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   38185篇
  免费   2239篇
  国内免费   285篇
林业   1576篇
农学   1412篇
基础科学   324篇
  5481篇
综合类   5650篇
农作物   1486篇
水产渔业   1796篇
畜牧兽医   19855篇
园艺   456篇
植物保护   2673篇
  2021年   363篇
  2020年   423篇
  2019年   468篇
  2018年   785篇
  2017年   829篇
  2016年   747篇
  2015年   626篇
  2014年   782篇
  2013年   1828篇
  2012年   1309篇
  2011年   1527篇
  2010年   1055篇
  2009年   1089篇
  2008年   1476篇
  2007年   1327篇
  2006年   1254篇
  2005年   1077篇
  2004年   1035篇
  2003年   1028篇
  2002年   910篇
  2001年   1244篇
  2000年   1230篇
  1999年   927篇
  1998年   387篇
  1997年   418篇
  1996年   341篇
  1995年   391篇
  1994年   341篇
  1992年   656篇
  1991年   780篇
  1990年   685篇
  1989年   720篇
  1988年   661篇
  1987年   623篇
  1986年   666篇
  1985年   591篇
  1984年   462篇
  1983年   412篇
  1979年   553篇
  1978年   431篇
  1977年   358篇
  1976年   365篇
  1975年   396篇
  1974年   459篇
  1973年   474篇
  1972年   447篇
  1970年   366篇
  1969年   400篇
  1968年   357篇
  1967年   359篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Three experiments were conducted to examine the effects of vitamin E supplementation on feedlot cattle. Vitamin E supplementation did not affect feedlot performance or carcass characteristics of cattle fed a high-concentrate diet (P greater than .1). The major finding was the effectiveness of vitamin E in extending the color stability of displayed beef (P less than .01). Color stability during display of longissimus lumborum steaks from cattle supplemented with 300 IU/d for 266 d, 1,140 IU/d for 67 d, or 1,200 IU/d for 38 d was extended by 2.5 to 4.8 d. Gluteus medius steaks had an extended color display life of 1.6 to 3.8 d. The accumulation of lipid oxidation products, but not aerobic microbes, associated with displayed longissimus lumborum was suppressed for muscle from vitamin E-supplemented steers. Taste panelists detected no difference among longissimus lumborum steaks from control and vitamin E-supplemented steers but found (P less than .01) steaks aged for 21 d to be more tender than steaks aged for 7 d. Supplementing cattle with vitamin E should reduce economic losses associated with discolored beef during retail display.  相似文献   
82.
83.
Seven wild-caught ball pythons (Python regius), including six gravid females and one male, were obtained from Africa and were housed in a government animal facility in Research Triangle Park, North Carolina. Upon arrival, the snakes were found to be infested with ticks (Aponomma latus), which were manually removed. Four weeks following arrival, vesicular skin lesions began to appear on the snakes. Despite treatment of all affected female snakes with amikacin (5 mg/kg i.m., every 3 days) and cefotaxime (25 mg/kg i.m., every 3 days), the condition progressed and five of the female snakes died 7 wk after arrival. The remaining male and one female improved after an increase in environmental temperature, with ecdysis followed by healing. Physiologic stress, ectoparasites, and shipping may have predisposed the snakes to sepsis.  相似文献   
84.
85.
1. Coir dust was evaluated as broiler litter in comparison with sawdust and rice husk using 135 commercial broilers. Forty-five broiler chicks were reared to 42 d on a 50 mm layer of each of these litters. 2. Birds reared on coir dust showed no difference in food consumption, body weight gain, food conversion efficiency production number and survivability in comparison to those reared on saw dust and rice husk. 3. It was concluded that coir dust is suitable as broiler litter when cheaply available.  相似文献   
86.
87.
88.
