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   8784篇
  免费   595篇
  国内免费   601篇
林业   387篇
农学   638篇
基础科学   115篇
  600篇
综合类   3582篇
农作物   504篇
水产渔业   448篇
畜牧兽医   1973篇
园艺   588篇
植物保护   1145篇
  2024年   30篇
  2023年   96篇
  2022年   247篇
  2021年   327篇
  2020年   307篇
  2019年   361篇
  2018年   245篇
  2017年   385篇
  2016年   499篇
  2015年   392篇
  2014年   422篇
  2013年   469篇
  2012年   668篇
  2011年   691篇
  2010年   563篇
  2009年   513篇
  2008年   477篇
  2007年   475篇
  2006年   428篇
  2005年   326篇
  2004年   268篇
  2003年   247篇
  2002年   174篇
  2001年   199篇
  2000年   163篇
  1999年   130篇
  1998年   119篇
  1997年   104篇
  1996年   95篇
  1995年   107篇
  1994年   70篇
  1993年   65篇
  1992年   52篇
  1991年   45篇
  1990年   61篇
  1989年   37篇
  1988年   30篇
  1987年   23篇
  1986年   19篇
  1985年   8篇
  1984年   3篇
  1983年   3篇
  1982年   4篇
  1981年   8篇
  1980年   7篇
  1979年   5篇
  1976年   1篇
  1973年   1篇
  1956年   3篇
  1955年   7篇
排序方式: 共有9980条查询结果,搜索用时 15 毫秒
61.
猪繁殖与呼吸综合征病毒缺失变异株的基因组特征   总被引:51,自引:1,他引:51  
对猪繁殖与呼吸综合征病毒(PRRSV)分离株HB2(sh)/2002的全基因组序列进行了测定与分析。该毒株基因组全长为15373nt(不包括PolyA尾),与国内外美洲型PRRSV分离株全序列相似性介于88.7%~95.1%之间。序列分析表明,该毒株是1个天然存在缺失的变异毒株,其ORFla的Nsp2存在编码12个氨基酸的连续36个核苷酸的缺失,ORF、3存在编码1个氨基酸的3个核苷酸的缺失。这是国内外首次发现PRRSV存在缺失变异现象,研究结果补充和丰富了PRRSV毒株的基因组信息数据,为深入研究该毒株的遗传与变异及其与生物学特性的关系奠定了基础。  相似文献   
62.
以猪瘟C-株弱毒疫苗株、经典强毒石门株和C-株全长cDNA为试验材料,以免疫荧光技术为主;结合ELISA和RT-PCR检测技术,对其在培养细胞中的增殖特性和表达规律进行了比较研究。同时筛选猪瘟病毒及其全长cDNA的敏感细胞,探索其增殖表达规律,以便为猪瘟病毒反向遗传操作提供技术方法和可操作的条件。  相似文献   
63.
为了提供有效的伪狂犬病疫苗,用鸡胚成纤维细胞扩大培养了PrV HB-98突变株(TK^-/gG^-/LacZ^+),研制了伪狂犬病基因缺失疫苗,并对该疫苗经肌肉接种、经口等免疫途径的最小免疫剂量进行了测定,同时也对4批疫苗的安全性、效力、免疫期和保存期进行了检测;同时将4批疫苗用于免疫23个猪场的母猪、新生仔猪和育肥猪进行区域试验。测定结果表明,疫苗经上述两种途径接种对不同阶段猪的最小免疫剂量均为10^5.0 TCID50;10倍免疫剂量的疫苗对初生仔猪、15日龄仔猪和妊娠母猪是安全的,免疫猪能抵抗强毒的攻击;疫苗在4℃和-20℃下分别可保存6个月和12个月。对伪狂犬病毒抗体阴性的70日龄商品猪和种猪的免疫期为6个月。田间试验表明,4批猪伪狂犬病基因缺失疫苗安全有效,并可用于仔猪发病时的紧急接种。为猪伪狂犬病基因工程疫苗的制备与应用提供了有力的依据。  相似文献   
64.

Background

There are conflicting reports of plasma lipoprotein lipid content in dogs with diabetes mellitus (DM).

Objectives

To determine lipoprotein lipid content of plasma of dogs with DM by spectrophotometry and ultracentrifugation; to compare lipoprotein lipid content in diabetic and healthy dogs; and to quantify apolipoprotein B‐100 (ApoB) in dogs with DM.

Animals

22 dogs with DM and 9 healthy dogs.

Methods

Cross‐sectional study. Triglyceride (TG), total cholesterol (TC), and high‐density lipoprotein cholesterol (HDL‐C) concentrations were measured by spectrophotometry. Very low‐density lipoprotein cholesterol (VLDL‐C) and low‐density lipoprotein cholesterol (LDL‐C) concentrations were calculated after ultracentrifugation. Non‐HDL‐C cholesterol was calculated by subtracting HDL‐C from TC. ApoB was quantified by ELISA. The Mann‐Whitney test was used for comparison of median lipoprotein concentrations, and Spearman's correlation was used to assess associations between ApoB and lipoprotein fractions.

Results

All values are reported in mg/dL. Median TG (122), TC (343.5), HDL‐C, (200), VLDL‐C, (27) LDL‐C (68), non‐HDL‐C (114), and ApoB (320) were significantly higher in dogs with DM, compared to healthy dogs (57, 197, 168, 12, 16, 31, and 258, respectively, P‐values 0.0079, <0.001, 0.029, 0.011, <0.001, <0.001, 0.025, respectively). A significant association was found between ApoB and LDL‐C (Spearman's rho = 0.41, P = 0.022) and between ApoB and non‐HDL‐C (Spearman's rho = 0.40, P = 0.027).

