全文获取类型
收费全文 | 5773篇 |
免费 | 719篇 |
国内免费 | 576篇 |
专业分类
化学 | 3412篇 |
晶体学 | 39篇 |
力学 | 141篇 |
综合类 | 72篇 |
数学 | 2565篇 |
物理学 | 839篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 114篇 |
2021年 | 153篇 |
2020年 | 161篇 |
2019年 | 186篇 |
2018年 | 134篇 |
2017年 | 227篇 |
2016年 | 272篇 |
2015年 | 213篇 |
2014年 | 345篇 |
2013年 | 548篇 |
2012年 | 389篇 |
2011年 | 389篇 |
2010年 | 356篇 |
2009年 | 384篇 |
2008年 | 420篇 |
2007年 | 437篇 |
2006年 | 302篇 |
2005年 | 279篇 |
2004年 | 200篇 |
2003年 | 197篇 |
2002年 | 169篇 |
2001年 | 184篇 |
2000年 | 138篇 |
1999年 | 128篇 |
1998年 | 88篇 |
1997年 | 82篇 |
1996年 | 80篇 |
1995年 | 76篇 |
1994年 | 61篇 |
1993年 | 62篇 |
1992年 | 61篇 |
1991年 | 44篇 |
1990年 | 15篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 17篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有7068条查询结果,搜索用时 187 毫秒
91.
The concept of the residence time τksp of an atom in a kink site has recently been suggested to understand the processes in electrochemical deposition of alloys
and intermetallic compounds. Different kink sites with different residence times must be defined for alloys and intermetallic
compounds. Based on this model, the finite Markov chain theory is applied to describe the selectivity of the growth process.
An analytical relationship between the alloy composition and the metal ion concentrations in the electrolyte is derived. General
model parameters are ratios g
i = K
ii/K
ij of equilibrium constants of the reaction of electrolyte ions with different kink sites on the surface (i, j representing different alloy components). These ratios are called selectivity constants. For simple conditions, the equation
g
i ≈ τii/τij connects the g
i values with the residence times. The theory is tested in the deposition of alloys Co-Ni (anomalous co-deposition) and Ni-Mo
(induced co-deposition). Additionally, Bi2Te3, an example of stoichiometric semiconductor deposition, is treated.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 10, pp. 1216–1223.
The text was submitted by the authors in English. 相似文献
92.
A series of poly [2-(dimethylamino)ethyl methacrylate (DMA)-sodium acrylate (SA)] diblock copolymers were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymerization exhibits controlled characters: well-controlled molecular weight, narrow molecular weight distribution, molecular weight increasing with polymerization time. The zwitterionic diblock copolymers show rich solution behaviors. Dynamic light scattering (DLS) indicated the formation of micelles and reverse micelles of copolymers is affected by net charge density of copolymers. Microcalorimetry studies showed that the lower critical solution temperature (LCST) increases with incorporation of hydrophilic segments in buffer. 相似文献
93.
94.
95.
侧链液晶聚合物的合成方法,可归纳为3类:一是烯基的单体,如甲基丙烯酸酯,或丙烯酸酯,氯代丙烯酸酯等,经自由基聚合反应,阴离子聚合反应及甲基丙烯酸酯的基团转移聚合反应,得到侧链液晶聚合物;二是变性反应,如聚硅氧烷与丙烯酸酯介 相似文献
96.
Synthesis and characterization of segmented liquid crystal poly(azoxy polyester-co-polyoxypropylene)
Jaine-Ming Huang Jen-Feng Kuo Chuh-Yung Chen 《Journal of polymer science. Part A, Polymer chemistry》1995,33(1):165-173
In this study a series of a segmented copolyester, poly(4,4′-dioxy-2,2′-dimethyl-azoxybenzene dodecanedioyl) (PMABD)-co-polyoxypropylene 400 (POP), was prepared. The chain length of PMABD studied (n) was varied from 7.8-18.2, and that of POP was unchanged. The intrinsic viscosity of the segmented copolyesters was 1.04-1.30, and the number average molecular weight obtained was 2.53 × 104?3.49 × 104 g/mol. The mesophase texture and thermal properties of the segmented copolyesters were measured as functions of n. It was found that the insert of flexible POP between those liquid crystalline domains of PMABD did affect thermotropic properties of PMABD. As the n value was 9.0 and 7.8 (or 7.4 and 8.6% by weight POP) the texture appeared as cholesteric-like oily streaks. The effect could not be attained by simply copolymerizing a mesogenic moiety with a pair of spacers of different lengths. The fluidity and domain structure of the flexible dodecanedioyl-POP-dodcanedioyl segments are taken into account for the obtained results. © 1995 John Wiley & Sons, Inc. 相似文献
97.
98.
不饱和链烃沸点的拓扑研究 总被引:4,自引:0,他引:4
基于邻接矩阵与边价 (fi)定义边价连接性指数 ( mF) ,其中的0 F ,1 F与 2 94种不饱和链烃 (包括烯烃、炔烃及烯炔烃 )的沸点 (Tb)关联 ,得到良好的数学模型 :ln( 70 0 -Tb) =6 5 2 3 3 1-0 0 0 4880 F2 -0 3 46771 F0 5(n =2 94,R =0 9979,R2 =0 995 8,F =3 490 4,S =5 12 ) ,该回归模型经Jackknife法检验具有总体稳健性 .可以预示 ,该指数将在定量构效关系研究中成为重要参数 . 相似文献
99.
The kinetics of radical telomerization of VDF at 141 °C, initiated by ditertbutylperoxide, in the presence of three chain transfer agents (CTAs), HCCl3, CCl4 and CCl3Br, are presented. The values of the chain transfer constants were assessed as 35, 0.25 and 0.06 at 141 °C for CCl3Br, CCl4 and HCCl3, respectively. The values of the degree of polymerization (DPn) were obtained for each CTA and were compared for the same CTA concentration. Hence, CCl3Br behaved as an efficient CTA towards VDF and usually afforded the monoadduct selectively, but in certain conditions the VDF diadduct can also be produced. In contrast, HCCl3 was not so efficient since a polymeric structure was identified as the major product. 相似文献
100.
Denote by *
n
the set of all k
*-cycle resonant hexagonal chains with n hexagons. For any B
n
*
n
, let m(B
n
) and i(B
n
) be the numbers of matchings (=the Hosoya index) and the number of independent sets (=the Merrifield–Simmons index) of B
n
, respectively. In this paper, we give a characterization of the k
*-cycle resonant hexagonal chains, and show that for any B
n
*
n
, m(H
n
)m(B
n
) and i(H
n
)i(B
n
), where H
n
is the helicene chain. Moreover, equalities hold only if B
n
=H
n
. 相似文献