全文获取类型
收费全文 | 635篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 572篇 |
晶体学 | 7篇 |
力学 | 1篇 |
数学 | 16篇 |
物理学 | 63篇 |
出版年
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 15篇 |
2013年 | 25篇 |
2012年 | 29篇 |
2011年 | 35篇 |
2010年 | 17篇 |
2009年 | 18篇 |
2008年 | 44篇 |
2007年 | 33篇 |
2006年 | 38篇 |
2005年 | 34篇 |
2004年 | 36篇 |
2003年 | 26篇 |
2002年 | 33篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1963年 | 2篇 |
排序方式: 共有659条查询结果,搜索用时 515 毫秒
31.
Akika Futamura Asuka Uemura Takeshi Imoto Dr. Yusuke Kitamura Dr. Hirotaka Matsuura Dr. Chun‐Xia Wang Toshiki Ichihashi Dr. Yusuke Sato Prof. Dr. Norio Teramae Prof. Dr. Seiichi Nishizawa Prof. Dr. Toshihiro Ihara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10526-10535
We propose a binary fluorimetric method for DNA and RNA analysis by the combined use of two probes rationally designed to work cooperatively. One probe is an oligonucleotide (ODN) conjugate bearing a β‐cyclodextrin (β‐CyD). The other probe is a small reporter ligand, which comprises linked molecules of a nucleobase‐specific heterocycle and an environment‐sensitive fluorophore. The heterocycle of the reporter ligand recognizes a single nucleobase displayed in a gap on the target labeled with the conjugate and, at the same time, the fluorophore moiety forms a luminous inclusion complex with nearby β‐CyD. Three reporter ligands, MNDS (naphthyridine–dansyl linked ligand), MNDB (naphthyridine–DBD), and DPDB (pyridine–DBD), were used for DNA and RNA probing with 3′‐end or 5′‐end modified β‐CyD – ODN conjugates. For the DNA target, the β‐CyD tethered to the 3′‐end of the ODN facing into the gap interacted with the fluorophore sticking out into the major groove of the gap site ( MNDS and DPDB ). Meanwhile the β‐CyD on the 5′‐end of the ODN interacted with the fluorophore in the minor groove ( MNDB and DPDB ). The results obtained by this study could be a guideline for the design of binary DNA/RNA probe systems based on controlling the proximity of functional molecules. 相似文献
32.
Dr. Kazukuni Tahara Yuki Yamamoto Dr. Dustin E. Gross Hiroyoshi Kozuma Yoko Arikuma Dr. Koji Ohta Dr. Yoshiko Koizumi Yuan Gao Dr. Yo Shimizu Prof. Shu Seki Dr. Kenji Kamada Prof. Jeffrey S. Moore Prof. Yoshito Tobe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11251-11260
We present herein the synthesis and properties of the largest hitherto unknown graphyne fragment, namely trigonally expanded tetrakis(dehydrobenzo[12]annulene)s (tetrakis‐DBAs). Intramolecular three‐fold alkyne metathesis reactions of hexakis(arylethynyl)DBAs 9 a and 9 b using Fürstner’s Mo catalyst furnished tetrakis‐DBAs 8 a and 8 b substituted with tert‐butyl or branched alkyl ester groups in moderate and fair yields, respectively, demonstrating that the metathesis reaction of this protocol is a powerful tool for the construction of graphyne fragment backbones. For comparison, hexakis(arylethynyl)DBAs 9 c – g have also been prepared. The one‐photon absorption spectrum of tetrakis‐DBA 8 a bearing tert‐butyl groups revealed a remarkable bathochromic shift of the absorption cut‐off (λcutoff) compared with those of previously reported graphyne fragments due to extended π‐conjugation. Moreover, in the two‐photon absorption spectrum, 8 a showed a large cross‐section for a pure hydrocarbon because of the planar para‐phenylene‐ethynylene conjugation pathways. Hexakis(arylethynyl)‐DBAs 9 c – e and 9 g and tetrakis‐DBA 8 b bearing electron‐withdrawing groups aggregated in chloroform solutions. Comparison between the free energies of 9 e and 8 b bearing the same substituents revealed the more favorable association of the latter due to stronger π–π interactions between the extended π‐cores. Polarized optical microscopy observations, DSC, and XRD measurements showed that 8 b and 9 e with branched alkyl ester groups displayed columnar rectangular mesophases. By the time‐resolved microwave conductivity method, the columnar rectangular phase of 8 b was shown to exhibit a moderate charge‐carrier mobility of 0.12 cm2 V?1 s?1. These results indicate that large graphyne fragments can serve as good organic semiconductors. 相似文献
33.
Toru Oba Yubi TatenoMisaki Ihara Takanori FukusumiNatsuki Takei Satoshi Ito 《Tetrahedron letters》2014
Radical reactions of a C3-vinylated chlorophyll derivative, methyl pyropheophorbide-a, which were induced by thiols and the conventional initiator azobisisobutyronitrile (AIBN) were examined in vitro for the first time. Thiyl radicals attacked regioselectively at the sole C3-vinyl group, and the anti-Markovnikov sulfanyl adducts were obtained as major products. The other peripheral substituents, as well as the chlorin macrocycle, remained intact. The AIBN-induced radical reaction competed with co-oxidation that afforded the C3-formyl chlorin. This method can open new routes to derivatization of vinyl chlorins. 相似文献
34.
