全文获取类型
收费全文 | 9835篇 |
免费 | 465篇 |
国内免费 | 43篇 |
专业分类
化学 | 7275篇 |
晶体学 | 32篇 |
力学 | 159篇 |
数学 | 1502篇 |
物理学 | 1375篇 |
出版年
2023年 | 77篇 |
2022年 | 107篇 |
2021年 | 154篇 |
2020年 | 229篇 |
2019年 | 199篇 |
2018年 | 146篇 |
2017年 | 120篇 |
2016年 | 415篇 |
2015年 | 379篇 |
2014年 | 401篇 |
2013年 | 476篇 |
2012年 | 662篇 |
2011年 | 704篇 |
2010年 | 503篇 |
2009年 | 410篇 |
2008年 | 652篇 |
2007年 | 576篇 |
2006年 | 541篇 |
2005年 | 554篇 |
2004年 | 472篇 |
2003年 | 338篇 |
2002年 | 311篇 |
2001年 | 156篇 |
2000年 | 129篇 |
1999年 | 149篇 |
1998年 | 115篇 |
1997年 | 158篇 |
1996年 | 109篇 |
1995年 | 109篇 |
1994年 | 105篇 |
1993年 | 92篇 |
1992年 | 88篇 |
1991年 | 58篇 |
1990年 | 42篇 |
1989年 | 68篇 |
1988年 | 54篇 |
1987年 | 31篇 |
1986年 | 31篇 |
1985年 | 45篇 |
1984年 | 36篇 |
1983年 | 22篇 |
1982年 | 45篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1975年 | 22篇 |
1973年 | 16篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Focant JF Reiner EJ Macpherson K Kolic T Sjödin A Patterson DG Reese SL Dorman FL Cochran J 《Talanta》2004,63(5):1231-1240
Comprehensive two-dimensional gas chromatography with isotope-dilution time-of-flight mass spectrometry (GC × GC-IDTOFMS) was used to measure polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), and coplanar polychlorinated biphenyl (cPCB) concentrations in ash, sediment, vegetation, and fish samples. The GC × GC capability was achieved by using a quad jet, dual stage, thermal modulator. Zone compression of the GC peaks from modulation resulted in a significant increase of the signal intensity over classical GC-IDTOFMS. The GC × GC column set used an Rtx-Dioxin 2 phase as the first dimension (1D) and an Rtx-500 as the second dimension (2D). The chromatographic separation of the 17 PCDD/Fs and the 4 cPCBs was attained in 1D except for 2,3,7,8-TCDD and CB126 for which deconvoluted ion currents (DIC) were required to be reported separately. The Rtx-500 phase separated the bulk matrix interfering compounds from the target analytes in 2D. The instrumental limit of detection (iLODs) was 0.5 pg for 2,3,7,8-TCDD. The calibration curves showed good correlation coefficients for all the compounds investigated in the concentration range of 0.5–200 pg. GC × GC-IDTOFMS results compared favorably to those from conventional isotope-dilution one-dimensional gas chromatography-high resolution mass spectrometry (GC-IDHRMS). The comprehensive mass analysis of the TOFMS further permitted the identification of other contaminants of concern in the samples. 相似文献
932.
933.
Sandra Hildebrandt Andreas Eva Philipp Komissinskiy Claudia Fasel Ingo Fritsch Lambert Alff 《Journal of Sol-Gel Science and Technology》2012,63(3):307-314
Sodium and lithium cobaltates are important materials for thermoelectric and battery applications due to their large thermoelectric power and ability to (de-) intercalate the alkali metal. For these applications, phase pure materials with controlled microstructure are required. We report on the sol?Cgel synthesis of sodium- and lithium-based materials by using acetate precursors. The produced Na2/3CoO2, Li(Ni1/3Mn1/3Co1/3)O2, and Li(Ni1/2Co1/2)O2 powders are phase pure with grain sizes below 1???m. X-ray diffraction and energy-dispersive spectral analyses show that the cation stoichiometry is preserved in the lithium-based compounds. Despite the low temperatures, the sodium content is reduced by 1/3 as compared to the initial value. Chemical phases of the investigated powders are formed in the sol?Cgel route at temperatures typically 100?C200?K lower than those used in the conventional solid-state synthesis of these materials. The suggested sol?Cgel synthesis is a low temperature process suited for production of phase pure and homogeneous materials with volatile cations. 相似文献
934.
AC Schmidt AV Nizovtsev A Scheurer FW Heinemann K Meyer 《Chemical communications (Cambridge, England)》2012,48(69):8634-8636
The new neopentyl (Neop)-substituted tris(aryloxide) U(iii) complex [(((Neop,Me)ArO)(3)tacn)U(III)] reacts with CO(2) to form CO and the bridging carbonate complex [{(((Neop,Me)ArO)(3)tacn)U(IV)}(2)(μ-CO(3))]. The uranium(iv) bridging oxo [{(((Neop,Me)ArO)(3)tacn)U(IV)}(2)(μ-O)] has been determined to be the intermediate in this reaction. For the first time, both U(iv) complexes can be reduced back to the U(iii) starting material. Thus, with KC(8) as reductant, [(((Neop,Me)ArO)(3)tacn)U(III)] engages in a synthetic cycle, in which CO(2) is converted to CO and CO(3)(2-). 相似文献
935.
