全文获取类型
收费全文 | 154366篇 |
免费 | 8524篇 |
国内免费 | 15123篇 |
专业分类
林业 | 10533篇 |
农学 | 8449篇 |
基础科学 | 7411篇 |
16297篇 | |
综合类 | 74775篇 |
农作物 | 10494篇 |
水产渔业 | 6062篇 |
畜牧兽医 | 24231篇 |
园艺 | 12087篇 |
植物保护 | 7674篇 |
出版年
2024年 | 1384篇 |
2023年 | 3310篇 |
2022年 | 7382篇 |
2021年 | 7189篇 |
2020年 | 6630篇 |
2019年 | 6647篇 |
2018年 | 4891篇 |
2017年 | 7355篇 |
2016年 | 4801篇 |
2015年 | 7580篇 |
2014年 | 8066篇 |
2013年 | 9410篇 |
2012年 | 13006篇 |
2011年 | 13450篇 |
2010年 | 12997篇 |
2009年 | 11424篇 |
2008年 | 11346篇 |
2007年 | 10374篇 |
2006年 | 8371篇 |
2005年 | 6548篇 |
2004年 | 4248篇 |
2003年 | 2659篇 |
2002年 | 2606篇 |
2001年 | 2501篇 |
2000年 | 2233篇 |
1999年 | 811篇 |
1998年 | 97篇 |
1997年 | 78篇 |
1996年 | 52篇 |
1995年 | 69篇 |
1994年 | 67篇 |
1993年 | 57篇 |
1992年 | 63篇 |
1991年 | 45篇 |
1990年 | 34篇 |
1989年 | 24篇 |
1988年 | 15篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 23篇 |
1979年 | 1篇 |
1966年 | 1篇 |
1965年 | 3篇 |
1962年 | 35篇 |
1958年 | 1篇 |
1956年 | 42篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
341.
AIM:To study the effects of airway and pulmonary inflammation on pulmonary arterial remodeling in rats with chronic bronchitis (CB) and emphysema.METHODS:Twenty-four male Wistar rats were divided into three groups (n=8): Group A: four-weeks CB and emphysema;Group B: six-weeks CB and emphysema group;Group C: normal control.The rat model of CB and emphysema was established by intratracheal instillation of lipopolysaccharide (LPS) and daily exposure to cigarette smog.The arterial blood gas analysis,pulmonary hemodynamics changes and cell counts in bronchoalveolar lavage fluid (BALF) were measured.The pathomorphological changes of airway inflammation,alveoli destruction and pulmonary arterial remodeling were observed by HE straining and triple straining.RESULTS:(1) The characteristic pathological changes of CB and emphysema were observed in group A and B.Neutrophils were the main cells infiltrated into the walls of airway in group A.Lymphocytes and macrophages were the main cells in group B.(2) Right ventricular systolic pressure (RVSP),mean pulmonary arterial pressure (mPAP),the ratio of the weight of right ventricle/left ventricle and septum (RV/LV+S) in group A and B were significantly higher than those in group C (P<0.05).The amount of muscular artery (MA) in group A and B were significantly higher than that in group C (P<0.05).(3) In group A and B,the levels of MA,RVSP,mPAP and RV/LV+S was correlated positively with the average alveolar area,the total cell counts and differential cell counts of neutrophils,lymphocytes and macrophages in BALF,and the level of infiltration into the walls of airway,respectively (P<0.05).The positive correlation was observed with the percentage of neutrophils,lymphocytes and macrophages between group A and B (P<0.05).The amounts of MA were also correlated positively with RVSP,mPAP and RV/LV+S (P<0.05).CONCLUSIONS:(1) The pulmonary artery hypertension,the right ventricular hypertrophy and the pulmonary arterial remodeling appeared before hypoxia.These may be related with the degree of the pulmonary inflammation.(2) The characteristic of pulmonary arterial remodeling was small artery organization,and correlated positively with the changes of hemodynamics. 相似文献
342.
