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   11283篇
  免费   3869篇
林业   157篇
农学   446篇
基础科学   14篇
  1325篇
综合类   20篇
农作物   118篇
水产渔业   2510篇
畜牧兽医   9298篇
园艺   7篇
植物保护   1257篇
  2024年   6篇
  2023年   93篇
  2022年   9篇
  2021年   130篇
  2020年   641篇
  2019年   1038篇
  2018年   987篇
  2017年   1053篇
  2016年   1017篇
  2015年   937篇
  2014年   1008篇
  2013年   1201篇
  2012年   632篇
  2011年   674篇
  2010年   751篇
  2009年   480篇
  2008年   373篇
  2007年   167篇
  2006年   178篇
  2005年   166篇
  2004年   235篇
  2003年   233篇
  2002年   275篇
  2001年   225篇
  2000年   220篇
  1999年   124篇
  1998年   173篇
  1997年   191篇
  1996年   163篇
  1995年   165篇
  1994年   144篇
  1993年   160篇
  1992年   176篇
  1991年   148篇
  1990年   192篇
  1989年   134篇
  1988年   114篇
  1987年   146篇
  1986年   56篇
  1985年   79篇
  1984年   83篇
  1983年   81篇
  1982年   39篇
  1981年   13篇
  1980年   8篇
  1978年   7篇
  1977年   8篇
  1975年   4篇
  1974年   2篇
  1970年   4篇
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
21.
22.
Six out of eight different Trichomonas gallinae strains isolated from racing pigeons proved to be resistant to the nitroimidazole drugs ronidazole, carnidazole and metronidazole. The minimal cytocidal concentration of ronidazole was determined in in vitro experiments. Moreover, a therapeutic dose for ronidazole was determined for the control of trichomoniasis in pigeons from which the resistant T. gallinae strains were isolated. It was a 5-fold increase of the recommended ronidazole dosage which eliminated the infection in affected pigeons.  相似文献   
23.
Precise localization of the needle tip during CT-guided percutaneous biopsy is considered to be a key element of a successful procedure. To ensure accuracy, the true needle tip must be differentiated from a false or simulated tip which appears when the CT slice encompasses only the shaft of an angled needle. By obtaining images of an aspiration biopsy needle inserted vertically into a phantom and then incrementally tilting the gantry, the authors were able to compare the characteristic features of the true tip to the simulated tip. The true tip was abrupt and distinct and had an adjacent flame-like low density artifact. The simulated tip was indistinct and tapered, yet still produced the adjacent artifact. We concluded that the shape and distinctness of the end portion of the needle itself, rather than the attendant artifact, were the most reliable criteria for accurate needle tip identification.  相似文献   
24.
25.
Lactate Kinetics in veterinary Critical Care: A Review   总被引:3,自引:0,他引:3  
Elevation in blood lactate concentration, with or without accompanying metabolic acidosis, is a hallmark finding in patients with circulatory compromise, and is also consistently noted in other conditions affecting critically ill or injured individuals. Little is reported in a veterinary literature regarding lactate measurement in the emergency and critical care setting, despite impressive reports of the clinical usefulness of lactate measurement in people. The purpose of this article is to review lactate kinetics and the clinical utility of lactate measurement. Limitations to lactate evaluation will also be discussed.  相似文献   
26.
27.
PULMONARY MINERALIZATION IN FOUR DOGS WITH CUSHING'S SYNDROME   总被引:1,自引:0,他引:1  
The clinical and imaging features of four dogs with Cushing's syndrome and pulmonary mineralization are reviewed. Three dogs presented with a primary complaint of respiratory distress/dyspnea. Three dogs had pituitary dependent Cushing's syndrome, while the remaining one dog had iatrogenic Cushing's syndrome. Each dog had clinical features typical for Cushing's syndrome. Two of the dogs were euthanized due to progressive hypoxemia. In each dog, the serum calcium, phosphorous, blood urea nitrogen and creatinine were normal.
