全文获取类型
收费全文 | 14908篇 |
免费 | 556篇 |
国内免费 | 6篇 |
专业分类
化学 | 10955篇 |
晶体学 | 87篇 |
力学 | 266篇 |
数学 | 2027篇 |
物理学 | 2135篇 |
出版年
2023年 | 119篇 |
2022年 | 76篇 |
2021年 | 131篇 |
2020年 | 211篇 |
2019年 | 239篇 |
2018年 | 215篇 |
2017年 | 223篇 |
2016年 | 511篇 |
2015年 | 465篇 |
2014年 | 498篇 |
2013年 | 953篇 |
2012年 | 1141篇 |
2011年 | 1234篇 |
2010年 | 667篇 |
2009年 | 512篇 |
2008年 | 1078篇 |
2007年 | 1057篇 |
2006年 | 958篇 |
2005年 | 907篇 |
2004年 | 744篇 |
2003年 | 614篇 |
2002年 | 529篇 |
2001年 | 194篇 |
2000年 | 178篇 |
1999年 | 113篇 |
1998年 | 93篇 |
1997年 | 89篇 |
1996年 | 135篇 |
1995年 | 83篇 |
1994年 | 70篇 |
1993年 | 94篇 |
1992年 | 78篇 |
1991年 | 60篇 |
1990年 | 53篇 |
1989年 | 45篇 |
1988年 | 46篇 |
1987年 | 44篇 |
1986年 | 65篇 |
1985年 | 93篇 |
1984年 | 80篇 |
1983年 | 48篇 |
1982年 | 71篇 |
1981年 | 74篇 |
1980年 | 72篇 |
1979年 | 55篇 |
1978年 | 54篇 |
1977年 | 41篇 |
1976年 | 49篇 |
1975年 | 28篇 |
1974年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
Fernandes-Ferreira M. Pais M. Salomé S. Novais J. M. 《Applied biochemistry and biotechnology》1991,28(1):169-181
Applied Biochemistry and Biotechnology - Micropropagated Euphorbia characias plants gave higher yields of crude oil than did wild ones. Leaves of either wild and micropropagated plants contained... 相似文献
42.
Margarita Valero Silvia M. B. Costa José R. Ascenso M. Mercedes Velázquez Licesio J. Rodríguez 《Journal of inclusion phenomena and macrocyclic chemistry》1999,35(4):663-677
The inclusion of the anti-inflammatory drug, Nabumetone, in -, - and hydroxypropyl--cyclodextrin (CDs) is studied using UV-VIS absorption and steady-state fluorescence emission. Binding constants and thermodynamic parameters of complex formation are determined by spectrofluorimetry. The inclusion phenomena of Nabumetone with the three cyclodextrins is compared with that of the well known similar anti-inflammatory drug Naproxen. In the case of Nabumetone pronounced differences are observed in the complexation process with each cyclodextrin whereas the respective Naproxen complexes are nearly identical. 1H-NMR experiments show that the inclusion process in Nabumetone can occur either through the substituents in the -2 (butanone) or -6 (methoxy) positions in the naphthalene ring. 相似文献
43.
Reguera Edilso Fernández-Bertrán José Balmaseda Jorge 《Transition Metal Chemistry》1999,24(6):648-654
Evidence in the literature on the synthesis of ferrous ferricyanide is critically discussed. Pyrolysis and pressure effects on Prussian Blue lead to ferrous ferrocyanide together with decomposition by-products, and not to ferrous ferricyanide. The latter compound could be a precursor in the formation of Turnbull's Blue or an excited state of Prussian Blue, but it is not a stable chemical species. 相似文献
44.
We consider an Ising model with Kac potential dK(¦x¦) which may have arbitrary sign, and show, following Gates and Penrose, that the free energy in the classical limit0+ can be obtained from a variational principle. When the Fourier transform of the potential has its maximum atp=0 one recovers the usual mean-field theory of magnetism. When the maximum occurs forp
00, however, one obtains an oscillatory or helicoidal phase in which the magnetization near the critical point oscillates with period 2/¦p
0¦. An example with a potential possessing parameter-dependent oscillations is shown to exhibit crossover phenomena and a multicritical Lifshitz point in the classical limit. 相似文献
45.
46.
The experimental testing of the Lorentz transformations is based on a family of sets of coordinate transformations that do not comply in general with the principle of equivalence of the inertial frames. The Lorentz and Galilean sets of transformations are the only member sets of the family that satisfy this principle. In the neighborhood of regular points of space-time, all members in the family are assumed to comply with local homogeneity of space-time and isotropy of space in at least one free-falling elevator, to be denoted as Robertson'sab initio rest frame [H. P. Robertson,Rev. Mod. Phys.
