全文获取类型
收费全文 | 1845篇 |
免费 | 46篇 |
国内免费 | 2篇 |
专业分类
化学 | 1322篇 |
晶体学 | 16篇 |
力学 | 34篇 |
数学 | 81篇 |
物理学 | 440篇 |
出版年
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 14篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 32篇 |
2015年 | 23篇 |
2014年 | 33篇 |
2013年 | 76篇 |
2012年 | 74篇 |
2011年 | 116篇 |
2010年 | 54篇 |
2009年 | 54篇 |
2008年 | 110篇 |
2007年 | 125篇 |
2006年 | 121篇 |
2005年 | 128篇 |
2004年 | 117篇 |
2003年 | 72篇 |
2002年 | 68篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 23篇 |
1998年 | 23篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 17篇 |
1994年 | 23篇 |
1993年 | 15篇 |
1992年 | 23篇 |
1991年 | 21篇 |
1989年 | 14篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 22篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 9篇 |
1972年 | 10篇 |
1970年 | 9篇 |
排序方式: 共有1893条查询结果,搜索用时 15 毫秒
11.
IR spectroscopic and volumetric study under reaction conditions of the mechanism of photocatalytic hydrogen production from gaseous methanol and water revealed that CO2 and H2 were produced by reaction between adsorbed CH3O(ad) and H2O. Another reaction path for H2 production, CH3 OH(ad) → H2 + HCHO, was suggested which is dominant in the absence of water. 相似文献
12.
13.
Hiroki Higuchi Hidetoshi Kawai Masakazu Ohkita Takanori Suzuki 《Tetrahedron letters》2004,45(15):3027-3030
The newly prepared tetracyanoanthraquinodimethane (TCNAQ) derivatives 1a,b with a chiral auxiliary are good electron acceptors and exhibit weak circular dichroism (CD) based on the absorption of TCNAQ. The twin-type electron acceptor 1c with two TCNAQ units shows larger ellipticity by exciton coupling. UV-vis, CD, and fluorescence spectra were changed drastically upon electrochemical reduction of 1c, which demonstrates the unprecedented three-way-output response system. 相似文献
14.
15.
Tsuyoshi Miura Satoshi Tsujino Kohtaro Goto Midori Noguchi Manabu Node Nobuyuki Imai 《Tetrahedron》2005,61(27):6518-6526
The use of the bisfluorous chain-type propanoyl (Bfp) group as a fluorous protective group made it possible to rapidly synthesize the Gb2 and Gb3 oligosaccharide derivatives by a simple fluorous-organic extraction purification. Furthermore, the fluorescence-labeled Gb2 and Gb3 oligosaccharides were prepared as a potential Vero Toxins detecting reagent. 相似文献
16.
Akira Okubo Hiroyuki Kawai Toshiro Matsunaga Tatsuji Chuman Sunao Yamazaki Shozo Toda 《Tetrahedron letters》1980,21(42):4095-4096
T1 gives a clue to assign cis- and trans-methyl carbons in 2-methyl-1-propenyl moiety. 相似文献
17.
Takanori Suzuki Prof. Shoko Tanaka Hidetoshi Kawai Dr. Kenshu Fujiwara Prof. 《化学:亚洲杂志》2007,2(1):171-177
The title heterocyclic donors undergo reversible C? C bond formation/cleavage upon electron transfer (dynamic redox behavior). The helical sense in both neutral and cationic states is interconvertible by facile ring flipping. The π‐type asymmetric center on the azepine nitrogen atom induces a significant degree of diasteromeric preference, thus endowing strong CD activity based on exciton coupling. Chiroptical properties could be modified not only by redox reactions but also by heat and protonation. The present redox pairs can serve as unprecedented three‐way‐input (e, H+, Δ) and two‐way‐output (UV/Vis, CD) response systems. 相似文献
18.
Summary DSC data on crystallization kinetics from the melt at different cooling rates of nylon 6 containing various amonts of untreated and surface-treated fillers, were analyzed in terms of a modified Kolmogorov-Avrami equation. It was established that mechanism of crystallinity development in molten nylon 6 does not change appreciably in presence of aminosilane-treated glass beads and small amounts of untreated glass beads, whereas time exponentn was found to decrease with increasing filler content in samples containing untreated glass beads and Aerosil. On the other hand, dependence of temperature of the onset of crystal nucleation on cooling rate obeyedm = 2 law for pure nylon 6 and samples containing surface-treated filler, whilem = 4 law seemed to hold for samples containing large amounts of untreated fillers at low cooling rates (m is the exponent at degree of supercooling). It was concluded that although isothermal conditions of crystallization should be preferred for further quantitative investigations of polymer-filler interactions in highly filled polymer melts, the above results qualitatively are consistent with trends discovered in isothermal crystallization experiments. 相似文献
19.
A porphyrin-DNA complex in which helical porphyrin assemblies were stacked as π-stacked aggregates on a DNA scaffold was found. The complex indicates the inversions of optical rotation by only the control of ionic equilibrium without any structural changes of DNA scaffold. 相似文献
20.
Matsuo G Kawamura K Hori N Matsukura H Nakata T 《Journal of the American Chemical Society》2004,126(44):14374-14376
Brevetoxin-B (BTX-B), produced by the red tide organism, Gymnodium breve Davis, is the first member of marine polycyclic ethers to be structurally elucidated and one of the most potent neurotoxins. The structural feature is a trans-fused polycyclic ether ring system with 23 stereocenters. Its unique, complex structure and potent biological activity have attracted the attention of synthetic organic chemists. Total synthesis of BTX-B has been accomplished via the coupling of the ABCDEFG and IJK-ring segments, each ether ring of which was stereoselectively and efficiently constructed on the basis of SmI2-induced intramolecular cyclization, 6-endo-cyclization of hydroxy epoxide, ring-closing olefin metathesis, and SmI2-induced intramolecular Reformatsky-type reaction. Several kinds of double reactions at the left and right sides were efficiently used through the synthesis. 相似文献