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   10051篇
  免费   523篇
  国内免费   738篇
林业   645篇
农学   736篇
基础科学   453篇
  1139篇
综合类   3470篇
农作物   636篇
水产渔业   570篇
畜牧兽医   2099篇
园艺   980篇
植物保护   584篇
  2024年   49篇
  2023年   146篇
  2022年   294篇
  2021年   349篇
  2020年   366篇
  2019年   481篇
  2018年   303篇
  2017年   432篇
  2016年   495篇
  2015年   465篇
  2014年   508篇
  2013年   566篇
  2012年   762篇
  2011年   873篇
  2010年   655篇
  2009年   608篇
  2008年   618篇
  2007年   657篇
  2006年   529篇
  2005年   378篇
  2004年   287篇
  2003年   243篇
  2002年   187篇
  2001年   157篇
  2000年   156篇
  1999年   127篇
  1998年   85篇
  1997年   87篇
  1996年   64篇
  1995年   67篇
  1994年   56篇
  1993年   51篇
  1992年   40篇
  1991年   33篇
  1990年   28篇
  1989年   22篇
  1988年   15篇
  1987年   15篇
  1986年   13篇
  1985年   12篇
  1984年   2篇
  1983年   6篇
  1982年   2篇
  1981年   4篇
  1980年   6篇
  1978年   2篇
  1977年   2篇
  1973年   1篇
  1956年   4篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Skeletal muscle genes are potential candidates for production and meat quality. Screening a subtracted cDNA library constructed with mRNA obtained from longissimus dorsi muscles of F1 hybrids Landrace × Yorkshire and their female parents Yorkshire, we isolated two partial sequences coding for the H3-K4-specific methyltransferase (KIAA1717) and skeletal muscle myosin regulatory light chain (HUMMLC2B) genes. Database search revealed KIAA1717 and HUMMLC2B encoded proteins with SET domain and EF-hand calcium binding motif, respectively. In the present work we identified their partial polymorphisms and two SNPs, one (C1354T) at the 3′ untranslated region (UTR) of KIAA1717 and one (A345G) at the SINE (PRE-1) element of HUMMLC2B, both created/disrupted a restriction site for endonuclease Msp I. The selected pigs were genotyped at the KIAA1717 C1354T and HUMMLC2B A345G sites by means of a PCR-RFLP protocol. Significant associations were observed for the KIAA1717 C1354T polymorphic site with meat marbling (longissimus doris (p < 0.05), biceps femoris (p < 0.01)) and intramuscular fat (p < 0.01). HUMMLC2B A345G were significantly associated with meat pH (longissimus doris (p < 0.05), biceps femoris (p < 0.01)), drip loss (p < 0.01), water holding capacity (p < 0.01) and meat color value (longissimus doris (p < 0.01), biceps femoris (p < 0.05)). Further studies are needed to confirm these preliminary results.  相似文献   
42.
Imaging and measurement of proliferation with computed tomography (CT) and positron emission tomography (PET) provide a noninvasive method for improved staging and monitoring of response to cancer treatment. We evaluated prospectively the proliferation marker 3'-deoxy-3'[18F] fluorothymidine (FLT) in the context of FLT-PET/CT for detection of early response, confirmation of posttreatment response, and prediction of relapse in dogs with non-Hodgkin's lymphoma. Nine dogs with non-Hodgkin's lymphoma who were scheduled to receive five cycles of an investigational cytotoxic chemotherapy agent were included. All dogs received baseline FLT-PET/CT imaging immediately before chemotherapy. Intent was to repeat imaging with FLT-PET/CT at various time points: group 1 ( n =4), 5 days after initiation of chemotherapy and 3 weeks following the last chemotherapy administration; group 2 ( n =5), before the fourth cycle of chemotherapy and 3 weeks following the last administration. Two dogs in group 2 did not undergo repeat PET/CT. Body mass standardized uptake values (SUV) for FLT were calculated for each dog. Eight dogs had initially increased FLT uptake (mean SUVmax=9.8 [2.6–22.3]). Mean SUV decreased significantly for the seven dogs that underwent follow-up PET/CT following chemotherapy (mean SUVmax=3.5 [1.1–7.9], P <0.016). Increased uptake preceded clinical and cytological evidence of relapse in two dogs. Ki-67 immunohistochemistry confirmed decreased proliferation corresponding to decreased SUV in three canine lymph node samples. FLT-PET/CT functional and anatomical imaging shows promise for the evaluation of response to cytotoxic chemotherapy in dogs with non-Hodgkin's lymphoma and for predicting relapse before standard clinical and clinicopathologic confirmation.  相似文献   
43.
We investigated the immune response induced by the Francisella (F.) tularensis live vaccine strain (LVS) and the Pohang isolate. After the Balb/c mice were infected intradermally (i.d) with 2 × 104 cfu of F. tularensis LVS and Pohang, respectively, their blood and organs were collected at different times; 0, 3, 6, 24, 72, 96, 120 and 168 h after infection. Using these samples, RT-PCR and ELISA analysis were carried out for the comparative study of the cytokines, including TNF-α, INF-γ, IL-2, IL-4, IL-10 and IL-12. In the Pohang-infected mice at 120 h, the liver showed a 53 times higher level of TNF-α and a 42 times higher level of IFN-γ than the respective levels at the early time points after infection. The levels of TNF-α and IFN-γ induced by LVS were 5 times lower than those induced by the Pohang isolate. Also, the organs from the Pohang-infected mice showed higher levels of TNF-α, IFN-γ, IL-10 and IL-12 than the levels in the LVS-infected mice. The blood from the Pohang-infected mice at 120 h revealed about a 40 times increased level of IFN-γ, and IL-10 was also increased by 4 times at 96 h compared to an early infection time point, while IL-4 was not induced during the whole infection period. These results suggest that F. tularensis may induce a Th1-mediated immune response to in vivo infection and the Pohang isolate has a higher capacity than the LVS to induce an acute immune response in Blab/c mice.  相似文献   
44.
