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1.
The crystal structure of Escherichia coli ornithine transcarbamoylase (OTCase, EC 2.1.3.3) complexed with the bisubstrate analog N-(phosphonacetyl)-L-ornithine (PALO) has been determined at 2.8-A resolution. This research on the structure of a transcarbamoylase catalytic trimer with a substrate analog bound provides new insights into the linkages between substrate binding, protein-protein interactions, and conformational change. The structure was solved by molecular replacement with the Pseudomonas aeruginosa catabolic OTCase catalytic trimer (Villeret, V., Tricot, C., Stalon, V. & Dideberg, O. (1995) Proc. Natl. Acad. Sci. USA 92, 10762-10766; Protein Data Bank reference pdb 1otc) as the model and refined to a crystallographic R value of 21.3%. Each polypeptide chain folds into two domains, a carbamoyl phosphate binding domain and an L-ornithine binding domain. The bound inhibitor interacts with the side chains and/or backbone atoms of Lys-53, Ser-55, Thr-56, Arg-57, Thr-58, Arg-106, His-133, Asn-167, Asp-231, Met-236, Leu-274, Arg-319 as well as Gln-82 and Lys-86 from an adjacent chain. Comparison with the unligated P. aeruginosa catabolic OTCase structure indicates that binding of the substrate analog results in closure of the two domains of each chain. As in E. coli aspartate transcarbamoylase, the 240s loop undergoes the largest conformational change upon substrate binding. The clinical implications for human OTCase deficiency are discussed. 相似文献
2.
Maria G Corradini Mark D Normand Micha Peleg 《Journal of the science of food and agriculture》2006,86(5):785-792
Currently, the sterility of heat‐processed food and pharmaceuticals is assessed in terms of an F0 value, based on the equivalence of the heat treatment to an isothermal process at a reference temperature. This F0 value, however, has a meaning if, and only if, the inactivation kinetics of the targeted spores (or cells) follow a first‐order relationship and the temperature dependence of the D value, the reciprocal of the rate constant, is log‐linear. There is growing evidence that these conditions are not satisfied by many spores, including those of Clostridium botulinum and vegetative cells. Consequently, a replacement for the F0 value is proposed in the form of a momentary equivalent time at the reference temperature based on the actual survival pattern of the spores, which need not be log‐linear. This equivalent time can be calculated together with the theoretical survival ratio in real time, thus enabling an operator to monitor the lethality of ongoing industrial heat processes. The concept is demonstrated with published survival data of C. botulinum, for which the Weibullian and log‐logistic models served as primary and secondary models, respectively. The safety factor according to the proposed method is in the number of added minutes of processing, beyond the theoretical time needed to reduce the survival ratio of the targeted spores or cells to a level that would produce practical (or commercial) sterility. Copyright © 2006 Society of Chemical Industry 相似文献
3.
M Peleg 《Critical reviews in food science and nutrition》1992,32(1):59-66
The validity of the WLF model with fixed "universal" coefficients was tested against that of the model original form with variable coefficients using published coefficients of polymers and amorphous sugars crystallization and viscosity data. The disagreement between the two versions of the model is particularly large at temperature ranges starting about 20 to 30 degrees K above the glass transition or reference temperature, excluding the former from being a model of general applicability. Because the WLF model mathematical structure entails the existence of an almost linear region near the reference temperature, establishment of its validity as a kinetic model and meaningful determination of its constants requires data spread over an extended temperature range, especially when the experimental results have a scatter. 相似文献
4.
This paper presents an efficient scheme maintaining a separator decomposition representation in dynamic trees using asymptotically optimal labels. In order to maintain the short labels, the scheme uses relatively low
message complexity. In particular, if the initial dynamic tree contains only the root, then the scheme incurs an O(log4
n) amortized message complexity per topology change, where n is the current number of vertices in the tree. As a separator decomposition is a fundamental decomposition of trees used
extensively as a component in many static graph algorithms, our dynamic scheme for separator decomposition may be used for
constructing dynamic versions to these algorithms. The paper then shows how to use our dynamic separator decomposition to
construct efficient labeling schemes on dynamic trees, using the same message complexity as our dynamic separator scheme.
