全文获取类型
收费全文 | 5517篇 |
免费 | 190篇 |
国内免费 | 1篇 |
专业分类
化学 | 3012篇 |
晶体学 | 21篇 |
力学 | 107篇 |
综合类 | 1篇 |
数学 | 623篇 |
物理学 | 1944篇 |
出版年
2020年 | 55篇 |
2019年 | 44篇 |
2018年 | 53篇 |
2017年 | 51篇 |
2016年 | 142篇 |
2015年 | 98篇 |
2014年 | 141篇 |
2013年 | 237篇 |
2012年 | 238篇 |
2011年 | 303篇 |
2010年 | 143篇 |
2009年 | 125篇 |
2008年 | 231篇 |
2007年 | 241篇 |
2006年 | 193篇 |
2005年 | 212篇 |
2004年 | 146篇 |
2003年 | 144篇 |
2002年 | 120篇 |
2001年 | 102篇 |
2000年 | 88篇 |
1999年 | 82篇 |
1998年 | 54篇 |
1997年 | 74篇 |
1996年 | 83篇 |
1995年 | 88篇 |
1994年 | 69篇 |
1993年 | 83篇 |
1992年 | 80篇 |
1991年 | 74篇 |
1990年 | 59篇 |
1989年 | 57篇 |
1988年 | 60篇 |
1987年 | 53篇 |
1986年 | 61篇 |
1985年 | 54篇 |
1984年 | 65篇 |
1983年 | 54篇 |
1982年 | 67篇 |
1981年 | 67篇 |
1980年 | 48篇 |
1979年 | 57篇 |
1978年 | 58篇 |
1977年 | 52篇 |
1976年 | 57篇 |
1975年 | 63篇 |
1967年 | 43篇 |
1964年 | 44篇 |
1962年 | 43篇 |
1956年 | 45篇 |
排序方式: 共有5708条查询结果,搜索用时 62 毫秒
991.
Limoges B Marchal D Mavré F Savéant JM Schöllhorn B 《Journal of the American Chemical Society》2008,130(23):7259-7275
The use of enzyme labeling techniques to convert biorecognition events into high sensitivity electrochemical signals may follow two different strategies. One, in which the current is the electrocatalytic response of a redox couple serving as cosubstrate to a redox enzyme label and another that consists in the detection of an electrochemically active product of the enzyme label. The theoretical relationships that link, in the latter case, the electrochemical current response to the amount of recognized labeled target analyte are established for steady-state diffusion-convection chronoamperometric regimes. Two governing parameters thus emerge. One measures the Michaelis-Menten competition in the enzyme kinetics. The other characterizes the competition between the enzymatic kinetics and the diffusion of the substrate. The electrochemical response is finally related to the labeled target analyte concentration in solution through the recognition isotherm. The direct electrochemical product detection thus provides a route to the characteristics of the recognition isotherm, which serves as a calibration curve in analytical applications. The establishment of further theoretical relationships allows one to surmise the increase in sensitivity that may be obtained by using cyclic voltammetry instead of steady-state chronoamperometry in standard electrochemical cells or by accumulation of the enzyme-product in cells of small volume/surface ratios. The theoretical predictions are tested with the example of the avidin-biotin recognition process in a system that involves alkaline phosphatase as enzyme label and 4-amino-2,6-dichlorophenyl phosphate as substrate, generating 4-amino-2,6-dichlorophenol as electrochemically active product. The advantages of the dichloro-substitution are discussed. The theoretical analysis is a requisite for a rational and realistic discussion of the analytical performances of the steady-state chronoamperometric and cyclic voltammetric approaches. These are shown to compare favorably with the best heterogeneous bioaffinity assays so far reported. 相似文献
992.
