全文获取类型
收费全文 | 5663篇 |
免费 | 235篇 |
国内免费 | 8篇 |
专业分类
林业 | 487篇 |
农学 | 209篇 |
基础科学 | 51篇 |
1333篇 | |
综合类 | 732篇 |
农作物 | 250篇 |
水产渔业 | 360篇 |
畜牧兽医 | 1890篇 |
园艺 | 171篇 |
植物保护 | 423篇 |
出版年
2023年 | 30篇 |
2022年 | 53篇 |
2021年 | 97篇 |
2020年 | 112篇 |
2019年 | 138篇 |
2018年 | 105篇 |
2017年 | 124篇 |
2016年 | 134篇 |
2015年 | 95篇 |
2014年 | 146篇 |
2013年 | 265篇 |
2012年 | 321篇 |
2011年 | 395篇 |
2010年 | 248篇 |
2009年 | 203篇 |
2008年 | 345篇 |
2007年 | 342篇 |
2006年 | 360篇 |
2005年 | 357篇 |
2004年 | 319篇 |
2003年 | 295篇 |
2002年 | 308篇 |
2001年 | 78篇 |
2000年 | 70篇 |
1999年 | 86篇 |
1998年 | 66篇 |
1997年 | 54篇 |
1996年 | 52篇 |
1995年 | 45篇 |
1994年 | 27篇 |
1993年 | 44篇 |
1992年 | 36篇 |
1991年 | 35篇 |
1990年 | 38篇 |
1989年 | 43篇 |
1988年 | 37篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 33篇 |
1984年 | 22篇 |
1983年 | 34篇 |
1982年 | 21篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1974年 | 15篇 |
1973年 | 18篇 |
1972年 | 14篇 |
排序方式: 共有5906条查询结果,搜索用时 0 毫秒
91.
Lahrmann KH Steinberg C Dahms S Heller P 《Berliner und Münchener tier?rztliche Wochenschrift》2003,116(1-2):67-73
A longitudinal observational study in 180 pig breeding herds was performed to calculate prevalences of herd specific factors as well as typical limb disorders and to estimate their associations in a 2-step regression analysis. Regarding herd size, genetics, feeding and weight gain herds were distributed almost equal. The population density and the hygiene status were considered proper in most herds. In the farrowing units partially slatted floors of metal or plastic with slats > 9 mm, in the weaning units fully slatted floors of plastic, and in the rearing units fully slatted floors of concrete were most common. Less than 6% of the farms housed their pigs on solid concrete with straw bedding. Herd prevalences of fault floors varied between 18 and 43%. As a herd health problem (morbidity > 25%) claw hematomas and limb abrasions in just 1-week old piglets, overgrown claws and bursa swellings in weaned pigs, and bursa swellings in rearing pigs were wide spread. Leg deformations by osteopathy or arthritis occurred only sporadically. In the risk analysis claw hematomas of piglets were associated with slatted floors, particulary with slats < 10 mm. Abrasions were associated with concrete and rough floor surfaces at all. Overgrown claws and bursa swellings in weaned and in rearing pigs were associated with damaged, slippery or rough floor surfaces. Other associations were not detected. The quality of floor might be more important than the type of housing. 相似文献
92.
93.
94.
95.
Change of porcine circovirus 2 target cells in pigs during development from fetal to early postnatal life 总被引:13,自引:0,他引:13
Change of porcine circovirus 2 (PCV2) target cells during development from fetal to postnatal life in pigs was examined. PCV2 inoculation was performed in fetuses in utero at either 57, 75 or 92 gestational days and in piglets at 1 day of age. Twenty-one days after virus inoculation, PCV2-infected cells in the heart, lungs, liver, spleen and inguinal lymph nodes were localized and immuno-phenotyped by double-immunofluorescence labeling using different cell markers and PCV2-antibodies. During fetal life, viral antigens were detected in cardiomyocytes, hepatocytes and macrophages and infected cell numbers decreased with increasing fetal age at inoculation. The heart contained the highest number of infected cells and cardiomyocytes were the main target cell. Postnatally, macrophages were the only target cell type in different organs and infected cell numbers were similar to those of fetuses inoculated at 92 days of gestation. One piglet showed exceptionally high number of infected cells in different organs with values 13-513-fold higher compared to littermates. In this piglet, the majority of infected cells in lymphoid tissues could not be typed. This study reveals that PCV2 target cells change from cardiomyocytes, hepatocytes and macrophages during fetal life to only macrophages postnatally. 相似文献
96.
