全文获取类型
收费全文 | 2462篇 |
免费 | 53篇 |
国内免费 | 11篇 |
专业分类
化学 | 1840篇 |
晶体学 | 9篇 |
力学 | 61篇 |
数学 | 320篇 |
物理学 | 296篇 |
出版年
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 25篇 |
2018年 | 24篇 |
2016年 | 34篇 |
2015年 | 36篇 |
2014年 | 38篇 |
2013年 | 141篇 |
2012年 | 115篇 |
2011年 | 108篇 |
2010年 | 87篇 |
2009年 | 89篇 |
2008年 | 103篇 |
2007年 | 111篇 |
2006年 | 117篇 |
2005年 | 122篇 |
2004年 | 105篇 |
2003年 | 100篇 |
2002年 | 95篇 |
2001年 | 39篇 |
2000年 | 42篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 31篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 34篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 31篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1985年 | 37篇 |
1984年 | 43篇 |
1983年 | 27篇 |
1982年 | 39篇 |
1981年 | 35篇 |
1980年 | 46篇 |
1979年 | 42篇 |
1978年 | 52篇 |
1977年 | 38篇 |
1976年 | 32篇 |
1975年 | 36篇 |
1974年 | 36篇 |
1973年 | 37篇 |
1972年 | 15篇 |
1966年 | 13篇 |
排序方式: 共有2526条查询结果,搜索用时 15 毫秒
981.
利用超简谐振动近似的有效二阶微扰法(VPT2)和变异微扰法(VCI-P)两种静态方法,以及在300和600K下的密度泛函分子动态轨线振动分析方法进行量子力学的振动计算. 比较了这四种方法对于基频跃迁频率和对应的中红外光谱在相同的B3LYP/6-31+G(d,p)基组描述电子结构前提下所得到的计算结果. 总结了对于半刚性和柔性分子的主要结果,并且对这些计算方法的优缺点进行了比较. 相似文献
982.
Didjour Albert Kambir Jean Brice Boti Ahmont Claude Landry Kablan Daouda Ballo Mathieu Paoli Virginie Brunini Flix Tomi 《Molecules (Basel, Switzerland)》2021,26(20)
The chemical variability and the in vitro anti-inflammatory activity of the leaf essential oil from Ivorian Isolona dewevrei were investigated for the first time. Forty-seven oil samples were analyzed using a combination of CC, GC(RI), GC-MS and 13C-NMR, thus leading to the identification of 113 constituents (90.8–98.9%). As the main components varied drastically from sample to sample, the 47 oil compositions were submitted to hierarchical cluster and principal components analyses. Three distinct groups, each divided into two subgroups, were evidenced. Subgroup I−A was dominated by (Z)-β-ocimene, β-eudesmol, germacrene D and (E)-β-ocimene, while (10βH)-1β,8β-oxido-cadina-4-ene, santalenone, trans-α-bergamotene and trans-β-bergamotene were the main compounds of Subgroup I−B. The prevalent constituents of Subgroup II−A were germacrene B, (E)-β-caryophyllene, (5αH,10βMe)-6,12-oxido-elema-1,3,6,11(12)-tetraene and γ-elemene. Subgroup II−B displayed germacrene B, germacrene D and (Z)-β-ocimene as the majority compounds. Germacrene D was the most abundant constituent of Group III, followed in Subgroup III−A by (E)-β-caryophyllene, (10βH)-1β,8β-oxido-cadina-4-ene, germacrene D-8-one, and then in Subgroup III−B by (Z)-β-ocimene and (E)-β-ocimene. The observed qualitative and quantitative chemical variability was probably due to combined factors, mostly phenology and season, then harvest site to a lesser extent. The lipoxygenase inhibition by a leaf oil sample was also evaluated. The oil IC50 (0.020 ± 0.005 mg/mL) was slightly higher than the non-competitive lipoxygenase inhibitor NDGA IC50 (0.013 ± 0.003 mg/mL), suggesting a significant in vitro anti-inflammatory potential. 相似文献
983.
984.
985.
986.
