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   28550篇
  免费   2223篇
  国内免费   3606篇
林业   3953篇
农学   1889篇
基础科学   631篇
  4248篇
综合类   9989篇
农作物   1191篇
水产渔业   4619篇
畜牧兽医   5040篇
园艺   1571篇
植物保护   1248篇
  2024年   130篇
  2023年   487篇
  2022年   881篇
  2021年   1088篇
  2020年   1165篇
  2019年   1551篇
  2018年   1046篇
  2017年   1669篇
  2016年   1745篇
  2015年   1420篇
  2014年   1633篇
  2013年   2057篇
  2012年   2370篇
  2011年   2199篇
  2010年   1824篇
  2009年   1670篇
  2008年   1427篇
  2007年   1563篇
  2006年   1278篇
  2005年   1008篇
  2004年   800篇
  2003年   727篇
  2002年   622篇
  2001年   572篇
  2000年   469篇
  1999年   446篇
  1998年   321篇
  1997年   305篇
  1996年   307篇
  1995年   304篇
  1994年   238篇
  1993年   221篇
  1992年   154篇
  1991年   148篇
  1990年   149篇
  1989年   115篇
  1988年   83篇
  1987年   62篇
  1986年   30篇
  1985年   22篇
  1984年   12篇
  1983年   5篇
  1982年   9篇
  1981年   8篇
  1980年   9篇
  1979年   6篇
  1978年   4篇
  1977年   5篇
  1976年   5篇
  1956年   5篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
The aim of this study was to assess the influence of growth on the pharmacokinetics of sodium salicylate (SS) in male turkeys. SS was administered intravenously at a dose of 50 mg/kg. Plasma drug concentrations were assessed by high‐performance liquid chromatography, and pharmacokinetic parameters were calculated by noncompartmental analysis. As the age increased from 6 to 13 weeks (body weight increase from 2.35 to 9.43 kg), median body clearance decreased from 1.34 to 0.87 ml/min/kg. This caused a significant increase in the median mean residence time from 3.42 to 4.44 hr. Elimination phase proved to be biphasic and two elimination half‐lives (T1/2el) were distinguished. Whereas T1/2el1 was found to increase with age by 128%, T1/2el2 represented a later but faster and less age‐dependent phase of elimination (increase by 56% in the respective groups). Volume of distribution decreased with age. These effects may lead to different therapeutic response to SS in turkeys of different age and body weights.  相似文献   
142.
We investigated effects of Rendement Napole (RN ) genotype on metabolic markers in Ossabaw pigs fed diets with different levels of dietary fat. Thirty‐two pigs, belonging to either the wild‐type (WT , rn+/rn+) or carrier (CAR , RN ?/rn+) genotypes (n  = 16/genotype), were divided into two dietary groups, (high fat [HF ] or low fat [LF ]) diets, for 12 weeks (n  = 8 pigs/genotype/diet) after which pigs were killed for gene expression analysis by RT ‐PCR . Feeding HF diet caused increased daily gain (ADG ,<  .05) and final body weight (BW ) (<  .05) in comparison with the LF diet (<  .05). Feed efficiency (gain:feed) was higher (<  .05) in pigs on the HF and was higher (<  .05) in CAR pigs compared to WT . There was genotype × diet interaction (=  .05) on final BW such that CAR animals on LF diet had the same final BW as animals of both genotypes on HF diet. Carrier pigs on LF diet had higher (<  .05) average daily gain and gain:feed than WT pigs. There was a trend (<  .08) for a higher feed consumption in pigs on the LF diet. Backfat thickness was higher (<  .01) in pigs on the HF diet. Serum triglyceride was higher (0.62 vs. 0.33 mg/dl, <  .01) in pigs on HF diet. Serum insulin was higher (<  .05) in CAR versus WT pigs (0.40 vs. 0.015 μg/ml). Pigs on the HF diet had a higher (<  .05) serum insulin compared to those on the LF diet (0.032 vs. 0.023 μg/ml). Carnitine palmitoyl transferase 1‐alpha was higher (<  .05) in the longissimus dorsi and semitendinosus muscles of pigs on HF diet. Acyl‐CoA oxidase I was elevated (<  .05) in the liver of pigs on HF diet. Fatty acid synthase was lower in the longissimus dorsi muscle, liver and mesenteric fat (<  .05) of carrier pigs. The RN gene regulates specific metabolic markers in the Ossabaw pigs.  相似文献   
143.
