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991.
Biosynthetic Origin of the Antibiotic Cyclocarbamate Brabantamide A (SB‐253514) in Plant‐Associated Pseudomonas. 下载免费PDF全文
Dr. Yvonne Schmidt Dr. Menno van der Voort Dr. Max Crüsemann Prof. Dr. Jörn Piel Michaele Josten Prof. Dr. Hans‐Georg Sahl Henrike Miess Prof. Dr. Jos M. Raaijmakers Prof. Dr. Harald Gross 《Chembiochem : a European journal of chemical biology》2014,15(2):259-266
Within the framework of our genome‐based program to discover new antibiotic lipopeptides from Pseudomonads, brabantamides A–C were isolated from plant‐associated Pseudomonas sp. SH‐C52. Brabantamides A–C displayed moderate to high in vitro activities against Gram‐positive bacterial pathogens. Their shared structure is unique in that they contain a 5,5‐bicyclic carbamate scaffold. Here, the biosynthesis of brabantamide A (SB‐253514) was studied by a combination of bioinformatics, feeding experiments with isotopically labelled precursors and in vivo and in vitro functional analysis of enzymes encoded in the biosynthetic pathway. The studies resulted in the deduction of all biosynthetic building blocks of brabantamide A and revealed an unusual feature of this metabolite: its biosynthesis occurs via an initially formed linear di‐lipopeptide that is subsequently rearranged by a novel FAD‐dependent Baeyer–Villiger monooxygenase. 相似文献
992.
Experimental validation of a flexible modeling approach for distillation columns with packings 下载免费PDF全文
The two main concepts for the modeling of distillation columns are the equilibrium‐stage (EQ) and the nonequilibrium‐stage (NEQ). A model is presented which combines decisive features of both conventional concepts. Based on the idea of a reduced nonequilibrium‐stage (RNEQ), this model can be used for the simulation of distillation columns with packings. In contrast to the conventional NEQ approach, this model neglects the influence of liquid side mass‐transfer coefficients, which ultimately allows to come up with only one empirical equation describing the overall mass transfer. Thus, a considerable reduction in model complexity is reached, which allows for an efficient consideration of new experimental distillation results. Fitted to experimental data, the model is able to predict, how different pressures and chemical systems might affect the separation efficiency. By comparing calculation results with experimentally determined separation efficiencies for three different packing types, these valuable RNEQ qualities are illustrated. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3833–3847, 2014 相似文献
993.
Eder G Schlögl S Macknapp K Heckl WM Lackinger M 《The Review of scientific instruments》2011,82(3):033701
We describe the setup, characteristics, and application of an in vacuo ion-sputtering and electron-beam annealing device for the postpreparation of scanning probes (e.g., scanning tunneling microscopy (STM) tips) under ultrahigh vacuum (UHV) conditions. The proposed device facilitates the straightforward implementation of a common two-step cleaning procedure, where the first step consists of ion-sputtering, while the second step heals out sputtering-induced defects by thermal annealing. In contrast to the standard way, no dedicated external ion-sputtering gun is required with the proposed device. The performance of the described device is demonstrated by SEM micrographs and energy dispersive x-ray characterization of electrochemically etched tungsten tips prior and after postprocessing. 相似文献
994.
Padavattan Govindaswamy Georg Süss-Fink Bruno Therrien 《Inorganic chemistry communications》2007,10(12):1489-1492
Two cationic pentamethylcyclopentadienyl metal-based hexanuclear complexes with trigonal prismatic architecture have been synthesised through a two-step strategy. The dinuclear complexes [M(η5- C5Me5)(μ-Cl)Cl]2 (M = rhodium and iridium) react with 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine (tpt) in dichloromethane to give the trinuclear complexes [Rh3(η5-C5Me5)3(μ3-tpt)Cl6] (1) and [Ir3(η5-C5Me5)3(μ3-tpt)Cl6] (2), respectively. Addition of silver triflate to 1 and 2 in dichloromethane connects two identical triangular panels to form the hexanuclear metallo-prismatic cations [Rh6(η5-C5Me5)6(μ3-tpt)2(μ-Cl)6]6+ (3) and [Ir6(η5-C5Me5)6(μ3-tpt)2(μ-Cl)6]6+ (4), respectively. Cations 3 and 4 have been isolated as their triflate salts and characterised by 1H NMR, IR and UV/visible spectroscopy. 相似文献
995.
