 | 197篇 |
1988年 | 213篇 |
1987年 | 157篇 |
1986年 | 177篇 |
1985年 | 149篇 |
1984年 | 125篇 |
1983年 | 121篇 |
1979年 | 156篇 |
1978年 | 116篇 |
1977年 | 106篇 |
1976年 | 97篇 |
1975年 | 159篇 |
1974年 | 145篇 |
1973年 | 131篇 |
1972年 | 145篇 |
1971年 | 120篇 |
1970年 | 88篇 |
1969年 | 105篇 |
1968年 | 118篇 |
1967年 | 133篇 |
1966年 | 107篇 |
1965年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Francili A. Molossi Bianca S. de Cecco Camila B. Pohl Rogrio B. Borges Luciana Sonne Saulo P. Pavarini David Driemeier 《Journal of veterinary diagnostic investigation》2021,33(4):677
We determined the prevalence of diseases and pathogens associated with mortality in beef cattle in the State of Rio Grande do Sul, Brazil, based on pathology laboratory submissions. Postmortem examinations were conducted on 1,277 beef cattle that died between 2008 and 2018. Information regarding age, time of the year, breed, and regional location were analyzed statistically. Most cattle were from the surrounding region of Porto Alegre, and 78.7% of the analyzed cases had diagnostic value. The diagnostic category with most cases was infectious and/or parasitic diseases (60%), followed by toxic and toxicoinfectious (25%). Most cases occurred in the fall. Major disease conditions identified included hemoprotozoal infection (18.2%), rabies (8.2%), and plant intoxications by Senecio spp. (8.5%) and Pteridium arachnoideum (4.6%). Hemoprotozoal infection occurred at a higher frequency in young cattle, mainly in animals up to 1 y old. Intoxication by Senecio spp. was more frequent in cattle 2–3 y old. 相似文献
44.
45.
46.
Brinkman EL Biller DS Armbrust LJ O'Brien RT 《Journal of the American Animal Hospital Association》2007,43(4):179-186
When performing abdominal ultrasonography in dogs, the right aspect of the liver, porta hepatis, right kidney, right adrenal gland, pancreas, and duodenum are often not fully visible from a ventral, or subcostal, approach. The right lateral intercostal plane is an alternative approach that allows evaluation of these structures. This report provides multiple case examples that demonstrate the sonographic anatomy via the right intercostal approach. Other cases are included to demonstrate indications for this approach. Animals in which the right intercostal approach may prove most useful include large- and giant-breed dogs; deep-chested dogs; dogs with gas distention of the stomach, duodenum, and colon; dogs with microhepatia; and those with abdominal effusion and pain. 相似文献
47.
Schmitz JA Vogt RJ Rupp GP Brodersen BW Abel JM Wohlers AR Marx DB 《Journal of veterinary medical education》2007,34(3):340-349
Nebraska veterinary practitioners were surveyed to collect data about background characteristics and other factors related to veterinarians' decision to include or not include food animals in their practices and to practice in rural versus urban communities. Background characteristics that were significantly (p < or = 0.05) associated with choosing food-animal practice included growing up on a working farm or ranch; having parents who owned livestock; growing up in a town with a population of less than 10,000; majoring in animal science at university; being male; and having a primary interest, at the time of entering veterinary college, in food animal-exclusive or mixed-animal veterinary practice. The primary factor for choosing the community in which to practice was rural/urban lifestyle for rural veterinarians, while this factor was second for urban veterinarians. For all groups of veterinarians, the primary consideration in selecting their current practice was the species orientation of the practice. The primary reason for not choosing food-animal practice was better working conditions and lifestyle in companion-animal practice, followed by greater interest elsewhere. 相似文献
48.
