全文获取类型
收费全文 | 312629篇 |
免费 | 16814篇 |
国内免费 | 761篇 |
专业分类
林业 | 24525篇 |
农学 | 14232篇 |
基础科学 | 3035篇 |
46932篇 | |
综合类 | 41490篇 |
农作物 | 17728篇 |
水产渔业 | 18151篇 |
畜牧兽医 | 131982篇 |
园艺 | 6522篇 |
植物保护 | 25607篇 |
出版年
2020年 | 2983篇 |
2019年 | 3794篇 |
2018年 | 4503篇 |
2017年 | 4947篇 |
2016年 | 5094篇 |
2015年 | 4473篇 |
2014年 | 5854篇 |
2013年 | 16422篇 |
2012年 | 8030篇 |
2011年 | 10475篇 |
2010年 | 8214篇 |
2009年 | 8636篇 |
2008年 | 9874篇 |
2007年 | 8977篇 |
2006年 | 9271篇 |
2005年 | 8565篇 |
2004年 | 8325篇 |
2003年 | 8144篇 |
2002年 | 7345篇 |
2001年 | 8175篇 |
2000年 | 7973篇 |
1999年 | 6921篇 |
1998年 | 4344篇 |
1997年 | 4412篇 |
1996年 | 4109篇 |
1995年 | 4782篇 |
1994年 | 4180篇 |
1993年 | 3902篇 |
1992年 | 5552篇 |
1991年 | 5842篇 |
1990年 | 5533篇 |
1989年 | 5499篇 |
1988年 | 4884篇 |
1987年 | 4975篇 |
1986年 | 5026篇 |
1985年 | 5150篇 |
1984年 | 4539篇 |
1983年 | 4192篇 |
1982年 | 3275篇 |
1981年 | 3154篇 |
1980年 | 3101篇 |
1979年 | 4140篇 |
1978年 | 3540篇 |
1977年 | 3200篇 |
1976年 | 3046篇 |
1975年 | 3038篇 |
1974年 | 3442篇 |
1973年 | 3399篇 |
1972年 | 3115篇 |
1971年 | 3031篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A survey of anthelmintic resistance on ten goat farms was carried out. The criterion for resistance was a faecal egg count reduction (FECR) of <90 percent based on arithmetic means of 11 to 19 goats per group. It was found that nine of the ten farms harboured nematodes resistant to oxfendazole when used at 5mg/kg although on two of these, the FECR's were 89.2 percent and 89.8 percent. Post treatment larval cultures indicated Haemonchus, Ostertagia and Trichostrongylus were the resistant genera involved. On none of the ten farms was resistance to oral ivermectin at 0.2mg/kg detected. 相似文献
992.
1. The effects of feeding two fats with different degrees of saturation on skin tearing, carcase quality and body fat composition were examined in male and female chickens.
2. No differences in growth or efficiency of food utilisation were apparent on feeding the more saturated fat. Skin tearing was slightly reduced and carcase quality slightly improved on feeding the more saturated fat for 28 d.
3. Decreases in linoleic acid content in intra‐abdominal fat were apparent after 14 d feeding the diet containing saturated fat. These decreases were greater after feeding the saturated fat for 28 d. 相似文献
993.
R W Markham E M Hodgkins 《Veterinary Clinics of North America: Small Animal Practice》1989,19(1):165-185
In recent decades, veterinary medicine has become more successful in prolonging the healthy, useful lives of pets. As a result, the practitioner spends a greater part of each practice day caring for the geriatric animal, both healthy and unhealthy. Because of their longevity, older pets are typically regular family members, with owners who seek the finest health care possible for their pets. The practice of geriatric medicine most properly should begin not when the dog or cat reaches some specific "golden" age, but rather when the wiggly, robust puppy or kitten receives its first examination. Like all parts of a sound preventive program, geriatric nutrition best follows from a well-considered juvenile and adult nutrition program. Furthermore, once it becomes senior, the "well" geriatric is as much a candidate for a diet designed especially to accommodate old age changes as is his unhealthy contemporary. In fact, evidence suggests that appropriate dietary management of the healthy, but often subclinical, patient may help postpone the signs of dysfunction and increase quality and length of life. A knowledge of the most significant nutrients and the impact of each on aging systems is now, and will become increasingly more, important to the progressive, skillful veterinarian. 相似文献
994.
