全文获取类型
收费全文 | 260917篇 |
免费 | 3195篇 |
国内免费 | 824篇 |
专业分类
电工技术 | 5137篇 |
综合类 | 331篇 |
化学工业 | 37443篇 |
金属工艺 | 10261篇 |
机械仪表 | 8504篇 |
建筑科学 | 6133篇 |
矿业工程 | 1076篇 |
能源动力 | 6402篇 |
轻工业 | 22902篇 |
水利工程 | 2565篇 |
石油天然气 | 3908篇 |
武器工业 | 68篇 |
无线电 | 34793篇 |
一般工业技术 | 50141篇 |
冶金工业 | 46841篇 |
原子能技术 | 5424篇 |
自动化技术 | 23007篇 |
出版年
2021年 | 2046篇 |
2019年 | 2034篇 |
2018年 | 3470篇 |
2017年 | 3538篇 |
2016年 | 3734篇 |
2015年 | 2323篇 |
2014年 | 4053篇 |
2013年 | 11308篇 |
2012年 | 6573篇 |
2011年 | 8891篇 |
2010年 | 6997篇 |
2009年 | 7871篇 |
2008年 | 8709篇 |
2007年 | 8650篇 |
2006年 | 7837篇 |
2005年 | 7184篇 |
2004年 | 6914篇 |
2003年 | 6749篇 |
2002年 | 6389篇 |
2001年 | 6485篇 |
2000年 | 6188篇 |
1999年 | 6268篇 |
1998年 | 14307篇 |
1997年 | 10322篇 |
1996年 | 8150篇 |
1995年 | 6430篇 |
1994年 | 5730篇 |
1993年 | 5591篇 |
1992年 | 4561篇 |
1991年 | 4214篇 |
1990年 | 4059篇 |
1989年 | 3786篇 |
1988年 | 3635篇 |
1987年 | 3178篇 |
1986年 | 3073篇 |
1985年 | 3622篇 |
1984年 | 3400篇 |
1983年 | 3051篇 |
1982年 | 2862篇 |
1981年 | 2973篇 |
1980年 | 2783篇 |
1979年 | 2666篇 |
1978年 | 2506篇 |
1977年 | 2949篇 |
1976年 | 3567篇 |
1975年 | 2325篇 |
1974年 | 2316篇 |
1973年 | 2330篇 |
1972年 | 1852篇 |
1971年 | 1751篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The cascade correlation is a very flexible, efficient and fast algorithm for supervised learning. It incrementally builds the network by adding hidden units one at a time, until the desired input/output mapping is achieved. It connects all the previously installed units to the new unit being added. Consequently, each new unit in effect adds a new layer and the fan-in of the hidden and output units keeps on increasing as more units get added. The resulting structure could be hard to implement in VLSI, because the connections are irregular and the fan-in is unbounded. Moreover, the depth or the propagation delay through the resulting network is directly proportional to the number of units and can be excessive. We have modified the algorithm to generate networks with restricted fan-in and small depth (propagation delay) by controlling the connectivity. Our results reveal that there is a tradeoff between connectivity and other performance attributes like depth, total number of independent parameters, and learning time. 相似文献
102.
103.
104.
This paper is a reply to Laviolette and Seaman's critical discussion of fuzzy set theory. Rather than questioning the interest of the Bayesian approach to uncertainty, some reasons why Bayesian find the idea of a fuzzy set not palatable are laid bare. Some links between fuzzy sets and probability that Laviolette and Seaman seem not to be aware of are pointed out. These links suggest that, contrary to the claim sometimes found in the literature, probability theory is not a special case of fuzzy set theory. The major objection to Laviolette and Seaman is that they found their critique on as very limited view of fuzzy sets, including debatable papers, while they fail to account for significant works pertaining to axiomatic derivation of fuzzy set connectives, possibility theory, fuzzy random variables, among others 相似文献
105.
