全文获取类型
收费全文 | 9977篇 |
免费 | 343篇 |
国内免费 | 48篇 |
专业分类
化学 | 6287篇 |
晶体学 | 174篇 |
力学 | 201篇 |
综合类 | 2篇 |
数学 | 1648篇 |
物理学 | 2056篇 |
出版年
2023年 | 53篇 |
2022年 | 162篇 |
2021年 | 155篇 |
2020年 | 153篇 |
2019年 | 191篇 |
2018年 | 215篇 |
2017年 | 258篇 |
2016年 | 482篇 |
2015年 | 364篇 |
2014年 | 453篇 |
2013年 | 822篇 |
2012年 | 552篇 |
2011年 | 630篇 |
2010年 | 438篇 |
2009年 | 339篇 |
2008年 | 599篇 |
2007年 | 520篇 |
2006年 | 448篇 |
2005年 | 376篇 |
2004年 | 339篇 |
2003年 | 266篇 |
2002年 | 220篇 |
2001年 | 182篇 |
2000年 | 134篇 |
1999年 | 84篇 |
1998年 | 88篇 |
1997年 | 67篇 |
1996年 | 81篇 |
1995年 | 71篇 |
1994年 | 64篇 |
1993年 | 62篇 |
1992年 | 57篇 |
1991年 | 81篇 |
1990年 | 56篇 |
1989年 | 78篇 |
1988年 | 68篇 |
1987年 | 57篇 |
1986年 | 56篇 |
1985年 | 120篇 |
1984年 | 116篇 |
1983年 | 78篇 |
1982年 | 75篇 |
1981年 | 81篇 |
1980年 | 72篇 |
1979年 | 68篇 |
1978年 | 43篇 |
1977年 | 45篇 |
1976年 | 54篇 |
1975年 | 51篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 326 毫秒
161.
Vilar RB da Silva R Schossler P Cataluña Veses R Piatnicki C Samios D Caramão EB 《Journal of chromatography. A》2003,985(1-2):367-373
This work reports preliminary studies on the characterisation of anhydrous ethanol (AEA) used as an automotive fuel mixed with gasoline in Porto Alegre (South Brazil). Pre-concentration of the impurities contained in 1000 ml of AEA was carried on through solid-phase extraction using XAD4 resin. The main compounds in the extract were identified by means of spectral data from the library of the equipment. The concentrate was then fractionated using a preparative liquid chromatographic column filled with activated silica gel and the elution procedure was carried out with, n-hexane, n-hexane-benzene (1:1, v/v) and dichloromethane. Prior to analysis by GC-MS, each fraction was reduced to 1 ml with a gentle stream of nitrogen. Saturated linear hydrocarbons and aromatic hydrocarbons eluted in the first fraction and oxygenated compounds such as aldehydes. ketones and alcohols, eluted in the second one. were the main compounds detected in the sample. 相似文献
162.
Summary Theortho-metallated complex [RhP3Pt] [P=P(OPh)3, P=P(OC6H4)(OPh)2] was obtained in the reaction of [RhP4]ClO4 with KOH. It reacts easily with proton donors HX (X=ClO4, F, Cl, SCN, or acetylacetonate) to produce complexes [RhP3X] when X is a strong donor. If X is a weaker donor (X=ClO4 or F), pentacoordinate compounds of the type [PhP4X] are formed. [RhP3P] reacts with acetylacetone (Hacac) to produce [Rh(acac)P2]. 相似文献
163.
Magdalena?SkompskaEmail author Mikhail?A.?Vorotyntsev 《Journal of Solid State Electrochemistry》2004,8(6):360-368
We report electrochemical studies on the influence of a small concentration of chloride ions on the electroactivity of the polymer matrix of polypyrrole (PPy), poly(N-methylpyrrole) [p(N-MePy)] and a poly(titanocene-propyl-pyrrole) derivative, p(Tc3Py) [Tc(CH2)3NC4H4; Tc=CpCpTiCl2; Cp=C5H5; Cp=C5H4] in acetonitrile (AN), tetrahydrofuran (THF) and N,N-dimethylformamide (DMF). The polymer films were obtained on Pt disc electrodes from AN solutions of the monomers containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte and then transferred to the corresponding monomer-free solution. Studies in Cl–-containing solutions have shown that the p(Tc3Py) matrix is very sensitive to the presence of Cl– ions in all the above solvents, namely that it was subjected to electrochemical degradation at potentials above 0.1 V vs. a Ag/0.01 M Ag+ in AN reference electrode. Degradation of the p(Tc3Py) matrix was also observed in chloride-free DMF+TBAPF6 solutions. Addition of chloride ions to the AN solution containing pyrrole, N-methylpyrrole or Tc3Py inhibits the deposition of the polymer films. On the other hand, we have found that PPy and p(N-MePy) matrices after their deposition in chloride-free AN solutions show much more stable redox responses in contact with chloride and/or DMF solutions. Possible mechanisms of these effects are discussed.Abbreviations AN
acetonitrile
- Cp
cyclopentadienyl
- DMF
N,N-dimethylformamide
- N-MePy
N-methylpyrrole
- p(N-MePy)
poly(N-methylpyrrole)
- PPy
polypyrrole
- p(Tc3Py)
poly[Tc(CH2)3NC4H4]
- Py
pyrrole
- Tc
titanocene=bis(cyclopentadienyl)titanium dichloride, Cp2TiCl2, or its radical CpCpTiCl2 (Cp=C5H4)
- Tc3Py
titanocene-propyl-pyrrole, Tc(CH2)3NC4H4
- THF
tetrahydrofuran
Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003) 相似文献
164.
