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   135810篇
  免费   7794篇
  国内免费   70篇
林业   5653篇
农学   4645篇
基础科学   862篇
  17502篇
综合类   18969篇
农作物   5092篇
水产渔业   7109篇
畜牧兽医   73013篇
园艺   1799篇
植物保护   9030篇
  2020年   1176篇
  2019年   1411篇
  2018年   2233篇
  2017年   2492篇
  2016年   2301篇
  2015年   2003篇
  2014年   2454篇
  2013年   5748篇
  2012年   4359篇
  2011年   5172篇
  2010年   3510篇
  2009年   3551篇
  2008年   5161篇
  2007年   4979篇
  2006年   4652篇
  2005年   4268篇
  2004年   4114篇
  2003年   4182篇
  2002年   3818篇
  2001年   4783篇
  2000年   4649篇
  1999年   3754篇
  1998年   1479篇
  1997年   1452篇
  1996年   1344篇
  1995年   1600篇
  1994年   1328篇
  1993年   1359篇
  1992年   2762篇
  1991年   2901篇
  1990年   2868篇
  1989年   2898篇
  1988年   2611篇
  1987年   2593篇
  1986年   2539篇
  1985年   2401篇
  1984年   1957篇
  1983年   1715篇
  1982年   1155篇
  1979年   1649篇
  1978年   1284篇
  1977年   1135篇
  1976年   1100篇
  1975年   1164篇
  1974年   1357篇
  1973年   1448篇
  1972年   1379篇
  1971年   1195篇
  1970年   1247篇
  1969年   1146篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The use of live animals for educational purposes is an old practice that is still employed in teaching and research institutions. However, there are several objections to this practice, whether for ethical or humanitarian reasons. Surgical techniques teaching using anatomical pieces and/or preserved cadavers promotes greater learning efficiency, provides exercise repetition and increases the confidence and satisfaction of the students when compared to the use of live animals. The current work aimed to analyse the feasibility of using fresh swine urinary bladder and small intestines (jejunum), obtained from slaughterhouses, fixed in 99.8% ethyl alcohol (EA) and preserved in sodium chloride hypersaturated solution (SCHS) at 30%, for 7, 14 and 21 days, as an alternative method for surgical skills training (SST). Swine viscera, fixed in EA and preserved in SCHS, presented a realistic appearance, absence of odour and maintained the viable morphological characteristics during the performance of the operative techniques. Preservation solutions had low cost, were easy to acquire and did not offers risks to human health. Therefore, urinary bladders and small intestines fixed in 99.8% EA for 30 days and maintained in 30% SCHS at different periods were demonstrated as a good viable option as a preservation method for surgical skills training.  相似文献   
992.
993.
994.
995.
996.
997.
998.
This study aimed to determine the usefulness of colour and pulsed Doppler modes for the accurate diagnosis of donkeys suffering from subfertility to determine whether testicular vascularity assessment could be an indicator for sperm functionality. The study sample was composed of 10 male donkeys with normospermia (control group) and 10 donkeys with hypospermia. Animals underwent scrotal circumference measurement, testicular Doppler examination, seminal evaluation, blood sampling and hormonal assay. Semen volume and concentration were significantly (p ≤ .05) lower in the subfertile group (30.25 ± 1.22 ml and 89.44 ± 2.55 × 106/ml) as compared with the control group (82.76 ± 1.65 ml and 452.78 ± 1.25 × 106/ml), and total sperm/ejaculation was significantly (p ≤ .05) higher in the normal donkeys (28.30 ± 2.32 × 109/total ejaculated) as compared with the subfertile group. Intratesticular coloured area showed a marked decline in the hypospermic males. There was no significant difference between the two groups in testosterone level, although the normal group showed an increase in nitric oxide metabolites. Both Doppler indices of the three branches of the testicular artery were elevated significantly (p ≤ .05) in abnormal donkeys, whereas Doppler peak systolic and end-diastolic velocities were increased in the normal group. Male donkeys with subfertility demonstrated lower arterial vascularity parameters in the form of intratesticular coloured area and blood flow rate; therefore, the most optimal parameters for differentiating subfertile hypospermic from normospermic donkeys were found to be the two Doppler indices, velocities parameters, testicular blood flow rate and nitric oxide levels.  相似文献   
999.
This report describes the clinical course and surgical findings of a 5-year-old Warmblood gelding referred for colic with a previous history of intermittent colic episodes, and gastric ulcers diagnosed by gastroscopy in the preceding months. The horse underwent medical treatment but remained painful and surgery was elected. The horse underwent an exploratory laparotomy during which an impaction was identified in the transverse colon that was associated with an approximately 1 metre segment of nasogastric tube. The foreign body was removed via an enterotomy in the left dorsal colon, and the horse recovered well from surgery. No complications were encountered post-operatively.  相似文献   
1000.
Scirrhous cord (SC) is an uncommon complication of castration, characterised by chronic infection of the spermatic cord remnant. It is reported that surgical excision of the infected tissue is the most effective means of treatment, but there are few published studies assessing the outcomes of horses treated for SC. The aims of this retrospective study were to describe the clinical features and short-term outcomes in horses treated for SC at two equine hospitals in the UK. The clinical records of horses diagnosed with SC over a 10-year period were reviewed. A diagnosis of SC was made if the gelding presented with typical clinical signs with confirmation at surgery. Thirty-two cases of SC were identified at the two equine hospitals. The mean age at presentation was 6 years (range 2–14 years, n = 22), and the median time from castration to presentation was 29.5 days (range 20–2500 days). Mean age at castration was 4.3 years (range 6 months to 10 years, n = 10). Clinical signs included scrotal swelling, discharging wounds, hindlimb lameness and pyrexia. Five horses demonstrated hyperfibrinogenaemia (n = 8). Microbial culture isolated various bacterial species. All 32 cases were treated with surgical excision of the infected tissue and discharged from the hospitals between 1 and 10 days post-operatively. A limitation of this study is that it was a retrospective study with no long-term follow-up available. It was concluded that the results of this study confirm that SC can present at variable time points following castration, even many years later, and that a variety of bacterial species may be involved. Surgical excision of infected tissue is a successful treatment with a good short-term prognosis for survival.  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