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   132647篇
  免费   6822篇
  国内免费   95篇
林业   5125篇
农学   3616篇
基础科学   900篇
  14138篇
综合类   27158篇
农作物   5065篇
水产渔业   5782篇
畜牧兽医   68539篇
园艺   1418篇
植物保护   7823篇
  2018年   1435篇
  2017年   1588篇
  2016年   1508篇
  2015年   1303篇
  2014年   1594篇
  2013年   4543篇
  2012年   3063篇
  2011年   3801篇
  2010年   2388篇
  2009年   2419篇
  2008年   3668篇
  2007年   3440篇
  2006年   3453篇
  2005年   3201篇
  2004年   3085篇
  2003年   3151篇
  2002年   3014篇
  2001年   3750篇
  2000年   3793篇
  1999年   2976篇
  1995年   1455篇
  1994年   1329篇
  1993年   1280篇
  1992年   2809篇
  1991年   3070篇
  1990年   2971篇
  1989年   2986篇
  1988年   2855篇
  1987年   2950篇
  1986年   3024篇
  1985年   2898篇
  1984年   2358篇
  1983年   2077篇
  1982年   1451篇
  1981年   1338篇
  1980年   1274篇
  1979年   2217篇
  1978年   1842篇
  1977年   1593篇
  1976年   1524篇
  1975年   1647篇
  1974年   2149篇
  1973年   2076篇
  1972年   2110篇
  1971年   2005篇
  1970年   1899篇
  1969年   1698篇
  1968年   1428篇
  1967年   1569篇
  1966年   1326篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Essential thrombocythaemia in an eight-year-old Irish setter is described. The condition is characterised by an autonomous overproduction of thrombocytes in the absence of overt leukaemia. This is believed to be the first recorded case of this condition in the dog. The paper describes the diagnosis and treatment by combination chemotherapy using vincristine, cytosine arabinoside, cyclophosphamide and prednisolone.  相似文献   
972.
An intra-abdominal testicular tumour was diagnosed in a 10-year-old, male, cryptorchid golden retriever. Upon surgical removal, torsion of the testis was found. The histopathological diagnosis was seminoma. The ultrasound examination in this case revealed a parenchymal mass lesion. An ultrasound examination is a useful supplemental diagnostic tool for differentiation of abdominal mass lesions.  相似文献   
973.
Adrenocortical function was assessed in dogs given a single intramuscular dose of either prednisone or triamcinolone acetonide (TCA; or saline solution to controls) to determine the duration of adrenocortical suppression caused by 2 commonly used glucocorticoids. The glucocorticoids were administered at recommended therapeutic doses; therefore, dogs given prednisone received a greater amount of glucocorticoid activity than did in dogs given TCA. Basal and ACTH-stimulated plasma cortisol concentrations, as determined by radioimmunoassay, were obtained once a week. Total intravascular eosinophil concentration and skin responses to intradermally injected histamine phosphate were quantitated. Dogs given TCA showed suppressed basal and ACTH-stimulated plasma cortisol concentrations 1 week after injection; the latter change persisted 2 weeks after injection. Adrenocortical function in 1 of 4 dogs given TCA remained suppressed for 4 weeks. In contrast, prednisone did not significantly alter adrenocortical function. Although intravascular eosinophil concentrations did not vary among groups, skin responses to intradermally injected histamine phosphate were reduced 6 days after prednisone and TCA were given.  相似文献   
974.
1. An experiment was done under commercial conditions to investigate the physiological effects of isolating broody turkey hens, for 72 h, in sand and wire floored pens on the third, 10th and 16th weeks of production.

2. Hens identified as broody and removed from the flock had higher plasma prolactin concentrations than the laying hens at each of the three experimental stages.

3. Confinement in sand and wire floored pens, induced a decline in plasma prolactin concentrations. This decline probably impeded immediate development of broody behaviour. Alternately, levels of prolactin higher than those of laying hens were again measured 7 and 14 days after treatment during third week but not after the 10 th and 16th week of production.

4. Confinement did not induce consistent changes in luteinising hormone (LH) and progesterone concentrations from one period to an other.

5. An increase in the plasma concentration of D‐(/?)‐hydroxybutyrate was observed in the hens which had an egg present in the oviduct on day 2, 3 and/or 4 of the treatment. Subsequently, a decrease in ovulation rate was observed in the hens with higher concentrations of D‐(β)‐hydroxybutyrate while under treatment, during the 10th week of production.

