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   147417篇
  免费   7269篇
  国内免费   93篇
林业   8776篇
农学   5450篇
基础科学   941篇
  19507篇
综合类   22130篇
农作物   7324篇
水产渔业   8399篇
畜牧兽医   68853篇
园艺   2722篇
植物保护   10677篇
  2020年   1177篇
  2019年   1375篇
  2018年   4538篇
  2017年   4801篇
  2016年   3185篇
  2015年   1800篇
  2014年   2238篇
  2013年   5295篇
  2012年   4829篇
  2011年   7038篇
  2010年   5164篇
  2009年   4501篇
  2008年   6189篇
  2007年   6100篇
  2006年   4381篇
  2005年   4169篇
  2004年   3940篇
  2003年   4115篇
  2002年   3596篇
  2001年   4154篇
  2000年   4292篇
  1999年   3372篇
  1998年   1474篇
  1997年   1387篇
  1996年   1288篇
  1995年   1530篇
  1994年   1358篇
  1993年   1238篇
  1992年   2589篇
  1991年   2700篇
  1990年   2592篇
  1989年   2614篇
  1988年   2374篇
  1987年   2349篇
  1986年   2427篇
  1985年   2340篇
  1984年   1881篇
  1983年   1677篇
  1982年   1149篇
  1979年   1748篇
  1978年   1397篇
  1977年   1153篇
  1976年   1212篇
  1975年   1292篇
  1974年   1500篇
  1973年   1514篇
  1972年   1405篇
  1971年   1304篇
  1970年   1251篇
  1969年   1284篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
As part of an experiment aiming to modify the meat fatty acid profile, this work studied the growth and carcass traits as affected by various dietary ratios of sunflower oil and linseed oil. A diet without added oil served as a control (C). Four other diets were equally 4% oil-enriched but they differed in the incorporation ratios of sunflower oil (S) to linseed oil (L), i.e. 4% S to 0% L (diet 4%S), 3% S to 1% L (diet 3:1%SL), 2% S to 2% L (diet 2:2%SL) and 0% S to 4% L (diet 4%L). The oil-rich diets had slightly higher digestible energy contents (11.4 vs 10.6 MJ/kg) than the C feed. In each group 10 litters of 7 to 9 Pannon White kits per litter were studied in the pre-weaning period from 21 to 35 days old. Growth and slaughter traits were assessed with 50 and 30 rabbits per group, respectively. No significant effects of diets were found on litter and doe performances. The only significant differences in growth performance of the C, 4%S, 3:1%SL, 2:2%SL and 4%L rabbits were for the 35–49 day feed intake (88, 86, 84, 84 and 83 g per day, respectively, = 0.046), the 35–84 day growth rate (36, 38, 37, 35 and 37 g/day, = 0.034) and the 84-day body weight (2608, 2703, 2664, 2565 and 2628 g, respectively, = 0.022). There were several significant differences in carcass traits including the weight of reference carcass (1357, 1391, 1388, 1380 and 1369 g, respectively, = 0.004) and left longisimus dorsi meat (78, 79, 81, 81 and 76 g, respectively, = 0.046) of rabbits. The diets had major effects on the L*, a* and b* colour values (lightness, redness and yellowness) of meat and fat. Carcass colour of the C and 4%S rabbits was closer and the 4%L rabbits was further from the European consumer's preference of light coloured, less red and slightly yellow rabbit meat. Our result reveals the importance of age and body weight at slaughter. Taking the growth and slaughter performances and, the recent belief of human health benefits from lower n− 6/n− 3 FAs dietary ratios into account, the 2:2%SL diet seems most appropriate if the interests of the raisers, meat processors and buyers are considered equally.  相似文献   
942.
ObjectiveTo determine the analgesic and systemic effects of epidural administration of ketamine, lidocaine or a combination of ketamine/lidocaine in standing cattle.Study designProspective, randomized, experimental trial.AnimalsSix healthy male cattle weighing between 335 and 373 kg.MethodsThe animals received 0.5 mg kg?1 of ketamine (K), 0.2 mg kg?1 of 2% lidocaine (L) or 0.25 mg kg?1 ketamine plus 0.1 mg kg?1 lidocaine (KL). All the drugs were injected into the dorsolumbar epidural space via a caudal approach through a non‐styletted multiple‐port catheter. Each animal received each treatment at random. Evaluations of analgesia, sedation, ataxia, heart rate, arterial pressure, respiratory rate, skin temperature and rectal temperature were obtained at 0 (basal), 5, 10, 15, 30, 45, 60, 75, 90 minutes after epidural injection, and then at 30‐minute intervals until loss of analgesia occurred. Skin temperature was taken at these intervals up to 60 minutes. All the animals received a standard noxious stimulus; a 4‐point scale was used to score the response. A second scale was used to score ataxia and a third for sedation.ResultsThe duration of analgesia in the upper and lower flanks in cattle was 140 ± 15, 50 ± 14 and 80 ± 22 minutes (mean ± SD) after dorsolumbar epidural KL, K or L, respectively. The cardiovascular changes were within acceptable limits in these clinically healthy cattle.ConclusionsDorsolumbar epidural administration of KL to cattle resulted in longer duration of analgesia of the upper and lower flanks in standing conscious cattle, than the administration of K or L alone.Clinical relevanceFurther research is necessary to determine whether this combination using this technique provides sufficient analgesia for flank surgery in standing cattle.  相似文献   
943.