Management of multidimensional discrete data 总被引:1,自引:0,他引:1
Peter Baumann Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):401-444
Spatial database management involves two main categories of data: vector and raster data. The former has received a lot of in-depth investigation; the latter still lacks a sound framework. Current DBMSs either regard raster data as pure byte sequences where the DBMS has no knowledge about the underlying semantics, or they do not complement array structures with storage mechanisms suitable for huge arrays, or they are designed as specialized systems with sophisticated imaging functionality, but no general database capabilities (e.g., a query language). Many types of array data will require database support in the future, notably 2-D images, audio data and general signal-time series (1-D), animations (3-D), static or time-variant voxel fields (3-D and 4-D), and the ISO/IEC PIKS (Programmer's Imaging Kernel System) BasicImage type (5-D). In this article, we propose a comprehensive support ofmultidimensional discrete data (MDD) in databases, including operations on arrays of arbitrary size over arbitrary data types. A set of requirements is developed, a small set of language constructs is proposed (based on a formal algebraic semantics), and a novel MDD architecture is outlined to provide the basis for efficient MDD query evaluation. 相似文献
106.
Wesley W. Chu Ph.D. Ion T. leong Ph.D. Ricky K. Taira Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):445-477
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach. 相似文献
107.
Robotica is a computer-aided design package for robotic nmanipulators developed at the Coordinated Science Laboratory at the University of Illinois at Urbana- Champaign. The package is a collection of function definitions for the Mathematica symbolic mathematics program. Robotica can be used either with an X- Windows graphical user interface (GUI) on a Sun Workstation or as an included function definition file within Mathematica. The primary feature of Robotica is the ability to compute, symbolically or numerically, the kinematic and dynamic equations of arbitrary robot systems utilizing the standard Denevit-Hartenburg (DH) kinematic convention. Robotica also provides the ability to visualize these arbitrary manipulators using the X- Windows graphical interface to the Mathematica graphics routines. The paper looks at the usage of Robotica at the Air Force Institute of Technology, comments on the features of Robotica, and needs for improvement and suggestions for future development 相似文献
108.
109.
B Blanc P Laloi D Atlan C Gilbert R Portalier 《Canadian Metallurgical Quarterly》1993,139(7):1441-1448
Lactobacillus helveticus ITGL1 is able to hydrolyse many amino-acyl and dipeptidyl-p-nitroanilides. Analysis of heat inactivation kinetics, metal ion and protease inhibitor effects, and the subcellular location of aminopeptidase activities in both the parental strain and mutants deficient in lysyl-p-nitroanilide hydrolysis, led to the characterization of two cell-wall-associated aminopeptidases, APII and APIV. APII, which catalysed L-lysine p-nitroanilide hydrolysis, was purified about 28-fold to homogeneity from cell-wall extracts of L. helveticus ITGL1 and characterized. The purified enzyme appeared to be monomeric, with a molecular mass of 97 kDa. Aminopeptidase activity was greatest at pH 6.5 and 50 degrees C. APII was completely inhibited by bestatin, chelating agents such as EDTA or 1,10-phenanthroline and the divalent cations Zn2+ and Cu2+. The activity of the EDTA-treated enzyme was restored by Co2+, Ca2+ or Mn2+. Although APII was able to degrade several dipeptides and tripeptides with hydrophobic N-terminal amino acid (Leu, Ala), it was inactive on peptides containing Pro or Gly, and may thus contribute to the development of cheese flavour by processing bitter peptides. 相似文献
110.
J. Jiang M. D. Olson 《International journal for numerical methods in engineering》1993,36(13):2219-2243
Numerical investigations are carried out to verify the new super element model developed in Reference 1 for non-linear analysis of stiffened box structures. The results presented here are obtained from a variety of examples which are chosen to illustrate the accuracy and convergence of the model in various applications. Good agreement is obtained for most of the problems considered and the present formulation is found to be accurate and economical for preliminary engineering design. 相似文献