A generalized increase in unstructured interstitial pulmonary opacity with diffuse mineralization was noted on thoracic radiographs of all dogs. In one dog, an ill-defined nodular interstitial pattern of mineralization was present. Delayed bone phase scintigraphy using 99mTechnetium methylene diphosphonate documented generalized pulmonary uptake in two dogs. 99mTechnetium labeled microaggregated albumin lung perfusion scans were normal in these two dogs. 99mTc-MDP scintigraphy can provide useful information in diagnosing pulmonary mineralization in Cushingoid dogs.  相似文献   
28.
Ultrasonography and MRI have become valuable tools for imaging of tendon injuries. The current study examines the histopathologic basis for the imaging abnormalities. Five injured equine forelimbs and two normal contralateral limbs were studied with high resolution real time ultrasound and MRI. Histologic sections were made and correlated with the diagnostic images. All lesions were readily seen by both modalities. Lesions characterized by hemorrhage, edma, and cellular infiltration were sonolucent on ultrasound and bright on MRI images. MRI returned to normal as fibrogenesis ensued. Ultrasound images remained abnormal until fibrillar reallgnment occured with completion of the healing process. High resolution real time ultrasound and MRI both accurately reflect the tissue abnormalities in acute tendon injuries. The injured horse does appear to be an effective model for correlative imaging studies of tendon injuries.  相似文献   
29.
The absence or presence of metastases on thoracic radiographs in 55 female dogs with mammary gland tumors was assessed by comparing the results of a single radiographic examination, using dorsoventral and left lateral views, with clinical and histologic follow-up data. Radiographic abnormalities found in dogs with thoracic metastases were classified as well-defined pulmonary nodules, ill-defined pulmonary nodules, and involvement of pleural effusion. No obvious difference in the effect on the right or left lung lobes was found. The sensitivity, specificity and accuracy for the detection of thoracic metastases were 65%, 97%, and 87%, respectively.  相似文献   
30.
Objective: To evaluate the ability of capnography to document proper placement of nasoesophageal (NE) and nasogastric (NG) feeding tubes. This study was conducted in 3 phases. Phase I of this study was designed in order to test the efficacy of capnography to distinguish placement of a feeding tube in the alimentary tract versus the respiratory tract. Phase II was designed in order to document that carbon dioxide (CO2) could be measured through a polyvinyl chloride (PVC) feeding tube. Phase III was performed in order to evaluate the technique of continuous monitoring during insertion of the feeding tube into the esophagus and stomach as would be performed during a clinical‐tube placement. Design: Prospective study. Setting: Research laboratory. Animals: 24 adult dogs. Interventions: In Phase I, sedated dogs were instrumented with an intratracheal catheter and an 8 French feeding tube placed nasally into the distal esophagus and later advanced into the stomach. In Phase II, dogs were anesthetized and an 8 French feeding tube was placed down the endotracheal tube, then into the esophagus and later advanced into the stomach. In Phase III, sedated dogs were instrumented with an 8 French feeding tube inserted intranasally and then advanced to the level of the nasopharynx, distal esophagus and, lastly, the stomach. Fluoroscopy was used in order to determine location of the feeding tube. Measurements and main results: Phase I measurements included respiratory rate and CO2 from the trachea, esophagus, and stomach and pH of gastric fluid sample. Phase II measurements included respiratory rate and CO2 from the endotracheal tube, feeding tube in the endotracheal tube, feeding tube in the distal esophagus, and feeding tube in the stomach. Phase III data collection included respiratory rate and CO2 as the tube was passed through the nasal cavity, nasopharynx, esophagus and stomach. Phase I fluid samples were collected from 5 of the 9 dogs and had pH values from 1.68 to 4.20. In both phases, values for the respiratory rate and CO2 from the esophagus and stomach were 0 ± 0, significantly lower (P < 0.001) than the values from the trachea. In Phase II, there was no significant difference between the respiratory rates (P = 0.886) and CO2 (P = 0.705) readings obtained from the endotracheal tube compared to readings from the feeding tube in the endotracheal tube. In Phase III, there was a significant difference (P < 0.001) between the respiratory rates and CO2 readings obtained from the nasal cavity and the nasopharynx when compared to those readings obtained from the esophagus and stomach. Measurement of CO2 and respiratory rate resulted in a reading of 0 every time the feeding tube was in the esophagus or stomach. Conclusions: Capnography may be used in order to detect airway placement of NE and NG tubes.  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