全文获取类型
收费全文 | 13636篇 |
免费 | 2331篇 |
国内免费 | 2005篇 |
专业分类
化学 | 10514篇 |
晶体学 | 131篇 |
力学 | 769篇 |
综合类 | 115篇 |
数学 | 1754篇 |
物理学 | 4689篇 |
出版年
2024年 | 24篇 |
2023年 | 283篇 |
2022年 | 366篇 |
2021年 | 445篇 |
2020年 | 648篇 |
2019年 | 557篇 |
2018年 | 475篇 |
2017年 | 444篇 |
2016年 | 632篇 |
2015年 | 671篇 |
2014年 | 812篇 |
2013年 | 1031篇 |
2012年 | 1216篇 |
2011年 | 1263篇 |
2010年 | 936篇 |
2009年 | 898篇 |
2008年 | 882篇 |
2007年 | 829篇 |
2006年 | 801篇 |
2005年 | 678篇 |
2004年 | 558篇 |
2003年 | 526篇 |
2002年 | 538篇 |
2001年 | 349篇 |
2000年 | 327篇 |
1999年 | 288篇 |
1998年 | 202篇 |
1997年 | 187篇 |
1996年 | 223篇 |
1995年 | 146篇 |
1994年 | 141篇 |
1993年 | 105篇 |
1992年 | 100篇 |
1991年 | 89篇 |
1990年 | 70篇 |
1989年 | 51篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 36篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1959年 | 1篇 |
1957年 | 3篇 |
1935年 | 1篇 |
1931年 | 1篇 |
1930年 | 3篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
组合证券投资的概率准则模型探讨 总被引:5,自引:0,他引:5
在基于概率准则的组合证券模型下,把实现一定收益率水平目标的概率优化模型的求解转化成易于求解的非线性规划问题,从而方便地得出模型的解及其意义;提出了概率准则下的β值组合证券投资决策模型,研究了它们解的存在性和求解的公式,并给出了上海股市股票的数值算例。 相似文献
22.
23.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
24.
A Promising MoO_x-based Catalyst for n-Heptane Isomerization 总被引:1,自引:0,他引:1
Song Hai CHAI Xin Ping WANG* Ying Jun WANG Tian Xi CAI State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 《中国化学快报》2003,14(7)
The increasing demand for higher-octane gasoline and the regulations limiting the amount of aromatics in the fuel motivate the interest in catalytic isomerization of n-alkanes. In the last ten years, transition metal oxides or oxycarbides based on molybdenum or tungstate have attracted much attention due to their high activity and isomerization selectivity compared to the conventional bifunctional supported platinum catalyst and high resistance to sulphur and nitrogen catalyst poisons1-5. Ma… 相似文献
25.
Yan WANG Rong Quan FENG 《数学学报(英文版)》2005,21(4):773-778
A Cayley map is a Cayley graph embedded in an orientable surface such that. the local rotations at every vertex are identical. In this paper, balanced regular Cayley maps for cyclic groups, dihedral groups, and generalized quaternion groups are classified. 相似文献
26.
Oriented 2-factorable graphs are reduced to bouquets by permutation voltage assignment in this paper. Introducing the concept ofk-class index of a permutation group, various oriented 2-factorable graphs are enumerated in this paper. 相似文献
27.
28.
29.
Ping Li Fei Rong Yibing Xie Van Hu Chunwei Yuan 《Journal of Analytical Chemistry》2004,59(10):939-944
S-naproxen imprinted polymer was prepared with acrylamide as a functional monomer, 1,4-butanediyl diacrylate as a new kind of crossliner, and 2,4,6-trimethylbenzoylphenyl-phosphinic acid ethyl ester as photoinitiator. Their UV and IR spectra were applied to study the interactions between the template and the monomer. Binding experiments showed that the S-naproxen imprinted polymer had better recognition capability for the template than that of a blank polymer. The adsorption distribution coefficient KD of S-naproxen on molecularly-imprinted polymer was 153.2 g/mL, and the separation factor was 1.95 when the initial concentration of substrate was 2.0 mmol/L. Scatchard curves suggested that there were two classes of binding sites in the imprinted polymer and only one class in the blank polymer. Computer simulation using Hyperchem showed the existence of the interactions between the template and the functional monomer as well as the models of the complexes formed by the template and the monomer. 相似文献
30.
Xin‐Gui Li Run‐Feng Chen Mei‐Rong Huang Mei‐Fang Zhu Qun Chen 《Journal of polymer science. Part A, Polymer chemistry》2004,42(9):2073-2092
A new series of copolymers was synthesized through the oxidative polymerization of pyrrole (PY) and o‐phenetidine (PHT) with inorganic oxidants in acidic media. The polymerization parameters including the mixing method of the oxidant with the comonomer, the comonomer ratio, the time, the temperature, the oxidant, the organic medium, and the acid were systematically optimized for the synthesis of copolymers with high yields, intrinsic viscosities, and solubility. The resultant copolymers were characterized by elemental analysis, infrared, ultraviolet–visible, solution high‐resolution 1H NMR and solid‐state high‐resolution 13C NMR, circular dichroism spectroscopy, and cyclic voltammetry. The results showed that the PY observed content in the copolymers was much higher than the PY feed content. The regular variation of the polymerization yield, intrinsic viscosity, solubility, macromolecular structure, and electroactivity of the resulting polymers with the comonomer ratio, together with the complete solubility of a PY/PHT (10/90) polymer in highly polar solvents, indicated the formation of real random copolymers containing both PY and PHT units rather than a mixture of two homopolymers. However, the polymers containing more than 59 mol % PY were not homogeneous copolymers consisting of soluble and insoluble parts. A semiquantitative relationship between the polymerization yield or solubility of the copolymers and the polarity index of the organic solvents was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2073–2092, 2004 相似文献