The potential energy surfaces of the S(0) and S(1)(pi(*)<--pi) states of the 2-naphthol(H(2)O)(n), n is an element of {1,2} clusters were explored at the level of coupled cluster (CC2) response theory. In the electronic ground state two different types of hydrogen-bonding networks coexist for n=2, (i) a cyclic one [similar to those of the water trimer and phenol(H(2)O)(2)] where the hydroxy group of the aryl alcohol acts simultaneously as H donor for the first, and as H acceptor for the second water molecule, and (ii) a hydrogen-bonding arrangement where the aromatic pi system is taking over the role as H acceptor. In the S(1) state, on the other hand, the cyclic conformers are unstable. Consequently, the first group of cyclic ground state conformers gives rise to broad unstructured band shapes in the absorption spectrum, whereas the second group of conformers involving the aromatic pi system gives rise to nicely structured band shapes. Based on these results the puzzling absorption spectrum of the n=2 cluster can properly be interpreted. 相似文献
993.
Ana Isabel González Flórez Eike Mucha Dr. Doo‐Sik Ahn Sandy Gewinner Dr. Wieland Schöllkopf Prof. Dr. Kevin Pagel Dr. Gert von Helden 《Angewandte Chemie (International ed. in English)》2016,55(10):3295-3299
Here we present a combined experimental and theoretical study on the secondary structure of isolated proteins as a function of charge state. In infrared spectra of the proteins ubiquitin and cytochrome c, amide I (C=O stretch) and amide II (N–H bend) bands can be found at positions that are typical for condensed‐phase proteins. For high charge states a new band appears, substantially red‐shifted from the amide II band observed at lower charge states. The observations are interpreted in terms of Coulomb‐driven transitions in secondary structures from mostly helical to extended C5‐type hydrogen‐bonded structures. Support for this interpretation comes from simple energy considerations as well as from quantum chemical calculations on model peptides. This transition in secondary structure is most likely universal for isolated proteins that occur in mass spectrometric experiments. 相似文献
994.
The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement 下载免费PDF全文
Dr. Sivil Kopilevich Dr. Hugo Gottlieb Dr. Keren Keinan‐Adamsky Prof. Dr. Achim Müller Prof. Ira A. Weinstock 《Angewandte Chemie (International ed. in English)》2016,55(14):4476-4481
In Nature, enzymes provide hydrophobic cavities and channels for sequestering small alkanes or long‐chain alkyl groups from water. Similarly, the porous metal oxide capsule [{MoVI6O21(H2O)6}12{(MoV2O4)30(L)29(H2O)2}]41? (L=propionate ligand) features distinct domains for sequestering differently sized alkanes (as in Nature) as well as internal dimensions suitable for multi‐alkane clustering. The ethyl tails of the 29 endohedrally coordinated ligands, L, form a spherical, hydrophobic “shell”, while their methyl end groups generate a hydrophobic cavity with a diameter of 11 Å at the center of the capsule. As such, C7 to C3 straight‐chain alkanes are tightly intercalated between the ethyl tails, giving assemblies containing 90 to 110 methyl and methylene units, whereas two or three ethane molecules reside in the central cavity of the capsule, where they are free to rotate rapidly, a phenomenon never before observed for the uptake of alkanes from water by molecular cages or containers. 相似文献
995.
Nitrogen‐Doped Ordered Mesoporous Carbon Supported Bimetallic PtCo Nanoparticles for Upgrading of Biophenolics 下载免费PDF全文
Dr. Guang‐Hui Wang Dr. Zhengwen Cao Dr. Dong Gu Norbert Pfänder Ann‐Christin Swertz Bernd Spliethoff Hans‐Josef Bongard Dr. Claudia Weidenthaler Dr. Wolfgang Schmidt Dr. Roberto Rinaldi Prof. Dr. Ferdi Schüth 《Angewandte Chemie (International ed. in English)》2016,55(31):8850-8855
Hydrodeoxygenation (HDO) is an attractive route for the upgrading of bio‐oils produced from lignocellulose. Current catalysts require harsh conditions to effect HDO, decreasing the process efficiency in terms of energy and carbon balance. Herein we report a novel and facile method for synthesizing bimetallic PtCo nanoparticle catalysts (ca. 1.5 nm) highly dispersed in the framework of nitrogen‐doped ordered mesoporous carbon (NOMC) for this reaction. We demonstrate that NOMC with either 2D hexagonal (p6m) or 3D cubic (Im m) structure can be easily synthesized by simply adjusting the polymerization temperature. We also demonstrate that PtCo/NOMC (metal loading: Pt 9.90 wt %; Co 3.31 wt %) is a highly effective catalyst for HDO of phenolic compounds and “real‐world” biomass‐derived phenolic streams. In the presence of PtCo/NOMC, full deoxygenation of phenolic compounds and a biomass‐derived phenolic stream is achieved under conditions of low severity. 相似文献
996.
