全文获取类型
收费全文 | 4957篇 |
免费 | 291篇 |
国内免费 | 48篇 |
专业分类
化学 | 3488篇 |
晶体学 | 27篇 |
力学 | 144篇 |
综合类 | 1篇 |
数学 | 705篇 |
物理学 | 931篇 |
出版年
2023年 | 40篇 |
2022年 | 45篇 |
2021年 | 83篇 |
2020年 | 106篇 |
2019年 | 112篇 |
2018年 | 85篇 |
2017年 | 86篇 |
2016年 | 211篇 |
2015年 | 171篇 |
2014年 | 167篇 |
2013年 | 282篇 |
2012年 | 377篇 |
2011年 | 418篇 |
2010年 | 233篇 |
2009年 | 183篇 |
2008年 | 337篇 |
2007年 | 266篇 |
2006年 | 231篇 |
2005年 | 258篇 |
2004年 | 212篇 |
2003年 | 188篇 |
2002年 | 169篇 |
2001年 | 81篇 |
2000年 | 62篇 |
1999年 | 57篇 |
1998年 | 50篇 |
1997年 | 45篇 |
1996年 | 68篇 |
1995年 | 27篇 |
1994年 | 44篇 |
1993年 | 59篇 |
1992年 | 44篇 |
1991年 | 32篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 49篇 |
1984年 | 40篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 25篇 |
1978年 | 25篇 |
1977年 | 15篇 |
1975年 | 15篇 |
1974年 | 19篇 |
1973年 | 17篇 |
排序方式: 共有5296条查询结果,搜索用时 27 毫秒
371.
An experimental technique utilizing high-pressure gas from an exploding wire is used to load long, hollow, thick-walled cylinders from the inside. Resulting plane-strain cylindrical stress waves are one-dimensional in nature. Asimultaneity of impact is studied with methods of high-speed photography and dynamic photoelasticity. 相似文献
372.
Low temperature 1H NMR and 13C NMR, and IR suggest that the -chloroperbenzoic acid (MCPBA) oxidation of neopentyl neopentanethiolsulfinate leads to the formation of (E)- and (Z)-2,2-dimethylpropanethial S-oxide, neopentyl neopentanethiolsulfonate, and other products. 相似文献
373.
A newly developed self-consistent-field molecular orbital theory is described and tested. The intermediate neglect of differential overlap (INDO) approximation is used, and all interaction integrals are differentiated according to their dependence upon 2s and 2p AO's. The bonding parameter βl is reformulated so that the model is calibrated to only one specific molecular property, namely, the ionization energy of Hi. We expect that this model will not be biased toward any special families of molecules. 相似文献
374.
Basurto S Torroba T Comes M Martínez-Máñez R Sancenón F Villaescusa L Amorós P 《Organic letters》2005,7(24):5469-5472
[structure: see text] A new sensory MCM-41-based material for the colorimetric sensing and discrimination of amines has been developed. 相似文献
375.
[reaction: see text] Rigid U-shaped molecules containing syn-facially situated quinoxaline rings have been synthesized in three steps, by a combination of the Diels-Alder reaction, the ruthenium-catalyzed oxidation, and the Zn(OAc)(2)-catalyzed condensation of the resulting bis-alpha-diketones with benzene-1,2-diamines. The unsymmetric bis-quinoxalines, with electronically different substituents, and the quinoxaline ring-attached alpha-diketones were also prepared. Their luminescence properties were examined and described. 相似文献
376.
May JP Brown LJ van Delft I Thelwell N Harley K Brown T 《Organic & biomolecular chemistry》2005,3(14):2534-2542
A non-fluorescent quencher, based on the diaminoanthraquinone Disperse Blue 3, has been incorporated into oligonucleotides at the 5'-end, the 3'-end and internally as a thymidine derivative. Fluorimetry and fluorogenic real-time PCR experiments demonstrate that the quencher is effective with a wide range of fluorescent dyes. The anthraquinone moiety increases the melting temperature of DNA duplexes, thus allowing shorter, more discriminatory probes to be used. The quencher has been used in Scorpion primers and TaqMan probes for human DNA sequence recognition and mutation detection. 相似文献
377.
Nafion membranes are used as semisolid electrolytes in methanol and hydrogen fuel cells. The ion conduction takes place through those hydrophilic channels in the Nafion that can provide continuous pathways through the membrane. There is as yet limited information about the density, the size, and the shape of these channels. We have developed two electrochemical methods of visualizing the pore structure which involve the creation of metal lithographs using the membrane pores as templates. In the experiments, the membrane is supported on a flat solid surface on one side, and is in contact with an electrolyte on the other side. Using hydrogen-terminated n-doped Si(111), we deposited gold from an electrolyte containing a gold salt. The Au ions traverse the membrane through the pores, reach the silicon surface, and are spontaneously reduced. A metallic Au deposit is formed on the silicon surface, at the base of the hydrophilic channel. The Au deposits are imaged after the membrane is dissolved. Another method involves supporting the membrane on a Pt surface and depositing silver wires through the hydrophilic channels of the membrane. The scanning electron microscope pictures of these wires provide an image of the size and the shape of the hydrophilic channels. 相似文献
378.
[structure: see text] A yttrium(III) complex derived from proligand 7c has been shown to be a superior catalyst for enantioselective intramolecular alkene hydroaminations that provide cyclic amines with ee's ranging from 69% to 89%. 相似文献
379.
Lev?B.?Levitin Tom?ToffoliEmail author Zac?Walton 《International Journal of Theoretical Physics》2005,44(2):219-228
We consider a fixed quantum measurement performed over n identical copies of quantum states. Using a rigorous notion of distinguishability based on Shannon’s 12th theorem, we show that in the case of a single qubit, the number of distinguishable states is
, where (α1,α2) is the angle interval from which the states are chosen. In the general case of an N-dimensional Hilbert space and an area Ω of the domain on the unit sphere from which the states are chosen, the number of distinguishable states is
. The optimal distribution is uniform over the domain in Cartesian coordinates. 相似文献
380.
Hydrogenation-induced metal-semiconductor transitions usually occur in simple systems based on rare earths and/or magnesium, accompanied by major reconstructions of the metal host (atom shifts >2 A). We report on the first such transition in a quaternary system based on a transition element. Metallic LaMg2Ni absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 which has a nearly unchanged metal host structure (atom shifts <0.7 A). The transition is induced by a charge transfer of conduction electrons into tetrahedral [NiH4]4- complexes having closed-shell electron configurations. 相似文献