全文获取类型
收费全文 | 1922篇 |
免费 | 62篇 |
国内免费 | 39篇 |
专业分类
林业 | 120篇 |
农学 | 103篇 |
基础科学 | 149篇 |
137篇 | |
综合类 | 683篇 |
农作物 | 41篇 |
水产渔业 | 78篇 |
畜牧兽医 | 521篇 |
园艺 | 134篇 |
植物保护 | 57篇 |
出版年
2023年 | 27篇 |
2022年 | 42篇 |
2021年 | 37篇 |
2020年 | 33篇 |
2019年 | 43篇 |
2018年 | 42篇 |
2017年 | 31篇 |
2016年 | 26篇 |
2015年 | 42篇 |
2014年 | 73篇 |
2013年 | 58篇 |
2012年 | 108篇 |
2011年 | 104篇 |
2010年 | 50篇 |
2009年 | 58篇 |
2008年 | 99篇 |
2007年 | 101篇 |
2006年 | 116篇 |
2005年 | 88篇 |
2004年 | 74篇 |
2003年 | 72篇 |
2002年 | 88篇 |
2001年 | 75篇 |
2000年 | 65篇 |
1999年 | 44篇 |
1998年 | 36篇 |
1997年 | 24篇 |
1996年 | 28篇 |
1995年 | 15篇 |
1994年 | 29篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1975年 | 5篇 |
1960年 | 7篇 |
1959年 | 8篇 |
1957年 | 5篇 |
1955年 | 4篇 |
1953年 | 5篇 |
排序方式: 共有2023条查询结果,搜索用时 15 毫秒
51.
52.
53.
宁夏彭阳县发展休闲农业的优劣势及发展措施 总被引:1,自引:0,他引:1
休闲农业是利用农业景观资源和农业生产条件,把田园景观、自然生态、环境资源、农林渔牧生产、农业经营活动及农村文化与农家生活结合,发展观光、休闲、旅游的一种新型农业生产经营形态。现以城阳乡杨坪村发展休闲农业为例,提出彭阳县发展休闲农业的见解。 相似文献
54.
新疆鬣蜥Aga ina stoliczkana (Blanford)主要分布在塔里木盆地的边缘地区,1988年4—7月、9—10月,笔者在阿克苏农一师五团对其进行了野外定点观察,逐月共解剖标本80条,89年4月在室内解剖32条,合计112条(雌性58条、雄性54条),记录精巢、卵巢发育情况,将固定的精巢,做成石蜡切片,并结合人工饲养观察,对新疆鬣蜥繁殖进行了研究。 相似文献
55.
OBJECTIVE: To characterize the cardiovascular effects of romifidine at doses ranging from 5 to 100 microg/kg of body weight, IV. ANIMALS: 25 clinically normal male Beagles. PROCEDURE: Romifidine was administered IV at a dose of 5, 10, 25, 50, or 100 microg/kg (n = 5/group). Heart rate, arterial pressure, central venous pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, body temperature, cardiac output, and PCV were measured immediately prior to and at selected times after romifidine administration. Cardiac index, stroke index, rate-pressure product, systemic and pulmonary vascular resistance indices, and left and right ventricular stroke work indices were calculated. Degree of sedation was assessed by an observer who was blinded to the dose administered. RESULTS: Romifidine induced a decrease in heart rate, pulmonary arterial pressure, rate-pressure product, cardiac index, and right ventricular stroke work index and an increase in central venous pressure, pulmonary capillary wedge pressure, and systemic vascular resistance index. In dogs given romifidine at a dose of 25, 50, or 100 microg/kg, an initial increase followed by a prolonged decrease in arterial pressure was observed. Arterial pressure immediately decreased in dogs given romifidine at a dose of 5 or 10 microg/kg. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that IV administration of romifidine induces dose-dependent cardiovascular changes in dogs. However, the 2 lowest doses (5 and 10 microg/kg) induced less cardiovascular depression, and doses > or = 25 microg/kg induced similar cardiovascular changes, suggesting that there may be a ceiling on the cardiovascular effects of romifidine. 相似文献
56.
We studied some clinical, biochemical and haematological variables in Desert (Najdi) sheep acutely stressed in the course of individual road transportation, and the influence thereon of pretreatment with tyrosine. Transportation for 30 min resulted in variable but statistically insignificant increases in heart, pulse and respiratory rates. It also caused significant increases in the plasma concentration of cortisol (from 43.5 to 101.7 mmol/L) and glucose (from 3.1 to 4.5 mmol/L), and a decrease in that of magnesium (from 0.85 to 0.72 mmol/L). The endogenous thiocyanate level was unaffected. The transportation stress also decreased the haematocrit (PCV) and the number of lymphocytes, and increased the concentration of haemoglobin. Pretreatment of sheep with tyrosine at a dose of 100 mg/kg by the intravenous route significantly ameliorated the stress-induced clinical, biochemical and haematological changes. The treatment caused no overt adverse effects. 相似文献
57.
58.
Simpson HV Simpson BH Simcock DC Reynolds GW Pomroy WE 《New Zealand veterinary journal》1999,47(1):20-24
AIMS: Both adult and larval Ostertagia circumcincta infections raise abomasal pH and serum gastrin and pepsinogen concentrations, either because of physical effects of the worms or from their chemical secretions. The study was designed to examine whether adult worms require contact with the gastric mucosa to effect changes in gastric secretion. METHODS: Abomasal pH and serum gastrin and pepsinogen concentrations were measured in four groups of sheep: Group A (n = 4): abomasal contents containing about 18,000 adult O. circumcincta were obtained from donor sheep, concentrated and infused into 5 microm mesh porous bags attached to surgically implanted abomasal cannulae. A second worm transplantation was carried out 1 week later to assess worm survival after 16 hours. Group B (n = 4): about 9000 adult worms, recovered after migration out of abomasal contents set in agar, were placed in small 5 microm mesh bags which were inserted through indwelling abomasal cannulae and left for 3 days. Group C (n = 2): about 3000 adult worms from the population recovered from agar were infused through abomasal cannulae which allowed. free movement in the abomasum. Group D (n = 3) was left uninfected. RESULTS: Worms transplanted directly into the abomasum (Group C) caused rapid and marked effects on abomasal secretion. Adult O. circumcincta died within 16 hours of transfer into the abomasum when they were restrained within porous bags. Nevertheless, in sheep receiving 18,000 worms, abomasal pH increased soon after new feed was presented on Days 1, 2 and 4 after worm transfer; serum gastrin was elevated in three sheep from 113 hours and serum pepsinogen increased in one animal. Sheep receiving 9000 worms showed similar trends but the results were equivocal. CONCLUSIONS: Adult O. circumcincta prevented from physical contact with the gastric mucosa by restraint in porous bags are able to raise abomasal pH. This study implicates parasite excretory-secretory products in mediating changes in gastric secretion caused by adult abomasal worms. 相似文献
59.
60.