全文获取类型
收费全文 | 1013篇 |
免费 | 36篇 |
国内免费 | 6篇 |
专业分类
化学 | 775篇 |
晶体学 | 17篇 |
力学 | 18篇 |
数学 | 32篇 |
物理学 | 213篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 9篇 |
2017年 | 23篇 |
2016年 | 17篇 |
2015年 | 26篇 |
2014年 | 28篇 |
2013年 | 55篇 |
2012年 | 82篇 |
2011年 | 78篇 |
2010年 | 39篇 |
2009年 | 41篇 |
2008年 | 64篇 |
2007年 | 66篇 |
2006年 | 80篇 |
2005年 | 72篇 |
2004年 | 53篇 |
2003年 | 61篇 |
2002年 | 43篇 |
2001年 | 26篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有1055条查询结果,搜索用时 897 毫秒
941.
The mass-resolved resonance enhanced two-photon ionization spectra of jet-cooled benzyl chloride were measured. Some low-frequency vibronic bands around the S1-S0 origin band were assigned to transitions of the internal rotational mode of the chloromethyl group. The internal rotational motion was analyzed by using the one-dimensional free rotor approximation. The conformation in the S1 state was found to be that in which the C-Cl bond lies in orthogonal to the benzene plane. For the species with m/e 126, the transition energy of the internal rotational bands corresponded well to the potential energy values of V2 = 1900 cm(-1) and V4 = 30 cm(-1) in the S1 state and the reduced rotational constant B values 0.50 and 0.47 cm(-1) in the S0 and S1 states, respectively. The B values obtained for the chlorine isotopomer (m/e 128) were slightly different. The S1 potential barrier height was found to be about 3 times larger than that for the S0 state. Molecular orbital calculations suggest that the difference between energies of the HOMO and LUMO with respect to the rotation of the chloromethyl group correspond approximately to the potential energy curve obtained for the S1 state. 相似文献
942.
943.
Hurok Oh Young-Jung Wee Jong-Sun Yun Hwa-Won Ryu 《Applied biochemistry and biotechnology》2003,107(1-3):603-613
The effect of various nitrogen sources on cell growth and lactic acid production was investigated. The most effective nitrogen
source was yeast extract; more yeast extract gave higher cell growth and lactic acid productivity. Yeast extract dosage and
cell growth were proportional up to a yeast extract concentration of 30 g/L, and lactic acid productivity was linearly correlated
up to a yeast extract dosage of 25 g/L. However, increasing the yeast extract content raises the total production cost of
lactic acid. Therefore, we attempted to find the optimum yeast extract dosage for a repeated-batch operation with cell recycling.
The results show that when using Enterococcus faecalis RKY1 only 26% of the yeast extract dosage for a conventional batch fermentation was sufficient to produce the same amount
of lactic acid, whereas the lactic acid concentration in the product stream (92–94 g/L) and lactic acid productivity (6.03–6.20
g/[L·h]) were similar to those of a batch operation. Furthermore, long-term stability was established. 相似文献
944.
Ki-Young Choi Hee-Kune Lee Ki-Jung Kim Haiil Ryu Kyu-Chul Lee Jaejung Ko Moon-Jip Kim 《Transition Metal Chemistry》2006,31(8):1093-1097
The complexes [Co(L)Cl2]Cl · 4H2O (1) and [Co(L)(N3)2]N3 · 2H2O (2) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,01.18,07.12]docosane) have been synthesized, and structurally characterized by X-ray crystallography, spectroscopy and cyclic voltammetry.
The crystal structure of (1) is centrosymmetric and the cobalt(III) atom has an axially elongated octahedral geometry with four nitrogen atoms of the
macrocycle and two chloride ligands. The cobalt(III) ion in (2) is coordinated to four nitrogen atoms from the macrocycle, and two azide ligands in an octahedral environment, which forms
the 1D polymer through hydrogen bonding contacts involving the cation, azide anion and solvent water molecules. Electronic
spectra of the complexes also exhibit a low-spin octahedral environment. Cyclic voltammetry of the complexes undergoes a one-electron
wave corresponding to Co(III)/Co(II) processes. The electronic spectra and electrochemical behaviors of the complexes are
significantly affected by the nature of the axial ligands. 相似文献
945.
Le YS Kim TE Kim BK Park YG Kim GM Jee SB Ryu KS Kim IK Kim JW 《Experimental & molecular medicine》2002,34(1):18-26
In an effort to understand whether HLA class I and II plays any role in the process of tumorigenesis and metastasis, we have immunohistochemically examined expression of HLA class I and II antigen by using the monoclonal antibodies (mAb) L368 (for beta2m of HLA class I), HC-10 (for HLA-B, C heavy chains), and LGII-612.14 (for HLA class II heavy chain) in 5 borderline serous malignancy (BSM), 20 serous adenocarcinomas (SA), 15 borderline mucinous malignancy (BMM), and 10 mucinous adenocarcinomas (MA) of human ovary tumor case tissues. In BSM, the distribution and intensity of HLA expressions failed to reach statistical significance. In SA, HLA class I beta2-microglobulin (beta2m), HLA-B, C heavy chains and HLA class II heavy chain antigen expressions were down-regulated. Although expressions of HLA-B, C heavy chains and class II heavy chain were down-regulated in metastatic SA, there were no differences in HLA expression levels between primary and metastatic lesions. In BMM, class II heavy chain expressions were down-regulated. In MA, beta2m, HLA-B, C heavy chains and class II heavy chain expressions were also down-regulated. Thus, we could distinguish the reduction or absence of HLA molecule expression was related to malignant potential. Loss of HLA class I and II molecules in invasive ovarian cancers raises the possibility that this could be a factor for tumor cells to retain invasiveness. 相似文献
946.
