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排序方式: 共有1759条查询结果,搜索用时 31 毫秒
21.
Andrea Schenkmayerová Anikó Bertóková Jana Šefčovičová Vladimír Štefuca Marek Bučko Alica Vikartovská Peter Gemeiner Ján Tkáč Jaroslav Katrlík 《Analytica chimica acta》2015
A microbial biosensor for 2-phenylethanol (2-PE) based on the bacteria Gluconobacter oxydans was developed and applied in monitoring of a biotechnological process. The cells of G. oxydans were immobilized within a disposable polyelectrolyte complex gel membrane consisting of sodium alginate, cellulose sulphate and poly(methylene-co-guanidine) attached onto a miniaturized Clark oxygen electrode, forming whole cell amperometric biosensor. Measured changes in oxygen concentration were proportional to changes in 2-PE concentration. The biosensor sensitivity was 864 nA mM−1 (RSD = 6%), a detection limit of 1 μM, and the biosensor response towards 2-PE was linear in the range 0.02–0.70 mM. The biosensor preserved 93% of its initial sensitivity after 7 h of continuous operation and exhibited excellent storage stability with loss of only 6% of initial sensitivity within two months, when stored at 4 °C. The developed system was designed and successfully used for an off-line monitoring of whole course of 2-PE biooxidation process producing phenylacetic acid (PA) as industrially valuable aromatic compound. The biosensor measurement did not require the use of hazardous organic solvent. The biosensor response to 2-PE was not affected by interferences from PA and phenylacetaldehyde at concentrations present in real samples during the biotransformation and the results were in a very good agreement with those obtained via gas chromatography. 相似文献
22.
Sustainable Synthesis of Chiral Tetrahydrofurans through the Selective Dehydration of Pentoses 下载免费PDF全文
Robert W. Foster Dr. Christopher J. Tame Dr. Dejan‐Krešimir Bučar Prof. Helen C. Hailes Dr. Tom D. Sheppard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):15947-15950
L ‐Arabinose is an abundant resource available as a waste product of the sugar beet industry. Through use of a hydrazone‐based strategy, L ‐arabinose was selectively dehydrated to form a chiral tetrahydrofuran on a multi‐gram scale without the need for protecting groups. This approach was extended to other biomass‐derived reducing sugars and the mechanism of the key cyclization investigated. This methodology was applied to the synthesis of a range of functionalized chiral tetrahydrofurans, as well as a formal synthesis of 3R‐3‐hydroxymuscarine. 相似文献
23.
Cooperative Crystallization of Heterometallic Indium–Chromium Metal–Organic Polyhedra and Their Fast Proton Conductivity 下载免费PDF全文
Dr. Quan‐Guo Zhai Chengyu Mao Dr. Xiang Zhao Dr. Qipu Lin Fei Bu Xitong Chen Prof. Dr. Xianhui Bu Prof. Dr. Pingyun Feng 《Angewandte Chemie (International ed. in English)》2015,54(27):7886-7890
Metal–organic polyhedra (MOPs) or frameworks (MOFs) based on Cr3+ are notoriously difficult to synthesize, especially as crystals large enough to be suitable for characterization of the structure or properties. It is now shown that the co‐existence of In3+ and Cr3+ induces a rapid crystal growth of large single crystals of heterometallic In‐Cr‐MOPs with the [M8L12] (M=In/Cr, L=dinegative 4,5‐imidazole‐dicarboxylate) cubane‐like structure. With a high concentration of protons from 12 carboxyl groups decorating every edge of the cube and an extensive H‐bonded network between cubes and surrounding H2O molecules, the newly synthesized In‐Cr‐MOPs exhibit an exceptionally high proton conductivity (up to 5.8×10?2 S cm?1 at 22.5 °C and 98 % relative humidity, single crystal). 相似文献
24.
