全文获取类型
收费全文 | 1058篇 |
免费 | 41篇 |
国内免费 | 4篇 |
专业分类
化学 | 842篇 |
晶体学 | 11篇 |
力学 | 10篇 |
数学 | 67篇 |
物理学 | 173篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 13篇 |
2020年 | 22篇 |
2019年 | 24篇 |
2018年 | 21篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 32篇 |
2014年 | 25篇 |
2013年 | 51篇 |
2012年 | 66篇 |
2011年 | 83篇 |
2010年 | 38篇 |
2009年 | 40篇 |
2008年 | 83篇 |
2007年 | 70篇 |
2006年 | 73篇 |
2005年 | 47篇 |
2004年 | 48篇 |
2003年 | 49篇 |
2002年 | 42篇 |
2001年 | 24篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1972年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有1103条查询结果,搜索用时 31 毫秒
871.
872.
Formal [4+2] Reaction between 1,3‐Diynes and Pyrroles: Gold(I)‐Catalyzed Indole Synthesis by Double Hydroarylation 下载免费PDF全文
Yuka Matsuda Saori Naoe Dr. Shinya Oishi Prof. Dr. Nobutaka Fujii Prof. Dr. Hiroaki Ohno 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1463-1467
Indole synthesis by a gold(I)‐catalyzed intermolecular formal [4+2] reaction between 1,3‐diynes and pyrroles has been developed. This reaction involves the hydroarylation of 1,3‐diynes with pyrroles followed by an intramolecular hydroarylation to give the 4,7‐disubstituted indoles. This reaction can also be applied to the synthesis of carbazoles when indoles are used as the nucleophiles instead of pyrroles. 相似文献
873.
874.
Prof. Dr. Itaru Nakamura Arinobu Hirayama Dr. Shinya Gima Prof. Dr. Masahiro Terada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):15816-15820
The Au-catalyzed reactions of O-homopropaylic oximes afforded the 3-alkenylated isoxazolines in good to high yields. The mechanistic studies suggest that the reaction proceeds through an exo-cyclization followed by intermolecular methylene group transfer. In addition, oligomeric species of the starting material were observed in the reaction mixture by mass spectra, supporting our proposed mechanism, which proceeds through a repeated intermolecular C−C bond forming process. 相似文献
875.
876.
Fast verified computation for solutions of algebraic Riccati equations arising in transport theory 下载免费PDF全文
A fast algorithm for enclosing the solution of the nonsymmetric algebraic Riccati equation arising in transport theory is proposed. The equation has a special structure, which is taken into account to reduce the complexity. By exploiting the structure, the enclosing process involves only quadratic complexity under a reasonable assumption. The algorithm moreover verifies the uniqueness and minimal positiveness of the enclosed solution. Numerical results show the efficiency of the algorithm. 相似文献
877.
Selective Aerobic Oxidation of Primary Alcohols to Aldehydes over Nb2O5 Photocatalyst with Visible Light 下载免费PDF全文
Dr. Shinya Furukawa Prof. Dr. Tetsuya Shishido Dr. Kentaro Teramura Prof. Dr. Tsunehiro Tanaka 《Chemphyschem》2014,15(13):2665-2667
Primary alcohols are selectively converted into aldehydes by using a Nb2O5 photocatalyst under visible‐light irradiation. A strong interaction between the alcohol and Nb2O5 generates a donor level within the forbidden band of Nb2O5, which provides a visible‐light‐harvesting ability. Over oxidation of aldehydes into carboxylic acids does not proceed under visible‐light irradiation. 相似文献
878.
Shinya Kitagawa Hiroki Buno Koichi Sakabe Hiroyuki Nakagawa Hajime Ohtani 《Journal of separation science》2014,37(21):3181-3187
Significant peak width reductions, or peak height enhancements, of angiotensins were observed when a high voltage was applied to hydrophilic interaction pressurized capillary electrochromatography using gradient elution with mobile phases containing perchloric acid. The investigation using a contactless conductivity detector revealed that perchloric acid was adsorbed on the surface of the stationary phase, when the acetonitrile content in the mobile phase was high, and released from the stationary phase by increasing the water content during a gradient procedure. The released perchloric acid formed a highly concentrated zone moving from the column inlet to the outlet. The electrochromatographic behavior of the analytes, primarily electrophoretic migration, was changed in this zone. As a consequence of the significant variation in migration velocity of the analytes, the sample band width was reduced similar fashion to on‐capillary concentration in capillary electrophoresis. Using this result, the reduction of band width and enhancement in separation efficiency was demonstrated in reversed‐phase pressurized electrochromatography, in which the conductivity of the mobile phase was significantly altered using a step gradient. The resolution between benzoic acid and 1‐naphthalene sulfonic acid was successfully improved from 2.7 to 4.3 by using the band width reduction method based on field‐amplified stacking. 相似文献
879.