Ilhyong Ryu Koichi Matsumoto Masato Ando Shinji Murai Noboru Sonoda 《Tetrahedron letters》1980,21(44):4283-4286
Siloxycyclopropanes were quantitatively converted to β-acetoxymercuri ketones by the reaction with mercuric acetate. Successive treatment with palladium chloride or palladium chloride/carbon monoxide gave α-methylene ketones or γ-ketoesters, respectively, in good yields. 相似文献
947.
Byung-Seon Choi Geun-Il Park Jung-Won Lee Ho-Yeon Yang Seung-Kon Ryu 《Journal of Radioanalytical and Nuclear Chemistry》2003,256(1):19-26
The complexes of six organic carboxylic acids (containing {O,O} donor atoms) with Bu2Sn(IV)2+ and Ph3Sn(IV)+ with ligand to metal ratios of 1 : 1 and 1 : 2, were prepared by two different methods. The FtIR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the {O,O} atoms of the ligands. It was found that in most cases the -COO-group was chelated to the central metal ions, but monodentate coordination was also sometimes observed. Complex formation was accompanied by a rearrangement of the hydrogen-bonding network existing in the ligands. The complexes probably have polymeric structures. Comparison of the experimental Mössbauer D values with those calculated on the basis of the point charge model formalism revealed that the organotin(IV) moiety has a trigonal-bipyramidal (tbp) geometry, and in certain cases a tetrahedral (tetr) geometry too. Finally, the local structure of the maleic acid complex formed with Bu2Sn(IV)2+ was determined by an EXAFS method. 相似文献
948.
Clarkson PJ Poole DJ Ryu CK Sharifi VN Swithenbank J Waarlo HJ Ardelt D Falk H 《Analytical and bioanalytical chemistry》2003,377(1):39-47
A system capable of continuously measuring a range of metallic elements in the effluent gas from incinerators and other similar industrial processes, and providing on-line results has been developed. With a state-of-the-art mobile laboratory measurements were taken from a UK municipal solid waste incinerator. The detection system used was an ICP-OES, with a modified torch to allow the introduction of flue gas directly into the plasma. Metals that were investigated were Ni, Hg, V, Al, Na, Ca, Cu, Sn, Pb, Sb, As, Cd and Tl, with limits of detection in the range 0.0004 mg m–3 to 0.1 mg m–3 being calculated. Emission measurements produced data that showed that the MSWI plants emission were significantly lower than the emission limits specified in EC 2000/76/EC. 相似文献
949.
Seong-Heun?Cho Jee-Hyun?Ryu Jung-Bae?Jun Kyung-Do?SuhEmail author 《Colloid and polymer science》2005,284(3):266-275
A flexible poly(dimethyl siloxane) diacrylate (PDMSDA) crosslinker was synthesized using different molecular weights of poly(dimethyl siloxane) (PDMS, M
n
=550, 1,700, 4,000 g/mol). The monodisperse polystyrene (PS) particles crosslinked with various contents of PDMSDA were prepared by dispersion polymerization, and applied as seed particles in the seeded polymerization. The crosslinking density of the PS particles was determined from the rate of transport of the monomer molecules to the crosslinked seed particles. It was confirmed that the monomer swelling capacity of seed particles and final morphological changes of polymer beads were determined significantly by the crosslinking density of the seed particles. In addition, the morphological change was not observed without the oligomer swelling step in the seeded polymerization due to the hydrophobic property of PDMS. When highly crosslinked seed particles were used in the seeded polymerization, peculiar morphology (doublet structure) of polymer beads appeared. 相似文献
950.
Masayoshi?OkuboEmail author Ryu?Takekoh Naohiko?Saito 《Colloid and polymer science》2003,281(10):945-950
Some factors contributing to the formation of an alternately multilayered structure of micron-sized, monodisperse poly(methyl methacrylate) (PMMA)/polystyrene (PS) (1/1, w/w) composite particles by reconstruction of the morphology with the solvent-absorbing/releasing method (SARM) were discussed. The original composite particles, which were produced by seeded dispersion polymerization (SDP) of styrene, had a core–shell structure. When PS/PMMA (1/1, w/w) composite particles produced by SDP of methyl methacrylate were treated by the SARM with toluene, the reconstructed morphology of the composite particles was not the multilayered structure but a hemisphere (or core–shell). The PS/PMMA composite particle contained less than 10 wt% PMMA- g-PS. On the other hand, the PMMA/PS composite particles contained about 40 wt% graft polymer. The graft polymer would exist at the interfaces of the alternate multilayers and decrease their interfacial energy. This was the main reason why the alternately multilayered structure was constructed by the SARM, though the total interfacial area between PMMA and PS layers in the multilayered particle is much larger than that of the hemisphere (or core–shell). 相似文献