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   14652篇
  免费   707篇
  国内免费   1798篇
林业   1771篇
农学   2267篇
基础科学   1374篇
  2684篇
综合类   4030篇
农作物   805篇
水产渔业   554篇
畜牧兽医   2156篇
园艺   430篇
植物保护   1086篇
  2024年   41篇
  2023年   144篇
  2022年   414篇
  2021年   583篇
  2020年   509篇
  2019年   495篇
  2018年   353篇
  2017年   467篇
  2016年   537篇
  2015年   701篇
  2014年   654篇
  2013年   731篇
  2012年   832篇
  2011年   997篇
  2010年   870篇
  2009年   864篇
  2008年   798篇
  2007年   887篇
  2006年   767篇
  2005年   733篇
  2004年   365篇
  2003年   324篇
  2002年   258篇
  2001年   278篇
  2000年   355篇
  1999年   413篇
  1998年   362篇
  1997年   354篇
  1996年   306篇
  1995年   310篇
  1994年   270篇
  1993年   223篇
  1992年   183篇
  1991年   173篇
  1990年   139篇
  1989年   122篇
  1988年   131篇
  1987年   60篇
  1986年   37篇
  1985年   21篇
  1984年   21篇
  1983年   21篇
  1982年   22篇
  1981年   10篇
  1980年   10篇
  1979年   7篇
  1965年   1篇
  1964年   3篇
  1956年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
The domestic yak (Bos grunniens) is an iconic symbol of animal husbandry on the Qinghai–Tibet Plateau. Long‐term domestication and natural selection have led to a wide distribution of yak, forming many ecological populations to adapt to the local ecological environment. High altitude is closely related to oxygen density, and it is an important environmental ecological factor for biological survival and livestock production. The aim of the present study was to perform a preliminary analysis to identify the candidate genes of altitude distribution adapted ecological thresholds in yak using next‐generation sequence technology. A total of 15,762,829 SNPs were obtained from 29 yaks with high‐ and low‐altitude distribution by genome‐wide sequencing. According to the results of the selective sweep analysis with FST and ZHp, 21 candidate genes were identified. 14 genes (serine/threonine protein kinase TNNI3K, TEN1, DYM, ITPR1, ZC4H2, KNTC1, ADGRB3, CLYBL, TANGO6, ASCC3, KLHL3, PDE4D, DEPDC1B and AGBL4) were grouped into 32 Gene Ontology terms, and four genes (RPS6KA6, ITPR1, GNAO1 and PDE4D) annotated in 35 pathways, including seven environmental information processing and one environmental adaptation. Therefore, the novel candidate genes found in the current study do not only support new theories about high‐altitude adaptation, but also further explain the molecular mechanisms of altitude adaptation threshold in yaks.  相似文献   
112.
北方寒地引种抗寒苜蓿品种试验   总被引:1,自引:0,他引:1  
1991、1992年两年对10个抗寒苜蓿品种进行了品种比较试验,鉴选出公农一号、草原一号、草原二号、甘农一号、图牧二号6个苜蓿良种。这些品种适应黑龙江垦区的生态条件,抗寒、抗病性强、长势好、产草量高、品质优良,可以在垦区三江平原推广种植。  相似文献   
113.
介绍一种新型燃气防泄漏多重保护装置的结构和工作原理,并阐述了控制系统的特点。实验表明,它能在燃气使用前进行检测及自动报警、发生火灾或温度过高时自动关闭燃气开关、用户忘记关闭总闸时定时自动关闭总阀,该装置具有反应灵敏、制动迅速的特点,能够从根本上检测预防燃气的泄漏问题,具有十分广阔的应用前景。  相似文献   
114.
湖南省根据地理区域和养殖业结构情况,合理布局建立了18个省级动物疫情测报站,通过对测报站辖区内及定点养殖场户的生产、免疫、疫病等情况进行持续跟踪调查和监测采样,评估动物群体免疫状态及疫情发生风险。管理上通过优化网络布局,提高诊断监测能力,通过强化培训和责任管理,提升动物疫情测报水平,确保了动物疫情测报质量。动物疫情测报站在发现新发重大动物疫病,评价强制免疫病种免疫效果,提供疫情预警预报基础数据以及指导养殖业生产等方面发挥了重要作用。今后需持续增加投入和监测科技含量,改善设施设备,稳定技术队伍,这是提高动物疫情测报监测的根本保障。  相似文献   
115.
The consistent failure to isolate bona fide pluripotent cell lines from livestock indicates that the underlying mechanisms of early lineage specification are poorly defined. Unlike other species, the contrivances of segregation have been comprehensively studied in the mouse. In mouse, FGF/MAPK signalling pathway dictates the segregation of hypoblast (primitive endoderm). However, it is not evident whether this mechanism is also conserved in livestock. Here, in this study, we examined the roles of FGF/MAP kinase signalling pathways in porcine parthenogenetic embryos during the early development. Porcine parthenogenetic embryos were cultured in the medium addition with FGFR inhibitor BGJ398 (10 μm ) or DEMOS. Pluripotency‐ and lineage‐related gene expressions in the early porcine embryos were determined. Compared to control, total cell numbers on day 7 were significantly higher (55 ± 5.96 vs 47 ± 1.97, p < 0.05) in embryos cultured in the presence of BGJ398, but had no significant effect on the rate of blastocyst development (47% vs 44%, p > 0.05). Nonetheless, BGJ398 treatment significantly augmented the expression of pluripotency and trophoblast marker genes (SOX2, OCT4, KLF4 and CDX2), but did not significantly change the expression of NANOG and hypoblast marker gene (GATA4). Furthermore, the addition of FGF signalling agonist (FGF2) during the embryo development significantly decreased the expression of pluripotency and trophoblast marker genes (SOX2, NANOG, KLF4 and CDX2), but no significant effect on the expression of OCT4 and GATA4 was observed. Here, we exhibit that inhibition of FGF signalling could improve the quality of the porcine embryo and escalate the chance to capture pluripotency. Besides, it also promotes the trophoblast development of porcine parthenogenetic embryo. In addition, the data suggested that FGF signalling pathway is dispensable for the segregation of hypoblast and epiblast lineages in porcine embryo during the early development.  相似文献   
116.
