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   6422篇
  免费   3375篇
林业   162篇
农学   437篇
基础科学   3篇
  1306篇
综合类   8篇
农作物   90篇
水产渔业   2505篇
畜牧兽医   4025篇
园艺   1篇
植物保护   1260篇
  2023年   7篇
  2022年   7篇
  2021年   130篇
  2020年   474篇
  2019年   1027篇
  2018年   895篇
  2017年   944篇
  2016年   935篇
  2015年   813篇
  2014年   803篇
  2013年   966篇
  2012年   453篇
  2011年   471篇
  2010年   594篇
  2009年   245篇
  2008年   224篇
  2007年   75篇
  2006年   95篇
  2005年   84篇
  2004年   96篇
  2003年   90篇
  2002年   106篇
  2001年   69篇
  2000年   107篇
  1999年   7篇
  1997年   13篇
  1996年   5篇
  1995年   4篇
  1994年   5篇
  1993年   6篇
  1990年   4篇
  1989年   2篇
  1986年   4篇
  1985年   1篇
  1984年   1篇
  1983年   2篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   6篇
  1977年   5篇
  1976年   2篇
  1975年   3篇
  1974年   2篇
  1973年   1篇
  1970年   4篇
  1968年   1篇
  1966年   1篇
  1963年   1篇
排序方式: 共有9797条查询结果,搜索用时 15 毫秒
101.
102.
The aim of the present study is to identify ostrich sex by using polymerase chain reaction (PCR) on micro amounts of DNA from blood, bloodstain and feathers. Sixteen male and 18 female ostriches were used as test individuals. Genomic DNA as a template was extracted by the Chelex method. Ostrsex‐P1 and P2 primers were designed to perform PCR amplification on the template. PCR products were checked using agarose gel electrophoresis with ethidium bromide staining and ostrich sex was determined directly by the bands shown on the gel. The results demonstrate that ostrich sex can be determined by the extraction of DNA from as little as 0.0125 μl blood using Chelex, whereby the use of large amounts of organic solvents such as phenol and chloroform are unnecessary. In addition, it is possible to identify ostrich sex using micro amounts of DNA extracted from bloodstains and/or feathers. The use of feathers particularly avoids unwanted sampling problems such as the difficulty of collecting ostrich blood, the stress to the ostrich caused by bleeding, and the demand for a lot of manpower for ostrich restraint.  相似文献   
103.
ObjectiveTo assess whether recovery from general anesthesia, in an illuminated or a darkened stall, has an effect on time to first movement, time to standing, and recovery score.Study designProspective randomized clinical study.AnimalsTwenty-nine healthy, 2- to 5-year-old horses undergoing surgical correction of dorsal displacement of the soft palate.MethodsEach horse was assigned randomly to recover in either an illuminated (n = 15) or a darkened stall (n = 14). For pre-anesthetic medication, all horses received intravenous (IV) xylazine (0.4 mg kg−1) and butorphanol (0.02 mg kg−1). Anesthesia was induced with midazolam (0.1 mg kg−1) and ketamine (2.2 mg kg−1) IV and maintained on isoflurane in oxygen. Vital parameters, end-tidal CO2 and isoflurane were recorded at 5-minute intervals. At the conclusion of anesthesia, horses were placed in either an illuminated or a darkened stall and xylazine (0.2 mg kg−1) IV was administered at extubation. Video cameras were used to record the horses while they were allowed to recover undisturbed. Video recordings were later viewed and recoveries were evaluated on a 100-point scale by three graders.ResultsHorses in illuminated and darkened recovery stalls were evaluated on total anesthesia time, minimum alveolar concentration hours of isoflurane, time to first movement, time to standing, and total recovery score. There were no significant differences between the two groups in any of the measured parameters.ConclusionRecovering horses in a darkened versus an illuminated recovery stall may provide no benefit.Clinical relevanceDarkening the recovery stalls for horses recovering from general anesthesia may be unnecessary.  相似文献   
104.
