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   206285篇
  免费   10782篇
  国内免费   142篇
林业   8853篇
农学   6380篇
基础科学   1399篇
  25605篇
综合类   37135篇
农作物   8331篇
水产渔业   9861篇
畜牧兽医   103700篇
园艺   2723篇
植物保护   13222篇
  2019年   1903篇
  2018年   2773篇
  2017年   3137篇
  2016年   2913篇
  2015年   2423篇
  2014年   3052篇
  2013年   8082篇
  2012年   5741篇
  2011年   7140篇
  2010年   4717篇
  2009年   4743篇
  2008年   7112篇
  2007年   6623篇
  2006年   6228篇
  2005年   5886篇
  2004年   5710篇
  2003年   5798篇
  2002年   5376篇
  2001年   6177篇
  2000年   6246篇
  1999年   4860篇
  1998年   2181篇
  1997年   2123篇
  1996年   1979篇
  1995年   2383篇
  1994年   2163篇
  1993年   2026篇
  1992年   4126篇
  1991年   4405篇
  1990年   4258篇
  1989年   4259篇
  1988年   3931篇
  1987年   3944篇
  1986年   4108篇
  1985年   4010篇
  1984年   3240篇
  1983年   2964篇
  1982年   1964篇
  1979年   3051篇
  1978年   2465篇
  1977年   2012篇
  1976年   2056篇
  1975年   2158篇
  1974年   2623篇
  1973年   2744篇
  1972年   2612篇
  1971年   2477篇
  1970年   2324篇
  1969年   2292篇
  1967年   1957篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
Eighty-four male white leghorn chickens were killed by CO2 gas to determine the type, rate, and sequence of microscopic postmortem changes in the adrenal glands of dry and wet intact carcasses. They were held at 29 or 18 C with 50% relative humidity for different times postmortem. The sequence of microscopic postmortem changes was similar in all chickens except at 18 C, when karyorrhexis of cortical and medullary cells was observed. Cellular changes occurred earlier at 29 C than at 18 C and in dry chickens but not in chickens wet with detergent solution before storage, although slight quantitative and qualitative differences between wet and dry chickens were noted. Medullary cells underwent postmortem changes earlier than cortical cells. Nuclei of medullary cells decreased in size, with chromatin clumping leading to pyknosis, followed by cytoplasmic vacuolation, cellular shrinkage, and finally karyolysis and cell dissociation. Cortical cells had nuclear chromatin marginated, nuclei reduced in size initially, and some nuclear fading, followed by pyknosis and karyolysis. Karyorrhexis was not a prominent feature of cortical and medullary cells, although it occasionally occurred before pyknosis. Cytoplasm of cortical cells remained eosinophilic, granular, and vacuolated, but vacuoles became finer later. Pyknotic medullary cells with vacuolated cytoplasm were observed as early as 3 hr postmortem, regardless of the temperature. Diffuse pyknosis of medullary cells was noted at 18 hr in chickens held at 29 C and at 48 hr in chickens held at 18 C. Marked cortical pyknosis was noted only at 36 hr in wet chickens held at 29 C, when bacterial invasion started. Dry chickens held 36 hr at 29 C had diffuse cellular dissociation, karyolysis and cytoplasmic acidophilia, and marked bacterial invasion. Erythrocytes were pyknotic and had cytoplasmolysis. It was concluded that adrenal glands may still be useful for histopathological examination before 18 hr at 29 C and before 48 hr at 18 C.  相似文献   
992.
993.
1. Activities of lipogenic enzymes and plasma very low density lipoprotein (VLDL) concentrations were measured in lines of chickens with large differences in food conversion efficiency (FCE) and body fat.

2. Hepatic activities of malate dehydrogenase [EC 1.1.1.40 (MD)] and ATP citrate lyase [EC 4.1.3.8 (CL)] were correlated with the proportion of both abdominal and total body fat (r = 0·50) but were poorly correlated with gain:food ratio.

3. Activities of MD and CL in plasma were low and variable and were not correlated with any other characteristics.

4. Plasma VLDL concentration was significantly correlated with the proportion of abdominal and total body fat (r = 0·59), and gain: food ratio (r = 0·36).

