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   188641篇
  免费   10558篇
  国内免费   159篇
林业   7973篇
农学   5926篇
基础科学   1201篇
  23283篇
综合类   31026篇
农作物   7233篇
水产渔业   9382篇
畜牧兽医   98977篇
园艺   2417篇
植物保护   11940篇
  2019年   1883篇
  2018年   2824篇
  2017年   3156篇
  2016年   2877篇
  2015年   2484篇
  2014年   3140篇
  2013年   7428篇
  2012年   5581篇
  2011年   6713篇
  2010年   4494篇
  2009年   4576篇
  2008年   6666篇
  2007年   6381篇
  2006年   5998篇
  2005年   5519篇
  2004年   5349篇
  2003年   5453篇
  2002年   4999篇
  2001年   6104篇
  2000年   6014篇
  1999年   4797篇
  1998年   1931篇
  1997年   1903篇
  1996年   1799篇
  1995年   2116篇
  1994年   1776篇
  1993年   1855篇
  1992年   3795篇
  1991年   4042篇
  1990年   3950篇
  1989年   4006篇
  1988年   3616篇
  1987年   3650篇
  1986年   3636篇
  1985年   3465篇
  1984年   2776篇
  1983年   2495篇
  1982年   1692篇
  1979年   2513篇
  1978年   1973篇
  1977年   1708篇
  1976年   1611篇
  1975年   1757篇
  1974年   2149篇
  1973年   2226篇
  1972年   2161篇
  1971年   1974篇
  1970年   2014篇
  1969年   1884篇
  1967年   1641篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The complement fixation test (CFT), the enzyme labelled immunosorbent assay (ELISA) and the gel diffusion precipitin test (GD) were compared, for the diagnosis of Brucella ovis infection in rams. The sensitivities of the tests in 109 rams which were shedding B. ovis in their semen were: CFT 96.3%; ELISA 97.2%; GD 91.7%. The specificities of the tests in 141 rams from non-infected flocks were: CFI 99.3%; ELISA 98.6%; GD 100%. Predictive values of the three tests were measured in 285 rams from infected flocks. Thirty-eight percent of these rams were shedding B. ovis in their semen. Predictive values of positive tests were: CFT 75.5%; ELISA 66.7%; GD 72.5%. Predictive values of negative tests were: CFI 97.1%; ELISA 97.6%; GD 93.8%.  相似文献   
992.
Two lactational intramammary antibiotic preparations (cloxacillin and oxytetracycline) were each used to treat eight goats by intramammary infusion in one half. The rate of release of the antibiotics was monitored by a diffusion assay based on the sensitive organism Bacillus stearothermophilus var. calidolactis. Cloxacillin was still detectable 156 hours after the final treatment while oxytetracycline was undetectable 108 hours following treatment. A small but significant amount of antibiotic was translocated between treated and untreated halves of the udder in both cases.  相似文献   
993.
The pharmacokinetics of fenbendazole and oxfendazole in cattle are described. The pharmacokinetics of oxfendazole were not significantly different when administered orally and by intra-ruminal injection. At a dose rate of 4.5 mg/kg, administered orally, fenbendazole gave rise to mean peak concentrations in plasma of fenbendazole and oxfendazole of 0.11 and 0.13 g/ml respectively. Oral administration of oxfendazole, at 4.5 mg/kg body weight, gave rise to plasma peak concentrations of fenbendazole and oxfendazole of 0.10 and 0.20 g/ml respectively. Following intra-ruminal administration of oxfendazole, the peak concentrations were 0.11 and 0.18 g/ml respectively.  相似文献   
994.
The intravenous administration of 0.75 gm glucose per kg and the measurement of serum glucose pretest and at 10, 20, 30, 60, 90 and 120 minutes constitute a satisfactory protocol for intravenous glucose tolerance testing of Rhesus (Macaca mulatto) and African Green (Cercopithecus aethiops) monkeys. No significant differences were noted between animals restrained with ketamine hydrochloride and those restrained with sodium pentobarbital, but the African Green males and females and the male Rhesus monkeys yielded significantly different results while being manually restrained.  相似文献   
995.
An unusual combination of blood cytopenias and monocytic proliferation was observed in a dog. Initial hematologic findings included severe thrombocytopenia, neutropenia, mild nonregenerative anemia and apparently normal bone marrow. Subsequently, a severe persistent monocytosis developed and the bone marrow became populated with monocytes and cytophagic macrophages. Splenomegaly was due to reticuloendothelial hyperplasia and extramedultary hematopoiesis. Treatment consisted of splenectomy and azathioprine but the response was poor and the dog was euthanized. Postmortem examination revealed a hypocellular bone marrow which contained moderate numbers of monocytes and plasma cells. Neoplastic proliferation was absent in visceral organs. No definite diagnosis was established; chronic blood cell consumption, perhaps immune-mediated, may have been responsible for the extensive reticuloendothelial hyperplasia and cytophagia.  相似文献   
996.
Pulmonic stenosis is caused by a malformed pulmonic valve, stricture of the right ventricular outflow tract or stricture of the pulmonary artery. English Bulldogs, Beagles, Samoyeds, Fox Terriers and Chihuahuas are predisposed. Clinical signs in severely affected dogs include exercise intolerance, stunting, dyspnea, syncope and ascites. Auscultation reveals a high-frequency, crescendo-decrescendo murmur during systole, loudest over the left side of the thorax, near the sternal cardiac border. An ECG may reveal a right-axis deviation of greater than 120 degrees, S waves in leads I, II and III, deep S waves in CV6LL, CV6LU and V10, Q waves deeper than 0.5 mv in leads II, III and AVF, and positive T waves in lead V10. Plain film LAT thoracic radiographs reveal an elevated carina, increased sternal contact of the heart, loss of the cranial cardiac waist and a widened cardiac silhouette, with normal pulmonary vasculature. A DV projection reveals an inverted "D" shape of the right ventricle and a pulmonary artery bulge. A nonselective angiocardiogram reveals poststenotic dilation of the main pulmonary artery. Treatment involves surgical correction of the stenosis.  相似文献   
997.
Factors affecting somatic cell counts and the association between somatic cell counts and milk production were evaluated. Data were collected from 748 Ontario Dairy Herd Improvement Corporation supervised herds that were on production and somatic cell count programs between April 1981 and March 1983. Two data files were created; one, the lactation summary file, contained one record per cow on each of 9406 Holsteins and the other, the test day file, included results of all tests during the complete lactation on each of the above cows. The latter file contained 85,236 records. Multiple curvilinear least squares regression was used to create five separate models. The dependent variables used in the models were natural logarithms (Loge) of the geometric mean of the somatic cell count for the lactation, 305 day milk production and breed class average for milk from the lactation summary file, and loge of the 24 hour somatic cell count and 24 hour milk production from the test day file. The somatic cell count at both the lactation and test day level increased with age up to approximately ten years and thereafter slowly decreased. The variable "days in milk" was not significantly associated with the lactation average somatic cell count. A curvilinear relationship was found between days in lactation at the time of test and the somatic cell count of 24 hour milk production. The somatic cell count increased until approximately 250 days in lactation and thereafter slowly decreased. It was found that the highest cell counts occurred in summer and the lowest in winter.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
998.
The cleistogamous species Collomia grandiflora produces dimorphic cross-incompatible flowers on a single plant. The open or chasmogamous flower has smaller, flask-shaped stigmatic papillae, larger pollen grains, longer styles, and faster pollen tube growth rates down the style than the closed or cleistogamous flower. In intermorph crosses, pollen tube growth rates are greatly decreased and fertilization does not occur.  相似文献   
999.
1000.
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