Cover Picture: Densely Packed Hydrophobic Clustering: Encapsulated Valerates Form a High‐Temperature‐Stable {Mo132} Capsule System (Angew. Chem. Int. Ed. 23/2016) 下载免费PDF全文
997.
Dr. M. Rita Correro Dr. Negar Moridi Hansjörg Schützinger Sabine Sykora Erik M. Ammann E. Henrik Peters Dr. Yves Dudal Prof. Dr. Philippe F.‐X. Corvini Prof. Dr. Patrick Shahgaldian 《Angewandte Chemie (International ed. in English)》2016,55(21):6285-6289
The fragile nature of most enzymes is a major hindrance to their use in industrial processes. Herein, we describe a synthetic chemical strategy to produce hybrid organic/inorganic nanobiocatalysts; it exploits the self‐assembly of silane building blocks at the surface of enzymes to grow an organosilica layer, of controlled thickness, that fully shields the enzyme. Remarkably, the enzyme triggers a rearrangement of this organosilica layer into a significantly soft structure. We demonstrate that this change in stiffness correlates with the biocatalytic turnover rate, and that the organosilica layer shields the enzyme in a soft environment with a markedly enhanced resistance to denaturing stresses. 相似文献
998.
J. A. Wolny Y. Garcia I. Faus S. Rackwitz K. Schlage H. -C. Wille V. Schünemann 《Hyperfine Interactions》2016,237(1):65
The results of the nuclear inelastic scattering (NIS)/nuclear resonance vibrational spectroscopy (NRVS) for the powder spectra of dimeric [Fe 2L5(NCS) 4] (L = N-salicylidene-4-amino-1,2,4-triazole) complex are presented. This system is spin crossover (SCO) material tagged with a fluorophore that can sense or “feel” the SCO signal ripping through the molecular network and thereby providing an opportunity to register the SCO transition. The spectra have been measured for the low-spin and high-spin phases of the complex. The high-spin isomer reveals one broad band above 200 cm ?1, while the low-spin one displays two intense bands in the range from 390 to 430 cm ?1, accompanied by a number of weaker bands below this area and one at ca. 490 cm ?1. A normal coordinate analysis based on density functional calculations yields the assignment of the spin marker bands to particular molecular modes. In addition the vibrational contribution to the spin transition has been estimated 相似文献
999.
T.?O.?BauerEmail author M.?Schmitz M.?Graf H.?Kelm H.-J.?Krüger V.?Schünemann 《Hyperfine Interactions》2016,237(1):78
The dinuclear complex [(Fe(L-N4Me2))2(BiBzIm)](ClO4)2?2EtCN (1) has been investigated by Mössbauer spectroscopy carried out in the temperature range from 5 to 150 K with externally applied magnetic fields of up to B = 5 T. By means of a consistent simulation of all experimental data sets within the Spin Hamiltonian formalism, the zero-field splitting D and the rhombicity parameter E/D of the ferrous high-spin (HS) site in this complex was determined to be D = ?15.0 ± 1.0 cm?1 and E/D = 0.33 respectively. The sign of the quadrupole splitting of the HS site is positive which indicates that this iron site of the dinuclear complex 1 has an electronic ground state with the dxy orbital being twofold occupied. 相似文献
1000.