全文获取类型
收费全文 | 9331篇 |
免费 | 1082篇 |
国内免费 | 1158篇 |
专业分类
化学 | 4976篇 |
晶体学 | 134篇 |
力学 | 1291篇 |
综合类 | 114篇 |
数学 | 1270篇 |
物理学 | 3786篇 |
出版年
2024年 | 9篇 |
2023年 | 76篇 |
2022年 | 136篇 |
2021年 | 189篇 |
2020年 | 276篇 |
2019年 | 220篇 |
2018年 | 243篇 |
2017年 | 293篇 |
2016年 | 356篇 |
2015年 | 276篇 |
2014年 | 454篇 |
2013年 | 612篇 |
2012年 | 509篇 |
2011年 | 601篇 |
2010年 | 498篇 |
2009年 | 617篇 |
2008年 | 609篇 |
2007年 | 684篇 |
2006年 | 570篇 |
2005年 | 532篇 |
2004年 | 504篇 |
2003年 | 443篇 |
2002年 | 365篇 |
2001年 | 322篇 |
2000年 | 297篇 |
1999年 | 280篇 |
1998年 | 217篇 |
1997年 | 181篇 |
1996年 | 179篇 |
1995年 | 146篇 |
1994年 | 124篇 |
1993年 | 77篇 |
1992年 | 96篇 |
1991年 | 92篇 |
1990年 | 71篇 |
1989年 | 59篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 42篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 15篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 23篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
41.
Aric Opdahl Roger A. Phillips Gabor A. Somorjai 《Journal of Polymer Science.Polymer Physics》2004,42(3):421-432
The surface compositions and morphologies of melt‐quenched blends of isotactic polypropylene (iPP) with aspecific poly(ethylene‐co‐propylene) rubber (aEPR) were characterized by atomic force microscopy, optical microscopy, and X‐ray photoelectron spectroscopy. The surface morphologies and compositions formed in the melt are frozen‐in by crystallization of the iPP component and, depending on the processing conditions, are enriched in iPP or aEPR or contain a phase‐separated mix of iPP and aEPR. Enrichment of iPP is observed for blends melted in open air, in agreement with earlier work showing the high surface activity of atactic polypropylene at open interfaces. Surface segregation of iPP is suppressed at confined interfaces. Blends melt‐pressed between hydrophilic and hydrophobic substrates have phase‐separated iPP and aEPR domains present at the surface, which grow in size as the melt time increases. Surface enrichment of aEPR is observed after exposing melt‐pressed blends to n‐hexane vapor, which preferentially solvates aEPR and draws it to the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 421–432, 2004 相似文献
42.
Per B. Zetterlund Kazuki Miyake Kunihiro Goto Bunichiro Yamada 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2640-2650
A detailed investigation of addition–fragmentation chain transfer (AFCT) in the free‐radical polymerization of methyl methacrylate (MMA) in the presence of methyl α‐(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (kadd) over 60–120 °C resulted in Eadd = 21.7 kJ mol?1 and Aadd = 2.18 × 106 M?1 s?1 and a very weak temperature dependence of the chain‐transfer constant (Eadd ≈ Ep). The rate coefficient for fragmentation of adduct radicals at 60 °C was estimated as kf ≈ 39 s?1 on the basis of experimental data of the MMA conversion and the concentration of 2‐carbomethoxy‐2‐propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2640–2650, 2004 相似文献
43.
44.
Some features of software implementation of the Pulay scaling procedure are considered. The advantages of the single value decomposition method for maintaining well-conditionality of the scale factor determination problem are demonstrated. The necessity of using a rational number of scale factors is shown. The possibility of obtaining transferable scale factors with the Pulay method and thus predict the vibrational spectra of related compounds is emphasized. 相似文献
45.
神经网络法计算镉(Ⅱ),羟基及碳酸根三元体系的形态分布 总被引:2,自引:0,他引:2
采用前馈线笥网络BP算法,计算了Cd62+-OH^-CO^2-3三元体系的累积稳定常数。用Hopfield反馈网络研究了体系中络合物的形态分布。溶液中溶解的CO2对lgβ1的计算结果有重要影响,对lgβ2,lgβ3,lgβ4的结果影响不大。 相似文献
46.
Riemannian manifolds for which a natural curvature operator has constant eigenvalues on circles are studied. A local classification in dimensions two and three is given. In the 3-dimensional case one gets all locally symmetric spaces and all Riemannian manifolds with the constant principal Ricci curvatures r
1 = r
2 = 0, r
3= 0 , which are not locally homogeneous, in general. 相似文献
47.
48.
1 Introduction Inrecentyears,boththetheoreticalandexperimentalinvestigationsonlasercoolingandtrappinghavebecomeoneofthemajorfieldsinatomic,molecularandoptical physics[1~ 8] .Thedevelopmentoflasercoolingandtrappingtechnologyisimportantfortheapplicationssu… 相似文献
49.
The theory of Ribaucour transformations for hypersurfaces in space forms is established. For any such hypersurface M, that admits orthonormal principal vector fields, it was shown the existence of a totally umbilic hypersurface locally associated to M by a Ribaucour transformation. A method of obtaining linear Weingarten surfaces in a three-dimensional space form is provided. By applying the theory, a new one-parameter family of complete constant mean curvature (cmc) surfaces in the unit sphere, locally associated to the flat torus, is obtained. The family contains a class of complete cmc cylinders in the sphere. In particular, one gets a family of complete minimal surfaces and minimal cylinders, locally associated to the Clifford torus.Mathematics Subject Classifications (2000): 53C20. 相似文献
50.
Frank Morgan 《Annals of Global Analysis and Geometry》2006,30(1):73-79
In a product M
1 × M
2 of Riemannian manifolds, the least perimeter required to enclose given volume among general regions is at least 1/√ 2 times that among regions of product form, assuming that the isoperimetric profiles of M
1 and M
2 are concave. This result sharpens earlier work of Grigor'yan, generalizes results of Bollobás and Leader and of Barthe, and yields a lower bound on the Cheeger isoperimetric constant of a product. 相似文献