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   78037篇
  免费   3526篇
  国内免费   1842篇
林业   4478篇
农学   4227篇
基础科学   1929篇
  8896篇
综合类   19015篇
农作物   3278篇
水产渔业   2997篇
畜牧兽医   33199篇
园艺   1099篇
植物保护   4287篇
  2021年   812篇
  2020年   818篇
  2019年   882篇
  2018年   897篇
  2017年   1125篇
  2016年   1059篇
  2015年   1141篇
  2014年   1264篇
  2013年   2706篇
  2012年   2243篇
  2011年   2394篇
  2010年   1938篇
  2009年   1718篇
  2008年   2301篇
  2007年   2286篇
  2006年   2260篇
  2005年   2127篇
  2004年   1694篇
  2003年   1705篇
  2002年   1621篇
  2001年   1751篇
  2000年   1798篇
  1999年   1641篇
  1998年   943篇
  1997年   849篇
  1996年   812篇
  1995年   878篇
  1994年   780篇
  1992年   1490篇
  1991年   1525篇
  1990年   1575篇
  1989年   1623篇
  1988年   1504篇
  1987年   1417篇
  1986年   1471篇
  1985年   1446篇
  1984年   1200篇
  1983年   1056篇
  1979年   1128篇
  1978年   916篇
  1977年   819篇
  1976年   768篇
  1975年   860篇
  1974年   1126篇
  1973年   1063篇
  1972年   1128篇
  1971年   1080篇
  1970年   1023篇
  1969年   874篇
  1967年   844篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Genetic diversity within and among 20 herbicide-resistant (HR) and 16 herbicide-susceptible (HS) Avena fatua multi-field populations was determined using 82 polymorphic loci resulting from two intersimple sequence repeat (ISSR) primers and one long-primer random amplified polymorphic DNA (LP-RAPD) primer. Collections from the Red River Valley of North Dakota and Minnesota, sampled in 1964 and 2000, represented A. fatua populations before and after intensive exposure to herbicides. A 1995 collection from south-west North Dakota represented A. fatua exposed to low herbicide selection. Despite differences in years of herbicide exposure among collections, both HR and HS populations from every collection maintained nearly similar levels of ISSR and RAPD diversity. Genetic differentiation among populations (GST) varied from 11% to 13% among HR populations and from 9% to 16% among HS populations, indicating that 84–91% of total variation remained within HS or within HR populations. Minimal difference in gene diversity between HR and HS is consistent with multiple origins of resistance, where HR A. fatua most likely evolved from diverse founding individuals.  相似文献   
103.
Canine distal renal tubular acidosis and urolithiasis   总被引:1,自引:0,他引:1  
Distal RTA is characterized by decreased distal renal tubular hydrogen ion secretion, decreased ability to acidify urine, hypercalciuria, hyperphosphaturia, hypocitraturia, and metabolic acidosis. Because of the resulting alterations in urine composition and pH, patients with distal RTA are predisposed to urolithiasis and renal calcification. Diagnosis of distal RTA is important because it is a potentially reversible disorder that, left untreated, may cause nephrocalcinosis, recurrent urolith formation, moderate to severe metabolic acidosis, and renal failure.  相似文献   
104.
针对采暖设计中的一些问题,提倡以自然科学理论指导采暖设计和设计上的创新,建议采暖设计规范化。  相似文献   
105.
The medical records from 95 cases of coxofemoral luxation in dogs and cats were reviewed. Unilateral craniodorsal luxation was most common, (78.1% of dogs, 72.7% of cats). Trauma from being struck by an automobile was the most frequent cause (59.0%). Treatment was closed (manual) or open (surgical) reduction. The failure rate following single closed reduction was 64.8%. The surgical reduction procedure included capsular repair (capsulorrhaphy) via a craniolateral approach to the hip or via trochanteric osteotomy or gluteal tenotomy. The success rate following reduction via the craniolateral approach was 82%; no failure was recorded with trochanteric transposition, but reluxa-tion followed the single gluteal tenotomy. The Ehmer sling was the most common external fixation and was kept in place an average of 12.5 days. Thirty-three animals were available for follow-up, and no difference was recorded in limb function between the two groups of animals treated by closed vs surgical reduction. Patients with degenerative joint disease at the time of luxation were less likely to be successfully reduced; 64.3% of these animals were eventually treated by femoral head and neck excision. Thirty-eight patients had associated major injuries. Long-term follow-up results were better in those patients with concomitant orthopedic injuries than in those without other injuries.  相似文献   
106.
107.
108.
109.
110.
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