全文获取类型
收费全文 | 22295篇 |
免费 | 2827篇 |
国内免费 | 2197篇 |
专业分类
化学 | 16488篇 |
晶体学 | 322篇 |
力学 | 1068篇 |
综合类 | 187篇 |
数学 | 2175篇 |
物理学 | 7079篇 |
出版年
2024年 | 40篇 |
2023年 | 290篇 |
2022年 | 591篇 |
2021年 | 637篇 |
2020年 | 695篇 |
2019年 | 695篇 |
2018年 | 569篇 |
2017年 | 555篇 |
2016年 | 938篇 |
2015年 | 912篇 |
2014年 | 1088篇 |
2013年 | 1547篇 |
2012年 | 1922篇 |
2011年 | 1978篇 |
2010年 | 1356篇 |
2009年 | 1201篇 |
2008年 | 1424篇 |
2007年 | 1247篇 |
2006年 | 1240篇 |
2005年 | 1170篇 |
2004年 | 921篇 |
2003年 | 811篇 |
2002年 | 863篇 |
2001年 | 579篇 |
2000年 | 532篇 |
1999年 | 473篇 |
1998年 | 357篇 |
1997年 | 310篇 |
1996年 | 309篇 |
1995年 | 295篇 |
1994年 | 242篇 |
1993年 | 222篇 |
1992年 | 203篇 |
1991年 | 171篇 |
1990年 | 159篇 |
1989年 | 125篇 |
1988年 | 100篇 |
1987年 | 74篇 |
1986年 | 77篇 |
1985年 | 82篇 |
1984年 | 45篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 30篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1977年 | 12篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1968年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
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
992.
He-Jin Lee Eun-Duk Cho Kyung Won Lee Jung-Hyun Kim Ssang-Goo Cho Seung-Jae Lee 《Experimental & molecular medicine》2013,45(5):e22
The accumulation of abnormal protein aggregates is a major characteristic of many neurodegenerative disorders, including Parkinson''s disease (PD). The intracytoplasmic deposition of α-synuclein aggregates and Lewy bodies, often found in PD and other α-synucleinopathies, is thought to be linked to inefficient cellular clearance mechanisms, such as the proteasome and autophagy/lysosome pathways. The accumulation of α-synuclein aggregates in neuronal cytoplasm causes numerous autonomous changes in neurons. However, it can also affect the neighboring cells through transcellular transmission of the aggregates. Indeed, a progressive spreading of Lewy pathology among brain regions has been hypothesized from autopsy studies. We tested whether inhibition of the autophagy/lysosome pathway in α-synuclein-expressing cells would increase the secretion of α-synuclein, subsequently affecting the α-synuclein deposition in and viability of neighboring cells. Our results demonstrated that autophagic inhibition, via both pharmacological and genetic methods, led to increased exocytosis of α-synuclein. In a mixed culture of α-synuclein-expressing donor cells with recipient cells, autophagic inhibition resulted in elevated transcellular α-synuclein transmission. This increase in protein transmission coincided with elevated apoptotic cell death in the recipient cells. These results suggest that the inefficient clearance of α-synuclein aggregates, which can be caused by reduced autophagic activity, leads to elevated α-synuclein exocytosis, thereby promoting α-synuclein deposition and cell death in neighboring neurons. This finding provides a potential link between autophagic dysfunction and the progressive spread of Lewy pathology. 相似文献
993.
A nontoxic heat-sensitive gel containing 1.5 % (w/v) agar and 25 % (w/v) bovine serum albumin (BSA) was fabricated in this study. Optical density measurements with 808 nm near-infrared (NIR) laser indicated that, in spite of its BSA content, the current agar + BSA gel remained similar to agar only gel in terms of its optical response to NIR laser. The thermal response of the current agar + BSA gel to high temperatures was quantified using magnetic resonance imaging (MRI). According to the MRI measurements of T2 relaxation rate as a function of heating temperature, the current agar + BSA gel showed a linear response to heating temperatures between 65 and 80 °C, while it remained thermally stable at temperatures up to 80 °C. Therefore, the current agar + BSA gel can be used as thermal dosimeters or volumetric heat-sensitive gel phantoms in typical thermal therapy regime. 相似文献
994.
A photoelectrochemical reactor constructed as a proton exchange membrane fuel cell was utilized to electrochemically enhance the photocatalytic decomposition of gas-phase isopropanol. Nafion membrane was employed to serve as solid electrolyte to establish an electrochemical circuit for the gaseous photocatalytic reaction. The electrical current density of photoanode was found to correspond to the variation of the applied bias and relative humidity of the inlet gas. Photocatalytic decomposition rate was remarkably increased by 20 % by applying a bias potential of 5 V. The effect of relative humidity exhibited multiple effects for membrane conductivity of Nafion and efficiency of photocatalytic decomposition reaction. 相似文献
995.
996.
997.
Yan Li Dr. Kazuki Fukushima Dr. Daniel J. Coady Dr. Amanda C. Engler Dr. Shaoqiong Liu Yuan Huang Dr. John S. Cho Dr. Yi Guo Dr. Lloyd S. Miller Dr. Jeremy P. K. Tan Dr. Pui Lai Rachel Ee Dr. Weimin Fan Prof. Yi Yan Yang Dr. James L. Hedrick 《Angewandte Chemie (International ed. in English)》2013,52(2):674-678
998.
999.
Based on quantum chemistry calculations combined with the Marcus–Hush electron transfer theory, we investigated the charge‐transport properties of oligothiophenes (nTs) and oligopyrroles (nPs) (n=6, 7, 8) as potential p‐ or n‐type organic semiconductor materials. The results of our calculations indicate that 1) the nPs show intrinsic hole mobilities as high as or even higher than those of nTs, and 2) the vertical ionization potentials (VIPs) of the nPs are about 0.6–0.7 eV smaller than the corresponding VIPs of the nTs. Based on their charge‐transport ability and hole‐injection efficiency, the nPs have potential as p‐type organic semiconducting materials. Furthermore, it was also found that the maximum values of the electron‐transfer mobility for the nTs are larger by one‐to‐two orders of magnitude than the corresponding maximum values of hole‐transfer mobility, which suggests that the nTs have the potential to be developed as promising n‐type organic semiconducting materials owing to their electron mobility. 相似文献
1000.
Hierarchical flower-like architectures of[Ni3(BTC)2·12H2O](BTC3=benzene-1,3,5-tricarboxylate) were successfully prepared by a simple solution-phase method under mild conditions without any template or surfactant.Phase-pure porous NiO nanocrystals were obtained by annealing the Ni-BTC complex without significant alteration in morphology.The product was characterized by X-ray diffraction techniques,field-emission scanning electron microscopy(FESEM).transmission electron microscopy(TEM) and high-resolution TEM(HRTEM).The catalytic effect of the NiO product was investigated on the thermal decomposition of ammonium perchlorate(AP) and it was found that the annealed NiO product has higher catalytic activity than the commercial NiO. 相似文献