全文获取类型
收费全文 | 663篇 |
免费 | 29篇 |
国内免费 | 4篇 |
专业分类
化学 | 508篇 |
晶体学 | 4篇 |
力学 | 11篇 |
数学 | 73篇 |
物理学 | 100篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 20篇 |
2015年 | 20篇 |
2014年 | 12篇 |
2013年 | 39篇 |
2012年 | 37篇 |
2011年 | 45篇 |
2010年 | 32篇 |
2009年 | 21篇 |
2008年 | 36篇 |
2007年 | 50篇 |
2006年 | 50篇 |
2005年 | 29篇 |
2004年 | 30篇 |
2003年 | 39篇 |
2002年 | 19篇 |
2001年 | 16篇 |
2000年 | 8篇 |
1999年 | 2篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
排序方式: 共有696条查询结果,搜索用时 15 毫秒
121.
Abe M Hattori M Takegami A Masuyama A Hayashi T Seki S Tagawa S 《Journal of the American Chemical Society》2006,128(24):8008-8014
A detailed study of the regioselectivity of 1,2-oxygen migration was conducted using the unsymmetrically substituted singlet 2,2-dialkoxy-1,3-diarylcyclopentane-1,3-diyls 5. The alkoxy group selectively migrates to the electron-donating p-methoxyphenyl-substituted carbon. The regioselective migration of oxygen clearly indicates a hyperconjugative resonance structure, that is, zwitterionic characteristics, in singlet 2,2-dialkoxy-1,3-diyls. This represents the first attempt to experimentally probe the contribution of hyperconjugation to stabilizing the singlet state. 相似文献
122.
Kimura H Fujiwara T Katoh T Nishide K Kajimoto T Node M 《Chemical & pharmaceutical bulletin》2006,54(3):399-402
(-)-Epibatidine, an excellent candidate of non-opioidal anesthesia, was formally synthesized in short steps from di-(l)-menthyl (R)-allene-1,3-dicarboxylate that was facilely prepared as a single isomer by means of crystallization-induced asymmetric transformation from a diastereomer mixture of (R)- and (S)-allene-1,3-dicarboxylates. Taking advantage of the chiral synthesis, derivatives of (-)-epibatidine were also prepared for targeting diagnostic agents that could bind nicotinic acetylcholine receptors (nAChRs) in the mammalian central nerve system. 相似文献
123.
The first series of triangular cluster complexes of [MCo(2)] (M = Rh, Ir, Ru) with a planar metalladithiolene ring coordinating in the eta(3)-bonding mode were synthesized, and the crystal structures, spectral and electrochemical properties, and thermochromism of these complexes were revealed. 相似文献
124.
The chemiluminescence (CL) mechanism of 3,4-bis(3-indolyl)-1H-pyrrole-2,5-dione (IPD) was investigated using liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) of the products formed after the IPD CL reaction. We found that IPD produced strong CL via the decomposition of dioxetane formed after oxidation of the maleimide and indole moieties in the presence of CH3CN, H2O2 and NaOH. The IPD CL was used for evaluating the antioxidant effect on curcumin and epigallocatechin gallate. 相似文献
125.
Vadim A. Soloshonok Hironari Ohkura Manabu Yasumoto 《Journal of fluorine chemistry》2006,127(7):930-935
An asymmetric synthesis of (S)- and (R)-3-amino-4,4,4-trifluorobutanoic acid via DBU-catalyzed asymmetric 1,3-proton shift transfer reaction of (Z)-3-[(R)-1-phenylethylamino]-4,4,4-trifluoro-N-[(R)-1-phenylethyl]but-2-enamide has been developed. The intermediate Schiff base (S,R′)-9 was found to be relatively configurationally stable under the highly basic reaction conditions allowing preparation of the target amino acid in high chemical yield and enantioselectivity. This method was demonstrated to be practical for large (>25 g) scale synthesis of the target β-amino acid. 相似文献
126.
