全文获取类型
收费全文 | 9960篇 |
免费 | 752篇 |
国内免费 | 886篇 |
专业分类
11598篇 |
出版年
2024年 | 11篇 |
2023年 | 134篇 |
2022年 | 334篇 |
2021年 | 518篇 |
2020年 | 350篇 |
2019年 | 426篇 |
2018年 | 393篇 |
2017年 | 304篇 |
2016年 | 463篇 |
2015年 | 608篇 |
2014年 | 764篇 |
2013年 | 801篇 |
2012年 | 930篇 |
2011年 | 912篇 |
2010年 | 533篇 |
2009年 | 480篇 |
2008年 | 525篇 |
2007年 | 507篇 |
2006年 | 425篇 |
2005年 | 337篇 |
2004年 | 253篇 |
2003年 | 289篇 |
2002年 | 205篇 |
2001年 | 165篇 |
2000年 | 147篇 |
1999年 | 151篇 |
1998年 | 90篇 |
1997年 | 73篇 |
1996年 | 90篇 |
1995年 | 66篇 |
1994年 | 44篇 |
1993年 | 33篇 |
1992年 | 54篇 |
1991年 | 40篇 |
1990年 | 26篇 |
1989年 | 33篇 |
1988年 | 13篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Yan J Wang Q Zheng X Sun H Zhou Y Li D Lin Y Wang X 《Biochemical and biophysical research communications》2012,417(2):842-846
Sensitization of cancer cells to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by luteolin has been suggested by in vitro studies. However, no in vivo experiment has been reported to validate the potentiation effect of luteolin on TRAIL's anticancer activity. In this report, we first confirmed that luteolin potentiates TRAIL-induced cytotoxicity in A549 cells and HeLa cells in association with increased activation of apoptosis. Then we performed an in vivo experiment with a non-small cell lung cancer xenograft mouse model, which showed for the first time that the in vivo anticancer activity of TRAIL was greatly enhanced by luteolin. Compared with that in untreated control or treatment with TRAIL or luteolin alone, inhibition of tumor growth and apoptotic cell death in xenograft tumors were significantly increased in animals receiving combination treatment with TRAIL and luteolin. Data from this study thus provide strong in vivo evidence supporting that luteolin is a potential sensitizer for TRAIL in anticancer therapy. 相似文献
102.
通过逆转录-聚合酶链反应从我国河南省2例重叠感染HCV或HBV/HDV的献血啼中,分离到HBVNS5区的部分cDNA,对其进行序列分析比较,结果表明,河南株HGVNS5工核苷酸与两中国HGV主同源性高于国外代表株(88.5-90.6%),但由核苷酸推导的氨基酸的同源性都无明显的地区性区别。HGVNS5区氨基酸序列较保守,缺乏明显高变区,中国4株HGV在7384位发生了由C→T的变异,从而导致一个人 相似文献
103.
104.
根癌农杆菌介导Bt基因转化水稻的研究 总被引:2,自引:0,他引:2
为了培育出无筛选标记基因的转基因水稻,试验将loxp-hpt-loxp基因与成基因连锁在-起转化水稻方法,得到loxp-hpt—loxp—Bt转基因水稻植株,再与同质的带有ere基因的水稻杂交,以定向删除潮霉素抗性筛选标记。试验表明以水稻品种“皖粳97”为供试材料,将成熟胚来源的愈伤组织用根癌农杆菌EHA105/pCAMBIA1305.1感染后,筛选出抗性愈伤组织并获得再生植株。经PCR验证,得到20棵转基因水稻植株。 相似文献
105.
中国仓鼠卵巢细胞(CHO-K1)经N-甲基-N'-硝基-N-亚硝基胍(MNNG)诱变和6-巯基鸟嘌呤(6-TG)选择,得到稳定的次黄嘌呤磷酸核糖转移酶(HPRT)缺陷细胞株,酶活性仅为野生型的6.5%。用磷酸钙共沉淀法和电脉冲法向HPRT-细胞转移人宫颈癌细胞(HeLaS_3)基因组DNA,纠正了CHO细胞的HPRT缺陷。酶活性提高了6.9倍,达到野生型的45%。用Alu序列探针进行分子杂交,证实经过基因转移并连续传代15次以上的受体细胞中含人DNA序列。表明人的有关基因已稳定地整合到CHO细胞的染色体中。 相似文献
106.
