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   594篇
  免费   17篇
电工技术   4篇
化学工业   166篇
金属工艺   30篇
机械仪表   11篇
建筑科学   21篇
能源动力   22篇
轻工业   44篇
水利工程   1篇
无线电   65篇
一般工业技术   98篇
冶金工业   45篇
原子能技术   5篇
自动化技术   99篇
  2023年   5篇
  2022年   10篇
  2021年   18篇
  2020年   8篇
  2019年   17篇
  2018年   13篇
  2017年   13篇
  2016年   16篇
  2015年   16篇
  2014年   31篇
  2013年   47篇
  2012年   37篇
  2011年   47篇
  2010年   33篇
  2009年   37篇
  2008年   36篇
  2007年   38篇
  2006年   15篇
  2005年   17篇
  2004年   12篇
  2003年   13篇
  2002年   12篇
  2001年   13篇
  2000年   8篇
  1999年   7篇
  1998年   7篇
  1997年   8篇
  1996年   4篇
  1995年   4篇
  1994年   8篇
  1993年   7篇
  1992年   2篇
  1991年   8篇
  1990年   4篇
  1989年   7篇
  1987年   2篇
  1986年   2篇
  1985年   4篇
  1984年   2篇
  1983年   2篇
  1982年   3篇
  1981年   4篇
  1980年   3篇
  1979年   1篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1974年   1篇
  1971年   1篇
  1966年   1篇
排序方式: 共有611条查询结果,搜索用时 15 毫秒
61.
The influence of wine polymers on the spontaneous precipitation of calcium tartrate in a model wine system has been examined. Rhamnogalacturonan‐I was identified as the most effective inhibitor (precipitation induction time of 180 min compared with 7 min for the standard model). It is argued that this is a consequence of rhamnogalacturonan‐I's ability to participate in the ‘egg‐box’ type sequestration of calcium ions. The more structurally complex rhamnogalacturonan‐II had only a minor influence on the induction time (22 min). Arabinogalactan proteins and mannoproteins also have little influence with induction times ranging from 12 to 15 min. An ultra‐filtration study of four Chardonnay wines, prepared with and without the use of pectolytic enzymes, was performed in a search for conditions that might maximise the concentration of rhamnogalacturonan‐I. However, rhamnogalacturonan‐I could not be identified in any of the four wines. Implications of these observations, specifically the need to understand the inhibition exerted by specific uronic acids, for winemaking and calcium tartrate precipitation are discussed.  相似文献   
62.
The direct metal deposition (DMD) with laser is a free-form metal deposition process for manufacturing dense pieces, which allows generating a prototype or small series of near net-shape structures. One of the most critical issues is that produced pieces have a deleterious surface finish which systematically requires post machining steps. This problem has never been fully addressed before.The present work describes investigations on the DMD process, using an Yb-YAG disk laser, and a widely used titanium alloy (Ti–6Al–4V) to understand the influence of the main process parameters on the surface finish quality. The focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish.In order to understand the physical mechanisms responsible for deleterious surface finishes, we have carried out: (1) a precise characterization of the laser beam and the powder stream; (2) a large number of multi-layered walls using different process parameters (P(W), V(m/min), Dm (g/min), Gaussian or uniform beam distribution); (3) a real time fast camera analysis of melt pool dynamics and melt-pool – powder stream coupling; (4) a characterization of wall morphologies versus process parameters using 2D and 3D profilometry.The results confirm that surface degradation depends on two distinct aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters. Last, a simple analytical model was proposed to correlate melt-pool geometries to resulting surface finishes.  相似文献   
63.
This study proposed and tested a theoretical factor structure for the Alcohol Expectancy Questionnaire (AEQ; S. A. Brown, M. S. Goldman, A. Inn, & L. R. Anderson [see record 1981-01217-001]). Factors were hypothesized to (a) reflect either positive or negative reinforcement, and (b) target either personal feelings or social contexts, resulting in 4 hypothesized factors (Social Enhancement, Social Coping, Personal Enhancement, Personal Coping). Participants were 180 male and 226 female undergraduates who completed the AEQ and additional self-report measures. Confirmatory factor analysis revealed that the hypothesized model fit the data. Post hoc adjustments further improved the model. Finally, a higher order factor model fit the data best. Factors correlated in hypothesized ways with other measures: (a) Only Personal Coping expectancies correlated with negative affect; (b) self-efficacy to resist drinking for emotional relief correlated highest with Personal Coping; and (c) self-efficacy to resist social pressure to drink correlated highest with Social Enhancement. Correlations with B. C. Leigh and A. W. Stacy's (see record 1993-35856-001) Drinking Expectancy Questionnaire indicated congruent and divergent validity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
64.
