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   3309篇
  免费   165篇
  国内免费   4篇
电工技术   65篇
化学工业   764篇
金属工艺   28篇
机械仪表   59篇
建筑科学   92篇
矿业工程   6篇
能源动力   118篇
轻工业   537篇
水利工程   17篇
石油天然气   8篇
无线电   260篇
一般工业技术   529篇
冶金工业   525篇
原子能技术   23篇
自动化技术   447篇
  2023年   17篇
  2022年   95篇
  2021年   135篇
  2020年   60篇
  2019年   59篇
  2018年   89篇
  2017年   61篇
  2016年   98篇
  2015年   99篇
  2014年   122篇
  2013年   201篇
  2012年   177篇
  2011年   214篇
  2010年   157篇
  2009年   146篇
  2008年   134篇
  2007年   118篇
  2006年   120篇
  2005年   87篇
  2004年   86篇
  2003年   87篇
  2002年   80篇
  2001年   47篇
  2000年   59篇
  1999年   58篇
  1998年   206篇
  1997年   136篇
  1996年   101篇
  1995年   71篇
  1994年   57篇
  1993年   47篇
  1992年   20篇
  1991年   24篇
  1990年   13篇
  1989年   18篇
  1988年   12篇
  1987年   13篇
  1986年   15篇
  1985年   10篇
  1984年   11篇
  1983年   13篇
  1982年   13篇
  1981年   13篇
  1980年   11篇
  1979年   5篇
  1978年   7篇
  1977年   15篇
  1976年   18篇
  1973年   4篇
  1972年   4篇
排序方式: 共有3478条查询结果,搜索用时 328 毫秒
101.
Searching information through the Internet often requires users to separately contact several digital libraries, use each library interface to author the query, analyze retrieval results and merge them with results returned by other libraries. Such a solution could be simplified by using a centralized server that acts as a gateway between the user and several distributed repositories: The centralized server receives the user query, forwards the user query to federated repositories—possibly translating the query in the specific format required by each repository—and fuses retrieved documents for presentation to the user. To accomplish these tasks efficiently, the centralized server should perform some major operations such as: resource selection, query transformation and data fusion. In this paper we report on some aspects of MIND, a system for managing distributed, heterogeneous multimedia libraries (MIND, 2001, http://www.mind-project.org). In particular, this paper focusses on the issue of fusing results returned by different image repositories. The proposed approach is based on normalization of matching scores assigned to retrieved images by individual libraries. Experimental results on a prototype system show the potential of the proposed approach with respect to traditional solutions.  相似文献   
102.
To ascertain the possible implications of the nitric oxide (NO*) producing system in striatal senescence, and by using immunohistochemistry and image-processing approaches, we describe the presence of the enzyme nitric oxide synthase (NOS), the NADPH-diaphorase (NADPH-d) histochemical marker, and nitrotyrosine-derived complexes (N-Tyr) in the striatum of adult and aged rats. The results showed neuronal NOS immunoreactive (nNOS-IR) aspiny medium-sized neurons and nervous fibres in both age groups, with no variation in the percentage of immunoreactive area but a significant decrease in the intensity and in the number of somata with age, which were not related to the observed increase with age of the striatal bundles of the white matter. In addition, NADPH-d activity was detected in neurons with morphology similar to that of the nNOS-IR cells; a decrease in the percentage of area per field and in the number of cells, but an increase in the intensity of staining for the NADPH-d histochemical marker, were detected with age. The number of neuronal NADPH-d somata was higher than for the nNOS-IR ones in both age groups. Moreover, N-Tyr-IR complexes were observed in cells (neurons and glia) and fibres, with a significant increase in the percentage of the area of immunoreaction, related to the increase of white matter, but a decrease in intensity for the aged group. On the other hand, we did not detect the inducible isoform (iNOS) either in adult or in aged rats. Taken together, these results support the contention that NADPH-d staining is not such an unambiguous marker for nNOS, and that increased protein nitration may participate in striatal aging.  相似文献   
103.
Context: Ketoprofen lysinate (KL) is one of the most widely used non-steroidal anti-inflammatory drugs in the symptomatic treatment of some chronic inflammatory diseases. Compared to ketoprofen, KL shows better pharmacokinetics and tolerability. However, due to its short half-life of 1–2?h, a multiple dose regimen is required for oral administration. Thus, the present work deals with its encapsulation in a hydrogel-based system by prilling in order to prolong its activity.

