全文获取类型
收费全文 | 81622篇 |
免费 | 5253篇 |
国内免费 | 7267篇 |
专业分类
林业 | 6160篇 |
农学 | 4993篇 |
基础科学 | 4245篇 |
8492篇 | |
综合类 | 38866篇 |
农作物 | 5893篇 |
水产渔业 | 3189篇 |
畜牧兽医 | 12867篇 |
园艺 | 5496篇 |
植物保护 | 3941篇 |
出版年
2024年 | 357篇 |
2023年 | 1552篇 |
2022年 | 3796篇 |
2021年 | 3558篇 |
2020年 | 3470篇 |
2019年 | 3247篇 |
2018年 | 2384篇 |
2017年 | 3983篇 |
2016年 | 2616篇 |
2015年 | 4040篇 |
2014年 | 4099篇 |
2013年 | 5030篇 |
2012年 | 6920篇 |
2011年 | 7071篇 |
2010年 | 6638篇 |
2009年 | 5728篇 |
2008年 | 5850篇 |
2007年 | 5490篇 |
2006年 | 4446篇 |
2005年 | 3590篇 |
2004年 | 2205篇 |
2003年 | 1556篇 |
2002年 | 1584篇 |
2001年 | 1531篇 |
2000年 | 1317篇 |
1999年 | 619篇 |
1998年 | 209篇 |
1997年 | 152篇 |
1996年 | 161篇 |
1995年 | 149篇 |
1994年 | 142篇 |
1993年 | 115篇 |
1992年 | 109篇 |
1991年 | 82篇 |
1990年 | 76篇 |
1989年 | 57篇 |
1988年 | 36篇 |
1987年 | 29篇 |
1986年 | 22篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 3篇 |
1964年 | 3篇 |
1962年 | 12篇 |
1957年 | 3篇 |
1956年 | 36篇 |
1955年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
运用灰色关联法原理,采用均方差法计算指标权重,根据近年来湖北省进行小型农田水利工程建设项目绩效评价的实际情况,建立了小型农田水利工程建设项目评价定性定量混合指标体系和模型,应用该模型和方法对湖北省2012年第二批20个小农水重点县工程建设项目进行了评价(作为研究,各县、市名以汉语拼音字头代替)。结果表明:LHK、SSS、ZJS、DJK、XTS等14个县为优秀,XCX、TMS、JSX等5个县为良好,CYX为一般,无及格等级的重点县。评价结果与实际基本相符。证明本文所提出的模型和方法可应用于实际,是一种快速便捷的评价工具。 相似文献
992.
993.
宽幅高效离心式双圆盘撒肥机设计与试验 总被引:3,自引:0,他引:3
为解决现有水旱田撒肥机械作业效率低、撒肥量调节技术落后、施肥均匀性稳定性差等实际问题,设计了一种同轴驱动的离心式双圆盘撒肥机。介绍了整机结构与工作参数,研究设计了撒肥传动系统、撒肥盘结构、排肥量液压调节装置等,并确定了关键结构和参数,同时进行了试验研究。试验结果显示,推肥板推肥角度-20°~30°可调,撒肥幅宽达到50m,总排肥量稳定性变异系数低于6%,施肥均匀性变异系数低于16%。研究结果表明,撒肥机工作性能稳定、撒肥量可控、抛撒均匀,整机设计满足水旱田宽幅高效撒肥作业要求。 相似文献
994.
995.
误差修正是实时洪水预报研究和应用中的重要内容,从修正模型降雨输入角度出发,提出了一种基于微分响应的降雨误差修正方法,并通过实例论证了该方法修正降雨量的适用性。该方法通过计算降雨所对应模型的微分响应来修正降雨,从而修正出口断面流量过程。将该修正方法结合新安江模型,对闽江建阳流域的19场历史洪水进行了有效性检验,结果表明:此方法对洪量、洪峰的修正效果明显,且能够显著提高洪水预报的合格率,修正后合格率由63.2%提高到94.7%。 相似文献
996.
997.
