全文获取类型
收费全文 | 1278篇 |
免费 | 19篇 |
专业分类
电工技术 | 22篇 |
综合类 | 1篇 |
化学工业 | 99篇 |
金属工艺 | 14篇 |
机械仪表 | 23篇 |
建筑科学 | 33篇 |
矿业工程 | 1篇 |
能源动力 | 15篇 |
轻工业 | 39篇 |
水利工程 | 2篇 |
石油天然气 | 6篇 |
无线电 | 210篇 |
一般工业技术 | 175篇 |
冶金工业 | 520篇 |
原子能技术 | 9篇 |
自动化技术 | 128篇 |
出版年
2021年 | 10篇 |
2020年 | 6篇 |
2018年 | 8篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 27篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 27篇 |
2009年 | 32篇 |
2008年 | 44篇 |
2007年 | 40篇 |
2006年 | 36篇 |
2005年 | 46篇 |
2004年 | 16篇 |
2003年 | 24篇 |
2002年 | 32篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 31篇 |
1998年 | 116篇 |
1997年 | 111篇 |
1996年 | 60篇 |
1995年 | 29篇 |
1994年 | 46篇 |
1993年 | 42篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 19篇 |
1978年 | 16篇 |
1977年 | 22篇 |
1976年 | 41篇 |
1975年 | 11篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1969年 | 8篇 |
1963年 | 6篇 |
排序方式: 共有1297条查询结果,搜索用时 15 毫秒
51.
52.
B. Mishori E. A. Katz D. Faiman A. Belu-Marian Yoram Shapira 《Fullerenes, Nanotubes and Carbon Nanostructures》2013,21(1):113-124
Abstract The electronic structure of polycrystalline C60 thin films has been investigated using surface photovoltage spectroscopy (SPS) and conductivity measurements. the films show n-type semiconductivity with an activation energy of ~ 0.8 eV as found from the temperature dependence of the conductivity at high temperatures. the electronic structure emerging from our SPS results comprises a 1.6 eV photo-conduction gap, a mobility gap of about 2.25 eV and two gap states, a donor and an acceptor, at 0.35 eV and (1.0-1.1) eV, respectively, below the photo-conduction edge. the results indicate the possibility of the existence of band tails, extending into the optical gap of these films, as well as other deep gap states. 相似文献
53.
The development of precise definitions of security for encryption, as well as a detailed understanding of their relationships,
has been a major area of research in modern cryptography.
Here, we focus on the case of private-key encryption. Extending security notions from the public-key setting, we define security
in the sense of both indistinguishability and non-malleability against chosen-plaintext and chosen-ciphertext attacks, considering
both non-adaptive (i.e., ``lunchtime') and adaptive oracle access (adaptive here refers to an adversary's ability to interact
with a given oracle even after viewing the challenge ciphertext). We then characterize the 18 resulting security notions in
two ways. First, we construct a complete hierarchy of security notions; that is, for every pair of definitions we show whether
one definition is stronger than the other, whether the definitions are equivalent, or whether they are incomparable. Second,
we partition these notions of security into two classes (computational or information-theoretic) depending on whether one-way
functions are necessary in order for encryption schemes satisfying the definition to exist. Perhaps our most surprising result
is that security against adaptive chosen-plaintext attack is (polynomially) equivalent to security against non-adaptive chosen-plaintext
attack. On the other hand, the ability of an adversary to mount a (non-adaptive) chosen-plaintext attack is the key feature
distinguishing computational and information-theoretic notions of security. These results hold for all security notions considered
here. 相似文献
54.
Web applications can be classified as hybrids between hypermedia and information systems. They have a relatively simple distributed architecture from the user viewpoint, but a complex dynamic architecture from the designer viewpoint. They need to respond to operation by an unlimited number of heterogeneously skilled users, address security and privacy concerns, access heterogeneous, up-to-date information sources, and exhibit dynamic behaviors that involve such processes as code transferring. Common system development methods can model some of these aspects, but none of them is sufficient to specify the large spectrum of Web application concepts and requirements. This paper introduces OPM/Web, an extension to the Object-Process Methodology (OPM) that satisfies the functional, structural and behavioral Web-based information system requirements. The main extensions of OPM/Web are adding properties of links to express requirements, such as those related to encryption; extending the zooming and unfolding facilities to increase modularity; cleanly separating declarations and instances of code to model code transferring; and adding global data integrity and control constraints to express dependence or temporal relations among (physically) separate modules. We present a case study that helps evaluate OPM/Web and compare it to an extension of the Unified Modeling Language (UML) for the Web application domain. 相似文献
55.
In this paper, a new distortion measure for electrocardiogram (ECG) signal compression, called weighted diagnostic distortion (WDD) is introduced. The WDD measure is designed for comparing the distortion between original ECG signal and reconstructed ECG signal (after compression). The WDD is based on PQRST complex diagnostic features (such as P wave duration, QT interval, T shape, ST elevation) of the original ECG signal and the reconstructed one. Unlike other conventional distortion measures [e.g. percentage root mean square (rms) difference, or PRD], the WDD contains direct diagnostic information and thus is more meaningful and useful. Four compression algorithms were implemented (AZTEC, SAPA2, LTP, ASEC) in order to evaluate the WDD. A mean opinion score (MOS) test was applied to test the quality of the reconstructed signals and to compare the quality measure (MOSerror) with the proposed WDD measure and the popular PRD measure. The evaluators in the MOS test were three independent expert cardiologists, who studied the reconstructed ECG signals in a blind and a semiblind tests. The correlation between the proposed WDD measure and the MOS test measure (MOSerror) was found superior to the correlation between the popular PRD measure and the MOSerror. 相似文献
56.
