全文获取类型
收费全文 | 21743篇 |
免费 | 2570篇 |
国内免费 | 2066篇 |
专业分类
化学 | 15678篇 |
晶体学 | 274篇 |
力学 | 988篇 |
综合类 | 137篇 |
数学 | 2434篇 |
物理学 | 6868篇 |
出版年
2024年 | 39篇 |
2023年 | 343篇 |
2022年 | 512篇 |
2021年 | 636篇 |
2020年 | 781篇 |
2019年 | 811篇 |
2018年 | 606篇 |
2017年 | 630篇 |
2016年 | 864篇 |
2015年 | 911篇 |
2014年 | 1039篇 |
2013年 | 1460篇 |
2012年 | 1694篇 |
2011年 | 1899篇 |
2010年 | 1268篇 |
2009年 | 1228篇 |
2008年 | 1416篇 |
2007年 | 1244篇 |
2006年 | 1111篇 |
2005年 | 953篇 |
2004年 | 826篇 |
2003年 | 733篇 |
2002年 | 722篇 |
2001年 | 557篇 |
2000年 | 465篇 |
1999年 | 357篇 |
1998年 | 270篇 |
1997年 | 250篇 |
1996年 | 290篇 |
1995年 | 239篇 |
1994年 | 255篇 |
1993年 | 207篇 |
1992年 | 174篇 |
1991年 | 148篇 |
1990年 | 159篇 |
1989年 | 133篇 |
1988年 | 120篇 |
1987年 | 88篇 |
1986年 | 96篇 |
1985年 | 134篇 |
1984年 | 88篇 |
1983年 | 83篇 |
1982年 | 59篇 |
1981年 | 56篇 |
1980年 | 51篇 |
1979年 | 36篇 |
1977年 | 40篇 |
1976年 | 37篇 |
1974年 | 48篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
961.
Da-Jeong Chang Seung-Hun Oh Nayeon Lee Chunggab Choi Iksoo Jeon Hyun Sook Kim Dong Ah Shin Seo Eun Lee Daehong Kim Jihwan Song 《Experimental & molecular medicine》2013,45(11):e53
The transplantation of neural precursor cells (NPCs) is known to be a promising approach to ameliorating behavioral deficits after stroke in a rodent model of middle cerebral artery occlusion (MCAo). Previous studies have shown that transplanted NPCs migrate toward the infarct region, survive and differentiate into mature neurons to some extent. However, the spatiotemporal dynamics of NPC migration following transplantation into stroke animals have yet to be elucidated. In this study, we investigated the fates of human embryonic stem cell (hESC)-derived NPCs (ENStem-A) for 8 weeks following transplantation into the side contralateral to the infarct region using 7.0T animal magnetic resonance imaging (MRI). T2- and T2*-weighted MRI analyses indicated that the migrating cells were clearly detectable at the infarct boundary zone by 1 week, and the intensity of the MRI signals robustly increased within 4 weeks after transplantation. Afterwards, the signals were slightly increased or unchanged. At 8 weeks, we performed Prussian blue staining and immunohistochemical staining using human-specific markers, and found that high percentages of transplanted cells migrated to the infarct boundary. Most of these cells were CXCR4-positive. We also observed that the migrating cells expressed markers for various stages of neural differentiation, including Nestin, Tuj1, NeuN, TH, DARPP-32 and SV38, indicating that the transplanted cells may partially contribute to the reconstruction of the damaged neural tissues after stroke. Interestingly, we found that the extent of gliosis (glial fibrillary acidic protein-positive cells) and apoptosis (TUNEL-positive cells) were significantly decreased in the cell-transplanted group, suggesting that hESC-NPCs have a positive role in reducing glia scar formation and cell death after stroke. No tumors formed in our study. We also performed various behavioral tests, including rotarod, stepping and modified neurological severity score tests, and found that the transplanted animals exhibited significant improvements in sensorimotor functions during the 8 weeks after transplantation. Taken together, these results strongly suggest that hESC-NPCs have the capacity to migrate to the infarct region, form neural tissues efficiently and contribute to behavioral recovery in a rodent model of ischemic stroke. 相似文献
962.
963.
964.
Jin Sung Park Da-Young Chang Ji-Hoi Kim Jin Hwa Jung JoonSeong Park Se-Hyuk Kim Young-Don Lee Sung-Soo Kim Haeyoung Suh-Kim 《Experimental & molecular medicine》2013,45(2):e10
Human mesenchymal stem cells (MSCs) have emerged as attractive cellular vehicles
to deliver therapeutic genes for ex-vivo therapy of diverse diseases;
this is, in part, because they have the capability to migrate into tumor or
lesion sites. Previously, we showed that MSCs could be utilized to deliver a
bacterial cytosine deaminase (CD) suicide gene to brain tumors. Here we
assessed whether transduction with a retroviral vector encoding CD gene
altered the stem cell property of MSCs. MSCs were transduced at passage 1 and
cultivated up to passage 11. We found that proliferation and differentiation
potentials, chromosomal stability and surface antigenicity of MSCs were not
altered by retroviral transduction. The results indicate that retroviral vectors
can be safely utilized for delivery of suicide genes to MSCs for
ex-vivo therapy. We also found that a single retroviral
transduction was sufficient for sustainable expression up to passage 10. The
persistent expression of the transduced gene indicates that transduced MSCs
provide a tractable and manageable approach for potential use in allogeneic
transplantation. 相似文献
965.
966.
967.
968.
969.
Dr. Markus Lampimäki Dr. Veronika Zelenay Dr. Adéla Křepelová Dr. Zhi Liu Rui Chang Dr. Hendrik Bluhm Dr. Markus Ammann 《Chemphyschem》2013,14(11):2419-2425
Ozone adsorption and decomposition on metal oxides is of wide interest in technology and in atmospheric chemistry. Here, ozone‐adsorption‐induced band bending is observed on Ti‐ and Fe‐oxide model surfaces under dry and humid conditions. Photoelectron spectroscopic studies indicate the effect of charge transfer to O3, which limits the surface coverage of the precursor to decomposition reactions. This is also consistent with the negative pressure dependence observed in previous studies. These results contribute to our fundamental understanding of ozone adsorption and decomposition mechanisms on metal oxides of environmental and technological relevance. 相似文献
970.
合成和表征了一种钴(Ⅱ)配合物,[CoLCl]2[CoLCl0.5(H2O)0.5]2ClO4·10H2O (1)(LH=(2-(二((1H-苯并咪唑-2-基)甲基)氨基)乙酸))。以3,5-二叔丁基儿茶酚(3,5-DTBC)为反应底物,用紫外光谱测试了1的儿茶酚酶催化活性。研究结果表明:在配合物的晶体结构中,不对称单元的2个Co(Ⅱ)都形成变形的三角双锥构型。在pH=5~11范围内,配合物1对3,5-DTBC的氧化显示了pH值依赖性,它的儿茶酚酶催化活性随着温度的升高而升高,并且其催化氧化3,5-DTBC的动力学符合米氏方程模型。 相似文献