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   93246篇
  免费   5122篇
  国内免费   41篇
林业   3910篇
农学   3011篇
基础科学   594篇
  11681篇
综合类   14900篇
农作物   3615篇
水产渔业   4570篇
畜牧兽医   48873篇
园艺   1068篇
植物保护   6187篇
  2018年   1288篇
  2017年   1445篇
  2016年   1358篇
  2015年   1115篇
  2014年   1391篇
  2013年   3516篇
  2012年   2555篇
  2011年   3005篇
  2010年   2055篇
  2009年   2084篇
  2008年   3064篇
  2007年   2935篇
  2006年   2661篇
  2005年   2554篇
  2004年   2359篇
  2003年   2542篇
  2002年   2282篇
  2001年   2876篇
  2000年   2812篇
  1999年   2269篇
  1998年   939篇
  1997年   1004篇
  1995年   1068篇
  1994年   922篇
  1993年   936篇
  1992年   1835篇
  1991年   2059篇
  1990年   1960篇
  1989年   1949篇
  1988年   1817篇
  1987年   1772篇
  1986年   1821篇
  1985年   1765篇
  1984年   1538篇
  1983年   1299篇
  1982年   944篇
  1979年   1471篇
  1978年   1130篇
  1977年   1060篇
  1976年   1030篇
  1975年   1084篇
  1974年   1311篇
  1973年   1325篇
  1972年   1251篇
  1971年   1164篇
  1970年   1121篇
  1969年   1132篇
  1968年   983篇
  1967年   1112篇
  1966年   926篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Diaphragmatic hernia. Analysis of fifty-six cases in dogs and cats   总被引:1,自引:0,他引:1  
A review of fifty-six cases of diaphragmatic hernia in the dog and cat is presented. These were admitted to the University of Glasgow Veterinary School between January 1972 and August 1978. Fifty-three of these cases were treated surgically but only twenty-nine survived to be discharged from the hospital. The reasons for the low survival rate are discussed in detail.  相似文献   
992.
993.
994.
Reference is made to work undertaken by Stehle (1983) on rapid semiquantitative determination of urinary protein in pigs for slaughter to identify premortal strain and stress, with additional studies being conducted into the suitability of the method. The investigations performed for this study covered urinary protein samples from 59 living and 762 slaughtered pigs. The Biophan E paper strip test was applied to groups of animals, and, when compared to high-accuracy laboratory determination of urinary protein, it provided sufficiently accurate information on the presence of stress-related proteinuria. Its accuracy, however, proved to be insufficient, when individual animals were examined. The number of clearly stressed slaughter pigs was unexpectedly high, although the same animals had been rated clinically inconspicuous prior to slaughter. Brief rest period resulted in significant rise of stress. The Biophan E paper strip test was found to be suitable for instantaneous determination of stress and strain on pigs for slaughter.  相似文献   
995.
Beef cows were used to determine if suckling influences release of LH via endogenous opioids at 28 +/- 4 d after parturition. Cows of similar weight and body condition (6.8 +/- .1, 1 = emaciated, 9 = obese) were assigned randomly to five groups (n = 6 to 7): 1) control-suckled/saline (suckled 15 min every 6 hr for 48 hr); 2) control-suckled/naloxone; 3) calf-removal/saline (calf removal for 52 hr); 4) calf-removal/naloxone; and 5) control-suckled/GnRH (Gonadotropin-Releasing Hormone). At 0 hr, saline was administered to all cows. This treatment was continued at 6 hr intervals for 24 hr. Either naloxone (0.5 mg/kg), GnRH (40 ng/kg) or saline was administered to cows in their respective groups every 6 hr during the ensuing 24-hr period in calf-removal groups, or immediately preceding each suckling episode in the control-suckled groups. Blood samples for analysis of luteinizing hormone (LH) were collected at 15-min intervals for 1 hr prior to and 3 hr after treatment at 0, 24, 36 and 48 hr. Cows were observed for estrus twice daily. All cows in the control-suckled/GnRH group released LH (P less than .05) in response to exogenous GnRH, indicating the presence of releasable quantities of the gonadotropin. Mean concentrations of LH were not effected (P greater than .05) by the control-suckled regime. However, calf-removal alone, or in combination with naloxone, increased (P less than .05) mean concentrations of LH by 48 hr.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
996.
