全文获取类型
收费全文 | 13383篇 |
免费 | 374篇 |
国内免费 | 46篇 |
专业分类
化学 | 10657篇 |
晶体学 | 73篇 |
力学 | 210篇 |
数学 | 1666篇 |
物理学 | 1197篇 |
出版年
2023年 | 107篇 |
2022年 | 447篇 |
2021年 | 505篇 |
2020年 | 282篇 |
2019年 | 331篇 |
2018年 | 253篇 |
2017年 | 216篇 |
2016年 | 435篇 |
2015年 | 441篇 |
2014年 | 416篇 |
2013年 | 829篇 |
2012年 | 859篇 |
2011年 | 968篇 |
2010年 | 587篇 |
2009年 | 580篇 |
2008年 | 818篇 |
2007年 | 798篇 |
2006年 | 681篇 |
2005年 | 621篇 |
2004年 | 524篇 |
2003年 | 441篇 |
2002年 | 430篇 |
2001年 | 164篇 |
2000年 | 133篇 |
1999年 | 110篇 |
1998年 | 115篇 |
1997年 | 102篇 |
1996年 | 127篇 |
1995年 | 87篇 |
1994年 | 84篇 |
1993年 | 77篇 |
1992年 | 60篇 |
1991年 | 75篇 |
1990年 | 54篇 |
1989年 | 72篇 |
1988年 | 62篇 |
1987年 | 49篇 |
1986年 | 52篇 |
1985年 | 63篇 |
1984年 | 82篇 |
1983年 | 43篇 |
1982年 | 66篇 |
1981年 | 58篇 |
1980年 | 55篇 |
1979年 | 46篇 |
1978年 | 54篇 |
1977年 | 38篇 |
1976年 | 32篇 |
1975年 | 24篇 |
1963年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A nonlinear model associated to the motion of a membrane is considered as limit of a sequence of approximate models, for which a global existence and uniqueness theorem can be proved. The paper investigates the relationship between the solutions of the real and approximate models. 相似文献
992.
Traversa Enrico Di Vona Maria Luisa Licoccia Silvia Sacerdoti Michele Carotta Maria Cristina Gallana Massimiliano Martinelli Giuliano 《Journal of Sol-Gel Science and Technology》2000,19(1-3):193-196
Pure, 5 at%, and 10 at% Ta- or Nb-doped TiO2 nanosized powders were prepared by the sol-gel method. The powders heated to 400°C have the crystalline anatase structure. While the pure TiO2 powder heated to 850°C has the rutile structure, the addition of Ta and Nb inhibited the anatase-to-rutile phase transformation at this temperature. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired at 650°C and 850°C for 1 h. SEM observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO2. The addition of Ta and Nb is effective to keep the TiO2 grain size at the nanometric level even at 850°C. Conductance measurements showed that a good gas response is observed only for the nanostructured titania-based films. The CO response of these materials is only slightly affected by humidity. 相似文献
993.
In this paper we determine the possible Hilbert functions ofa CohenMacaulay local ring of dimension d and multiplicitye, in the case where the embedding dimension v satisfies v =e + d 3 and the CohenMacaulay type is less thanor equal to e 3. 1991 Mathematics Subject Classification:primary 13D40; secondary 13P99. 相似文献
994.
John M. Howie Maria Isabel Marques Ribeiro 《Southeast Asian Bulletin of Mathematics》2000,24(2):231-237
This paper is concerned with the application of two possible definitions of rank to certain well-known semigroups.AMS Subject Classification (2000), 20M10 相似文献
995.
