全文获取类型
收费全文 | 949篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
化学 | 646篇 |
晶体学 | 17篇 |
力学 | 3篇 |
数学 | 28篇 |
物理学 | 275篇 |
出版年
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 21篇 |
2015年 | 22篇 |
2014年 | 21篇 |
2013年 | 48篇 |
2012年 | 37篇 |
2011年 | 47篇 |
2010年 | 38篇 |
2009年 | 40篇 |
2008年 | 71篇 |
2007年 | 60篇 |
2006年 | 69篇 |
2005年 | 56篇 |
2004年 | 36篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1975年 | 8篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1971年 | 8篇 |
1970年 | 4篇 |
排序方式: 共有969条查询结果,搜索用时 15 毫秒
61.
Yuetao Zhang Garret M. Miyake Eugene Y.‐X. Chen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2010,122(52):10356-10360
62.
The effect of specific surface area of TiO<Subscript>2</Subscript> on the thermal decomposition of ammonium perchlorate 总被引:1,自引:0,他引:1
The thermal decomposition of ammonium perchlorate (AP) is considered to be the first step in the combustion of AP-based composite
propellants. In this report, the effect of the specific surface area of titanium oxide (TiO2) catalysts on the thermal decomposition characteristics of AP was examined with a series of thermal analysis experiments.
It was clear that the thermal decomposition temperature of AP decreased when the specific surface area of TiO2 increased. It was also possible that TiO2 influences the frequency factor of AP decomposition because there was no observable effect on the activation energy. 相似文献
63.
Kota Tanaka Saki Okamura Ken Shibata Naoki Ikenaga Nobuyuki Tanaka Kazumi Hakamada Jun Miyake 《Research on Chemical Intermediates》2016,42(11):7723-7730
Renewable energy is regarded as a clean energy source but has some problems, one of which is intermittency. To reduce this, the time-delay of hydrogen production by photosynthetic bacteria can be effective. In this study, we qualitatively evaluated the time-delay of hydrogen production by photosynthetic bacteria under various irradiation conditions, and we also quantitatively evaluated it by fitting the experimental data and the hydrogen production model with a genetic algorithm. As a result of model fitting, we found that the relationship between the lengths of the optimized time-delay of hydrogen production by photosynthetic bacteria and the amount of light irradiation is linear. And we also found that the time-delay of hydrogen production by photosynthetic bacteria had an upper limit under low light intensity. We have suggested the existence of an energy store mechanism in photosynthetic bacteria. 相似文献
64.
Dr. Eiji Yamamoto Kiyotaka Izumi Ryosuke Shishido Prof. Dr. Tomohiro Seki Noriaki Tokodai Prof. Dr. Hajime Ito 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(49):17547-17551
The first dimesitylboryl substitution of aryl halides with a silylborane bearing a dimesitylboryl group in the presence of alkali‐metal alkoxides is described. The reactions of aryl bromides or iodides with Ph2MeSi?BMes2 and Na(OtBu) afforded the desired aryl dimesitylboranes in good to high yields and with high borylation/silylation ratios. Selective reaction of the sterically less‐hindered C?Br bond of dibromoarenes provided monoborylated products. This reaction was used to rapidly construct a D‐π‐A aryl dimesityl borane with a non‐symmetrical biphenyl spacer. 相似文献
65.
The enzymatic resolution products [(1R,4aR,8aR)-1,2,3,4,4a,5,6,7,8,8a-decahydro-5,5,8a-trimethyl-2-oxo-trans-naphthalene-1-methanol-2-ethylene acetal (8aR)-7 (98% ee) and {acetate of (1S,4aS,8aS)-1,2,3,4,4a,5,6,7,8,8a-decahydro-5,5,8a-trimethyl-2-oxo-trans-naphthalene-1-methanol-2-ethylene acetal} (8aS)-9 (>99% ee)] obtained by the lipase-catalyzed enantioselective acetylation of (±)-7 in the presence of vinyl acetate as an acyl donor were converted to the ,β-unsaturated ketones (8aR)-6 and (8aS)-6, respectively. Concise syntheses of (+)-totarol 1, (+)-podototarin 2 and (+)-sempervirol 3 were achieved based on Michael reactions between (8aS)-6 and the appropriate β-keto ester followed by aldol condensation. The first chiral syntheses of (+)-jolkinolides E 4 and D 5 were achieved from (5R,10R,12R)-12-hydroxypodocarpa-8(14)-en-13-one 15 derived from (8aR)-6. 相似文献
66.
Ninomiya Kazuhiko Kudo Takuto Strasser Patrick Terada Kentaro Kawai Yosuke Tampo Motonobu Miyake Yasuhiro Shinohara Atsushi Kubo Kenya M. 《Journal of Radioanalytical and Nuclear Chemistry》2019,320(3):801-805
Journal of Radioanalytical and Nuclear Chemistry - Elemental isotopic ratios are measured in various research fields and provide useful information regarding age, origin, geological and biological... 相似文献
67.
