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   332篇
  免费   40篇
  国内免费   1篇
电工技术   8篇
化学工业   69篇
金属工艺   12篇
机械仪表   15篇
建筑科学   5篇
矿业工程   1篇
能源动力   14篇
轻工业   61篇
水利工程   4篇
石油天然气   2篇
无线电   43篇
一般工业技术   40篇
冶金工业   44篇
原子能技术   1篇
自动化技术   54篇
  2023年   7篇
  2022年   9篇
  2021年   12篇
  2020年   10篇
  2019年   9篇
  2018年   13篇
  2017年   16篇
  2016年   14篇
  2015年   10篇
  2014年   17篇
  2013年   23篇
  2012年   22篇
  2011年   25篇
  2010年   16篇
  2009年   15篇
  2008年   17篇
  2007年   14篇
  2006年   13篇
  2005年   5篇
  2004年   11篇
  2003年   6篇
  2002年   4篇
  2001年   6篇
  2000年   4篇
  1999年   5篇
  1998年   18篇
  1997年   10篇
  1996年   7篇
  1995年   7篇
  1994年   3篇
  1993年   5篇
  1992年   2篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1980年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1966年   1篇
排序方式: 共有373条查询结果,搜索用时 297 毫秒
51.
Good survival rates have been reported for resected early gastric adenocarcinoma (EGC) in patients found via screening procedures. However, the prevalence of Helicobacter pylori in EGC in unscreened populations is unclear. The major purpose of this investigation was to analyze the clinical experience and incidence of H. pylori in unscreened patients presenting with EGC at Charity Hospital over a 34-year period. From 1963 through 1997, the tumor registry at Charity Hospital compiled data on 2497 patients evaluated for gastric carcinoma. Of these patients, 26 (1%) had lesions that were confined to the mucosa or submucosa, i.e., T1N0M0 (American Joint Commission on Cancer classification). Pathology specimens and medical records were retrieved for confirmation of diagnosis and retrospective analysis for H. pylori. H. pylori was analyzed by Steiner staining and immunohistochemistry using a polyclonal antibody. EGC was detected in 12 men and 14 women with a mean age of 62 years. Upper gastrointestinal X-ray studies were performed on 19 of the 26 patients and failed to conclusively demonstrate a lesion in any case. Endoscopy was performed on 22 patients, and preoperative biopsies were positive in 95 per cent of these. Operative procedures included 2 local excisions and 22 subtotal and 2 total gastrectomies. No extended nodal dissections were performed. Microscopic evaluation revealed lesions limited to the mucosa in 63 per cent of cases and involving the submucosa in 37 per cent of the cases. Of the 14 patients evaluable of H. pylori, 79 per cent were positive for the bacterium. The status of 2 patients is unknown, and only 1 patient died of the original gastric cancer, for a disease-free survival of 96 per cent. The 5-year and 10-year overall survival rates were calculated to be 50 per cent and 21 per cent, respectively, when all causes of death were taken into consideration. Median follow-up of the survivors was 64 months. Resection of early gastric carcinoma in unscreened patients without extended lymphadenectomy yielded excellent results. H. pylori was present in 79 per cent of cases. These data suggest an association between H. pylori and EGC. Whether H. pylori infection is an etiologic factor in gastric cancer remains an area of active research.  相似文献   
52.
53.
A mosquito pathogenic strain of Bacillus sphaericus carried out the conjugal transfer of plasmid pAM beta 1 to other strains of its own and two other serotypes. However, it was unable to conjugate with mosquito pathogens from three other serotypes, with B. sphaericus of other DNA homology groups or with three other species of Bacillus. Conjugation frequency was highest with a strain having an altered surface layer (S layer). Conjugal transfer of pAM beta 1 was not detected in mosquito larval cadavers. B. sphaericus 2362 was unable to mobilize pUB110 for transfer to strains that had served as recipients of pAM beta 1. These observations suggest that it is unlikely that genetically engineered B. sphaericus carrying a recombinant plasmid could pass that plasmid to other bacteria.  相似文献   
54.
The authors investigated development of the concept of division in young children. Experiment 1 examined whether children who can share are able to understand the inverse divisor–quotient relationship in partitive division tasks when asked to judge the relative size of 2 shared sets. Experiment 2 investigated whether young children understand the same inverse relation in quotitive tasks in which they were asked to judge the relative number of sets to be formed. The ability to compare share-outs and to take into account the inverse divisor–quotient relationship was present in approximately half of the 6-year-olds; age improvements were significant between 5 and 7 years. Partitive tasks, which are more similar to sharing, were easier than quotitive tasks, which seem to involve the coordination between sharing and part-whole concepts. This is evidence that children's initial understanding of division might be based on the action schema of sharing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
55.
56.
