全文获取类型
收费全文 | 3993篇 |
免费 | 171篇 |
国内免费 | 14篇 |
专业分类
化学 | 3113篇 |
晶体学 | 42篇 |
力学 | 40篇 |
数学 | 221篇 |
物理学 | 762篇 |
出版年
2023年 | 22篇 |
2022年 | 23篇 |
2021年 | 43篇 |
2020年 | 72篇 |
2019年 | 96篇 |
2018年 | 69篇 |
2017年 | 41篇 |
2016年 | 103篇 |
2015年 | 86篇 |
2014年 | 128篇 |
2013年 | 207篇 |
2012年 | 229篇 |
2011年 | 265篇 |
2010年 | 141篇 |
2009年 | 117篇 |
2008年 | 213篇 |
2007年 | 205篇 |
2006年 | 202篇 |
2005年 | 205篇 |
2004年 | 178篇 |
2003年 | 166篇 |
2002年 | 157篇 |
2001年 | 93篇 |
2000年 | 90篇 |
1999年 | 57篇 |
1998年 | 36篇 |
1997年 | 47篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 33篇 |
1993年 | 41篇 |
1992年 | 37篇 |
1991年 | 46篇 |
1990年 | 49篇 |
1989年 | 32篇 |
1988年 | 43篇 |
1987年 | 43篇 |
1986年 | 35篇 |
1985年 | 60篇 |
1984年 | 44篇 |
1983年 | 22篇 |
1982年 | 34篇 |
1981年 | 36篇 |
1980年 | 22篇 |
1979年 | 36篇 |
1978年 | 33篇 |
1977年 | 41篇 |
1976年 | 31篇 |
1975年 | 22篇 |
1973年 | 22篇 |
排序方式: 共有4178条查询结果,搜索用时 234 毫秒
81.
A novel biosensor for the determination of biochemical oxygen demand (BOD) was developed using potassium hexacyanoferrate(III) [HCF(III)] as a mediator. The sensor element consists of a three-electrode system, with both working and counter electrodes compactly integrated as a disposable using etching and electroplating processes. Pseudomonas fluorescens biovar V (isolated from a wastewater treatment plant) was immobilized on the surface of the working electrode using poly(vinyl alcohol)-quaternized stilbazol (PVA-SbQ) photopolymer gel. Synthetic wastewater described by the Organization for Economic Cooperation and Development (OECD) was used as a standard solution instead of glucose-glutamic acid synthetic wastewater. The conditions of amperometric measurement were optimized at +600 mV (vs. Ag/AgCl) operating potential, namely 40 mM HCF(III) in a 0.1 M phosphate buffer (pH 7.0) at 20 degrees C. The sensor response was linear from 15 up to 200 mg O l-1 BOD. The response time was 15 min at 200 mg O l-1 BOD. To demonstrate the wide metabolic range of activity of the sensor, the sensor response to 14 substances in four categories of organic compounds was investigated. Further, it was shown that the response of this BOD sensor was not influenced in samples with low concentrations of dissolved oxygen under the measuring conditions used. For real wastewaters, the BOD values were determined using the sensor and compared favorably with those determined by the conventional BOD5 method. 相似文献
82.
Kyoji Tsubakiyama Togoro Matsuo Takashi Sasaki Kenzo Yoshida Takashi Fujimura Kunio Araki 《Journal of polymer science. Part A, Polymer chemistry》1979,17(1):173-184
γ-Ray-induced polymerizations of ferrocenylmethyl methacrylate (FMMA) in crystalline and amorphous states were investigated with kinetical and ESR methods. In the crystalline state the polymerization of FMMA proceeded slowly and gave low-molecular-weight polymers, whereas in the amorphous state it proceeded rapidly and gave polymers of much higher molecular weight. Molecular weight distributions of these polymers were binodal. The temperature dependence and the dose-rate dependence of the polymerization rates were different between the two states. Wide-line nuclear magnetic resonance (NMR) spectra of the amorphous monomer suggested that the polymerization proceeded in a supercooled state. Electron spin resonance (ESR) spectra of γ-irradiated FMMA and 1,1′-ferrocenyl-di(methyl methacrylate) showed that ferrocene radicals and methacrylic radicals were formed simultaneously at low temperature; with increasing temperature the former radicals disappeared, whereas the latter changed into growing chain radicals. The yields of radicals were relatively low; this means that ferrocene groups in the monomers behave as a radiation energy absorber. 相似文献
83.
