全文获取类型
收费全文 | 9397篇 |
免费 | 1678篇 |
国内免费 | 2258篇 |
专业分类
化学 | 6728篇 |
晶体学 | 295篇 |
力学 | 520篇 |
综合类 | 345篇 |
数学 | 1412篇 |
物理学 | 4033篇 |
出版年
2024年 | 15篇 |
2023年 | 115篇 |
2022年 | 271篇 |
2021年 | 325篇 |
2020年 | 347篇 |
2019年 | 344篇 |
2018年 | 322篇 |
2017年 | 394篇 |
2016年 | 361篇 |
2015年 | 450篇 |
2014年 | 564篇 |
2013年 | 706篇 |
2012年 | 788篇 |
2011年 | 795篇 |
2010年 | 695篇 |
2009年 | 675篇 |
2008年 | 805篇 |
2007年 | 729篇 |
2006年 | 693篇 |
2005年 | 596篇 |
2004年 | 527篇 |
2003年 | 345篇 |
2002年 | 406篇 |
2001年 | 375篇 |
2000年 | 377篇 |
1999年 | 216篇 |
1998年 | 122篇 |
1997年 | 92篇 |
1996年 | 73篇 |
1995年 | 94篇 |
1994年 | 104篇 |
1993年 | 89篇 |
1992年 | 75篇 |
1991年 | 65篇 |
1990年 | 73篇 |
1989年 | 37篇 |
1988年 | 40篇 |
1987年 | 27篇 |
1986年 | 32篇 |
1985年 | 24篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
A rigid-triangle velocity field for combined backward-forward extrusion based on the experiments and the slip-line field is proposed in this paper. The flow separation point in the rigid-triangle velocity field is defined in accordance with the slip-line theory. A formula of minimum upper bound solution for the punch pressure of the combined extrusion is derived. The values from this formula are compared with those from the slip-line solution and with experimental results. The formula of upper bound solution can be used in practice. 相似文献
992.
Rhodium‐Catalyzed Enantioselective Intramolecular CH Silylation for the Syntheses of Planar‐Chiral Metallocene Siloles
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Qing‐Wei Zhang Kun An Li‐Chuan Liu Yuan Yue Prof. Dr. Wei He 《Angewandte Chemie (International ed. in English)》2015,54(23):6918-6921
Reported herein is the rhodium‐catalyzed enantioselective C? H bond silylation of the cyclopentadiene rings in Fe and Ru metallocenes. Thus, in the presence of (S)‐TMS‐Segphos, the reactions took place under very mild conditions to afford metallocene‐fused siloles in good to excellent yields and with ee values of up to 97 %. During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric C? H silylations. 相似文献
993.
Jaehun Lee Byung-il Choi Seo Young Park Su Yeon An Jiyou Han Jong-Hoon Kim 《Experimental & molecular medicine》2015,47(7):e174
The milk fat globule-EGF-factor 8 protein (MFG-E8) has been identified in various tissues, where it has an important role in intercellular interactions, cellular migration, and neovascularization. Previous studies showed that MFG-E8 is expressed in different cell types under normal and pathophysiological conditions, but its expression in hematopoietic stem cells (HSCs) during hematopoiesis has not been reported. In the present study, we investigated MFG-E8 expression in multiple hematopoietic tissues at different stages of mouse embryogenesis. Using immunohistochemistry, we showed that MFG-E8 was specifically expressed in CD34+ HSCs at all hematopoietic sites, including the yolk sac, aorta-gonad-mesonephros region, placenta and fetal liver, during embryogenesis. Fluorescence-activated cell sorting and polymerase chain reaction analyses demonstrated that CD34+ cells, purified from the fetal liver, expressed additional HSC markers, c-Kit and Sca-1, and that these CD34+ cells, but not CD34− cells, highly expressed MFG-E8. We also found that MFG-E8 was not expressed in HSCs in adult mouse bone marrow, and that its expression was confined to F4/80+ macrophages. Together, this study demonstrates, for the first time, that MFG-8 is expressed in fetal HSC populations, and that MFG-E8 may have a role in embryonic hematopoiesis. 相似文献
994.
