全文获取类型
收费全文 | 1204篇 |
免费 | 34篇 |
国内免费 | 9篇 |
专业分类
化学 | 795篇 |
晶体学 | 77篇 |
力学 | 16篇 |
数学 | 79篇 |
物理学 | 280篇 |
出版年
2023年 | 13篇 |
2022年 | 25篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 33篇 |
2018年 | 33篇 |
2017年 | 34篇 |
2016年 | 34篇 |
2015年 | 40篇 |
2014年 | 55篇 |
2013年 | 102篇 |
2012年 | 64篇 |
2011年 | 93篇 |
2010年 | 46篇 |
2009年 | 47篇 |
2008年 | 77篇 |
2007年 | 47篇 |
2006年 | 46篇 |
2005年 | 28篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 36篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 6篇 |
排序方式: 共有1247条查询结果,搜索用时 0 毫秒
21.
S Chandrasekhar G Chandrashekar B Nagendra Babu K Vijeender K Venkatram Reddy 《Tetrahedron letters》2004,45(28):5497-5499
A facile synthesis of symmetrical and unsymmetrical ethers is achieved by reductive coupling of carbonyl compounds with alkoxysilanes. This reaction is performed using inert polymethylhydrosiloxane as the hydride source and B(C6F5)3 as the catalytic activator of the PMHS. 相似文献
22.
A simple and efficient method for the preparation of isonucleoside 7 is described. The preparation of 1,4-anhydroxylitol 4, a key intermediate, is described by intramolecular cyclization of (2S,3R,4R)-3,5-dibenzyloxypentan-1,2,4-triol 3 using diethyl carbonate and NaH. 相似文献
23.
N. Seshu Babu 《Tetrahedron letters》2007,48(43):7642-7645
The intermolecular hydroamination of vinyl arene derivatives has been efficiently carried out using a tungstophosphoric acid (TPA) catalyst under solvent free and mild reaction conditions. The present protocol provides an environmentally benign, easy to handle and highly active solid acid catalyst for hydroamination of vinyl arenes. The catalyst yields both hydroamination and hydroarylation products and the selectivity mostly depends on the reaction conditions. 相似文献
24.
G. N. Babu P. H. Lu S. L. Hsu James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1984,22(1):213-223
The effect of parasubstituents on the radiation chemistry of poly(α-methylstyrene) (PMS) was compared for the fluoro (PFMS), chloro (PCMS), bromo (PBMS), isopropyl (PiPMS), and methoxy (PMeOM) derivatives. Radiolysis yields, ESR spectra, and GC? MS analysis of products were obtained. PMS and PFMS have similar low radiolysis yields, products, and product distributions. Only main-chain radicals which persist to 200° were observed. PCMS has increased values of Gs, Gx, and Gr. The product analysis results suggest that the presence of chlorine contributes to the primary process by dissociative electron capture and enhances the cleavage of α-methyl group. Irradiation of PBMS caused crosslinking and yielded few volatile products. PMeOMS and PiPMS gel readily by γ-irradiation and may be useful as negative radiation resists. 相似文献
25.
Copolymerizations of methyl methacrylate (MMA) and butyl methacrylate (BMA) with vinyltriacetoxysilane (VTAS) have been carried out in bulk at 70°. The compositions of the copolymers were determined from their silicon contents; the reactivity ratios were calculated by the Kelen-Tüdős method. For MMA/VTAS, r1 = 7.75 ± 0.31 and for BMA/VTAS, r1 = 4.62 ± 0.15; in both systems, r2 is zero, indicating that VTAS does not homopolymerize under the experimental conditions. The influence of the silicon comonomer on properties of the copolymers, such as solubility annd thermal behaviour, was studied. 相似文献
26.
Coupling of Fmoc-amino acid chlorides mediated by activated commercial zinc dust for the synthesis of peptides is described. The reaction is carried out in an organic medium. The necessity of using an inorganic base like NaHCO3/Na2CO3 or an organic base like DIEA/NMM/TEA/pyridine is circumvented. The coupling is reasonably fast, clean, racemization free and high yielding. 相似文献
27.
28.
29.
30.
Summary We consider the finite element approximation of the 2D elasticity problem when the Poisson ratiov is close to 0.5. It is well-known that the performance of certain commonly used finite elements deteriorates asv0, a phenomenon calledlocking. We analyze this phenomenon and characterize the strength of the locking androbustness of varioush-version schemes using triangular and rectangular elements. We prove that thep-andh-p versions are free of locking with respect to the error in the energy norm. A generalization of our theory to the 3D problem is also discussed.The work of this author was supported in part by the Office of Naval Research under Naval Research Grant N00014-90-J-1030The work of this author was supported in part by the Air Force Office of Scientific Research, Air Force Systems Command, U.S. Air Force, under grant AFOSR 89-0252 相似文献