Colley PA Verstraete FJ Kass PH Schiffman P 《American journal of veterinary research》2002,63(4):546-550
OBJECTIVE: To determine elemental composition of teeth with and without odontoclastic resorption lesions (ORL) in cats. SAMPLE POPULATION: Normal teeth from 22 cadaver cats and ORLaffected teeth from 21 cats admitted to the veterinary hospital for dental treatment. PROCEDURE: An electron microprobe was used to analyze weight percentages of calcium, phosphorus, fluorine, sodium, magnesium, sulfur, potassium, and iron in enamel, dentin, and cementum. RESULTS: Calcium and phosphorus were the most abundant elements. Fluorine, sodium, and magnesium combined were < 5% and sulfur, potassium, and iron combined were < 0.1% of total elemental composition. In enamel of normal teeth, a significant sex-by-jaw location interaction was seen in mean (+/- SD) phosphorus content, which was higher in mandibular teeth of females (1764+/-0.41%) but lower in mandibular teeth of males (16.71+/-0.83%). Mean iron content in dentin of normal teeth was significantly lower in mandibular teeth than maxillary teeth (0.014+/-0.005% vs 0.023+/-0.019%). Mean enamel sodium content was significantly higher (0.77+/-0.046% vs 0.74+/-0.025) and mean enamel iron content was significantly lower (0.017+/-0.008% vs 0.021+/-0.005%) in ORLaffected teeth, compared with normal teeth. In cementum, mean fluorine content was significantly lower (2.98%+/-0.27 vs 2.99+/-0.20%) and mean magnesium content was significantly lower (0.54+/-0.13% vs 0.60+/-0.13%) in ORL affected teeth, compared with normal teeth. CONCLUSIONS AND CLINICAL RELEVANCE: Results of our study establish baseline mineral content of enamel, dentin, and cementum for normal teeth in cats. Minimal differences in mineral content of enamel and cementum of normal and ORL-affected teeth were detected. 相似文献
97.
98.
99.
Sting R Kopp J Mandl J Seeh C Seemann G Kimmig P Schmitt K Mentrup T 《Berliner und Münchener tier?rztliche Wochenschrift》2002,115(9-10):360-365
Investigations of 1167 dairy cows out of 105 herds with fertility disorders on secretion of Coxiella burnetii (C. burnetii) by the genitals as well as serological studies of these animals using ELISA demonstrated that C. burnetii infections are significantly associated with abortions but not with repeated inseminations without success or vaginal excretions. The demonstration of an increased risk of infections for persons caring for those dairy herds could be shown by a total of 253 serological studies. A comparison of these studies of farmers caring for dairy herds suffering from abortions a seroprevalence of > or = 20% showed that these persons revealed significantly more frequent antibodies against C. burnetii than farmers of the group compared with. Further studies showed that in herds suffering from abortions a seroprevalence of > or = 20% means an additional risk of infections of farmers. Vice versa abortions of the cows in herds with a seroprevalence of > or = 20% imply an additional infectious risk. 相似文献
100.
Wagner AE Walton JA Hellyer PW Gaynor JS Mama KR 《Journal of the American Veterinary Medical Association》2002,221(1):72-75
OBJECTIVE: To compare indicators of postoperative pain and behavior in dogs with and without a low-dose ketamine infusion added to usual perioperative management. DESIGN: Prospective, randomized, blinded clinical study. ANIMALS: 27 dogs undergoing forelimb amputation. PROCEDURE: Dogs were anesthetized with glycopyrrolate, morphine, propofol, and isoflurane. Thirteen dogs were treated with ketamine IV, as follows: 0.5 mg/kg (0.23 mg/lb) as a bolus before surgery, 10 microg/kg/min (4.5 microg/lb/min) during surgery, and 2 microg/kg/min (0.9 microg/lb/min) for 18 hours after surgery. Fourteen dogs received the same volume of saline (0.9% NaCl) solution. All dogs received an infusion of fentanyl (1 to 5 microg/kg/h [0.45 to 2.27 pg/lb/h]) for the first 18 hours after surgery. Dogs were evaluated for signs of pain before surgery, at the time of extubation, and 1, 2, 3, 4, 12, and 18 hours after extubation. Owners evaluated their dogs' appetite, activity, and wound soreness on postoperative days 2, 3, and 4. RESULTS: Dogs that received ketamine infusions had significantly lower pain scores 12 and 18 hours after surgery and were significantly more active on postoperative day 3 than dogs that received saline solution infusions. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that perioperative administration of low doses of ketamine to dogs may augment analgesia and comfort in the postoperative surgical period. 相似文献