全文获取类型
收费全文 | 4747篇 |
免费 | 154篇 |
国内免费 | 8篇 |
专业分类
化学 | 3459篇 |
晶体学 | 10篇 |
力学 | 119篇 |
数学 | 706篇 |
物理学 | 615篇 |
出版年
2020年 | 68篇 |
2019年 | 64篇 |
2018年 | 45篇 |
2017年 | 42篇 |
2016年 | 106篇 |
2015年 | 91篇 |
2014年 | 121篇 |
2013年 | 172篇 |
2012年 | 225篇 |
2011年 | 268篇 |
2010年 | 140篇 |
2009年 | 128篇 |
2008年 | 202篇 |
2007年 | 222篇 |
2006年 | 198篇 |
2005年 | 207篇 |
2004年 | 200篇 |
2003年 | 136篇 |
2002年 | 129篇 |
2001年 | 85篇 |
2000年 | 75篇 |
1999年 | 76篇 |
1998年 | 59篇 |
1997年 | 83篇 |
1996年 | 79篇 |
1995年 | 59篇 |
1994年 | 73篇 |
1993年 | 54篇 |
1992年 | 49篇 |
1991年 | 52篇 |
1990年 | 43篇 |
1989年 | 41篇 |
1988年 | 41篇 |
1987年 | 49篇 |
1986年 | 50篇 |
1985年 | 63篇 |
1984年 | 64篇 |
1983年 | 45篇 |
1982年 | 58篇 |
1981年 | 31篇 |
1980年 | 46篇 |
1979年 | 55篇 |
1978年 | 40篇 |
1977年 | 46篇 |
1976年 | 37篇 |
1975年 | 29篇 |
1974年 | 36篇 |
1972年 | 30篇 |
1968年 | 292篇 |
1967年 | 92篇 |
排序方式: 共有4909条查询结果,搜索用时 46 毫秒
921.
922.
Frank Seela Kuiying Xu Henning Eickmeier 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(6):o408-o410
In the title compound, 4‐amino‐7‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐5‐fluoro‐7H‐pyrrolo[2,3‐d]pyrimidine, C11H13FN4O3, the conformation of the glycosyl bond lies between anti and high anti [χ = −101.1 (3)°]. The furanose moiety adopts the S‐type sugar pucker (2T3), with P = 164.7 (3)° and τ = 40.1 (2)°. The extended structure is a three‐dimensional hydrogen‐bond network involving a C—H⋯F, two N—H⋯O and two O—H⋯O hydrogen bonds. 相似文献
923.
Frank Seela Anup M. Jawalekar Henning Eickmeier 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(6):o387-o389
In the title compound, C12H13N3O5, the conformation of the glycosylic bond is anti [torsion angle = −105.3 (2)°]. The 2′‐deoxyribofuranose moiety adopts an S‐type sugar pucker and the orientation of the exocyclic C—C bond is −sc (trans). 相似文献
924.
Dirk Lützenkirchen‐Hecht Hans‐Henning Strehblow 《Surface and interface analysis : SIA》2009,41(10):820-829
Silver (II) oxide layers (AgO) were prepared by anodic oxidation of pre‐oxidized, Ag2O‐covered silver electrodes in 1 M NaOH (pH 13.8). The oxidized electrodes were investigated using a combination of electrochemical techniques, ex situ X‐ray photoelectron spectroscopy (XPS) and in situ surface‐sensitive grazing incidence X‐ray absorption spectroscopy (EXAFS) under full potential control. The application of these different techniques leads to a detailed, consistent picture of the anodic silver (II) oxide layer formation. The experiments have shown that the chemical composition of the AgO layer varies significantly with oxidation potential, revealing a decreasing oxygen deficiency with increasing anodization potential and oxidation time. XPS as well as EXAFS experiments support the interpretation of the oxide as a mixed valence Ag + Ag3 + O2 with different contributions of Ag + and Ag3 + species, depending on potential and anodization time. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
925.
