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   3332篇
  免费   348篇
  国内免费   217篇
林业   51篇
农学   88篇
基础科学   8篇
  75篇
综合类   1005篇
农作物   83篇
水产渔业   414篇
畜牧兽医   2048篇
园艺   104篇
植物保护   21篇
  2024年   17篇
  2023年   50篇
  2022年   87篇
  2021年   139篇
  2020年   151篇
  2019年   205篇
  2018年   111篇
  2017年   180篇
  2016年   204篇
  2015年   162篇
  2014年   170篇
  2013年   185篇
  2012年   211篇
  2011年   225篇
  2010年   161篇
  2009年   186篇
  2008年   140篇
  2007年   157篇
  2006年   137篇
  2005年   132篇
  2004年   128篇
  2003年   79篇
  2002年   68篇
  2001年   66篇
  2000年   60篇
  1999年   43篇
  1998年   56篇
  1997年   40篇
  1996年   31篇
  1995年   47篇
  1994年   42篇
  1993年   28篇
  1992年   30篇
  1991年   26篇
  1990年   26篇
  1989年   36篇
  1988年   11篇
  1987年   14篇
  1986年   7篇
  1985年   3篇
  1984年   6篇
  1982年   4篇
  1980年   8篇
  1979年   6篇
  1978年   3篇
  1977年   2篇
  1975年   2篇
  1974年   4篇
  1973年   4篇
  1956年   3篇
排序方式: 共有3897条查询结果,搜索用时 15 毫秒
21.
Judith A.  Hudson  DVM  PhD  Susan T.  Finn-Bodner  DVM  MS  Joan R.  Coates  DVM  Donald C.  Sorjonen  DVM  MS  Stephen T.  Simpson  DVM  MS  James C.  Wright  DVM  PhD  Jan E.  Steiss  DVM  PhD  Nancy R.  Cox  DVM  PhD  Dana M.  Vaughn  DVM  PhD  Starr C.  Miller  BS  Scott A.  Brown  DVM  PhD  Phillip D.  Garrett  DVM  MS 《Veterinary radiology & ultrasound》1995,36(6):542-547
Doppler ultrasonography of the spinal cord was performed in 34 normal, anesthetized dogs following hemilaminectomy. This study was part of an investigation to evaluate the efficacy of a 21-aminosteroid compound and high dose methylprednisolone for the treatment of spinal cord trauma. Grey-scale images of the canine spinal cord were similar to those described for the spinal cord of people. Doppler waveforms of intraparenchymal spinal arteries exhibited high end diastolic blood flow velocities, indicating low resistance to flow. Doppler values (mean ± SD) for arteries immediately ventrolateral to the central canal were: Peak Systolic Velocity = 5.78 ± 2.5 cm/sec, Minimum Diastolic Velocity = 3.5 ± 1.62 cm/sec, Mean Velocity = 4.45 ± 1.96 cm/sec, Minimum Diastolic Velocity = 3.5 ± 1.62 cm/sec, Mean Velocity = 4.45 ± 1.96 cm/sec, Systolic/Diastolic ratio = 169 ± 0.19, Pulsatility Index = 0.53 ± 0.09, and Resistance Index = 0.4 ± 0.06.  相似文献   
22.
The aim of the present work was to investigate the effect of Rhus coriaria L. inclusion to the diet on some biochemical, haematological parameters and the level of antioxidant status of male rabbits. Adult rabbits were divided into five groups: one control (C) and four experimental groups. Experimental animals received sumac per os in feed in various doses (0.50%, 0.75%, 1.00% and 1.50%) for 90 days. Significant increase in PDWc (platelet distribution width) in E3 group when compared with control group was recorded. Sumac administration resulted in decreased cholesterol levels in all experimental groups vs. control group. Significantly lower level of cholesterol was found in E4 group with highest dose of sumac (1.50%). Higher values of total antioxidant status (TAS) and albumins were observed in all experimental groups in comparison with control group. A significant increase in TAS was detected in group E1 and E4. Concentrations of albumins were significantly higher in groups E3 and E4 vs. control group. Sumac administration had no significant effect on bilirubin content. In conclusion, these results show a positive effect of sumac consumption on antioxidant status and cholesterol level in adult male rabbits.  相似文献   
23.
The objective of this study was to investigate the effects of oxytocin infusion on corpus luteum (CL) function during early to mid-diestrus by measuring luteal size (LS) and luteal blood flow (LBF) along with plasma levels of progesterone (P4) and prostaglandin metabolites (13,14-dihydro-15-keto-prostaglandin F, PGFM). On day (D) 7 of the estrus cycle (D1 = ovulation), seven cows received 100 IU of oxytocin (OXY) or placebo (PL) following a Latin square design. LS and LBF increased in both groups over time and no differences were observed between the groups. PGFM did not differ either within the groups over time or between the groups at any time point. P4 of the OXY group was higher compared to that of the the PL group 360 min after the infusion (p = 0.01) and tended to be higher at the time points 450 min, 48 h, and 72 h (all p = 0.08). Results from this study support the hypothesis that OXY is not directly involved in the mechanism(s) governing blood flow of the CL and has no remarkable effects either on luteal size or P4 and PGFM plasma levels. Further investigation is needed to elucidate the role of OXY in CL blood flow during early and late luteal phases.  相似文献   
24.