Phytochemical compositions of five varieties of black soybeans (Glycine max) and their stabilities at room temperature, 4 and −80 °C over 14 months were determined by HPLC systems with electrochemical (ECD) and UV detectors. Polyphenol profiling was carried out by a liquid chromatography–electrospray ionisation-mass spectrometry (LC–ESI-MS) with orbitrap as a mass analyser in both positive and negative ion modes, and polyphenols in aglycone forms were quantified by HPLC–ECD. Five different varieties of black soybeans (G. max) contained 249–405 μg/g dry wt of γ-tocopherol and 6.76–14.98 μg/g dry wt of lutein. Major polyphenols in black soybeans (G. max) were daidzein (193–288 μg/g dry wt) and genistein (145–223 μg/g dry wt), mainly present as glucosides and acetyl glucosides. No significant decrease was found in total phenols of black soybeans (G. max) stored at room temperature, 4 or −80 °C for 14 months. On the other hand, lutein and γ-tocopherol degraded significantly within a month of storage at room temperature (p < 0.01), whereas they remained stable up to 6 months at 4 °C and up to 14 months at −80 °C. The current study indicates that black soybeans (G. max) are rich source of γ-tocopherol and phenols (isoflavones, flavonols, flavan-3-ols, proanthocyanidins and anthocyanin) and that the levels vary depending upon varieties. In addition, storage at low temperature is recommended to reduce the loss of fat-soluble phytochemicals in black soybeans (G. max) over an extended period of time.  相似文献   
57.
PPARγ agonist DIM‐Ph‐4‐CF 3 , a template for RXRα agonist (E)‐3‐[5‐di(1‐methyl‐1H‐indol‐3‐yl)methyl‐2‐thienyl] acrylic acid: DIM‐Ph‐CF3 is reported to inhibit cancer growth independent of PPARγ and to interact with NR4A1. As both receptors dimerize with RXR, and natural PPARγ ligands activate RXR, DIM‐Ph‐4‐CF3 was investigated as an RXR ligand. It displaces 9‐cis‐retinoic acid from RXRα but does not activate RXRα. Structure‐based direct design led to an RXRα agonist.

  相似文献   

58.
2-Propanol and molecular H2 (in methanol (MeOH) and MeOH–water) were examined as reducing agents for the liquid phase hydrodechlorination (HDC) of dioxins over 2 wt.% Pd/γ-Al2O3. Different amounts of NaOH were added to the reaction mixtures. The 2-propanol and H2(g)/MeOH systems presented similar HDC activity. Notwithstanding, Pd sintering and graphitic carbon directly bonded to Pd on catalyst surface was observed on samples used with H2(g)/MeOH. The addition of water to H2(g)/MeOH decreased Pd sintering and favored dissolution of sodium compounds. However, dioxin degradation efficiency diminished. By contrast, 2-propanol acting both as reducing agent and solvent provided hydrogen to the HDC reaction, avoided metal sintering and Pd–C formation. Besides, almost complete dioxin degradation under mild reaction conditions was obtained. Kinetic experiments of dioxin HDC with 2-propanol showed a maximum net reaction rate and turnover frequency (TOF) for a given initial concentration of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). After that value, both reaction rate and TOF decreased. On the other hand, reaction rates and TOFs of dioxin-like polychlorinated biphenyls (DL-PCBs) linearly increased with concentration.  相似文献   
59.
In this study sequential steps were used to treat and immobilize oil constituents of an oil sludge-contaminated soil. Initially, the contaminated soil was oxidized by a Fenton type reaction (13 wt% for H(2)O(2); 10mM for Fe(2+)). The oxidative treatment period of 80 h was carried out under three different pH conditions: 20 h at pH 6.5, 20 h at pH 4.5, and 40 h at pH 3.0. The oxidized contaminated sample (3 kg) was stabilized and solidified for 2h with clay (1 kg) and lime (2 kg). Finally, this mixture was solidified by sand (2 kg) and Portland cement (4 kg). In order to evaluate the efficiency of different processes to treat and immobilize oil contaminants of the oil sludge-contaminated soil, leachability and solubility tests were performed and extracts were analyzed according to the current Brazilian waste regulations. Results showed that the Fenton oxidative process was partially efficient in degrading the oil contaminants in the soil, since residual concentrations were found for the PAH and BTEX compounds. Leachability tests showed that clay-lime stabilization/solidification followed by Portland cement stabilization/solidification was efficient in immobilizing the recalcitrant and hazardous constituents of the contaminated soil. These two steps stabilization/solidification processes are necessary to enhance environmental protection (minimal leachability) and to render final product economically profitable. The treated waste is safe enough to be used on environmental applications, like roadbeds blocks.  相似文献   
60.
This paper presents a novel ac uninterruptible-power-system (UPS) scheme with high power factor, which offers excellent characteristics such as sinusoidal input current, sinusoidal output voltage, fast regulation of the ac mains, galvanic isolation, and fast transient response. The proposed converter includes the offline–online concept, which avoids the continuous charging and discharging of the battery as it occurs in a typical online UPS. Analysis and design considerations, as well as simulation and experimental results, are given in this paper.   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