Real‐Time Monitoring of Cancer Cell Metabolism and Effects of an Anticancer Agent using 2D In‐Cell NMR Spectroscopy
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. He Wen Yong Jin An Wen Jun Xu Prof. Keon Wook Kang Prof. Sunghyouk Park 《Angewandte Chemie (International ed. in English)》2015,54(18):5374-5377
Altered metabolism is a critical part of cancer cell properties, but real‐time monitoring of metabolomic profiles has been hampered by the lack of a facile method. Here, we propose real‐time metabolomic monitoring of live cancer cells using 13C6‐glucose and heteronuclear two‐dimensional (2D) NMR. The method allowed for metabolomic differentiation between cancer and normal cells on the basis of time‐dependent changes in metabolite concentrations. Cancer cells were found to have large in‐ and out‐flux of pyruvate as well as increased net production of alanine and acetate. The method also enabled evaluation of the metabolic effects of galloflavin whose anticancer effects have been attributed to its specific inhibition of lactate dehydrogenase. Our approach revealed previously unknown functional targets of galloflavin, which were further confirmed at the protein levels. Our method is readily applicable to the study of metabolic alterations in other cellular disease model systems. 相似文献
995.
Visible‐Light‐Promoted Iminyl‐Radical Formation from Acyl Oximes: A Unified Approach to Pyridines,Quinolines, and Phenanthridines
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Heng Jiang Xiaode An Kun Tong Tianyi Zheng Prof. Dr. Yan Zhang Prof. Dr. Shouyun Yu 《Angewandte Chemie (International ed. in English)》2015,54(13):4055-4059
A unified strategy involving visible‐light‐induced iminyl‐radical formation has been established for the construction of pyridines, quinolines, and phenanthridines from acyl oximes. With fac‐[Ir(ppy)3] as a photoredox catalyst, the acyl oximes were converted by 1 e? reduction into iminyl radical intermediates, which then underwent intramolecular homolytic aromatic substitution (HAS) to give the N‐containing arenes. These reactions proceeded with a broad range of substrates at room temperature in high yield. This strategy of visible‐light‐induced iminyl‐radical formation was successfully applied to a five‐step concise synthesis of benzo[c]phenanthridine alkaloids. 相似文献
996.
Synthesis of 2D/2D Structured Mesoporous Co3O4 Nanosheet/N‐Doped Reduced Graphene Oxide Composites as a Highly Stable Negative Electrode for Lithium Battery Applications
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Palanichamy Sennu Hyo Sang Kim Jae Youn An Dr. Vanchiappan Aravindan Prof. Yun‐Sung Lee 《化学:亚洲杂志》2015,10(8):1776-1783
Mesoporous Co3O4 nanosheets (Co3O4‐NS) and nitrogen‐doped reduced graphene oxide (N‐rGO) are synthesized by a facile hydrothermal approach, and the N‐rGO/Co3O4‐NS composite is formulated through an infiltration procedure. Eventually, the obtained composites are subjected to various characterization techniques, such as XRD, Raman spectroscopy, surface area analysis, X‐ray photoelectron spectroscopy (XPS), and TEM. The lithium‐storage properties of N‐rGO/Co3O4‐NS composites are evaluated in a half‐cell assembly to ascertain their suitability as a negative electrode for lithium‐ion battery applications. The 2D/2D nanostructured mesoporous N‐rGO/Co3O4‐NS composite delivered a reversible capacity of about 1305 and 1501 mAh g?1 at a current density of 80 mA g?1 for the 1st and 50th cycles, respectively. Furthermore, excellent cyclability, rate capability, and capacity retention characteristics are noted for the N‐rGO/Co3O4‐NS composite. This improved performance is mainly related to the existence of mesoporosity and a sheet‐like 2D hierarchical morphology, which translates into extra space for lithium storage and a reduced electron pathway. Also, the presence of N‐rGO and carbon shells in Co3O4‐NS should not be excluded from such exceptional performance, which serves as a reliable conductive channel for electrons and act as synergistically to accommodate volume expansion upon redox reactions. Ex‐situ TEM, impedance spectroscopy, and XPS, are also conducted to corroborate the significance of the 2D morphology towards sustained lithium storage. 相似文献
997.