Specifically, we construct efficient routing schemes on dynamic trees, for both the designer and the adversary port models,
which maintain optimal labels, up to a multiplicative factor of O(log log n). In addition, it is shown how to use our dynamic separator decomposition scheme to construct dynamic labeling schemes supporting
the ancestry and NCA relations using asymptotically optimal labels, as well as to extend a known result on dynamic distance
labeling schemes.
Supported in part at the Technion by an Aly Kaufman fellowship.
Supported in part by a grant from the Israel Science Foundation. 相似文献
5.
Nguyen Dieu My T. Fard Golnar Gharooni Atkins Ashley Bontempo Paul Iuzzolino Michael L. Peleg Orit 《Artificial Life and Robotics》2023,28(1):1-7
Artificial Life and Robotics - Honey bees (Apis mellifera L.) are social insects that makes frequent use of volatile pheromone signals to collectively navigate unpredictable and unknown... 相似文献
6.
7.
This paper deals with compact label-based representations for trees. Consider an n-node undirected connected graph G with a predefined numbering on the ports of each node. The all-ports tree labeling ℒ
all
gives each node v of G a label containing the port numbers of all the tree edges incident to v. The upward tree labeling ℒ
up
labels each node v by the number of the port leading from v to its parent in the tree. Our measure of interest is the worst case and total length of the labels used by the scheme, denoted
M
up
(T) and S
up
(T) for ℒ
up
and M
all
(T) and S
all
(T) for ℒ
all
. The problem studied in this paper is the following: Given a graph G and a predefined port labeling for it, with the ports of each node v numbered by 0,…,deg (v)−1, select a rooted spanning tree for G minimizing (one of) these measures. We show that the problem is polynomial for M
up
(T), S
up
(T) and S
all
(T) but NP-hard for M
all
(T) (even for 3-regular planar graphs). We show that for every graph G and port labeling there exists a spanning tree T for which S
up
(T)=O(nlog log n). We give a tight bound of O(n) in the cases of complete graphs with arbitrary labeling and arbitrary graphs with symmetric port labeling. We conclude by
discussing some applications for our tree representation schemes.
A preliminary version of this paper has appeared in the proceedings of the 7th International Workshop on Distributed Computing
(IWDC), Kharagpur, India, December 27–30, 2005, as part of Cohen, R. et al.: Labeling schemes for tree representation. In:
Proceedings of 7th International Workshop on Distributed Computing (IWDC), Lecture Notes of Computer Science, vol. 3741, pp. 13–24
(2005).
R. Cohen supported by the Pacific Theaters Foundation.
P. Fraigniaud and D. Ilcinkas supported by the project “PairAPair” of the ACI Masses de Données, the project “Fragile” of
the ACI Sécurité et Informatique, and by the project “Grand Large” of INRIA.
A. Korman supported in part by an Aly Kaufman fellowship.
D. Peleg supported in part by a grant from the Israel Science Foundation. 相似文献
8.
