全文获取类型
收费全文 | 5585篇 |
免费 | 257篇 |
国内免费 | 1055篇 |
专业分类
化学 | 5976篇 |
晶体学 | 153篇 |
力学 | 41篇 |
综合类 | 52篇 |
数学 | 56篇 |
物理学 | 619篇 |
出版年
2024年 | 7篇 |
2023年 | 39篇 |
2022年 | 97篇 |
2021年 | 110篇 |
2020年 | 125篇 |
2019年 | 119篇 |
2018年 | 129篇 |
2017年 | 169篇 |
2016年 | 162篇 |
2015年 | 135篇 |
2014年 | 202篇 |
2013年 | 612篇 |
2012年 | 279篇 |
2011年 | 295篇 |
2010年 | 236篇 |
2009年 | 304篇 |
2008年 | 292篇 |
2007年 | 390篇 |
2006年 | 353篇 |
2005年 | 352篇 |
2004年 | 355篇 |
2003年 | 276篇 |
2002年 | 238篇 |
2001年 | 205篇 |
2000年 | 176篇 |
1999年 | 150篇 |
1998年 | 127篇 |
1997年 | 114篇 |
1996年 | 115篇 |
1995年 | 118篇 |
1994年 | 112篇 |
1993年 | 93篇 |
1992年 | 85篇 |
1991年 | 53篇 |
1990年 | 37篇 |
1989年 | 37篇 |
1988年 | 42篇 |
1987年 | 17篇 |
1986年 | 30篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有6897条查询结果,搜索用时 47 毫秒
1.
Prof. Dr. Frank Glorius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8047-8051
A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N‐heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups. 相似文献
2.
Yu. M. Smirnov 《Journal of Applied Spectroscopy》2006,73(6):785-791
Dissociative excitation of the lead atom in e-PbI2 collisions has been studied experimentally. 27 excitation cross sections were measured for an energy of the exciting electrons
equal to 100 eV. Nine optical excitation functions were recorded with variation of the electron energy in the range 0–100
eV. The most probable reaction channels for low electron energies are discussed, as well as the ratio of the dissociative
excitation cross sections for the lead atom in e-PbI2 and e-PbCl2 collisions.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 701–706, November–December, 2006. 相似文献
3.
Guido Wauters Jacques Dewaele Carlo Vandecasteele Richard Dams 《Mikrochimica acta》1989,98(4-6):157-162
Proton activation analysis was used for the determination of cadmium and lead in three sediment reference materials. The method is based on the111,112Cd(p, xn)111 In and the206,207,208Pb(p, xn)206Bi reactions.111In and206Bi were chemically separated by anion exchange. The results obtained were taken into account for the certification of the materials and are in the excellent agreement with the certified values. 相似文献
4.
A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl3. The method is also highly selective for monoprotection of symmetrical diols. 相似文献
5.
Aromatic nitro compounds were reduced to the corresponding symmetrically substituted azo compounds using lead as catalyst and triethylammonium formate as hydrogen donor. Various azo compounds containing additional reducible substituents including halogens, nitrile, acid, phenol, ester, methoxy functions, etc, have been synthesized in a single step by the use of this reagent. The conversion is reasonably fast, clean, high yielding and occurs at room temperature in methanol. 相似文献
6.
H. Kaczmarek J. Kowalonek Z. Klusek S. Pierzgalski S. Datta 《Journal of Polymer Science.Polymer Physics》2004,42(4):585-602
The photooxidative degradation of blends (in a full range of compositions) of amorphous poly(vinyl chloride) (PVC) with semicrystalline poly(ethylene oxide) (PEO) in the form of thin films is investigated using absorption spectroscopy (UV–visible and Fourier transform infrared) and atomic force microscopy (AFM). The amount of insoluble gel formed as a result of photocrosslinking is estimated gravimetrically. It is found that the PVC/PEO blendsí susceptibility to photooxidative degradation differs from that pure of the components and depends on the blend composition and morphology. Photoreactions such as degradation and oxidation are accelerated whereas dehydrochlorination is retarded in blends. The photocrosslinking efficiency in PVC/PEO blends is higher than in PVC; moreover, PEO is also involved in this process. AFM images showing the lamellar structure of semicrystalline PEO in the blend lead to the conclusion that the presence of PVC does not disturb the crystallization process of PEO. The changes induced by UV irradiation allow the observation of more of the distinct PEO crystallites. This is probably caused by recrystallization of short, more mobile chains in degraded PEO or by partial removal of the less stable amorphous phase from the film surface. These results confirm previous information on the miscibility of PVC with PEO. The mechanism of the interactions between the components and the blend photodegradation are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 585–602, 2004 相似文献
7.
Three N-3-phenyl-2-propenoyl amino acids were synthesized through interaction between 3-phenyl-2-propenoyl chloride and amino acids in alkaline with a high Yield.Structure of the products were identified by elemental analysis,IR and NMR spectroscopy. 相似文献
8.
PinHuaLI LeiWANG MinWANG JinCanYAN 《中国化学快报》2004,15(11):1295-1298
A Glaser coupling reaction of terminal alkynes in the presence of nickel chloride withoutany organics and bases in hot water has been developed, which produces the correspondinghomo-coupling products in good yields. 相似文献
9.