全文获取类型
收费全文 | 1925篇 |
免费 | 36篇 |
国内免费 | 2篇 |
专业分类
化学 | 1469篇 |
晶体学 | 18篇 |
力学 | 36篇 |
数学 | 126篇 |
物理学 | 314篇 |
出版年
2023年 | 10篇 |
2022年 | 76篇 |
2021年 | 67篇 |
2020年 | 45篇 |
2019年 | 74篇 |
2018年 | 66篇 |
2017年 | 65篇 |
2016年 | 76篇 |
2015年 | 57篇 |
2014年 | 62篇 |
2013年 | 123篇 |
2012年 | 96篇 |
2011年 | 113篇 |
2010年 | 76篇 |
2009年 | 77篇 |
2008年 | 100篇 |
2007年 | 69篇 |
2006年 | 71篇 |
2005年 | 68篇 |
2004年 | 35篇 |
2003年 | 43篇 |
2002年 | 48篇 |
2001年 | 31篇 |
2000年 | 23篇 |
1999年 | 27篇 |
1998年 | 25篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1991年 | 12篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 23篇 |
1972年 | 11篇 |
1970年 | 14篇 |
1969年 | 8篇 |
1967年 | 7篇 |
排序方式: 共有1963条查询结果,搜索用时 0 毫秒
11.
E. V. Petrova T. I. Izaak D. A. Filonenko A. P. Astashkina V. I. Otmakhov G. G. Volokitin 《Colloid Journal》2007,69(6):777-781
Peculiarities of the extraction of metal ions from aqueous solutions by fibrous polypropylene have been investigated. It has been found that metal ion adsorption proceeds owing to the existence of a gas-liquid-hydrophobic polymer boundary line. The process mechanism has been discussed. 相似文献
12.
13.
14.
Three new Ni(BDC)/2,2'-bipy compounds, Ni2(BDC)(HBDC)2(2,2'-bipy)2 (2), Ni3(BDC)3(2,2'-bipy)2 (3), and Ni(BDC)(2,2-bipy)2.2H2O (5), in addition to the previously reported Ni(BDC)(2,2'-bipy).0.75H2BDC (1) and Ni(BDC)(2,2'-bipy)(H2O) (4) [BDC = 1,4-benzenedicarboxylate; 2,2'-bipy = 2,2'-bipyridine], have been synthesized by hydrothermal reactions. A systematic investigation of the effect of the reaction temperature and pH resulted in a series of compounds with different compositions and dimensionality. The diverse product slate illustrates the marked sensitivity of the structural chemistry of polycarboxylate aromatic ligands to synthesis conditions. Compound 1, which has a channel structure containing guest H2BDC molecules, is formed at the lowest pH. The guest H2BDC molecules are connected by hydrogen bonds and form extended chains. At a slightly higher pH, a dimeric molecular compound 2 is formed with a lower number of protonated carboxylate groups per nickel atom and per BDC ligand. Reactions at higher temperature and the same pH lead to the transformation of 1 and 2 into the two-dimensional, layered trinuclear compound 3. As the pH is increased, a one-dimensional polymer 4 is formed with a water molecule coordinated to Ni2+. Bis-monodentate and bischelating BDC ligands alternate along the chain to give a crankshaft rather than a regular zigzag arrangement. A further increase of the pH leads to the one-dimensional chain compound 5, which has two chelating 2,2'-bipy ligands. Crystal data: 2, triclinic, space group P, a = 7.4896(9) angstroms, b = 9.912(1) angstroms, c = 13.508(2) angstroms, alpha = 86.390(2) degrees , beta = 75.825(2) degrees, gamma = 79.612(2) degrees, Z = 2; 3, orthorhombic, space group Pbca, a = 9.626(2) angstroms, b = 17.980(3) angstroms, c = 25.131(5) angstroms, Z = 4; 5, orthorhombic, space group Pbcn, a = 14.266(2) angstroms, b = 10.692(2) angstroms, c = 17.171(2) angstroms, Z = 8. 相似文献
15.
V. N. Charushin G. M. Petrova G. G. Aleksandrov L. G. Egorova A. I. Chernishev E. O. Sidorov N. A. Klyuev O. N. Chupakhin 《Chemistry of Heterocyclic Compounds》1987,23(4):426-435
Dibenzo[d,k]-1,3,6,10-tetraazatetracyclo[7.3.1.02,7.06,13]trideca-4,11-dienes undergo addition reactions at the C(2) carbon atom with alcohols and thiols, accompanied by cleavage of the C-N bond of the imidazoline ring, to generate diquinoxalino[1,2-a2,3-d]pyrrole derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 513–522, April, 1987. 相似文献
16.
