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排序方式: 共有125条查询结果,搜索用时 15 毫秒
1.
A method to identify core documents within a given subject domain has been developed by the author. The method builds on the
concept of polyrepresentation by using different search rationales in several databases and isolating the overlaps between
them. This paper delineates the ideas behind the method and describes the study done to measure its effectiveness.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Summary
We report the synthesis of some new backbone fluorinated
polymers of the poly(phenylenevinylene) type. The new polymers
were characterised by NMR, SEC and X-ray powder diffraction. The
charge carrier mobilities were determined using pulse radiolysis
time resolved microwave conductivity (PR-TRMC) and the carrier
mobilities were compared to the similar non-fluorinated
analogues. The changes in charge carrier mobilities as a
function of molecular substitution pattern is discussed in terms
of other materials properties such as electronic structure and
absorption properties. The major result is that it was found
possible for this type of material to alter the electronic
energy levels by molecular substitution without imparting
significant changes in the magnitude of the charge carrier
mobilities and the optical properties. 相似文献
3.
4.
5.
Mie Lillethorup Mikkel Kongsfelt Marcel Ceccato Bjarke B. E. Jensen Bjarke Jørgensen Steen U. Pedersen Kim Daasbjerg 《Small (Weinheim an der Bergstrasse, Germany)》2014,10(5):922-934
Electrografting using aryldiazonium salts provides a fast and efficient technique to functionalize commercially available 3?5 layered graphene (vapour‐deposited) on nickel. In this study, Raman spectroscopy is used to quantify the grafting efficiency of cyclic voltammetry which is one of the most versatile, yet simple, electrochemical techniques available. To a large extent the number of defects/substituents introduced to the basal plane of high‐quality graphene by this procedure can be controlled through the sweeping conditions employed. After extended electrografting the defect density reaches a saturation level (~1013 cm?2) which is independent of the quality of the graphene expressed through its initial content of defects. However, it is reached within fewer voltammetric cycles for low‐quality graphene. Based on these results it is suggested that the grafting occurs (a) directly at defect sites for, in particular, low‐quality graphene, (b) directly at the basal plane for, in particular, high‐quality graphene, and/or (c) at already grafted molecules to give a mushroom‐like film growth for all films. Moreover, it is shown that a tertiary alkyl bromide can be introduced at a given surface density to serve as radical initiator for surface‐initiated atom transfer radical polymerization (SI‐ATRP). Brushes of poly(methyl methacrylate) are grown from these substrates, and the relationship between polymer thickness and sweeping conditions is studied. 相似文献
6.
PURPOSE: We evaluated whether adult fertility potential was better when unilateral orchiopexy was done at ages 2 to 6 years or later, and we identified those at risk for infertility. MATERIALS AND METHODS: Unilateral orchiopexy was performed simultaneously with testicular biopsy in 11 patients 2.8 to 6.8 years old and in 54, 10.0 to 11.9 years old. In adulthood measurement of testicular volume, serum follicle-stimulating hormone, luteinizing hormone and testosterone was done, as well as analysis of semen specimens. RESULTS: At orchiopexy the 2 groups were statistically similar, and statistically similar fertility potentials were found in adulthood. Five of the 65 patients (7.7%, 95% confidence limits 2.5 to 17%) may experience infertility, representing 33% of both groups with less than 1% of the age matched number of spermatogonia per tubular transverse section (approximately no germ cells) in the biopsy specimen at orchiopexy. CONCLUSIONS: Between ages 2 and 12 years the timing of unilateral orchiopexy may vary without an effect on subsequent fertility potential. When biopsy at surgery lacks germ cells, there is an approximately 33% age independent risk of subsequent infertility. Otherwise patients may be fertile after unilateral orchiopexy between ages 2 and 12 years. 相似文献
7.
String matching and compression are two widely studied areas of computer science. The theory of string matching has a long
association with compression algorithms. Data structures from string matching can be used to derive fast implementations of
many important compression schemes, most notably the Lempel—Ziv (LZ77) algorithm. Intuitively, once a string has been compressed—and
therefore its repetitive nature has been elucidated—one might be tempted to exploit this knowledge to speed up string matching.
The Compressed Matching Problem is that of performing string matching in a compressed text, without uncompressing it. More formally, let T be a text, let Z be the compressed string representing T , and let P be a pattern. The Compressed Matching Problem is that of deciding if P occurs in T , given only P and Z . Compressed matching algorithms have been given for several compression schemes such as LZW.
In this paper we give the first nontrivial compressed matching algorithm for the classic adaptive compression scheme, the
LZ77 algorithm. In practice, the LZ77 algorithm is known to compress more than other dictionary compression schemes, such
as LZ78 and LZW, though for strings with constant per bit entropy, all these schemes compress optimally in the limit. However,
for strings with o(1) per bit entropy, while it was recently shown that the LZ77 gives compression to within a constant factor of optimal, schemes
such as LZ78 and LZW may deviate from optimality by an exponential factor. Asymptotically, compressed matching is only relevant
if |Z|=o(|T|) , i.e., if the compression ratio |T|/|Z| is more than a constant. These results show that LZ77 is the appropriate compression method in such settings.