Yoshikazu Okamoto Graham J. Kemp Tomonori Isobe Eisuke Sato Yuji Hirano Junichi Shoda Manabu Minami 《Magnetic resonance imaging》2014
Several studies have proposed the cell membrane as the main water diffusion restricting factor in the skeletal muscle cell. We sought to establish whether a particular form of exercise training (which is likely to affect only intracellular components) could affect water diffusion. The purpose of this study is to characterise prospectively the changes in diffusion tensor imaging (DTI) eigenvalues of thigh muscle resulting from hybrid training (HYBT) in patients with non-alcoholic fatty liver disease (NAFLD). Twenty-one NAFLD patients underwent HYBT for 30 minutes per day, twice a week for 6 months. Patients were scanned using DTI of the thigh pre- and post-HYBT. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), the three eigenvalues lambda 1 (λ1), λ2, λ3, and the maximal cross sectional area (CSA) were measured in bilateral thigh muscles: knee flexors (biceps femoris (BF), semitendinosus (ST), semimembranous (SM)) and knee extensors (medial vastus (MV), intermediate vastus (IV), lateral vastus (LV), and rectus femoris (RF)), and compared pre- and post-HYBT by paired t-test. Muscle strength of extensors (P < 0.01), but not flexors, increased significantly post-HYBT. For FA, ADC and eigenvalues, the overall picture was of increase. Some (P < 0.05 in λ2 and P < 0.01 in λ1) eigenvalues of flexors and all (λ1-λ3) eigenvalues of extensors increased significantly (P < 0.01) post-HYBT. HYBT increased all 3 eigenvalues. We suggest this might be caused by enlargement of muscle intracellular space. 相似文献
127.
128.
Manabu Ichikawa Yo-ichi Ishikawa Takashi Wakasugi Kohei Kadono 《Journal of luminescence》2012,132(3):784-788
Emission properties were investigated in the infrared region for Ga2S3-GeS2-Sb2S3 glasses doped with Ho3+. We performed Judd–Ofelt analysis and lifetime measurements of the 5I4, 5I5, and 5I6 levels, which are the initial levels of the mid-infrared emissions between 3 to 5 μm of Ho3+. The quantum efficiencies reached approximately 18%, 64%, and ~100% for the 5I4, 5I5, and 5I6, respectively. Population analyses were carried out from the relative intensities of the emissions in the near-infrared region. We investigated the dependences on the Ho3+ ion concentration of the population ratio of the initial levels to the final levels, [initial]/[final], of the mid-infrared emissions. The population ratio of [5I5]/[5I6] decreased with increase of the Ho3+ concentration while those of [5I4]/[5I5] and [5I6]/[5I7] increased. Particularly, the former, [5I4]/[5I5], rapidly increased because of the strong concentration quenching of the 5I5 level through cross relaxation. It was found that the population inversion for the 4.8 μm emission due to the transition, 5I4→5I5, was achieved at high Ho3+ concentration in the present experiments. 相似文献
129.
Akio Saito Manabu Tojo Hikaru Yanai Fukiko Wada Muga Nakagawa Midori Okada Azusa Sato Rieko Okatani Takeo Taguchi 《Journal of fluorine chemistry》2012
CrCl2/Mn-mediated transformation of various dibromofluoromethylcarbinyl esters including carboxylates, carbonates and carbamates provided 1-fluoro-1-alkenyl esters via [2,3]-sigmatropic rearrangement of ester group. Reaction proceeded by using CrCl2/Mn system under mild conditions (in THF at room temperature) to give 1-fluoro-1-alkenyl esters in good yield with an excellent Z selective manner. 1-Fluoro-1-alkenyl ester thus obtained acts as a double acyl donor in the reaction with necleophiles such as amine, thiol, alcohol as well as bifunctional necleophiles such as ethylene diamine derivative. 相似文献
130.
Kanno M Nakamura K Kanai E Hoki K Kono H Tanaka M 《The journal of physical chemistry. A》2012,116(9):2177-2183
There have been a growing number of articles that report dramatic improvements in the experimental performance of chemical reactions by microwave irradiation compared to that under conventional heating conditions. We theoretically examined whether nonthermal microwave effects on intramolecular reactions exist or not, in particular, on Newman-Kwart rearrangements and intramolecular Diels-Alder reactions. The reaction rates of the former calculated by the transition state theory, which consider only the thermal effects of microwaves, agree quantitatively with experimental data, and thus, the increases in reaction rates can be ascribed to dielectric heating of the solvent by microwaves. In contrast, for the latter, the temperature dependence of reaction rates can be explained qualitatively by thermal effects but the possibility of nonthermal effects still remains regardless of whether competitive processes are present or not. The effective intramolecular potential energy surface in the presence of a microwave field suggests that nonthermal effects arising from potential distortion are vanishingly small in intramolecular reactions. It is useful in the elucidation of the reaction mechanisms of microwave synthesis to apply the present theoretical approach with reference to the experiments where thermal and nonthermal effects are separated by screening microwave fields. 相似文献