Novel manufacturing process of hollow polymer microspheres 总被引:1,自引:0,他引:1
A novel manufacturing process of gas-filled, hollow, poly-butyl-2-cyanoacrylate (PBCA) microspheres in an aqueous phase is the subject of this paper. The two-step process enables the control of the particle-wall size, as well as the particle size. Particles of this type are useful in the medical and pharmaceutical industry for diagnostic purposes in connection with ultrasound and for life or food science applications, such as taste masking, release on demand, etc. Depending upon the process conditions, the particle size ranges from 1 to . The microparticles are formed by using surfactant-stabilized microbubbles, which act as a template. At the interfacial area of these templates, PBCA nanoparticles create deposits that form the particle wall, as the result of a partial filming process. The density of the particles has been calculated as ranging from 100 up to and the volume fraction of the entrapped gas can be 5% or more. The developed process can operate on a scale of several kilograms. 相似文献
996.
We present a detailed electron diffraction study of individual single-walled carbon nanotubes. A novel sample preparation procedure provides well-separated, long and straight individual single-shell nanotubes. Diffraction experiments are carried out at 60 kV, below the threshold for knock-on damage in carbon nanotubes. We describe experimental parameters that allow single-tube electron diffraction experiments with widely available thermal emission transmission electron microscopes. Further, we review the simulation of diffraction patterns for these objects. 相似文献
997.
Friction forces in the tip–sample contact govern the dynamics of contact mode atomic force microscopy. In ambient conditions typical contact radii between tip and sample are in the order of a few nanometers. In order to account for the large interaction area the dynamics of contact mode atomic force microscope (AFM) is investigated under the assumption of a multi-asperity contact interface between tip and sample. Thus, the kinetic friction force between tip and sample is the product of the real contact area between both solids and the interfacial shear strength. The velocity strengthening of the lateral force is modeled assuming a logarithmic relationship between shear-strength and velocity. Numerical simulations of the system dynamics with this empirical model show the existence of two different regimes in contact mode AFM: steady sliding and stick–slip where the tip undergoes periodically stiction and kinetic friction. The state of the system depends on the scan velocity as well as on the velocity dependence of the interfacial friction force between tip and sample. Already small viscous damping contributions in the tip–sample contact are sufficient to suppress stick–slip oscillations. 相似文献
998.
Simultaneous double-disk grinding (DDG) is a novel and powerful technology for precision-machining mono-crystalline silicon slices (“wafers”). With DDG the extreme degrees of planarity can be achieved, which the fabrication of micro-electronic devices with minimum lateral feature dimensions of 90 nm and below demands. In DDG, both sides of the wafer are ground simultaneously between two opposite grinding wheels on collinear spindle axes. It is a chuck-less process, in which the workpiece is machined in “free-floating” fashion. Machining kinematics, removal mechanism, and resulting wafer shape differ from those known from (chuck-mounted) single-side grinding or double-sided batch lapping, which are conventionally used in mechanical wafer shaping. This article explains the kinematics of DDG and derives the basic, method-inherent features always observed on DDG-ground wafers from simple kinematic considerations without further model assumptions: global wafer shape, center dip (“navel”), edge thickness roll-off, and symmetries. The expected results are compared with experimental data. 相似文献
999.
Suelen Barg Dietmar Koch Maxim Pulkin Georg Grathwohl 《Journal of Materials Science》2008,43(2):483-488
The sintering behavior of borosilicate and soda-lime mono-sized glass beads was investigated with the aim to fabricate transparent
porous glass balls and cylinders. As the glasses tend to crystallize, temperatures where the sintering was in advantage compared
to crystallization were used. Isothermal studies were undertaken for modeling the evolution of sintering necks as a function
of radii of beads, temperature and time. The Frenkel model of viscous flow was applied to predict first and second stage of
sintering. As the sintering of the glasses without crystallization was only possible at high temperatures the process is very
fast and has to be controlled precisely. The results of this work were applied for the fabrication of porous bodies with specific
characteristics: different geometries and sizes, transparency, high porosities to be achieved during first stage sintering
of spherical glass beads. The porous parts with these characteristics are used for the investigation of hydrodynamic processes
in the pore network of glass parts. 相似文献
1000.
Ohne Zusammenfassung
Zuschriften zum Studierendenforum bitte an:
Universit?t Bayreuth
Lehrstuhl BWL VII (Wirtschaftsinformatik)
Prof. Dr. Torsten Eymann
Redaktion Studierendenforum
z. Hd. Dipl.-Wirtschaftsinformatiker Stefan K?nig
Universit?tsstra?e 30
95447 Bayreuth
E-Mail: stefan.koenig@uni-bayreuth.de 相似文献