This article discusses the influence of future changes in the demographics of working populations and the characteristics of the workplace on research, development, and policy for training systems. Analyses of these changes indicate that there will be more expectations that training programs will serve as a positive hope to maximize the potential of each person. This will result in increased emphasis on research to identify abilities required to perform more cognitively complex jobs. Also, research on basic skill and support programs to permit unskilled youth to enter the world of work will be required. In addition, there will be a need for research on training necessary to help future managers and leaders work with members of a more diverse work force. Finally, the implications of these changes suggest that we need policies that consider research and development on retraining as a national need to help all individuals maximize their individual talents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
65.
 We construct new families of quaternary periodic sequences having good autocorrelation properties that are useful for the synchronisation of messages in multiple access communications systems. The design of these quaternary periodic sequences makes use of a general construction based on the Gray map starting from couples of binary words with particular weight or correlation properties. Received: June 26, 2000; revised version: January 21, 2002  相似文献   
66.
We present detailed experimental and numerical investigations of resonances in deep nanogroove gratings in metallic substrates. These plasmonic nanocavity gratings feature enhanced fields within the grooves that enable a large enhancement of linear and nonlinear optical processes. This enhancement relies on both localized and propagating surface plasmons on the nanopatterned surface. We show that the efficiency of optical processes such as Raman scattering and four-wave mixing is dramatically enhanced by plasmonic nanocavity gratings.  相似文献   
67.
Gut microbiota alterations are intimately linked to chronic constipation upon aging. We investigated the role of targeted changes in the gut microbiota composition in the relief of constipation symptoms after rhubarb extract (RE) supplementation in middle-aged volunteers. Subjects (95% women, average 58 years old) were randomized to three groups treated with RE at two different doses determined by its content of rhein (supplementation of 12.5 mg and 25 mg per day) vs. placebo (maltodextrin) for 30 days. We demonstrated that daily oral supplementation of RE for 30 days was safe even at the higher dose. Stool frequency and consistency, and perceived change in transit problem, transit speed and difficulty in evacuating, investigated by validated questionnaires, were improved in both groups of RE-treated volunteers compared to placebo. Higher abundance of Lachnospiraceae (mainly Roseburia and Agathobacter) only occurred after RE treatment when present at low levels at baseline, whereas an opposite shift in short-chain fatty acid (SCFA) levels was observed in both RE-treated groups (increase) and placebo (decrease). Fecal Lachnospiraceae and SCFA were positively correlated with stool consistency. This study demonstrates that RE supplementation promotes butyrate-producing bacteria and SCFA, an effect that could contribute to relieving chronic constipation in middle-aged persons.  相似文献   
68.
Bacillus Calmette-Guérin (BCG) instillations for the treatment of non-muscle-invasive bladder cancer patients can result in significant side effects and treatment failure. Immune checkpoint blockade and/or decreasing tumor-infiltrating myeloid suppressor cells may be alternative or complementary treatments. Here, we have characterized immune cell infiltration and chemoattractant molecules in mouse orthotopic MB49 bladder tumors. Our data show a 100-fold increase in CD45+ immune cells from day 5 to day 9 tumors including T cells and mainly myeloid cells. Both monocytic myeloid-derived suppressor-cells (M-MDSC) and polymorphonuclear (PMN)-MDSC were strongly increased in day 9 tumors, with PMN-MDSC representing ca. 70% of the myeloid cells in day 12 tumors, while tumor associated macrophages (TAM) were only modestly increased. The kinetic of PD-L1 tumor expression correlated with published data from patients with PD-L1 expressing bladder tumors and with efficacy of anti-PD-1 treatment, further validating the orthotopic MB49 bladder-tumor model as suitable for designing novel therapeutic strategies. Comparison of chemoattractants expression during MB49 bladder tumors grow highlighted CCL8 and CCL12 (CCR2-ligands), CCL9 and CCL6 (CCR-1-ligands), CXCL2 and CXCL5 (CXCR2-ligands), CXCL12 (CXCR4-ligand) and antagonist of C5/C5a as potential targets to decrease myeloid suppressive cells. Data obtained with a single CCR2 inhibitor however showed that the complex chemokine crosstalk would require targeting multiple chemokines for anti-tumor efficacy.  相似文献   
69.
Evidence is given for the involvement of hydrophobic interactions in the retention of hydrocarbons in oil fields. A prerequisite is that the surface of the reservoir rock has to be hydrophobic. This was obtained through adsorption of lipophilic polar compounds. The isotherms for the adsorption of dodecylamine hydrochloride and N-hexadecylpyridine hydrochloride were plotted. The treated quartz could take up large amounts of toluene. The relationships between some features of the isotherms and the retention phenomenon have been analysed. The effect of water-structuring additives (e.g. LiF, CaCl2, NaF and guanidine hydrochloride) on the recovery of hydrocarbons was investigated by means of static and dynamic methods.  相似文献   
70.
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