全文获取类型
收费全文 | 10786篇 |
免费 | 1637篇 |
国内免费 | 3449篇 |
专业分类
化学 | 8369篇 |
晶体学 | 450篇 |
力学 | 1047篇 |
综合类 | 150篇 |
数学 | 2506篇 |
物理学 | 3350篇 |
出版年
2024年 | 40篇 |
2023年 | 99篇 |
2022年 | 242篇 |
2021年 | 327篇 |
2020年 | 416篇 |
2019年 | 393篇 |
2018年 | 364篇 |
2017年 | 575篇 |
2016年 | 718篇 |
2015年 | 499篇 |
2014年 | 679篇 |
2013年 | 1361篇 |
2012年 | 960篇 |
2011年 | 918篇 |
2010年 | 796篇 |
2009年 | 789篇 |
2008年 | 795篇 |
2007年 | 784篇 |
2006年 | 692篇 |
2005年 | 606篇 |
2004年 | 533篇 |
2003年 | 456篇 |
2002年 | 419篇 |
2001年 | 361篇 |
2000年 | 304篇 |
1999年 | 287篇 |
1998年 | 240篇 |
1997年 | 205篇 |
1996年 | 172篇 |
1995年 | 174篇 |
1994年 | 146篇 |
1993年 | 96篇 |
1992年 | 89篇 |
1991年 | 53篇 |
1990年 | 57篇 |
1989年 | 37篇 |
1988年 | 37篇 |
1987年 | 19篇 |
1986年 | 10篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
931.
首先提出力学系统高阶速度能定理,阐明了系统高阶速度能量的物理意义;然后提出力学系统有势的一般判据.在此基础上,引入高阶Lagrange函数,得出完整有势力学系统的高阶Lagrange方程,并得到系统高阶循环积分和高阶广义能量积分.
关键词:
高阶速度能定理
有势力学系统
高阶Lagrange方程
高阶Lagrange函数 相似文献
932.
Antonio Roviello Fabio Borbone Antonio Carella Rosita Diana Giuseppina Roviello Barbara Panunzi Antonio Ambrosio Pasqualino Maddalena 《Journal of polymer science. Part A, Polymer chemistry》2009,47(10):2677-2689
The synthesis and the chemical physical characterization of new photoluminescent (PL) chromophores and polymers are reported. Chromophores (oligo‐PPV symmetric derivatives ending with amino groups) are strong blue emitters with a PL quantum yield of ~70% in dioxane solution. They have been used to prepare polyamides by reaction with aliphatic acyl dichlorides in which emitting and non emitting units are alternated. PL properties of the synthesized polyamides have been evaluated in solution and reveal a strong blue emission (PL quantum yield ~60%), To increase the solubility of these systems, oligomers have been purposely prepared and then characterized. They show a peculiar white emission when excited in DMF solution; to get insight into this interesting behavior, asymmetric monoacetylated chromophores have been prepared as model compounds for the chromophoric end groups of the polyamide chains. The emission spectra of these compounds reveal a broad excimeric yellow emission which is responsible, along with the blue emission of the inner chromophoric units, of the overall white emission of the oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2677–2689, 2009 相似文献
933.
Yohei Uchiyama Shohei Iwasaki Chiaki Ueoka Takashi Fukui Kenzo Okamoto Masayuki Yamaguchi 《Journal of Polymer Science.Polymer Physics》2009,47(4):424-433
Effect of mixing and processing conditions at T‐die extrusion on the structure and mechanical properties is studied for isotactic polypropylene (PP) containing a small amount of β‐form nucleating agent, N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide. It is found that trigonal β crystals are predominantly formed in the extruded samples containing the nucleating agent irrespective of the mixing and processing conditions, leading to the marked mechanical toughness. On the contrary, the molecular orientation is significantly affected by the mixing and processing conditions. In particular, it should be noted that PP molecules in the extruded sheet which was mixed at high temperature (260 °C) and extruded at low temperature (200 °C) orient perpendicular to the applied flow direction. As a result, the sheet shows anomalous mechanical anisotropy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 424–433, 2009 相似文献
934.
Xinjian Cheng Sie Chin Tjong Qiang Zhao Robert K. Y. Li 《Journal of polymer science. Part A, Polymer chemistry》2009,47(18):4547-4554
This article presents a facile method to prepare silver/polystyrene composite microspheres. In this approach, monodispersed polystyrene (PS) particles were synthesized with carboxyl acid groups on the surfaces of the PS particles via dispersion polymerization at first. With the addition of [Ag(NH3)2]+ to the PS dispersion, [Ag(NH3)2]+ was absorbed to the surfaces of the PS particles, and then by heating the system, [Ag(NH3)2]+ complex ions were reduced to silver to form the Ag/PS composite microspheres. In the synthesis of PS dispersion, PVP was used as dispersant to stabilize the PS particles, it also acted as reducing agent in the reduction of [Ag(NH3)2]+ complex ions to silver, so no additional reducing agent was needed. The resulting composite microspheres were characterized by TEM, SEM, XPS, and XRD. The catalytic properties and surface‐enhance Raman scattering (SERS) was studied as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4547–4554, 2009 相似文献
935.