  相似文献   
994.
995.
A modified lateral spinal decompression technique was performed in 61 dogs with thoracolumbar disc protrusion. Myelography combined with plain radiography and neurological examination determined the side of greatest compression in 93 per cent of the dogs. Disc material was retrieved in 98 per cent of the cases. Of the 35 non-ambulatory dogs, 95 per cent regained the ability to walk. The recovery time was three weeks.  相似文献   
996.
Abass, B.T., Weaver, B.M.Q., Staddon, G.E., Waterman, A.W. Pharmacokinetics of thiopentone in the horse. J. vet. Pharmacol. Therap . 17 , 331–338.
The pharmacokinetics of thiopentone sodium administered intravenously as a single dose (11 mg/kg) were studied in acepromazine pre-medicated horses and ponies in which anaesthesia was maintained with either halothane (Group 1) or isoflurane (Group 2). The results showed that the disposition kinetics of thiopentone in horses and ponies were best described by a three-compartment open model. In plasma, a very short initial distribution phase in both horses and ponies, half-life 1.4 ± 1.2 min (mean ± SD) and 1.3 ± 0.7 min, respectively, was obtained, which was followed by a second comparatively slower redistribution phase, half-life 16 ± 12 min and 11 ± 5 min, respectively. The volume of distribution for the drug was large, especially in the ponies which received isoflurane (1127 ± 86 ml/kg). compared to the horses which received halothane (742 ± 89 ml/kg). The drug had a somewhat shorter elimination half-life in the horses (147 ± 21 min) than in the ponies (222 ± 44 min), but no obvious difference in clearance of the drug was observed between the horses (3.5 ± 0.5 ml/min/kg) and ponies (3.6 ± 0.8 ml/min/kg).  相似文献   
997.
An animal trauma triage (ATT) scoring system was devised to provide stratification of veterinary trauma patient populations based upon severity of injury. A retrospective population of 101 trauma patients and a prospective population of 88 patients were used to evaluate the predictive power of the ATT scoring system for survival seven days after initial presentation of the emergency service. In Both groups, the mean ATT score for survivors was significantly lower than the mean ATT score for non-survivors. In a logistic regression mode, the ATT score was found to be a significant predictor of the likelihood of survival seven days after initial presentation for both populartions. Each point increase in the ATT score resulted in a 2.3–2.6 times decreased likelihood of survival. The ATT scoring system is a useful objective classification scheme for predicting the likelihood to survive a traumatic incident and can serve as prototype for severity of injuroy scoring systems for the veterinary trauma patient.  相似文献   
998.
999.
A corn culture of Fusarium roseum was added to a standard corn-soybean swine gestation ration. Low, middle, and high dosage mixed feeds contained 7, 38, and 64 mg of zearalenone/kg of feed (7, 38, and 64 ppm) and 0.5, 2.5, and 4.5 mg of deoxynivalenol/kg, respectively. Control feed was the standard ration without added F roseum corn culture. Mature gilts were bred by natural service and fed control or F roseum molded feed from 3 to 34 days after breeding. The main effect of the molded feed was an inhibition of fetal development, with decreased numbers of fetuses present in treated animals at slaughter (38 to 43 days after breeding). Normal litters were present in 7 of 8 control animals, in 2 of 4 gilts given the low-dosage feed, in 1 of 4 gilts given the medium dosage, and in 0 of 4 given the high-dosage feed. Corpora lutea were maintained in all treated animals, as evidenced by serum progesterone concentrations. Serum estradiol concentrations were decreased in gilts in the middle- and high-dosage groups. The genital system of the gilts fed low- and middle-dosage feeds had a gross and microscopic appearance similar to that of the pregnant controls and reflected prolonged progesterone stimulation. Morphologic changes in the genital system of the high-dosage group were intermediate between changes induced by progesterone and those induced by estrogen. Clinical signs of hyperestrogenism and partial feed refusal were noticed in only some of the high-dosage group animals.  相似文献   
1000.

Epizootiological aspects of porcine respiratory diseases which were encountered in Quebec from September 1980 until February 1981  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