6. These data confirm that the effectiveness of the traditional methods for broodiness prevention under commercial conditions is related to the induction of a decrease of prolactin.  相似文献   

975.
An 8-year-old Haflinger mare with a 10-day-old foal at foot was referred with mild abdominal pain. On the basis of clinical examination, blood and peritoneal fluid analysis, the cause of pain was suspected septic peritonitis. The horse was initially managed medically, with the horse placed in box confinement under close monitoring. No permission was given for an exploratory laparotomy, and it was decided to perform a diagnostic laparoscopy in the standing horse. The laparoscopy revealed a 360-degree anticlockwise partial duodenal volvulus of the caudal descending duodenum, which was manually reduced (hand-assisted laparoscopy). After the release, the mesentery of the duodenum showed an ischaemic band (yellowish white and dark red with a hyperaemic side) and the duodenum had a distinct ischaemic ring (orally and aborally) distinguishing the incarcerated part from the normal duodenum. Ten minutes after the release, the colour remained the same. In conjunction with the owner, it was decided to euthanise the pony. Pathology confirmed the presence of a strangulation ring and the ischaemic condition of the involved duodenum.  相似文献   
976.
To improve his position as an exporter of pedigree animals, an owner wished to establish his herd as serologically negative for infectious bovine rhinotracheitis (IBR). After a test on all animals older than six months the herd was split into seronegative and seropositive groups. The seronegative group was tested four times during the first year, twice during the second year and given a final test 12 months later; any positive animals were removed. The results indicated that in the right circumstances the establishment of an IBR seronegative hard is practicable.  相似文献   
977.
A study was conducted to contrast the dyschondroplasia-inducing capability of several species of Fusarium with that of the natural fungi found in poultry diets and litter. Day-old broiler chicks were fed pure corn cultures of specific fungal isolates for 3 weeks. Humoral immunity to sheep red blood cells (SRBC), body weight, valgus and varus leg deformities, incidence of dyschondroplasia, and mechanical properties of the tibiotarsi were examined. F. equiseti #15 was the only fungal isolate to induce dyschondroplasia to any significant degree, which confirmed previous work in Minnesota. This isolate also suppressed growth rate and humoral immunity, although dyschondroplasia sometimes did occur without associated immunosuppression and growth depression. Bone strength of the tibiotarsal diaphysis was normal, and gross lesions of valgus and varus leg deformities did not appear to be related to the incidence of dyschondroplasia in the 3-week-old chicks.  相似文献   
978.
Pharmacokinetics of amikacin in cats   总被引:1,自引:0,他引:1  
Six mixed-breed adult cats were given 5 mg of amikacin sulfate/kg of body weight by rapid IV, IM, and SC routes of administration. The serum concentration-vs-time data were analyzed, using a noncompartmental model. The harmonic mean +/- pseudo-SD of the effective half-life of amikacin was 78.8 +/- 19.3 minutes after IV administration, 118.7 +/- 14.4 minutes after IM administration, and 117.7 +/- 12.8 minutes after SC administration. The arithmetic mean +/- SD of mean residence time was 118.3 +/- 21.7 minutes, 173.4 +/- 19.9 minutes, and 171.7 +/- 19.1 minutes after IV, IM, and SC drug administration, respectively. The mean apparent volume of distribution at steady state was 0.17 +/- 0.02 L/kg, and the mean total body clearance was 1.46 +/- 0.26 ml/min/kg. Mean bioavailability was 95 +/- 20% after IM administration and 123 +/- 33% after SC drug administration. A recommended dosage of 10 mg/kg, q 8 h can be expected to provide a therapeutic serum concentration of amikacin with a mean steady-state concentration of 14 micrograms/ml. The SC route of administration is preferred, because of rapid absorption, good bioavailability, and ease of administration.  相似文献   
979.
1. Male broiler chickens were killed at various times up to 36 h after withdrawal of food; hepatic and muscle glycogen concentrations and pH were compared with those of control birds given continuous access to food and water. 2. Liver glycogen was reduced to negligible concentrations (less than 1 mg/g) within 6 h of food deprivation and the initial pH was elevated. 3. Withdrawal of food had no effect on glycogen concentrations in the m. pectoralis superficialis (PS) but reduced them in the m. biceps femoris (BF); the reduction was significant after 12 h. Ultimate pH was elevated by fasting in the BF, but not the PS.  相似文献   
980.
Seizures as a manifestation of primary hyperparathyroidism in a dog   总被引:1,自引:0,他引:1  
Hypercalcemia caused by primary hyperparathyroidism was believed to be responsible for seizures in a dog. A diagnostic evaluation showed no primary causes of seizures. After surgical excision of the adenomatous parathyroid gland, phenobarbital treatment was discontinued, without recurrence of seizures.  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