全文获取类型
收费全文 | 6986篇 |
免费 | 422篇 |
出版年
2023年 | 53篇 |
2022年 | 94篇 |
2021年 | 176篇 |
2020年 | 114篇 |
2019年 | 134篇 |
2018年 | 198篇 |
2017年 | 143篇 |
2016年 | 226篇 |
2015年 | 375篇 |
2014年 | 349篇 |
2013年 | 525篇 |
2012年 | 574篇 |
2011年 | 545篇 |
2010年 | 346篇 |
2009年 | 324篇 |
2008年 | 391篇 |
2007年 | 385篇 |
2006年 | 389篇 |
2005年 | 362篇 |
2004年 | 326篇 |
2003年 | 286篇 |
2002年 | 287篇 |
2001年 | 47篇 |
2000年 | 33篇 |
1999年 | 47篇 |
1998年 | 60篇 |
1997年 | 65篇 |
1996年 | 33篇 |
1995年 | 51篇 |
1994年 | 42篇 |
1993年 | 34篇 |
1992年 | 25篇 |
1991年 | 34篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 31篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1974年 | 9篇 |
1965年 | 8篇 |
排序方式: 共有7408条查询结果,搜索用时 15 毫秒
941.
942.
Opposite enantiomers of a chiral fragrance may exhibit different olfactory activities making a synthesis in high enantiomeric purity commercially and scientifically interesting. Accordingly, the asymmetric synthesis of four chiral odorants, Fixolide, Phenoxanol, Citralis, and Citralis Nitrile, has been investigated with the aim to develop practically feasible processes. In the devised synthetic schemes, the key step that leads to the formation of the stereogenic center is the homogeneous asymmetric hydrogenation of a prochiral olefin. By an appropriate choice of the catalyst and the reaction conditions, Phenoxanol, Citralis, and Citralis Nitrile were obtained in high enantiomeric purity, and odor profiles of the single enantiomers were determined. 相似文献
943.
Protein phosphorylation plays a central role in many signal transduction pathways that mediate biological processes. Novel quantitative mass spectrometry-based methods have recently revealed phosphorylation dynamics in animals, yeast, and plants. These methods are important for our understanding of how differential phosphorylation participates in translating distinct signals into proper physiological responses, and shifted research towards screening for potential cancer therapies and in-depth analysis of phosphoproteomes. In this review, we aim to describe current progress in quantitative phosphoproteomics. This emerging field has changed numerous static pathways into dynamic signaling networks, and revealed protein kinase networks that underlie adaptation to environmental stimuli. Mass spectrometry enables high-throughput and high-quality analysis of differential phosphorylation at a site-specific level. Although determination of differential phosphorylation between treatments is analogous to detecting differential gene expression, the large body of statistical techniques that has been developed for analysis of differential gene expression is not generally applied for detecting differential phosphorylation. We suggest possible improvements for analysis of quantitative phosphorylation by increasing the number of biological replicates and adapting statistical tests used for gene expression profiling and widely implemented in freely available software tools. 相似文献
944.
The present paper will present a survey on features of a number of non-specialized off-the-shelf JPEG2000 viewers, seen from the point of view of digital microscopy. Selected viewers were tested within a number of usage scenarios, including: i) open a conformance test JPEG2000 file; ii) open a large JPEG2000 file; iii) moving from one point to another; iv) changing resolution/magnification. For each scenario, data recorded included: successful or unsuccessful operation; time needed for conclusion; occasional problems.Preliminary results demonstrate that JPEG2000 conformance as stated by many viewers is only limited to some of the possibilities of the JPEG2000 standard, in particular for what regards file size. 相似文献
945.
946.
947.
948.
949.
950.
Ruvolo VR Kurinna SM Karanjeet KB Schuster TF Martelli AM McCubrey JA Ruvolo PP 《The Journal of biological chemistry》2008,283(51):35474-35485
Protein phosphatase 2A (PP2A) is a heterotrimer comprising catalytic, scaffold, and regulatory (B) subunits. There are at least 21 B subunit family members. Thus PP2A is actually a family of enzymes defined by which B subunit is used. The B56 family member B56alpha is a phosphoprotein that regulates dephosphorylation of BCL2. The stress kinase PKR has been shown to phosphorylate B56alpha at serine 28 in vitro, but it has been unclear how PKR might regulate the BCL2 phosphatase. In the present study, PKR regulation of B56alpha in REH cells was examined, because these cells exhibit robust BCL2 phosphatase activity. PKR was found to be basally active in REH cells as would be predicted if the kinase supports B56alpha-mediated dephosphorylation of BCL2. Suppression of PKR promoted BCL2 phosphorylation with concomitant loss of B56alpha phosphorylation at serine 28 and inhibition of mitochondrial PP2A activity. PKR supports stress signaling in REH cells, as suppression of PKR promoted chemoresistance to etoposide. Suppression of PKR promoted B56alpha proteolysis, which could be blocked by a proteasome inhibitor. However, the mechanism by which PKR supports B56alpha protein does not involve PKR-mediated phosphorylation of the B subunit at serine 28 but may involve eIF2alpha activation of AKT. Phosphorylation of serine 28 by PKR promotes mitochondrial localization of B56alpha, because wild-type but not mutant S28A B56alpha promoted mitochondrial PP2A activity. Cells expressing wild-type B56alpha but not S28A B56alpha were sensitized to etoposide. These results suggest that PKR regulates B56alpha-mediated PP2A signaling in REH cells. 相似文献