Abul K. Mallik Hongdeng Qiu Makoto Takafuji Hirotaka Ihara 《Analytical and bioanalytical chemistry》2014,406(14):3507-3515
This work reports a new imidazolium and l-alanine derived copolymer-grafted silica stationary phase for ready separation of complex isomers using high-performance liquid chromatography (HPLC). For this purpose, 1-allyl-3-octadecylimidazolium bromide ([AyImC18]Br) and N-acryloyl-l-alanine sodium salt ([AAL]Na) ionic liquids (IL) monomers were synthesized. Subsequently, the bromide counteranion was exchanged with the 2-(acrylamido)propanoate organic counteranion by reacting the [AyImC18]Br with excess [AAL]Na in water. The obtained IL cation–anion monomer pair was then copolymerized on mercaptopropyl-modified silica (Sil-MPS) via a surface-initiated radical chain-transfer reaction. The selective retention behaviors of polycyclic aromatic hydrocarbons (PAHs), including some positional isomers, steroids, and nucleobases were investigated using the newly obtained Sil-poly(ImC18-AAL), and octadecyl silylated silica (ODS) was used as the reference column. Interesting results were obtained for the separation of PAHs, steroids, and nucleobases with the new organic phase. The results showed that the Sil-poly(ImC18-AAL) presented multiple noncovalent interactions, including hydrophobic, π–π, carbonyl–π, and ion–dipole interactions for the separation of PAHs and dipolar compounds. Only pure water was sufficient as the mobile phase for the separation of the nucleobases. Ten nucleosides and bases were separated, using only water as the mobile phase, within a very short time using the Sil-poly(ImC18-AAL), which is otherwise difficult to achieve using conventional hydrophobic columns such as ODS. The combination of electrostatic and hydrophobic interactions are important for the effective separation of such basic compounds without the use of any organic additive as the eluent on the Sil-poly(ImC18-AAL) column. Figure
Separation of pyrimidines including (5) 5-fluorouracil, (6) uracil, (7) 5-bromouracil, (8) thymine, (9) cytosine, and (10) 4,6-diaminopyrimidine on Sil-poly(ImC18-AAL). Mobile phase, pure water; column temperature, 40 °C; flow rate, 1.00 ml min–1 相似文献
35.
36.
Akira Nishimura Ryouga Shimada Yoshito Sakakibara Akira Koshio Eric Hu 《Molecules (Basel, Switzerland)》2021,26(10)
The aim of this study is to clarify the effect of doped metal type on CO2 reduction characteristics of TiO2 with NH3 and H2O. Cu and Pd have been selected as dopants for TiO2. In addition, the impact of molar ratio of CO2 to reductants NH3 and H2O has been investigated. A TiO2 photocatalyst was prepared by a sol-gel and dip-coating process, and then doped with Cu or Pd fine particles by using the pulse arc plasma gun method. The prepared Cu/TiO2 film and Pd/TiO2 film were characterized by SEM, EPMA, TEM, STEM, EDX, EDS and EELS. This study also has investigated the performance of CO2 reduction under the illumination condition of Xe lamp with or without ultraviolet (UV) light. As a result, it is revealed that the CO2 reduction performance with Cu/TiO2 under the illumination condition of Xe lamp with UV light is the highest when the molar ratio of CO2/NH3/H2O = 1:1:1 while that without UV light is the highest when the molar ratio of CO2/NH3/H2O = 1:0.5:0.5. It is revealed that the CO2 reduction performance of Pd/TiO2 is the highest for the molar ratio of CO2/NH3/H2O = 1:1:1 no matter the used Xe lamp was with or without UV light. The molar quantity of CO per unit weight of photocatalyst for Cu/TiO2 produced under the illumination condition of Xe lamp with UV light was 10.2 μmol/g, while that for Pd/TiO2 was 5.5 μmol/g. Meanwhile, the molar quantity of CO per unit weight of photocatalyst for Cu/TiO2 produced under the illumination condition of Xe lamp without UV light was 2.5 μmol/g, while that for Pd/TiO2 was 3.5 μmol/g. This study has concluded that Cu/TiO2 is superior to Pd/TiO2 from the viewpoint of the molar quantity of CO per unit weight of photocatalyst as well as the quantum efficiency. 相似文献
37.
Takayama K Arakida Y Dixit T Iwashita T Kono T Nakamura E Otsuka K Shimosaki Y Torikai K Wake M 《Physical review letters》2007,98(5):054801
We report an experimental demonstration of the induction synchrotron, the concept of which has been proposed as a future accelerator for the second generation of neutrino factory or hadron collider. The induction synchrotron supports a superbunch and a superbunch permits more charge to be accelerated while observing the constraints of the transverse space-charge limit. By using a newly developed induction acceleration system instead of radio-wave acceleration devices, a single proton bunch injected from the 500 MeV booster ring and captured by the barrier bucket created by the induction step voltages was accelerated to 6 GeV in the KEK proton synchrotron. 相似文献
38.
The intramoleculae Diels-Alder reaction of cyclohexenone having an unsaturated ester side chain afforded tricyclo[4.3.1.0(3,7)]decanone in both a regio- and stereoselective manner under TMSCl-NEt(3)-ZnBr(2) conditions. Unexpectedly, the regiochemical control was against the conventional orbital requirement. 相似文献
39.
[reaction: see text] Via an X-ray analysis, the sulfonamide bearing R(1) = i-Pr, R(2) = Me, and R(3) = Me is shown to be a tridentate ligand to a Cr(III) salt. This class of ligands, represented by R(1) = t-Bu, R(2) = 2-naphthyl, and R(3) = Me, is effective to achieve an asymmetric Ni/Cr-mediated coupling reaction and, with the C14-C38 segment of halichondrins, its synthetic potential has been demonstrated. A possible mechanism is suggested for the process. 相似文献
40.
[structure: see text] The first total synthesis of the mycolactones is reported. This work unambiguously confirms our earlier relative and absolute stereochemical assignment of the mycolactones. 相似文献