Yutaka T Obara S Ogawa S Nozaki K Ikeda N Ohno T Ishii Y Sakai K Haga MA 《Inorganic chemistry》2005,44(13):4737-4746
A series of novel emissive Ir(III) complexes having the coordination environments of [Ir(N--N--N)2]3+, [Ir(N--N--N)(N--N)Cl]2+, and [Ir(N--N--N)(N--C--N)]2+ with 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine (L1, N--N--N), 1,3-bis(1-methyl-benzimidazol-2-yl)benzene (L2H, N--C--N), 4'-(4-methylphenyl)-2,2':6',2' '-terpyridine (ttpy, N--N--N), and 2,2'-bipyridine (bpy, N--N) have been synthesized and their photophysical and electrochemical properties studied. The Ir(III) complexes exhibited phosphorescent emissions in the 500-600 nm region, with lifetimes ranging from approximately 1-10 micros at 295 K. Analysis of the 0-0 energies and the redox potentials indicated that the lowest excited state of [Ir(L1)(L2)]2+ possessed the highest contribution of 3MLCT (MLCT = metal-to-ligand charge transfer) among the Ir(III) complexes, reflecting the sigma-donating ability of the tridentate ligand, ttpy < L1 < L2. The emission quantum yields (phi) of the Ir(III) complexes ranged from 0.037 to 0.19, and the highest phi value (0.19) was obtained for [Ir(L1)(bpy)Cl]2+. Radiative rate constants (k(r)) were 1.2 x 10(4) s(-1) for [Ir(ttpy)2]3+, 3.7 x 10(4) s(-1) for [Ir(L1)(bpy)Cl]2+, 3.8 x 10(4) s(-1) for [Ir(ttpy)(bpy)Cl]2+, 3.9 x 10(4) s(-1) for [Ir(L1)2]3+, and 6.6 x 10(4) s(-1) for [Ir(L1)(L2)]2+. The highest radiative rate for [Ir(L1)(L2)]2+ with the highest contribution of 3MLCT could be explained in terms of the singlet-triplet mixing induced by spin-orbit coupling of 5d electrons in the MLCT electronic configurations. 相似文献
68.
Motokura K Fujita N Mori K Mizugaki T Ebitani K Kaneda K 《Journal of the American Chemical Society》2005,127(27):9674-9675
A Ti4+-exchanged montmorillonite (Ti4+-mont) and a hydrotalcite (HT) are strong solid Br?nsted acid and base, and these two clay catalysts could be used in a single reactor without neutralization of active sites. Because the Ti4+-mont have active acid site in the narrow interlayers, the base sites of large HT particles show no interaction with the acid sites. A variety of acid and base reactions, such as esterification, acetalization, deacetalization, aldol reaction, Michael reaction, and epoxidation, proceeded using both the Ti4+-mont and the HT in a single reactor. 相似文献
69.
Shigekazu Ito Hideaki Miyake Hiroki Sugiyama Masaaki Yoshifuji 《Heteroatom Chemistry》2005,16(5):357-360
Kinetically stabilized 2‐lithio‐1‐(2,4,6‐tri‐t‐butylphenyl)‐1‐phosphapropene was allowed to react with a bulky phosphaalkyne Mes*CP (Mes* = 2,4,6‐t‐Bu3C6H2) followed by quenching with iodomethane or benzyl bromide to give the corresponding 1,3‐diphosphabuta‐1,3‐dienes. The presence of the bulky Mes* group on the 1‐phosphorus atom prevents intramolecular [2+2] cyclization and gave the PC PC skeleton, whereas Mes*CP reacted with half an equivalent of nucleophile to afford the PCPC four‐membered ring compounds. X‐ray crystallography of 4‐benzyl‐1,3‐diphosphabuta‐1,3‐diene confirmed the molecular structure showing conjugation on the 1,3‐diphosphabuta‐1,3‐diene moiety. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:357–360, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20104 相似文献
70.
The binding constants of 1-alkanols with α-cyclodextrin (α-CD) were determined by indirect competitive potentiometry, although potentiometry is usually inapplicable to nonionic compounds. This novel method utilizes competitive binding of 1-alkanol and octyltrimethylammonium bromide (OTAB) to α-CD in aqueous media, where the concentration of free OTAB depending on the competitive binding is monitored with an OTAB-selective electrode. Therefore, the concentration of 1-alkanol is indirectly estimated from the observed electromotive force. The binding constants of 1-propapnol, 1-butanol, 1-hexanol, and 1-octanol with α-CD, obtained by this method, are close to the literature values. The implications and limitations of this indirect competitive potentiometry were discussed. 相似文献