YANG Yang XU Hou-qiang CHEN Wei ZHOU Di XU Min ZHANG Qing-qing ZHAO Huan-ping SUN Cheng-juan WANG Yuan-yuan ZHANG Ming YANG Tao 《中国畜牧兽医》2017,44(12):3401-3409
The objective of this study was to clone PDK4 and FGF10 genes, and investigate the expression level of PDK4 and FGF10 genes mRNA in different tissues of Large White pig and Congjiang Xiang pig. The PDK4 and FGF10 genes were cloned by RT-PCR and analyzed by bioinformatics, the relative expression of PDK4 and FGF10 genes were detected by Real-time PCR. The results showed that the coding region of PDK4 gene was 1 224 bp, encoding 407 amino acids; The coding region of FGF10 gene was 636 bp and encoded 211 amino acids. The homologies of nucleotide sequences of PDK4 gene with sheep, horse and human were 93%, 92% and 91%,respectively. The homologies of nucleotide sequences of FGF10 gene with sheep, cattle, human and mouse were 94%,93%, 93% and 90%, respectively. The phylogenetic tree of PDK4 gene showed that the genetic relationship of Congjiang Xiang pig, cattle and sheep were very close, the phylogenetic tree of FGF10 gene indicated that the genetic relationship of Congjiang Xiang pig, cattle, sheep, human and macaque were very close, but the genetic relationship of Congjiang Xiang pig, rat and chicken were far away. Real-time PCR results showed that, in different tissues of Congjiang Xiang pig,PDK4 gene expression in kidney tissue was higher than other tissues, with a higher expression in stomach and adipose as well,FGF10 gene expression in stomach tissue was higher than other tissues, with a higher expression in kidney and adipose as well, but both of PDK4 and FGF10 genes expression were the lowest in longissimus dorsi. In different tissues of Large White pig, both of PDK4 and FGF10 genes were expressed the highest in adipose than other tissues, PDK4 gene expression in longissimus dorsi was the lowest, while the FGF10 gene expression the lowest in heart. This study successfully cloned the PDK4 and FGF10 genes of Large White pig and Congjiang Xiang pig,and detected the relative expression of PDK4 and FGF10 genes in different tissues of Large White pig and Congjiang Xiang pig, and also provided scientific basis for further study on regulation of PDK4 and FGF10 genes on lipid metabolism and deposition. 相似文献
343.
豆禾间作是有效提高土地利用率的方式,有利于缓解江淮地区草地面积不足的情况。本研究在2017-2018年,通过对五个播种比例下的金花菜(Medicago polymorpha L.)+燕麦(Avena sativa L.)间作与箭筈豌豆(Vicia sativa L.)+燕麦间作进行比较;通过其产量及营养价值等数据评价其优劣。结果表明,箭筈豌豆与燕麦比例3.3:8的间作具有最高总干草产量,为1 595.72 g·m-2。金花菜与燕麦比例6.6:4的间作具有最高的土地当量比和土地利用率,分别为1.36和132.58%,且总干草产量第二。竞争力指数表明金花菜的种群竞争力要高于箭筈豌豆。在营养价值方面,金花菜+燕麦间作更具优势;燕麦与金花菜间作后的粗蛋白含量达到13.88%~14.09%,高于箭筈豌豆间作中的13.19%~13.44%。综合来看,两种间作模式各有优劣,以燕麦产量为导向时,箭筈豌豆+燕麦比例为6.6:4和3.3:8的间作模式更优;而若是只考虑最高的土地利用率,则金花菜+燕麦比例为6.6:4的间作模式更优。 相似文献
344.
345.