A. V. Kashevskii M. A. Mamalyga T. L. Petrova A. Yu. Safronov V. N. Kizhnyaev 《Russian Journal of Applied Chemistry》2007,80(2):316-321
Copolymers of 1-vinyl-1,2,4-triazole and 5-vinyltetrazole with 1,1,5-trihydrooctafluoropentyl methacrylate and 1,1,7-trihydrododecafluoroheptyl methacrylate were prepared under the conditions of radical initiation. These copolymers were used for modification of the surface of a glassy carbon electrode, and the effect of the modification on the electrochemical behavior of the electrode in anodic oxidation of dopamine and NO was studied. The possibility of enhancing the selectivity of the electrochemical sensor for monitoring NO in biological media was demonstrated. 相似文献
17.
The formation of negative hydrogen ions in a conventional hollow cathode discharge has been investigated. A mixture of Ne and H2 proved to be more advantageous compared to pure hydrogen. The study has been performed by solving the electron Boltzmann equation, coupled with a system of balance equations for neon and hydrogen neutral and charged particles. The vibrational distribution function of hydrogen has been calculated. Our calculations show unusually high population of vibrationally excited hydrogen molecules in a Ne–H2 mixture, which explains the high density of negative hydrogen ions under optimal conditions (total gas pressure of few Torr, hydrogen number mole fraction of 1–10% and discharge current of 10–100 mA). Line intensities originating from highly excited neon states vs. hydrogen pressure have been calculated and a comparison with existing experimental results has been made. 相似文献
18.
Mangos MM Min KL Viazovkina E Galarneau A Elzagheid MI Parniak MA Damha MJ 《Journal of the American Chemical Society》2003,125(3):654-661
The ability of modified antisense oligonucleotides (AONs) containing acyclic interresidue units to support RNase H-promoted cleavage of complementary RNA is described. Manipulation of the backbone and sugar geometries in these conformationally labile monomers shows great benefits in the enzymatic recognition of the nucleic acid hybrids, while highlighting the importance of local strand conformation on the hydrolytic efficiency of the enzyme more conclusively. Our results demonstrate that the duplexes support remarkably high levels of enzymatic degradation when treated with human RNase HII, making them efficient mimics of the native substrates. Furthermore, interesting linker-dependent modulation of enzymatic activity is observed during in vitro assays, suggesting a potential role for this AON class in an RNase H-dependent pathway of controlling RNA expression. Additionally, the butyl-modified 2'F-ANA AONs described in this work constitute the first examples of a nucleic acid species capable of eliciting high RNase H activity while possessing a highly flexible molecular architecture at predetermined sites along the AON. 相似文献
19.
Nikolina L. Petrova Dimitar S. Todorovsky Veselinka G. Vasileva 《Central European Journal of Chemistry》2005,3(2):263-278
Mn-, LaMn- and LaCaMn-citrates were synthesized at 60–120°C in ethylene glycol medium using chlorides or nitrates as metal
sources. Their composition, IR spectra and thermal decomposition were studied. Equimolar La/Mn ratio has been established
in the complex, prepared from chloride solution with the same initial composition of the metals. In the isolated three-metallic
complex the molar ratio of the metals deviates from the composition in the initial solution. The final products of the heating
of Mn- and mixed-metal LaMn-citrates at 1000°C are phase-homogeneous Mn3O4 (hausmannite) and LaMnO3 respectively. Parasitic phase(s) are observed in LaxCa1−xMnyO3, produced from LaCaMn-citrate. 相似文献
20.
Single crystals of two structural modifications of high-temperature dysprosium titanate Dy2TiO were grown. Using X-ray diffraction, the crystal structure of the cubic modification (space group Fd3m, a = 10.28(1)Å, Z = 10.4) was refined and the structure of a new monoclinic modification (space group B2/m, a = 10.33(1)Å, b = 3.653(5)Å, c = 7.306(6)Å, β = 90.00(7)°, Z = 2.4), which crystallizes in minor amounts together with the cubic phase, was determined. The lowering of symmetry from cubic to monoclinic is due to different distributions of the Dy3+ and Ti4+ cations over the sites present in the cubic cell. 相似文献