Oyama MA Sisson DD Prosek R Bulmer BJ Luethy MW Fuentes VL 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2007,21(6):1272-1279
BACKGROUND: Dilated cardiomyopathy (DCM) is characterized by reduced systolic function, heightened sympathetic tone, and high morbidity and mortality. Little is known regarding the safety and efficacy of beta-blocker treatment in dogs with DCM. HYPOTHESIS: Carvedilol improves echocardiographic and neurohormonal variables in dogs with DCM over a 4-month treatment period. METHODS: Prospective, placebo-controlled, double-blinded randomized study. Dogs with DCM underwent echocardiography, ECG, thoracic radiographs, and neurohormonal profiling, followed by titration onto carvedilol (0.3 mg/kg q12h) or placebo over a 4-week period and subsequently received 3 months of therapy. Primary study endpoints included left ventricular volume and function. RESULTS: Sixteen dogs received carvedilol and 7 received placebo. At study end, 13 carvedilol dogs and 5 placebo dogs were alive. There was no difference in the mean percentage change in left ventricular volume at end-diastole (LVVd), left ventricular end-systolic volume (LVVs), and ejection fraction (EF) between treatment groups, suggesting that both groups experienced similar amounts of disease progression. Carvedilol treatment did not result in significant changes in neurohormonal activation, radiographic heart size, heart rate, or owner perceived quality-of-life. Baseline B-type natriuretic peptide (BNP) predicted dogs in the carvedilol-treated group that maintained or improved their EF over the study duration. CONCLUSIONS AND CLINICAL IMPORTANCE: Carvedilol administration did not improve echocardiographic or neurohormonal indicators of heart function. The lack of effect may be related to severity of disease, carvedilol dose, or brevity of follow-up time. Statistical power of the present study was adversely affected by a high fatality rate in study dogs and small sample size. 相似文献
49.
Nielsen L Toft N Eckersall PD Mellor DJ Morris JS 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2007,21(6):1231-1236
BACKGROUND: The acute-phase protein C-reactive protein (CRP) is used as a diagnostic and prognostic marker in humans with various neoplasias, including non-Hodgkin's lymphoma. OBJECTIVE: To evaluate if CRP could be used to detect different remission states in dogs with lymphoma. ANIMALS: Twenty-two dogs with untreated multicentric lymphoma. METHODS: Prospective observational study. Blood samples were collected at the time of diagnosis, before each chemotherapy session, and at follow-up visits, resulting in 287 serum samples. RESULTS: Before therapy, a statistically significant majority of the dogs (P = .0019) had CRP concentrations above the reference range (68%, 15/22). After achieving complete remission 90% (18/20) of the dogs had CRP concentrations within the reference range, and the difference in values before and after treatment was statistically significant (P < .001). CRP concentrations of dogs in complete remission (median, 1.91; range, 0.2-103) were significantly different (P = .031) from those of dogs with partial remission (median, 2.48; range, 0-89), stable disease (median, 1.77; range, 1.03-42.65), or progressive disease (median, 8.7; range, 0-82.5). There was profound variation of CRP measurements within each dog. CONCLUSIONS: CRP is useful in determining complete remission status after treatment with cytotoxic drugs. However, the individual variation between dogs means CRP concentration is not sufficiently different in other remission states to permit its use in monitoring progression of the disease. Greater reliability in determining remission status might be achieved by combining CRP concentration with other serum markers. 相似文献
50.
Irrigation and food security in the 21st century 总被引:1,自引:0,他引:1
Global food projections indicate that food prices in the next threedecades will likely be stable or decline, but progress inreducing malnutrition in developing countries will be slow. Smallshortfalls in crop productivity growth would lead to rising foodprices and worsening malnutrition. Increased food production fromirrigation is essential, and will require expansion of irrigatedarea and water supplies, and improved efficiency of use of existingwater supplies. Neither of these growth factors will prove easy, andboth will require complex institutional and policy reforms. Failureto meet food production needs through efficient expansion andintensification of irrigated agriculture would increase pressure onland resources and hasten the process of environmental degradation.Irrigation and water development strategies have been hampered bya lack of understanding of the links between water scarcity, foodproduction, food security, and environmental sustainability.Research to improve this understanding would have high payoffs. 相似文献