84.
85.
Nobuo Yoshida 《Probability Theory and Related Fields》1993,94(4):473-488
Summary We formulate and prove a large deviation principle for the (r, p)-capacity on an abstract Wiener space. As an application, we obtain a sharpening of Strassen's law of the iterated logarithm in terms of the capacity. 相似文献
86.
87.
We report here the synthesis of homogeneous polymer hybrids of poly(diallyl phthalate) (PDAP) and silica by utilizing π–π interactions. Use of arylalkoxysilanes such as phenyltrimethoxysilane (PhTMOS), phenethyltrimethoxysilane (PhenethylTMOS) and mesityltrimethoxysilane (MesTMOS) as sources for inorganic phases resulted in optically transparent PDAP-silica polymer hybrids in a wide range of organic and inorganic content ratios. On the other hand, alkoxysilanes such as tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS) and i-butyltrimethoxysilane (iBuTMOS) resulted in phase separated, turbid solids. A mixture of tetramethoxysilane (TMOS) and PhTMOS was also studied for the synthesis of PDAP-silica gel polymer hybrids to control the cross-linking density in the inorganic phase. Homogeneity was found to be improved with an increase in PhTMOS content. These homogeneous PDAP polymer hybrids were found to have high thermal stability which wasachieved by nano-scale dispersion of PDAP in silica through extensiveinterface interactions. The homogeneity of the polymer hybrids was confirmed by SEM and TEM, which demonstrate a nanometer level integration of the organic polymer and the inorganic phase. 相似文献
88.
Treatment of 3,4-alkadienyl carbonates 2a-i with a low-valent titanium reagent diisopropoxy(eta(2)-propene)titanium (1), readily generated by the reaction of Ti(O-i-Pr)(4) with 2 i-PrMgCl, resulted in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford vinyltitanium compounds 3 which, in turn, reacted with H(3)O(+), D(2)O, or iodine to give alpha-substituted beta,gamma-unsaturated esters 4 in good to excellent yields. The olefin moiety of the hydrolysis product 4 has (Z)-geometry mainly except for 4h. Starting from chiral 2f or 2g, the reaction proceeded stereospecifically to give optically active alpha-substituted beta,gamma-unsaturated ester 4f or 4g having (Z)-olefin geometry exclusively. 相似文献
89.
We have prepared polycrystalline samples of Sr3YCo4O10.56, Sr2.4Ca0.6YCo4O10.54, and Sr3YCo3.76Mn0.24O10.59, and found that these materials show unusual impurity effects on their transport and magnetic properties. A tiny amount of impurities such as Mn or Ca suppresses room-temperature ferromagnetism of Sr3YCo4O10.56. With the suppression, their resistivities and thermopowers are also dramatically changed. We propose that the unusual impurity effects are caused by the suppression of orbital ordering. 相似文献
90.
New substrates and reaction conditions which may be expected to yield phenyl cation intermediates have been investigated. The approaches used were: (a) solvolysis of PhX in fluorinated alcohols, where X = ? N (O) = NOTs (tosyloxyazoxy), ? N (O) = NONf (Nf = C4F9SO) and ? OSO2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document} (CH3)3ōTf (Tf=CF3SO); (b) solvolysis of ArBr, PhOTf and PhOSO2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document}(CH3)3ōTf (phenyl ‘betylate triflate’) in super-acid solvents (FSO3H · SbF5, SbF5, AgSbF6). Analysis of the product mixtures provided no evidence for the intermediacy of phenyl cations as a major pathway in any of the reactions. This result is remarkable, since the ‘betylate’, for example, is a better leaving group by a factor of at least 105 than the ‘super’ leaving group triflate in the solvolysis of alkyl sulfonates. These results are a further indication of the extremely low stability of phenyl cations, as well as of the very special properties of the nitrogen leaving group in arenediazonium ions. 相似文献