S A Robertson 《Veterinary Clinics of North America: Small Animal Practice》1989,19(2):289-306
The body regulates pH closely to maintain homeostasis. The pH of blood can be represented by the Henderson-Hasselbalch equation: pH = pK + log [HCO3-]/PCO2 Thus, pH is a function of the ratio between bicarbonate ion concentration [HCO3-] and carbon dioxide tension (PCO2). There are four simple acid base disorders: (1) Metabolic acidosis, (2) respiratory acidosis, (3) metabolic alkalosis, and (4) respiratory alkalosis. Metabolic acidosis is the most common disorder encountered in clinical practice. The respiratory contribution to a change in pH can be determined by measuring PCO2 and the metabolic component by measuring the base excess. Unless it is desirable to know the oxygenation status of a patient, venous blood samples will usually be sufficient. Metabolic acidosis can result from an increase of acid in the body or by excess loss of bicarbonate. Measurement of the "anion-gap" [(Na+ + K+) - (Cl- + HCO3-)], may help to diagnose the cause of the metabolic acidosis. Treatment of all acid-base disorders must be aimed at diagnosis and correction of the underlying disease process. Specific treatment may be required when changes in pH are severe (pH less than 7.2 or pH greater than 7.6). Treatment of severe metabolic acidosis requires the use of sodium bicarbonate, but blood pH and gases should be monitored closely to avoid an "overshoot" alkalosis. Changes in pH may be accompanied by alterations in plasma potassium concentrations, and it is recommended that plasma potassium be monitored closely during treatment of acid-base disturbances. 相似文献
995.
The paper describes pathomorphological findings in two dogs and one cat with the intention to clarify whether these animals died by drowning. The investigations are supplemented by experimental results of water instillation into the lung to induce signs of emphysema aquosum post mortem. Additionally, histopathology of the skin lesions due to water exposition after death are demonstrated by systematic investigations of four different localizations for 10 days. Critical evaluation of the results and literature references in human forensic pathology indicate that post mortem findings as described in this paper, especially those of the so called "drowning lung" can be attributed to death by drowning. 相似文献
996.
Piper EL 《New Zealand veterinary journal》1989,37(4):173-174
997.
998.
Organochlorine insecticide problems in livestock 总被引:1,自引:0,他引:1
M F Raisbeck J D Kendall G E Rottinghaus 《Veterinary Clinics of North America: Food Animal Practice》1989,5(2):391-410
1. Antidotal therapy for acute OC intoxications is symptomatic and supportive. Use sedatives to control convulsions and AC to adsorb any pesticide remaining in the gut, and wash topical exposures. 2. Published kinetics should be applied to field situations with caution. In general, residues decline relatively quickly immediately following the last exposure; thereafter, the rate slows considerably. The elimination-rate constant and, hence, the half-life of any given OC is dependent on many variables that usually are not known under field conditions. This fact may result in serious errors if literature values are relied on too heavily in predicting the outcome of "natural" contamination. As a rule of thumb, elimination data derived from animals experimentally fed to plateau concentrations may be regarded as fairly conservative for such purposes, if the contaminated animals are maintained in a normal fashion. Probably the least risky method of predicting return to marketability is using frequent samples, taken at regular intervals (for example, 1 to 2 weeks) during the first month after last exposure, to adjust literature values. 3. Residues from larger dosages and shorter exposures tend to be smaller in proportion to dose and are eliminated more quickly than those resulting from longer exposures and smaller doses. 4. Activated charcoal is of universal benefit only if given immediately after exposure. 5. Pharmaceutical modifiers of xenobiotic metabolism such as phenobarbital are of very limited value. The particular type and amount of residual OC and the potential economic benefit of therapy should be considered thoroughly before undertaking such therapy. In most cases, the expense won't be justified. 6. Mineral oil increases the fecal excretion of some OC. Fecal excretion, however, is so small in relation to total body burdens that even a several-fold increase may not be useful economically except when residue concentrations are low to start with. 7. Nutritional strategies have the advantage of being very cheap. Practitioners should remember, however, that tissue concentrations actually may increase as body fat decreases. The costs of maintaining animals for an extra 6 to 10 months should be considered before undertaking such an effort.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
999.
Blood platelets and bone marrow megakaryocytes from a dog with essential thrombocythemia were analyzed by transmission electron microscopy and compared with those of control dogs. Platelets varied in size and shape and contained enlarged and dilated open canalicular systems. Megakaryocytes were dysmorphic and had evidence of abnormal maturation, with large numbers of megakaryoblasts containing alpha granules and poorly organized and reduplicated demarcation membranes. The fewer, more mature megakaryocytes lacked normal cytoplasmic organization. Most notable was the absence of well-demarcated "platelet fields," due to the excessive and disorderly array of demarcation membranes. 相似文献
1000.