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   145829篇
  免费   8298篇
  国内免费   83篇
林业   5384篇
农学   4360篇
基础科学   1030篇
  16861篇
综合类   25490篇
农作物   5401篇
水产渔业   7324篇
畜牧兽医   76239篇
园艺   1782篇
植物保护   10339篇
  2018年   1792篇
  2017年   1981篇
  2016年   1861篇
  2015年   1627篇
  2014年   1988篇
  2013年   5421篇
  2012年   3817篇
  2011年   4784篇
  2010年   2965篇
  2009年   2998篇
  2008年   4716篇
  2007年   4498篇
  2006年   4365篇
  2005年   4059篇
  2004年   3971篇
  2003年   3968篇
  2002年   3905篇
  2001年   4704篇
  2000年   4552篇
  1999年   3701篇
  1998年   1469篇
  1997年   1488篇
  1996年   1401篇
  1995年   1748篇
  1994年   1581篇
  1993年   1508篇
  1992年   3158篇
  1991年   3286篇
  1990年   3332篇
  1989年   3326篇
  1988年   3054篇
  1987年   3141篇
  1986年   3223篇
  1985年   3089篇
  1984年   2608篇
  1983年   2310篇
  1982年   1579篇
  1981年   1474篇
  1980年   1427篇
  1979年   2317篇
  1978年   1909篇
  1977年   1626篇
  1976年   1443篇
  1975年   1540篇
  1974年   2076篇
  1973年   2086篇
  1972年   2058篇
  1971年   1825篇
  1970年   1716篇
  1969年   1572篇
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
721.
The rapid column method described, unlike AOAC method 7.056, determines both neutral ("crude") and total fat in canned pet foods, and uses nonflammable solvent mixtures and simple laboratory equipment. Neutral fat values are obtained by eluting the column with dichloromethane, whereas total fat values are determined by using dichloromethane-methanol (9 + 1). For 7 samples analyzed in triplicate, fat ranged from 2.9 to 10.8%. Neutral fat values by the dry column method were significantly lower (P less than 0.05) than were those by 7.056 (6.29 vs 6.49), although these differences were practically unimportant. Total fat determinations by the dry column method and by 7.056 yielded overall means of 7.40 and 6.49%, respectively. The 0.91% mean difference is significant (P less than 0.01) and represents a more complete extraction of polar lipids by the proposed method.  相似文献   
722.
1. The ovulatory cycle of the domestic hen (Gallus domesticus) was postulated to be the result of the interaction of two independent systems.

2. A circadian system was postulated to control the restriction of ovulation to an 8‐h period of the day under conventional 14 h light: 10 h dark regimes.

3. The final phase of follicular maturation was postulated to commence after ovulation of the preceding ovum in the hierarchy.

4. Ovulation was postulated to occur when a mature follicle was present in the ovary during the appropriate phase of the circadian‐linked system.

5. The predicted times of oviposition were within the standard error of the observed times of oviposition under 21‐, 24‐ and 28‐h photoschedules.

6. It was concluded that this hypothesis for the control of the ovulatory cycle of the hen is consistent with current knowledge.  相似文献   

723.
1. To test the preferences of hens for particular social conditions when laying, they were provided with choices of nest‐sites varying in seclusion. Three experimental conditions were used.

2. In Experiment 1, nest‐site selection by members of a group of light hybrids was studied in a complex pen‐system. Eggs were clumped in distribution ; only one individual laid in the most secluded part of the system.

3. Experiment 2 provided light hybrids with an extensive outdoor area, but similarly clumped laying was observed; there was no indication that hens attempted to find concealment for nesting.

4. In Experiment 3, hens from a group of light hybrids just coming into lay and from a group of mature medium hybrids were tested singly, in an area that included a cage containing some of their flockmates. Most subjects from both groups laid near the other birds rather than in isolation.

5. In semi‐intensive conditions, the majority of hens are apparently gregarious rather than solitary in their nesting behaviour.  相似文献   

724.
Salmon poisoning disease in dogs has previously been reported in North America only along the western coast of the U.S.A. This paper presents the findings from eight affected dogs recently diagnosed on Vancouver Island, Canada. The clinical signs shown by these dogs were lethargy, anorexia, pyrexia and lymph node enlargement. The causative agent, Neorickettsia helminthoeca was observed in macrophages obtained from lymph node aspirates. This organism is transmitted to dogs in cysts of the fluke Nanophyetus salmincola salmincola within the tissues of the salmon or trout. The presence of fluke eggs in the feces of dogs showing typical signs is very suggestive of a diagnosis of salmon poisoning disease. Appropriate treatment, including chloramphenicol or oxytetracycline and fluid therapy, resulted in recovery. Prevention of salmon poisoning disease in endemic areas can be achieved by advising owners against allowing their dogs to eat raw salmon or trout. We suggest, based on the diagnoses made in these eight dogs, that Vancouver Island now be considered an endemic area for salmon poisoning disease.  相似文献   
725.
726.
A nine year old Hereford crossbred cow with a history of progressive neurological signs was referred to the Western College of Veterinary Medicine, Saskatoon. A large intracranial mass, histologically identified as a schwannoma, was found to be compressing the left brain stem and appeared to have arisen from the left fifth cranial nerve.  相似文献   
727.
728.
A retrospective morbidity and mortality study was carried out on 125 case records of cattle involving xylazine/halothane anesthesia at the Ontario Veterinary College, Guelph between May 1979 and February 1983.  相似文献   
729.
730.
A seven month old domestic shorthaired male cat was presented with a known history of acetaminophen ingestion. Clinical findings included icterus, depression, hypothermia, tachypnea and pronounced edema of the head and neck. Treatment was aimed at providing substrate to assist in conjugation of the drug and reversing methemoglobinemia. Administration of oral acetylcysteine, ascorbic acid and IV fluids was insufficient in this case due to a delay in initiation of treatment. The salient postmortem findings were icterus, subcutaneous and pulmonary edema and evidence of hemolysis in the liver, spleen and urinary tract.  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