全文获取类型
收费全文 | 4519篇 |
免费 | 137篇 |
国内免费 | 6篇 |
专业分类
化学 | 3266篇 |
晶体学 | 61篇 |
力学 | 49篇 |
综合类 | 2篇 |
数学 | 166篇 |
物理学 | 1118篇 |
出版年
2023年 | 27篇 |
2022年 | 29篇 |
2021年 | 37篇 |
2020年 | 64篇 |
2019年 | 71篇 |
2018年 | 52篇 |
2017年 | 24篇 |
2016年 | 81篇 |
2015年 | 99篇 |
2014年 | 83篇 |
2013年 | 219篇 |
2012年 | 212篇 |
2011年 | 216篇 |
2010年 | 141篇 |
2009年 | 152篇 |
2008年 | 214篇 |
2007年 | 252篇 |
2006年 | 217篇 |
2005年 | 242篇 |
2004年 | 193篇 |
2003年 | 171篇 |
2002年 | 171篇 |
2001年 | 114篇 |
2000年 | 109篇 |
1999年 | 72篇 |
1998年 | 51篇 |
1997年 | 39篇 |
1996年 | 79篇 |
1995年 | 53篇 |
1994年 | 48篇 |
1993年 | 66篇 |
1992年 | 64篇 |
1991年 | 64篇 |
1990年 | 52篇 |
1989年 | 55篇 |
1988年 | 50篇 |
1987年 | 57篇 |
1986年 | 50篇 |
1985年 | 85篇 |
1984年 | 69篇 |
1983年 | 39篇 |
1982年 | 50篇 |
1981年 | 45篇 |
1980年 | 53篇 |
1979年 | 55篇 |
1978年 | 45篇 |
1977年 | 32篇 |
1976年 | 37篇 |
1974年 | 27篇 |
1973年 | 25篇 |
排序方式: 共有4662条查询结果,搜索用时 31 毫秒
81.
Mitsuru Ueda Hiroya Sugita Masaki Sato 《Journal of polymer science. Part A, Polymer chemistry》1986,24(5):1019-1026
A convenient method for the synthesis of poly(benzoxazole)s of high molecular weights has been developed. These polymers were prepared readily by direct polycondensation of aromatic dicarboxylic acids containing phenyl either structure with 3,3′-dihydroxybenzidine dihydrochloride using phosphorus pentoxide/methanesulfonic acid (PPMA) as condensing agent and solvent. Polycondensations proceeded fast and was completed within 5 h at 140°C and produced poly(benzoxazole)s with inherent viscosities up to 4.6 dL/g. Model compound work was performed in detail to demonstrate the feasibility of the reaction for polymer formation. The thermogravimetry of the aromatic poly(benzoxazole)s showed 10% weight loss in air and nitrogen at 450–505°C and 465–535°C, respectively. 相似文献
82.
Whenp-toluidine is added to an aqueous solution of CTAB, a remarkable increase of viscosity is accompanied by a spectacular elasticity. We detected the existence of extremely elongated rod-like micelles in electron micrographs. SAXS measurements indicate a closely packed array of cylindrical rod-like micelles, brought about when solutions flow through a thin capillary. A scattering maximum ofd=160 Å almost corresponds to the distance between the nearest neighbours of the cylindrical rod-like micelles. This value agrees with the diameter measured on electron micrographs. The second broad peak (d=75 Å) is assigned to a subsidiary maximum of the shape function of the cylinder with infinite length. 相似文献
83.
Synthesis of diphenyl cucurbit[6]uril (CB[6]) has been achieved via co-oligomerization of diphenyl glycoluril and unsubstituted glycoluril. The unsymmetrically substituted CB[6], Ph(2)CB[6], was further converted to a rotaxane incorporating bis(dinitrophenyl)spermine. [reaction: see text] 相似文献
84.
[structure: see text] Absolute stereochemistry of amphidinolides G (1) and H (2), potent cytotoxic 27- and 26-membered macrolides, respectively, isolated from a marine dinoflagellate Amphidinium sp., was determined by X-ray diffraction analysis, synthesis of a degradation product (3) of 2, and interconversion between 1 and 2. 相似文献
85.
