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   942篇
  免费   57篇
  国内免费   3篇
电工技术   3篇
综合类   1篇
化学工业   385篇
金属工艺   15篇
机械仪表   20篇
建筑科学   34篇
能源动力   27篇
轻工业   124篇
水利工程   6篇
石油天然气   5篇
无线电   31篇
一般工业技术   215篇
冶金工业   45篇
原子能技术   10篇
自动化技术   81篇
  2024年   5篇
  2023年   18篇
  2022年   118篇
  2021年   78篇
  2020年   38篇
  2019年   44篇
  2018年   24篇
  2017年   43篇
  2016年   28篇
  2015年   22篇
  2014年   36篇
  2013年   63篇
  2012年   51篇
  2011年   66篇
  2010年   40篇
  2009年   48篇
  2008年   49篇
  2007年   30篇
  2006年   46篇
  2005年   14篇
  2004年   20篇
  2003年   18篇
  2002年   19篇
  2001年   17篇
  2000年   6篇
  1999年   7篇
  1998年   6篇
  1997年   1篇
  1996年   5篇
  1995年   4篇
  1994年   3篇
  1993年   1篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1989年   4篇
  1988年   4篇
  1987年   3篇
  1985年   3篇
  1984年   2篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   2篇
  1976年   1篇
  1972年   1篇
  1969年   1篇
  1968年   1篇
  1963年   2篇
  1961年   1篇
排序方式: 共有1002条查询结果,搜索用时 31 毫秒
131.
BACKGROUND: The in situ technique (IS) is used for characterising, screening and evaluating feedstuffs in ruminants. However, it is often not adapted to the particular characteristics of feeds (i.e. kinetics of starchy feeds with a standard framework used in forage). This may lead to potential biases in the final conclusions. In two successive experiments, we evaluated the degradative characteristics of conventional (CON) and unconventional (UNC) starchy feedstuffs (ING) and factors affecting their washable fractions (WF). The suitability of IS was then assessed. RESULTS: Two well‐defined ruminal fermentation patterns (CON and UNC) were observed. The WF and insoluble washable (ISWF) fractions were affected by ING, state of presentation [WAY, fresh (F) or pre‐dried (D)], particle size (PSI) and their interactions. The UNC and F feeds had greater WF and ISWF than CON and D, respectively. Increasing PSI linearly reduced WF and its proportion of ISWF. CONCLUSION: The PSI and WAY are critical factors to consider when designing experiments for the evaluation of starchy feedstuffs for ruminants using IS. It is still very risky to propose ‘standard’ parameters as this will always depend on the particular ING evaluated. Conducting pre‐evaluation tests before implementing each research protocol could help to refine the procedure. Copyright © 2009 Society of Chemical Industry  相似文献   
132.
Protein Blocks (PBs) are a widely used structural alphabet describing local protein backbone conformation in terms of 16 possible conformational states, adopted by five consecutive amino acids. The representation of complex protein 3D structures as 1D PB sequences was previously successfully applied to protein structure alignment and protein structure prediction. In the current study, we present a new model, PYTHIA (predicting any conformation at high accuracy), for the prediction of the protein local conformations in terms of PBs directly from the amino acid sequence. PYTHIA is based on a deep residual inception-inside-inception neural network with convolutional block attention modules, predicting 1 of 16 PB classes from evolutionary information combined to physicochemical properties of individual amino acids. PYTHIA clearly outperforms the LOCUSTRA reference method for all PB classes and demonstrates great performance for PB prediction on particularly challenging proteins from the CASP14 free modelling category.  相似文献   
133.
Chronic headache is a topical problem of neurology, psychiatry and general practice. The medication-overuse headache (MOH) is one of the leading pathologies in the structure of chronic headache. However, early diagnosis of the MOH is challenging. We analyzed potential proteomic biomarkers of serum and urine in patients with MOH. Methods: We searched PubMed, Springer, Scopus, Web of Science, ClinicalKey, and Google Scholar databases for English publications over the past 10 years using keywords and their combinations. Results: We found and analyzed seven studies that met the search criteria for the purpose of the review, including 24 serum proteomic biomarkers and 25 urine proteomic biomarkers of MOH. Moreover, the candidate genes and locus of the studied serum (vitamin D-binding protein, lipocalin-type prostaglandin D2 synthase, apolipoprotein E, etc.) and urine proteomic biomarkers (uromodulin, alpha-1-microglobulin, zinc-alpha-2-glycoprotein, etc.) of MOH are presented in this review. Conclusions: The serum and urine proteomic biomarkers of MOH can potentially help with the identification of patients with MOH development. Due to the relevance of the problem, the authors believe that further investigation of the MOH proteomic biomarkers in different ethnic and racial groups of patients with primary headache is necessary. In addition, it is important to investigate whether medications of different drug classes influence the levels of serum and urine proteomic biomarkers.  相似文献   
134.