本试验旨在通过基因工程方法获得重组肌肉生长抑制素蛋白。根据基因库肌肉生长抑制素基因序列设计合成特异性引物,引物两端分别加上EcoRⅠ和SalⅠ酶切位点及保护碱基,提取汉普夏猪的骨骼肌总RNA,用RT-PCR方法扩增肌肉生长抑制素全长基因,并将其克隆到pMD18-T载体上,测序后EcoRⅠ和SalⅠ双酶切,克隆到pET-30a( )中,构建原核表达载体pET-30a-M,将重组表达质粒转化至E.coliBL21(DE3)中,诱导表达。结果表明,成功扩增出肌肉生长抑制素全长基因;克隆载体经过DNA序列测定,所得基因与国外报道的完全一致;成功构建原核表达载体pET-30a-M;经IPTG诱导,表达出了6×His-M融合蛋白,用组氨酸标签抗体做Western印记证明产物大约48 ku,与预期大小相符,肌肉生长抑制素蛋白在大肠杆菌中成功的进行了表达。 相似文献
346.
将猪传染性胃肠炎病毒的N基因克隆到表达载体pET28a后,转化到BL21(DE3)大肠杆菌表达系统中.通过筛选表达温度和IPTG的浓度,使N基因在原核表达系统中表达并使目的表达产物产量达到最高值.将诱导表达的产物进行SDS-PAGE蛋白电泳和Western检验,证明该表达产物是猪传染性胃肠炎病毒的N蛋白.试验结果说明,猪传染性胃肠炎病毒N基因能够在原核表达系统中大量表达,而且表达的蛋白质具有生物学活性. 相似文献
347.
对山西菜田捕食性食蚜蝇优势种及对菜蚜的控制效果进行了研究,菜田常见捕食性食蚜蝇有黑带食蚜蝇,大灰食蚜蝇,斜斑鼓额食蚜蝇,野食蚜蝇,四条小食蚜蝇,短翅细腹食蚜蝇6种,以黑带食蚜蝇种群数量最大,平均占全年发生总量的36.3%,通过对食蚜蝇产卵量,卵化率,幼虫期捕食量和羽化率测试,筛选出的黑带食蚜蝇,大灰食蚜蝇,斜斑鼓额食蚜蝇幼虫对菜蚜均有较强的捕食能力,其中黑带食蚜蝇为山西菜田菜蚜捕食性食蚜蝇优势种,用黑带食蚜蝇三龄幼虫对菜蚜进行防治试验,结果以1:180防效最佳,72h后控制效果达93.5%。 相似文献
348.
349.
利用土壤深层水分渗漏仪和水分自动监测系统获取相应的监测数据,分析干旱区季节性河流(库姆塔格沙漠东南部崔木土沟)沟道内部的洪水入渗过程及不同深度土壤水分变化规律。结果表明:①
河道内以砂粒为主,土壤最大持水量在26.08%~31.75%。② 监测期内,每次洪水过程,水分均能入渗到200 cm以下的土层,但50 cm以下土层的水分入渗基本为非饱和入渗;每次入渗过程,湿润锋到达土层的深度与入渗时间具有良好的线性相关关系,但这一相关关系在春、夏季具有明显的分异,春季水分入渗更为缓慢。③
监测期内,160 cm土层共出现4次明显的连续渗漏过程,渗漏总量为2 165.8 mm,最大渗漏强度为21.4 mm·(2h)-1,160 cm土壤水分渗漏速率随土壤水分含量增加呈指数增加趋势,但每次开始出现连续渗漏的土壤初始含水率并不一致。该研究可为进一步揭示干旱区河流廊道生态系统生存、变化提供了科学支撑。 相似文献
350.
为探讨秃尾河流域径流量对气候变化的关系,利用秃尾河流域1970~2005年36 a来的气温、降水和天然径流量数据,对该流域气温、降水和径流量年际和季节性的变化特征及趋势进行了分析,研究了气候因子与径流量的相关性.研究结果表明:秃尾河流域年平均气温呈现明显升高趋势,以冬季升温为主;年降水表现为缓慢减少趋势,降水减少主要表... 相似文献