Yasushi Shigeri Shinya Ikeda Akikazu Yasuda Masanori Ando Hiroaki Sato Tomoya Kinumi 《Journal of mass spectrometry : JMS》2014,49(8):742-749
The reagents 19 hydrazide and 14 hydrazine were examined to function as reactive matrices for matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) to detect gaseous aldehydes. Among them, two hydrazide (2‐hydroxybenzohydrazide and 3‐hydroxy‐2‐naphthoic acid hydrazide) and two hydrazine reagents [2‐hydrazinoquinoline and 2,4‐dinitrophenylhydrazine (DNPH)] were found to react efficiently with carbonyl groups of gaseous aldehydes (formaldehyde, acetaldehyde and propionaldehyde); these are the main factors for sick building syndrome and operate as reactive matrices for MALDI‐MS. Results from accurate mass measurements by JMS‐S3000 Spiral‐TOF suggested that protonated ion peaks corresponding to [M + H]+ from the resulting derivatives were observed in all cases with the gaseous aldehydes in an incubation, time‐dependent manner. The two hydrazide and two hydrazine reagents all possessed absorbances at 337 nm (wavelength of MALDI nitrogen laser), with, significant electrical conductivity of the matrix crystal and functional groups, such as hydroxy group and amino group, being important for desorption/ionization efficiency in MALDI‐MS. To our knowledge, this is the first report that gaseous molecules could be derivatized and detected directly in a single step by MALDI‐MS using novel reactive matrices that were derivatizing agents with the ability to enhance desorption/ionization efficiency. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
880.
Binding of Scandium Ions to Metalloporphyrin–Flavin Complexes for Long‐Lived Charge Separation 下载免费PDF全文
Prof. Dr. Takahiko Kojima Ryosuke Kobayashi Dr. Tomoya Ishizuka Shinya Yamakawa Dr. Hiroaki Kotani Dr. Tatsuaki Nakanishi Dr. Kei Ohkubo Dr. Yoshihito Shiota Prof. Dr. Kazunari Yoshizawa Prof. Dr. Shunichi Fukuzumi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15518-15532
A porphyrin–flavin‐linked dyad and its zinc and palladium complexes (MPor?Fl: 2 ?M, M=2 H, Zn, and Pd) were newly synthesized and the X‐ray crystal structure of 2 ?Pd was determined. The photodynamics of 2 ?M were examined by femto‐ and nanosecond laser flash photolysis measurements. Photoinduced electron transfer (ET) in 2 ?H2 occurred from the singlet excited state of the porphyrin moiety (H2Por) to the flavin (Fl) moiety to produce the singlet charge‐separated (CS) state 1(H2Por.+?Fl.?), which decayed through back ET (BET) to form 3[H2Por]*?Fl with rate constants of 1.2×1010 and 1.2×109 s?1, respectively. Similarly, photoinduced ET in 2 ?Pd afforded the singlet CS state, which decayed through BET to form 3[PdPor]*?Fl with rate constants of 2.1×1011 and 6.0×1010 s?1, respectively. The rate constant of photoinduced ET and BET of 2 ?M were related to the ET and BET driving forces by using the Marcus theory of ET. One and two Sc3+ ions bind to the flavin moiety to form the Fl?Sc3+ and Fl?(Sc3+)2 complexes with binding constants of K1=2.2×105 M ?1 and K2=1.8×103 M ?1, respectively. Other metal ions, such as Y3+, Zn2+, and Mg2+, form only 1:1 complexes with flavin. In contrast to 2 ?M and the 1:1 complexes with metal ions, which afforded the short‐lived singlet CS state, photoinduced ET in 2 ?Pd???Sc3+ complexes afforded the triplet CS state (3[PdPor.+?Fl.??(Sc3+)2]), which exhibited a remarkably long lifetime of τ=110 ms (kBET=9.1 s?1). 相似文献