全文获取类型
收费全文 | 947篇 |
免费 | 27篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 147篇 |
金属工艺 | 2篇 |
机械仪表 | 13篇 |
建筑科学 | 29篇 |
能源动力 | 21篇 |
轻工业 | 94篇 |
水利工程 | 24篇 |
石油天然气 | 1篇 |
无线电 | 54篇 |
一般工业技术 | 125篇 |
冶金工业 | 364篇 |
原子能技术 | 6篇 |
自动化技术 | 90篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 27篇 |
2020年 | 11篇 |
2019年 | 22篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 20篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 31篇 |
2012年 | 44篇 |
2011年 | 84篇 |
2010年 | 40篇 |
2009年 | 48篇 |
2008年 | 51篇 |
2007年 | 67篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 23篇 |
2003年 | 27篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 36篇 |
1997年 | 31篇 |
1996年 | 20篇 |
1995年 | 22篇 |
1994年 | 20篇 |
1993年 | 16篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 8篇 |
1974年 | 3篇 |
1971年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有974条查询结果,搜索用时 15 毫秒
1.
2.
A new method for the detection and quantitation of aflatoxin B1 in liquids is described. The method is based on the SOS Chromotest, in which damage caused by aflatoxin B1 to the DNA of suitably engineered E. coli induces beta-galactosidase. Aflatoxin B1 developing in orange juice inoculated with spores of Aspergillus parasiticus is detectable equally well by TLC as by the SOS-Chromotest. 相似文献
3.
Suárez-Orozco Carola; Gaytán Francisco X.; Bang Hee Jin; Pakes Juliana; O'Connor Erin; Rhodes Jean 《Canadian Metallurgical Quarterly》2010,46(3):602
Immigration to the United States presents both challenges and opportunities that affect students' academic achievement. Using a 5-year longitudinal, mixed-methods approach, we identified varying academic trajectories of newcomer immigrant students from Central America, China, the Dominican Republic, Haiti, and Mexico. Latent class growth curve analysis revealed that although some newcomer students performed at high or improving levels over time, others showed diminishing performance. Multinomial logistic regressions identified significant group differences in academic trajectories, particularly between the high-achieving youth and the other groups. In keeping with ecological–developmental and stage–environment fit theories, School Characteristics (school segregation rate, school poverty rate, and student perceptions of school violence), Family Characteristics (maternal education, parental employment, and household structure), and Individual Characteristics (academic English proficiency, academic engagement, psychological symptoms, gender, and 2 age-related risk factors, number of school transitions and being overaged for grade placement) were associated with different trajectories of academic performance. A series of case studies triangulate many of the quantitative findings as well as illuminate patterns that were not detected in the quantitative data. Thus, the mixed-methods approach sheds light on the cumulative developmental challenges that immigrant students face as they adjust to their new educational settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
Craighead W. Edward; Sheets Erin S.; Craighead Linda Wilcoxon; Madsen Joshua W. 《Canadian Metallurgical Quarterly》2011,2(2):83
Major depressive disorder (MDD) is characterized by a high risk of recurrence, especially among individuals whose initial episode occurs during adolescence. Identifying predictors of recurrence of MDD among young samples is therefore of paramount clinical importance. Survival analytic models were used to evaluate the effects of dysfunctional cognitions and Axis II personality pathology on MDD recurrence in a sample of 130 previously, but not currently, depressed young adults. Participants were initially assessed for depression, dysfunctional attitudes, and personality pathology during their first semester in college and then reevaluated via the Longitudinal Interval Follow-up Evaluation interview every 6 months for 18 months. Baseline level of depressive symptoms significantly (HR-1.07, p = .002) predicted recurrence of MDD. In the survival analyses with baseline level of depression serving as a current mood state covariate, overall personality pathology (HR-1.04, p DSM–IV personality disorder cluster scores uniquely predicted recurrence. We discussed the theoretical, empirical, and clinical implications of these findings, and we noted the limitations of the study. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
5.
Cobalt disilicide is grown epitaxially on (100) Si from a 15 nm Co/2 nm Ti bilayer by rapid thermal annealing (RTA) at 900°C.
Polycrystalline CoSi2 is grown on (100) Si using a 15 nm Co layer and the same annealing condition. Silicide/p+-Si/n-Si diodes are made using the silicide as dopant source:11B+ ions are implanted at 3.5–7.5 kV and activated by RTA at 600–900°C. Shallow junctions with total junction depth (silicide
plus p+ region) measured by high-resolution secondaryion mass spectroscopy of 100 nm are fabricated. Areal leakage current densities
of 13 nA/cm2 and 2 nA/cm2 at a reverse bias of -5V are obtained for the epitaxial silicide and polycrystalline silicide junctions, respectively, after
700°C post-implant annealing. 相似文献
6.
