全文获取类型
收费全文 | 9984篇 |
免费 | 609篇 |
国内免费 | 879篇 |
专业分类
林业 | 725篇 |
农学 | 600篇 |
基础科学 | 344篇 |
1012篇 | |
综合类 | 4877篇 |
农作物 | 604篇 |
水产渔业 | 394篇 |
畜牧兽医 | 1576篇 |
园艺 | 906篇 |
植物保护 | 434篇 |
出版年
2024年 | 88篇 |
2023年 | 211篇 |
2022年 | 495篇 |
2021年 | 465篇 |
2020年 | 455篇 |
2019年 | 433篇 |
2018年 | 293篇 |
2017年 | 490篇 |
2016年 | 346篇 |
2015年 | 473篇 |
2014年 | 526篇 |
2013年 | 695篇 |
2012年 | 934篇 |
2011年 | 881篇 |
2010年 | 899篇 |
2009年 | 749篇 |
2008年 | 749篇 |
2007年 | 624篇 |
2006年 | 505篇 |
2005年 | 365篇 |
2004年 | 239篇 |
2003年 | 133篇 |
2002年 | 135篇 |
2001年 | 135篇 |
2000年 | 99篇 |
1999年 | 32篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1981年 | 2篇 |
1962年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
[目的]分析评价金针菇菌株的农艺性状及其遗传多样性,为金针菇种质资源分类鉴定、保藏及遗传育种等提供理论参考.[方法]采用拮抗对峙试验、ISSR标记分析和农艺性状测定相结合的方法综合分析29株采自山东和江苏地区的金针菇菌株遗传多样性,并利用NTSYSpc 2.11F计算菌株间遗传相似系数,采用非加权配对算数平均法(UPGMA)构建聚类树状图.[结果]29株金针菇菌株间有246组发生拮抗反应,有160组未发生拮抗反应.供试菌株的菌盖和菌柄颜色有黄色、浅黄色、乳白色和白色4种,菌柄长度15.00~21.20 cm,菌盖直径0.73~1.72 cm,单袋产量332~513 g,生育期41~68 d.白色或乳白色金针菇菌株的生物学效率为73.0%~102.6%,生育期48~68 d;黄色或浅黄色金针菇菌株的生物学效率为66.4%~87.2%,生育期41~58 d,表明白色或乳白色金针菇菌株较黄色或浅黄色菌株产量较高,商品性状优良,但生育期较长.筛选出的8条ISSR引物共计扩增多态性位点270个,多态性比率为94%.供试金针菇菌株遗传相似系数为0.860~0.900,在遗传相似系数0.870处,29株金针菇菌株可分为五大类群.[结论]菌株间是否发生拮抗反应与菌株子实体颜色无关.江苏和山东两地区的金针菇菌株具有较丰富的遗传差异和遗传多样性,但亲缘关系较近. 相似文献
192.
193.
AIM: To observe the effect of ischemic preconditioning (IPC) on the subsequent permanent ischemic rat retina. METHODS: A model of two-vessel occlusion (2VO) was used to give an ischemic insult to rat retina. Bilateral carotid arteries were occluded directly in the simple ischemic groups. A procedure of double 2 min ischemia- 3 min reperfusion was applied to IPC groups before their carotid arteries were occluded. Experimental control groups received the same operation except that their exposed vessels were not occluded. Other 6 normal rats served as immunohistochemical controls. Eyeballs were taken out after being subjected to 1, 3 and 7 days of ischemia. The morphometry of retina was measured by stereologic methods. The apoptosis during the retinal ischemia was detected by TUNEL. Immunohistochemistry staining was used for the localization of bcl-2 in retina. RESULTS: In IPC groups, the thickness of retina was thinner than that in simple ischemic groups. The apoptosis was less when compared with the simple ischemic groups at the same ischemic time. The apoptotic cells show only in INL and the apoptosis of RGCs was not appeared until 7 days postischemia. There was no significant difference of the numerical density of RGCs at the different time after the operation. The bcl-2 immunoreactivity was weaker than that of the simple ischemic groups too. CONCLUSION: IPC reduced the injury caused by ischemia in retina, showing a protective effect. 相似文献
194.
安哥拉山羊与建昌黑山羊及其杂种后代的DNA指纹分析 总被引:5,自引:0,他引:5
以 (CA/GATA/TCC) 5探针 ,HinfI酶切 ,研究安哥拉山羊和建昌黑山羊及安哥拉山羊与建昌黑山羊级进杂交的F2 、F3的DNA指纹图谱。结果 ,在供试山羊中 ,个体平均检出 1 8.2± 0 .4条谱带 ,安哥拉山羊、F2 、F3的鉴别机率分别为 1 .38× 1 0 - 12 ,1 .1 8× 1 0 - 13,0 .50× 1 0 - 10 ;群体内相似系数安哥拉山羊为0 .4 539,F2 为 0 .4 0 77,F3为 0 .61 1 1 ;亲子鉴定的父权概率W =0 .9889;安哥拉山羊与建昌黑山羊比较 ,2 .3kb和 8.6kb谱带为安哥拉山羊的特异谱带 相似文献
195.
AIM:To investigate endocrine differentiation and its mechanism in endometrial carcinoma.METHODS:Endocrine cells (EC) were identified by immunohistochemical staining of chromogranin A in 50 cases of endometrioid adenocarcinoma and 20 cases of normal endometrium. Double-label techniques were used for simultaneous demonstration of the CgA and cytokeratin.RESULTS:The positive rate of CgA in endometrioid adenocarcinoma was 44.0%, and was significant higher than that in normal endometrium (15.0%, P<0.05). Scanty EC was present in normal endometrium. The number and staining intensity of EC in endometrioid adenocarcinoma were greater than that in normal. Co-expression of CgA and cytokeratin were detected in endometrioid adenocarcinoma.CONCLUSION:The presence of endocrine cells in endometrioid adenocarcinoma showed heterogeneity of tumors. The occurrence of "Multidirectional differentiation cells" within the endometrioid adenocarcinoma may indicate that endocrine cells derive from malignant cells of multidirectional differentiation. 相似文献
196.