We propose finitely convergent methods for solving convex feasibility problems defined over a possibly infinite pool of constraints. Following other works in this area, we assume that the interior of the solution set is nonempty and that certain overrelaxation parameters form a divergent series. We combine our methods with a very general class of deterministic control sequences where, roughly speaking, we require that sooner or later we encounter a violated constraint if one exists. This requirement is satisfied, in particular, by the cyclic, repetitive and remotest set controls. Moreover, it is almost surely satisfied for random controls.
相似文献165.
J. Płonka 《Algebra Universalis》1995,33(4):441-457
Presented by B. Jónsson. 相似文献
166.
Jarosław Cel 《Journal of Geometry》1995,53(1-2):28-36
It is proved for a nonempty proper subset S of a real topological linear space L that kerS ={convAz: z bdryS} and for a close connected nonconvex subset S of L that kerS ={convAz: z slncS}, where bdryS and slncS denote the sets of boundary points and strong local nonconvexity points of S, respectively, and Az = {s S: z is clearly visible from s via S}.This extends previous results and, combined with standard techniques, yields among others two Krasnosel'skii-type characterizations for the dimension of kerS in Rd in case of a nonempty proper set S with bdryS bounded and a closed connected nonconvex set S with lncS bounded.The assumption of boundedness of S turns out to be irrelevant in these criteria.Herrn Professor Dr. Wilhelm Stoll gewidmetResearch partially supported by the grant PB 2 1140 91 01 相似文献
167.
C. T. Zhang M. Sferrazza R. H. Mayer Z. W. Grabowski P. Bhattacharyya P. J. Daly R. Broda B. Fornal W. Królas T. Pawłat G. de Angelis D. Bazzacco S. Lunardi C. Rossi-Alvarez 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(1):11-12
Using an 11.4MeV/u136Xe beam of the UNILAC accelerator of GSI and anatW target, A=184 isobars were produced and separated by using an on-line mass separator. A new isomeric state was found in184Hf. This state decays with a half-life of 48(10) s and emits three -rays of 73, 482, and 555 keV as well as lower-lying cascade transitions. The hindrance of the 73 keV-E1 transition with K=8 is compared with those of other even-even hafnium isotopes. The half-life of184Lu was estimated to be between 15 and 25s. 相似文献
168.
We prove that certain two-point Padé approximants occupying the diagonal of the Padé table form monotone sequences of lower and upper bounds uniformly converging to a Stieltjes function. The results can be applied to the theory of inhomogeneous media for the calculation of the bounds on the effective transport coefficients of heterogeneous materials. 相似文献
169.
Jarosław Pykacz 《International Journal of Theoretical Physics》1994,33(7):1403-1416
A new, physically more plausible definition of a fuzzy quantum logic is proposed. It is shown that this definition coincides with the previously studied definition of a fuzzy quantum logic; therefore it defines objects which are traditional quantum logics with ordering sets of states. The new definition is expressed exclusively in terms of fuzzy set operations which are generated by connectives of multiple-valued logic studied by ukasiewicz at the beginning of the 20th century. Therefore, the logic of quantum mechanics is recognized as a version of infinite-valued ukasiewicz logic. 相似文献
170.
The charge transfer compound TDAE-C60 (TDAE — tetrakis-dimethylamino-ethylene) is so far the only known C60 based molecular ferromagnet. The ESR spectra of TDAE-C60 single crystals demonstrate that freshly grown regularly shaped single crystals show at first an AFM (antiferromagnetic)-like behavior which changes upon annealing at room temperature in vacuum to a FM (ferromagnetic) one. It thus seems that annealing induces a change in the relative orientation of the distorted C 60 ? ions resulting in a change in the sign of the effective magnetic interactions between neighboring C 60 ? ions. A structural transition in the TDAE methyl protons at 250 K seems to be connected with this process. Here we review the structure, the ESR spectra, the proton NMR spectra and the13C NMR spectra of TDAE-C60. 相似文献