全文获取类型
收费全文 | 2753篇 |
免费 | 102篇 |
国内免费 | 18篇 |
专业分类
化学 | 1824篇 |
晶体学 | 12篇 |
力学 | 53篇 |
数学 | 514篇 |
物理学 | 470篇 |
出版年
2023年 | 25篇 |
2022年 | 26篇 |
2021年 | 77篇 |
2020年 | 80篇 |
2019年 | 65篇 |
2018年 | 60篇 |
2017年 | 61篇 |
2016年 | 115篇 |
2015年 | 88篇 |
2014年 | 93篇 |
2013年 | 222篇 |
2012年 | 234篇 |
2011年 | 242篇 |
2010年 | 130篇 |
2009年 | 118篇 |
2008年 | 170篇 |
2007年 | 166篇 |
2006年 | 160篇 |
2005年 | 116篇 |
2004年 | 107篇 |
2003年 | 83篇 |
2002年 | 78篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 32篇 |
1998年 | 18篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 7篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有2873条查询结果,搜索用时 15 毫秒
971.
Regina Cisternas Eduardo Mu?oz Rodrigo Henr��quez Ricardo C��rdova Heike Kahlert Ulrich Hasse Fritz Scholz 《Journal of Solid State Electrochemistry》2011,15(11-12):2461-2468
Prussian blue (PB) can be deposited from colloidal solutions (5.4?×?10?3?molPB?L?1, 0.01?mol?L?1 KNO3) on glassy carbon, either by potential cycling or potentiostatically, provided that the deposition potential is more positive than ?0.2?V vs. Hg/Hg2Cl2. Depending on the deposition potential, the PB particles form either a single layer of Everitt??s salt, of PB, or multilayers of Berlin green. Also depending on the electrode potential, the deposition was accompanied by currents which were either only of capacitive nature, or represent the sum of capacitive and faradaic currents. The currents were always limited by the diffusion of the colloidal particles to the electrode surface, i.e., they obeyed the Cottrell equation. The PB layers were characterized by in situ atomic force microscopy. 相似文献
972.
Sen SS Hey J Eckhardt M Herbst-Irmer R Maedl E Mata RA Roesky HW Scheer M Stalke D 《Angewandte Chemie (International ed. in English)》2011,50(52):12510-12513
Don't count on counterions: The cyclic five-membered CSi(3)P cation 1 is synthesized in the reaction of benzamidinato-stabilized chlorosilylene and methyl phosphaalkyne. The presence of four π?electrons in 1 means it can be considered as a formal, heavier analogue of the cyclopentadienyl cation. Surprisingly the small counteranion (Cl(-)) does not contribute to the ring stability. 相似文献
973.
Bargueño P Pérez de Tudela R Miret-Artés S Gonzalo I 《Physical chemistry chemical physics : PCCP》2011,13(3):806-810
Interactions which do not conserve parity might influence chiral compounds giving rise to a parity violating energy difference (PVED) that might have affected the evolution towards homochirality. However, this tiny effect predicted by electroweak-quantum chemistry calculations is easily masked by thermal effects, making it desirable to reach cold regimes in the laboratory. As an alternative route to the detection of the PVED, we study a simplified model of Bose-Einstein condensation of a sample of non-interacting chiral molecules, showing that it leads to a nonzero optical activity of the condensate and also to a subcritical temperature in the heat capacity, due to the internal structure of the molecule characterized by tunneling and parity violation. This predicted singular behavior found for the specific heat, below the condensation temperature, might shed some light on the existence of the thus far elusive PVED between enantiomers. 相似文献
974.
Modelling of disorder in organic crystals is highly desirable since it would allow thermodynamic stabilities and other disorder-sensitive properties to be estimated for such systems. Two disordered organic molecular systems are modeled using a symmetry-adapted ensemble approach, in which the disordered system is treated as an ensemble of the configurations of a supercell with respect to substitution of one disorder component for another. Computation time is kept manageable by performing calculations only on the symmetrically inequivalent configurations. Calculations are presented on a substitutionally disordered system, the dichloro/dibromobenzene solid solution, and on an orientationally disordered system, eniluracil, and the resultant free energies, disorder patterns, and system properties are discussed. The results are found to be in agreement with experiment, when some physically implausible configurations are removed from the ensemble average for eniluracil, highlighting the dangers of a completely automated approach to organic crystal thermodynamics which ignores the barriers to equilibration once the crystal has been formed. 相似文献
975.