3H—萱草根素在小鼠体内吸收分布,排泄和代谢的初步观察   总被引:3,自引:1,他引:3  
本文应用放射性同位素示综技术,初步观察了~3H-萱草根素在小鼠体内吸收分布、排泄和代谢的全过程。~3H-萱草根素口服后0.5小时,小鼠血液中放射性即达到高峰,并以低浓度维持96小时以上;其随血液循环分布于各组织器官,以胃肠组织含量最高,其次是肝脏和脾脏。萱草根素有蓄积性;一次给药和以同等剂量分次(每天一次,三天)投药后的相同时间,各组织中~3H-萱草根素的含量差异不显著。主要排泄途径是粪便,其次是尿液。经有机溶剂处理后的尿液分为水、脂二相,其放射性测量和薄板层析放射自显影结果均表明:~3H-萱草根素在体内经过代谢后结构发生了变化,从尿液中排出的不是萱草根素原形,而是其代谢产物。  相似文献   
45.
Follistatin-like 3 (FSTL3) is a regulator of cellular apoptosis and was previously identified via RNA-Seq to be associated with follicular development in mammalian ovaries. However, the mechanism underlying the FSTL3 regulation of oestrus in sheep remained poorly understood. In this study, the oestrogen (E2) and progesterone (P4) concentrations in blood were detected, and the expression level and functional analysis of FSTL3 in the ovary were studied during the different reproductive stage in Aohan fine wool sheep (seasonal breeding breed in China). The concentrations of E2 and P4 at the anestrus were significantly lower compared to dioestrus, proestrus and oestrus stages. Higher expression levels of FSTL3 were observed in the sheep ovary, hypothalamus, and thyroid. During different reproductive stages, higher expression levels were found during the stages of dioestrus and proestrus, while lower levels were found during the oestrus and anestrus stages. Functional analysis of FSTL3 was performed in primary granulosa cells (GCs) of sheep. The concentration of E2 increased significantly after RNAi interference of FSTL3, while the P4 level decreased. FSTL3 can decrease P4 levels, which might be involved in mediating oestrous cycle in sheep.  相似文献   
46.
47.
小RNA病毒属于单股正链RNA病毒,包括肠道病毒属、鼻病毒属、心脏病毒属、口疮病毒属和肝病毒属等几个主要的属.口蹄疫病毒(FMDV)、脊髓灰质炎病毒(PV)、丙型肝炎病毒(HCV)、脑心肌炎病毒(EMCV)是该科病毒的典型代表.小RNA基因组的末端具有非编码区(UTR),是病毒基因组复制的主要调控位点,3'非编码(3'...  相似文献   
48.
甲状腺激素对乌骨鸡蛋白质沉积影响的研究   总被引:1,自引:0,他引:1  
选用640只雪峰鸟骨鸡,分别饲喂添加不同水平(0.1,0.3,0.5mg/kg)的甲状腺激素(T3);5~8周龄分成2个组,一组停止添加T,,另一组继续添加T3,以研究甲状腺激素(T3)对雪峰乌鸡蛋白质沉积是否具有后续作用。结果表明:(1)甲状腺激素在2周龄以前可显著(P〈0.01)提高鸟骨鸡的蛋白质沉积;适合量为0.1mg/kg;(2)在乌骨鸡后期日粮中继续添加T3,则乌骨鸡的生长和蛋白质沉积被抑制;后期日粮中停止添加T3后,T3对乌骨鸡蛋白质沉积的抑制作用被解除,生长得到恢复。  相似文献   
49.
从河北沧州分离到一株疑似猪繁殖与呼吸综合征病毒,接种Marc-145细胞,经4代盲传,出现细胞病变,经鉴定为PRRSV,命名为HB-3(cz)株。根据GenBank公布的PRRSV JXA1株ORF6基因的核苷酸序列,设计并合成一对特异性引物(P1/P2),用RT-PCR方法扩增完整ORF6基因,将扩增产物连接到pGM-T载体并转化克隆菌,阳性重组质粒PGM-M进行序列测定与分析。后将克隆质粒PGM-M双酶切后连接原核表达载体pET-32a(+),在Rosseta-DE3中成功获得表达,经Western-blotting分析表明,表达蛋白与阳性血清发生特异性反应。  相似文献   
50.
Antibody response to an antigen involves the co-operation between three types of cells: macrophages, T cells and B cells. The cognate interactions between these cells play a fundamental role in the expression of a specific antibody response, but the last is modulated by antigen-nonspecific soluble factors produced either by macrophages or by T cells. Macrophages elaborate a spectrum of molecules modulating the function of lymphoid cells; among them are IL1 and prostaglandins of the E series, which are respectively enhancer and inhibitor of the antibody response in vitro. These molecules alter T cell and B cell activities through different mechanisms involving activation or inhibition of IL2 production, or alteration of cells surface antigens. However, the cellular events following the fixation of soluble factor on its receptors are not known.  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