全文获取类型
收费全文 | 1708篇 |
免费 | 69篇 |
国内免费 | 12篇 |
专业分类
化学 | 1417篇 |
晶体学 | 23篇 |
力学 | 21篇 |
数学 | 121篇 |
物理学 | 207篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 25篇 |
2019年 | 34篇 |
2018年 | 24篇 |
2017年 | 17篇 |
2016年 | 47篇 |
2015年 | 30篇 |
2014年 | 46篇 |
2013年 | 123篇 |
2012年 | 101篇 |
2011年 | 116篇 |
2010年 | 79篇 |
2009年 | 59篇 |
2008年 | 109篇 |
2007年 | 102篇 |
2006年 | 96篇 |
2005年 | 91篇 |
2004年 | 84篇 |
2003年 | 78篇 |
2002年 | 63篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 23篇 |
1998年 | 16篇 |
1997年 | 25篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 21篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1970年 | 7篇 |
1969年 | 10篇 |
1968年 | 6篇 |
排序方式: 共有1789条查询结果,搜索用时 46 毫秒
71.
72.
Yusuke Yoshimura Ryuichiro Hibi Akiho Nakata Moeka Togashi Shoujiro Ogawa Takayuki Ishige Mamoru Satoh Fumio Nomura Tatsuya Higashi 《Biomedical chromatography : BMC》2019,33(7)
A liquid chromatography/electrospray ionization–tandem mass spectrometry‐based method was developed for the identification of the conjugation positions of the monoglucuronides of 25‐hydroxyvitamin D3 [25(OH)D3] and 24,25‐dihydroxyvitamin D3 [24,25(OH)2D3] in human urine. The method employed derivatization with 4‐(4‐dimethylaminophenyl)‐1,2,4‐triazoline‐3,5‐dione to convert the glucuronides into fragmentable derivatives, which provided useful product ions for identifying the conjugation positions during the MS/MS. The derivatization also enhanced the assay sensitivity and specificity for urine sample analysis. The positional isomeric monoglucuronides, 25(OH)D3‐3‐ and ‐25‐glucuronides, or 24,25(OH)2D3‐3‐, ‐24‐ and ‐25‐glucuronides, were completely separated from each other under the optimized LC conditions. Using this method, the conjugation positions were successfully determined to be the C3 and C24 positions for the glucuronidated 25(OH)D3 and 24,25(OH)2D3, respectively. The 3‐glucuronide was not present for 24,25(OH)2D3, unlike 25(OH)D3, thus we found that selective glucuronidation occurs at the C24‐hydroxy group for 24,25(OH)2D3. 相似文献
73.
74.
For a spatial characteristic, there exist commonly fat-tail frequency distributions of fragment-size and -mass of glass, areas enclosed by city roads, and pore size/volume in random packings. In order to give a new analytical approach for the distributions, we consider a simple model which constructs a fractal-like hierarchical network based on random divisions of rectangles. The stochastic process makes a Markov chain and corresponds to directional random walks with splitting into four particles. We derive a combinatorial analytical form and its continuous approximation for the distribution of rectangle areas, and numerically show a good fitting with the actual distribution in the averaging behavior of the divisions. 相似文献
75.
Prof. Tomoaki Tanase Miho Tanaka Mami Hamada Yuka Morita Dr. Kanako Nakamae Prof. Yasuyuki Ura Prof. Takayuki Nakajima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(35):8219-8224
A new linear tetraphosphine containing a PNP phosphazane bridge, rac-bis[(diphenylphosphinomethyl)phenylphosphino]phenylamine (rac-dpmppan), was synthesized and utilized to support a series of Pd/Pt mixed metal tetranuclear chains, [Pd4−nPtn(μ-rac-dpmppan)2(XylNC)2](PF6)2 (XylNC=xylyl isocyanide; n=0: Pd4 ( 1 ), 1: PtPd3 ( 2 ), 2: PtPd2Pt ( 3 ), 2: Pt2Pd2 ( 4 ), 3: Pt2PdPt ( 5 )), in which the number and positions of additional Pt atoms were successfully controlled depending on the respective synthetic procedures using transformations from 1 to 3 through 2 and from 4 to 5 by redox-coupled exchange reactions. The 31P{1H} NMR and ESI mass spectra and X-ray diffraction analyses revealed almost identical tetranuclear structures, with slight contraction of metal-metal bonds according to incorporation of Pt atoms. The electronic absorption spectra of 1 – 5 exhibited characteristic bands at 635–510 nm with an energy propensity depending on the number and positions of Pt centres, which were assigned to HOMO (dσ*σσ*) to LUMO (dσ*σ*σ*) transition by theoretical calculations. The present results demonstrated that the electronic structures of Pd/Pt mixed-metal tetranuclear complexes are finely tuned as orbital-overlapping alloyed metal chains by atomically precise Pt incorporation in the Pd4 chain. 相似文献
76.