A solute transport through a porous medium is examined provided that the fluid leaving the porous sample returns back in a continuous way. The porous medium is thus included into a closed hydrodynamic circuit. This cycling process is suggested as an experimental tool to determine porous medium parameters describing transport. In the present paper the mathematical theory of this method is developed. For the advective type of transport with solute retention and degradation in porous medium, the system of transport equations in a closed circuit is transformed to a delay differential equation. The exact analytical solution to this equation is obtained. The solute concentration manifests both the oscillatory and monotonous behaviors depending on system parameters. The number of oscillation splashes is shown to be always finite. The maximum/minimum points are determined as solutions of a polynomial equation whose degree depends on the unknown solution itself. The cyclic methods to determine porous medium parameters as porosity and retention rate are developed. 相似文献
25.
Christophe Felder Constantin Oltean Mikhail Panfilov Michel Buès 《Comptes Rendus Mecanique》2004,332(3):223-229
The investigation of non-reactive miscible solute dispersion in a vertical Hele–Shaw cell is considered. An asymptotic method is used to extend Taylor model to the case of the fluid density, the dynamic viscosity and the molecular diffusion coefficient are solute concentration-dependent. It is demonstrated that the averaged variables over the gap are governed by a convection–dispersion equation in which the dispersion tensor is concentration-dependent. To cite this article: C. Felder et al., C. R. Mecanique 332 (2004). 相似文献
26.
A new formulation for the modeling of density coupled flow and transport in porous media is presented. This formulation is based on the development of the mass balance equation by using the conservative form. The system of equations obtained by coupling the flow and transport equations using a state equation is solved by a combination of the mixed hybrid finite element method (MHFEM) and the discontinuous finite element method (DFEM). The former is applied in order to solve the flow equation and the dispersive part of the transport equation, whilst the latter is used to solve the advective part of the transport equation. Although the advantages of the MHFEM are known (efficiency calculation of velocity field and continuity of fluxes from one element to an adjacent one), its application in a classical development form (volumetric fluxes as unknowns) leads to the non-conservative version of the mass balance equation. The associated matrix of the system of equations obtained by hybridization is positive definite but non-symmetrical. By using a new approach (mass fluxes as unknowns) the conservative form of the continuity equation is preserved and the associated matrix of the system of equations obtained by hybridization becomes symmetrical. When applied to Elder's problem involving a strong density contrast, this new approach, with a lower calculation cost, leads to similar or identical results to those found in the specialized literature. The comparison between the conservative and non-conservative formulations solved with the same MHFEM and DFEM combination emphasizes the rigor and the pertinence of this new approach. Furthermore, we show the existence of a limit refinement defining the stability of the numerical solution for Elder's problem. 相似文献
27.
一种薄板弯曲问题的四边形位移单元 总被引:32,自引:0,他引:32
本文基于修正势能泛函,引入广义协调的概念,导出了一种具有12个自由度的薄板弯曲四边形位移单元LGC—Q12,这种单元协调性好,列式简单,计算精度高。并且能近似地通过分片检验。 相似文献
28.
29.
The aim of this study is the investigation of the effects of density and viscosity contrasts on miscible displacements when
the regime is stable. It has been possible to quantify these effects by using an empirical model which takes into account
both the physical properties of the liquids and the hydrodynamic parameters in different configurations of a miscible displacement
involving distilled water and a calcium chloride solution. The introduction of a method for measuring electrical conductivities
within the porous medium itself (without disturbing the flow) has enabled us to monitor the change in the mixing zone throughout
the entire length of the flow path. A stability criterion based on hydrodynamic parameters has been established that depends
on two dimensionless numbers. 相似文献
30.
Mikhail Panfilov Constantin Oltean Irina Panfilova Michel Buès 《Comptes Rendus Mecanique》2003,331(1):41-48
The quadratic law of laminar flow through porous media at high Reynolds numbers, which is well confirmed by the multiple experimental data, is shown to give rise to three fundamental paradoxes. All them can be resolved by assuming the singular structure of flow. The singularity is produced by the formation of jet brunches which invade the stagnant zones and sharply loss their kinetic energy. The numerical simulation confirms this effect. To cite this article: M. Panfilov et al., C. R. Mecanique 331 (2003). 相似文献