全文获取类型
收费全文 | 1603篇 |
免费 | 31篇 |
国内免费 | 13篇 |
专业分类
化学 | 1174篇 |
晶体学 | 14篇 |
力学 | 12篇 |
数学 | 82篇 |
物理学 | 365篇 |
出版年
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 7篇 |
2017年 | 12篇 |
2016年 | 26篇 |
2015年 | 19篇 |
2014年 | 26篇 |
2013年 | 79篇 |
2012年 | 96篇 |
2011年 | 102篇 |
2010年 | 59篇 |
2009年 | 58篇 |
2008年 | 81篇 |
2007年 | 92篇 |
2006年 | 99篇 |
2005年 | 105篇 |
2004年 | 76篇 |
2003年 | 84篇 |
2002年 | 73篇 |
2001年 | 43篇 |
2000年 | 34篇 |
1999年 | 23篇 |
1998年 | 19篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 25篇 |
1993年 | 14篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 26篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 14篇 |
1974年 | 6篇 |
1973年 | 11篇 |
排序方式: 共有1647条查询结果,搜索用时 31 毫秒
51.
A case of giant internal carotid ophthalmic aneurysm was presented. In order to clarify whether the patient could tolerate carotid occlusion, a balloon clamping test was performed. before surgery. The cerebral blood flow was measured using early imaging by single photon emission computed tomography (SPECT) with N-isopropyl-(iodine-123)-p-iodoamphetamine (123I-IMP). When the balloon clamping test was performed the tracer was injected, and scanning was performed 35 minutes after removing the catheter. This tracer enabled a "memory of blood flow" during temporary ischemia to determine the character of quick diffusion and slow wash out, that could not be performed by other methods of cerebral blood flow measurement. SPECT with 123I-IMP can simplify the measurement of cerebral blood flow during the balloon clamping test. 相似文献
52.
Ai Suzuki Parasuraman Selvam Tomonori Kusagaya Seiichi Takami Momoji Kubo Akira Imamura Akira Miyamoto 《International journal of quantum chemistry》2005,102(3):318-327
The decomposition reaction dynamics of 2,3,4,4′,5‐penta‐chlorinated biphenyl (2,3,4,4′,5‐PeCB), 3,3′,4,4′,5‐penta‐chlorinated biphenyl (3,3′,4,4′,5‐PeCB), and 2,3,7,8‐tetra‐chlorinated dibenzo‐p‐dioxin (2,3,7,8‐TCDD) was clarified for the first time at atomic and electronic levels, using our novel tight‐binding quantum chemical molecular dynamics method with first‐principles parameterization. The calculation speed of our new method is over 5000 times faster than that of the conventional first‐principles molecular dynamics method. We confirmed that the structure, energy, and electronic states of the above molecules calculated by our new method are quantitatively consistent with those by first‐principles calculations. After the confirmation of our methodology, we investigated the decomposition reaction dynamics of the above molecules and the calculated dynamic behaviors indicate that the oxidation of the 2,3,4,4′,5‐PeCB, 3,3′,4,4′,5‐PeCB, and 2,3,7,8‐TCDD proceeds through an epoxide intermediate, which is in good agreement with the previous experimental reports and consistent with our static density functional theory calculations. These results proved that our new tight‐binding quantum chemical molecular dynamics method with first‐principles parameterization is an effective tool to clarify the chemical reaction dynamics at reaction temperatures. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
53.
Nomura S Itoh T Nakasho H Uno T Kubo M Sada K Inoue K Miyata M 《Journal of the American Chemical Society》2004,126(7):2035-2041
Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes (methoxy (1a), ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized. Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1a-A) and needles (1a-B), needles (1c-A) and plates (1c-B), prisms (1e-A) and plates (1e-B), and prisms (1f-A) and needles (1f-B)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state, 1a-A, 1e-A, and 1f-A polymerized topochemically to give crystalline polymers. For their thermal polymerizations in the solid state, in addition to 1a-A, 1e-A, and 1f-A, 1e-B and 1f-B polymerized, but polymers formed from the 1e-B and 1f-B were amorphous. The packing of quinodimethane molecules in the crystals was defined by four kinds of parameters, stacking distance (d(s)), the distance between the reacting exomethylene carbon atoms (d(cc)), the angles formed between the stacking axis and longer axis of the monomer molecule (theta(1)), and the shorter axis of the monomer molecule (theta(2)), and then the polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these parameters. 相似文献
54.
Hiromi Matsushita Ritsuko Nagao Masayuki Nogami Toshihiro Kasuga Tomokatsu Hayakawa 《Journal of Sol-Gel Science and Technology》2000,19(1-3):559-562
High proton-conducting P2O5-SiO2 glass was applied to the electrolyte of the hydrogen concentration cell for hydrogen gas sensing. 5P2O5·95SiO2 glass was prepared using the sol-gel method and its electrical conductivity and electromotive force were measured at 50°C as a function of both the ambient humidity and hydrogen gas concentration. The electrical conductivities increased with increasing humidity and reached 10–2 S/cm at 90% relative humidity. The electromotive force of the hydrogen concentration cell, where the glass was used as a membrane, showed good Nernstian response to hydrogen pressure in the high relative humidity region. 相似文献
55.
