全文获取类型
收费全文 | 1990篇 |
免费 | 98篇 |
国内免费 | 7篇 |
专业分类
化学 | 1270篇 |
晶体学 | 7篇 |
力学 | 102篇 |
综合类 | 1篇 |
数学 | 383篇 |
物理学 | 332篇 |
出版年
2024年 | 4篇 |
2023年 | 14篇 |
2022年 | 13篇 |
2021年 | 35篇 |
2020年 | 41篇 |
2019年 | 26篇 |
2018年 | 43篇 |
2017年 | 37篇 |
2016年 | 51篇 |
2015年 | 75篇 |
2014年 | 92篇 |
2013年 | 160篇 |
2012年 | 143篇 |
2011年 | 168篇 |
2010年 | 108篇 |
2009年 | 73篇 |
2008年 | 138篇 |
2007年 | 128篇 |
2006年 | 115篇 |
2005年 | 106篇 |
2004年 | 75篇 |
2003年 | 60篇 |
2002年 | 66篇 |
2001年 | 22篇 |
2000年 | 30篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 17篇 |
1995年 | 24篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有2095条查询结果,搜索用时 15 毫秒
121.
Aïssa Wade 《Annals of Global Analysis and Geometry》2008,33(3):207-217
Poisson fiber bundles are studied. We give sufficient conditions for the existence of a Dirac structure on the total space
of a Poisson fiber bundle endowed with a compatible connection. We also provide some examples.
相似文献
122.
Souad Mokrane Laïd Makhloufi Nicolas Alonso-Vante 《Journal of Solid State Electrochemistry》2008,12(5):569-574
Conducting polypyrrole (PPy)/C (Vulcan XC-72) composite materials were synthesized by chemical polymerization method. These
materials were used as matrix to support platinum nanoparticles, which were produced by the carbonyl chemical route. For the
same catalyst loading (50 μg cm−2), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum
toward the oxygen reduction reaction in acid medium. The variation of the PPy/C ratio determines the so-called substrate effect
for electrocatalysis.
Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to
interfacial electrochemistry. 相似文献
123.
Yohann Catel Michel Degrange Loïc Le Pluart Pierre‐Jean Madec Thi‐Nhàn Pham Fei Chen Wayne D. Cook 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5258-5271
Four new monomers, 3‐(N‐methylacrylamido)propylidenebisphosphonic acid, 3‐(N‐propyl‐acrylamido)propylidenebisphosphonic acid, 3‐(N‐hexylacrylamido)propylidenebisphosphonic acid, and 3‐(N‐octylacrylamido)propylidenebisphosphonic acid, have been synthesized in good yields and fully characterized by 1H, 13C, 31P NMR, and HRMS. The copolymerization of these monomers with N,N′‐diethyl‐1,3‐bis(acrylamido)propane (DEBAAP) has been investigated with differential scanning calorimetry. These mixtures show a higher reactivity than DEBAAP. New self‐etch dental primers, based on these acrylamide monomers, have been formulated. Dentin shear bond strength measurements have shown that primers based on these bisphosphonic acids assure a strong bond between the tooth substance and a dental composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5258–5271, 2009 相似文献
124.
125.
The fabrication of a novel sheathless interface for capillary electrophoresis–electrospray–mass spectrometry (CE–ESI–MS) is described. A programmable CO2 laser was used to ablate small channels in the walls of a polyimide capillary near the terminus. Subsequent exposure of the channel region to a cellulose acetate solution followed by drying resulted in the formation of an electrically conductive semi-permeable membrane. Application of an appropriate voltage to the reservoir resulted in the simultaneous establishment of an electrical connection for CE and ESI. Interface viability was demonstrated by conducting a CE separation of a peptide mixture, with detection accomplished via positive ion mode ESI–MS. For the peptide Val-Tyr-Val, a limit of detection of 0.1 femtomole (S/N 3) was achieved using single reaction monitoring. Attributes of the interface include structural robustness, ease of fabrication, minimal interface dead volume, and the ability to alter post-separation analyte ionization status by use of appropriate buffers in the interface reservoir. 相似文献
126.
Mariem Nafti Radhouane Chakroun Chiraz Hannachi Bechir Hamrouni Habib Nouaïgui 《Analytical letters》2017,50(12):2012-2022
Hexavalent chromium Cr(VI) is a well-established carcinogen associated with lung, nasal, and sinus cancer. Cr(VI) threshold limit values in workroom air have been recently lowered. Consequently, the currently available analytical methods are insufficiently sensitive or high cost. In this paper, a simple, cost-effective, sensitive, and reproducible method using solid-phase extraction with electrothermal atomic absorption spectrometry for determination of hexavalent chromium in airborne samples is reported. The method validation included selectivity, linearity, accuracy, and precision. Interferences from other ions likely to be present in airborne samples, including trivalent chromium, were tested and selectivity was demonstrated. The detection and quantification limits were, respectively, as low as 0.1 and 0.4?µg?L?1. The linearity ranged from 0.5 to 50.0?µg?L?1, with a regression coefficients exceeding 0.998. The extraction recovery exceeded 98%. The developed method was successfully compared with a reference spectrophotometric method. The performances achieved were similar to ion chromatography and high-performance liquid chromatography approaches. The novel method was tested on airborne samples collected from the workplace. The method’s performance suggests that it may be an alternative to high-cost techniques for monitoring occupational exposure to hexavalent chromium. 相似文献
127.