Detection of the synergetic effects between variants, such as single-nucleotide polymorphisms (SNPs), is crucial for understanding the genetic characters of complex diseases. Here, we proposed a two-step approach to detect differentially inherited SNP modules (synergetic SNP units) from a SNP network. First, SNP-SNP interactions are identified based on prior biological knowledge, such as their adjacency on the chromosome or degree of relatedness between the functional relationships of their genes. These interactions form SNP networks. Second, disease-risk SNP modules (or sub-networks) are prioritised by their differentially inherited properties in IBD (Identity by Descent) profiles of affected and unaffected sibpairs. The search process is driven by the disease information and follows the structure of a SNP network. Simulation studies have indicated that this approach achieves high accuracy and a low false-positive rate in the identification of known disease-susceptible SNPs. Applying this method to an alcoholism dataset, we found that flexible patterns of susceptible SNP combinations do play a role in complex diseases, and some known genes were detected through these risk SNP modules. One example is GRM7, a known alcoholism gene successfully detected by a SNP module comprised of two SNPs, but neither of the two SNPs was significantly associated with the disease in single-locus analysis. These identified genes are also enriched in some pathways associated with alcoholism, including the calcium signalling pathway, axon guidance and neuroactive ligand-receptor interaction. The integration of network biology and genetic analysis provides putative functional bridges between genetic variants and candidate genes or pathways, thereby providing new insight into the aetiology of complex diseases. 相似文献
107.
本文对棕黑锦蛇(Elaphe schrenckii)进行分类学等研究,棕黑锦蛇被认为包含两个亚种:指名亚种(Elaphe s.schrenckii)和赤峰亚种(Elaphe s.anomala),但也有学者将后者提升为种,即赤峰锦蛇(Elaphe anomala).有关该种分类问题,仍需要进一步综合考虑形态学和分子系统学分类研究.作为我国东北和华北地区体形最大的蛇种,棕黑锦蛇具有重要的生态和经济价值,但目前对其生物学特性和生态学研究极为有限,人工驯养繁育技术不成熟,过度利用导致野外种群遭到严重破坏.建议加强棕黑锦蛇生态学和人工繁育技术的研究,为有效保护和可持续利用提供科学依据. 相似文献
108.
丙型肝炎病毒RNA打点杂交检测方法同RT-PCR方法的比较 总被引:1,自引:0,他引:1
采用HCV基因组结构区C区cDNA探针和非结构区NS3-4区cDNA探针,建立了用打点杂交(dotblothybridization)检测血清中HCVRNA的方法,同采用HCV基因组5’端非编码区的一对寡核苷酸引物通过逆转录-聚合酶链式反应(RT-PCR)检测血清中HCVRNA的方法相比较,发现两种方法都能快速早期和特异地检出血清中HCVRNA,但RT-PCR法敏感性优于RNA打点杂交法。对于无血清学指标的慢性NANB肝炎病人的诊断,可采用这两种方法。这两种方法的敏感性在很大程度上依赖于引物和探针的敏感性,以及RNA提取方法。RT-PCR法适用于诊断病毒血症和复制,打点杂交法适用于研究HCVRNA量的变化,对治疗的评价,以及为实验筛选较高滴度的HCVRNA阳性样本。 相似文献
109.
比哈小爪螨实验种群生命表的研究 总被引:2,自引:0,他引:2
本文研究了比哈小爪螨5个温度梯度的实验种群生命表.结果表明15 ℃时内禀增长率和周限增长率均最小,分别为0.0235和1.0238,种群倍增时间最长(29.47 d);35 ℃时内禀增长率和周限增长率均最大,分别为0.3069和0.3592,种群倍增时间最短(2.26 d),说明高温有利于该螨种群的增长.25 ℃时净增殖率最大(56.30).35 ℃的世代生长周期最短(11.97 d).15 ℃时其寿命最长(98.90±20.77 d),35 ℃时寿命最短(19.00±3.11 d).最高平均产卵量71.60粒/雌和最高日平均产卵量4.10粒/雌/天均在25 ℃时出现.15 ℃时平均产卵量最低(8.80粒/雌),日平均产卵量仅有0.34粒/雌/天.最大日产卵量出现在35 ℃时(12.00粒/雌/天). 相似文献
110.
Atomic force microscopy (AFM), transmission electron microscopy (TEM), and confocal laser scanning microscopy were used to investigate the effects of a 50 Hz 0.4 mT magnetic field (MF) on the clustering of purified epidermal growth factor receptors (EGFRs) and EGFRs in Chinese hamster lung (CHL) cell membrane. The results demonstrate that exposing purified EGFRs to the MF for 30 min induces receptor clustering. The peak height of apparent clusters increased from 1.42 +/- 0.18 (sham-exposed) to 3.08 +/- 0.38 nm (exposed) while the mean half-width increased from 21.7 +/- 2.2 to 33.0 +/- 4.0 nm. A similar effect was also observed by TEM. Treatment of purified EGFR with PD153035 (PD), an EGFR-specific tyrosine kinase (TK) inhibitor, inhibited the MF-induced EGFR clustering of the purified proteins, an effect also observed for the receptors in cell membrane in the absence of EGF. These results strongly suggest that the 50 Hz 0.4 mT MF interferes with the EGFR signaling pathway, most likely by interacting with the cytoplasmic TK domain. 相似文献