Moon Taesup Weissman T. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2008,54(2):692-708
The problem of discrete universal filtering, in which the components of a discrete signal emitted by an unknown source and corrupted by a known discrete memoryless channel (DMC) are to be causally estimated, is considered. A family of filters are derived, and are shown to be universally asymptotically optimal in the sense of achieving the optimum filtering performance when the clean signal is stationary, ergodic, and satisfies an additional mild positivity condition. Our schemes are comprised of approximating the noisy signal using a hidden Markov process (HMP) via maximum-likelihood (ML) estimation, followed by the use of the forward recursions for HMP state estimation. It is shown that as the data length increases, and as the number of states in the HMP approximation increases, our family of filters attains the performance of the optimal distribution-dependent filter. An extension to the case of channels with memory is also established. 相似文献
7.
Cohen A. Merhav N. Weissman T. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2007,53(9):3001-3020
We investigate the problem of scanning and prediction (ldquoscandiction,rdquo for short) of multidimensional data arrays. This problem arises in several aspects of image and video processing, such as predictive coding, for example, where an image is compressed by coding the error sequence resulting from scandicting it. Thus, it is natural to ask what is the optimal method to scan and predict a given image, what is the resulting minimum prediction loss, and whether there exist specific scandiction schemes which are universal in some sense. Specifically, we investigate the following problems: first, modeling the data array as a random field, we wish to examine whether there exists a scandiction scheme which is independent of the field's distribution, yet asymptotically achieves the same performance as if this distribution were known. This question is answered in the affirmative for the set of all spatially stationary random fields and under mild conditions on the loss function. We then discuss the scenario where a nonoptimal scanning order is used, yet accompanied by an optimal predictor, and derive bounds on the excess loss compared to optimal scanning and prediction. This paper is the first part of a two-part paper on sequential decision making for multidimensional data. It deals with clean, noiseless data arrays. The second part deals with noisy data arrays, namely, with the case where the decision maker observes only a noisy version of the data, yet it is judged with respect to the original, clean data. 相似文献
8.
Weissman T. Ordentlich E. Weinberger M.J. Somekh-Baruch A. Merhav N. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2007,53(4):1253-1264
We consider the filtering problem, where a finite-alphabet individual sequence is corrupted by a discrete memoryless channel, and the goal is to causally estimate each sequence component based on the past and present noisy observations. We establish a correspondence between the filtering problem and the problem of prediction of individual sequences which leads to the following result: Given an arbitrary finite set of filters, there exists a filter which performs, with high probability, essentially as well as the best in the set, regardless of the underlying noiseless individual sequence. We use this relationship between the problems to derive a filter guaranteed of attaining the "finite-state filterability" of any individual sequence by leveraging results from the prediction problem 相似文献
9.
Duc T. Duong Chenchen Wang Erin Antono Michael F. Toney Alberto Salleo 《Organic Electronics》2013,14(5):1330-1336
We investigate the chemical and structural properties of solution-processed thin films of P3HT blended with p-type dopant F4TCNQ. The maximum in-plane electrical conductivity of doped films is observed at a molar doping fraction of 0.17, in agreement with the binding mechanism of F4TCNQ:P3HT complexes. Through the use of X-ray diffraction, a previously unreported crystalline phase is observed for P3HT films doped above a critical threshold concentration. This crystalline phase involves the incorporation of F4TCNQ molecules into ordered polymer regions and ultimately improves charge dissociation, leading to higher carrier density in thin film. Finally, optical absorption and X-ray diffraction reveal that the chemical state of P3HT in solution has a dramatic impact on the electrical and structural properties of the blended films. 相似文献
10.
Wei Hu Zhi Ren Junpeng Li Erin Askounis Zhixin Xie Qibing Pei 《Advanced functional materials》2015,25(30):4827-4836
Dielectric elastomers have been widely investigated for muscle‐like soft actuators and capacitive sensors. Mechanical properties play a central role in the performances of the active material. Most elastomers have specific moduli pre‐determined by the polymers' molecular structures, which are not suitable for applications in changing working conditions as natural muscles are capable of. Here new dielectric elastomers are described exhibiting variable moduli controlled via thermal treatment. The elastomers contain furan‐maleimide Diels–Alder adduct moieties to administer the crosslinking densities of the elastomeric networks via reversible Diels–Alder/retro‐Diels–Alder cycloaddition reaction, resulting in changes in the elastomers' moduli. One of the synthesized elastomers has moduli that can be controlled between 0.17 and 0.52 MPa incrementally and reversibly. Capacitive strain sensors based on this elastomer can be operated in both rigid and soft modes to achieve variable sensing response up to 30% linear strain. Actuators were fabricated and operated in both high strain mode (35% actuation area strain at 65 MV m?1) and high force output mode (0.55 MPa at 104 MV m?1). The elastomers can exhibit a range of stress–strain outputs in similar fashion as muscle. 相似文献