全文获取类型
收费全文 | 2384篇 |
免费 | 62篇 |
国内免费 | 8篇 |
专业分类
化学 | 1554篇 |
晶体学 | 42篇 |
力学 | 86篇 |
数学 | 567篇 |
物理学 | 205篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 61篇 |
2020年 | 40篇 |
2019年 | 43篇 |
2018年 | 30篇 |
2017年 | 21篇 |
2016年 | 62篇 |
2015年 | 66篇 |
2014年 | 51篇 |
2013年 | 118篇 |
2012年 | 106篇 |
2011年 | 145篇 |
2010年 | 91篇 |
2009年 | 81篇 |
2008年 | 123篇 |
2007年 | 102篇 |
2006年 | 131篇 |
2005年 | 122篇 |
2004年 | 107篇 |
2003年 | 89篇 |
2002年 | 78篇 |
2001年 | 31篇 |
2000年 | 18篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 20篇 |
1996年 | 42篇 |
1995年 | 25篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 21篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 19篇 |
1982年 | 20篇 |
1981年 | 20篇 |
1980年 | 28篇 |
1979年 | 26篇 |
1978年 | 17篇 |
1976年 | 16篇 |
1975年 | 13篇 |
1915年 | 9篇 |
1906年 | 7篇 |
排序方式: 共有2454条查询结果,搜索用时 15 毫秒
991.
Lionello Pogliani Giuseppe Ranieri Luigi Coppola 《Journal of mathematical chemistry》1996,19(1):33-41
In this paper, the performance of a diagrammatic method based on geometric and algebraic considerations is illustrated. This method, based on the particular symmetry of a thermodynamic diagram, allows to obtain the most important thermodynamic expressions of a simple system. In fact, these thermodynamic expressions can be developed with the application of various geometric patterns to the proposed diagram. The particular symmetry of the thermodynamic diagram allows to develop a matrix formulation of the different geometric patterns. This matrix formalism requires that the thermodynamic parameters of the diagram be recast in a vectorial form.On sabbatical leave from November 1995 until October 1996. Address during this period: Centro de Quimica Fisica Molecular, Univerdade Técnica de Lisboa, IST, Av. Rovisco Pais, 1096 Lisboa-Codex, Portugal. 相似文献
992.
Sebastiano Pappalardo Francesco Bottino Luigi Giunta Marek Pietraszkiewicz Jerzy Karpiuk 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(3):387-392
Two calix[4]arenes with four 2-pyridyhnethyl-l-oxide pendant groups at the lower rim have been synthesized, and their Tb(III) and Eu(III) complexes are fluorescent upon UV light excitation at 312 nm. The complexes are not stable in aqueous solution, completely losing their luminescent properties. 相似文献
993.
994.
Mino R. Caira Luigi R. Nassimbeni Janet L. Scott Fumio Toda 《Journal of chemical crystallography》1994,24(8):495-501
The crystal structures and thermal analyses of the host compound, N,N,N,N-tetraisopropylfumaride, witho-cresol,m-cresol and water are reported and compared to that of thep-cresol complex previously reported in an attempt to elucidate the reasons for host selectivity. 相似文献
995.
Summary Some examples of classes of conditional equations coming from information theory, geometry and from the social and behavioral sciences are presented. Then the classical case of the Cauchy equation on a restricted domain is extensively discussed. Some results concerning the extension of local homomorphisms and the implication -additivity implies global additivity are illustrated. Problems concerning the equations[cf(x + y) – af(x) – bf(y) – d][f(x + y) – f(x – f(y)] = 0[g(x + y) – g(x) – g(y)][f(x + y) – f(x) – f(y)] = 0f(x + y) – f(x) – f(y) V (a suitable subset of the range) are presented.The consideration of the conditional Cauchy equation is subsequently focused on the case when it makes sense to interpret as a binary relation (orthogonality):f: (X, +, ) (Y, +);f(x + z) = f(x) + f(z) (x, z Z; x z). A brief sketch on solutions under regularity conditions is given. It is then shown that all regularity conditions can be removed. Finally, several applications (also to physics and to the actuarial sciences) are discussed. In all these cases the attention is focused on open problems and possible extensions of previous results. 相似文献
996.
A Zinc(II)-Driven Intramolecular Photoinduced Electron Transfer 总被引:1,自引:0,他引:1
997.
