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   2155篇
  免费   10篇
  国内免费   11篇
林业   58篇
农学   15篇
基础科学   1篇
  525篇
综合类   502篇
农作物   38篇
水产渔业   17篇
畜牧兽医   903篇
园艺   28篇
植物保护   89篇
  2023年   9篇
  2022年   15篇
  2021年   9篇
  2020年   4篇
  2019年   8篇
  2018年   8篇
  2017年   7篇
  2016年   6篇
  2015年   8篇
  2014年   12篇
  2013年   10篇
  2012年   209篇
  2011年   263篇
  2010年   44篇
  2009年   27篇
  2008年   173篇
  2007年   187篇
  2006年   164篇
  2005年   162篇
  2004年   158篇
  2003年   126篇
  2002年   133篇
  2001年   67篇
  2000年   98篇
  1999年   30篇
  1998年   8篇
  1997年   7篇
  1996年   10篇
  1995年   11篇
  1994年   17篇
  1993年   12篇
  1992年   17篇
  1991年   17篇
  1990年   14篇
  1989年   17篇
  1988年   7篇
  1987年   8篇
  1986年   3篇
  1985年   4篇
  1984年   6篇
  1983年   3篇
  1980年   7篇
  1978年   4篇
  1976年   4篇
  1966年   3篇
  1963年   3篇
  1909年   2篇
  1908年   4篇
  1902年   2篇
  1897年   4篇
排序方式: 共有2176条查询结果,搜索用时 15 毫秒
51.
与传统的光合作用Z方案不同,本实验证明具有光系统Ⅱ(PSⅡ)而无光系统I(PSI)的衣藻(Chalmydomonas)突变体,可以利用空气中的CO2作为碳源进行光合自养生长,同时释放氧气,PSI缺失突变体在缺氧或有21%O2的空气中,当光强为200μE/m^2/s时,它的光合自养作用都非常稳定,而且,野生型衣藻及较高等的植物中也存在的这种足以能维持细胞生长及代谢的PSⅡ光合作用,这些突变体能借助空  相似文献   
52.
试验旨在研究虾青素和平衡不同时间对猪精子冷冻保存效果的影响。试验分为6组,空白对照组(冷冻保存I液)和试验组(冷冻保存I液中添加0.5 mmol/L虾青素,降温平衡时间分别为2、4、6、8、12 h)。结果表明:与空白对照组相比,平衡6 h的猪精子在解冻后各项运动参数均显著提高;平衡4、6、8 h组的精子活力、质膜完整性、顶体完整性、线粒体膜电位、DNA完整率显著提高,活性氧含量显著降低;平衡2、4、6 h组的超氧化物歧化酶、过氧化氢酶、谷胱甘肽过氧化物酶3种抗氧化酶活性显著提高,ATP含量显著提高;平衡6 h组的丙二醛水平降低4.74%(P<0.05)。综上,冷冻保存I液中添加0.5 mmol/L虾青素对猪精子冷冻保存具有一定的改善作用,其中以平衡6 h的效果最佳,能够显著提高猪精子冷冻保存效果。  相似文献   
53.
Five coronaviruses (CoVs) were detected in diarrheal feces from four zoo ruminant species: one wisent (Bison bonasus), two Himalayan tahr (Hemitragus jemlahicus), one sitatunga (Tragelaphus spekii), and one nyala (Tragelaphus angasii). We sequenced and analyzed the spike (S) and hemagglutinin/esterase (HE) genes of these viruses and compared the nucleotide (nt) and deduced amino acid (aa) sequences with those of other bovine CoV (BcoV) strains. Comparison of the entire deduced aa sequences of the S and HE glycoproteins revealed no specific differences that would account for discrimination between bovine-like CoV strains from zoo ruminants and BcoVs strains. In addition, the 99.9% aa identity among the five CoV strains revealed that the ruminants were infected by the same strain. Phylogenetically, bovine-like CoVs belong to group 2a CoVs, which are related most closely to the BcoV strains recently isolated in Korea. These data suggest that cattle are potential reservoirs for CoVs that are capable of infecting zoo ruminants.  相似文献   
54.
For the evaluation of canine gastric motility with ultrasonography, contraction number of pyloric antrum and gastric emptying time (GET) by area and volume method developed by Bolondi et al.'s method were studied in 14 dogs. All experimental dogs were administered with saline and soup solution (10 ml/kg, B.W.). The mean values of contraction number of pyloric antrum in saline and soup group were 4.19 +/- 1.30/min and 4.82 +/- 0.65/min before feeding, and overall mean values were 4.66 +/- 1.37/min and 5.13 +/- 1.71/min, respectively. The mean values of the GET by area and volume method were 36.73 +/- 11.27, 40.00 +/- 8.87 min in saline group and 61.35 +/- 17.58, 59.11 +/- 14.46 min in soup group. In the GET in saline and soup groups, there was no significant difference between the area and volume method (p>0.05). Therefore, Bolondi et al.'s method by ultrasound can be used to evaluate the antropyloric motility and gastric emptying time with area and volume methods. The area method is easier to determine the GET than the volume method, but the latter is more accurate.  相似文献   
55.
56.