该试验应用原子吸收光谱法对冀东地区干乳期奶牛基础混合日粮中的铜、铁、锰、锌含量进行测定和盈缺分析,以便为干乳期奶牛日粮配制提供借鉴。试验结果表明,基础混合日粮中铁、铜、锰和锌含量分别为299.87,14.38,37.70和32.67mg/kg。其中,铁含量为NRC(2001)报道干乳期奶牛铁需要量的16倍,是其他文献报道需要量的3倍;铜含量达到干乳期奶牛需要量;锰、锌的含量达到NRC(2001)报道干乳期奶牛铁需要量,而低于文献推荐需要量。  相似文献   
117.
Chlamydia spp. are obligate intracellular gram-negative bacteria that cause a wide range of significant diseases in humans and animals worldwide, resulting in significant economic losses. Chlamydial infection in cattle has been reported in many countries including China. However, there has been no survey of chlamydial infection of dairy cattle in Guangzhou, southern China. The objective of the present investigation was to examine the chlamydial seroprevalence in dairy cattle in Guangzhou, subtropical southern China by using an indirect hemagglutination assay (IHA). The overall seroprevalence of chlamydial infection in dairy cattle was 7.25% (29/400). Greater than or equal to eight-yr-old dairy cattle had the highest seroprevalence (10.34%), followed by those that were ≥ 6 years old or < 7 years old dairy cattle (10.20%), although there were no statistically significant differences among different groups (P > 0.05). Dairy cattle with 5 pregnancies had the highest seroprevalence (10.81%). These results indicate that chlamydial infection was present in dairy cattle in Guangzhou, subtropical southern China, and integrated strategies and measures should be executed to control and prevent chlamydial infection and disease outbreak in the study region.  相似文献   
118.
为了解正安县山羊主要疫病的发展趋势,通过虎红平板凝集试验、正向间接血凝试验、酶联免疫吸附试验等方法对正安县引进山羊进行布鲁氏杆菌病、O型口蹄疫、AsiaI型口蹄疫、山羊传染性胸膜肺炎、山羊痘等主要疫病血清抗体的检测。结果表明,O型口蹄疫、AsiaI型口蹄疫和山羊痘免疫抗体阳性率分别为79.42%、81.18%和99.58%,未免疫的布鲁氏杆菌病、羊传染性胸膜肺炎的丝状支原体山羊亚种和绵羊肺炎支原体未免疫抗体阳性率分别为0%、0%和3.81%。监测结果为山羊健康的引进、培育和扩繁提供了一些基础数据,对指导养羊生产有一定的意义。  相似文献   
119.
microRNA (miRNA) and piwi‐interacting RNA (piRNA) are two classes small non‐coding regulatory RNAs that play crucial roles in multiple biological processes such as spermatogenesis. However, there are no published studies on conjoint analysis of miRNA and piRNA profiles among cattle, yak and their interspecies (the dzo) using sequencing technology. Next‐generation sequencing technology was used to profile miRNAs and piRNAs among those three ruminants to elucidate their functions. A total of 119, 14 and six differentially expressed miRNAs were obtained in cattle vs. dzo, cattle vs. yak and yak vs. dzo comparison groups, while there were 873, 1,065 and 1,158 differentially expressed piRNAs in those three comparison groups. The expression of three miRNAs was validated in the three ruminants, and the results suggested that the miRNA expression profiles data could represent actual miRNA expression levels. Moreover, the putative targets of differentially expressed miRNAs were predicted by their own genome, it is worth to note that both the cattle and yak genome were used for dzo, then the targets were subjected to GO enrichment and KEGG pathway analysis, revealing the likely roles for these differentially expressed miRNAs in spermatogenesis. In conclusion, this study provided a useful resource for further elucidation of the miRNAs and piRNAs regulatory roles in spermatogenesis. It may also facilitate the development of therapeutic strategies for dzo reproduction research.  相似文献   
120.
披碱草属四种植物主要形态特征的变异性比较   总被引:2,自引:1,他引:2  
应用变异系数、主成分分析、系统聚类分析方法,对披碱草属四种不同生境来源的18个居群的180份材料进行形态特征比较分析.变异系数分析结果表明:(1)披碱草属4种植物的不同居群在形态特征上具有变异性;(2)不同居群内及居群间的形态特征存在一定程度的变异;(3)穗部形态特征中的颖及稃特征是种间和种以下分类的重要依据.主成分分析结果表明:颖长、颖脉数、外稃长、内稃长、小穗长、小穗宽等是种间分类的重要特征指标.系统聚类分析法分析表明:在欧式距离等于5时可将来自不同生境的18个居群分为3类,经鉴定第一类为披碱草和老芒麦,第二类为麦宾草,第三类是圆柱披碱草;其中麦宾草的归类清晰.  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