全文获取类型
收费全文 | 15940篇 |
免费 | 742篇 |
国内免费 | 140篇 |
专业分类
化学 | 10837篇 |
晶体学 | 103篇 |
力学 | 435篇 |
数学 | 2755篇 |
物理学 | 2692篇 |
出版年
2023年 | 140篇 |
2022年 | 255篇 |
2021年 | 330篇 |
2020年 | 402篇 |
2019年 | 386篇 |
2018年 | 256篇 |
2017年 | 224篇 |
2016年 | 607篇 |
2015年 | 478篇 |
2014年 | 566篇 |
2013年 | 869篇 |
2012年 | 1124篇 |
2011年 | 1315篇 |
2010年 | 675篇 |
2009年 | 584篇 |
2008年 | 987篇 |
2007年 | 944篇 |
2006年 | 937篇 |
2005年 | 837篇 |
2004年 | 727篇 |
2003年 | 505篇 |
2002年 | 521篇 |
2001年 | 177篇 |
2000年 | 148篇 |
1999年 | 150篇 |
1998年 | 118篇 |
1997年 | 129篇 |
1996年 | 170篇 |
1995年 | 106篇 |
1994年 | 112篇 |
1993年 | 120篇 |
1992年 | 86篇 |
1991年 | 93篇 |
1990年 | 71篇 |
1989年 | 72篇 |
1988年 | 84篇 |
1987年 | 72篇 |
1986年 | 67篇 |
1985年 | 99篇 |
1984年 | 105篇 |
1982年 | 115篇 |
1981年 | 122篇 |
1980年 | 97篇 |
1979年 | 84篇 |
1978年 | 113篇 |
1977年 | 92篇 |
1976年 | 73篇 |
1975年 | 71篇 |
1974年 | 64篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Kelley BD Booth J Tannatt M Wub QL Ladner R Yuc J Potter D Ley A 《Journal of chromatography. A》2004,1038(1-2):121-130
Polypeptides for use in affinity chromatography of factor VIII were identified using phage display technology. Phage libraries were designed to express polypeptide fusions containing five to seven residues flanked by two cysteines that form a disulfide bond. Individual bacteriophage were selected for the ability of these polypeptides to bind factor VIII, and then release the protein under mild elution conditions. Strong consensus sequences were observed that appear to be necessary for this reversible interaction. Chemically synthesized ligands identified by this screening were immobilized onto a chromatographic support and used for affinity purification of factor VIII from a complex feedstream. A chromatographic step was developed that provided a 10000-fold reduction in host cell proteins and DNA, while providing exceptional product recovery. 相似文献
92.
Merkx M Kopp DA Sazinsky MH Blazyk JL Müller J Lippard SJ 《Angewandte Chemie (International ed. in English)》2001,40(15):2725
The cover picture shows in the background the whole cell of a methanotrophic bacterium on which are superimposed components of methane monooxygenase (the structure of the hydroxylase component (top), one of the two four-helix bundles that house the catalytic diiron centers (left)) and a schematic diagram of the catalytic cycle by which the enzyme converts dioxygen and methane into methanol and water. More about this unusual enzyme system is reported by Lippard et al. on p. 2782 ff. 相似文献
93.
Monot Frédéric Benoit Yves Ballerini Daniel Vandecasteele Jean-Paul 《Applied biochemistry and biotechnology》1990,(1):375-386
Utilization of lipases for synthesis of esters of hydrophilic polyols has been investigated. The choice of a suitable solvent
is crucial in this type of reaction. An interesting case is fatty acid esters from neopentylpolyols, such as trimethylolpropane,
which are of great interest as high temperature lubricants. Enzymatic synthesis of trimethylolpropane tricaprylate was studied
as an alternative to chemical manufacturing. Triester production occurred only if the water produced by esterification was
continuously removed from the medium. In these condition, kinetics of appearance and transformation of mono-, di- and triesters
were determined in order to define optimal conditions. 相似文献
94.
Schell Daniel J. Walter Pamela J. Johnson David K. 《Applied biochemistry and biotechnology》1992,34(1):659-665
Applied Biochemistry and Biotechnology - The enzymatic digestibility of a pretreated substrate is enhanced by increasing the severity of the pretreatment conditions, apparently because a greater... 相似文献
95.