Bluetongue virus type 16, isolated from sheep in Egypt, was injected to 4 normally cycling Barki ewes and caused high levels of inhibin. This was assayed by a biological method, using suppression of the luteinising hormone (LH) of castrated rats. Albumin (fraction 2) was injected to normally cycling ewes. The sera of injected ewes were investigated 1 day after injection and weekly up to the 4th one injection. There was a gradual decrease of LH (4.8 +/- 0.52 I.U./ml serum) until the minimum level (1.17 +/- 0.25 I.U./ml serum) was reached, in comparison to the control serum LH which was 5.26 +/- 0.52 I.U./ml serum during the dioestrous phase.  相似文献   
997.
The effects of feeding different levels of milk to diarrheic calves (n = 19) supplemented with oral electrolytes were investigated. In the early stages of the disease the calves were fed either enough milk to maintain normal growth in a healthy calf, one half that volume or no milk. The three groups were further subdivided according to whether or not the electrolyte solution contained bicarbonate. A full milk ration allowed uninterrupted weight gains of 1% body weight/day (p = 0.003), but caused greater inappetence (p = 0.003 to 0.037) at the beginning of the trial than lower levels of milk intake. Electrolyte solutions with bicarbonate reduced growth rates in milk fed calves (p = 0.014). The density of fat stores increased with the level of milk feeding (p = 0.04 to 0.053). The mitotic index of the duodenal mucosa increased with milk feeding (p = 0.08), indicating a superior mucosal regeneration potential. Thymic atrophy was pronounced in those calves fed no milk (p = 0.001). It was concluded that the continued feeding of milk to diarrheic calves was beneficial. Electrolyte solutions containing bicarbonate should be avoided when milk is fed to diarrheic calves.  相似文献   
998.
The effect of chronic lead intoxication in mature chickens   总被引:1,自引:0,他引:1  
In a study of chronic lead intoxication in mature chickens, blood lead levels were significantly lower in hens than in roosters receiving the same oral dose of lead. It was then shown that eggshells from lead-treated hens contained 6-12 times the lead concentration of eggshells from control hens. Similarly, the lead content of egg yolks from treated hens was significantly higher than yolks from controls. Lead-treated hens laid significantly more eggs during the period of observation of nearly 3 years because of the increased frequency of laying cycles, which was almost three times that of control hens. A further observation was histologic damage to the mature testes of the rooster.  相似文献   
999.
Gastro-oesophageal reflux together with sliding hiatus hernia is reported in a dog, associated with laryngeal paralysis. Diagnosis was made following endoscopy and fluoroscopy. Surgical treatment of the laryngeal paralysis resulted in complete remission of clinical signs.  相似文献   
1000.
Twenty-four adult Indian elephants (Elephas maximus indicus) of both sexes and different ages and weights, belonging to the Temple Devaswoms, the Forest Department of the Government of Kerala and the Gemini Circus formed the experimental subjects from which formulae were derived to predict the total surface area from either body measurements or areas of individual regions. Several models, using the parameters studied either singly or in combination, were tried independently for males and females and also for adults irrespective of sex. The best prediction of total surface area (S) in m2 was obtained for adults irrespective of sex by using the two parameters, the height at the shoulders (H) in m and forefoot pad circumference (FFC) in m in the formula S=–8.245+6.807H+7.073FFC. No significant improvement in the accuracy of prediction resulted from the use of the independent best fit formulae for males and females. The conventional method of using the exponential of body weight (kg) for predicting suface area was not found to yield an equivalent accuracy in these animals.  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