Link-based information structures such as the web can be enhanced through the addition of hotlinks. Assume that each node in the information structure is associated with a weight representing the access frequency of the node by users. In order to access a particular node, the user must follow a path leading to it from the root. By adding new hotlinks to the tree, it may be possible to reduce the access cost of the system, namely, the expected number of steps needed to reach a leaf from the root, assuming the user can decide which hotlinks to follow in each step. The hotlink assignment problem involves finding a set of hotlinks (with at most K=O(1) hotlinks emanating from every node) maximizing the gain in the expected cost. The paper addresses this problem in two user models, namely, the traditional clairvoyant user model employed in [P. Bose, J. Czyzowicz, L. Gasieniec, E. Kranakis, D. Krizanc, A. Pelc, M.V. Martin, Strategies for hotlink assignments, in: Proc. 11th Symp. on Algorithms and Computation, 2000, pp. 23–34; E. Kranakis, D. Krizanc, S. Shende, Approximating hotlink assignments, in: Proc. 12th Symp. on Algorithms and Computation, 2001, pp. 756–767; P. Bose, D. Krizanc, S. Langerman, P. Morin, Asymmetrical communication protocols via hotlink assignments, in: Proc. 9th Colloq. on Structural Information and Communication Complexity, 2002, pp. 33–39; R. Matichin, D. Peleg, Approximation algorithm for hotlink assignments in web directories, in: Proc. Workshop on Algorithms and Data Structures, 2003, pp. 271–280] and the more realistic greedy user model recently introduced in [O. Gerstel, S. Kutten, R. Matichin, D. Peleg, Hotlink enhancement algorithms for web directories, in: Proc. 14th Symp. on Algorithms and Computation, 2003, pp. 68–77], and presents a polynomial time 2-approximation algorithm for the hotlink assignment problem on rooted directed trees. 相似文献
9.
Distance labeling schemes are composed of a marker algorithm for
labeling the vertices of a graph with short labels, coupled with a
decoder algorithm allowing one to compute the distance between
any two vertices directly from their labels (without using any additional
information).
As applications for distance labeling schemes
concern mainly large and dynamically changing networks,
it is of interest to study distributed dynamic labeling schemes.
The current paper considers the problem on dynamic trees,
and proposes efficient distributed schemes for it.
The paper first presents a labeling scheme for distances in the dynamic
tree model, with amortized message complexity O(log2
n) per operation,
where n is the size of the tree at the time the operation takes place.
The protocol maintains O(log2
n) bit labels.
This label size is known to be optimal even in the static scenario.
A more general labeling scheme is then introduced for the dynamic tree
model, based on extending an existing static tree labeling
scheme to the dynamic setting. The approach fits a number of
natural tree functions, such as distance, separation level, and flow.
The main resulting scheme incurs an overhead
of an O(log n) multiplicative factor in both the label size and
amortized message complexity in the case of dynamically growing
trees (with no vertex deletions).
If an upper bound on n is known in advance,
this method yields a different tradeoff, with an
O(log2
n/log log n) multiplicative overhead on the label
size but only an O(log n/log log n) overhead on the amortized
message complexity.
In the fully dynamic model the scheme also incurs an increased
additive overhead in amortized communication, of O(log2
n)
messages per operation. 相似文献
10.
The resource discovery problem was introduced by Harchol-Balter,
Leighton, and Lewin. They developed a number of algorithms
for the problem in the weakly connected directed graph model. This model is a
directed logical graph that represents the vertices’ knowledge about the topology
of the underlying communication network.
The current paper proposes a deterministic algorithm for the
problem in the same model,
with improved time, message, and communication complexities.
Each previous algorithm had a complexity that was higher at least in one of the
measures. Specifically, previous deterministic solutions required either time linear
in the diameter of the initial network, or communication complexity $O(n^3)$ (with
message complexity $O(n^2)$), or message complexity $O(|E_0| \log n)$ (where $E_0$
is the arc set of the initial graph $G_0$). Compared with the main randomized
algorithm of Harchol-Balter, Leighton, and Lewin, the time complexity is reduced
from $O(\log^2n)$ to\pagebreak[4] $O(\log n )$, the message complexity from $O(n \log^2 n)$ to
$O(n \log n )$, and the communication complexity from $O(n^2 \log^3 n)$ to
$O(|E_0|\log ^2 n )$.
\par
Our work significantly extends the connectivity algorithm of Shiloach
and Vishkin which was originally given for a parallel model of computation.
Our result also confirms a conjecture of Harchol-Balter, Leighton, and
Lewin, and addresses an open question due to Lipton. 相似文献