N. S. Papageorgiou 《Journal of Optimization Theory and Applications》1987,53(2):259-268
In the present paper, we generalize, within the family of convex-valued multifunctions, a selection theorem of Cole (Ref. 1). This then leads us to prove some new results concerning Cesari's property (Q) and to the introduction of the Cesari limit of sets, which is then compared to the Kuratowski-Mosco limit.This work was done while the author was a visiting professor at the University of Pavia, Pavia, Italy. Financial support was provided by CNR and by NSF Grant No. 84-03135. 相似文献
936.
A study of the d.ynamical fluctuation properties at various c.m.energies in e~ e~- collisions is performed using the Monte Carlo method.The results suggest that,after the normalized factorial moments of 3-dimensional phase space are analyzed using an isotropical phase space partition,the NFM describing non- linear dynamical properties show a power-law scaling,i.e.,the dynamical fluctuations in higher dimensional phase space are isotropic.For c.m.energies s~(1/2)≤80 GeV,the scaling exponentsφ_q increase rapidly with the c.m.energy and for c.m.energies s~(1/2)>80 GeV,theφ_q gradually saturate. 相似文献
937.
给出了拓扑线性空间中的一个Drop定理.利用此Drop定理,证明了拓扑线性空间中的每个序列紧凸集具有Drop性质;每个可数紧闭凸集具有拟Drop性质.而且结出了拓扑线性空间中Drop性质和拟Drop性质的序列流特征.也讨论了Drop性质和拟Drop性质与泛函取极值之间的联系. 相似文献
938.
Min Ren Aili Wang Chen Ge Chunyan Liu Longbao Yu Tingshun Jiang Yumin Liu Ying Hang 《Applied Surface Science》2008,254(22):7314-7320
TiO2-coated sericite powders were prepared by the chemical deposition method starting from lamellar sericite and TiCl4 in the presence or absence of La3+ cations. After calcination at 900 °C for 1 h, the resultant TiO2 nanoparticles on the sericite surfaces existed in anatase phase. The light scattering indexes of the TiO2-coated lamellar sericite powders were dozens of times higher than that of the naked lamellar sericite powders. The presence of La3+ in the deposition solution was beneficial to the formation of the small-sized anatase TiO2 nanoparticles, resulting in the formation of the dense and uniform island-like TiO2 coating layers in a large range of the weight ratios of TiO2 to sericite from 5% to 20%. The TiO2-coated lamellar sericite powders prepared in the presence of La3+ had higher light scattering index than that prepared in the absence of La3+. XPS analysis shows that when La3+ cations were absent in the reaction solution, TiO2 coating layers anchored at the sericite surface via the Ti-O-Si and Ti-O-Al bonds. The presence of La3+ cations caused the formation of Si-O-La and Al-O-La bonds at the sericite surface and Ti-O-La bond at the surface of TiO2 coating layers. After coating TiO2 on the sericite surface, the yellowness of the TiO2-coated sericite powders obviously increased and the brightness slightly decreased. 相似文献
939.
Austin Samakande Ronald D. Sanderson Patrice C. Hartmann 《Journal of polymer science. Part A, Polymer chemistry》2008,46(21):7114-7126
RAFT grafted montmorillonite (MMT) clays [i.e., N,N‐dimethyl‐N‐(4‐(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium‐MMT (PCDBAB‐MMT) and N‐(4‐((((dodecylthio)carbonothioyl)thio)methyl)benzyl)‐N,N‐dimethylethanammo‐nium‐MMT (DCTBAB‐MMT)] of various loadings were dispersed in styrene (S) monomer and the resultant mixtures emulsified and sonicated in the presence of a hydrophobe (hexadecane) into miniemulsions. The stable miniemulsions thus obtained were polymerized to yield encapsulated polystyrene‐clay nanocomposites (PS‐CNs). The molar mass and polydispersity index (PDI) of the PS‐CNs depended on the amount of RAFT agent in the system, in accordance with the features of the RAFT process. The morphology of the PS‐CNs ranged from partially exfoliated to an intercalated morphology, depending on the percentage clay loading. The thermomechanical properties of the PS‐CNs were better than those of the neat PS polymer, and were dependent on the molar mass, PS‐CN morphology and clay loading. The similarities and differences of the PS‐CNs prepared here by miniemulsion polymerization were compared to those prepared using the same RAFT agents and polymer system by bulk polymerization (as reported by us in a previous article). © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7114–7126, 2008 相似文献
940.
Diomedes Barcenas 《Czechoslovak Mathematical Journal》2001,51(3):493-504
Some criteria for weak compactness of set valued integrals are given. Also we show some applications to the study of multimeasures on Banach spaces with the Radon-Nikodym property. 相似文献