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   24458篇
  免费   1950篇
  国内免费   1787篇
  28195篇
  2024年   55篇
  2023年   301篇
  2022年   794篇
  2021年   1285篇
  2020年   886篇
  2019年   1040篇
  2018年   1031篇
  2017年   748篇
  2016年   1069篇
  2015年   1467篇
  2014年   1723篇
  2013年   1890篇
  2012年   2247篇
  2011年   1927篇
  2010年   1168篇
  2009年   1018篇
  2008年   1201篇
  2007年   1063篇
  2006年   921篇
  2005年   809篇
  2004年   693篇
  2003年   629篇
  2002年   544篇
  2001年   481篇
  2000年   419篇
  1999年   403篇
  1998年   255篇
  1997年   269篇
  1996年   256篇
  1995年   242篇
  1994年   220篇
  1993年   136篇
  1992年   206篇
  1991年   145篇
  1990年   130篇
  1989年   109篇
  1988年   73篇
  1987年   94篇
  1986年   56篇
  1985年   56篇
  1984年   43篇
  1983年   30篇
  1982年   30篇
  1981年   19篇
  1980年   8篇
  1979年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
构建了含有pGHcDNA的重组痘苗病毒,用ELISA证明该重组病毒在被感染的h143细胞中,可表达出猪生长激素并将之分泌到培养基中,表达量约为1.05μg/10 ̄6细胞(24h)。用定位免疫化学法进一步证明该病毒可感染小鼠并在小鼠体内表达pGHcDNA。同时还构建了含双拷贝pGHcDNA的重组痘苗病毒,并证明其pGH表达量比单拷贝重组病毒有明显提高,约为1.50μg/10 ̄6细胞(24h)。  相似文献   
102.
用苯甲基磺酰氟(PMSF)和H_2Se相继处理铜锌超氧化物岐化酶(Cu,Zn-SOD),将酶分子中的丝氨酸(Ser)转化为硒代半胱氨酸(SeCys),从而引入了谷胱甘肽过氧化物酶(GPX)的催化基团,使其在SOD酶活性大部分保留的情况下,具有GPX活性,其GPX活力是PZ51活力的30倍。研究了双功能酶的最佳制备条件,包括PMSF的剂量、反应最适温度及H_2Se处理时间等,并用电子能谱、DTNB等方法测定了双功能酶的硒含量;测定了双功能酶对不同底物的米氏常数及双功能酶的荧光光谱、紫外吸收光谱及稳定性。  相似文献   
103.
本文首次报道了新家6各民族6134人(南3181人、女2953人)的指纹白线出现频率。结果表明,白线频率女高于男,民族间亦有差异,其中维吾尔、哈萨克、鸟孜别克族频率接近。塔吉克族居住高寒高原地区,属白色人种,频率明显低于以上3个民族,锡伯族和汉族生活习惯近似,且高于以上4个民族,作者认为,白线出现频率的高低与种族、性别、年龄和群体生长环境及生活习惯有关。We’ve studied 6134 individuals (male 3181, fimale 2953) of six nationalities in Xinjiang.The result is that the white line of hand print is associated with rae,sex,age,grow environments of groups and life habbits.The ifference of races is:The appearant rates of white line of Weivuerite,Hasakese and Wuzibese are near,Tajike’s rate is lower than xiboman’s and han are higher than others.  相似文献   
104.
105.
106.
RFLP tagging of a new semidwarfing gene in rice   总被引:6,自引:0,他引:6  
A new rice semidwarfing gene which is not allelic tosd1, temporarily designated assdg, might be of use as a new source of semidwarfism in rice breeding programs. We report here the identification of a DNA marker closely linked to this gene. The DNA marker was identified by testing 120 mapped rice RFLP makers as hybridization probes for Southern analysis of a pair of nearly isogenic lines with or withoutsdg. Linkage association of the marker with the gene was verified using a F2 population segregating for semidwarfism. RFLP analysis showed thatsdg is closely linked to a single-copy DNA clone RZ182 on chromosome 5, with a distance of 4.3 centiMorgans between them. This marker may facilitate early selection for the semidwarfing gene in rice breeding programs  相似文献   
107.