Conclusions and Clinical Importance

Dyslipidemia of dogs with DM is characterized by pronounced increases in LDL‐C and non‐HDL‐C concentrations, although all lipoprotein fractions are significantly increased. Knowledge of specific lipoprotein fraction alterations in dogs with DM can enhance treatment options for diabetic dyslipidemia in dogs.  相似文献   
65.
66.
67.
为探究亚高山雌雄异株草本植物乳白香青对生境的适应方式,通过测定5个草地群落(A-老芒麦改良草地,B-虉草改良草地,C-天然草地,D-天然草甸,E-沙化草地)中乳白香青种群数、种群密度和面积、分布系数、性比组成,以及雌雄株构件性状、生物量配比、水分分配及抗性物质含量等参数,研究群落组成对乳白香青种群特征、雌雄株形态可塑性及抗性的影响。结果表明,5个草地群落的优势种、群落密度、基盖度、物种密度和优势种高度及土壤理化性状的显著差异(P<0.05),使不同群落中乳白香青种群特征显著不同,群落类型对种群特征参数影响顺序为种群面积>种群密度>性比>年龄结构>种群数>分布系数;D群落中乳白香青种群数和分布系数最高,C中乳白香青种群面积和密度最大,E中乳白香青种群数仅分别为D和C中的30.21%和35.11%,分布系数仅为C中的36.04%;群落类型对乳白香青种群年龄结构和性比有显著影响(P<0.05),雌株数为雄株的2.22~7.03倍;叶数和叶面积、株高和茎径、根长、小花数和苞片层数有显著的性别差异(P<0.05),群落类型对雌雄株的叶数和叶面积、株高、根数、花序数和小花数有显著影响,对雄株茎径和苞片层数有显著影响;雄株总生物量和花分配比显著高于雌株,而根分配比显著低于雌株(P<0.05),群落类型对乳白香青生物量配比有显著影响,雌株生物量配比受影响顺序为花>总生物量>叶>根>茎,雄株受影响顺序为花>茎>叶>总生物量>根;雄株茎、叶、花含水量显著高于雌株(P<0.05),根含水量在性别间和群落间差异较小,雌株构件含水量受群落类型影响顺序为花>茎>叶>根,雄株为叶>茎>花>根。雄株中MDA含量高于雌株,雌株中H2O2含量及T-AOC活性大于雄株(P<0.05),群落组成对雌、雄株中H2O2和MDA含量及T-AOC活性有极显著影响(P<0.01)。A和B中H2O2和MDA含量最低,E中H2O2和MDA达最大值,而T-AOC活性最低。雌、雄个体均能依据群落生境调整生长策略,通过构件性状、生物量配比、水分分配和抗性生理等适应性变化,使种群具有与生境匹配的种群特征,利于提高种群适合度和生活史完成。  相似文献   
68.
This study was conducted to compare the pharmacokinetic profiles of conventional (Fungizone®) and liposomal amphotericin B (AmBisome®) formulations in order to predict their therapeutic properties, and evaluate their potential differences in veterinary treatment. For this purpose, twelve healthy mixed breed dogs received both drugs at a dose of 0.6 mg/kg by intravenous infusion over a 4‐min period in a total volume of 40 ml. Blood samples were collected at 0, 0.5, 1, 1.5, 2, 3, 4, 8, 12, 24, 48, 72 and 96 hr after dosing, and concentrations of drug in plasma were determined by high‐performance liquid chromatography (HPLC). Pharmacokinetics was described by a two‐compartment model. Although both formulations were administered at the same doses (0.6 mg/kg), the plasma pharmacokinetics of liposomal amphotericin B differed significantly from those of amphotericin B deoxycholate in healthy dogs (p < .05). Liposomal amphotericin B showed markedly higher peak plasma concentrations (approximately ninefold greater) and higher area under the plasma concentration curve values (approximately 14‐fold higher) compared to conventional formulation. It is concluded that AmBisome® reached higher plasma concentration and lower distribution volume and had a longer half‐life compared to Fungizone®, and therefore, AmBisome® is reported to be an appropriate and effective choice for the treatment of systemic mycotic infections in dogs.  相似文献   
69.
AIM: To investigate a possible interaction between lolitrem B and ergovaline by comparing the incidence and severity of ryegrass staggers in sheep grazing ryegrass (Lolium perenne) containing lolitrem B or ryegrass containing both lolitrem B and ergovaline.

METHODS: Ninety lambs, aged approximately 6 months, were grazed on plots of perennial ryegrass infected with either AR98 endophyte (containing lolitrem B), standard endophyte (containing lolitrem B and ergovaline) or no endophyte, for up to 42 days from 2 February 2010. Ten lambs were grazed on three replicate plots per cultivar. Herbage samples were collected for alkaloid analysis and lambs were scored for ryegrass staggers (scores from 0–5) weekly during the study. Any animal which was scored ≥4 was removed from the study.

RESULTS: Concentrations of lolitrem B did not differ between AR98 and standard endophyte-infected pastures during the study period (p=0.26), and ergovaline was present only in standard endophyte pastures. Ryegrass staggers was observed in sheep grazing both the AR98 and standard endophyte plots, with median scores increasing in the third week of the study. Prior to the end of the 42-day grazing period, 22 and 17 animals were removed from the standard endophyte and AR98 plots, respectively, because their staggers scores were ≥4. The cumulative probability of lambs having scores ≥4 did not differ between animals grazing the two pasture types (p=0.41).

CONCLUSIONS AND CLINICAL RELEVANCE: There was no evidence for ergovaline increasing the severity of ryegrass staggers induced by lolitrem B. In situations where the severity of ryegrass staggers appears to be greater than that predicted on the basis of concentrations of lolitrem B, the presence of other tremorgenic alkaloids should be investigated.  相似文献   

70.
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   
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