全文获取类型
收费全文 | 412篇 |
免费 | 14篇 |
专业分类
化学 | 296篇 |
晶体学 | 9篇 |
力学 | 13篇 |
数学 | 24篇 |
物理学 | 84篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 18篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 16篇 |
2012年 | 23篇 |
2011年 | 15篇 |
2010年 | 18篇 |
2009年 | 15篇 |
2008年 | 22篇 |
2007年 | 9篇 |
2006年 | 19篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 22篇 |
2002年 | 25篇 |
2001年 | 13篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 18篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有426条查询结果,搜索用时 0 毫秒
1.
The diffusion-segregation boron distribution in the silicon dioxide-silicon system upon oxidation in different environments is studied by secondary-ion mass spectrometry and numerical simulation. The coefficient of boron segregation at the SiO2/Si interface and the enhancement of boron diffusion in silicon as functions of the type of oxidizing environment (dry oxygen, wet oxygen, and the presence of hydrochloric acid vapor), the orientation of the silicon surface, and the temperature of oxidizing annealing are obtained. A qualitative model is proposed based on the assumption that the segregation mass transfer of boron through the SiO2/Si interface is associated with the generation of nonequilibrium intrinsic interstitials. 相似文献
2.
I. A. Zyryanova L. V. Baikalova O. A. Tarasova A. V. Afonin V. A. Kukhareva M. A. Maksimova B. A. Trofimov 《Russian Journal of General Chemistry》2005,75(8):1283-1289
With respect to Co2+, Ni2+, Zn2+,Cd2+, Cu2+, Pd2+, and Sn4+ salts, 1-isopropenyl-substituted imidazole, 2-methylimidazole, and pyrazole behave as monodentate ligands with only one coordination center on the N1 and N2 atoms, respectively; 1-isopropenylpyrazole under complex-formation conditions is dealkylated to form pyrazole complexes. The reaction with HCl leaves the unsaturated substituent in 1-isopropenylimidazole intact and yields corresponding hydrochlorides by the N3 atom of the heterocycle. The least basic 1-isopropenylpyrazole takes up HCl also by the double bond of the alkenyl group. 相似文献
3.
Reaction of benzothiazole-2-thione and benzothiazole-2-one with acetylene in the presence of potassium hydroxide or cadmium acetate gives 2-vinylthiobenzothiazole and 3-vinylbenzothiazol-2-one, respectively. Benzothiazole-2-thione is partially convened to benzothiazol-2-one by the action of Cd(OAc)2. Under vinylation conditions the latter also forms 2-vinylthioaniline.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 270–271, February, 1991. 相似文献
4.
Powder X-ray diffraction study of sodium salts of 1-hydroxyethane-1'1-diphosphonic acid (H4L)of the compositions NaH3L·H2O, Na2H2L·4H2O, Na3HL·5.5H2O showed that these compounds aresingle-phase. Some of their properties were determined. The possibility of preparing salts of other compositionswas examined. 相似文献
5.
N. A. Nedolya N. P. Papsheva A. V. Afonin B. A. Trofimov 《Russian Chemical Bulletin》1990,39(8):1724-1725
Previously unreported N,N-bis(2-vlnyloxyethyl)carbodiimide was synthesized by the reaction of N,N -bis(2-vinyloxyethyl)thiourea with yellow mercuric oxide in CH2Cl2 at room temperature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1897–1898, August, 1990. 相似文献
6.
Baikalova L. V. Zyryanova I. A. Tarasova O. A. Chipanina N. N. Shmidt E. Yu. Kashik T. V. Afonin A. V. Sinegovskaya L. M. Vashchenko A. V. Trofimov B. A. 《Russian Journal of General Chemistry》2003,73(10):1634-1640
1-Allenylpyrazole and 1-allenyl-1,2,4-triazole react with hydrogen chloride via proton addition at the pyridine-like nitrogen atom (N2 and N4, respectively). In the reaction with 1-allenylpyrazole, 1-[(E)-3-chloro-1-propenyl]pyrazole is also formed via regio- and stereoselective addition of hydrogen chloride to the propadienyl group. 1-Allenylpyrazole and 1-allenyl-1,2,4-triazole act as unidentate ligands with respect to Co, Ni, Cu, Zn, Cd, Pd, and Sn, the donor centers being N2 and N4, respectively. Apart from mononuclear coordination compounds, 1-allenylpyrazole gives rise to polymeric complexes which contain units and blocks formed by the free ligand. 相似文献
7.
A. V. Afonin 《Russian Chemical Bulletin》1991,40(6):1282-1285
1H and13C NMR spectroscopy indicates the low efficiency of specific intramolecular C-H...Hal (Hal=F, Cl, Br) interactions in comparison with analogous C-H...Y (Y=N, O, S) interactions despite their formal similarity. This is seen in the absence of anomalous downfield PMR shifts of the hydrogen atom and increase in the corresponding direct13C-1H coupling.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1442–1446, June, 1991. 相似文献
8.
A. V. Afonin M. A. Andriyankov M. V. Nikitin Z. M. Garashchenko M. Ya. Khil'ko 《Chemistry of Heterocyclic Compounds》1991,27(8):863-866
A weak hydrogen bond with the participation of the vinyl group -hydrogen atom arises in 2-vinyloxypyridine and 2-vinylthiopyridine, which primarily exist in the s-trans-conformation, according to the 1H and 13C NMR data. This interaction does not take place in 2-vinyloxymethyl- and 2-vinyloxyethylpyridines, which primarily exist in the s-cis-conformation. The C-H...N intramolecular interaction also does not occur in o-vinyloxyaniline due to the specific features of the stereoelectronic state of the amino group nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1077–1081, August, 1991. 相似文献
9.
10.
Solid state (19)F NMR revealed the conformation and alignment of the fusogenic peptide sequence B18 from the sea urchin fertilization protein bindin embedded in flat phospholipid bilayers. Single (19)F labels were introduced into nine distinct positions along the wild-type sequence by substituting each hydrophobic amino acid, one by one, with L-4-fluorophenylglycine. Their anisotropic chemical shifts were measured in uniaxially oriented membrane samples and used as orientational constraints to model the peptide structure in the membrane-bound state. Previous (1)H NMR studies of B18 in 30% TFE and in detergent micelles had shown that the peptide structure consists of two alpha-helical segments that are connected by a flexible hinge. This helix-break-helix motif was confirmed here by the solid-state (19)F NMR data, while no other secondary structure (beta-sheet, 3(10)-helix) was compatible with the set of orientational constraints. For both alpha-helical segments we found that the helical conformation extends all the way to the respective N- and C-termini of the peptide. Analysis of the corresponding tilt and azimuthal rotation angles showed that the N-terminal helix of B18 is immersed obliquely into the bilayer (at a tilt angle tau approximately 54 degrees), whereas the C-terminus is peripherally aligned (tau approximately 91 degrees). The azimuthal orientation of the two segments is consistent with the amphiphilic distribution of side-chains. The observed 'boomerang'-like mode of insertion into the membrane may thus explain how peptide binding leads to lipid dehydration and acyl chain perturbation as a prerequisite for bilayer fusion to occur. 相似文献