全文获取类型
收费全文 | 31459篇 |
免费 | 1155篇 |
国内免费 | 188篇 |
专业分类
化学 | 22133篇 |
晶体学 | 239篇 |
力学 | 696篇 |
数学 | 4544篇 |
物理学 | 5190篇 |
出版年
2023年 | 189篇 |
2022年 | 211篇 |
2021年 | 418篇 |
2020年 | 549篇 |
2019年 | 533篇 |
2018年 | 372篇 |
2017年 | 321篇 |
2016年 | 823篇 |
2015年 | 732篇 |
2014年 | 876篇 |
2013年 | 1529篇 |
2012年 | 1897篇 |
2011年 | 2103篇 |
2010年 | 1244篇 |
2009年 | 1071篇 |
2008年 | 1786篇 |
2007年 | 1716篇 |
2006年 | 1690篇 |
2005年 | 1559篇 |
2004年 | 1397篇 |
2003年 | 1068篇 |
2002年 | 1102篇 |
2001年 | 532篇 |
2000年 | 458篇 |
1999年 | 462篇 |
1998年 | 433篇 |
1997年 | 403篇 |
1996年 | 437篇 |
1995年 | 357篇 |
1994年 | 392篇 |
1993年 | 379篇 |
1992年 | 325篇 |
1991年 | 232篇 |
1990年 | 290篇 |
1989年 | 243篇 |
1988年 | 242篇 |
1987年 | 225篇 |
1986年 | 208篇 |
1985年 | 337篇 |
1984年 | 336篇 |
1983年 | 223篇 |
1982年 | 271篇 |
1981年 | 260篇 |
1980年 | 272篇 |
1979年 | 235篇 |
1978年 | 271篇 |
1977年 | 255篇 |
1976年 | 202篇 |
1974年 | 194篇 |
1973年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
191.
Thomas Andreae 《Results in Mathematics》2002,41(1-2):18-25
Recent results on the immersion relation for graphs are applied to show that there exist (uncountable) graphs A and G such that G contains n disjoint copies of A for each positive integer n, but the graph N0A consisting of infinitely many disjoint copies of A does not embed in G, where by ‘embedding’ we mean ‘immersion in the weak sense’. 相似文献
192.
193.
Stefanie M. Walz Thomas E. Malner Ulrich Mueller Rolf Muelhaupt 《Journal of Polymer Science.Polymer Physics》2003,41(4):360-367
We explored phase separation and self‐assembly of perfluoroalkyl segments at the surface of polymer films obtained from latices of semifluorinated acrylate copolymers and the corresponding latex blends of nonfluorinated and semifluorinated polyacrylates. With laser‐induced secondary mass spectrometry the fluorine distribution was measured after annealing above the minimum film‐forming temperature of the polymers up to a depth of several micrometers. Depth profiles of a semifluorinated acrylate homopolymer and latex blends thereof with fluorine‐free alkylacrylates with 25, 50, and 75 mol % semifluorinated acrylate as well as a copolymer comprised of alkyl acrylate and semifluorinated acrylate (50/50 mol %) were investigated. In the case of latex blends containing both semifluorinated polyacrylates and fluorine‐free or low‐fluorine polymers, self‐assembly accounted for enrichment of the perfluoroalkyl segments at the surface. Coatings exhibiting low surface energy and having a substantially reduced total fluorine content were obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 360–367, 2003 相似文献
194.
195.
The first object of this paper is to introduce a new evolution equation for the characteristic function of the boundary Γ
of a Lipschitzian domain Ω in the N-dimensional Euclidean space under the influence of a smooth time-dependent velocity field. The originality of this equation is that the evolution takes place in an Lp-space with respect to the (N − 1)-Hausdorff measure. A second more speculative objective is to discuss how that equation can be relaxed to rougher velocity
fields via some weak formulation. A candidate is presented and some of the technical difficulties and open issues are discussed.
Continuity results in several metric topologies are also presented. The paper also specializes the results on the evolution
of the oriented distance function to initial sets with zero N-dimensional Lebesgue measure. 相似文献
196.
Marco Sangermano Roberta Bongiovanni Giulio Malucelli Aldo Priola Richard R. Thomas Charles M. Kausch Yongsin Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):6943-6951
New fluorinated, polyfunctional propenyl ether functionalized resins were synthesized, and their behavior in cationic photopolymerization was investigated. The photopolymerization proceeded efficiently with a high double‐bond conversion (>90%), giving rise to UV‐cured coatings characterized by low glass‐transition temperatures (?33 °C ≤ glass‐transition temperature ≤ ?15 °C) and hydrophobic surface properties. A fluorinated additive was also employed as a reactive additive in the cationic photopolymerization of trimethylolpropane tripropenyl ether, increasing the double‐bond conversion, polymer network flexibility, thermal stability, and surface hydrophobicity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6943–6951, 2006 相似文献
197.
Xinyu Huang Roham Solasi Yue Zou Matthew Feshler Kenneth Reifsnider David Condit Sergei Burlatsky Thomas Madden 《Journal of Polymer Science.Polymer Physics》2006,44(16):2346-2357
The life of proton exchange membrane fuel cells (PEMFC) is currently limited by the mechanical endurance of polymer electrolyte membranes and membrane electrode assemblies (MEAs). In this paper, the authors report recent experimental and modeling work toward understanding the mechanisms of delayed mechanical failures of polymer electrolyte membranes and MEAs under relevant PEMFC operating conditions. Mechanical breach of membranes/MEAs in the form of pinholes and tears has been frequently observed after long‐term or accelerated testing of PEMFC cells/stacks. Catastrophic failure of cell/stack due to rapid gas crossover shortly follows the mechanical breach. Ex situ mechanical characterizations were performed on MEAs after being subjected to the accelerated chemical aging and relative humidity (RH) cycling tests. The results showed significant reduction of MEA ductility manifested as drastically reduced strain‐to‐failure of the chemically aged and RH‐cycled MEAs. Postmortem analysis revealed the formation and growth of mechanical defects such as cracks and crazing in the membranes and MEAs. A finite element model was used to estimate stress/strain states of an edge‐constrained MEA under rapid RH variations. Damage metrics for accelerated testing and life prediction of PEMFCs are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2346–2357, 2006 相似文献
198.
199.
200.
Philippe Boyer Gilles Renversez Evgeny Popov Michel Nevière 《Optical and Quantum Electronics》2006,38(1-3):217-230
The present work adapts a recent grating theory called “Fast Fourier factorization” to cylindrical coordinates in order to study microstructured optical fibers (MOFs). Compared with the classical differential method, this new differential method takes into account the truncation of Fourier series and the discontinuities of the fields across the diffracting surface with the help of new factorization rules. The main advantage of this method is that the directrix of the diffracting cylindrical surface is arbitrary and permits anisotropic and inhomogeneous media although its numerical application needs longer computation time, compared with other well-known numerical methods. The S-propagation algorithm is used to avoid numerical contaminations. The numerical results are validated and compared with the well-established Multipole method in the case of a MOF with six circular cylinders. Further, a new cross-sectional profile (with sectorial inclusions) that the Multipole method cannot consider is studied. 相似文献