全文获取类型
收费全文 | 95650篇 |
免费 | 10861篇 |
国内免费 | 33589篇 |
出版年
2024年 | 350篇 |
2023年 | 2086篇 |
2022年 | 3500篇 |
2021年 | 5088篇 |
2020年 | 4512篇 |
2019年 | 5176篇 |
2018年 | 4059篇 |
2017年 | 3528篇 |
2016年 | 4128篇 |
2015年 | 5876篇 |
2014年 | 7599篇 |
2013年 | 7309篇 |
2012年 | 9671篇 |
2011年 | 9314篇 |
2010年 | 7003篇 |
2009年 | 6925篇 |
2008年 | 7630篇 |
2007年 | 7182篇 |
2006年 | 6605篇 |
2005年 | 5646篇 |
2004年 | 4642篇 |
2003年 | 4016篇 |
2002年 | 3442篇 |
2001年 | 2932篇 |
2000年 | 2695篇 |
1999年 | 1911篇 |
1998年 | 1110篇 |
1997年 | 824篇 |
1996年 | 699篇 |
1995年 | 562篇 |
1994年 | 487篇 |
1993年 | 386篇 |
1992年 | 425篇 |
1991年 | 359篇 |
1990年 | 304篇 |
1989年 | 267篇 |
1988年 | 239篇 |
1987年 | 205篇 |
1986年 | 191篇 |
1985年 | 175篇 |
1984年 | 110篇 |
1983年 | 128篇 |
1982年 | 145篇 |
1981年 | 80篇 |
1980年 | 29篇 |
1979年 | 42篇 |
1978年 | 41篇 |
1977年 | 30篇 |
1957年 | 32篇 |
1950年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
51.
52.
After observing specimens of Calligonum pumilum Losinsk. and C. juochiangense Y. X. Liou in both the field and in herbarium collections, it was found that the morphological characters of these two species are quite different, especially with respect of the twisted direction of fruit ribs, number of bristle rows along each rib, rigidity and degree of interweaving of bristles, as well as their geographic distribution. Therefore, it is concluded that C. pumilum and C. juochiangense should be accepted as two independent species. 相似文献
53.
54.
55.
56.
57.
目的对virB2基因编码蛋白进行分析,为virB2基因及其编码蛋白功能提供实验依据。方法利用多种生物学软件以及网站对VirB2蛋白的结构和功能进行分析预测,VirB2蛋白序列通过基因推导获得并由生物公司合成,然后通过免疫动物实验制备鼠抗VirB2蛋白多克隆抗体,同时设计进行VirB2蛋白细胞毒试验(MTT法)。结果virB2基因编码蛋白属于疏水性蛋白,为鞭毛样结构,有较强的细胞毒作用。结论对VirB2蛋白的结构和功能进行了分析预测,证明VirB2蛋白在H.pylori相关的致病性特别是引起胃黏膜炎症方面起到一定的作用,能够为研究H.pylori致病机制提供帮助。 相似文献
58.
Xin Deng Guoli Zhang Ling Zhang Yan Feng Zehong Li GuangMou Wu Yuhuan Yue Gensong Li Yu Cao Ping Zhu 《PloS one》2015,10(11)
Non-viral gene delivery system with many advantages has a great potential for the future of gene therapy. One inherent obstacle of such approach is the uptake by endocytosis into vesicular compartments. Receptor-mediated gene delivery method holds promise to overcome this obstacle. In this study, we developed a receptor-mediated gene delivery system based on a combination of the Pseudomonas exotoxin A (PE), which has a receptor binding and membrane translocation domain, and the hyperthermophilic archaeal histone (HPhA), which has the DNA binding ability. First, we constructed and expressed the rPE-HPhA fusion protein. We then examined the cytotoxicity and the DNA binding ability of rPE-HPhA. We further assessed the efficiency of transfection of the pEGF-C1 plasmid DNA to CHO cells by the rPE-HPhA system, in comparison to the cationic liposome method. The results showed that the transfection efficiency of rPE-HPhA was higher than that of cationic liposomes. In addition, the rPE-HPhA gene delivery system is non-specific to DNA sequence, topology or targeted cell type. Thus, the rPE-HPhA system can be used for delivering genes of interest into mammalian cells and has great potential to be applied for gene therapy. 相似文献
59.
Mutations in the conserved C-terminal sequence in thyroid hormone receptor dissociate hormone-dependent activation from interference with AP-1 activity. 总被引:4,自引:2,他引:2 下载免费PDF全文
60.
A Positive GATA Element and a Negative Vitamin D Receptor-Like Element Control Atrial Chamber-Specific Expression of a Slow Myosin Heavy-Chain Gene during Cardiac Morphogenesis 总被引:1,自引:0,他引:1 下载免费PDF全文
Gang Feng Wang William Nikovits Jr. Mark Schleinitz Frank E. Stockdale 《Molecular and cellular biology》1998,18(10):6023-6034
We have used the slow myosin heavy chain (MyHC) 3 gene to study the molecular mechanisms that control atrial chamber-specific gene expression. Initially, slow MyHC 3 is uniformly expressed throughout the tubular heart of the quail embryo. As cardiac development proceeds, an anterior-posterior gradient of slow MyHC 3 expression develops, culminating in atrial chamber-restricted expression of this gene following chamberization. Two cis elements within the slow MyHC 3 gene promoter, a GATA-binding motif and a vitamin D receptor (VDR)-like binding motif, control chamber-specific expression. The GATA element of the slow MyHC 3 is sufficient for expression of a heterologous reporter gene in both atrial and ventricular cardiomyocytes, and expression of GATA-4, but not Nkx2-5 or myocyte enhancer factor 2C, activates reporter gene expression in fibroblasts. Equivalent levels of GATA-binding activity were found in extracts of atrial and ventricular cardiomyocytes from embryonic chamberized hearts. These observations suggest that GATA factors positively regulate slow MyHC 3 gene expression throughout the tubular heart and subsequently in the atria. In contrast, an inhibitory activity, operating through the VDR-like element, increased in ventricular cardiomyocytes during the transition of the heart from a tubular to a chambered structure. Overexpression of the VDR, acting via the VDR-like element, duplicates the inhibitory activity in ventricular but not in atrial cardiomyocytes. These data suggest that atrial chamber-specific expression of the slow MyHC 3 gene is achieved through the VDR-like inhibitory element in ventricular cardiomyocytes at the time distinct atrial and ventricular chambers form. 相似文献