双峰驼水代谢与血液中无机离子浓度的动态关系   总被引:5,自引:1,他引:5  
对双峰驼禁水15d,于禁水前、后及暴饮后采血,测定其血液中多种无机离子的浓度变化。结果表明,全血碳酸氢盐含量在禁水期变化极显著,与禁水前相比,冬季试验升高28.09%,夏季试验升高26.59%;暴饮后快速下降,冬、夏季试验分别比禁水前低9.5%和7.8%,4d后恢复正常。血清中K+和Fe2+含量未见统计学差异。血清中Na+、Cl-、Ca2+、Mg2+、和P3+的含量于禁水期逐渐上升,暴饮后快速下降,其变化均有显著差异,其中Na+的正常值显著高于其他反刍动物。结果表明,双峰驼在禁水期具有较高的血液渗透压和碱储量,其对保证缺水时血液酸碱平衡的调节,维持血容量,保证机体正常水代谢功能具有重要作用,是骆驼耐干渴的重要原因之一。  相似文献   
25.
26.
通过雏鸡MDV攻毒试验选择抗马立克氏病亲本   总被引:1,自引:0,他引:1  
宫桂芬  程光潮 《中国家禽》1999,21(10):11-12
对F0、F1、F2亲本经继代No.614血型基因选择后繁殖的F2、F3雏鸡,10日龄以马立克氏病强毒(MDV)攻击至60日龄的死亡率,其父母亲对No.614抗血清呈阳性反应的试验组显著低于其父母亲对此抗血清呈阴性反应的对照组。试验组25个家系中,有14个家系的F2雏鸡死亡率显著低于对照组;F3雏鸡有21个家系的死亡率低于对照组,其中8个家系具有统计意义。肿瘤发生率,以肾脏和腺胃最高,肺脏和神经组织最低。综合血型抗原检测和MDV攻毒结果,从试验组25个家系中选留强MDV抗性家系留种繁殖,继代选育。  相似文献   
27.
Pregnancy is characterized by transient changes in the maternal immune system, also evident at peripheral level. The present study analyzes the kinetics and possible factors affecting peripheral white blood cell populations throughout pregnancy in a herd of high-producing dairy cows chronically infected or not with Neospora caninum. We examined 54 pregnant parous cows: 29 Neospora-seronegative and 25 Neospora-seropositive cows. Blood samples were collected on Days 90, 120, 150, 180 and 210 of gestation. General Linear Model (GLM) repeated measures analysis of variance showed that the interaction Neospora-seropositivity × parity significantly affected total leukocyte, neutrophil and monocyte counts with lower levels of total leukocytes, lower neutrophil and higher monocyte counts recorded in primiparous Neospora-seropositive cows. In addition, N. caninum-seropositive cows had significantly increased monocyte counts on Day 180 of gestation compared to seronegative ones. Other factors significantly associated with changes in total and/or differential leukocyte profiles were period of pregnancy, season, twin pregnancy and milk production. In conclusion, a parity-associated effect of chronic N. caninum infection was observed on peripheral blood cell profiles in dairy cattle during gestation.  相似文献   
28.
Information regarding the susceptibility of swine lymphocytes to PCV2 is rather limited. To further explore and characterize the PCV2 infection in swine lymphocytes, an in vitro model using concanavalin A (Con A)-stimulated peripheral blood lymphocytes (PBLs) obtained from clinically healthy PCV2-carrier pigs was introduced. It was found that the PCV2 antigen-containing rate was below 2% in PBLs from healthy PCV2-free pigs following treated simultaneously with Con A and PCV2. However, significantly higher PCV2 antigen- and nucleic acid-containing rates could be seen in Con A-stimulated PBLs from clinically healthy PCV2-carrier pigs. Prior to Con A treatment, both of the PCV2 antigen- and nucleic acid-containing rates in PBLs from healthy PCV2-carrier pigs were less than 1%; however, they reached 22.1+/-5.7% by flow cytometry and 27.1+/-6.5% by in situ hybridization, respectively, at 4-day post-incubation with Con A. Phenotyping of PCV2 antigen-containing cells revealed that PCV2-positive cells could be detected in both T and B lymphocyte populations within which IgM-positive B lymphocytes appeared to have a relatively higher positive rate. The Con A-stimulated PBLs also displayed a significantly higher viral load by the measurement of either PCV2 DNA copy number or viral titer when compared with the non-treated PBLs from healthy PCV2-carrier pigs. The results indicate that PBLs, especially IgM-bearing B lymphocytes, are indeed susceptible to PCV2 infection and PCV2 is capable of replicating in dividing lymphocytes. This activation-induced replication may explain in part the pathogenesis of lymphoid depletion in PMWS-affected pigs.  相似文献   
29.
乳猪小肠内葡萄糖的分布状况既与饲料的碳水化合物种类和数量相关,也与小肠的不同部位相关,十二指肠段和空肠段分别是乳糖、淀粉类碳水化合物分解和葡萄糖吸收的主要部位血糖浓度离肝脏越远含量越低,而与饲料中糖类含量的多少无关。  相似文献   
30.
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