全文获取类型
收费全文 | 83567篇 |
免费 | 945篇 |
国内免费 | 406篇 |
专业分类
电工技术 | 771篇 |
综合类 | 2317篇 |
化学工业 | 11363篇 |
金属工艺 | 4784篇 |
机械仪表 | 3019篇 |
建筑科学 | 2156篇 |
矿业工程 | 564篇 |
能源动力 | 1106篇 |
轻工业 | 3579篇 |
水利工程 | 1266篇 |
石油天然气 | 343篇 |
无线电 | 9231篇 |
一般工业技术 | 16254篇 |
冶金工业 | 2623篇 |
原子能技术 | 253篇 |
自动化技术 | 25289篇 |
出版年
2018年 | 14448篇 |
2017年 | 13374篇 |
2016年 | 9955篇 |
2015年 | 599篇 |
2014年 | 221篇 |
2013年 | 180篇 |
2012年 | 3130篇 |
2011年 | 9400篇 |
2010年 | 8270篇 |
2009年 | 5533篇 |
2008年 | 6761篇 |
2007年 | 7776篇 |
2006年 | 111篇 |
2005年 | 1203篇 |
2004年 | 1125篇 |
2003年 | 1167篇 |
2002年 | 534篇 |
2001年 | 94篇 |
2000年 | 174篇 |
1999年 | 59篇 |
1998年 | 52篇 |
1997年 | 28篇 |
1996年 | 43篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 23篇 |
1988年 | 9篇 |
1969年 | 24篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1964年 | 11篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
1953年 | 5篇 |
1952年 | 6篇 |
1951年 | 4篇 |
1950年 | 6篇 |
1949年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
With the introduction of the Regular Membership Constraint, a new line of research has opened where constraints are based
on formal languages. This paper is taking the next step, namely to investigate constraints based on grammars higher up in
the Chomsky hierarchy. We devise a time- and space-efficient incremental arc-consistency algorithm for context-free grammars,
investigate when logic combinations of grammar constraints are tractable, show how to exploit non-constant size grammars and
reorderings of languages, and study where the boundaries run between regular, context-free, and context-sensitive grammar
filtering. 相似文献
952.
AND/OR search spaces accommodate advanced algorithmic schemes for graphical models which can exploit the structure of the
model. We extend and evaluate the depth-first and best-first AND/OR search algorithms to solving 0-1 Integer Linear Programs (0-1 ILP) within this framework. We also include a class
of dynamic variable ordering heuristics while exploring an AND/OR search tree for 0-1 ILPs. We demonstrate the effectiveness
of these search algorithms on a variety of benchmarks, including real-world combinatorial auctions, random uncapacitated warehouse
location problems and MAX-SAT instances. 相似文献
953.
The subgraph isomorphism problem consists in deciding if there exists a copy of a pattern graph in a target graph. We introduce
in this paper a global constraint and an associated filtering algorithm to solve this problem within the context of constraint
programming. The main idea of the filtering algorithm is to label every node with respect to its relationships with other
nodes of the graph, and to define a partial order on these labels in order to express compatibility of labels for subgraph
isomorphism. This partial order over labels is used to filter domains. Labelings can also be strengthened by adding information
from the labels of neighbors. Such a strengthening can be applied iteratively until a fixpoint is reached. Practical experiments
illustrate that our new filtering approach is more effective on difficult instances of scale free graphs than state-of-the-art
algorithms and other constraint programming approaches. 相似文献
954.
When numerical CSPs are used to solve systems of n equations with n variables, the preconditioned interval Newton operator plays two key roles: First it allows handling the n equations as a global constraint, hence achieving a powerful contraction. Second it can prove rigorously the existence of
solutions. However, none of these advantages can be used for under-constrained systems of equations, which have manifolds
of solutions. A new framework is proposed in this paper to extend the advantages of the preconditioned interval Newton to
under-constrained systems of equations. This is achieved simply by allowing domains of the NCSP to be parallelepipeds, which
generalize the boxes usually used as domains. 相似文献
955.