Salvatore Giuffrida Guglielmo G. Condorelli Lucia L. Costanzo Giorgio Ventimiglia Raffaella Lo Nigro Maria Favazza Enrico Votrico Corrado Bongiorno Ignazio L. Fragalà 《Journal of nanoparticle research》2007,9(4):611-619
Liquid Phase Photo-Deposition (LPPD) technique has been used to obtain both colloidal particles and thin films of metallic
and chloride nickel from solutions of only precursor Ni(acac)2 (acac=2,4-pentandionato). Metallic nickel was obtained from ethanol solutions by direct nickel(II) photoreduction at 254 nm
and by acetone sensitised reaction at 300 nm. In this latter process the rate was higher than in the first one. NiCl2 was formed from CCl4 solution by a solvent-initiated reaction. TEM analysis, performed on colloidal particles of nickel, showed that their dimensions
are in the range 2–4 nm. The films did not present carbon contamination and were characterized by AFM, XPS and GIXRD. Metallic
films consisted of particles of 20–40 nm that are the result of the aggregation of smaller crystallites (4–5 nm). Larger agglomerations
(around 200 nm) have been observed for NiCl2 films. 相似文献
996.
José R. B. Gomes Emanuel A. Sousa Jorge M. Gonçalves Luís Gales Ana M. Damas Paula Gomes Siddharth Pandey William E. Acree Jr Maria D. M. C. Ribeiro da Silva 《Journal of Physical Organic Chemistry》2007,20(7):491-498
The gaseous standard molar enthalpies of formation of two 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐1,4‐dioxide has been obtained by X‐ray crystallography showing that the two N? O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas‐phase after computations performed at the B3LYP/6‐311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N? O bonds for quinoxaline 1,4‐dioxide derivatives. As found previously, similar N? O bond lengths in quinoxaline‐1,4‐dioxide compounds are not linked with N? O bonds having the same strength. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
997.
Yao-li Chuang Maria R. D’Orsogna Lincoln S. Chayes 《Physica D: Nonlinear Phenomena》2007,232(1):33-47
We study a class of swarming problems wherein particles evolve dynamically via pairwise interaction potentials and a velocity selection mechanism. We find that the swarming system undergoes various changes of state as a function of the self-propulsion and interaction potential parameters. In this paper, we utilize a procedure which connects a class of individual-based models to their continuum formulations and determine criteria for the validity of the latter. H-stability of the interaction potential plays a fundamental role in determining both the validity of the continuum approximation and the nature of the aggregation state transitions. We perform a linear stability analysis of the continuum model and compare the results to the simulations of the individual-based one. 相似文献
998.
Sulphur-headgroup organic molecules have been chemisorbed on Cu(1 0 0) as self-assembled monolayers (SAMs) in highly-ordered two-fold symmetry structures, and the electronic states induced at the interface have been measured by photoemission: a close similarity of the main interface states for methane-thiolate and mercaptobenzoxazole on Cu(1 0 0) in the same p(2 × 2)-phase is observed. The bonding states for methane-thiolate/Cu(1 0 0) in the p(2 × 2) and c(2 × 2) structures have been compared to ab-initio calculation of the total density of states (DOS) for the S/Cu(1 0 0) system in the same phases. The major role of the S-Cu bonding to determine the density of state evolution at the interface is brought to light. The observed differences in the two phases depend mainly on the charge distribution associated to the different molecular packing, with a minor role of the radical group. 相似文献
999.
A simple method to produce silver nanoparticles on a glass surface from silver nanolayer deposited by magnetron sputtering and thermal annealed is presented. Localized surface plasmon resonance of nanoparticles shows a red shift depending on the silver nanolayer thickness, the refractive index and the thickness of an ultra-thin silicon compound adsorbed on the surface. A highly enhanced Raman spectrum of the characteristic groups of a silicon compound adsorbed on the nanoparticles surface was obtained. 相似文献
1000.
Maria?Jo?o?Ferreira Javier?Gutiérrez García Jorge?PicadoEmail author 《Applied Categorical Structures》2011,19(2):469-487
We characterize normal and extremally disconnected biframes in terms of the insertion of a continuous real function in between
given lower and upper semicontinuous real functions and show this to be the common root of several classical and new insertion
results concerning topological spaces, bitopological spaces, ordered topological spaces and locales. 相似文献