This study was to investigate the effects of in ovo feeding (IOF) L‐arginine (Arg) solution on the development of digestive organs, the duodenal mucosa of broiler embryos and hatchlings, and the growth performance of chicks during the first week post‐hatch. A total of 720 fertilized eggs with similar weight were randomly allocated to three groups, consisting of eight replicates of 30 eggs each. Three treatments were arranged as non‐injected control, diluent‐injected (0.75% NaCl solution) group and Arg solution‐injected group containing 1% Arg, dissolved in diluent. At 17.5 days of incubation, 0.6 ml of IOF solution was injected into amniotic fluid of each egg of injected groups. Results showed IOF of Arg solution increased (p < .05) the chick embryo weight at 19 days of incubation; the body weight gain of post‐hatch broilers during 1–7 days; the weights of liver, pancreas, proventriculus and gizzard; the concentrations of duodenal ghrelin, vasoactive intestinal peptide and glucagon‐like peptide 2; and the duodenum mucosal enzyme activities of alkaline phosphatase, maltase, sucrase and inducible nitric oxide synthase of 7‐day‐old post‐hatch broilers compared with other groups. The IOF of Arg solution also increased (p < .05) the villus height (VH) and the ratio of VH to crypt depth (CD) and decreased (p < .05) the CD in duodenum of broiler embryos and post‐hatch hatchlings, except for the CD at 19 days of incubation. In conclusion, IOF of 1% Arg solution into the amnion at 17.5 days of incubation could improve the development of digestive organs, the duodenal morphology, the releasing of gastrointestinal hormones and mucosal enzyme activities of broiler embryos and hatchlings and finally the growth performance of chicks during the first week post‐hatch. Therefore, IOF of appropriate Arg solution could be an effective technology for regulating early nutrition supply and subsequent growth development in poultry industry.  相似文献   
144.
Foal first diarrhoea is one of the most prominent problems in the early life of horses. Probiotics might have the potency to prevent or at least diminish neonatal diarrhoea. We hypothesised that the treatment of foals with probiotic strains of Lactobacillus rhamnosus and Enterococcus faecium starting early after birth and then daily over 2 weeks would prevent or mitigate foal heat diarrhoea. The influence of this probiotic treatment on diarrhoea incidence and growth and health performance of young foals was investigated. Thirty‐four foals were randomly allocated to two groups. From day 1 to 14 of life, the foals received either placebo (PG, n = 16) or the probiotic treatment (TG, n = 18). Clinical examination was performed, and the faeces consistency score (FCS, 1–5; with diarrhoea defined by ≤3) was recorded once per day in weeks 1 and 2 and once weekly in weeks 3–8 of life (WL). The body height was measured at birth and after two and eight WL. Diarrhoea occurred in the 1st WL in 19% and 61% of PG and TG foals respectively. In the 1st WL, diarrhoea lasted 0.3 ± 0.8 and 1.6 ± 1.4 days in PG and TG foals respectively. In the 2nd WL, diarrhoea occurred in 94% and 84% of PG and TG foals, respectively, and lasted for 3.0 ± 1.5 and 3.7 ± 1.6 days respectively. At least two periods of diarrhoea developed in 33% and 65% of PG and TG foals respectively. The TG foals grew slightly slower than the PG foals. The results indicated that the probiotic treatment of neonatal foals as performed in this study was not suitable to reduce diarrhoea within the first two WL, because contrary to the hypothesis, the TG foals suffered more frequently and for longer periods from diarrhoea than the PG foals.  相似文献   
145.
