全文获取类型
收费全文 | 21230篇 |
免费 | 2555篇 |
国内免费 | 5279篇 |
专业分类
化学 | 21212篇 |
晶体学 | 539篇 |
力学 | 913篇 |
综合类 | 177篇 |
数学 | 1879篇 |
物理学 | 4344篇 |
出版年
2024年 | 30篇 |
2023年 | 202篇 |
2022年 | 525篇 |
2021年 | 565篇 |
2020年 | 726篇 |
2019年 | 569篇 |
2018年 | 580篇 |
2017年 | 642篇 |
2016年 | 927篇 |
2015年 | 819篇 |
2014年 | 1115篇 |
2013年 | 1713篇 |
2012年 | 2055篇 |
2011年 | 1293篇 |
2010年 | 1075篇 |
2009年 | 1337篇 |
2008年 | 1476篇 |
2007年 | 1552篇 |
2006年 | 1456篇 |
2005年 | 1325篇 |
2004年 | 1257篇 |
2003年 | 1045篇 |
2002年 | 836篇 |
2001年 | 676篇 |
2000年 | 677篇 |
1999年 | 641篇 |
1998年 | 549篇 |
1997年 | 478篇 |
1996年 | 451篇 |
1995年 | 440篇 |
1994年 | 367篇 |
1993年 | 275篇 |
1992年 | 331篇 |
1991年 | 233篇 |
1990年 | 189篇 |
1989年 | 136篇 |
1988年 | 112篇 |
1987年 | 76篇 |
1986年 | 81篇 |
1985年 | 62篇 |
1984年 | 45篇 |
1983年 | 23篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1973年 | 3篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
以MCl2和配体L(L=1,10-菲罗啉-5,6-二酮)为原料,合成了标题配合物MLCl2,M=NiⅡ,CuⅡ,ZnⅡ,并经元素分析、热谱、IR和摩尔电导表征.三者均为四配位的电中性配合物,热稳定性高于500K,易溶于DMF、DMSO和吡啶,可溶于乙腈和水.它们在DMF中于350nm和315nm附近显示出强的M-L荷移跃迁 相似文献
132.
E.C. Reynhardt L. Latanowicz 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):195-208
Equations for the temperature dependence of proton and deuteron spin–lattice relaxation rates and second moments due to a complex motion consisting of classical jumps over a potential barrier and quantum mechanical tunneling through the barrier have been derived. Asymmetric double and triple potential wells are considered. These equations have been employed to analyze proton spin–lattice relaxation data for solid naphthazarin in the laboratory and rotating frames as a function of temperature. It is shown that tunneling plays an important role in the proton transfer dynamics of this compound. 相似文献
133.
134.
Andrea Bianco Giacomo Iardino Chiara Bertarelli Luciano Miozzo Giuseppe Zerbi 《Applied Surface Science》2007,253(20):8360-8364
Polyamide 6 (PA6) nanofibers were prepared from formic acid solutions by using electrospinning technique. The fibers were smooth, defects free and with diameters smaller than 200 nm. Small amounts of a perfluorinated acridine were added as dopant to the feed solution to modify the wettability of the fibers. The effect of doping on the contact angle values is well apparent. The contact angle values go from 50° of pure PA6 to 120° when 6% of acridine is added. A comparison between fibers and films of pure and doped polyamide 6 was carried out in order to determine the effect of morphology on wettability. Thermal annealing near the Tg of the polymer promoted the segregation of the molecules to the surface, reaching contact angles of 131° with smaller amounts (4%) of acridine. The surface segregation was also promoted by time aging. 相似文献
135.
136.
Yiwang Chen Dongmei Liu Qilan Deng Xiaohui He Xiaofeng Wang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3434-3443
The direct preparation of grafting polymer brushes from commercial poly (vinylidene fluoride) (PVDF) films with surface‐initiated atom transfer radical polymerization (ATRP) is demonstrated. The direct initiation of the secondary fluorinated site of PVDF facilitated grafting of the hydrophilic monomers from the PVDF surface. Homopolymer brushes of 2‐(N,N‐dimethylamino)ethyl methacrylate (DMAEMA) and poly (ethylene glycol) monomethacrylate (PEGMA) were prepared by ATRP from the PVDF surface. The chemical composition and surface topography of the graft‐functionalized PVDF surfaces were characterized by X‐ray photoelectron spectroscopy, attenuated total reflectance/Fourier transform infrared spectroscopy, and atomic force microscopy. A kinetic study revealed a linear increase in the graft concentration of poly[2‐(N,N‐dimethylamino)ethyl methacrylate] (PDMAEMA) and poly[poly(ethylene glycol) monomethacrylate] (PPEGMA) with the reaction time, indicating that the chain growth from the surface was consistent with a controlled or living process. The living chain ends were used as macroinitiators for the synthesis of diblock copolymer brushes. The water contact angles on PVDF films were reduced by the surface grafting of DMAEMA and PEGMA. Protein adsorption experiments revealed a substantial antifouling property of PPEGMA‐grafted PVDF films and PDMAEMA‐grafted PVDF films in comparison with the pristine PVDF surface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3434–3443, 2006 相似文献
137.
138.
139.
Bernhard Krötz 《Japanese Journal of Mathematics》2007,2(2):303-311
In this paper we raise a question about the boundary of the crown domain of a Riemannian symmetric space X. In case X is of Hermitian type we give an affirmative answer. 相似文献
140.
A cobalt‐containing monodentate phosphine [(μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)4][μ2‐η2‐PhC≡CP(i‐Pr)2] 2f , was prepared from the reaction of (μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)6 1 with PhC≡CP(i‐Pr)2. It was accompanied by an oxidized compound, [(μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)4][μ2‐η2‐PhC≡CP(=O)(i‐Pr2)] 2fo during the chromatographic process. Further reaction of 2f with Mo(CO)6 resulted in the formation of a 2f ‐ligated molybdenum complex 4 , [(μ2‐PPh2CH2PPh2‐κ2P)Co2(CO)4][μ2‐η2‐PhC≡CP(i‐Pr2)‐κP]‐Mo(CO)5. 相似文献