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   720篇
  免费   20篇
电工技术   23篇
化学工业   170篇
金属工艺   22篇
机械仪表   32篇
建筑科学   21篇
矿业工程   1篇
能源动力   21篇
轻工业   112篇
水利工程   2篇
无线电   28篇
一般工业技术   121篇
冶金工业   101篇
原子能技术   37篇
自动化技术   49篇
  2024年   2篇
  2023年   2篇
  2022年   10篇
  2021年   14篇
  2020年   6篇
  2019年   16篇
  2018年   15篇
  2017年   20篇
  2016年   16篇
  2015年   6篇
  2014年   22篇
  2013年   51篇
  2012年   32篇
  2011年   54篇
  2010年   40篇
  2009年   43篇
  2008年   45篇
  2007年   35篇
  2006年   32篇
  2005年   17篇
  2004年   11篇
  2003年   24篇
  2002年   16篇
  2001年   12篇
  2000年   14篇
  1999年   13篇
  1998年   37篇
  1997年   26篇
  1996年   22篇
  1995年   7篇
  1994年   7篇
  1993年   12篇
  1992年   5篇
  1991年   2篇
  1989年   2篇
  1988年   3篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1983年   4篇
  1982年   4篇
  1981年   2篇
  1979年   2篇
  1978年   3篇
  1977年   7篇
  1976年   8篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1964年   1篇
排序方式: 共有740条查询结果,搜索用时 12 毫秒
71.
72.
In this paper, a desktop-size NC machine tool is first presented to have multi-application function, such as 3D-machining modes with and without handling a machining force, and profiling-control modes with and without using stick-slip motion. The NC machine tool consists of three single-axis devices with a high resolution of 1???m in position. A ball end mill called router bit or a thin wood-stick tool can be attached to the tip of the z-axis. The proposed machine tool realizes compliant motion required for the profiling control along a desired trajectory. The profiling-control mode can be applied to the lapping process of a metallic LED lens cavity. Next, a control strategy with fine stick-slip motion is further added to the profiling-control system to improve the lapping performance. The fine stick-slip motion is generated orthogonally to the direction of the tool movement. Generally, the stick-slip motion is an undesirable phenomenon to be eliminated in precision machineries. However, the proposed machine tool employs the fine stick-slip motion to partly regulate slight finishing energy. The effectiveness of the machine tool is demonstrated through an actual machining test of a wood material and a lapping test of a metallic LED lens cavity.  相似文献   
73.
Ultra high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) determination of four paraben preservatives (methyl, ethyl, propyl and butyl) and two antimicrobial agents (triclosan and triclocarban) belonging to personal care products (PCPs) in 20 species of fish from Manila Bay (Philippines) was performed. Detection of PCPs with greater frequency indicates the ubiquitous contamination of Manila Bay. Concentrations of total paraben were one order of magnitude higher than the antimicrobials in almost all fish, except in Stolephorus indicus and Leiognathus equulus. A positive correlation was observed between parabens concentration and fish length (r = 0.31-0.49; p<0.05 to <0.001) and fish weight (r = 0.28-0.49; p<0.05 to <0.001), but not for the antimicrobials. The estimated dietary exposure values of the four parabens in the Philippines through fish is four orders of magnitude lower than the acceptable daily intake (ADI) of 10mg/kg/day, but the values of antimicrobials are just half of the ADI of TCS. To our knowledge, this is the first report of PCPs contamination in fish from Philippines.  相似文献   
74.
The XT-ADS, an accelerator-driven system for an experimental demonstration, has been investigated in the framework of IP EUROTRANS FP6 project. In this study, the sensitivity and uncertainty analyses were performed to comprehend the reliability of the XT-ADS neutronic design.  相似文献   
75.
We describe a technique, simpler than earlier ones, for using SPICE in the computation of the 1/f, step, and delta noise indices of linear and time-valiant filters. The method is based on obtaining a weighting function from the results of simulation and is demonstrated for triangular and trapezoidal shapers. The results are compared with those obtained by direct calculation. The greatest discrepancies occur when the method is applied to gated integrators, but the errors are probably due to artifacts not related to the basic method described here  相似文献   
76.
Concurrent exposure to ionizing radiation (IR) and psychological stress (PS) may affect the development of adverse health consequences in scenarios such as space missions, radiotherapy and nuclear accidents. IR can induce DNA damage and cell apoptosis in the kidneys, thus potentially leading to renal fibrosis, which is the ultimate outcome of various chronic progressive nephropathies and the morphological manifestation of a continuous coordinated response after renal injury. However, little is known regarding the effects of concurrent IR exposure and PS on renal damage, particularly renal fibrosis. In this study, using a chronic restraint-induced PS (CRIPS) model, we exposed Trp53-heterozygous mice to total body irradiation with 0.1 or 2 Gy 56Fe ions on the eighth day of 28 consecutive days of a restraint regimen. At the end of the restraint period, the kidneys were collected. The histopathological changes and the degree of kidney fibrosis were assessed with H&E and Masson staining, respectively. Fibronectin (FN) and alpha smooth muscle actin (α-SMA), biomarkers of fibrosis, were detected by immunohistochemistry. Analysis of 8-hydroxy-2 deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, was performed with immunofluorescence, and terminal deoxynucleotidyl transferase-mediated nick end labeling assays were used to detect apoptotic cells. Histopathological observations did not indicate significant structural damage induced by IR or CRIPS + IR. Western blotting revealed that the expression of α-SMA was much higher in the CRIPS + IR groups than the CRIPS groups. However, no differences in the average optical density per area were observed for FN, α-SMA and 8-OHdG between the IR and CRIPS + IR groups. No difference in the induction of apoptosis was observed between the IR and CRIPS + IR groups. These results suggested that exposure to IR (0.1 and 2 Gy 56Fe ions), 28 consecutive days of CRIPS or both did not cause renal fibrosis. Thus, CRIPS did not alter the IR-induced effects on renal damage in Trp53-heterozygous mice in our experimental setup.  相似文献   
77.
