全文获取类型
收费全文 | 35851篇 |
免费 | 2117篇 |
国内免费 | 30篇 |
专业分类
电工技术 | 230篇 |
综合类 | 20篇 |
化学工业 | 6516篇 |
金属工艺 | 611篇 |
机械仪表 | 686篇 |
建筑科学 | 915篇 |
矿业工程 | 72篇 |
能源动力 | 552篇 |
轻工业 | 5431篇 |
水利工程 | 311篇 |
石油天然气 | 117篇 |
武器工业 | 7篇 |
无线电 | 1220篇 |
一般工业技术 | 5540篇 |
冶金工业 | 11224篇 |
原子能技术 | 118篇 |
自动化技术 | 4428篇 |
出版年
2024年 | 76篇 |
2023年 | 287篇 |
2022年 | 305篇 |
2021年 | 755篇 |
2020年 | 653篇 |
2019年 | 741篇 |
2018年 | 1332篇 |
2017年 | 1298篇 |
2016年 | 1347篇 |
2015年 | 1034篇 |
2014年 | 1214篇 |
2013年 | 2562篇 |
2012年 | 1905篇 |
2011年 | 1738篇 |
2010年 | 1423篇 |
2009年 | 1270篇 |
2008年 | 1231篇 |
2007年 | 1166篇 |
2006年 | 771篇 |
2005年 | 670篇 |
2004年 | 635篇 |
2003年 | 569篇 |
2002年 | 556篇 |
2001年 | 404篇 |
2000年 | 386篇 |
1999年 | 549篇 |
1998年 | 3450篇 |
1997年 | 2245篇 |
1996年 | 1398篇 |
1995年 | 802篇 |
1994年 | 642篇 |
1993年 | 778篇 |
1992年 | 213篇 |
1991年 | 232篇 |
1990年 | 176篇 |
1989年 | 193篇 |
1988年 | 191篇 |
1987年 | 168篇 |
1986年 | 132篇 |
1985年 | 163篇 |
1984年 | 124篇 |
1983年 | 100篇 |
1982年 | 145篇 |
1981年 | 156篇 |
1980年 | 179篇 |
1979年 | 78篇 |
1978年 | 89篇 |
1977年 | 352篇 |
1976年 | 756篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The MultiDimER model is a conceptual model used for representing a multidimensional view of data for Data Warehouse (DW) and
On-Line Analytical Processing (OLAP) applications. This model includes a spatial extension allowing spatiality in levels,
hierarchies, fact relationships, and measures. In this way decision-making users can represent in an abstract manner their
analysis needs without considering complex implementation issues and spatial OLAP tools developers can have a common vision
for representing spatial data in a multidimensional model. In this paper we propose the transformation of a conceptual schema
based on the MultiDimER constructs to an object-relational schema. We based our mapping on the SQL:2003 and SQL/MM standards
giving examples of commercial implementation using Oracle 10g with its spatial extension. Further we use spatial integrity
constraints to ensure the semantic equivalence of the conceptual and logical schemas. We also show some examples of Oracle
spatial functions, including aggregation functions required for the manipulation of spatial data. The described mappings to
the object-relational model along with the examples using a commercial system show the feasibility of implementing spatial
DWs in current commercial DBMSs. Further, using integrated architectures, where spatial and thematic data is defined within
the same DBMS, facilitates the system management simplifying data definition and manipulation.
相似文献
Esteban ZimányiEmail: |
992.
Alvarez I Carrascal M Canals F Muixí L Abián J Jaraquemada D 《Proteomics. Clinical applications》2007,1(3):286-298
HLA class I molecules present peptides on the cell surface to CD8(+) T cells. The repertoire of peptides that associate to class I molecules represents the cellular proteome. Therefore, cells expressing different proteomes could generate different class I-associated peptide repertoires. A large number of peptides have been sequenced from HLA class I alleles, mostly from lymphoid cells. On the other hand, T cell immunotherapy is a goal in the fight against cancer, but the identification of T cell epitopes is a laborious task. Proteomic techniques allow the definition of putative T cell epitopes by the identification of HLA natural ligands in tumor cells. In this study, we have compared the HLA class I-associated peptide repertoire from the hepatocellular carcinoma (HCC) cell line SK-Hep-1 with that previously described from lymphoid cells. The analysis of the peptide pool confirmed that, as expected, the peptides from SK-Hep-1 derive from proteins localized in the same compartments as in lymphoid cells. Within this pool, we have identified 12 HLA class I peptides derived from HCC-related proteins. This confirms that tumor cell lines could be a good source of tumor associated antigens to be used, together with MS, to define putative epitopes for cytotoxic T cells from cancer patients. 相似文献
993.
Guidelines for the incremental identification of aspects in requirements specifications 总被引:1,自引:0,他引:1
Jorge García-Duque Martín López-Nores José J. Pazos-Arias Ana Fernández-Vilas Rebeca P. Díaz-Redondo Alberto Gil-Solla Manuel Ramos-Cabrer Yolanda Blanco-Fernández 《Requirements Engineering》2006,11(4):239-263
The desired principle of separation of concerns in software development can be jeopardized by the so-called crosscutting concerns, which tend to be scattered over (and tangled with) the functionality of the modular units of a system. The correct identification of such concerns (and their encapsulation into separate artifacts) is thereby considered a way to improve software understanding and evolution. Pursuing a proper management of concerns from the requirements engineering stage can greatly benefit the entire software life-cycle. In this paper, we propose conceptual guidelines on how to perform the identification of crosscutting concerns in the process of building requirements specifications. We argue that the identification must be carried out in an incremental way, to encapsulate apart the crosscutting concerns even if they have not emerged completely yet.