Core–Shell Carbon‐Coated CuO Nanocomposites: A Highly Stable Electrode Material for Supercapacitors and Lithium‐Ion Batteries
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Tao Wen Dr. Xi‐Lin Wu Dr. Shouwei Zhang Prof. Xiangke Wang Prof. An‐Wu Xu 《化学:亚洲杂志》2015,10(3):595-601
Herein we present a simple method for fabricating core–shell mesostructured CuO@C nanocomposites by utilizing humic acid (HA) as a biomass carbon source. The electrochemical performances of CuO@C nanocomposites were evaluated as an electrode material for supercapacitors and lithium‐ion batteries. CuO@C exhibits an excellent capacitance of 207.2 F g?1 at a current density of 1 A g?1 within a potential window of 0–0.46 V in 6 M KOH solution. Significantly, CuO electrode materials achieve remarkable capacitance retentions of approximately 205.8 F g?1 after 1000 cycles of charge/discharge testing. The CuO@C was further applied as an anode material for lithium‐ion batteries, and a high initial capacity of 1143.7 mA h g?1 was achieved at a current density of 0.1 C. This work provides a facile and general approach to synthesize carbon‐based materials for application in large‐scale energy‐storage systems. 相似文献
998.
Proteasome inhibitors have revolutionized the treatment of multiple myeloma, and validated the therapeutic potential of the ubiquitin proteasome system (UPS). It is believed that in part, proteasome inhibitors elicit their therapeutic effect by inhibiting the degradation of misfolded proteins, which is proteotoxic and causes cell death. In spite of these successes, proteasome inhibitors are not effective against solid tumors, thus necessitating the need to explore alternative approaches. Furthermore, proteasome inhibitors lead to the formation of aggresomes that clear misfolded proteins via the autophagy–lysosome degradation pathway. Importantly, aggresome formation depends on the presence of polyubiquitin tags on misfolded proteins. We therefore hypothesized that inhibitors of ubiquitin conjugation should inhibit both degradation of misfolded proteins, and ubiquitin dependent aggresome formation, thus outlining the path forward toward more effective anticancer therapeutics. To explore the therapeutic potential of targeting the UPS to treat solid cancers, we have developed an inhibitor of ubiquitin conjugation (ABP A3) that targets ubiquitin and Nedd8 E1 enzymes, enzymes that are required to maintain the activity of the entire ubiquitin system. We have shown that ABP A3 inhibits conjugation of ubiquitin to intracellular proteins and prevents the formation of cytoprotective aggresomes in A549 lung cancer cells. Furthermore, ABP A3 induces activation of the unfolded protein response and apoptosis. Thus, similar to proteasome inhibitors MG132, bortezomib, and carfilzomib, ABP A3 can serve as a novel probe to explore the therapeutic potential of the UPS in solid and hematological malignancies. 相似文献
999.
1000.
Qingbao Song Xiaoxia An Fengfeng Che Tianhua Shen 《Journal of heterocyclic chemistry》2015,52(5):1496-1502
Di‐DACH‐pyridylamide ligands, symmetrical bridged bis‐Schiff base, and spiro pyrrolizines as catalysts in the synthesis of dihydropyrimidinethiones (DHPMs) using the Biginelli reaction is first reported. This new protocol has the advantages of environmental friendliness, short reaction time, excellent yields, and simple post‐treatment procedure. A series of DHPMs were obtained in high yields (up to 98%) in only 6 h. Moreover, based on the optimized condition, a novel Biginelli‐like reaction was first developed. 相似文献