Companion animals are exposed to similar environmental conditions and carcinogens as humans. In some animal cancers, there also appears to be the same genetic changes associated as in humans. However, little work has been carried out in cancer biomarker identification in animals. The recent dramatic advances in molecular medicine, genomics, proteomics and translational research will allow biomarker identification, which may provide the best strategies for veterinarians and clinicians to combat disease by early diagnosis and administration of effective treatments. Proteomics may have important applications in cancer diagnosis, prognosis and predictive clinical outcome that could directly change clinical practice by affecting critical elemen‐ts of care and management. This review summarizes the advances in proteomics that has propelled us to this exciting age of clinical proteomics, and highlights the future work that is required for this to become a reality. In this review, we will discuss the available proteomic technologies and their limitations, and highlight the key areas of research and how they have been used to discover cancer biomarkers. The principles described here are equally applicable to human and animal disease, but implementation of ‘omic’ technologies requires stringent guidelines for collection of clinical material, the application of analytical techniques and interpretation of the data.  相似文献   
105.
The majority of the known prognostic factors in dogs with lymphoma have been evaluated before treatment commences or at the time of diagnosis. Prognostic factors evaluated during the initial phase of treatment are less described but may provide important clinical information. In this retrospective study, 82 canine lymphoma patients were categorized according to the weight change between diagnosis and after 5 weeks of chemotherapy. Dogs that gained greater than 5% or lost greater than 5% of initial body weight were categorized as increased‐ or decreased‐weight groups, respectively. Those in which weight changed less than 5% were categorized as the maintained‐weight group. The median progression‐free survival (PFS) in the increased‐weight group, maintained‐weight group and decreased‐weight group was 226, 256 and 129 days, respectively. The decreased‐weight group had significantly shorter PFS than the increased and maintained groups (P = .023, P = .003, respectively). The median survival time (ST) in the increased‐weight group, maintained‐weight group and decreased‐weight group was 320, 339 and 222 days, respectively. There was no significant difference in ST among the three groups (P = .128). In Cox‐regression results, weight change group and initial body weight were significant risk factors associated to PFS (P = .007, P = .001, respectively) while only patient's initial body weight was a significant risk factor to ST (P = .013). In conclusion, evaluation of initial body weight and weight changes over time can provide valuable information regarding PFS and ST in dogs with multicentric lymphoma.  相似文献   
106.
107.
Objective – To determine whether older dogs will have a more pronounced pro‐inflammatory response and blunted anti‐inflammatory response to pathogen‐associated molecular patterns (PAMPs) compared with younger dogs. Design – Prospective. Setting – University teaching hospital. Animals – Thirty‐eight privately owned sexually altered dogs of various ages. Interventions – Blood was collected for HCT, WBC count, plasma biochemical analysis, and whole blood culture. Whole blood was stimulated with lipopolysaccharide (LPS) or, lipoteichoic acid or, peptidoglycan or, addition of phosphate‐buffered saline. Tumor necrosis factor (TNF), interleukin (IL)‐6, and IL‐10 production from whole blood were compared among young, middle aged, and geriatric dogs. Measurements and Main Results – LPS, lipoteichoic acid, and peptidoglycan stimulated significant TNF, IL‐6, and IL‐10 production from canine whole blood compared with phosphate‐buffered saline. Whole blood from geriatric dogs had a blunted IL‐10 response to LPS stimulation and middle‐aged dogs had increased LPS‐induced TNF production compared with the other groups. Conclusion – PAMPs from gram‐positive and gram‐negative bacteria stimulate TNF, IL‐6, and IL‐10 production from canine whole blood. The inflammatory mediator response to PAMPs from gram‐negative bacteria alters with age and may be one factor contributing to mortality in geriatric dogs with sepsis.  相似文献   
108.