Objective: In this paper, we propose alginate and pectin as carriers and release tailoring agent for the development of hydrogel-based beads for KL retarded and sustained release.

Materials and methods: Beads were produced by a Nisco Encapsulator® using alginate or pectin. Operative variables were optimized to produce beads with desired morphology and size. Solid state properties were analyzed by SEM and DSC. Drug release performance was studied by Pharmacopeia pH-change assay to simulate gastrointestinal environment.

Results and discussion: Prilling technique was successfully used to encapsulate high soluble drugs as KL in polysaccharides-based hydrogels. Pectin proved to be a proper polymer able to encapsulate ketoprofen lysine salt. Formulation (F8) showed good morphological properties and size, high drug content (15.6%) and encapsulation efficiency (93.5%) and promising drug release profiles. Hosting F8 in an acid-resistant capsule (DR®caps) a delivery platform has been developed to control KL release in a delayed (90?min lag time) and prolonged way (270?min complete release).

Conclusion: The platform may be proposed as potentially useful in the oral administration of NSAIDs in chronic inflammatory diseases affected by circadian rhythm.  相似文献   
104.
105.
SMYD3 is a multifunctional epigenetic enzyme with lysine methyltransferase activity and various interaction partners. It is implicated in the pathophysiology of cancers but with an unclear mechanism. To discover tool compounds for clarifying its biochemistry and potential as a therapeutic target, a set of drug-like compounds was screened in a biosensor-based competition assay. Diperodon was identified as an allosteric ligand; its R and S enantiomers were isolated, and their affinities to SMYD3 were determined (KD=42 and 84 μM, respectively). Co-crystallization revealed that both enantiomers bind to a previously unidentified allosteric site in the C-terminal protein binding domain, consistent with its weak inhibitory effect. No competition between diperodon and HSP90 (a known SMYD3 interaction partner) was observed although SMYD3–HSP90 binding was confirmed (KD=13 μM). Diperodon clearly represents a novel starting point for the design of tool compounds interacting with a druggable allosteric site, suitable for the exploration of noncatalytic SMYD3 functions and therapeutics with new mechanisms of action.  相似文献   
106.
107.
Biodiesel is an alternative non-petroleum based fuel, consisting of alkyl esters obtained either by esterification of free fatty acids with low molecular weight alcohols, or by transesterification of triglycerides. The realization of a biodiesel unit can pose several safety issues and inherent safety application opportunities as the production involves the transport, use and storage of hazardous materials, either flammable or toxic. In the experimental phase, we studied, at laboratory scale, different alkali catalysts and the relevant reaction parameters, considering inherent safety opportunities. An accurate kinetic model of the transesterification process was developed and validated, allowing to provide possible minimization and simplification plant options.  相似文献   
108.
109.
Maize germ is a by‐product of the maize milling process that is characterised by a high nutritional value. Currently, heat treatments are employed to prevent full‐fat maize germ from spoilage. The aim of this research was to study the effect of five dry‐heat treatments on the nutritional value of full‐fat maize germ. The results confirmed that after each dry‐heat treatment, the lipase activity decreases but the use of high temperatures could be detrimental for phytosterol and thiamine concentrations. The main negative effects have been observed after treatments at 140 °C for 30 min and 160 °C for 10 min. No significant difference has been observed for protein, ash or fatty acid contents. The treatment at 140 °C for 20 min resulted an optimal combination between temperature and heating time to inactivate lipase without altering deeply the nutritional value and the colour of maize germ.  相似文献   
110.
The goal of the study was to obtain spaghetti enriched with pea flour with sensory properties close to conventional pasta. To this aim, the study has been organised in two subsequent trials. In the first, the pea flour amount added to the spaghetti was continuously increased until the overall sensory quality reached its threshold value (pea flour concentration = 15%). In fact, the spaghetti samples supplemented with 15% pea flour (15%S‐P) showed less elasticity, unpleasant colour and higher firmness compared to the control sample (CTRL). The second step was aimed to improve the overall sensory quality of the 15%S‐P spaghetti by means of guar gum (GUAR). The sample with GUAR (15%S‐P/GUAR) showed a pleasant colour, odour and taste. Furthermore, the 15%S‐P/GUAR sample recorded a low starch digestibility value (i.e. 54) and a higher soluble fibre content with respect to the 15%S‐P sample.  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