首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2954篇
  免费   233篇
  国内免费   7篇
电工技术   47篇
综合类   16篇
化学工业   669篇
金属工艺   88篇
机械仪表   74篇
建筑科学   271篇
矿业工程   24篇
能源动力   90篇
轻工业   146篇
水利工程   28篇
石油天然气   2篇
无线电   230篇
一般工业技术   671篇
冶金工业   133篇
原子能技术   11篇
自动化技术   694篇
  2023年   63篇
  2022年   70篇
  2021年   117篇
  2020年   106篇
  2019年   102篇
  2018年   120篇
  2017年   95篇
  2016年   148篇
  2015年   134篇
  2014年   155篇
  2013年   221篇
  2012年   235篇
  2011年   266篇
  2010年   173篇
  2009年   164篇
  2008年   162篇
  2007年   163篇
  2006年   98篇
  2005年   85篇
  2004年   76篇
  2003年   51篇
  2002年   64篇
  2001年   28篇
  2000年   26篇
  1999年   29篇
  1998年   32篇
  1997年   32篇
  1996年   22篇
  1995年   19篇
  1994年   14篇
  1993年   15篇
  1992年   17篇
  1991年   13篇
  1990年   8篇
  1989年   3篇
  1988年   6篇
  1986年   3篇
  1985年   8篇
  1984年   9篇
  1983年   7篇
  1982年   2篇
  1981年   4篇
  1980年   2篇
  1979年   3篇
  1978年   3篇
  1977年   2篇
  1976年   2篇
  1975年   4篇
  1972年   2篇
  1961年   2篇
排序方式: 共有3194条查询结果,搜索用时 15 毫秒
31.
Sulfuric acid-catalyzed hydrolysis of cellulose commonly isolates cellulose nanocrystals (CNCs). Neutralizing the reactant solution with sodium hydroxide facilitates efficient downstream processing, but residual salt remains in the product. This study examines the reinforcing effects of CNCs from suspensions that contain residual salt on the mechanical properties of thermoplastic starch nanocomposites. By reinforcing starch films with up to 5 wt% CNCs, stiffness and strength are improved by 118% and 79%, respectively, indicating a good dispersion of CNCs in the starch matrix. Compared to nanocomposites incorporating salt-free CNCs, the remaining salt has no significant impact on the material's mechanical performance. The results indicate great potential of CNCs containing residual salt as biobased, low-cost nanofiller in hydrophilic polymer matrices.  相似文献   
32.
We aimed to assess the in vitro antimicrobial activity and the in vivo effect on the murine fecal microbiome and volatile organic compound (VOC) profile of (S)-reutericyclin. The antimicrobial activity of (S)-reutericyclin was tested against Clostridium difficile, Listeria monocytogenes, Escherichia coli, Enterococcus faecium, Staphylococcus aureus, Staphylococcus (S.) epidermidis, Streptococcus agalactiae, Pseudomonas aeruginosa and Propionibacterium acnes. Reutericyclin or water were gavage fed to male BALBc mice for 7 weeks. Thereafter stool samples underwent 16S based microbiome analysis and VOC analysis by gas chromatography mass spectrometry (GC-MS). (S)-reutericyclin inhibited growth of S. epidermidis only. Oral (S)-reutericyclin treatment caused a trend towards reduced alpha diversity. Beta diversity was significantly influenced by reutericyclin. Linear discriminant analysis Effect Size (LEfSe) analysis showed an increase of Streptococcus and Muribaculum as well as a decrease of butyrate producing Ruminoclostridium, Roseburia and Eubacterium in the reutericyclin group. VOC analysis revealed significant increases of pentane and heptane and decreases of 2,3-butanedione and 2-heptanone in reutericyclin animals. The antimicrobial activity of (S)-reutericyclin differs from reports of (R)-reutericyclin with inhibitory effects on a multitude of Gram-positive bacteria reported in the literature. In vivo (S)-reutericyclin treatment led to a microbiome shift towards dysbiosis and distinct alterations of the fecal VOC profile.  相似文献   
33.
Due to the increasing importance of producing and consuming energy more sustainably, Energy Informatics (EI) has evolved into a thriving research area within the CS/IS community. The article attempts to characterize this young and highly dynamic field of research by describing current EI research topics and methods and provides an outlook of how the field might evolve in the future. It is shown that two general research questions have received the most attention so far and are likely to dominate the EI research agenda in the coming years: How to leverage information and communication technology (ICT) to (1) improve energy efficiency, and (2) to integrate decentralized renewable energy sources into the power grid. Selected EI streams are reviewed, highlighting how the respective research questions are broken down into specific research projects and how EI researchers have made contributions based on their individual academic background.  相似文献   
34.
Multispectral palmprint is considered as an effective biometric modality to accurately recognize a subject with high confidence. This paper presents a novel multispectral palmprint recognition system consisting of three functional blocks namely: (1) novel technique to extract Region of Interest (ROI) from the hand images acquired using a contact less sensor (2) novel image fusion scheme based on dependency measure (3) new scheme for feature extraction and classification. The proposed ROI extraction scheme is based on locating the valley regions between fingers irrespective of the hand pose. We then propose a novel image fusion scheme that combines information from different spectral bands using a Wavelet transform from various sub-bands. We then perform the statistical dependency analysis between these sub-bands to perform fusion either by selection or by weighted fusion. To effectively process the information from the fused image, we perform feature extraction using Log-Gabor transform whose feature dimension is reduced using Kernel Discriminant Analysis (KDA) before performing the classification by employing a Sparse Representation Classifier (SRC). Extensive experiments are carried out on a CASIA multispectral palmprint database that shows the strong superiority of our proposed fusion scheme when benchmarked with contemporary state-of-the-art image fusion schemes.  相似文献   
35.
The combination of ubiquitous and social computing is an emerging research area which integrates different but complementary methods, techniques, and tools. In this paper, we focus on the Ubicon platform, its applications, and a large spectrum of analysis results. Ubicon provides an extensible framework for building and hosting applications targeting both ubiquitous and social environments. We summarize the architecture and exemplify its implementation using four real-world applications built on top of Ubicon. In addition, we discuss several scientific experiments in the context of these applications in order to give a better picture of the potential of the framework, and discuss analysis results using several real-world data sets collected utilizing Ubicon.  相似文献   
36.
We present a wearable input system which enables interaction through 3D handwriting recognition. Users can write text in the air as if they were using an imaginary blackboard. The handwriting gestures are captured wirelessly by motion sensors applying accelerometers and gyroscopes which are attached to the back of the hand. We propose a two-stage approach for spotting and recognition of handwriting gestures. The spotting stage uses a support vector machine to identify those data segments which contain handwriting. The recognition stage uses hidden Markov models (HMMs) to generate a text representation from the motion sensor data. Individual characters are modeled by HMMs and concatenated to word models. Our system can continuously recognize arbitrary sentences, based on a freely definable vocabulary. A statistical language model is used to enhance recognition performance and to restrict the search space. We show that continuous gesture recognition with inertial sensors is feasible for gesture vocabularies that are several orders of magnitude larger than traditional vocabularies for known systems. In a first experiment, we evaluate the spotting algorithm on a realistic data set including everyday activities. In a second experiment, we report the results from a nine-user experiment on handwritten sentence recognition. Finally, we evaluate the end-to-end system on a small but realistic data set.  相似文献   
37.
The self-assembly polymerization of ditopic macromolecules via metal–ligand binding is a facile route for the preparation of metallo-supramolecular polymers (MSPs). We herein review our recent work focused on the synthesis and investigation of metallo-supramolecular polymers based on 2,6-bis(1′-methylbenzimidazolyl)pyridine endcapped poly(p-phenylene ethynylene) and poly(p-xylene) macromonomers. These materials are readily solution-processable and display appreciable mechanical properties as well as other attractive properties such as specific opto/electrical functions or high thermal stability. Our work illustrates that metallosupramolecular polymerization offers an attractive approach to assemble high-molecular-weight macromolecules from well-defined, easy to process precursors. Variation of the ditopic ligands and metal ions allows one to easily tailor the desired properties. This paper is dedicated to Professor Ian Manners and his scientific accomplishments.  相似文献   
38.
Temporal dynamics of social interaction networks as well as the analysis of communities are key aspects to gain a better understanding of the involved processes, important influence factors, their effects, and their structural implications. In this article, we analyze temporal dynamics of contacts and the evolution of communities in networks of face-to-face proximity. As our application context, we consider four scientific coil- ferences. On a structural level, we focus on static and dynamic properties of the contact graphs. Also, we analyze the resulting community structure using state-of-the-art automatic community detection algorithms. Specifically, we analyze tile evolution of contacts and communities over time to consider the stability of the respective conmmnities. Furthermore, we assess different factors which have an influence on the quality of com- munity prediction. Overall, we provide first important insights into the evolution of contacts and communities in face-to-face contact networks.  相似文献   
39.