21, 378 (1949)].Without any further assumptions, it is shown that Robertson's rest frame becomes a preferred frame for all member sets of the Robertson family except for, again, Galilean and Einstein's relativities. If one now assumes the validity of Maxwell-Lorentz electrodynamics in the preferred frame, a different electrodynamics spontaneously emerges for each set of transformations. The flat space-time of relativity retains its relevance, which permits an obvious generalization, in a Robertson context, of Dirac's theory of the electron and Einstein's gravitation. The family of theories thus obtained constitutes a covering theory of relativistic physics.A technique is developed to move back and forth between Einstein's relativity and the different members of the family of theories. It permits great simplifications in the analysis of relativistic experiments with relevant Robertson's subfamilies. It is shown how to adapt the Clifford algebra version of standard physics for use with the covering theory and, in particular, with the covering Dirac theory.Part of this work was done at the Department of Physics, Utah State University, Logan, Utah 84322. 相似文献
47.
The spherical-model limitn of then-vector model in a random field, with either a statistically independent distribution or with long-range correlated random fields, is studied to demonstrate the correctness of the replica method in which then and replica limits limits are interchanged, provided the replica and thermodynamic limits are taken in the right order, in the case of long-range correlated random fields. A scaling form for the two-point correlation function relevant to the first-order phase transition below the lower critical dimensionality of the random system is also obtained. 相似文献
48.
Mazzaglia A Angelini N Lombardo D Micali N Patané S Villari V Scolaro LM 《The journal of physical chemistry. B》2005,109(15):7258-7265
The interaction between the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin (TPPS) and cationic vesicles formed by heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-cyclodextrin (SC6CDNH2) has been investigated in detail through a combination of elastic light scattering (ELS), quasi-elastic light scattering (QELS), zeta potential measurements, and time-resolved fluorescence anisotropy. ELS experiments provided the first structural characterization of these cationic vesicles both in the absence and in the presence of TPPS porphyrin, modeling the system as a spherical particle described by a single thin shell form factor. The structure of mixed hetero-aggregates is modulated by charge and size of the two components as function of different porphyrin/cyclodextrin (CD) molar ratios. At the limiting molar ratio studied, the absolute value of zeta potential (/zeta/ = 12.5 mV) seems to be a reference value for the formation of stable colloidal CD vesicular aggregates at thermodynamic equilibrium. New insights on the structure of these heterotopic colloids have been obtained by analysis of rotational correlation times at different molar ratios exploiting time-resolved fluorescence anisotropy experiments. At high porphyrin loads, the anisotropy decays behave as monoexponentials and the rotational correlation times (1-2 ns) together with the r(0) values close to zero suggest the presence of small amounts of TPPS embedded in a hydrophobic environment either in monomeric or in aggregated form. At the lower porphyrin/CD molar ratios, the anisotropy decays exhibit a double-exponential behavior showing a predominant component with a slow rotational correlation time (20-25 ns) and limiting anisotropy values of approximately 0.15. This component has been assigned to molecules that are more stabilized onto the CD vesicles, that is, porphyrins embedded into the oligo-ethylene "wall" of the CD vesicles. Scanning near-field optical microscopy of the samples evaporated on glass surfaces gave further insights on the morphology and optical properties of these systems, confirming the embedding of TPPS on the vesicles and evidencing the role of the solvent. 相似文献
49.
José Glaüco Ribeiro Tostes 《Theoretical chemistry accounts》1981,59(3):229-235
Certain features of the chemist's molecular structure model, viz. size and shape, are retrieved even in the best non-adiabatic variational calculations thus far carried out for ground states of H
2
+
and H2. Those features do not conflict with the full symmetry of exact molecular eigenstates, once they are properly understood as correlation effects. 相似文献
50.
Leonard S Van Schepdael A Iványi T Lázár I Rosier J Vanstockem M Vermeersch H Hoogmartens J 《Electrophoresis》2005,26(3):627-632
A capillary electrophoretic (CE) method was developed for the separation of diastereoisomers of a new human immunodeficiency virus (HIV) protease inhibitor TMC114. In total 16 isomers of this drug have been synthesized (eight pairs of enantiomers). We succeeded in the separation of the eight diastereoisomers, but no enantiomers could be separated. Because of the high similarity and water-insolubility of these isomers, the separation is a real challenge. Different CE modes were tried out: capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), micellar electrokinetic capillary chromatography (MEKC), and microemulsion electrokinetic capillary chromatography (MEEKC). Only MEEKC offered resolution of these compounds. 相似文献