We present an LZ77 compressed matching algorithm which runs in time O(n log
2
u/n + p) where n=|Z| , u=|T| , and p=|P| . Compare with the na?ve ``decompresion' algorithm, which takes time Θ(u+p) to decide if P occurs in T . Writing u+p as (n u)/n+p , we see that we have improved the complexity, replacing the compression factor u/n by a factor log
2
u/n . Our algorithm is competitive in the sense that O(n log
2
u/n + p)=O(u+p) , and opportunistic in the sense that O(n log
2
u/n + p)=o(u+p) if n=o(u) and p=o(u) .
Received December 20, 1995; revised October 29, 1996, and February 6, 1997. 相似文献
8.
Kacper Januchta Theany To Mikkel S. Bødker Tanguy Rouxel Morten M. Smedskjaer 《Journal of the American Ceramic Society》2019,102(8):4520-4537
Due to an increasing demand for oxide glasses with a better mechanical performance, there is a need to improve our understanding of the composition-structure-mechanical property relations in these brittle materials. At present, some properties such as Young's modulus can to a large extent be predicted based on the chemical composition, while others—in particular fracture-related properties—are typically optimized based on a trial-and-error approach. In this work, we study the mechanical properties of a series of 20 glasses in the quartenary Na2O–Al2O3–B2O3–SiO2 system with fixed soda content, thus accessing different structural domains. Ultrasonic echography is used to determine the elastic moduli and Poisson's ratio, while Vickers indentation is used to determine hardness. Furthermore, the single-edge precracked beam method is used to estimate the fracture toughness (KIc) for some compositions of interest. The compositional evolutions of Vickers hardness and Young's modulus are in good agreement with those predicted from models based on bond constraint density and strength. Although there is a larger deviation, the overall compositional trend in KIc can also be predicted by a model based on the strength of the bonds assumed to be involved in the fracture process. 相似文献
9.
Frederik C. Krebs Kristian O. Sylvester‐Hvid Mikkel Jrgensen 《Progress in Photovoltaics: Research and Applications》2011,19(1):97-112
A compact platform for testing solar cells is presented. The light source comprises a multi‐wavelength high‐power LED (light emitting diode) array allowing the homogenous illumination of small laboratory solar cell devices (substrate size 50 × 25 mm) within the 390–940 nm wavelength range. The spectrum can be synthesized by independent tuning of the 18 different wavelengths to mimic AM1.5G as well as various indoor lamp spectra. The intensity can be controlled with a 214‐bit accuracy and intensities up to 3 suns are possible with an approximate AM1.5G spectral distribution. For several wavelengths intensities up to 10 suns is possible, and for a few wavelengths up to 30 suns can be reached. The setup is equipped with reference diodes and an optical fibre coupling enabling calibration, monitoring and control of the light impinging on the sample. Through a computer controlled interface, it is possible to perform all the commonly employed measurements on the solar cell at very high speed without moving the sample. In particular, the LED‐based illumination system provides an alternative to light‐biased incident photon‐to‐current efficiency measurement to be performed which we demonstrate. Both top and bottom contact is possible and the atmosphere can be controlled around the sample during measurements. The setup was developed for the field of polymer and organic solar cells with particular emphasis on enabling different laboratories to perform measurements in the same manner and obtain a common basis for comparing data. The use of the platform is demonstrated using a standard P3HT:PCBM polymer solar cell but is generally applicable to any solar cell technology with a spectral response in the 390–950 nm region. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
Dr. Michael R. Mortensen Dr. Mikkel B. Skovsgaard Prof. Kurt V. Gothelf 《Chembiochem : a European journal of chemical biology》2019,20(21):2711-2728
The plethora of methods developed for the creation of protein conjugates often differs significantly with regard to the heterogeneity of the resulting products, in the degree of genetic manipulation of the protein required, and in the technical skills required to perform the conjugation procedure. Affinity-guided protein conjugation is a protein labeling methodology based on noncovalent binding interactions between a labeling probe and the protein of interest. These interactions increase the local concentration of a reactive group in the probe on the protein surface thus facilitating the conjugation in proximity of the complexation site. The ability to produce high-quality conjugates from nongenetically modified proteins both in vitro, but also in cells, demonstrates the power of affinity-guided protein conjugation. Here, we present the progress of affinity-guided protein conjugation in relation to selective protein labeling in living systems and the formation of high-quality protein conjugates. Furthermore, the probe design will be discussed in relation to the utility of the probe for labeling in vitro or in living systems. 相似文献