MAO Qian-qian ZHOU Ling TANG Qing-hai BU Bin TANG Cun-duo JIAO Zhu-jin YAO Lun-guang KAN Yun-chao YANG Jian-wei CUI Shang-jin 《中国畜牧兽医》2016,43(7):1659-1666
This study was aimed to prepare canine parvovirus (CPV) VP2 protein polyclonal antibody.The recombinant expression vector pET28a-CPV-VP2 was constructed and transfromed into E.coli BL21 (DE3),the expression of recombinant proteins was induced by IPTG from which the fusion protein was identified by SDS-PAGE.The target protein was purified and emulsify with adjuvant,the prepared immunogen was inoculated into rabbit by subcutaneous injections to prepare of VP2 protein specific polyclonal antibody.The immuno-activity,titers,neutralization titers of the prepared polyclonal antibody were determined by immunoperoxidase monolayer assay (IPMA).The results showed that the expressed recombinant protein VP2 (rVP2) existed in the form of inclusion body with a molecular weight of 72 ku.The prepared polyclonal antibody titer was 1 600 dilution,the virus titer was 107 TCID50/mL,the neutralizing titer was 1∶2 884.The antibodies showed specific reaction with CPV.In conclusion,rVP2 specific polyclonal antibody showed wonderful immunocompetence,specificity and neutralizing activity,providing foundation for the development of genetic vaccine and clinical therapeutic method. 相似文献
998.
To study the effect of weaning stress on dairy buffalo calves,5 healthy calves were chosen and weaned,and the blood samples were collected at 1 day before weaning,and 1,14 and 21 days after weaning to analysis blood physiology and biochemistry indexes and immune function.The results showed that the count of white blood cell,lymphocyte,erythrocyte,monocytes and hematocrit,aspartate aminotransferase activity,blood glucose,cortisol and immunoglobulin G contents of dairy buffalo calves were no significant difference between before and after weaning treatments (P > 0.05).The count of neutrophils at 21 d after weaning were significantly lower than that of 1 d before weaning of dairy buffalo calves (P < 0.05).However,lactate dehydrogenase and alanine aminotransferase activity in weaned treatments were significantly higher than those of animals in the treatment before weaning (P < 0.05).The serum urea nitrogen of dairy buffalo calves at 21 d after weaning was significantly higher than that of 1 d before weaning (P < 0.05) and hemoglobin content at 21 d after weaning was significantly lower than that at 1 day before weaning (P < 0.05).It indicated that the physiological and immunity function of dairy buffalo calves were challenged under weaning stress. 相似文献
999.
In order to detect the clinical efficacy of oligosaccharide sulfate(DEAE) and dextran sulfate (DS-4000) against bovine mastitis,56 cows with bovine mastitis were divided into 5 groups (DEAE group,DS-4000 group,DEAE+penicillin group,DS-4000+penicillin group and penicillin group),and their breasts were perfusion with different drugs twice one day for 3 days.The effective rates of drugs were observed by clinic symptoms.Milk samples were collected before and after treatment of drugs,and the bacterial negative conversion rate of each group were detected by microbial examination.The results showed that total effective rates of 5 groups were 10.00%,20.00%,58.33%,75.00% and 50.00%,respectively,and the bacterial negative conversion rates were 0,12.50%,50.00%,54.55% and 44.44%,respectively.In conclusion,the curative efficiencies of the polysaccharides against bovine mastitis were weak,but it could be improved by combination with penicillin. 相似文献
1000.
FAN Xin-hao WANG Zi-shuai LIANG Guo-ming YANG Ya-lan LI Kui SONG De-gui TANG Zhong-lin 《中国畜牧兽医》2016,43(10):2621-2627
This research was aimed to study whether the lncRNA would have effects on the structure and constitution of the intestinal microbial colonies in mice.High throughout sequencing was used to sequence and analyze the intestinal microbial colonies in both transgenic and non-transgenic mice of three months old.We conducted comparison and t-test at the level of phylum and genus.The result showed that transferred into long non-coding RNA genes GTL2 (lncRNA-GTL2),the mouse intestinal microbial colony structure and composition had no significant differences in the overall,within the same gender,but there were individual differences.Therefore,this study didn't find that long non-coding RNA transfered had a significant impact on the intestinal microflorain the phylum and genus level. 相似文献