To clarify the role of serotonin (5‐HT) in the regulatory mechanism of L‐tryptophan (TRP)‐induced growth hormone (GH) secretion in cattle, changes in 5‐HT concentrations in the cerebrospinal fluid (CSF) in the third ventricle (3V) and GH in plasma before and after the peripheral infusion of TRP were determined simultaneously. The direct effect of TRP on GH release from the dispersed anterior pituitary cells was also assessed. A chronic cannula was placed in 3V by stereotaxic surgery, then CSF and blood were withdrawn under physiological conditions. TRP (38.5 mg/kg BW) was infused through an intravenous catheter from 12.00 to 14.00 hours and CSF and blood sampling were performed from 11.00 to 18.00 hours at 1‐h intervals. The concentration of 5‐HT in CSF was determined by high‐performance liquid chromatography with electrochemical detection. GH, melatonin (MEL), and cortisol (CORT) concentrations were measured by radio‐immunoassay and enzyme‐immunoassay. Concentrations of 5‐HT were increased by TRP infusion. The TRP infusion significantly increased GH release. On the other hand, TRP did not stimulate GH release from the bovine pituitary cells. MEL and CORT concentrations were not altered by TRP infusion. These results suggest that TRP induced GH release via the activation of serotonergic neurons in cattle.  相似文献   
109.
This experiment was conducted to investigate the difference between ruminal (solid feed, SF) and abomasal (liquid feed, LF) feeding on the plasma leptin concentration in sheep. The experiment consisted of 2 weeks to adapt the animals to SF, 4 weeks of feeding on SF, 2 weeks adaptation to LF, 8 weeks of feeding on LF, 2 weeks of adaptation to SF, and 4 weeks of feeding on SF. The LF directory flowed into the abomasums of sheep by bottle feeding. Plasma leptin concentration before morning feeding was almost constant in the SF periods, whereas it showed between‐day variations when measured during the LF periods. Mean plasma leptin levels were higher for LF (7.77 ± 0.76 ng/mL; mean ± SE) than for SF periods (3.95 ± 0.16 ng/mL; mean ± SE). Although plasma leptin concentration did not show any change after feeding in the SF and LF periods, plasma insulin and glucose levels increased within 15 min after liquid abomasal feeding, but not after solid ruminal feeding. The high plasma leptin concentration during the LF periods in weaned sheep could be due to change of digestible energy intake and changes in plasma insulin and glucose levels accompanying the changes in digestive processes and nutrient supply.  相似文献   
110.
Reasons for performing study: An improvement in sperm quality after single layer centrifugation (SLC) has been seen in previous studies using small sample sizes (for example, n = 10 stallions). There is a need to investigate whether this improvement is repeatable over several breeding seasons with a larger number of stallions (n ≥ 30 stallions). Objective: To make a retrospective analysis of the results of SLC performed on more than 250 sperm samples (176 ejaculates) from 31 stallions in 3 consecutive breeding seasons. Methods: Sperm quality (motility, proportion of morphologically normal spermatozoa and the proportion of spermatozoa with undamaged chromatin) was assessed before and after SLC. Results: All parameters of sperm quality examined were significantly better in sperm samples after SLC than in their unselected counterparts (P<0.001 for each parameter). The yield of spermatozoa obtained after SLC was influenced by the type of extender used and also by the concentration of spermatozoa in the original ejaculate, with fewer spermatozoa being recovered when the loading dose contained a high concentration of spermatozoa. The optimal concentration was approximately 100 × 106/ml. Sperm concentration in the samples loaded on to the colloid influenced the sperm yield while the type of semen extender affected sperm quality and survival. Furthermore, the scaled‐up SLC method was found to be suitable for use with a range of ejaculates, with similar sperm kinematics being observed for standard and scaled‐up preparations. Conclusions: SLC consistently improved the quality of stallion sperm samples from a large number of ejaculates. The method could be scaled‐up, allowing larger volumes of ejaculate to be processed easily from a wide range of stallions.  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