首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   145571篇
  免费   8126篇
  国内免费   85篇
林业   5380篇
农学   4353篇
基础科学   1029篇
  16816篇
综合类   25419篇
农作物   5402篇
水产渔业   7307篇
畜牧兽医   75981篇
园艺   1768篇
植物保护   10327篇
  2018年   1791篇
  2017年   1977篇
  2016年   1857篇
  2015年   1624篇
  2014年   1982篇
  2013年   5397篇
  2012年   3799篇
  2011年   4773篇
  2010年   2949篇
  2009年   2988篇
  2008年   4702篇
  2007年   4484篇
  2006年   4352篇
  2005年   4051篇
  2004年   3949篇
  2003年   3947篇
  2002年   3874篇
  2001年   4690篇
  2000年   4538篇
  1999年   3691篇
  1998年   1463篇
  1997年   1488篇
  1996年   1393篇
  1995年   1744篇
  1994年   1577篇
  1993年   1503篇
  1992年   3150篇
  1991年   3279篇
  1990年   3323篇
  1989年   3321篇
  1988年   3050篇
  1987年   3132篇
  1986年   3222篇
  1985年   3087篇
  1984年   2606篇
  1983年   2309篇
  1982年   1574篇
  1981年   1471篇
  1980年   1427篇
  1979年   2316篇
  1978年   1909篇
  1977年   1623篇
  1976年   1441篇
  1975年   1540篇
  1974年   2074篇
  1973年   2086篇
  1972年   2053篇
  1971年   1816篇
  1970年   1712篇
  1969年   1571篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
951.
952.
Efficient oral endotracheal intubation of laboratory animals is a challenging technique in veterinary research. This study introduces a miniaturized lighted stylet for rabbit intubation. An experiment with repeated measures on two factors was used to assess the feasibility and efficacy of this method. The first factor compared stylet intubation vs. laryngoscopic intubation. The second compared three practitioners, one with prior experience and two without. Success rates on the initial attempt were not statistically different (χ2 = 2.46, P = 0.12). The time difference between methods was significant (F = 41.007, P < 0.001), although the effect of practitioners was not (F = 1.038, P = 0.365). The mean ± SD of the intubation time, combining results from the three practitioners, was 20.34 ± 17.15 s for the stylet method and 57.58 ± 64.21 s for the laryngoscopic method. The results of this study demonstrate that lighted stylet intubation is efficient, robust, and independent of practitioner experience.  相似文献   
953.
954.
955.
Cryptorchidism is a developmental disorder which can be diagnosed by a variety of different tests. Still, equine field veterinarians often rely on endocrine markers to detect retained testicular tissue. This report describes the value of anti-Müllerian hormone (AMH) as a diagnostic marker for cryptorchidism in three stallions suspected of cryptorchidism, with equivalent serum testosterone concentrations. A single measurement of AMH identified cryptorchidism, with inconclusive testosterone concentrations as either gelding or stallion. Furthermore, a human chorionic gonadotropin (hCG) stimulation test or surgery was performed to support the diagnostic value of AMH. To conclude, the endocrine panel for cryptorchidism should be expanded to include determination of serum AMH, as this determination can increase the diagnostic accuracy of a single blood sample.  相似文献   
956.
957.
958.
Faecal nitrogen (FN) concentration is used as a marker for habitat quality and digestive efficiency in free‐ranging herbivores. In herbivores, FN can be separated into undigested plant N (analysed as the N concentration of the neutral detergent residue) and metabolic faecal N (MFN). It has been suggested that by differential analysis of the faecal fibre‐bound N, the MFN fraction can be further split into a bacterial N and an endogenous N fraction [Hesta et al., Br. J. Nutr. 90 (2003) 1007]. We applied these methods to 96 faecal samples of 48 mammalian herbivore species from zoos. Species were grouped into coprophageous and non‐coprophageous hindgut fermenters and ruminating and non‐ruminating foregut fermenters. Diet was not controlled. The FN decreased with body mass, possibly reflecting higher proportions of concentrates in diets of smaller animals. The proportion of MFN increased with FN, indicating that higher quality food might enhance the gastrointestinal bacterial flora. The only outlier to this pattern was the lesser panda (Ailurus fulgens), confirming the low relevance of fermentative digestion in this herbivorous ‘carnivore’. No relevant differences between the four digestion types were noted. The proportion of endogenous faecal N (32–80% of FN) was always higher than that of bacterial faecal N (7–30%), which contradicts basal understanding of herbivore digestive physiology. Thus, the method of Hesta et al. (2003) does not appear applicable to herbivores. While the results do not exclude the possibility that detailed differences might occur between digestion types, they indicate a high degree of similarity between herbivores that rely on bacterial fermentation, regardless of their digestion type, with respect to metabolic faecal losses.  相似文献   
959.
Reasons for performing study: Type 2 diabetes mellitus (T2DM) is diagnosed rarely in equine practice although it may be under‐recognised. A greater awareness of the condition and therapeutic considerations would be to the benefit of such cases presenting in practice. More investigation into the pharmacological management of these cases is needed. Objectives: Three cases of diabetes mellitus were investigated using a specific test for insulin sensitivity and pancreatic β cell function in order to define accurately and characterise the existence of T2DM in all 3 subjects. Methods: The insulin‐modified frequently sampled i.v. glucose tolerance test was performed in each case and the data so obtained were subject to minimal model analysis of insulin‐glucose dynamics. Cases were then monitored following treatment using a combination of dietary modification, metformin, glibenclamide and pergolide. Results: Marked insulin resistance was identified in each case and, furthermore, severe pancreatic β cell dysfunction was present therefore classifying each case as end stage T2DM. Treatment was nevertheless associated with restoration of normoglycaemia in all cases. Conclusions: T2DM in horses may be more common than generally considered. In some cases individuals may respond to therapy aimed at restoring insulin sensitivity and pancreatic function. Drugs used in other species for the treatment of T2DM have not yet been adequately tested in horses. Potential relevance: T2DM should be considered as an important differential diagnosis in mature to elderly horses and ponies suffering from weight loss, polydipsia and polyuria. Clinicians should be encouraged to offer treatment and management advice when such cases are encountered.  相似文献   
960.
This report describes a successful surgical repair of medial patellar luxation in a Miniature Shetland pony where manual reduction of the patella was not possible. The surgical procedure involves transection of the medial femoropatellar ligament to facilitate patellar release, the placement of a prosthetic suture to replace the lateral femoropatellar ligament and reinforcement of the lateral retinaculum by the use of a mesh implant. This is a newly described surgical technique for the rare but recognised condition of a medial luxation of the patella.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号