全文获取类型
收费全文 | 710篇 |
免费 | 48篇 |
专业分类
化学 | 510篇 |
力学 | 8篇 |
数学 | 69篇 |
物理学 | 171篇 |
出版年
2023年 | 12篇 |
2022年 | 6篇 |
2021年 | 24篇 |
2020年 | 19篇 |
2019年 | 10篇 |
2018年 | 19篇 |
2017年 | 6篇 |
2016年 | 28篇 |
2015年 | 33篇 |
2014年 | 34篇 |
2013年 | 45篇 |
2012年 | 47篇 |
2011年 | 58篇 |
2010年 | 34篇 |
2009年 | 20篇 |
2008年 | 39篇 |
2007年 | 31篇 |
2006年 | 42篇 |
2005年 | 29篇 |
2004年 | 34篇 |
2003年 | 23篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 14篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1974年 | 4篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1962年 | 2篇 |
1957年 | 3篇 |
1940年 | 2篇 |
排序方式: 共有758条查询结果,搜索用时 78 毫秒
81.
Dr. Thomas Schwarze Janine Riemer Dr. Sascha Eidner Prof. Hans‐Jürgen Holdt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11306-11310
A highly K+‐selective two‐photon fluorescent probe for the in vitro monitoring of physiological K+ levels in the range of 1–100 mM is reported. The two‐photon excited fluorescence (TPEF) probe shows a fluorescence enhancement (FE) by a factor of about three in the presence of 160 mM K+, independently of one‐photon (OP, 430 nm) or two‐photon (TP, 860 nm) excitation and comparable K+‐induced FEs in the presence of competitive Na+ ions. The estimated dissociation constant (Kd) values in Na+‐free solutions (KdOP=(28±5) mM and KdTP=(36±6) mM ) and in combined K+/Na+ solutions (KdOP=(38±8) mM and KdTP=(46±25) mM ) reflecting the high K+/Na+ selectivity of the fluorescent probe. The TP absorption cross‐section (σ2PA) of the TPEF probe+160 mM K+ is 26 GM at 860 nm. Therefore, the TPEF probe is a suitable tool for the in vitro determination of K+. 相似文献
82.
Sascha Kurz 《Designs, Codes and Cryptography》2017,85(1):97-106
A partial \((k-1)\)-spread in \({\text {PG}}(n-1,q)\) is a collection of \((k-1)\)-dimensional subspaces with trivial intersection. So far, the maximum size of a partial \((k-1)\)-spread in \({\text {PG}}(n-1,q)\) was known for the cases \(n\equiv 0\pmod k\), \(n\equiv 1\pmod k\), and \(n\equiv 2\pmod k\) with the additional requirements \(q=2\) and \(k=3\). We completely resolve the case \(n\equiv 2\pmod k\) for the binary case \(q=2\). 相似文献
83.
Synthetic musk odours and patchouli oil are widely used in the production of cosmetics and scented household goods. In many perfumes one or both substances are key fragrances to create a unique and luxury odour. While patchouli oil is an essential oil from the patchouli plant, natural musk is historically an animal secrete which is derived from a gland of the muskdeer. The progress in organic synthesis has led to numerous synthetic musk‐like fragrance compounds. Both methods, the plant based production as well as the industrial synthesis of fragrances are connected to challenges such as ethic concerns and possible environmental risks. Therefore, sustainable chemical processes as well as biotechnological methods for the future production of important perfumery ingredients are developed. 相似文献
84.
We extend the multirate GARK approach by Günther and Sandu [1, 2] to the case of non-constant micro steps per macro step to be able to cover time adaptivity, arriving at our so-called TAMGARK scheme and derive order conditions for arbitrary non-constant micro step sizes. The TAMGARK scheme is applied to the classical piston problem [3] to study the interaction between the piston and inviscid fluid flow in one spatial dimension. We demonstrate the functionality of the chosen time-adaptation strategy and the ability of the overall scheme to preserve the order of the basic schemes. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
85.
86.
Recent studies in ultrafast electron crystallography (UEC) using a reflection diffraction geometry have enabled the investigation of a wide range of phenomena on the femtosecond and picosecond time scales. In all these studies, the analysis of the diffraction patterns and their temporal change after excitation was performed within the kinematical scattering theory. In this contribution, we address the question, to what extent dynamical scattering effects have to be included in order to obtain quantitative information about structural dynamics. We discuss different scattering regimes and provide diffraction maps that describe all essential features of scatterings and observables. The effects are quantified by dynamical scattering simulations and examined by direct comparison to the results of ultrafast electron diffraction experiments on an in situ prepared Ni(100) surface, for which structural dynamics can be well described by a two-temperature model. We also report calculations for graphite surfaces. The theoretical framework provided here allows for further UEC studies of surfaces especially at larger penetration depths and for those of heavy-atom materials. 相似文献
87.