A chemical treatment to remove residual CeO2 phase on CeO2–ZrO2 (CZ) solid solution was carried out. A CZ was treated by H2O2 for the reduction of Ce4+ to Ce3+ and then HNO3 for the dissolution of Ce3+ compounds (H–CZ). H2-TPR, TEM-EDX and XPS analyses revealed the removal of CeO2 phase and the homogeneous distribution of Ce species. About 20% improvement in oxygen storage capacity (OSC) of H–CZ was confirmed at 773 K by the weight measurements under H2/N2 and air atmospheres, indicating that the HNO3/H2O2 treatment was effective to avoid the deterioration of the OSC by segregated CeO2 on the CZ binary oxides.  相似文献   
78.
Recently, we have reported that anthocyanins show strong antioxidative activity, but no attention has been paid to anthocyanins from the viewpoint of the reaction mechanism of alkylperoxyl radicals; therefore, we investigated the reaction products of antioxidative anthocyanins (cyanidin 3-O-β-d-glucoside). Cyanidin 3-O-β-d-glucoside was reacted with 2,2′-azobis(2,4-dimet hylvaleronitrile) to generate the alkylperoxyl radicals, and the reaction products were isolated by high-performance liquid chromatography. The products were identified as 4,6-dihydroxy-2-O-β-d-glucosyl-3-oxo-2,3-dihydrobenzofuran and protocatechuic acid. Based on reaction products, the antioxidative mechanism of cyanidin 3-O-β-d-glucoside may be different from that of α-tocopherol; cyanidin 3-O-β-d-glucoside would produce another radical scavenger, as it would break down the structure and scavenge the radicals.  相似文献   
79.
Protein phosphorylation/dephosphorylation on tyrosine residues are regulated by tyrosine kinases/phosphatases. The tyrosine phosphatase SH-PTP2 (PTP1D, PTP2C) interacts physically through its SH2 domain with phosphorylated epidermal growth factor receptor (EGFR). In KB cells, an oral epidermoid carcinoma, high epidermal growth factor (EGF) concentrations (10-9, 10-8 and 10-7 M) downregulate its receptor for the duration of the incubation with EGF. Thus, it was hypothesized that in KB cells, SH-PTP2 expression would also be downregulated by high EGF concentrations. This hypothesis was investigated by incubating the KB cells with increasing concentrations of EGF (0, 10-11, 10-10, 10-9, 10-8, 10-7 M) and by evaluating the expression of SH-PTP2 protein under these conditions. This study showed that EGF 10-7 and 10-8 M significantly decreased SH-PTP2 protein expression compared to controls. EGF 10-10 and 10-11 M did not change the expression of SH-PTP2 protein. We conclude that high EGF concentrations downregulate the expression of SH-PTP2 protein.  相似文献   
80.
STUDY OBJECTIVE: To evaluate the long-term efficacy of laparoscopic Burch urethropexy. DESIGN: Pilot study. SETTING: Private practice. PATIENTS: Thirty-five consecutive women (average age 45.5 yrs, average parity 2.3, average weight 67.7 kg) treated for genuine stress incontinence between May 1992 and July 1994. INTERVENTIONS: Urethropexy was performed with curved needle suturing in 7 women, straight needle suturing in 5, and Stamey needle suturing in 23. Twenty-five (71.4%) patients had concomitant pelvic surgery. MEASUREMENTS AND MAIN RESULTS: Wilcoxon two-sample, chi2, and Fisher's exact tests were performed to determine which variables were significantly associated with surgical success. Average operating time was 190 minutes, hospitalization 24 hours, and catheterization 5 days. The cure rate of stress incontinence was 89% 3 months and 86% 1 year after surgery. At average follow-up of 34 months, only 68.6% of patients reported complete or almost complete cure, 11.4% were improved, and 20% were complete failures. The only operative variable approaching statistical significance for predicting surgical success was type of suture needle (p = 0.07), with the Stamey needle group having the highest cure rate. Women who were cured or almost cured had a significantly shorter follow-up than those who were improved or failures (p = 0.001). CONCLUSION: The success rate of laparoscopic Burch urethropexy compares with that of open Burch procedure at 1 year, but drops considerably thereafter.  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