Total internal reflection microscopy was used to directly measure the interaction potentials between a micron-sized silica sphere and a flat silica surface in the presence of a linear poly(N-isopropylacrylamide) (PNIPAM) aqueous solution. When the PNIPAM concentration was low, no discernible forces were detected. A further increase in PNIPAM concentration resulted in a long-range attraction which was likely due to a combined of the reduced electrostatic interaction between the silica particle and the flat surface after the polymer adsorption and polymer bridges formation. On the other hand, for a fixed PNIPAM concentration, the interaction potential profiles between the particle and flat surface were once again characterized by attraction as temperature was increased. This attractive force can be explained in terms of the conformational changes of PNIPAM chains at the surfaces, which subsequently affected the polymer adsorption and enhanced the segment–segment interaction among the adsorbed polymer chains. 相似文献
128.
Sémeril D Matt D Toupet L Oberhauser W Bianchini C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(46):13843-13849
The two rhodium complexes [Rh(acac)(L(R))] (L(R)=(S,S)-5,11,17,23-tetra-tert-butyl-25,27-di(OR)-26,28-bis(1,1'-binaphthyl-2,2'-dioxyphosphanyloxy)calix[4]arene; 6: R=benzyl, 7: R=fluorenyl), each based on a hemispherical chelator forming a pocket about the metal centre upon chelation, are active in the hydroformylation of 1-octene and styrene. As expected for this family of diphosphanes, both complexes resulted in remarkably high selectivity towards the linear aldehyde in the hydroformylation of 1-octene (l/b≈15 for both complexes). Linear aldehyde selectivity was also observed when using styrene, but surprisingly only 6 displayed a marked preference for the linear product (l/b=12.4 (6) vs. 1.9 (7)). A detailed study of the structure of the complexes under CO or CO/H(2) in toluene was performed by high-pressure NMR (HP NMR) and FT-IR (HP-IR) spectroscopies. The spectroscopic data revealed that treatment of 6 with CO gave [Rh(acac)(CO)(η(1)-L(benzyl))] (8), in which the diphosphite behaves as a unidentate ligand. Subsequent addition of H(2) to the solution resulted in a well-defined chelate complex with the formula [RhH(CO)(2)(L(benzyl))] (9). Unlike 6, treatment of complex 7 with CO only led to ligand dissociation and concomitant formation of [Rh(acac)(CO)(2)], but upon addition of H(2) a chelate complex analogous to 9 was formed quantitatively. In both [RhH(CO)(2)(L(R))] complexes the diphosphite adopts the bis-equatorial coordination mode, a structural feature known to favour the formation of linear aldehydes. As revealed by variable-temperature NMR spectroscopy, these complexes show the typical fluxionality of trigonal bipyramidal [RhH(CO)(2)(diphosphane)] complexes. The lower linear selectivity of 7 versus 6 in the hydroformylation of styrene was assigned to steric effects, due to the pocket in which the catalysis takes place being less adapted to accommodate CO or larger olefins and, therefore, possibly leading to facile ligand decoordination. This interpretation was corroborated by an X-ray structure determination carried out for 7. 相似文献
129.
Palladium-based catalysts were prepared by the ion-exchange method with dealuminated HY zeolite as support. The support dealumination
was realised using acid solution of HNO3, HCl or H2SiF6. The high activity of prepared catalysts for methane combustion was observed. This activity was dependent on the Al concentration,
structural and textural properties of the support changed after the dealumination. Especially, Pd loaded on supports developing
a second pore system, and having the highest Si/Al ratio, was more active than that on unmodified supports. It was also expected
that the active sites in the methane combustion, which are suspected to be PdO, were influenced by the acidic properties of
the support. 相似文献
130.
Razika Brahimi Mohamed Trari Aïssa Bouguelia Yassine Bessekhouad 《Journal of Solid State Electrochemistry》2010,14(7):1333-1338
The delafossite CuAlO2 single crystal, prepared by the flux method, is a low mobility p-type semiconductor with a hole mobility of 1.2 × 10−5 cm−2 V−1 s−1. The chronoamperometry showed an electrochemical O2− insertion with a diffusion coefficient D
303K of 3.3 × 10−18 cm2 s−1. The thermal variation of D in the range 293–353 K gave an enthalpy of diffusion (ΔH) of 44.7 kJ mol−1. CuAlO2 is photoactive, and the Mott–Schottky plot indicates a flat band potential of +0.42 V vs saturated calomel electrode and
a holes density (N
A) of 1016 cm−3. The photocurrent spectra have been analyzed by using the Gartner model from which the absorption coefficients and diffusion
lengths were determined. An optical transition at 1.66 eV, indirectly allowed, has been obtained. The spectral photoresponse
provides a high absorption at 480 nm. The low quantum yield (η) is attributed to a small depletion length (440 nm) and a hole diffusion width (271 nm) compared to a very large penetration
depth (12 μm). 相似文献