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   81908篇
  免费   5046篇
  国内免费   770篇
林业   3139篇
农学   2489篇
基础科学   674篇
  9785篇
综合类   16380篇
农作物   3019篇
水产渔业   3739篇
畜牧兽医   42467篇
园艺   1121篇
植物保护   4911篇
  2021年   718篇
  2020年   797篇
  2019年   977篇
  2018年   1345篇
  2017年   1551篇
  2016年   1376篇
  2015年   1320篇
  2014年   1495篇
  2013年   2896篇
  2012年   2855篇
  2011年   3448篇
  2010年   2277篇
  2009年   2162篇
  2008年   3070篇
  2007年   2948篇
  2006年   2653篇
  2005年   2574篇
  2004年   2297篇
  2003年   2350篇
  2002年   2201篇
  2001年   2484篇
  2000年   2528篇
  1999年   1939篇
  1998年   789篇
  1997年   705篇
  1995年   740篇
  1993年   664篇
  1992年   1526篇
  1991年   1716篇
  1990年   1640篇
  1989年   1588篇
  1988年   1472篇
  1987年   1526篇
  1986年   1572篇
  1985年   1396篇
  1984年   1187篇
  1983年   1015篇
  1982年   679篇
  1979年   1055篇
  1978年   829篇
  1977年   672篇
  1976年   711篇
  1975年   746篇
  1974年   1003篇
  1973年   984篇
  1972年   951篇
  1971年   878篇
  1970年   851篇
  1969年   804篇
  1967年   701篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
961.
An ELISA was developed to detect circulating antigens of Toxoplasma gondii in the serum of cats. For the experiment, toxoplasmosis was induced in a group of cats by oral administration of bradyzoites. An ELISA that detects anti-Toxoplasma IgG, an ELISA to detect circulating antigens, and fecal examinations were performed on samples from each cat for 1 year after inoculation. When coupled with IgG-class antibody measurement, antigen detection can aid in the diagnosis of some cases of subclinical feline toxoplasmosis.  相似文献   
962.
963.
964.
965.
966.
Gross and microscopic lesions observed in bovine and porcine hemorrhagic septicemia, and in bovine Pasteurella multocida endotoxemia are described. Widely distributed hemorrhages, edema, and general hyperemia were the most obvious tissue changes observed in the infected calves. Pneumonia was a constant lesion. Aerosol exposure produced a multiple focal fibrinosuppurative pneumonia, while intranasal and intramuscular inoculation resulted in generalized interstitial pneumonia. A slight lymphadenitis and degenerative changes in hepatic and renal parenchymal cells were also observed.

The predominant lesions observed in infected pigs were a diffuse, extensive, fibrinous pneumonia and fibrinous polyserositis. Edema and general hyperemia were observed, but the widespread hemorrhages which occurred in the calves were not present. Acute lymphadenitis and renal tubule vacuolar degeneration were observed. A slight amount of cloudy swelling and focal areas of necrosis were found in the liver.

Lesions in a calf that died following administration of Past. multocida endotoxin were widely distributed hemorrhages, edema, and general hyperemia. These lesions were especially evident in the lungs, and indicated widespread vascular alteration.

  相似文献   
967.
968.

Background

Cough often is reported as the primary clinical sign of congestive heart failure (CHF) in dogs with chronic degenerative myxomatous mitral valve disease (MMVD). Concurrent airway disease and compression of the left mainstem bronchus by a large left atrium also have been proposed as potential causes of coughing in these patients.

Objectives

To investigate the association between the presence of coughing and different potential causes of cough, including CHF, abnormal radiographic airway pattern, and cardiomegaly in dogs affected by naturally acquired MMVD.

Animals

Two hundred six client‐owned dogs.

Methods

Retrospective analysis performed on medical records of dogs affected by MMVD that underwent full cardiac evaluation, including echocardiographic examination and thoracic radiography.

Results

Univariate analyses showed that CHF is not a predictor of coughing (OR = 1.369; 0.723, 2.594), whereas abnormal radiographic airway pattern (OR = 3.650; 2.051, 6.496) and increased left atrial size observed radiographically (OR = 3.637; 1.904, 6.950) or echocardiographically (OR = 2.553; 1.436, 4.539) were significantly associated with coughing in dogs with MMVD. The same risk factors were significant in multivariate analyses.

Conclusions and Clinical Importance

This study indicates that CHF is not significantly associated with coughing in dogs with MMVD. Instead, abnormal radiographic airway pattern and left atrial enlargement are associated with coughing in these patients. This important finding should be taken into account when considering diagnosis and clinical management of CHF in these dogs.  相似文献   
969.
Forty-three randomly selected farms located throughout South Island, excluding the Nelson region, were surveyed for anthelmintic usage and for sheep nematodes resistant to anthelmintics.

Most farmers had used both benzimidazole and non-benzimidazole broad-spectrum drenches on their properties in previous years.

Sheep were being drenched, on average, 5.6 times within their first year of life but much less frequently thereafter. Commercial interests played the dominant role in helping farmers formulate their drenching policies. On each farm 24 numbered ewe replacement lambs, born during the spring of 1980, were sampled for faeces at the beginning of the trial to provide material for egg counts and larval cultures. The lambs were weighed and divided into three groups of eight. One group received thiabendazole (TBZ) at 66 mg/kg, the second levamisole (LEV) at 8 mg/kg while the third remained untreated as controls. All were resampled 4 to 10 days later.

On 32 (88%) of the 40 farms where drenching trials were successfully carried out during autumn 1981, the faecal egg count depression (FECD) following treatment with either drench was 100%. On one farm TBZ was less than 100% effective as gauged by FECD. LEV proved to be less than 100% effective on 7 farms. On one farm the FECD was less than 80%, on 2 between 90% and 95% and on 4 between 95% and 99%.  相似文献   
970.
Summary

The prevalence of allergy, lung function disorders, and bronchial hyperreactivity was studied in 102 Dutch veterinarians, subdivided into five professional groups (predominantly working with either swine, cattle, poultry, companion animals, or as a non‐practitioner). The mean age of the participants was 43 years; 6 participants were females. Twenty‐two per cent of the participants were overweight, and relatively more non‐practitioners than practitioners were overweight. Approximately 23% of the vets reported complaints of prolonged fatigue. The data suggest a relationship between complaints of prolonged fatigue and a more than average number of daily working hours. Only a small proportion of vets were sensitized against several allergens. There were no significant differences in prevalence of distinct lung function disorders or bronchial hyperreactivity between professional groups. It is hypothesized that the respiratory complaints (chronic coughing, chronic phlegm production, stuffed nose, sneezing) reported by the vets predominantly working in swine and/or poultry practice could be caused by irritation and/or inflammation of the first part of the trachea‐bronchial tree that has no measurable and permanent consequences for changes in lung function or increased bronchial hyperreactivity. The results of a skin test against allergens and determination of allergen‐specific IgE in blood indicated that the respiratory complaints were probably not related to allergy against the panel of allergens tested.  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