Daniel Tholen Roderick Chappel Barbara Francis 《Accreditation and quality assurance》2006,11(8-9):400-407
International requirements for PT and EQA state that providers must demonstrate that samples are homogeneous and stable. However, testing for homogeneity and stability can be expensive, use samples that could otherwise serve as quality-control materials, and can also fail to detect significant inhomogeneity and instability. In some situations it may be preferable to use the results from participants to identify problems with sample lots, if historic results follow predictable distributions and a statistical decision rule can be produced. An unusually high proportion of incorrect results may indicate that samples were inhomogeneous or unstable. Conditions under which this can be demonstrated are discussed, and the efficacy of the proposal is demonstrated with two examples. This procedure is especially effective when there are a large number of participants and/or a historic small proportion of incorrect results. Providers who adopt this proposal will need to retain samples for testing and assume the risk of distributing bad samples.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia 相似文献
96.
Daniel C.S. Tse Theodore Kuwana Garfield P. Royer 《Journal of Electroanalytical Chemistry》1979,98(2):345-353
Methylaminopropylviologen (MAV) was covalently attached to glassy carbon electrodes via cyuranic chloride. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of bound MAV on the electrode surfaces. Electrochemical experiments of these electrodes indicated that the bound MAV was stable and electrochemically active for extended periods of time in aqueous media. The surface coverage of MAV was in the range, of 2.0–3.0×10?10 mol cm?2. 相似文献
97.
98.
The rotational contour of the 4683 Å emission band of the o-xylyl radical was studied at high resolution. Calculations of the rotational contour of this hybrid band were made in the rigid rotor approximation for various sets of values of the excited state rotational constants and directions of the transition moment μ. Matching of computed and experimental rotational features showed that μ is oriented at +37° or ?37° with respect to the b inertial axis. The nature of the excited states of o-xylyl and the methyl-to-ring interaction are discussed with respect to these two possible assignments 相似文献
99.
Sébastien Fiorucci Jer?me Golebiowski Daniel Cabrol-Bass Serge Antonczak 《Chemphyschem》2004,5(11):1726-1733
Flavonoids are naturally occurring phenol derivatives present in substantial amounts in a large variety of plants, fruits and vegetables daily eaten by humans. Most of these compounds exhibit several interesting biological activities, such as antiradical and antioxidant actions. Indeed, by complexation with specific enzymes, flavonoids are notably liable to metabolize molecular dioxygen. On the basis of experimental results describing oxygenolysis of the flavonoid quercetin, activated by the enzyme quercetin 2,3-dioxygenase (2,3-QD),ur attention has focused on the role of metal center in the activation of the substrate quercetin. Thus, in the present study, by means of DFT calculations at the B3LYP/ 6-31(+)G* level on model molecular systems, we describe different mechanisms for dioxygen metabolization by quercetin. Stationary points are described, and energetic and structural analyses along the reaction paths are reported. Our calculations show that the copper cation must act as an oxidant towards the substrate and that the reaction proceeds through a 1,3-cycloaddition. 相似文献
100.
Electroosmotic flow (EOF) is a phenomenon associated with the movement of an aqueous solution induced by the application of an electric field in microchannels. The characteristics of EOF depend on the nature of the surface potential, i.e., whether it is uniform or nonuniform. In this paper, a lattice Boltzmann model (LBM) combined with the Poisson-Boltzmann equation is used to simulate flow field in a rectangular microchannel with nonuniform (step change) surface potentials. The simulation results indicate that local circulations can occur near a heterogeneous region with nonuniform surface potentials, in agreement with those by other authors. Largest circulations, which imply a highest mixing efficiency due to convection and short-range diffusion, were found when the average surface potential is zero, regardless of whether the distribution of the heterogeneous patches is symmetric or asymmetric. In this work, we have illustrated that there is a trade-off between the mixing and liquid transport in EOF microfluidics. One should not simply focus on mixing and neglect liquid transport, as performed in the literature. Excellent mixing could lead to a poor transport of electroosmotic flow in microchannels. 相似文献