Home monitoring of blood glucose (HMBG) concentrations has been recommended in the monitoring of human diabetics for 3 decades. During the last number of years, it also gained popularity in long-term follow-up of diabetic cats and dogs. The aim of this retrospective study was to evaluate the practical feasibility of and identify the major problems encountered with HMBG in diabetic pets. A standard questionnaire was filled in by owners of 9 diabetic pets monitored with HMBG. The need for more than 1 puncture to obtain a blood drop, the creation of a sufficient blood drop, the need for assistance in restraining the pet, and the resistance of the pet were the most frequently encountered problems during HMBG. The major obstacles for the owners to start with HMBG were also identified. In conclusion, HMBG is a practical and simple technique for most owners and, overall, owners were satisfied.  相似文献   
89.
AIMS: To determine the influence of copper (Cu) supplementation by injection of mares in late gestation on the frequency and severity of osteochondrosis (OC) lesions in their foals at around 160 days of age. To determine if there was any influence of the concentration of Cu in the liver, growth rate, birthweight, weight at 160 days of age, fatness, sex, or year of birth of the foal on the frequency and severity of OC lesions. To determine the influence of dam's age, and sex and birthweight of the foal on the growth rate from birth to 160 days of age, and weight at 160 days of age. METHODS: Thirty-three Thoroughbred foals, born in two consecutive years, were weighed every 2 weeks from birth. The dams had been supplemented with parenteral Cu or saline during late gestation, and the supplementation regimens were different in each year. Foals had liver biopsies harvested at birth for determination of Cu concentration. Pasture samples were collected every 4-8 weeks for analysis of concentration of Cu and zinc (Zn). At 160 days of age, articular cartilage of long bones was examined. Gross lesions were counted and scored, then sawn and radiographed, and processed for histopathology. Lesions were given radiographic scores and histopathological scores. Maximum scores for each lesion were combined to give a total OC score for each joint and each foal. The fatness of 20 foals (10 each from Years 1 and 2) at 160 days of age was determined chemically. RESULTS: Supplementation of dams with Cu had no significant effect on the concentration of Cu in the liver of foals at birth, or on the frequency or severity of lesions in articular cartilage at 160 days of age. The Cu and Zn concentrations of pasture were similar in Years 1 and 2, and were lower than current recommendations. All foals in Year 2, and 9/10 foals in Year 1 had irregularities in cartilage that was confirmed histologically to be indicative of OC. The average number of lesions per foal was 4.7 (SD 1.1) and 5.7 (SD 1.1) in Years 1 and 2, respectively. However, the severity of the lesions was considered mild, and no foals showed any clinical evidence of OC while alive. The number of lesions in the tarsocrural (TC) joint and the TC OC score at 160 days were positively associated with average daily weight gain (ADG) in the previous 4 weeks (p=0.005 and p=0.001, respectively). There was no significant effect of sex, fatness, birthweight, weight at 160 days of age, or year of birth of the foal on the frequency and severity of OC lesions. CONCLUSIONS: Many of the lesions classified as OC, using classification systems described by other authors, were likely to be normal variations of the process of endochondral ossification. Despite the high frequency of such lesions, they were considered to be of minor significance and none were clinically evident. The distribution of lesions was not typical, and most probably reflected the subtlety of the lesions. These results support the hypothesis that Cu is an over-emphasised factor in the aetiopathogenesis of OC. The relationship between subtle macroscopic lesions and lesions resulting in clinical signs of disease requires further investigation.  相似文献   
90.
A captive 16-year-old male camel (Camelus ferus bactrianus) was euthanized after a prolonged period of inappetence leading to cachexia. At necropsy, there was a 7 cm large, tan, firm, well-demarcated nodule in the tunica muscularis and serosa of the distal region of C3. Histologically, a gastric adenocarcinoma was diagnosed. Numerous metastases were found in the liver and the hepatic lymph nodes, in the wall of the portal vein and the aorta, in the lung, heart, and pleura parietalis. Osseous metaplasia was found within the pleural and aortic metastases. In the mucosa of the glandular region of the C3 compartment a diffuse marked hypertrophy of rugae resembling cerebral convolutions was observed. The lesion was characterized by glandular hyperplasia and stromal inflammation and oedema. These changes closely resembled Menétrier's disease described in humans. To our knowledge, this is the first report of concomitant metastatic gastric adenocarcinoma and gastric hyperplasia in a camel.  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