The standard interpretation of quantum physics (QP) and some recent generalizations of this theory rest on the adoption of a rerificationist theory of truth and meaning, while most proposals for modifying and interpreting QP in a realistic way attribute an ontological status to theoretical physical entities (ontological realism). Both terms of this dichotomy are criticizable, and many quantum paradoxes can be attributed to it. We discuss a new viewpoint in this paper (semantic realism, or briefly SR), which applies both to classical physics (CP) and to QP. and is characterized by the attempt of giving up verificationism without adopting ontological realism. As a first step, we construct a formalized observative language L endowed with a correspondence truth theory. Then, we state a set of axioms by means of L which hold both in CP and in QP. and construct a further language Lv which can express bothtestable andtheoretical properties of a given physical system. The concepts ofmeaning andtestability do not collapse in L and Le hence we can distinguish between semantic and pragmatic compatibility of physical properties and define the concepts of testability and conjoint testability of statements of L and Le. In this context a new metatheoretical principle (MGP) is stated, which limits the validity of empirical physical laws. By applying SR (in particular. MGP) to QP, one can interpret quantum logic as a theory of testability in QP, show that QP is semantically incomplete, and invalidate the widespread claim that contextuality is unavoidable in QP. Furthermore. SR introduces some changes in the conventional interpretation of ideal measurements and Heisenbergs uncertainty principle. 相似文献
998.
Gavin R. Brown Mino R. Caira Luigi R. Nassimbeni Bosch van Oudtshoorn 《Journal of inclusion phenomena and macrocyclic chemistry》1996,26(4):281-294
Inclusion of the non-steroidal anti-inflammatory drug ibuprofen by permethylated-cyclodextrin (TRIMEB) was investigated by thermal analysis and X-ray diffraction. Reaction between racemic ibuprofen and TRIMEB yielded a mixture of isomorphous crystals of TRIMEB - (R)-ibuprofen and TRIMEB — (S)-ibuprofen. The single crystal chosen for X-ray analysis was found to contain the (S)-isomer of the drug. The crystal is orthorhombic, space groupP212121, witha = 15. 232(7) Å,b = 21.327(7) Å,c = 27.597(7) Å andZ = 4. The structure was solved using the coordinates for the rigid portion of the cyclodextrin molecule of the isomorphous complex with (S)-naproxen. Refinement by full-matrix least-squares techniques gave a finalR factor of 0.079 for 7473 unique observed reflections. The isobutyl group of (S)-ibuprofen is included in the cyclodextrin cavity through hydrophobic forces, with the propionic acid group protruding from theO(2),O(3) face. The lack of chiral discrimination of the host TRIMEB towards ibuprofen as guest was confirmed by a combination of X-ray diffraction methods, thermal analysis and polarimetry. 相似文献
999.
Nardi L 《Journal of chromatography. A》2003,985(1-2):93-98
Capillary extractors are proposed as samplers-preconcentrators to overcome losses of volatile organic compounds found using "classical" solid-phase microextraction fiber-holder samplers. A set of equal-size extractors was used to extract in-tube an aqueous solution of benzene, toluene, ethylbenzene and xylenes (BTEX) at 146 ppb. After storage for 6-30 days at 0-4 degrees C (or -15 degrees C) GC analyses were carried out to study BTEX recovery. Results demonstrated that sample preservation was very good: recovery was higher than 98% after 6 days, and more than 95% after 30 days. Capillary extractors, due to their high performance in preserving sample integrity, represent a real breakthrough for on-site sampling of volatile compounds by solid-phase pre-concentration techniques. 相似文献
1000.
Luigi Turrio-Baldassarri Alessandro di Domenico Annarita Fulgenzi Cinzia La Rocca Nicola Iacovella Fabrizio Rodriguez Fabrizio Volpi 《Mikrochimica acta》1996,123(1-4):45-53
The use of isotopically labeled internal standards in the analysis of organic microcontaminants entails the determination of relative response factors (RRFs) of the unlabeled with respect to the labeled compounds. RRFs were measured daily during 28 replicate polychlorobiphenyl (PCB) analyses on two different sets of samples. Daily RRFs allowed more precise results to be attained than those provided by mean RRFs, the latter being the mean of all the daily RRFs obtained during the same series of analyses. Analytical applications to food matrices are presented, including the PCB contamination profile of an olive oil and that found in a matrix of Italian national mean diet. Based on the latter sample, also the polycyclic aromatic hydrocarbon (PAH) daily intake of Italians is assessed. Seven PAHs are determined. 相似文献