Michael Veith Shuhua Ren Matthias Wittmar Henning Bolz 《Journal of solid state chemistry》2009,182(10):2930-640
The subsolidus phase relations of the ternary system CuO-TiO2-CaO sintered at 950 °C in air have been determined by powder X-ray diffraction method. Only one ternary compound CaCu3Ti4O12 was found in this system. From room-temperature dielectric property mapping at 10 kHz, a giant dielectric constant (εr>104) was observed for most of the ceramic composites in the CuO-rich region and in the region along the CaO-CuO binary line. The composites in the CaCu3Ti4O12-rich region were found to give a comparable giant dielectric constant when sintered at 1050 °C. The particular microstructure of larger grains with predominant phase surrounded by smaller grains with the secondary phases was found in such composites with a high dielectric constant. The relations between structures and dielectric properties were investigated. An internal barrier layer capacitance effect is the most probable mechanism to explain this particular dielectric behavior. 相似文献
926.
Anna Evans Anja Bieberle-Hütter Henning Galinski Jennifer L. M. Rupp Thomas Ryll Barbara Scherrer René Tölke Ludwig J. Gauckler 《Monatshefte für Chemie / Chemical Monthly》2009,140(9):975-983
Abstract Micro-solid oxide fuel cells (micro-SOFC) are predicted to be of high energy density and are potential power sources for portable
electronic devices. A micro-SOFC system consists of a fuel cell comprising a positive electrode-electrolyte-negative electrode
(i.e. PEN) element, a gas-processing unit, and a thermal system where processing is based on micro-electro-mechanical-systems
fabrication techniques. A possible system approach is presented. The critical properties of the thin film materials used in
the PEN membrane are discussed, and the unsolved subtasks related to micro-SOFC membrane development are pointed out. Such
a micro-SOFC system approach seems feasible and offers a promising alternative to state-of-the-art batteries in portable electronics.
Graphical abstract Graphical Abstract text
相似文献
927.
Tae-Soo You Jing-Tai Zhao Rainer Pttgen Walter Schnelle Ulrich Burkhardt Yuri Grin Gordon J. Miller 《Journal of solid state chemistry》2009,182(9):2430-2442
Two isoelectronic series, Eu(Ga1−xTtx)2 (Tt=Si, Ge, 0≤x≤1), have been synthesized and characterized by powder and single-crystal X-ray diffraction, physical property measurements, and electronic structure calculations. In Eu(Ga1−xSix)2, crystal structures vary from the KHg2-type to the AlB2-type, and, finally, the ThSi2-type structure as x increases. The hexagonal AlB2-type structure is identified for compositions 0.18(2)≤x<0.70(2) with Ga and Si atoms statistically distributed in the polyanionic 63 nets. As smaller Si atoms replace Ga atoms while the number of valence electrons increases, the lattice parameters, unit cell volumes, and Ga–Si distances in this phase region decrease significantly. Although aspects of X-ray diffraction results suggest puckering of the 63 nets for the Si-richest example of the AlB2-type Eu(Ga1−xSix)2, the complete experimental evidence remains inconclusive. On the other hand, in Eu(Ga1−xGex)2, six different structural types were observed as x varies. In addition to EuGa2 (KHg2-type; space group Imma) and EuGe2 (own structure type, space group P3¯m1), the ternary phases studied show four different structures: the AlB2-type for Ga-rich compositions; the YPtAs-type structure for EuGaGe; and two new structures, which are intergrowths of the YPtAs-type EuGaGe and EuGe2, for Ge-rich compositions. These two Ge-rich phases include: (1) Eu(Ga0.45(2)Ge0.55(2))2 containing two YPtAs-type motifs of EuGaGe plus one EuGe2 motif; and (2) Eu(Ga0.40(2)Ge0.60(2))2 containing one YPtAs-type motif alternating with a split site at and z=0.4798(2) with ca. 50% site occupancy by Ga and Ge along the c-axis. Magnetic susceptibilities of three Eu(Ga1−xGex)2 compounds display Curie–Weiss behavior above ca. 100 K, and show effective magnetic moments indicative of divalent Eu with a 4f7 electronic configuration, consistent with. X-ray absorption spectra (XAS). Density of states (DOS) and crystal orbital Hamilton population (COHP) analyses, based on first principles electronic structure calculations, rationalize the observed homogeneity ranges of the AlB2-type phases in both systems and the structural variations as a function of Tt content. 相似文献
928.