Özlem Usluer Christian Kästner Mamatimin Abbas Christoph Ulbricht Vera Cimrova Andreas Wild Eckhard Birckner Nalan Tekin Niyazi Serdar Sariciftci Harald Hoppe Silke Rathgeber Daniel A. M. Egbe 《Journal of polymer science. Part A, Polymer chemistry》2012,50(16):3425-3436
This article reports on the synthesis, characterization, and properties of various anthracene‐containing poly (p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene) (PPE‐PPV) polymers (AnE‐PVs) bearing statistical distributions of various side chains. Primarily, the ratio of linear octyloxy and branched 2‐ethylhexyloxy side chains at the poly(p‐phenylene vinylene) (PPV) parts was varied, leading to the polymers stat, stat1, and stat2. Furthermore, polymers also containing asymmetric substituted PPV and poly(p‐phenylene ethynylene) units (bearing methoxy and 2‐ethylhexyloxy side chains) were prepared yielding stat3, stat4, and stat5. These materials exhibit a broad variation in their photovoltaic properties. It is once more shown that side chains and their distribution can crucially affect the photovoltaic device performance. The introduction of units with asymmetric substitution into these systems seems to be harmful for their utilization in photovoltaic applications. Organic field‐effect transistors were fabricated to investigate hole mobilities in these new materials. Large variance was observed, falling in the range of almost two orders of magnitude, indicating rather different π–π stacking behavior of the polymer backbones owing to side‐chain modifications. Moreover, a selection of the new polymeric systems was investigated regarding their potential for light‐emitting diode (LED) applications. Polymer LEDs using the polymers AnE‐PVstat, ‐stat3, ‐stat4, and ‐stat5, as the active layer showed turn‐on voltage of ~2 V and exhibited red light emission. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
936.
937.
Andreas Lemmerer Manuel A. Fernandes 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(5):o188-o194
Six ammonium carboxylate salts, namely cyclopentylammonium cinnamate, C5H12N+·C9H7O2−, (I), cyclohexylammonium cinnamate, C6H14N+·C9H7O2−, (II), cycloheptylammonium cinnamate form I, C7H16N+·C9H7O2−, (IIIa), and form II, (IIIb), cyclooctylammonium cinnamate, C8H18N+·C9H7O2−, (IV), and cyclododecylammonium cinnamate, C12H26N+·C9H7O2−, (V), are reported. Salts (II)–(V) all have a 1:1 ratio of cation to anion and feature three N+—H...O− hydrogen bonds forming one‐dimensional hydrogen‐bonded columns consisting of repeating R43(10) rings, while salt (I) has a two‐dimensional network made up of alternating R44(12) and R68(20) rings. Salt (III) consists of two polymorphic forms, viz. form I having Z′ = 1 and form II with Z′ = 2. The latter polymorph has disorder of the cycloheptane rings in the two cations, as well as whole‐molecule disorder of one of the cinnamate anions. A similar, but ordered, Z′ = 2 structure is seen in salt (IV). 相似文献
938.
Saul H. Lapidus Andreas Lemmerer Joel Bernstein Peter W. Stephens 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(9):o335-o337
A further example of using a covalent‐bond‐forming reaction to alter supramolecular assembly by modification of hydrogen‐bonding possibilities is presented. This concept was introduced by Lemmerer, Bernstein & Kahlenberg [CrystEngComm (2011), 13 , 55–59]. The title structure, C9H11N3O·C7H6O4, which consists of a reacted niazid molecule, viz.N′‐(propan‐2‐ylidene)nicotinohydrazide, and 2,4‐dihydroxybenzoic acid, was solved from powder diffraction data using simulated annealing. The results further demonstrate the relevance and utility of powder diffraction as an analytical tool in the study of cocrystals and their hydrogen‐bond interactions. 相似文献
939.
Lisa Roeder Philipp Bender Andreas Tschöpe Rainer Birringer Annette M. Schmidt 《Journal of polymer science. Part A, Polymer chemistry》2012,50(24):1772-1781
The mechanical characterization of complex soft matter by quasi-static magnetometry using nanoscopic magnetic probes is demonstrated for model hydrogels doped with two types of elongated magnetic nanoparticles. Chemically crosslinked poly(acrylamide) (PAAm) hydrogels serve as the matrix in which nickel nanorods or weakly magnetized hematite (α-Fe2O3) ellipsoids are embedded as local probes. We investigated the swelling behavior of the ferrogels in order to verify that their equilibrium swelling degree in water is not influenced by the probes, shows a good correlation with the Frenkel–Flory–Rehner model. The proposed magnetomechanical method relies on a correlation between the shear modulus of the PAAm hydrogel matrix and the coercive fields of the corresponding isotropic ferrogels. By extending the Stoner–Wohlfarth model for single-domain blocked magnetic particles by a term for particle rotation in an elastic matrix, information on the shear modulus of the matrix can be obtained. Comparison of the results with the expected relation from rubber elasticity theory illustrates both the general potential as well as the limits of the approach. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
940.