One hundred fifty-three sows (average parity of 2.2) were used to determine the effects of dietary electrolyte balance (calculated as mEq/kg of diet for Na + K - Cl) on sows and their litters during lactation. The sows were fed corn-soybean meal-based diets (1.0% lysine, 1.0% valine, 0.95% Ca, and 0.80% P; as-fed basis) starting on d 109 of gestation and throughout the 21-d lactation experiment. Dietary electrolyte balance (dEB) was 0, 100, 200, 350, and 500 mEq/kg (as-fed basis), well above and below the dEB of 185 mEq/kg found in a simple corn-soybean meal-based lactation diet. To achieve the desired dEB, diets had the following: 1) 1.8% HCl (6 N) and 1.06% CaCl2, 2) 1.0% CaCl2, 3) 0.04% NaHCO3, 4) 1.29% NaHCO3, and 5) 2.54% NaHCO3 (as-fed basis). Increasing dEB increased blood pH (linear and quadratic effects, P < 0.001), partial pressure of carbon dioxide (linear effect, P < 0.001), HCO3- concentration (linear and quadratic effects, P < 0.001), and blood base excess (linear and quadratic effects, P < 0.001). However, increased dEB resulted in lower blood concentrations of K (linear and quadratic effects, P < 0.04), Cl (linear and quadratic effects, P < 0.001), and ionized Ca (linear and quadratic effects, P < 0.001). Changing dEB did not affect ADFI; water usage, litter weight gain; sow weight change; sow backfat change; percentages of CP, lactose, and fat in the milk; percentage of sows returning to estrus; days to estrus; and number of pigs born alive in the subsequent litter (P = 0.06). However, piglet survivability to d 10 and overall was greatest with the lower dEB treatments (linear effect, P < 0.05). The pH (linear and quadratic effects, P < 0.001) and colony forming units of total bacteria (linear effect, P < 0.03) in the urine increased as dEB of the diet was increased. In conclusion, dEB had pronounced effects on the physiological status of sows and decreasing dEB below that in a simple corn-soybean meal-based diet decreased bacterial counts in the urine and increased piglet survivability. However, milk composition, sow and litter weights at weaning, and subsequent rebreeding performance of the sows were not affected by dEB.  相似文献   
57.
酉荞1号是应用系谱育种方法育成的优质、高产、稳定的苦荞新品种.该品种在重庆市苦荞区域试验中平均单产为127.38 kg/667 m2,比对照九江苦荞增产18.13%,全生育期83 d,平均株高102 cm,分枝数5.6个,主茎节数14.2节,单株粒重20.0 g,千粒重20.5 g,粗蛋白含量为10.4%,类黄酮含量为2.04%,籽粒出粉率为63.5%,适宜重庆市各荞麦产区种植.  相似文献   
58.
Antibacterial and antifungal activity of pinosylvin, a constituent of pine   总被引:1,自引:0,他引:1  
Lee SK  Lee HJ  Min HY  Park EJ  Lee KM  Ahn YH  Cho YJ  Pyee JH 《Fitoterapia》2005,76(2):258-260
The antibacterial and antifungal activities of pinosylvin (3,5-dihydroxy-trans-stilbene), a constituent of pine, were studied and compared with those of resveratrol (3,5,4'-trihydroxy-trans-stilbene). Pinosylvin exhibited more potent growth inhibitory activity against Candida albicans and Saccharomyces cerevisiae.  相似文献   
59.
Kim KJ  Yoon KY  Lee BY 《Fitoterapia》2012,83(6):1105-1109
Type 2 diabetes mellitus is a multisystem disease that is characterized by hyperglycemia and is associated with the dysfunction and failure of various organs. The control of postprandial hyperglycemia is important in the prevention and intervention of type 2 diabetes. Fucoidan has several biological activities in vitro and in vivo. However, the effect of fucoidan on hyperglycemia in non-diabetic and diabetic mice has not been investigated. This study was undertaken to study the effects of different molecular weight forms (5 kilodalton (k), 5-30 k and crude) of fucoidan on oral glucose tolerance tests in non-diabetic mice and on food intake, weight gain, fasting blood glucose and blood biochemistry of db/db mice. Treatment with 200 mg/mL 5 k, 5-30 k and crude fucoidan substantially prevented hyperglycemia according to oral glucose tolerance tests in non-diabetic mice. In addition, fucoidan fractions significantly reduced blood glucose levels in diabetic mice.  相似文献   
60.
Choi YJ  Yoon JH  Cha SW  Lee SG 《Fitoterapia》2011,82(6):911-919
Ginsenoside Rh1 has been reported to possess antiallergic and anti-inflammatory activities, but its effects on monocytes remain to be determined. Herein, we investigated the effects of Rh1 on the expression of MCP-1 and CCR2, activation of MAPK signaling, and chemotaxis of monocytes. Treatment of Rh1 decreased the levels of MCP-1 and CCR2 and the expression of VLA5 and activated β1 integrin on the cell surface, and attenuated the phosphorylation of MAPKs. Based on these results, the inhibitory effects of Rh1 on monocyte function should be regarded as a promising new anti-inflammatory response with a potential therapeutic role against inflammation-dependent diseases.  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