Using background knowledge to rank itemsets 总被引:1,自引:1,他引:0
Assessing the quality of discovered results is an important open problem in data mining. Such assessment is particularly vital
when mining itemsets, since commonly many of the discovered patterns can be easily explained by background knowledge. The
simplest approach to screen uninteresting patterns is to compare the observed frequency against the independence model. Since
the parameters for the independence model are the column margins, we can view such screening as a way of using the column
margins as background knowledge. In this paper we study techniques for more flexible approaches for infusing background knowledge.
Namely, we show that we can efficiently use additional knowledge such as row margins, lazarus counts, and bounds of ones.
We demonstrate that these statistics describe forms of data that occur in practice and have been studied in data mining. To
infuse the information efficiently we use a maximum entropy approach. In its general setting, solving a maximum entropy model
is infeasible, but we demonstrate that for our setting it can be solved in polynomial time. Experiments show that more sophisticated
models fit the data better and that using more information improves the frequency prediction of itemsets. 相似文献
956.
In this paper, we investigate how to modify the naive Bayes classifier in order to perform classification that is restricted
to be independent with respect to a given sensitive attribute. Such independency restrictions occur naturally when the decision
process leading to the labels in the data-set was biased; e.g., due to gender or racial discrimination. This setting is motivated
by many cases in which there exist laws that disallow a decision that is partly based on discrimination. Naive application
of machine learning techniques would result in huge fines for companies. We present three approaches for making the naive
Bayes classifier discrimination-free: (i) modifying the probability of the decision being positive, (ii) training one model
for every sensitive attribute value and balancing them, and (iii) adding a latent variable to the Bayesian model that represents
the unbiased label and optimizing the model parameters for likelihood using expectation maximization. We present experiments
for the three approaches on both artificial and real-life data. 相似文献
957.
958.
959.
The k Nearest Neighbor (kNN) join operation associates each data object in one data set with its k nearest neighbors from the same or a different data set. The kNN join on high-dimensional data (high-dimensional kNN join) is a very expensive operation. Existing high-dimensional kNN join algorithms were designed for static data sets and therefore
cannot handle updates efficiently. In this article, we propose a novel kNN join method, named kNNJoin
+, which supports efficient incremental computation of kNN join results with updates on high-dimensional data. As a by-product,
our method also provides answers for the reverse kNN queries with very little overhead. We have performed an extensive experimental
study. The results show the effectiveness of kNNJoin+ for processing high-dimensional kNN joins in dynamic workloads. 相似文献
960.
An important query for spatio-temporal databases is to find nearest trajectories of moving objects. Existing work on this
topic focuses on the closest trajectories in the whole data space. In this paper, we introduce and solve constrained k-nearest neighbor (CkNN) queries and historical continuous CkNN (HCCkNN) queries on R-tree-like structures storing historical information about moving object trajectories. Given a trajectory
set D, a query object (point or trajectory) q, a temporal extent T, and a constrained region CR, (i) a CkNN query over trajectories retrieves from D within T, the k (≥ 1) trajectories that lie closest to q and intersect (or are enclosed by) CR; and (ii) an HCCkNN query on trajectories retrieves the constrained k nearest neighbors (CkNNs) of q at any time instance of T. We propose a suite of algorithms for processing CkNN queries and HCCkNN queries respectively, with different properties and advantages. In particular, we thoroughly investigate two types of CkNN queries, i.e., CkNNP and CkNNT, which are defined with respect to stationary query points and moving query trajectories, respectively; and two types of
HCCkNN queries, namely, HCCkNNP and HCCkNNT, which are continuous counterparts of CkNNP and CkNNT, respectively. Our methods utilize an existing data-partitioning index for trajectory data (i.e., TB-tree) to achieve low
I/O and CPU cost. Extensive experiments with both real and synthetic datasets demonstrate the performance of the proposed
algorithms in terms of efficiency and scalability. 相似文献