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   7670篇
  免费   318篇
  国内免费   8篇
林业   340篇
农学   398篇
基础科学   90篇
  1080篇
综合类   437篇
农作物   297篇
水产渔业   237篇
畜牧兽医   4035篇
园艺   132篇
植物保护   950篇
  2023年   36篇
  2022年   34篇
  2021年   78篇
  2020年   96篇
  2019年   107篇
  2018年   122篇
  2017年   126篇
  2016年   132篇
  2015年   112篇
  2014年   155篇
  2013年   533篇
  2012年   360篇
  2011年   416篇
  2010年   217篇
  2009年   209篇
  2008年   378篇
  2007年   381篇
  2006年   315篇
  2005年   321篇
  2004年   322篇
  2003年   279篇
  2002年   275篇
  2001年   251篇
  2000年   227篇
  1999年   212篇
  1998年   62篇
  1997年   58篇
  1996年   66篇
  1995年   67篇
  1994年   46篇
  1993年   55篇
  1992年   113篇
  1991年   123篇
  1990年   145篇
  1989年   122篇
  1988年   112篇
  1987年   91篇
  1986年   77篇
  1985年   92篇
  1984年   76篇
  1983年   50篇
  1982年   37篇
  1981年   45篇
  1980年   48篇
  1979年   48篇
  1974年   31篇
  1973年   32篇
  1972年   40篇
  1971年   42篇
  1969年   31篇
排序方式: 共有7996条查询结果,搜索用时 62 毫秒
991.
Sorghum (Sorghum bicolor (L.) Moench) is an important food crop in arid and semi-arid tropics where it is grown mainly due to its drought tolerance. In Ethiopia, sorghum is grown in different agro-ecological zones primarily for food. Landraces are widely cultivated in the region due to their adaptation to the growing conditions and other characteristics such as food quality, quantity, and quality of by-products. The objective of this research was to determine the genetic variation in protein, mineral composition, total starch and its components in sorghum landraces collected from the western regions of Ethiopia. Sorghum whole grains were analyzed for crude protein, total starch and its components, and mineral profile (calcium, magnesium, potassium, phosphorus, iron, manganese, zinc, and sodium). The analysis of variance showed significant differences among the sorghum landraces in nutritional composition. There was highly significant correlation between phosphorus and magnesium, and between zinc and phosphorus and protein which indicated that some interaction existed in absorption and translocation between minerals and protein content. The genetic variation found among the sorghum landrace accessions in chemical composition can be exploited in the breeding program.  相似文献   
992.
993.
994.
995.
The objective of this study was to determine the effect of dietary nitrate on methane emission and rumen fermentation parameters in Nellore × Guzera (Bos indicus) beef cattle fed a sugarcane based diet. The experiment was conducted with 16 steers weighing 283 ± 49 kg (mean ± SD), 6 rumen cannulated and 10 intact steers, in a cross-over design. The animals were blocked according to BW and presence or absence of rumen cannula and randomly allocated to either the nitrate diet (22 g nitrate/kg DM) or the control diet made isonitrogenous by the addition of urea. The diets consisted of freshly chopped sugarcane and concentrate (60:40 on DM basis), fed as a mixed ration. A 16-d adaptation period was used to allow the rumen microbes to adapt to dietary nitrate. Methane emission was measured using the sulfur hexafluoride tracer technique. Dry matter intake (P = 0.09) tended to be less when nitrate was present in the diet compared with the control, 6.60 and 7.05 kg/d DMI, respectively. The daily methane production was reduced (P < 0.01) by 32% when steers were fed the nitrate diet (85 g/d) compared with the urea diet (125 g/d). Methane emission per kilogram DMI was 27% less (P < 0.01) on the nitrate diet (13.3 g methane/kg DMI) than on the control diet (18.2 g methane/kg DMI). Methane losses as a fraction of gross energy intake (GEI) were less (P < 0.01) on the nitrate diet (4.2% of GEI) than on the control diet (5.9% of GEI). Nitrate mitigated enteric methane production by 87% of the theoretical potential. The rumen fluid ammonia-nitrogen (NH(3)-N()) concentration was significantly greater (P < 0.05) for the nitrate diet. The total concentration of VFA was not affected (P = 0.61) by nitrate in the diet, while the proportion of acetic acid tended to be greater (P = 0.09), propionic acid less (P = 0.06) and acetate/propionate ratio tended to be greater (P = 0.06) for the nitrate diet. Dietary nitrate reduced enteric methane emission in beef cattle fed sugarcane based diet.  相似文献   
996.
A good intake of fluids and essential nutrients in the first fourteen days is of vital importance to recuperating animals. Moreover, it is important to encourage cats and dogs to eat after illness or surgery, in order to promote optimal functioning of the gut and the immune system. Enteral nutrition is to be preferred to nasogastric feeding or parenteral nutrition. In the first stage of recovery, during the first 24 to 48 hours, it is important to feed the gut' with nutrients, and thereafter, in the second stage of recovery (after day 3), the calorie intake can be increased. Timely nutritional support with nutraceuticals, such as arginine, glutamine, taurine, long-chain polyunsaturated omega-3 fatty acids, and prebiotic fibres, can considerably shorten the recovery period of cats and dogs after illness or surgery  相似文献   
997.
998.
999.
1000.
CKRD     
Boersma A  van Look W 《Tijdschrift voor diergeneeskunde》2012,137(5):341; discussion 341
  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