全文获取类型
收费全文 | 132460篇 |
免费 | 7269篇 |
国内免费 | 93篇 |
专业分类
林业 | 5381篇 |
农学 | 4269篇 |
基础科学 | 831篇 |
17035篇 | |
综合类 | 21482篇 |
农作物 | 5393篇 |
水产渔业 | 6688篇 |
畜牧兽医 | 67961篇 |
园艺 | 1800篇 |
植物保护 | 8982篇 |
出版年
2020年 | 1177篇 |
2019年 | 1375篇 |
2018年 | 2031篇 |
2017年 | 2330篇 |
2016年 | 2095篇 |
2015年 | 1742篇 |
2014年 | 2224篇 |
2013年 | 5290篇 |
2012年 | 4114篇 |
2011年 | 5093篇 |
2010年 | 3245篇 |
2009年 | 3389篇 |
2008年 | 4971篇 |
2007年 | 4666篇 |
2006年 | 4353篇 |
2005年 | 4088篇 |
2004年 | 3850篇 |
2003年 | 3973篇 |
2002年 | 3542篇 |
2001年 | 4150篇 |
2000年 | 4252篇 |
1999年 | 3372篇 |
1998年 | 1474篇 |
1997年 | 1387篇 |
1996年 | 1288篇 |
1995年 | 1529篇 |
1994年 | 1358篇 |
1993年 | 1231篇 |
1992年 | 2584篇 |
1991年 | 2700篇 |
1990年 | 2591篇 |
1989年 | 2611篇 |
1988年 | 2368篇 |
1987年 | 2348篇 |
1986年 | 2427篇 |
1985年 | 2340篇 |
1984年 | 1881篇 |
1983年 | 1677篇 |
1982年 | 1149篇 |
1979年 | 1748篇 |
1978年 | 1397篇 |
1977年 | 1151篇 |
1976年 | 1212篇 |
1975年 | 1292篇 |
1974年 | 1500篇 |
1973年 | 1514篇 |
1972年 | 1405篇 |
1971年 | 1304篇 |
1970年 | 1251篇 |
1969年 | 1283篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Gardner RB Hart KA Stokol T Divers TJ Flaminio MJ 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2006,20(1):198-203
A 5-week-old Fell Pony colt was examined for fever, lethargy, and anemia. The colt had been lethargic for 1 week before examination, had continued to nurse, had a temperature of 104°F (40°C), and was treated with ceftiofur (5 mg/kg IM q12h). Approximately 36 hours before examination, the colt developed watery diarrhea. Blood work performed by the referring veterinarian on the day of admission revealed a PCV of 10%. 相似文献
993.
J.C. Bambou W. Cei S. Camous H. Archimède A. Decherf L. Philibert C. Barbier N. Mandonnet E. González-García 《Veterinary parasitology》2013,191(3-4):284-292
The objective of this study was to compare the effects of the type of Haemonchus contortus experimental infection (trickle infection, TI versus single infection, SI) on feed intake, nutrients digestibility, parasitological and haematological measures, and plasma leptin in Creole kids. The animals were infected over 2 periods (challenge 1 and challenge 2) of 6 weeks each, corresponding respectively to the primary and the secondary infection. Periods prior infection (1 week each) were considered as controls. The primary infection was realized with 35 Creole kids (18.40 ± 3.76 kg BW) housed in individual boxes and fed a hay-based diet. The secondary infection continued with 29 kids (21.90 ± 3.40 kg BW) from the initial 35. A total of 6 kids and 8 kids were slaughtered for measuring nematode burden at the end of the primary and the secondary infection, respectively. Measurements of nutrients digestibility were made at 0, 3 and 5 weeks post-infection for both challenges. Faecal egg count (FEC), blood eosinophilia and packed cell volume (PCV) were monitored weekly. Feed intake (dry matter intake, DMI) and nutrients digestibility were negatively affected by H. contortus infection only during the primary infection. Plasma leptin changed significantly over time (P = 0.0002) but was not affected by the infection type. Effect of infection type was observed only on crude protein digestibility during the primary infection, which was lower in the TI group (P < 0.01). The overall level of blood eosinophilia was significantly higher in the TI group (P < 0.0001) during both challenges. The overall FEC mean was significantly higher in the SI compared with the TI groups, during both challenges (P < 0.02). These results were related to the mean female length significantly higher in the SI group compared with the TI group during challenge 1 (P = 0.004), and the number of adult nematode significantly lower in the TI group compared with the SI group during the challenge 2 (P = 0.05). The results showed that the response of Creole kids to H. contortus experimental infection was in part dependent on the type of experimental infection. Our data suggest that plasma leptin would not be involved in the response of Creole kids against H. contortus infection, as no relationship between its plasma level and the transient reduction in voluntary feed intake observed in both groups during the primary infection was observed. 相似文献
994.
Terrie A. Becerra David M. Engle R. Dwayne Elmore Samuel D. Fuhlendorf 《Strength and Conditioning Journal》2013,66(5):529-538
Recent opposition to the rangeland management paradigm of achieving uniform, moderate grazing across entire landscapes has emerged because heterogeneity is recognized as the foundation of biodiversity, ecosystem resilience, and multifunctionality of agricultural landscapes. Agriculture production goals appear to drive the traditional rangeland management focus on homogeneity and uniformity. To determine if preference for homogeneity is a broadly applicable social construct or one limited to agricultural producers, we determined preferences for heterogeneous grassland landscapes expressed by three study populations—managers of working lands (ranchers), natural resource professionals (grassland/rangeland specialists), and the general population living in rangeland regions within the US Great Plains. We distributed surveys that included photographs of landscapes and patterned images to assess preference. Preference for heterogeneous landscapes among ranchers, natural resource professionals, and the general population in our study area were generally consistent with the central paradigm of managing rangeland for homogeneity. However, we discovered that people, across geographic location and population group, clearly prefer heterogeneous patterned images to homogeneous patterned images. This suggests that preference for homogeneity is acquired. 相似文献
995.