This study was to investigate the effect of oxidized wheat gluten (OG) on growth performance, gut morphology and its oxidative states of broilers. One hundred and eighty‐day‐old male broilers (10 chicks/pen) were randomly allocated into three dietary treatments: control diet (CON), diet with 8% wheat gluten (WG) and diet with 8% OG with six pens/treatment. Body weight (BW) (21 and 35 days) and average daily gain (ADG) (1–21 days and 22–35 days) decreased (p < .05) and feed conversion ratio (FCR) (1–21 days and 22–35 days) increased (p < .05) in OG treatment. Feed intake (FI) decreased (p < .05) in WG and OG treatments during 22–35 days. However, FI was not influenced by dietary treatments during 1–21 days (p > .05). The OG‐fed broilers had a lower faecal pH value (p < .05) and higher faecal moisture content (p < 05) at 14, 21, 28 and 35 days. Villus height, crypt depth and V/C value were not different (p > .05) among treatments at 21 and 35 days. Lipid peroxidation (LPO) (21 and 35 days) and malondialdehyde (MDA) (35 days) content in crop of OG treatment increased (p < .05). Oxidized glutathione (GSSG) (21 days), LPO (21 and 35 days) and MDA (21 and 35 days) content in ileum of OG treatment increased (p < .05). The reduced glutathione/oxidized glutathione (GSH/GSSG) (21 days) and (GSH) (35 days) in ileum of OG treatment decreased (p < .05). The present findings indicate that OG might be a stressor for broiler gut, which could induce oxidative stress both in crop and in ileum, and the diarrhoea as well. The growth performance of broiler was consequently depressed.  相似文献   
146.
Studies have found that a dietary supplement of Bacillus amyloliquefaciens improved the growth performance, increased the nutrient digestibility of hosts and modulated the intestinal microflora. A total of 360 1‐day‐old Ross broilers were randomly divided into three treatments: a control group with a basal diet, an antibiotic group with a basal diet and added colistin sulphate, and a probiotics group with a basal diet and added Bacillus amyloliquefaciens. The HiSeq high‐throughput sequencing analysis of 16S rRNA was used to investigate the differences in birds’ caecal microflora, and metabolomics was used to analyse changes in caecal metabolites. Results showed that the supplementation of Bacillus amyloliquefaciens significantly improved the BW and ADG compared with the control birds. Results of sequencing indicated that (i) 645, 670, 596 unique operational taxonomic units (OTUs) were found in birds supplemented with Bacillus amyloliquefaciens on day 7, 21 and 42, separately, (ii) due to the diversity and relative abundance of the birds’ caecal microflora, the OTUs of the caecal microflora clustered according to age and treatment, except on day 42, (iii) among the six predominate families (Ruminococcaceae, Lachnospiraceae, Enterobacteriaceae, Erysipelotrichaceae, Lactobacillaceae and Rikenellaceae), the supplementation of Bacillus amyloliquefaciens significantly increased Enterobacteriaceae on day 42, (iv) Bacillus amyloliquefaciens increased the relative abundance of Faecalibacterium and Ruminococcus on day 21, increased the Faecalibacterium and Blautia and decreased the Ruminococcus on day 42. The metabolomics of caecal metabolites showed that the dietary Bacillus amyloliquefaciens changed the caecal metabolites involved of amino acid metabolism and glyceride metabolism, and the antibiotics changed the caecal metabolites that were related to carbohydrates and amino acid metabolism on day 21.  相似文献   
147.
Two 125‐day experiments of the same design were conducted to evaluate the effects of a heterotrophically grown microalgae (AURA) containing docosahexaenoic acid (DHA) on pig performance, carcass traits and the fatty acid composition of lean and adipose tissue. In each experiment, 144 Hypor pigs were blocked by sex, allocated to three treatment groups, and fed 0, 0.25% or 0.50% AURA in isonutritive, isocaloric diets. Pigs were weighed on days 0, 28, 56, 84 and 112. Feed and water intakes were measured every 28 days. Pigs were slaughtered on day 125. Data from the two studies were analysed as a single data set. Performance and carcass traits did not differ between treatments. Both microalgae treatment levels enriched (< .05) Longissimus lumborum (LL) and backfat in DHA and improved (< .05) their ratios of n‐6 to n‐3 fatty acids.  相似文献   
148.