H. Yasuda Toshihiro Hirotsu 《Journal of polymer science. Part A, Polymer chemistry》1977,15(11):2749-2771
Plasma polymerizations of mixture of acetylene-N2, acetylene-H2O, were investigated by using an electrodeless glow discharge from a 13.5-MHz radiofrequency source. Properties of plasma polymers were examined as functions of mole ratios of N2 and/or H2O to acetylene. The concentration of trapped free radicals and the internal stress in a plasma polymer decreased as the mole ratio of N2 or H2O increased. Water showed the most pronounced effects in those properties at the mole ratio of 0.3. Gas permeabilities increased by the copolymerization of N2 and/or H2O. Surface energies were also investigated by analysis of contact angles of liquids. Copolymerization of N2 caused a remarkable increase in polar contribution of surface energy. Some fundamental aspects of flow-rate pressure relationship of mixed gases are presented. 相似文献
56.
Toshihiro Otsuki Masa-Aki Kakimoto Yoshio Imai 《Journal of polymer science. Part A, Polymer chemistry》1989,27(5):1775-1780
Wholly aromatic random copolyamides of high molecular weights were prepared by the high-temperature solution polycondensation of an aromatic diisocyanate, 4,4′-methylenedi(phenyl isocyanate) or 2,4-tolylene diisocyanate, with a mixture of isophthalic acid and 4,4′-oxydibenzoic acid. Glass transition temperatures of the polyamides and copolyamides were between 229 and 273°C; this depended on the combination of diisocyanates and dicarboxylic acids used. These aromatic copolyamides showed better solubility in various organic solvents and reduced crystallinity, compared to the corresponding homopolyamides. The copolyamides prepared from 2,4-tolylene diisocyanate had greater solubility and higher glass transition temperatures than those obtained from 4,4′-methylenedi(phenyl isocyanate). 相似文献
57.
Sumitra Tavornvipas Hidetoshi Arima Fumitoshi Hirayama Kaneto Uekama Toshihiro Ishiguro Masahide Oka Kenichi Hamayasu Hitoshi Hashimoto 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):391-394
Some physicochemical and biological properties of a new branched cyclodextrin, 6-O--(4-O--d-glucuronyl)-d-glucosyl--cyclodextrin GUG--CyD) were investigated. Further, theinteraction of GUG--CyD with several drugs was studied by the solubility and spectroscopic methods, and compared with those of parent -CyD and 6-O--maltosyl--CyD(2--CyD).The hemolytic activity of GUG--CyD on rabbit erythrocytes was lower than those of -CyD and 2--CyD. GUG--CyD and 2--CyD showed negligible cytotoxicity on Caco-2 cells up to at least 0.1 M. The inclusion ability of GUG--CyD to neutral and acidic drugs was comparable to or slightly smaller than those of -CyD and 2--CyD, probably because of a steric hindrance of the branched sugar. On the other hand, GUG--CyD showed greater affinity for the basic drugs, compared with -CyD and 2--CyD, owing to the electrostatic interaction of its carboxylate anion with positive charge of basic drugs. Thus GUG--CyD may be useful as a safe solubilizing agent particularly for basic drugs. 相似文献
58.
Shuichi Naito Shigeru Aida Toshiki Kasahara Toshihiro Miyao 《Research on Chemical Intermediates》2006,32(3-4):279-290
In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO2. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)2(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMSI effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO?H2 reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support. 相似文献
59.
Joonho Lee Wataru Shimoda Toshihiro Tanaka 《Monatshefte für Chemie / Chemical Monthly》2005,40(10):1829-1834
Temperature dependence of the surface tension of liquid Sn–Ag and Sn–Cu base lead-free solder alloys and oxygen partial pressure
dependence of liquid Sn–Ag alloy were evaluated using the experimental data obtained, respectively, by the constrained drop
method and the sessile drop method in the previous studies [1, 2]. The temperature dependences of the surface tension have
maximum positive values when the mol fraction of Ag and Cu is about 0.7, while those for pure liquid Sn, Ag, and Cu have negative
values. The calculated values based on Butler’s equations were found to be in reasonable agreement with those of the experimental data. The oxygen partial pressure dependences
of the surface tension of liquid Sn–Ag alloys at 1253 K have a minimum value when the mol fraction of Ag is about 0.9 and
the oxygen partial pressure is less than about 10−13 atm. From this, it is considered that the oxygen adsorption increased by adding Ag to Sn when the mol fraction of Ag is less
than 0.9. 相似文献
60.
Minemura Y Ito S Miyao T Naito S Tomishige K Kunimori K 《Chemical communications (Cambridge, England)》2005,(11):1429-1431
In preferential CO oxidation in H2-rich gas, K-Pt/Al2O3(K/Pt = 10) was very effective in decreasing CO concentration below 10 ppm in the 375-410 K range, and the turnover frequency of the K-Pt/Al2O3 was 20 times as high as that of Pt/Al2O3 at 353 K; furthermore, the activity of CO oxidation was promoted drastically by the presence of H2. 相似文献