全文获取类型
收费全文 | 23527篇 |
免费 | 4044篇 |
国内免费 | 3288篇 |
专业分类
化学 | 17429篇 |
晶体学 | 355篇 |
力学 | 1332篇 |
综合类 | 199篇 |
数学 | 2147篇 |
物理学 | 9397篇 |
出版年
2024年 | 74篇 |
2023年 | 391篇 |
2022年 | 791篇 |
2021年 | 905篇 |
2020年 | 1017篇 |
2019年 | 966篇 |
2018年 | 888篇 |
2017年 | 800篇 |
2016年 | 1180篇 |
2015年 | 1192篇 |
2014年 | 1457篇 |
2013年 | 1905篇 |
2012年 | 2074篇 |
2011年 | 2105篇 |
2010年 | 1545篇 |
2009年 | 1503篇 |
2008年 | 1696篇 |
2007年 | 1552篇 |
2006年 | 1387篇 |
2005年 | 1183篇 |
2004年 | 946篇 |
2003年 | 779篇 |
2002年 | 821篇 |
2001年 | 642篇 |
2000年 | 454篇 |
1999年 | 429篇 |
1998年 | 331篇 |
1997年 | 303篇 |
1996年 | 278篇 |
1995年 | 219篇 |
1994年 | 173篇 |
1993年 | 149篇 |
1992年 | 129篇 |
1991年 | 126篇 |
1990年 | 91篇 |
1989年 | 68篇 |
1988年 | 48篇 |
1987年 | 42篇 |
1986年 | 43篇 |
1985年 | 45篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 5篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
X. Dong 《Discrete and Computational Geometry》2002,27(1):85-97
We prove that the homotopy types of two naturally defined simplicial complexes are related in the following way: one is homotopy
equivalent to a multiple suspension of the canonical Alexander dual of the other. These simplicial complexes arise in free
resolutions of semigroup rings and modules. The relation between their homotopy types was conjectured by Reiner, and was suggested
by a homological consequence of a result due independently to Danilov and Stanley on canonical modules of normal semigroup
rings. Our proof is purely topological, and gives an alternative proof of their result. We also prove a generalization of
a result of Hochster saying that these rings are Cohen—Macaulay, and indicate a new proof of Ehrhart's reciprocity law for
rational polytopes.
Received October 3, 2000, and in revised form April 2, 2001, and May 10, 2001. Online publication November 7, 2001. 相似文献
2.
3.
4.
A (w,r) cover‐free family is a family of subsets of a finite set such that no intersection of w members of the family is covered by a union of r others. A (w,r) superimposed code is the incidence matrix of such a family. Such a family also arises in cryptography as the concept of key distribution pattern. In the present paper, we give some new results on superimposed codes. First we construct superimposed codes from super‐simple designs which give us results better than superimposed codes constructed by other known methods. Next we prove the uniqueness of the (1,2) superimposed code of size 9 × 12, the (2,2) superimposed code of size 14 × 8, and the (2,3) superimposed code of size 30 × 10. Finally, we improve numerical values of upper bounds for the asymptotic rate of some (w,r) superimposed codes. © 2004 Wiley Periodicals, Inc. 相似文献
5.
6.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
7.
Dong‐Guk Yu Jeong Ho An 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5608-5616
Ultrafine black particles, ranging in diameter from 1 to 3 μm, were prepared by dispersion polymerization in a methanol/water mixture with vinyl monomers, nonpolymerizable Sudan black B dyes, and fluorescein isothiocyanate labeled charge control additives. Both the ratio of the methanol to the water dispersion medium and the polymeric stabilizer concentration had significant effects on the particle size. The important role of the stabilizer concentration lay in the particle formation step, during which it determined the particle stability and final particle size. These could affect the extent of the aggregation of nuclei by changing the adsorption rate of the stabilizer and the viscosity of the dispersion medium, resulting in smaller particles. The fluorescent‐labeled charge control additives strongly affected the electrophoretic mobility. A small concentration of fluorescent‐labeled charge control additives increased the electrophoretic mobility. However, a further addition reduced the electrophoretic mobility of the polymer particles. The concentration dependence of the fluorescent‐labeled charge control additives on the deposition behavior in the polymer particles was successfully imaged and thereafter quantified by image analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5608–5616, 2004 相似文献
8.
Dong‐Cheol Shin Yun‐Hi Kim Hong You Jae Gyu Jin Soon‐Ki Kwon 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5636-5646
A poly(p‐phenylenevinylene) (PPV) derivative containing a bulky (2,2‐diphenylvinyl)phenyl group in the side chain, EHDVP‐PPV, was synthesized by Gilch route. The reduced tolane‐bisbenzyl (TBB) defects, as well as the structure of the polymer, was confirmed by various spectroscopic methods. The intramolecular energy transfer from the (2,2‐diphenylvinyl)phenyl side group to the PPV backbone was studied by UV‐vis and photoluminescence (PL) of the obtained polymer and model compound. The polymer film showed maximum absorption and emission peaks at 454 and 546 nm, respectively, and high PL efficiency of 57%. A yellow electroluminescence (λmax = 548 nm) was obtained with intensities of 6479 cd/m2 when the light‐emitting diodes of ITO/PEDOT/EHDVP‐PPV/LiF/Al were fabricated. The maximum power efficiency of the devices was 0.729 lm/W with a turn‐on voltage of 3.6 V. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5636–5646, 2004 相似文献
9.
Dong Il Han Hoe Jin Hah Hong-Woo Park Sang Man Koo 《Journal of Sol-Gel Science and Technology》2004,32(1-3):47-51
Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of RaSi(OR)3/RbSi(OR)3 or RaSi(OR)3/TEOS (Ra: phenyl; Rb: vinyl, methyl). 相似文献
10.
The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004 相似文献