Elisabeth Schmoeger Eva Berger Alexandru Trefilov Alois Jungbauer Rainer Hahn 《Journal of chromatography. A》2009,1216(48):8460-8469
Refolding of proteins must be performed under very dilute conditions to overcome the competing aggregation reaction, which has a high reaction order. Refolding on a chromatography column partially prevents formation of the intermediate form prone to aggregation. A chromatographic refolding procedure was developed using an autoprotease fusion protein with the mutant EDDIE from the Npro autoprotease of pestivirus. Upon refolding, self-cleavage generates a target peptide with an authentic N-terminus. The refolding process was developed using the basic 1.8-kDa peptide sSNEVi-C fused to the autoprotease EDDIE or the acidic peptide pep6His, applying cation and anion exchange chromatography, respectively. Dissolved inclusion bodies were loaded on cation exchange chromatographic resins (Capto S, POROS HS, Fractogel EMD SO3−, UNOsphere S, SP Sepharose FF, CM Sepharose FF, S Ceramic HyperD F, Toyopearl SP-650, and Toyopearl MegaCap II SP-550EC). A conditioning step was introduced in order to reduce the urea concentration prior to the refolding step. Refolding was initiated by applying an elution buffer containing a high concentration of Tris–HCl plus common refolding additives. The actual refolding process occurred concurrently with the elution step and was completed in the collected fraction. With Capto S, POROS HS, and Fractogel SO3−, refolding could be performed at column loadings of 50 mg fusion protein/ml gel, resulting in a final eluate concentration of around 10–15 mg/ml, with refolding and cleavage step yields of around 75%. The overall yield of recovered peptide reached 50%. Similar yields were obtained using the anion exchange system and the pep6His fusion peptide. This chromatographic refolding process allows processing of fusion peptides at a concentration range 10- to 100-fold higher than that observed for common refolding systems. 相似文献
929.
The TiNiSi type intermetallic compounds RERhZn (RE = Y, Sm, Gd–Lu) were synthesized by induction melting of the elements in sealed tantalum ampoules. They were characterized by X-ray powder diffraction. Five structures were refined from single crystal X-ray diffractometer data: Pnma, Z = 4, a = 699.7(2), b = 405.6(2), c = 816.9(2) pm, wR2 = 0.038, 628 F2 values for SmRhZn, a = 696.1(2), b = 405.6(1), c = 811.9(3) pm, wR2 = 0.028, 886 F2 values for GdRhZn, a = 692.8(1), b = 403.0(1), c = 809.5(2) pm, wR2 = 0.039, 562 F2 values, for TbRhZn, a = 690.6(3), b = 401.50(9), c = 808.2(2) pm, wR2 = 0.036, 763 F2 values, for DyRhZn, and a = 688.6(5), b = 399.6(4), c = 808.3(7) pm, wR2 = 0.048, 546 F2 values for HoRhZn with 20 variables for each refinement. The rhodium atoms have coordination number 9 (5 RE + 4 Zn atoms) in the form of a tricapped trigonal prism. Together the rhodium and zinc atoms build up three-dimensional [RhZn] networks with short Rh–Zn (263–269 pm in GdRhZn) and Zn–Zn (296 pm in GdRhZn) distances. The gadolinium atoms bind to the [RhZn] network by Gd–Rh bonds (292–294 pm). Magnetic susceptibility measurements show Pauli paramagnetism for YRhZn and van Vleck paramagnetism for SmRhZn. The remaining RERhZn compounds are Curie–Weiss paramagnets which show magnetic ordering at low temperatures. 相似文献
930.
Henning A. Höppe Dr. 《Angewandte Chemie (International ed. in English)》2009,48(20):3572-3582
Energy efficiency is in! New inorganic luminescent materials can help to increase energy efficiency when used in plasma display panels and white‐light‐emitting diodes (see color diagram; mixing the three emissions A–C produces any given point within the triangle). In mercury‐free fluorescent lamps these phosphors might contribute to environmental protection, and they provide better scintillation materials for medical diagnostics.