东北农牧交错区与牧区畜牧业生产不同,其中一个重要的不同点就是农牧交错区具有多种农副产品,这些农副产品在枯草期成为家畜丰富的干物质来源。而这些农副产品由于所含蛋白、纤维、口感等存在很大差异,因而家畜对其有不同的采食行为。对10种东北农牧交错区枯草期最主要的补饲物进行家畜采食行为的试验,为家畜的日常补饲及管理提供参考资料。结果表明:绿豆秸秆、葵盘、葵叶、羊草、玉米叶为补饲物的首选。 相似文献
197.
多花木蓝和二色胡枝子种子硬实特性与活力关系的研究 总被引:6,自引:0,他引:6
将多花木蓝和二色胡枝子种子在恒温25℃下吸胀,每24 h取出吸胀种子,14 d后未吸胀的种子为硬实种子(H)。硬实种子切破种皮后吸胀24 h,与非硬实种子进行发芽试验和各项活力指标测定。结果显示,每日内吸胀的种子数量随时间推移以一定的比例下降,多花木蓝种子吸胀相对缓慢,第5天以后吸胀率降到1%以下,胡枝子种子第3天以后吸胀率就降到1%以下。2种牧草种子都显示出硬实种子的发芽率、发芽指数和活力指数、脱氢酶活性、酸性磷酸酯酶活性均高于非硬实种子,而电导率值、浸出液可溶性糖含量和丙二醛含量低于非硬实种子,这表明硬实种子的活力高于非硬实种子。而非硬实种子中,根据以上各活力指标判断,晚吸胀的种子比早吸胀的种子活力高。 相似文献
198.
Canine coronavirus (CCoV) and feline coronavirus (FCoV) belong to α-genus coronavirus of coronavirus family,porcine transmissible gastroenteritis virus (TGEV),porcine epidemic diarrhea virus (PEDV) also belong to the same genus.Genetic evolution analysis showed that different genotype of the virus could produce new variant strains through gene recombination,which caused great obstacles to the diagnosis and control of the disease.β-genus coronaviruses include bovine coronavirus (BCoV),canine respiratory coronavirus (CRCoV) and severe acute respiratory syndrome coronavirus (SARS-CoV).Among them,CRCoV has the highest homology with BCoV,but there are great differences in genomic structure,pathogenic mechanism and infection symptoms between this kind of coronavirus and α-coronavirus.CCoV and FCoV are widely spreading around the world,characterized by high morbidity and low mortality.Due to the characteristics of RNA virus and the influence of environmental selection pressure,the viruses continue to mutate and evolve,and new virulent strains appear one after another.The virulence of feline infectious peritonitis virus (FIPV) is greatly enhanced,some specific point mutations in the virus genome change the cellular tropism against the host.The pathogenesis of the virus mainly depends on the antibody-dependent enhancement (ADE) induced by virus infection.The epidemiological investigation and prevention and control of CCoV and FCoV should not only rely on the single factor of vaccine immunity,but also comprehensively consider the virulence of the virus,environmental conditions,pet self-immune resistance, and so on.The identification of CCoV and FCoV should be based on clinical symptoms,combined with routine hematological examination,serum biochemical examination and laboratory diagnosis techniques to prevent false positive and false negative results. 相似文献
199.
应用RT-PCR技术从经植物血凝素(PHA)刺激诱导的奶牛脾脏淋巴细胞总RNA中扩增出牛-γ干扰素基因(bovine interferon-γ,BovIFN-γ)cDNA,并克隆到pGEM-T easy载体中,经过限制性酶切分析和测序证实,所克隆到的基因编码区序列与已报道的序列完全一致.将含信号肽的BoIFN-γ基因整个编码区cDNA亚克隆到杆状病毒转座载体pFastBac Ⅰ中,构建了转移载体pFastBac 1-BoIFN-γ,转座到宿主菌DH10 Bac中,在含庆大霉素、四环素、卡那霉素、IPTG和X-gal的KGTIX LB平板上筛选白色菌落,提取DNA获得重组穿梭载体Bacmid-BoIFN-γ质粒,与脂质体共转染Sf9细胞,产生有感染力的重组杆状病毒reBac-BoIFN-γ.重组病毒经过传代扩增感染Sf9细胞,通过IFA试验、Western-blot和抗病毒活性测定证实,BoIFN-γ基因在感染的昆虫细胞和上清中得到了表达,上清中活性可达2.651×105U/mL.表达条件优化结果表明,不同MOI对rBoIFN-γ的表达产量影响不大,上清中干扰素活性在感染后5 d达到高峰. 相似文献
200.
基于MODIS数据的中国草地生态体系价值估算研究 总被引:5,自引:0,他引:5
在传统的草原生态系统价值估算的基础上,利用遥感技术,以谢高地等人计算出来的各种草地类型单位面积价值量为经济参数,利用2003年MODIS数据估算的中国草原生态系统服务价值约折合US$311.48×108,并从草地类型和省区等角度分别进行区域分析,表明我国草原生态系统服务价值呈现出农牧交错带较高且逐渐向牧区递减的特征,说明牧区草原生态系统退化比较严重,草原生态功能保护意识需要进一步加强。 相似文献