The study aimed to investigate the effects of maternal dietary methyl donors on the performance of sows and their offspring, and the associated hepatic insulin‐like growth factor‐1 (IGF‐1) expression of the offspring. A total of 24 multiparous sows were randomly fed the control (CON) or the CON diet supplemented with methyl donors (MD) at 3 g/kg betaine, 15 mg/kg folic acid, 400 mg/kg choline and 150 μg/kg VB12, from mating until delivery. After farrowing, sows were fed a common lactation diet through a 28‐days lactation period and six litters per treatment were selected to be fed until at approximately 110 kg BW. Maternal MD supplementation resulted in greater birthweight (< 0.05) and increased the piglet weights (< 0.01) and litter weights (< 0.05) at the age of day 28, compared with that in CON group. The offspring pigs in the MD group had greater ADG (< 0.05) and tended to lower F:G ratio (= 0.07) compared with that of CON group from day 28 to 180 of age. The offspring pigs from MD group had greater serum IGF‐1 concentrations and expressions of hepatic IGF‐1 gene and muscular IGF‐1 receptor (IGF‐1r) protein at birth (< 0.05), and greater hepatic IGF‐1 protein (= 0.03) and muscular IGF‐1r gene expressions (< 0.05) at slaughter, than that from the CON group. Moreover, the methylation at the promoter of IGF‐1 gene in the liver of newborn piglets and finishing pigs was greater in the MD group than that of the CON group (< 0.05). In conclusion, maternal MD supplementation throughout gestation could enhance the birthweight and postnatal growth rate of offspring, associated with an increased expression of the IGF‐1 gene and IGF‐1r, as well as the altered DNA methylation of IGF‐1 gene promotor.  相似文献   
149.
Ductus venosus (DV) closure plays a key role in hepatic circulation adaptation to postnatal metabolic function, and DV patency might develop a congenital portosystemic shunt (CPSS). The noninvasive Color Flow Mapping (CFM) examination, a validated method to diagnose CPSS in adult dogs, is routinely performed to assess DV closure after birth in humans. This study aimed to describe the feasibility of the ultrasonographic evaluation of the DV after birth and to determine its closure time in healthy Great Dane neonates. Patency of DV in serial Color Flow Mapping (CFM) examinations and bodyweight (BW) were recorded on Days 0‐3‐6‐9 in 24 neonates that were classified as having patent (PDV) or closed ductusvenosus (CDV) basing on CFM signal presence/absence. Since the 3rd day, DV diameter was recorded. Data were analysed by ANOVA (p < 0.05). All dogs resulted healthy 1 year later. The number of PDV and CDV puppies at birth was not different on Day 3 (24 and 0 vs. 22 and 2, PDV and CDV, respectively), whereas it resulted different on Days 6 (24 and 0 vs. 14 and 10) and 9 (24 and 0 vs. 0 and 24); on Day 3, it was different compared to Days 6 and 9; on Day 6, it was different from Day 9. Reduction of DV diameter resulted positively related to neonatal BW growth. The CFM evaluation of DV closure after birth in Great Dane puppies represents a feasible technique. Present results suggest the time of functional closure in normal neonates within 9 days after birth. Thus, CFM examination, as an early screening test for DV patency evaluation, performed 10 days after birth, may identify suspicious dogs at risk that would require further investigations. Further studies are needed to deepen the role of a delayed closure in low bodyweight and preterm puppies.  相似文献   
150.
A pot experiment was conducted in a climate‐controlled greenhouse to investigate the growth, physiology and yield of potato in response to salinity stress under biochar amendment. It was hypothesized that addition of biochar may improve plant growth and yield by mitigating the negative effect of salinity through its high sorption ability. From tuber bulking to harvesting, the plants were exposed to three saline irrigations, that is 0, 25 and 50 mm NaCl solutions, respectively, and two levels of biochar (0 % and 5 % W/W) treatments. An adsorption study was also conducted to study the Na+ adsorption capability of biochar. Results indicated that biochar was capable to ameliorate salinity stress by adsorbing Na+. Increasing salinity level resulted in significant reductions of shoot biomass, root length and volume, tuber yield, photosynthetic rate (An), stomatal conductance (gs), midday leaf water potential, but increased abscisic acid (ABA) concentration in both leaf and xylem sap. At each salinity level, incorporation of biochar increased shoot biomass, root length and volume, tuber yield, An, gs, midday leaf water potential, and decreased ABA concentration in the leaf and xylem sap as compared with the respective non‐biochar control. Decreased Na+, Na+/K+ ratio and increased K+ content in xylem with biochar amendment also indicated its ameliorative effects on potato plants in response to salinity stress. The results suggested that incorporation of biochar might be a promising approach for enhancing crop productivity in salt‐affected soils.  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