全文获取类型
收费全文 | 25086篇 |
免费 | 15507篇 |
国内免费 | 3篇 |
出版年
2023年 | 12篇 |
2022年 | 85篇 |
2021年 | 387篇 |
2020年 | 2182篇 |
2019年 | 3712篇 |
2018年 | 3814篇 |
2017年 | 4092篇 |
2016年 | 4075篇 |
2015年 | 3977篇 |
2014年 | 3613篇 |
2013年 | 4032篇 |
2012年 | 1692篇 |
2011年 | 1414篇 |
2010年 | 2991篇 |
2009年 | 1751篇 |
2008年 | 623篇 |
2007年 | 224篇 |
2006年 | 217篇 |
2005年 | 265篇 |
2004年 | 249篇 |
2003年 | 237篇 |
2002年 | 231篇 |
2001年 | 244篇 |
2000年 | 183篇 |
1999年 | 128篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1980年 | 2篇 |
1975年 | 2篇 |
1972年 | 4篇 |
1959年 | 4篇 |
1958年 | 10篇 |
1957年 | 7篇 |
1956年 | 11篇 |
1955年 | 12篇 |
1954年 | 4篇 |
1953年 | 9篇 |
1952年 | 2篇 |
1951年 | 10篇 |
1950年 | 5篇 |
1949年 | 3篇 |
1948年 | 2篇 |
1873年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
151.
The adsorption of chiral Gly‐Pro dipeptide on Cu(110) has been characterized by combining in situ polarization modulation infrared reflection absorption spectroscopy (PM‐RAIRS) and X‐ray photoelectron spectroscopy (XPS). The chemical state of the dipeptide, and its anchoring points and adsorption geometry, were determined at various coverage values. Gly‐Pro molecules are present on Cu(110) in their anionic form (NH2/COO−) and adsorb under a 3‐point binding via both oxygen atoms of the carboxylate group and via the nitrogen atom of the amine group. Low‐energy electron diffraction (LEED) and scanning tunneling microscopy (STM) have shown the presence of an extended 2D chiral array, sustained via intermolecular H‐bonds interactions. Furthermore, due to the particular shape of the molecule, only one homochiral domain is formed, creating thus a truly chiral surface. Chirality 27:411–416, 2015. © 2015 Wiley Periodicals, Inc. 相似文献
152.
In vitro improvement of quail primordial germ cell expansion through activation of TGF‐beta signaling pathway 下载免费PDF全文
153.
154.
155.
Tai‐An Chiang Yu‐Lin Yang Ya‐Ying Yang Min‐Hsiu Hu Pei‐Fen Wu Shu‐Fen Liu Ruay‐Ming Huang Tung‐Nan Liao Chien‐Ya Hung Tsung‐Jen Hung Tao‐Chen Lee 《Journal of cellular biochemistry》2010,109(4):663-671
Hyperosmolarity plays an essential role in the pathogenesis of diabetic tubular fibrosis. However, the mechanism of the involvement of hyperosmolarity remains unclear. In this study, mannitol was used to evaluate the effects of hyperosmolarity on a renal distal tubule cell line (MDCK). We investigated transforming growth factor‐β receptors and their downstream fibrogenic signal proteins. We show that hyperosmolarity significantly enhances the susceptibility to exogenous transforming growth factor (TGF)‐β1, as mannitol (27.5 mM) significantly enhanced the TGF‐β1‐induced increase in fibronectin levels compared with control experiments (5.5 mM). Specifically, hyperosmolarity induced tyrosine phosphorylation on TGF‐β RII at 336 residues in a time (0–24 h) and dose (5.5–38.5 mM) dependent manner. In addition, hyperosmolarity increased the level of TGF‐β RI in a dose‐ and time‐course dependent manner. These observations may be closely related to decreased catabolism of TGF‐β RI. Hyperosmolarity significantly downregulated the expression of an inhibitory Smad (Smad7), decreased the level of Smurf 1, and reduced ubiquitination of TGF‐β RI. In addition, through the use of cycloheximide and the proteasome inhibitor MG132, we showed that hyperosmolarity significantly increased the half‐life and inhibited the protein level of TGF‐β RI by polyubiquitination and proteasomal degradation. Taken together, our data suggest that hyperosmolarity enhances cellular susceptibility to renal tubular fibrosis by activating the Smad7 pathway and increasing the stability of type I TGF‐β receptors by retarding proteasomal degradation of TGF‐β RI. This study clarifies the mechanism underlying hyperosmotic‐induced renal fibrosis in renal distal tubule cells. J. Cell. Biochem. 109: 663–671, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
156.
Chick embryos grown in ex ovo culture by the modified Cornish pasty method reported in Nagai, Lin and Sheng in this issue. 相似文献
157.
Sam Mugume Colin A. Chapman Gilbert Isabirye‐Basuta Emily Otali 《African Journal of Ecology》2015,53(4):465-472
Tropical forests contain much of the world's biodiversity, yet their rate of decline is increasing. The strategy most frequently used to protect this biodiversity is to make parks and reserves. While there is a great deal of research on the effectiveness of parks for protecting biodiversity, there is little research on how well extractive reserves conserve biodiversity. Here, we evaluate the effectiveness of four forest reserves in western Uganda at maintaining populations of primates and compare census data from the reserves to data from the neighbouring well‐protected Kibale National Park. The relative abundance of the five most common primates in the park was approximately four times that of the forest reserves. In the forest reserves, evidence of new human encroachment was seen every 500 m, while in the park it was seen every 100,000 m. Two recommendations emerge from our research: (i) for forest reserves, such as those studied here, to have conservation value for primates, extraction must be reduced and (ii) until the long‐term viability of the populations in forest reserves can be ascertained, they should not be considered in estimates of the sizes of endangered species protected ranges. 相似文献
158.
159.