全文获取类型
收费全文 | 263篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 221篇 |
晶体学 | 1篇 |
数学 | 29篇 |
物理学 | 24篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 14篇 |
2011年 | 20篇 |
2010年 | 15篇 |
2009年 | 13篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有275条查询结果,搜索用时 781 毫秒
91.
Takahiro Kishima Dr. Takahiro Matsumoto Dr. Hidetaka Nakai Prof. Shinya Hayami Dr. Takehiro Ohta Prof. Seiji Ogo 《Angewandte Chemie (International ed. in English)》2016,55(2):724-727
Dioxygen‐tolerant [NiFe] hydrogenases catalyze not only the conversion of H2 into 2 H+ and 2 e? but also the reduction of O2 to H2O. Chemists have sought to mimic such bifunctional catalysts with structurally simpler compounds to facilitate analysis and improvement. Herein, we report a new [NiFe]‐based catalyst for O2 reduction via an O2 adduct. Structural investigations reveal the first example of a side‐on iron(IV) peroxo complex. 相似文献
92.
Kobayashi S Atuchi N Wakamatsu H Hattori M Kawada A Asano K 《Chemical & pharmaceutical bulletin》2007,55(11):1585-1592
The interaction between growth inhibition and chirality, especially of diastereomers, has an important modifying effect on cancer cell proliferation. Previously, we have reported on the design, synthesis, and chemical properties of a series of novel, double-stranded peptides, (y-AA-x-AA)(2)-(CH(2))(12), with -y-AA-x-AA- and -z-AA-y-AA-x-AA- sequences conjugated to the spacer. Here, we extend those results by showing that (D-, L-) and (L-, D-) diastereomers are more potent inhibitors of tyrosine phosphorylation than (L-, L-). Although the replacement of the L-Phe-L-Phe sequence with L-Tyr-L-Phe produces a less active inhibitor, the double-stranded peptide conjugated with L-Tyr-D-Phe is more active than that conjugated with L-Tyr-L-Phe. In addition, we show that SDS-PAGE gel profiles of tyrosine phosphorylation following treatment with bis(y-Tyr-x-Phe)-N,N-dodecane-1,12-diamine appear very similar to profiles of tyrosine phosphorylation following treatment with an analog of the tyrosine kinase inhibitor, erbstatin. Moreover, the level of autophosphorylation of the epidermal growth factor receptor kinase domain (EGFRKD) treated with bis(L-Tyr-D-Phe)-N,N-dodecane-1,12-diamine was lower than that seen following treatment with bis(L-Phe-D-Phe)-N,N-dodecane-1,12-diamine. These data provide new insights for the control of cancer cell proliferation through drug designs which replace the less active -L-Phe-L-Phe- (and -D-Phe-L-Phe-) with the more active -L-Tyr-L-Phe- (and -L-Tyr-D-Phe-) sequence. 相似文献
93.
We used Raman micro-spectroscopy technique to analyze the molecular changes associated with oral squamous cell carcinoma (SCC) cells in the form of frozen tissue. Previously, Raman micro-spectroscopy technique on human tissue was mainly based on spectral analysis, but we worked on imaging of molecular structure. In this study, we evaluated the distribution of four components at the cell level (about 10 μm) to describe the changes in protein and molecular structures of protein belonging to malignant tissue. We analyzed ten oral SCC samples of five patients without special pretreatments of the use of formaldehyde. We obtained cell level images of the oral SCC cells at various components (peak at 935 cm−1: proline and valine, 1004 cm−1: phenylalanine, 1223 cm−1: nucleic acids, and 1650 cm−1: amide I). These mapping images of SCC cells showed the distribution of nucleic acids in the nuclear areas; meanwhile, proline and valine, phenylalanine, and amide I were detected in the cytoplasm areas of the SCC cells. Furthermore, the peak of amide I in the cancer area shifts to the higher wavenumber side, which indicates the α-helix component may decrease in its relative amounts of protein in the β-sheet or random coil conformation. Imaging of SCC cells with Raman micro-spectroscopy technique indicated that such a new observation of cancer cells is useful for analyzing the detailed distribution of various molecular conformation within SCC cells. 相似文献
94.
Yamada H Matsuzaki Y Higashii T Kazama S 《The journal of physical chemistry. A》2011,115(14):3079-3086
We used density functional theory (DFT) calculations with the latest continuum solvation model (SMD/IEF-PCM) to determine the mechanism of CO(2) absorption into aqueous solutions of 2-amino-2-methyl-1-propanol (AMP). Possible absorption process reactions were investigated by transition-state optimization and intrinsic reaction coordinate (IRC) calculations in the aqueous solution at the SMD/IEF-PCM/B3LYP/6-31G(d) and SMD/IEF-PCM/B3LYP/6-311++G(d,p) levels of theory to determine the absorption pathways. We show that the carbamate anion forms by a two-step reaction via a zwitterion intermediate, and this occurs faster than the formation of the bicarbonate anion. However, we also predict that the carbamate readily decomposes by a reverse reaction rather than by hydrolysis. As a result, the final product is dominated by the thermodynamically stable bicarbonate anion that forms from AMP, H(2)O, and CO(2) in a single-step termolecular reaction. 相似文献
95.
Koshima H Takechi K Uchimoto H Shiro M Hashizume D 《Chemical communications (Cambridge, England)》2011,47(41):11423-11425
Platelike microcrystals of N-3,5-di-tert-butylsalicylidene-3-nitroaniline repeatedly bend and straighten upon alternate irradiation with UV and visible light. The mechanism of bending was elucidated by X-ray crystallographic analyses before and after photoirradiation. 相似文献
96.