Soybean is believed to be a diploidized tetraploid generated from an allotetraploid ancestor. In this study, we used hypomethylated genomic DNA as a source of probes to investigate the genomic structure and methylation patterns of duplicated sequences. Forty-five genomic clones from Phaseolus vulgaris and 664 genomic clones from Glycine max were used to examine the duplicated regions in the soybean genome. Southern analysis of genomic DNA using probes from both sources revealed that greater than 15% of the hypomethylated genomic regions were only present once in the soybean genome. The remaining ca. 85% of the hypomethylated regions comprise duplicated or middle repetitive DNA sequences. If only the ratio of single to duplicate probe patterns is considered, it appears that 25% of the single-copy sequences have been lost. By using a subset of probes that only detected duplicated sequences, we examined the methylation status of the homeologous genomes with the restriction enzymes MspI and HpaII. We found that in all cases both copies of these regions were hypomethylated, although there were examples of low-level methylation. It appears that duplicate sequences are being eliminated in the diploidization process. Our data reveal no evidence that duplicated sequences are being silenced by inactivation correlated with methylation patterns.  相似文献   
108.
The maturation and envelopment of varicella-zoster virus (VZV) was studied in infected human embryonic lung fibroblasts. Transmission electron microscopy confirmed that nucleocapsids acquire an envelope from the inner nuclear membrane as they enter the perinuclear-cisterna-rough endoplasmic reticulum (RER). Tegument is not detectable in these virions; moreover, in contrast to the mature VZV envelope, the envelope of VZV in the RER is not radioautographically labeled in pulse-chase experiments with [3H]mannose, and it lacks gpI immunoreactivity and complex oligosaccharides. This primary envelope fuses with the RER membrane (detected in cells incubated at 20 degrees C), thereby releasing nucleocapsids to the cytosol. Viral glycoproteins, traced by transmission electron microscopy radioautography in pulse-chase experiments with [3H]mannose, are transported to the trans-Golgi network (TGN) by a pathway that runs from the RER through an intermediate compartment and the Golgi stack. At later chase intervals, [3H]mannose labeling becomes associated with enveloped virions in post-Golgi locations (prelysosomes and plasma membrane). Nucleocapsids appear to be enveloped by wrapping in specialized cisternae, identified as the TGN with specific markers. Tegument-like material adheres to the cytosolic face of the concave surface of TGN sacs; nucleocapsids adhere to this protein, which is thus trapped between the nucleocapsid and the TGN-derived membrane that wraps around it. Experiments with brefeldin A suggest that tegument may bind to the cytosolic tails of viral glycoproteins. Fusion and fission convert the TGN-derived wrapping sacs into an inner enveloped virion and an outer transport vesicle that carries newly enveloped virions to cytoplasmic vacuoles. These vacuoles are acidic and were identified as prelysosomes. It is postulated that secreted virions are partially degraded by their exposure to the prelysosomal internal milieu and rendered noninfectious. This process explains the cell-associated nature of VZV in vitro; however, the mechanism by which the virus escapes diversion from the secretory pathway to the lysosomal pathway in vivo remains to be determined.  相似文献   
109.
湘北烟区烟青虫发生情况研究   总被引:2,自引:0,他引:2  
刘见平  汪明达 《昆虫知识》1994,31(3):153-155
烟青虫在湘北烟区1年发生5代,第一至四代危害烟草,第五代在其他作物上取食。自然条件下,世代重叠比较明显,幼虫发生与危害最大的是第一代,危害时期是5月下旬至6月下旬,同时,还得出了烟青虫各代的发生期、历期及其发育起点温度和有效积温。  相似文献   
110.
野生大豆种子蛋白含量差异的生理及结构基础的探讨   总被引:1,自引:0,他引:1  
利用SDS-聚丙烯酰胺凝胶电泳、电子显微镜、蛋白及酰脲含量测定等技术,对高蛋白含量(50.7% )的50359 和低蛋白含量(40.8% )的50305 两个野生大豆在种子发育过程中贮藏蛋白积累的速率、蛋白组分合成的起始时间、蛋白体发育的进程以及幼茎的酰脲含量进行了比较研究。结果表明:野生大豆50359的高蛋白含量是与其种子发育过程中较高的植株酰脲含量、较早较快的贮藏蛋白合成及积累速率,液泡中高效的蛋白贮藏方式以及蛋白体在子叶细胞中占有较大体积相联系的  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