944.
This study aimed to evaluate effects of orally administered copper (Cu) to Chios sheep breed on serum levels of aspartate aminotransferase (AST), l-alanine aminotransferase (ALT), lactate deydrogenase (LDH) and alkaline phosphatase (ALP), in order to establish a practical and effective method in diagnosing the prehemolytic stage of chronic Cu poisoning. Eighteen ewes were allocated to three treatments of six ewes and fed a diet that contained 16.4 mg/day of Cu. Ewes in treatment Cu-0 received no additional Cu (control), while those in treatments Cu-60 and Cu-95 received 60 and 95 mg additional Cu/day, respectively, as an oral solution of copper sulfate. Therefore the ewes in treatment Cu-0, Cu-60 and Cu-95 consumed 16.4, 76.4 and 111.4 mg Cu/day, respectively. Serum enzyme levels were similar among treatments and all ewes remained clinically healthy until the end of the experiment. Results suggest that Chios ewes exhibit tolerance to Cu supplementation for up to 6 weeks.  相似文献   
945.
946.
Background: Episodic collapse in horses has equine welfare and human safety implications. There are, however, no published case series describing this syndrome. Objectives: To characterize the cause and outcomes for horses referred for investigation of episodic collapse. Animals: Twenty‐five horses referred for investigation of single or multiple episodes of collapse. Methods: Retrospective study. Clinical records from the Dick Vet Equine Hospital, University of Edinburgh from November 1995 to July 2009 were searched using the following keywords: collapse, collapsing, fall, syncope. Collapse was defined as an incident in which the horse lost postural tone with or without progression to recumbency and with or without loss of consciousness. Long‐term follow‐up information was obtained by telephone conversation with the owner. Results: A final diagnosis was reached in 11 cases, namely cardiac arrhythmia (4), right‐sided heart failure (1), hypoglycemia (2), generalized seizures (2), and sleep disorder (2). A presumptive diagnosis was reached in 8 cases, namely neurocardiogenic syncope (5), exercise‐induced pulmonary hemorrhage (2), and generalized seizures (1). No diagnosis was reached in 6 cases despite comprehensive investigations. Three horses were euthanized at presentation. Treatment was attempted in 9 horses with 6 cases having successful outcome before discharge. Follow‐up information was available for 14 of 19 horses discharged from the hospital. Only 1 of these horses was observed to collapse after discharge. Conclusions and Clinical Importance: Definitive diagnosis was more likely to be reached in cases with multiple episodes of collapse. Horses in which 1 episode of collapse occurred did not necessarily collapse again.  相似文献   
947.
Two clinical cases of accidental entrapment of cats in front-loading washing machines are described. One cat died the day after presentation as a result of aspiration pneumonia and head trauma, despite supportive care. The second cat survived with supportive treatment, but developed dermatologic complications 10 d later.  相似文献   
948.
949.
To establish a well-tolerated technique for recording electrocardiograms (ECGs) and a reference range for the normal pet rabbit ECG, 46 healthy pet rabbits were studied. The following reference ranges were calculated. Heart rate was 198 to 330 bpm. P waves had a duration of 0.01 to 0.05 seconds and an amplitude of 0.04 to 0.12 mV. The P-R interval was 0.04 to 0.08 seconds and the duration of the QRS complex was 0.02 to 0.06 seconds. The amplitude of the R wave was 0.03 to 0.39 mV. The Q-T interval was 0.08 to 0.16 seconds. The amplitude of the T wave was 0.05 to 0.17 mV. Mean electrical axis was found to be -43° to +80°. Evidence of variation due to breed or bodyweight was not found to be significant, except for a quadratic relationship between R wave amplitude and bodyweight. The ECG recording technique used in this study for pet rabbits was well tolerated and shown to be both reliable and repeatable.  相似文献   
950.
Objective To evaluate the effects of time on cellular localization of Visudyne® after local injection. Animals Twenty athymic nude mice. Procedures A squamous cell carcinoma (SCC) cell line (A‐431) was injected into right and left dorsolumbar subcutaneous tissue of each mouse, representing treatment (T) and control (C) tumors. In experiment 1 (Exp 1; n = 10) and 2 (Exp 2; n = 10), the T tumors received a local injection of Visudyne® (0.1 mg/cm3), and C tumors received an equal dose of 5% dextrose in water (D5W). Mice were randomly subdivided into two groups (A and B; n = 5 per group). Mice in Exp 1A and B were sacrificed 1 and 30 min after local injection, respectively. Experiment 1A and B tumors were evaluated by fluorescence microscopy to determine drug localization. Experiment 2A and B tumors were exposed to LED illumination 1 and 30 min after injection, respectively, and evaluated by transmission electron microscopy (TEM) to determine ultrastructural tumor cell damage. Results Fluorescence was detected within the cytoplasm of T tumors in both Exp 1A and B. Significance was detected in fluorescence intensity between T1 min vs. T30 min (P = 0.03) and between T1 min and C1 min tumors (P = 0.01), respectively. Tumors in Exp 2A and B demonstrated evidence of apoptotic cell death. Conclusions Fluorescence microscopy demonstrated higher Visudyne® concentration within SCC cytoplasm of 1 min compared with 30‐min tumors. Transmission electron microscopy results revealed that tumors treated by photodynamic therapy (PDT) within 30 min of local injection undergo cellular apoptosis.  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