Torigoe H Rahman SM Takuma H Sato N Imanishi T Obika S Sasaki K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(9):2742-2751
Due to the instability of pyrimidine motif triplex DNA at physiological pH, triplex stabilization at physiological pH is crucial in improving its potential in various triplex-formation-based strategies in vivo, such as gene expression regulation, genomic DNA mapping, and gene-targeted mutagenesis. To this end, we investigated the thermodynamic and kinetic effects of our previously reported chemical modification, 2'-O,4'-C-aminomethylene-bridged nucleic acid (2',4'-BNA(NC)) modification of triplex-forming oligonucleotide (TFO), on triplex formation at physiological pH. The thermodynamic analyses indicated that the 2',4'-BNA(NC) modification of TFO increased the binding constant of the triplex formation at physiological pH by more than 10-fold. The number and position of the 2',4'-BNA(NC) modification in TFO did not significantly affect the magnitude of the increase in the binding constant. The consideration of the observed thermodynamic parameters suggested that the increased rigidity and the increased degree of hydration of the 2',4'-BNA(NC)-modified TFO in the free state relative to the unmodified TFO may enable the significant increase in the binding constant. Kinetic data demonstrated that the observed increase in the binding constant by the 2',4'-BNA(NC) modification resulted mainly from the considerable decrease in the dissociation rate constant. The TFO stability in human serum showed that the 2',4'-BNA(NC) modification significantly increased the nuclease resistance of TFO. Our results support the idea that the 2',4'-BNA(NC) modification of TFO could be a key chemical modification to achieve higher binding affinity and higher nuclease resistance in the triplex formation under physiological conditions, and may lead to progress in various triplex-formation-based strategies in vivo. 相似文献
97.
Bimala Pangeni Hari Paudyal Katsutoshi Inoue Hidetaka Kawakita Keisuke Ohto Shafiq Alam 《Cellulose (London, England)》2012,19(2):381-391
Novel utilization of cotton cellulose was developed by chemically modifying with concentrated sulfuric acid to prepare a novel
kind of adsorption gel for gold. The adsorption behaviors of the gel were investigated for various metals from acidic chloride
media. The gel was found to be highly selective for Au(III) over other precious and base metals tested over the whole concentration
range of hydrochloric acid. The maximum adsorption capacity for Au(III) was evaluated as 6.21 mmol/g at 303 K. The amount
of adsorbed Au(III) was increased with increasing temperature. A kinetic study for the adsorption of Au(III) at various temperatures
confirmed the endothermic adsorption process following pseudo-first order kinetics. The activation energy was evaluated as
78.8 kJ/mol. Interestingly, it was found that the adsorbed Au(III) was reduced to elemental form which was evidenced by the
clearly visible elemental gold particles which was further confirmed by means of the X-ray diffraction spectrum and optical
microscope image of the gel after the adsorption of Au(III). The mechanism of Au(III) adsorption on the cotton gel and its
reduction to elemental gold was proved from the results of IR-spectra. The main mechanism could be explained in terms of the
coordination of Au(III) to oxygen atom of C–O–C linkage of cross linked cotton gel and to the oxygen atoms of the hydroxyl
groups at C2 and C3 atoms of pyranose ring of cotton cellulose followed by the reduction to metallic gold. The adsorbed gold in the cotton gel
can easily be recovered by incineration. 相似文献
98.
Funai T Miyazaki Y Aotani M Yamaguchi E Nakagawa O Wada S Torigoe H Ono A Urata H 《Angewandte Chemie (International ed. in English)》2012,51(26):6464-6466
Silver turns up the A-C: In the presence of Ag(I) ions, a DNA polymerase incorporated deoxyadenosine (from dATP) at the site opposite cytosine in the template strand to afford the full-length product (see scheme), meaning that DNA polymerases prefer a C-Ag(I)-A base pair to the more thermodynamically stable C-Ag(I)-C base pair. 相似文献
99.
Hidetaka Tobita 《Macromolecular theory and simulations》2011,20(3):179-190
In the ATRP and SFRP miniemulsion polymerization, a particle size range may exist in which the polymerization rate is larger than that of the corresponding bulk polymerization. Here, MC simulations are applied to clarify the reason for the acceleration. It is shown that the statistical variation of the trapping agent concentration (fluctuation effect) dominates the acceleration for good living conditions, while the segregation effect is important when the bimolecular termination is significant. Even for the segregation‐dominated conditions, the polymerization rate cannot be predicted accurately without accounting for the fluctuation effect.
100.
Kunihiko Takabe Yasuhiro Iida Hidetaka Hiyoshi Masatoshi Ono Yoshihiko Hirose Yoshitaka Fukui Hidemi Yoda Nobuyuki Mase 《Tetrahedron: Asymmetry》2000,11(24):4825-4829
Enantioselective acetylation of 2-carbamoylmethyl-1,3-propanediol derivatives was catalyzed effectively by lipase PS to give monoacetates with high enantioselectivity: The enantioselectivity depended on the 2-carbamoylmethyl groups. The reaction of N-monoalkylcarbamoylmethyl-1,3-propanediol afforded the monoacetate with the (S)-configuration, whereas N,N-dialkylcarbamoylmethyl-1,3-propanediol gave the monoacetate with the (R)-configuration. 相似文献