Godau T Bleifuss SM Müller AL Roth T Hoffmann S Heinemann FW Burzlaff N 《Dalton transactions (Cambridge, England : 2003)》2011,40(24):6547-6554
One-pot syntheses of three new enantiopure heteroscorpionate ligands derived from (+)-camphor or (-)-menthone are described. The ligands are obtained by reacting pyrazoles derived from (+)-camphor or (-)-menthone with sodium hydride and thionyl chloride. Subsequent reactions with pyridine and various aldehydes afford the tripod ligands in multi-gram amounts. Especially the menthopyrazole based ligand 6 showed encouraging ee values up to 69% in the Cu(I) catalysed enantioselective cyclopropanation of styrene with ethyl diazoacetate. 相似文献
88.
Linden AH Lange S Franks WT Akbey U Specker E van Rossum BJ Oschkinat H 《Journal of the American Chemical Society》2011,133(48):19266-19269
Methods enabling structural studies of membrane-integrated receptor systems without the necessity of purification provide an attractive perspective in membrane protein structural and molecular biology. This has become feasible in principle since the advent of dynamic nuclear polarization (DNP) magic-angle-spinning NMR spectroscopy, which delivers the required sensitivity. In this pilot study, we observed well-resolved solid-state NMR spectra of extensively (13)C-labeled neurotoxin II bound to the nicotinic acetylcholine receptor (nAChR) in native membranes. We show that TOTAPOL, a biradical required for DNP, is localized at membrane and protein surfaces. The concentration of active, membrane-attached biradical decreases with time, probably because of reactive components of the membrane preparation. An optimal distribution of active biradical has strong effects on the NMR data. The presence of inactive TOTAPOL in membrane-proximal situations but active biradical in the surrounding water/glycerol "glass" leads to well-resolved spectra, yet a considerable enhancement (ε = 12) is observed. The resulting spectra of a protein ligand bound to its receptor are paving the way for further DNP investigations of proteins embedded in native membrane patches. 相似文献
89.
Sascha Dietrich 《Journal of organometallic chemistry》2011,696(13):2491-2498
The synthesis and properties of heterobimetallic Ti-Cd complexes of type {[Ti](μ-η1:η2-CCR)2}CdX2 ([Ti] = Ti(η5-C5H4SiMe3)2; R = SiMe3: 3a, X = Cl; 3b, X = Br; 3c, X = I; R = Fc: 3d, X = Br; Fc = Fe(η5-C5H4)(η5-C5H5) is reported. These compounds were accessible by treatment of [Ti](CCR)2 (1a, R = SiMe3; 1b, R = Fc) with the cadmium salts CdX2 (2a, X = Cl; 2b, X = Br; 2c, X = I) in a 1:1 M ratio in diethyl ether. Dissolving, for example, 3b in tetrahydrofuran afforded coordination polymer [Cd(μ-Br)2(thf)2]n (4) along with the tweezer molecule 1a. Treatment of 3b with two equiv of LiCCFc (5) gave {[Ti](μ-η1:η2-CCSiMe3)2}Cd(CCFc)2 (6) which eliminated at ambient temperature the all-carbon buta-1,3-diyne FcCC-CCFc (7) producing 1a and elemental Cd. The same reaction behavior was observed, when 2b was reacted with 5. The thus obtained bis(alkynyl) cadmium complex Cd(CCFc)2 (8) is redox-active at low temperature producing 7 and Cd(0). When mercury halides HgX2 (9a, X = Cl; 9b, X = Br) are used, then the titanocene dihalides [Ti]X2 (10a, X = Cl; 10b, X = Br) together with Me3SiCC-CCSiMe3 (11) and Hg(0) were formed. Nevertheless, mercury acetylides were available by treatment of Hg(OAc)2 (12) with HCCFc (13) in a 1:2 M ratio. Thus obtained Hg(CCFc)2 (14) gave with [CuBr] (15) coordination polymer [{Hg(η2-CCFc)2}(Cu2(μ-Br)2]n (16), while with [AgPF6] oxidation of the ferrocenyl moieties took place affording dicationic [Hg(CCFc)2]2+ (18).The structures of 3b and 4 in the solid state are reported. Compound 3b shows the typical characteristics for heterobimetallic organometallic π-tweezer complexes with cadmium in a tetrahedral environment, while 4 corresponds to a one-dimensional coordination polymer in which the Cd(II) ions are linked in a edge-sharing fashion by bromide bridges in the pseudo-equatorial plane. The appropriate tetrahydrofuran molecules are completing the pseudo-octahedral coordination sphere at cadmium.The cyclic voltammogram of 14 is reported showing a single reversible redox event at E0 = 0.108 V with ΔEp = 76 mV indicating that there is no communication between the Fc termini along the mercury acetylide unit. 相似文献
90.