A bicuspid aortic valve (BAV) demonstrating moderate valvular stenosis and mild insufficiency was identified in an asymptomatic 1-year-old male cryptorchid English bulldog by transthoracic and transesophageal echocardiography. The BAV was most consistent with type 3 morphology, based upon human classification. Pulmonary valve dysplasia with mild pulmonary stenosis and a suspected persistent left cranial vena cava were also identified. Although BAV is the most common congenital cardiac malformation in humans, it is rare in the dog. 相似文献
996.
997.
Lenhardt L Cigankova V Zibrin M Kocisova J Tomkova I Sabo V Boda K Dadasheva OA Gurieva TS Mozes S 《Acta veterinaria》2001,70(2):127-131
The effect of microgravity on functional development of the small intestine of Japanese quails incubated for 2-3 d and hatched on the orbital station MIR was examined. After 5 d of space flight duodenal and jejunal alkaline phosphatase (AP) activity of the experimental group was compared with the AP activity in quails of the same age hatched on the Earth (laboratory controls). Short-term microgravity leading to decreased food intake resulted in significant increase of AP activity in both duodenal and jejunal enterocytes (P<0.001) of the experimental quails. The results suggest that increased AP activity probably reflects the delayed functional development of the small intestine as a consequence of inappropriate food intake during non-physiological conditions of space flight. 相似文献
998.
Sokkar SM Hamouda MA El-Rahman SM 《Journal of veterinary medicine. B, Infectious diseases and veterinary public health》2001,48(7):529-536
The endometrial necropsies of 165 she donkeys were examined and the endometria were classified into four grades according to histological features (I, IIa, IIb, III). Category I was observed in 86 cases (52.12%) and diagnosed as normal endometria. Category IIa was observed in 18 cases (10.91%) and diagnosed as slight endometritis. Category IIb was observed in 28 cases (16.97%) and diagnosed as moderate endometritis (two to four nests/field), while category III was observed in 33 cases (20%) and diagnosed as severe endometritis (eight nests/field). A bacteriological examination was carried out and oestrogen and progesterone were estimated. Our results indicate that endometritis and the prognosis of fertility in she donkeys were more or less parallel to mares. 相似文献
999.
Interstitial lung disease in West Highland White Terriers 总被引:3,自引:0,他引:3
Progressive respiratory failure and pulmonary fibrosis in West Highland White Terriers (WHWT) is an apparently genetic disorder of unknown pathogenesis. This study characterizes the light microscopic, ultrastructural, and immunohistochemical features of affected WHWT in comparison with lesions in usual interstitial pneumonia (UIP) of humans. Lesions in WHWT were confined to the expansion of the interstitial space of alveolar septa by extracellular matrix (ECM) determined to be mixtures of type-I and -III collagens. Features of UIP such as intra-alveolar fibroblastic foci, subpleural distribution, and honeycombing were not observed in six WHWT. Comparison with normal dogs showed no apparent increase in septal myofibroblasts. Ultrastructually, the ECM in alveolar septa consisted of large aggregates of periodic collagen filaments underlying alveolar capillaries that were surrounded by thick bands of amorphous to fine fibrillar matrix. This study suggests that chronic pulmonary disease of WHWT is a result of aberrant collagen regulation. 相似文献
1000.
Jacob F Polzin DJ Osborne CA Neaton JD Kirk CA Allen TA Swanson LL 《Journal of the American Veterinary Medical Association》2005,226(3):393-400
OBJECTIVE: To determine whether urine protein-to-creatinine ratio (UP:C) > or = 1.0 at initial diagnosis of chronic renal failure (CRF) is associated with greater risk of development of uremic crises, death, and progression of renal failure in dogs. DESIGN: Prospective cohort study. ANIMALS: 45 dogs with CRF PROCEDURE: Dogs were prospectively assigned to 2 groups on the basis of initial UP:C < 1.0 or 2 > or = 1.0. The association between magnitude of proteinuria and development of uremic crises and death was determined before and after dogs with initial UP:C > or =1.0 were assigned to 3 subgroups and compared with dogs with initial UP:C < 1.0. Changes in reciprocal serum creatinine concentration were used to estimate decrease in renal function. RESULTS: Initially, dogs had similar clinical characteristics with the exception of systolic blood pressure and UP:C. Relative risks of development of uremic crises and death were approximately 3 times higher in dogs with UP:C > or =1.0, compared with dogs with UP:C < 1.0. Relative risk of adverse outcome was approximately 1.5 times higher for every 1-unit increment in UP:C. The decrease in renal function was of greater magnitude in dogs with UP:C > or =1.0, compared with dogs with UP:C < 1.0. CONCLUSIONS AND CLINICAL RELEVANCE: Initial UP:C > or =1.0 in dogs with CRF was associated with greater risk of development of uremic crises and death, compared with dogs with UP:C < 1.0. Initial determinations of UP:C in dogs with naturally occurring CRF may be of value in refining prognoses. 相似文献