Kengo Shamoto Atsushi Miyazaki Mika Matsukura Yuki Kobayashi Takayuki Shioiri 《合成通讯》2013,43(10):1425-1431
A nonenzymatic kinetic resolution of (±)-trans-2-arylcyclohexanols was carried out by esterification using polymer-supported N,N′-dicyclohexylcarbodiimide (DCC), dimethylaminopyridine (DMAP), and 3β-acetoxyetienic acid. The efficiency of the kinetic resolution was comparable to the enzymatic method when arylcyclohexanols bearing a condensed-aromatic ring were used. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communication® to view the free supplemental file. 相似文献
77.
Prof. Dr. Yasuchika Hasegawa Takafumi Matsui Dr. Yuichi Kitagawa Dr. Takayuki Nakanishi Dr. Tomohiro Seki Prof. Dr. Hajime Ito Prof. Dr. Yuta Nakasaka Prof. Dr. Takao Masuda Prof. Dr. Koji Fushimi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(53):12308-12315
Oxygen-sensitive and near-infrared (NIR) luminescent YbIII coordination polymers incorporating ligands based on pyrene derivatives were synthesized: YbIII–TBAPy and YbIII–TIAPy (TBAPy: 1,3,6,8-tetrakis(p-benzoate)pyrene; TIAPy: 1,3,6,8-tetrakis(3,5-isophthalic acid)pyrene). The coordination structures of these materials have been characterized by means of electrospray ionization mass spectrometry, X-ray diffraction analysis, and thermogravimetric analysis. Moreover, the porous structure of YbIII–TIAPy has been evaluated by measuring its N2 adsorption isotherm. The NIR luminescence properties of YbIII–TBAPy and YbIII–TIAPy have been examined by acquiring emission spectra and determining emission lifetimes under air or argon and in vacuo. YbIII–TIAPy exhibited high thermal stability (with a decomposition temperature of 400 °C), intense luminescence (with an emission quantum yield under argon of 6.6 %), and effective oxygen-sensing characteristics. These results suggest that NIR luminescent YbIII coordination polymers prepared using pyrene derivatives could have applications in novel thermo-stable oxygen sensors. 相似文献
78.
Prof. Dr. Tomoaki Tanase Dr. Kanako Nakamae Yume Okawa Mami Hamada Dr. Arimasa Matsumoto Prof. Dr. Takayuki Nakajima Prof. Dr. Takuya Nakashima Prof. Dr. Tsuyoshi Kawai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(8):e202104060
A P-stereogenic linear tetraphosphine tetraoxide, (R,R)- or (S,S)-dpmppm(=O)4, was synthesized to prepare C2 dinuclear M(hfa)3 complexes (M=Eu, Tb, Y) as the first example of lanthanide(III) complexes with P-chiral multidentate phosphine oxides. The mononuclear M(hfa)3 complexes (M=Eu, Y) with a P-chiral diphosphine dioxide, tpdpb(=O)2, were also prepared, and comparison of their photophysical properties for the EuIII complexes revealed that significant chiral induction from the P-chiral centers arises on the achiral M(hfa)3 units through intramolecular π-π stacking constraint in the dinuclear system. 相似文献
79.
Kisuke Tabata Naoya Jinno Keiichi Noda Masahiko Hashimoto Kazuhiko Tsukagoshi 《Chromatographia》2012,75(7-8):423-428
Tube radical distribution chromatography (TRDC) uses an untreated open tubular capillary tube and a ternary mixture of solvents (water and hydrophilic/hydrophobic organic solvents) as a carrier solution. A model analyte mixture comprising 1-naphthol, 1-naphthoic acid, 1-naphthalenesulfonic acid, 2,6-naphthalenedisulfonic acid, and 1,3,6-naphthalenetrisulfonic acid was examined by the TRDC and capillary zone electrophoresis (CZE) systems that comprised mainly a capillary tube and a detector. In the TRDC system the elution order of analytes could be changed by altering the component ratios of the solvents, whereas in the CZE system the elution order was changed by altering the electroosmotic flow direction. The experimental data obtained provide clues about the features and utility of TRDC as a new separation method. 相似文献
80.