Annette Thierry Cyril Mathieu Christine Straup Jean‐Claude Wittmann Bernard Lotz Victor Da Costa Jacques Le Moigne 《Macromolecular Symposia》2001,166(1):43-58
Control of structural order at the molecular level for both conventional linear polymers and conjugated polymers with valuable opto‐electronic properties has major consequence on the macroscopic properties of these polymers. Though the traditional means of orientation of polymer was mechanical deformation, presently extensive works are concerned with a more controlled way of orientation: epitaxial crystallisation. Most of the first documented examples of epitaxial growth of conventional polymers on single crystals followed the well‐established geometrical rules of best matching. However, recent examples show off more subtle rules of selection. Analogous cases, following or breaking the matching rules, have been observed for diacetylenes ordered via epipolymerisation on single crystals. Hereafter, representative examples of the structural matching rules are depicted first, and then recent examples, which depart from the simple geometrical fitting, are described. The analysis of the former leads to define the subtle matching rules applying for polymers linked to their conformational adaptability. The analysis of the latter gives the opportunity to discuss the relative influence of geometrical and molecular interactions between the deposit and the substrate. 相似文献
987.
Gilles Tiraboschi Nohad Gresh Claude Giessner‐Prettre Lee G. Pedersen David W. Deerfield 《Journal of computational chemistry》2000,21(12):1011-1039
In this study we compare the binding energies of polycoordinated complexes of Zn2+ within cavities composed of model “hard” (H2O, OH−) or “soft” (CH3SH, CH3S−) ligands. Ab initio supermolecule computations are performed at the HF and MP2 levels using extended basis sets to determine the binding energies and their components as a function of: the number of ligands, ranging from three to six; the net charge of the cavity; and the “hard” versus “soft” character of the ligands. These ab initio computations are used to test the reliability of the SIBFA molecular mechanics procedure, originally formulated and calibrated on the basis of ab initio computations, for such charged systems. The SIBFA intermolecular interaction energies match the corresponding ab initio values using a coreless effective potential split‐valence basis set with a relative error of ≤3%. Extensions to binuclear Zn2+ complexes, such as those that occur in the Zn‐binding sites of Gal4 and β‐lactamase proteins, are performed to test the applicability of the methodology for such systems. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1011–1039, 2000 相似文献
988.
Anne Veyland Laurent Dupont Jean Rimbault Jean‐Claude Pierrard Michel Aplincourt 《Helvetica chimica acta》2000,83(2):414-427
The interactions between carbonate ions and zirconium oxychloride are studied by potentiometry, dialysis, and 13C‐ and 17O‐NMR spectroscopy in aqueous media. The nature of the soluble carbonatohydroxo complexes depends on the proportions of hydrogencarbonate and carbonate ions in solution before the addition of zirconium oxychloride. Carbonate media lead to polynuclear entities containing no more than two complexed carbonate ions per Zr4+. The presence of hydrogencarbonate favors the formation of less condensed and more carbonated complexes such as [Zr(CO3)4]4−. The polycondensation degree of the species decreases when the number of carbonates linked per Zr4+ increases. In all complexes, the carbonate is bidentate, and the metal atoms are linked via hydroxo bridges. The complexation of carbonate with Zr4+ occurs for a total carbonate concentration higher than 0.1M . Consequently, in natural medium, the speciation of this metal is governed only by the formation of hydroxo complexes. 相似文献
989.
Lise Negrel Raymonde Baltenweck Gerard Demangeat Franoise Le Bohec-Dorner Camille Rustenholz Amandine Velt Claude Gertz Eva Bieler Markus Dürrenberger Pascale Gombault Philippe Hugueney Olivier Lemaire 《Molecules (Basel, Switzerland)》2022,27(10)
The grapevine fanleaf virus (GFLV), responsible for fanleaf degeneration, is spread in vineyards by the soil nematode Xiphinema index. Nematicide molecules were used to limit the spread of the disease until they were banned due to negative environmental impacts. Therefore, there is a growing interest in alternative methods, including plant-derived products with antagonistic effects to X. index. In this work, we evaluated the nematicidal potential of the aerial parts and roots of four Fabaceae: sainfoin (Onobrychis viciifolia), birdsfoot trefoil (Lotus corniculatus), sweet clover (Melilotus albus), and red clover (Trifolium pratense), as well as that of sainfoin-based commercial pellets. For all tested plants, either aerial or root parts, or both of them, exhibited a nematicidal effect on X. index in vitro, pellets being as effective as freshly harvested plants. Comparative metabolomic analyses did not reveal molecules or molecule families specifically associated with antagonistic properties toward X. index, suggesting that the nematicidal effect is the result of a combination of different molecules rather than associated with a single compound. Finally, scanning electron microscope observations did not reveal the visible impact of O. viciifolia extract on X. index cuticle, suggesting that alteration of the cuticle may not be the primary cause of their nematicidal effect. 相似文献
990.