全文获取类型
收费全文 | 7811篇 |
免费 | 808篇 |
国内免费 | 529篇 |
专业分类
化学 | 5525篇 |
晶体学 | 96篇 |
力学 | 407篇 |
综合类 | 46篇 |
数学 | 691篇 |
物理学 | 2383篇 |
出版年
2024年 | 8篇 |
2023年 | 109篇 |
2022年 | 173篇 |
2021年 | 284篇 |
2020年 | 271篇 |
2019年 | 265篇 |
2018年 | 192篇 |
2017年 | 208篇 |
2016年 | 307篇 |
2015年 | 279篇 |
2014年 | 360篇 |
2013年 | 552篇 |
2012年 | 698篇 |
2011年 | 696篇 |
2010年 | 493篇 |
2009年 | 432篇 |
2008年 | 544篇 |
2007年 | 459篇 |
2006年 | 433篇 |
2005年 | 371篇 |
2004年 | 319篇 |
2003年 | 263篇 |
2002年 | 262篇 |
2001年 | 166篇 |
2000年 | 126篇 |
1999年 | 123篇 |
1998年 | 107篇 |
1997年 | 84篇 |
1996年 | 85篇 |
1995年 | 74篇 |
1994年 | 48篇 |
1993年 | 55篇 |
1992年 | 50篇 |
1991年 | 53篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1973年 | 4篇 |
1971年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有9148条查询结果,搜索用时 15 毫秒
951.
Lee PH Mo J Kang D Eom D Park C Lee CH Jung YM Hwang H 《The Journal of organic chemistry》2011,76(1):312-315
Pd-catalyzed cross-coupling reactions of aryl iodides containing not only an electron-donating group but also an electron-withdrawing group on the aryl ring with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield. 相似文献
952.
953.
Biliverdin reductase A (BLVRA), an enzyme that converts biliverdin to bilirubin, has recently emerged as a key regulator of the cellular redox cycle. However, the role of BLVRA in the aging process remains unclear. To study the role of BLVRA in the aging process, we compared the stress responses of young and senescent human diploid fibroblasts (HDFs) to the reactive oxygen species (ROS) inducer, hydrogen peroxide (H2O2). H2O2 markedly induced BLVRA activity in young HDFs, but not in senescent HDFs. Additionally, depletion of BLVRA reduced the H2O2-dependent induction of heme oxygenase-1 (HO-1) in young HDFs, but not in senescent cells, suggesting an aging-dependent differential modulation of responses to oxidative stress. The role of BLVRA in the regulation of cellular senescence was confirmed when lentiviral RNAi- transfected stable primary HDFs with reduced BLVRA expression showed upregulation of the CDK inhibitor family members p16, p53, and p21, followed by cell cycle arrest in G0-G1 phase with high expression of senescence-associated β-galactosidase. Taken together, these data support the notion that BLVRA contributes significantly to modulation of the aging process by adjusting the cellular oxidative status. 相似文献
954.
Ningning Zhao Kang Wang Wenjun Li Yongzhong Bian Changyan Sun Zhidong Chang Hongxia Fan 《Solid State Sciences》2011,13(11):1948-1953
A series of transition metal coordination polymers [Co(H3L)2(4,4′- bpy)(H2O)2]n?n(4,4′-bpy) (1), [Ni(H2L)(4,4′-bpy)(H2O)2]n (2), [Co2(L)(phen)2(H2O)4]n?(H2O)2n (3), and [Ni2(L)(phen)2(H2O)4]n?(H2O)2n (4) have been assembled from a semirigid multicarboxylate ligand 3,3′-(1,4-phenylenebis(oxy))diphthalic acid (H4L) with the help of 4,4′-bipyridine (4,4′-bpy) ligand or 1,10-phenanthroline (phen) ligand. X-ray single crystal diffraction analysis reveals that complex 1 crystallizes in the space group of P − 1 and displays a one-dimensional (1D) chain structure constructed from 4,4′-bpy ligand and H3L ligand, which was further interlinked to form a three-dimensional network via hydrogen bonds. In complex 2, Ni(II) atoms are coordinated by L ligand in monodentate fashion to form alternate left- and right-helices, which are further bridged together by the coordination interactions between Ni(II) atoms and 4,4′-bpy, leading to a 2-fold (4, 4)-connected interpenetrating network. Isostructural complexes 3 and 4 belong to the space group P − 1 and display a 1D chain structure constructed from phen and L ligands, which was further interlinked to form a 2D plane via π–π interactions. In addition, their thermal and luminescent properties were also investigated. 相似文献
955.
Lee B Kang SH Kang D Lee KH Cho J Nam W Han OH Hur NH 《Chemical communications (Cambridge, England)》2011,47(40):11219-11221
A solid hydrazine was isolated as a crystalline powder by reacting aqueous hydrazine with supercritical CO(2). Its structure determined by single crystal X-ray diffraction shows a zwitterionic form of NH(3)(+)NHCO(2)(-). The solid hydrazine is remarkably stable but is as reactive as liquid hydrazine even in the absence of solvents. 相似文献
956.
Catalytic membrane reactors which carry out separation and reaction in a single unit are expected to be a promising approach to achieve green and sustainable chemistry with less energy consumption and lower pollution. This article presents a review of the recent progress of dense ceramic catalytic membranes and membrane reactors, and their potential applications in energy and environmental areas. A basic knowledge of catalytic membranes and membrane reactors is first introduced briefly, followed by a short discussion on the membrane materials including their structures, composition and strategies for material development. The configuration of catalytic membranes, the design of membrane reaction processes and the high temperature sealing are also discussed. The performance of catalytic membrane reactors for energy and environmental applications are summarized and typical catalytic membrane reaction processes are presented and discussed. Finally, current challenges and difficulties related to the industrialization of dense ceramic membrane reactors are addressed and possible future research is also outlined. 相似文献
957.
In a free solution of 10.0 mM Gly-Gly (pH 8.2), the flow directions of native-DNA and DNA molecules intercalated with the fluorescent dye YOYO-1 were reversed in the microchip channel. These results clearly showed that in a confined space and under specific environmental conditions, the fluorescent dye modified the original properties and behavior of the native-DNA molecule. 相似文献
958.
Lee SK Cho JM Goo Y Shin WS Lee JC Lee WH Kang IN Shim HK Moon SJ 《Chemical communications (Cambridge, England)》2011,47(6):1791-1793
A highly processable, new semiconducting polymer, PCDTTz, based on alternating thiazolothiazole and carbazole units was synthesized. The new polymer exhibited a field-effect carrier mobility of up to 3.8 × 10(-3) cm(2) V(-1) s(-1) and bulk heterojunction solar cells made from PCDTTz produced a power conversion efficiency of 4.88% under AM 1.5 G (100 mW cm(-2)) conditions. 相似文献
959.
Murale DP Lee KM Kim K Churchill DG 《Chemical communications (Cambridge, England)》2011,47(46):12512-12514
A novel fluorescent difluoroboroazaoxobenzazulene dye has been synthesized from commercially available substrates in "one pot"; it was characterized structurally and spectroscopically, derivatized and finally compared to a related BODIPY system that demonstrates "turn-on" H(+) (42-fold) and F(-) (~5-fold) responses. 相似文献
960.
Graphite nanofibers (GNFs), on which surface graphite edges were reconstructed into nano-loops, were explored as a cathode catalyst support for fuel cells. The high degree of graphitization, as well as the surface-reconstructed nano-loops that possess topological defects for uniform metal deposition, resulted in an improved performance of the GNF-supported Pt catalyst. 相似文献