相似文献
Yolanda Blanco-FernándezEmail: |
994.
K. Čipková 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2006,10(6):471-475
In the paper we introduce a relation on the class of monounary algebras by means of -homomorphisms. It is a quasiorder. We take a subclass of containing monounary algebras satisfying the property We characterize algebras in by the notions of a degree and properties of their -endomorphisms. We apply the results to finite monounary algebras.
Supported by grant VEGA 1/0161/03 相似文献
995.
Free binary decision diagrams (FBDDs) are graph-based data structures representing Boolean functions with the constraint (additional
to binary decision diagram) that each variable is tested at most once during the computation. The function EARn is the following Boolean function defined for n × n Boolean matrices: EARn(M) = 1 iff the matrix M contains two equal adjacent rows. We prove that each FBDD computing EARn has size at least
and we present a construction of such diagrams of size approximately
. 相似文献
996.
Callahan SP Bavoil L Pascucci V Silva CT 《IEEE transactions on visualization and computer graphics》2006,12(5):1307-1314
We describe a new progressive technique that allows real-time rendering of extremely large tetrahedral meshes. Our approach uses a client-server architecture to incrementally stream portions of the mesh from a server to a client which refines the quality of the approximate rendering until it converges to a full quality rendering. The results of previous steps are re-used in each subsequent refinement, thus leading to an efficient rendering. Our novel approach keeps very little geometry on the client and works by refining a set of rendered images at each step. Our interactive representation of the dataset is efficient, light-weight, and high quality. We present a framework for the exploration of large datasets stored on a remote server with a thin client that is capable of rendering and managing full quality volume visualizations. 相似文献
997.
Konyha Z Matković K Gracanin D Jelović M Hauser H 《IEEE transactions on visualization and computer graphics》2006,12(6):1373-1385
The analysis and exploration of multidimensional and multivariate data is still one of the most challenging areas in the field of visualization. In this paper, we describe an approach to visual analysis of an especially challenging set of problems that exhibit a complex internal data structure. We describe the interactive visual exploration and analysis of data that includes several (usually large) families of function graphs fi(x, t). We describe analysis procedures and practical aspects of the interactive visual analysis specific to this type of data (with emphasis on the function graph characteristic of the data). We adopted the well-proven approach of multiple, linked views with advanced interactive brushing to assess the data. Standard views such as histograms, scatterplots, and parallel coordinates are used to jointly visualize data. We support iterative visual analysis by providing means to create complex, composite brushes that span multiple views and that are constructed using different combination schemes. We demonstrate that engineering applications represent a challenging but very applicable area for visual analytics. As a case study, we describe the optimization of a fuel injection system in diesel engines of passenger cars 相似文献
998.
Attempts to carry out the hydroformylation of allyldiethylamine homogeneously catalyzed by rhodium complexes led to unexpected formation of N,N,N,N-tetraethyl-1,4-diaminobutane and 4-(diethylamino)-1-butanole as final products. The role of the catalyst on the product formation and the reaction mechanism are briefly discussed. 相似文献
999.
V. Kolář 《Acta Mechanica》1993,100(1-2):125-128
Summary There is presented a direct evaluation of the departure from the eddy-viscosity model. This, widely used, concept of a clear physical meaning has usually been tested experimentally via simultaneous turbulence modelling of an eddy-viscosity coefficient
T
. Hence, the effect of the basic model assumption remains more or less latent. In the following we propose a characteristic measure for a direct determination of the departure from the eddy-viscosity model, i.e. independently from the choice of
T
-modelling from a great variety of available forms. 相似文献
1000.
DW Morck JK Merrill BE Thorlakson ME Olson LV Tonkinson JW Costerton 《Canadian Metallurgical Quarterly》1993,202(2):273-277
The prophylactic administration of injectable tilmicosin for pneumonia in weaned beef calves was investigated in 1,806 animals. Comparisons were made among calves receiving an "on-arrival" injection of tilmicosin, calves receiving a single injection of long-acting oxytetracycline, and calves receiving no prophylaxis. Morbidity and mortality attributable to pneumonia, morbidity and mortality attributable to all causes, and case fatality were significantly lower in the group of calves that received tilmicosin, compared with calves that received long-acting oxytetracycline and calves that received no prophylactic antibiotic. Mean time to initial pneumonia treatment was significantly extended in calves that received prophylaxis, compared with those that received no antibiotic on arrival at the feedlot. Calves that received tilmicosin gained significantly more weight than calves that received oxytetracycline. Calves that were not treated for pneumonia during the trial period gained significantly more weight than did those calves that were treated for pneumonia regardless of experimental group. The majority of mortalities were attributable to fibrinous pneumonia (31/34). Important bacterial isolates (Pasteurella spp, Haemophilus somnus, Actinomyces pyogenes) obtained at necropsy did not have resistance to tilmicosin in association with administration of tilmicosin as prophylaxis for pneumonia. However, bacterial resistance to trimethoprim/sulfonamide and to oxytetracycline were commonly found in these postmortem isolates. 相似文献