全文获取类型
收费全文 | 4304篇 |
免费 | 269篇 |
国内免费 | 39篇 |
专业分类
化学 | 3385篇 |
晶体学 | 40篇 |
力学 | 111篇 |
数学 | 218篇 |
物理学 | 858篇 |
出版年
2023年 | 38篇 |
2022年 | 105篇 |
2021年 | 105篇 |
2020年 | 80篇 |
2019年 | 91篇 |
2018年 | 71篇 |
2017年 | 67篇 |
2016年 | 156篇 |
2015年 | 148篇 |
2014年 | 183篇 |
2013年 | 284篇 |
2012年 | 409篇 |
2011年 | 409篇 |
2010年 | 235篇 |
2009年 | 200篇 |
2008年 | 307篇 |
2007年 | 258篇 |
2006年 | 233篇 |
2005年 | 240篇 |
2004年 | 195篇 |
2003年 | 175篇 |
2002年 | 183篇 |
2001年 | 67篇 |
2000年 | 45篇 |
1999年 | 39篇 |
1998年 | 37篇 |
1997年 | 33篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1986年 | 6篇 |
1985年 | 16篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1967年 | 5篇 |
1964年 | 4篇 |
1961年 | 4篇 |
排序方式: 共有4612条查询结果,搜索用时 15 毫秒
1.
2.
3.
In this paper, we shall find the uniquerational price associated with the exchange option. Also, we find the decomposition of Snell envelope and value function of the American exchange option. 相似文献
4.
5.
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
6.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
7.
Hyun Joo Rhee 《Tetrahedron letters》2004,45(43):8019-8022
Stereoselective synthesis of (+)-lauthisan has been accomplished starting from d-glyceraldehyde acetonide by combination of diastereoselective alkylation and ring-closing metathesis. High degree of 1,3-asymmetric induction has been realized in ether system. 相似文献
8.
Sang‐Uk Kim Choonkeun Lee Saimani Sundar Wonbong Jang Seung‐Jin Yang Haksoo Han 《Journal of Polymer Science.Polymer Physics》2004,42(23):4303-4312
A series of polyimides were synthesized from 2,2‐Bis(3,4‐dicarboxyphenyl)hexafluoropropane, 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane, and 4,4′‐oxydianiline by chemical imidization. The effects of the diamine ratios on the properties of the films were evaluated through the study of their thermal, electrical, and morphological properties. All the polymers exhibited better solubility in most of the organic solvents and hence were easily processable. Polyimides with more 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane exhibited better solubility and a low refractive index, which is highly desired for microelectronic applications. The dielectric constant and birefringence were strongly dependent on the fluorine content. With an increase in the fluorine substitution, both the dielectric constant and birefringence decreased. All the polymers exhibited high thermal stability (>400 °C). The absence of crystalline melting in differential scanning calorimetry and broad wide‐angle X‐ray diffraction patterns revealed the amorphous nature of the polymers, which was due to the presence of bulky CF3 groups and hinged ether linkages of the diamine component. The residual stress values decreased with an increase in the 4,4′‐oxydianiline content, and the results were in agreement with the dielectric constant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4303–4312, 2004 相似文献
9.
Won Keun Son Ji Ho Youk Taek Seung Lee Won Ho Park 《Journal of Polymer Science.Polymer Physics》2004,42(1):5-11
Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004 相似文献
10.
A signal registration strategy from micropatterned immunosensors that converts antigen-antibody binding reactions into electrochemical signals was demonstrated. An array-type micropatterned gold electrode on a silicon wafer was fabricated, containing two electrode geometries of rectangular (100 microm x 500 microm) and circular (r. 50 microm) types, exhibiting electrochemical characteristics of bulk and micro-electrodes, respectively. Ferritin was employed as a model analyte for immunosensing because it has an advantageous molecular structure for functionalization to the sensing interface, and is regarded as a general marker protein for tumors and cancer recurrence. With the fabricated and ferritin-functionalized immunosensors, biospecific interactions were performed with antiferritin antiserum and secondary antibody samples, followed by electrochemical signaling via an immunoprecipitation reaction by the label enzyme. Under the optimized affinity-surface construction steps and reaction conditions, both types of microfabricated electrodes exhibited well-defined calibration results as a function of the protein concentration in antiserum samples. Furthermore, circular-type micropatterned immunoelectrodes exhibited voltammetric characteristics of microelectrodes, which is advantageous in terms of sensor operation under a fixed potential and low signal drift during the signaling reaction compared with the bulk-type electrodes. The results support that the employed signaling method with the proposed immunosensor configuration is fit for sensor miniaturization and integration to future biomicrosystems. 相似文献