Scale-up of wet granulation in a vertical high shear mixer was conducted. Pharmaceutical excipient powders composed of lactose, cornstarch and micro-crystallinecellulose, and hydroxypropylcellulose as a binder were mixed together and then granulated with purified water under various operating conditions and vessel scales. A novel internal stress measurement system was developed and stress of normal and tangential directions that granules received from the agitator blade during the granulation was continuously measured. The results indicated that granules received stress mainly from the tangential direction, which also showed the largest value near at the vessel wall. The effects of the agitator tip speed and the centrifugal acceleration on the measured stress was investigated. It was found that the tip speed of the agitator blade could be the main factor for the granule growth. The physical properties such as strength, size distribution and compressibility of granules prepared by changing the operating conditions and the vessel scales were evaluated and the scale-up characteristics of high shear granulation were investigated experimentally. The results showed that these physical properties had linear correlations with the tip speed. It was finally concluded that the scale-up of high shear granulation could be well conducted by means of the tip speed of the agitator blade. 相似文献
86.
Sato H Tashiro K Shinmori H Osuka A Aida T 《Chemical communications (Cambridge, England)》2005,(18):2324-2326
Upon complexation with 4,4[prime or minute]-bipyridine, a cyclic dimer of a fused porphyrin zinc complex, having two pi-electronically coupled binding sites, shows a strong negative cooperativity in the second guest binding, to allow stepwise formation of 1 : 1 and 1 : 2 inclusion complexes. 相似文献
87.
Makoto Yuasa Aritomo Yamaguchi Kenichi Oyaizu Yosuke Fujito Mizuki Kitao Tsuyoshi Sato 《先进技术聚合物》2005,16(9):702-705
meso‐Substituted cobalt porphyrins adsorbed on carbon black were prepared as catalysts for the electroreduction of O2. The catalyst, which was prepared by using a homogenizer in mixing cobalt tetraethylporphyrin and carbon black, gave rise to electroreduction of O2 at a remarkably positive potential (Ep = 0.45 V versus saturated calomel electrode (SCE)) and showed a high selectively for the four‐electron reduction (n = 3.8). Electrochemical study and extended X‐ray absorption fine structure (EXAFS) analysis revealed that the adsorbed face‐to‐face dimeric aggregates of cobalt porphyrin molecules were highly efficient catalysts for electroreduction of O2. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
88.
A nondestructive photon activation procedure with 30 MeV bremsstrahlung followed by high-resolution gamma-spectrometry has
been applied to the multielement determination in tobacco leaves and commercial cigarettes. The elements determined by this
method included essential minor elements such as Ca, Cl, K and Mg, essential trace elements such as Fe, Mn and Zn, and possibly
toxic elements such As and Sb. The NBS Orchard Leaves could successfully be used as a comparative standard. The method is
quite simple and gives good reproducible results for at least 12 elements. 相似文献
89.
Morita Y Murata T Fukui K Yamada S Sato K Shiomi D Takui T Kitagawa H Yamochi H Saito G Nakasuji K 《The Journal of organic chemistry》2005,70(7):2739-2744
[structure: see text] Novel hydrogen-bonded charge-transfer salts of TCNQ with mono- and diprotonated 4,4'-biimidazolium were synthesized in order to demonstrate the high potential of the 4,4'-biimidazole system in a molecular conductor from the viewpoint of crystal engineering and electronic modulation. Crystal structure analyses of neutral 4,4'-biimidazole and TCNQ salts revealed the formation of two types of hydrogen-bonding modes of the 4,4'-biimidazole moiety depending on the protonated states. Neutral 4,4'-biimidazole possessed a linear chain mode of hydrogen-bonding to construct two-dimensional network. In the TCNQ salt of monoprotonated 4,4'-biimidazolium, the 4,4'-biimidazole moiety formed a dimer by a complementary mode of hydrogen-bonding. In contrast, the salt of diprotonated 4,4'-biimidazolium showed a double linear chain mode of hydrogen-bonding to construct a three-dimensional network. The formation of two types of hydrogen-bonding modes made the difference in the stacking patterns of TCNQ columns and in their transport properties. The TCNQ salt of diprotonated 4,4'-biimidazolium exhibited high electrical conductivity (sigma(rt) = 1.1 x 10(-1) S cm(-1)). 相似文献
90.