We have devised a protocol for enzyme-free insertion of dehydroalanine, dehydrobutyrine and thioether crosslinks into translated peptides. In vitro translation using 4-selenalysine and 4-selenoisoleucine as substitutes for lysine and isoleucine yields peptides that can be converted to polycyclic structures using mild chemistry in water. This methodology presents a gateway for exploring the potential of artificial lantipeptides as scaffolds for drug development. 相似文献
976.
Sousa A Casal S Bento A Malheiro R Oliveira MB Pereira JA 《Molecules (Basel, Switzerland)》2011,16(11):9025-9040
Commercial stoned table olives named "alcaparras" from Trás-os-Montes (Portugal) were chemically characterized. During three consecutive years (2004-2006) 30 samples (10 per year) were examined for their nutritional value (moisture, crude protein, total fat, ash, carbohydrates, and energy), with a detailed report of the fatty acids and tocopherols composition. Water was the major constituent (72.5 ± 5.5%), followed by fat (14.6 ± 5.1%). The average amount of protein and ash were 1.1% and 3.4%, respectively, reporting unusual ash values for table olives, related to the technological process. One hundred grams of fresh stoned table olives presented an average energetic value of 156 kcal, lower than most table olives. The lipids are rich in oleic acid (average of 77.7 ± 2.0%), followed by palmitic acid and linoleic acid. Samples showed an average of total tocopherols of 1.2 mg/100 g of fresh weight, being α-tocopherol the most abundant. Table olives are important sources of MUFA, as olive oil, recognized as a preventive factor in diseases in which free radicals are implicated, complemented by the amounts of vitamin E, with both antioxidant and vitamin action. 相似文献
977.
978.
Blois Lucca Neto Albano N. Carneiro Longo Ricardo L. Costa Israel F. Paolini Tiago B. Brito Hermi F. Malta Oscar L. 《Optics and Spectroscopy》2022,130(1):10-17
Optics and Spectroscopy - Eu3+ complexes and specially β-diketonate compounds are well known and studied in several areas due to their luminescence properties, such as sensors and lightning... 相似文献
979.
Oliveira SR Nogueira LJ Augusti R Stoianoff MA Aguilar CM Rocha WR Donnici CL 《Rapid communications in mass spectrometry : RCM》2012,26(3):377-384
Sodium adducts of six organosulfur‐α,ω‐ditetrazole compounds (Tz‐(CH2)n‐S(O)m‐(CH2)n‐Tz; where Tz = tetrazole ring; n = 2, 3; m = 0, 1, 2) were generated via electrospray ionization (ESI) and their fragmentation pattern assessed via collision‐induced dissociation (CID). Two main dissociation channels were observed: (a) losses of N2 and HN3 from the tetrazole rings; (b) cleavage of the C–S bond. The sulfoxides pass predominantly through the second fragmentation pathway, but for the sulfides and sulfones the tetrazole ring fragmentation occurs. Theoretical calculations at the B3LYP/6‐31 + G(d,p) level indicate that for all the adducts (sulfide, sulfoxide, and sulfone) the dissociation pathway that leads to product ions arising from loss of N2 was the most exothermic. Based on these results and assumptions, it was postulated that the dissociation of the sulfoxide adducts occurs under kinetic control (N2‐loss pathway via a much more energetic transition state). For the sulfide and sulfone adducts, on the other hand, the dissociation process takes place via a thermodynamically controlled process. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
980.
Gabriela C. Tavares Maria Elisa S. R. Silva Ricardo G. Sousa Roberto F. S. Freitas 《Macromolecular Symposia》2012,319(1):10-14
Summary: In this work, the use of a temperature-sensitive polymer gel, poly(N-isopropylacrylamide), for the concentration of whey proteins was studied. The studied variables were: gel mass/solution volume ratio and concentration temperature. The concentration percentage and the selectivity were determined. The gel 20 × 5 (20% w/w total monomer/solution and 5% w/w crosslinking agent/total monomer), contacted with whey proteins solutions, at 5 °C and at 20 °C, was capable of concentrating the solution, in protein, from 10 to 33%, depending on the gel mass/solution volume ratio. The separation efficiencies, for the different studied systems, varied from around 40 to 80%. The results were discussed in the context of gels thermodynamics and through correlations between synthesis parameters and structure of the obtained gels. The obtained results for the concentration of whey proteins solutions, by using temperature-sensitive polymer gel, poly(N-isopropylacrylamide), showed that the Gel Process can indeed be used as an advantageous alternative for such separation, either from an economic or from an environmental view point. 相似文献