BACKGROUND: The infrared coagulator, a by-product of laser technology, has been used in dermatology in a variety of settings. During hair transplantation sessions, we observed a significant reduction of the donor ellipse width while performing hemostasis with the infrared coagulator. OBJECTIVE: Quantitative assessment of the donor wound width after infrared coagulator use, and correlation to the number of previous transplant sessions and patients' age. METHODS: Twenty-four patients (22 men, two women) underwent hair transplantation. The infrared coagulator was utilized for hemostasis with a pulse duration of 2.5 seconds. RESULTS: The infrared coagulator produced an average donor area decrease of 42%, while achieving rapid hemostasis. No correlation was demonstrated to number of previous transplant sessions or patients' age. CONCLUSIONS: The infrared coagulator significantly decreases the donor wound width while providing hemostasis. Advantages include the potential of larger donor strip harvest, minimal tissue manipulation, and less traumatic closure. 相似文献
57.
B Susskind RH Kerman R Nelson J Gregory T La A Bayat M Dang C Van Buren S Katz BD Kahan 《Canadian Metallurgical Quarterly》1998,66(12):1823-1826
BACKGROUND: Disadvantages inherent to complement-dependent cytotoxicity cross-match (CDC XM) methods are the requirements for complement and viable target cells, detection of antibodies (Abs) against non-HLA antigens, and subjective scoring. Cross-Stat (SangStat Medical Corp., Menlo Park, CA), a recently developed enzyme-linked immunosorbent assay XM procedure for the detection of IgG anti-donor HLA Abs, is theoretically devoid of these flaws. METHODS: We compared results of Cross-Stat and our standard anti-human globulin (AHG)-enhanced CDC XM procedure on 524 sera from 230 transplant candidates, which were evaluated against 51 cadaveric donors. RESULTS: There was a significant correlation between AHG-CDC IgG XM and Cross-Stat results (P<0.001). For false negative sera, repeat AHG-CDC IgG XMs were still positive after platelet absorption, indicating that the Abs present were either non-HLA Abs or anti-HLA class II. Flow cytometry testing of false positive sera usually (42/62) substantiated Cross-Stat results, indicating that the discrepancy with AHG-CDC IgG XM is caused by greater sensitivity of Cross-Stat. Relative to the AHG-CDC XM, the sensitivity of Cross-Stat was 100%, the specificity was 93%, the positive predictive value was 73%, and the negative predictive value was 100%. A technical shortcoming of the Cross-Stat assay is that the frequency of indeterminate samples in the assays was 15%. Among 49 Cross-Stat negative vs. 13 Cross-Stat positive primary cadaveric renal allograft recipients (all AHG-CDC IgG-XM negative), there was no statistical difference in overall graft survival. CONCLUSION: Given the important theoretical advantages of enzyme-linked immunosorbent assay-based XM methods over the CDC XM, however, further testing of the clinical relevance of the Cross-Stat is warranted. 相似文献
58.
T Katz 《Canadian Metallurgical Quarterly》1995,1(1):11-14
Distribution of Corynebacterium kutscheri was determined in 41 rats housed in a conventionally managed colony that were infected naturally and subclinically. At 2, 5, 10, 20 and 25 months after initial isolation of C. kutscheri, attempts were made to isolate C. kutscheri from 17 sites, with a new selective medium, FNC agar. In total, the prevalence (97.6%) of C. kutscheri isolation was significantly (P < 0.001) higher than the frequency (70.7%) of antibody detection. None of the rats manifested any distinct clinical signs of disease and macroscopic lesions caused by C. kutscheri were not detected. In 40 rats with subclinical infection, the organisms were most frequently isolated from the oral cavity, esophagus, cecal contents, and colon and rectum (> 95.0%). The isolation rate was next highest in the trachea, submaxillary lymph nodes, and nasal cavity (47.5 to 52.5%). The organisms hardly colonized the lung, liver, and kidney. Mean numbers of organisms found in the esophagus, cecal contents, and colon and rectum ranged from 10(3.9) to 10(4.2) CFU/g, and were significantly (P < 0.05, P < 0.01) high in comparison with those in the lung. These results indicated that many healthy rats in the naturally infected colony harbored C. kutscheri, and the organisms colonized the oral cavity, esophagus, cecal contents, and colon and rectum most frequently. 相似文献
59.
AM Katz 《Canadian Metallurgical Quarterly》1998,2(4):233-5; quiz 248
This article takes three different approaches to the question of whether the failing heart is in an energy-starved state. A brief historical overview introduces the issue and points out problems in both models and methods. Second, current information regarding the energetic state of the failing heart is examined. Finally, the mechanistic and therapeutic implications of a defect in energy production are described. 相似文献
60.