Definition of problem

At least in some cases, testing for aneuploidy as part of preimplantation genetic diagnosis (PGD) can be medically useful for pregnancy care. The current legal situation in Germany seems to not generally exclude PGD to detect a maldistribution of chromosomes in an embryo, but testing would require approval by a PGD ethics committee on a case-by-case basis and a well-reasoned application by the concerned woman. This article examines ethically and legally whether fundamental reasons prevent PGD commissions from admitting requests to perform aneuploidy tests as part of PGD.

Arguments

Three constellations – each with differing ethical implications – can be distinguished in which testing for aneuploidy could be considered or could occur: Testing for aneuploidy can (i) be the main reason for in vitro fertilization (IVF), which in itself is not medically indicated; (ii) IVF is done as infertility treatment in which case PGD and aneuploidy testing could be done additionally; or (iii) PGD with IVF is indicated in order to prevent a congenital disease or chromosomal aberration leading to a diagnosis of aneuploidy as an incidental or additional finding. Ethical arguments which could lead to a general rejection of aneuploidy testing are the prevention of discrimination against people with aneuploidy, as well as the protection of embryos. These concerns oppose constellation (i), but do not apply to (ii) and (iii). Yet there are at least three ethical arguments in favour of an admissibility of a request for aneuploidy testing: the “good practice” of IVF, the duty to the emerging child and the parent’s right to have a voice in the discussion.

Conclusion

Aneuploidy testing as part of PGD is not ruled out by legal or ethical reasons and should be openly discussed by the relevant German ethics commissions.
  相似文献   
40.
An optimized equipment design for natural gas processing and liquefaction plants becomes increasingly difficult with changing process conditions: Particularly low values of surface tension create rising challenges on the design of phase separators and column internals. The TERESA test rig at HZDR was designed to allow the investigation of multiphase thermohydraulics and phase separator performance under critical fluid properties in industrial dimensions. A versatile pipe test section is available in DN200 and equipment internals may be tested in a sectional DN300/DN500 test separator. The applied test fluid shows a high vapor-liquid density difference between 1470 and 940 kg m−3, viscosity as low as 0.12 mm2s−1, and surface tension down to 1.3 mN m−1. Volumetric liquid and vapor flow rates may be varied up to 9 and 530 m3h−1 in the test rig, respectively.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号