全文获取类型
收费全文 | 266325篇 |
免费 | 3365篇 |
国内免费 | 830篇 |
专业分类
电工技术 | 5217篇 |
综合类 | 334篇 |
化学工业 | 38535篇 |
金属工艺 | 10372篇 |
机械仪表 | 8600篇 |
建筑科学 | 6460篇 |
矿业工程 | 1079篇 |
能源动力 | 6547篇 |
轻工业 | 23328篇 |
水利工程 | 2592篇 |
石油天然气 | 3918篇 |
武器工业 | 70篇 |
无线电 | 35113篇 |
一般工业技术 | 51059篇 |
冶金工业 | 47794篇 |
原子能技术 | 5467篇 |
自动化技术 | 24035篇 |
出版年
2021年 | 2115篇 |
2019年 | 2123篇 |
2018年 | 3557篇 |
2017年 | 3610篇 |
2016年 | 3831篇 |
2015年 | 2422篇 |
2014年 | 4183篇 |
2013年 | 11630篇 |
2012年 | 6786篇 |
2011年 | 9183篇 |
2010年 | 7235篇 |
2009年 | 8099篇 |
2008年 | 8998篇 |
2007年 | 8889篇 |
2006年 | 8046篇 |
2005年 | 7343篇 |
2004年 | 7064篇 |
2003年 | 6897篇 |
2002年 | 6558篇 |
2001年 | 6578篇 |
2000年 | 6253篇 |
1999年 | 6361篇 |
1998年 | 14390篇 |
1997年 | 10396篇 |
1996年 | 8231篇 |
1995年 | 6519篇 |
1994年 | 5817篇 |
1993年 | 5688篇 |
1992年 | 4643篇 |
1991年 | 4282篇 |
1990年 | 4133篇 |
1989年 | 3873篇 |
1988年 | 3686篇 |
1987年 | 3225篇 |
1986年 | 3144篇 |
1985年 | 3709篇 |
1984年 | 3456篇 |
1983年 | 3126篇 |
1982年 | 2929篇 |
1981年 | 3033篇 |
1980年 | 2833篇 |
1979年 | 2722篇 |
1978年 | 2557篇 |
1977年 | 3012篇 |
1976年 | 3621篇 |
1975年 | 2378篇 |
1974年 | 2360篇 |
1973年 | 2376篇 |
1972年 | 1884篇 |
1971年 | 1773篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
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
52.
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
53.
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
54.
55.
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
56.
57.
CF Wippermann RG Huth FX Schmidt J Thul M Betancor D Schranz 《Canadian Metallurgical Quarterly》1996,22(5):467-471
OBJECTIVE: To compare a system that continuously monitors cardiac output by the Fick principle with measurements by the thermodilution technique in pediatric patients. DESIGN: Prospective direct comparison of the above two techniques. SETTING: Pediatric intensive care unit of a university hospital. PATIENTS: 25 infants and children, aged 1 week to 17 years (median 10 months), who had undergone open heart surgery were studied. Only patients without an endotracheal tube leak and without a residual shunt were included. METHODS: The system based on the Fick principle uses measurements of oxygen consumption taken by a metabolic monitor and of arterial and mixed venous oxygen saturation taken by pulse- and fiberoptic oximetry to calculate cardiac output every 20s. INTERVENTIONS: In every patient one pair of measurements was taken. Continuous Fick and thermodilution cardiac output measurements were performed simultaneously, with the examiners remaining ignorant of the results of the other method. RESULTS: Cardiac output measurements ranged from 0.21 to 4.55 l/min. A good correlation coefficient was found: r2 = 0.98; P < 0.001; SEE = 0.41 l/min. The bias is absolute values and in percent of average cardiac output was - 0.05 l/min or - 4.4% with a precision of 0.32 l/min or 21.3% at 2 SD, respectively. The difference was most marked in a neonate with low cardiac output. CONCLUSION: Continuous measurement of cardiac output by the Fick principle offers a convenient method for the hemodynamic monitoring of unstable infants and children. 相似文献
58.
59.
This paper discusses the essential elements for successful Total Quality Management (TQM) implementation in hospital, and the challenges that occur with such implementation. Guidelines for this implementation are provided to show how TQM tools can be used effectively in hospitals. 相似文献
60.
G Mangiapan M Vokurka L Schouls J Cadranel D Lecossier J van Embden AJ Hance 《Canadian Metallurgical Quarterly》1996,34(5):1209-1215
The rapid identification of mycobacterial DNA in clinical samples by PCR can be useful in the diagnosis of tuberculous infections, but several large studies have found that the sensitivity of this approach is not better than that of culture. In order to improve the sensitivity of detection of mycobacterial DNA in clinical specimens from patients with paucibacillary forms of tuberculosis, we have developed a procedure permitting the specific capture of mycobacterial DNA in crude samples prior to amplification, thereby concentrating the target sequences and removing irrelevant DNA and other potential inhibitors of the amplification reaction (sequence capture-PCR). By using this approach to capture and amplify two different sequences specific for organisms of the Mycobacterium tuberculosis complex (IS6110 and the direct repeat region), it was possible to detect as little as one genome of mycobacterial DNA in samples containing up to 750 micrograms of total DNA, representing a 10- to 100-fold increase in sensitivity compared with that obtained by purifying total DNA prior to amplification. Detection of the IS6110 sequence in pleural fluid samples from patients with tuberculous pleurisy by sequence capture-PCR gave positive results in 13 of 17 cases, including 3 of 3 culture-positive samples and 10 of 14 culture-negative samples. In contrast, when total DNA was purified from these samples by adsorption to a silica matrix prior to amplification, only the three culture-positive samples were positive by PCR. The sensitivity of detection of the direct repeat sequence in these samples by sequence capture-PCR was similar to that of IS6110 and, in addition, permitted immediate typing of the strains from some patients. We conclude that sequence capture-PCR improves the sensitivity of detection of mycobacterial DNA in paucibacillary samples. This approach should be useful in detecting rare target sequences from organisms implicated in other pathologic processes. 相似文献