New optical coating design algorithm with the equivalent layers theory is presented. The algorithm is based on the merit-function-constrained optimization in the accessible domain of equivalent phase thicknesses and equivalent refractive indices. It allows for creation of design coatings with sophisticated narrowband spectral characteristics. (  相似文献   
135.
Determination of actual parameters of manufactured optical coatings (reverse engineering of optical coatings) provides feedback to the design-production chain and thus plays an important role in raising the quality of optical coatings production. In this paper, the reliability of reverse engineering results obtained using different types of experimental data is investigated. Considered experimental data include offline normal incidence transmittance data, offline ellipsometric data, and online transmittance monitoring data recorded during depositions of all coating layers. Experimental data are obtained for special test quarter-wave mirrors with intentional errors in some layers. These mirrors were produced by a well-calibrated magnetron-sputtering process. The intentional errors are several times higher than estimated errors of layer thickness monitoring, and the reliability of their detection is used as a measure of reliability of reverse engineering results. It is demonstrated that the most reliable results are provided by online transmittance data.  相似文献   
136.
Nanostructured materials have been widely studied due to the improvement of their mechanical properties comparing to those of coarse grain materials. The present work intended to analyze the microstructure and microhardness of Zr-2.5Nb processed by high-pressure torsion (HPT), one of the severe plastic deformation techniques. The deformations were carried out at room temperature using a pressure of 5?GPa and 5 anvil turns. Vickers indentation was used to evaluate the microhardness of the samples. Transmission electron microscopy and X-ray diffraction were used to analyze the microstructure. The results showed a significant refinement from the initial microstructure achieving nanometric grain size around 50?nm and phase transformation α?→?ω?+?βI induced by shear. The Vickers microhardness values of the material submitted to HPT technique were significantly higher than those of non-deformed material. Also, HPT procedure resulted in a huge grain refinement of the material and in phase transformation.  相似文献   
137.
Irradiation with helium ions is an effective method for triggering ferromagnetism in graphite. Chemical inertness of helium suggests that local magnetic moment formation is determined solely by the intrinsic carbon defects created during the target damage. Interacting moments are located in two places: in the vicinity of the sample surface and near the point of maximum defect generation.  相似文献   
138.
Recent research on the dynamics of planar grain boundaries is reviewed. Novel measuring techniques developed for in situ observation and recording of magnetically and stress driven grain boundary migration are presented. The results of migration measurements obtained on bismuth, zinc and aluminum bicrystals are addressed. The experiments revealed that the inclination of a 〈112〉 tilt boundary in Bi has a very strong influence on its mobility. The migration of planar 〈10$ \bar 1 $ \bar 1 0〉 tilt grain boundaries with different misorientation angles was measured in situ in bicrystals of high purity zinc. The results proved that there is a pronounced misorientation dependence of grain boundary mobility in the investigated angular range. The shear stress induced migration of planar symmetric 〈100〉 tilt boundaries in aluminum bicrystals was observed to be accompanied by a lateral translation of the adjacent grains. The coupling between boundary motion and shearing is not confined to low angle and some low Σ high angle boundaries, but occurs also for noncoincidence high angle 〈100〉 tilt boundaries. It has been found that also for stress induced grain boundary motion there is a misorientation dependence of the migration activation parameters. Lower values of the activation enthalpy and the pre-exponential mobility factor can be associated with boundaries with tilt angles close to low Σ CSL orientation relationships.  相似文献   
139.
140.
The present paper examines two aspects of the problem of critical conditions of jerky flow in alloys, or the Portevin–Le Chatelier (PLC) effect. Recent development of dynamic strain aging (DSA) models proved their capacity to qualitatively reproduce complex non-monotonic behavior of the critical strain, providing that the parameters of theory are allowed to depend on strain. Experimental measurements of such strain dependences have been realized for the first time and used to revise the predictions of the critical strain and stress relaxation kinetics upon abrupt strain-rate changes. On the other hand, it is usually omitted from consideration that the PLC stress serrations can last very short time in comparison with the characteristic time of stress transients. The development of stress drops was studied with the aid of the acoustic emission (AE) technique. It is shown that such macroscopic instabilities are caused by clustering of AE events which otherwise occur all the time, including the periods of smooth plastic flow. The role of synchronization of dislocation avalanches in the development of abrupt stress serrations and its relationship with the predictions of the local DSA models is discussed.  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