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   980篇
  免费   47篇
  国内免费   7篇
电工技术   9篇
综合类   1篇
化学工业   383篇
金属工艺   37篇
机械仪表   29篇
建筑科学   41篇
矿业工程   2篇
能源动力   50篇
轻工业   99篇
水利工程   14篇
石油天然气   23篇
无线电   47篇
一般工业技术   157篇
冶金工业   64篇
原子能技术   7篇
自动化技术   71篇
  2023年   7篇
  2022年   29篇
  2021年   25篇
  2020年   32篇
  2019年   42篇
  2018年   39篇
  2017年   21篇
  2016年   27篇
  2015年   30篇
  2014年   37篇
  2013年   98篇
  2012年   47篇
  2011年   70篇
  2010年   41篇
  2009年   38篇
  2008年   34篇
  2007年   34篇
  2006年   36篇
  2005年   20篇
  2004年   15篇
  2003年   15篇
  2002年   18篇
  2001年   13篇
  2000年   11篇
  1999年   9篇
  1998年   13篇
  1997年   15篇
  1996年   9篇
  1995年   14篇
  1994年   8篇
  1993年   11篇
  1992年   13篇
  1991年   11篇
  1990年   7篇
  1989年   9篇
  1988年   11篇
  1987年   7篇
  1986年   8篇
  1985年   10篇
  1984年   8篇
  1983年   10篇
  1980年   14篇
  1977年   5篇
  1976年   7篇
  1974年   6篇
  1973年   5篇
  1971年   6篇
  1970年   5篇
  1967年   5篇
  1966年   6篇
排序方式: 共有1034条查询结果,搜索用时 15 毫秒
91.
Gelatin was doped with 1 %, 3 %, 5 % and 10 % cadmium sulfide nanoparticles in weight concentrations forming the gelatin-cadmium sulfide nanocomposites and irradiated by various electron beam doses equals 50 kGy, 75 kGy, 100 kGy, and 150 kGy using 3 MeV – 3 mA electron accelerator. The applied alternating current electrical field frequency ranging from 70 Hz to 5 MHz is what caused the fluctuation in dielectric properties and alternating current electrical conductivity of these nanocomposites. The results showed that the films of 1 %, 3 %, 5 %, and 10 % for blank (nanocomposite film without electron beam irradiation) nanocomposites had the highest dielectric parameters (έ, ϵ′′, tan δ) at 0.5 kHz with values of (0.696, 0.0233, 0.034), (0.533, 0.0114, 0.0215), (0.402, 0.001196, 0.003), and (0.459, 0.00418, 0.0091), respectively. However, the lowest dielectric parameters were (0.645, 0.00618, 0.0066), (0.523, 0.00165, 0.0215), (0.417, 0.00035, 0.0008), and (0.455, 0.00066, 0.0015) at 5 MHz, respectively. The highest conductivity values for blank nanocomposites of 1 %, 3 %, 5 %, and 10 % were 1.79×10−4 S/m, 1.45×10−4 S/m, 1.16×10−4 S/m, 1.27×10−4 S/m at 5 MHz, and the lowest values were 1.92×10−8 S/m, 1.49×10−8 S/m, 1.13×10−8 S/m, 1.26×10−8 S/m at 0.5 kHz, respectively. For irradiated nanocomposites at 5 MHz, the dielectric constant order for 1 % was 100 kGy, 150 kGy, 50 kGy, and 75 kGy with values 0.63, 0.537, 0.532, and 0.523, respectively. For 10 % weight concentration, the order was 50 kGy, 100 kGy, 150 kGy, and 75 kGy with values 0.515, 0.477, 0.47, and 0.437, respectively. Otherwise the dielectric constant order for 3 % and 5 % was 100 kGy, 75 kGy, 150 kGy, and 50 kGy. The highest dielectric properties and conductivity values for blank and irradiated nanocomposites were observed at 100 kGy for 1 %, 3 %, and 5 %.  相似文献   
92.
Amyotrophic Lateral Sclerosis (ALS), neurodegenerative motor neuron disorder is characterized as multisystem disease with important contribution of genetic factors. The etiopahogenesis of ALS is not fully elucidate, but the dominant theory at present relates to RNA processing, as well as protein aggregation and miss-folding, oxidative stress, glutamate excitotoxicity, inflammation and epigenetic dysregulation. Additionally, as mitochondria plays a leading role in cellular homeostasis maintenance, a rising amount of evidence indicates mitochondrial dysfunction as a substantial contributor to disease onset and progression. The aim of this review is to summarize most relevant findings that link genetic factors in ALS pathogenesis with different mechanisms with mitochondrial involvement (respiratory chain, OXPHOS control, calcium buffering, axonal transport, inflammation, mitophagy, etc.). We highlight the importance of a widening perspective for better understanding overlapping pathophysiological pathways in ALS and neurodegeneration in general. Finally, current and potentially novel therapies, especially gene specific therapies, targeting mitochondrial dysfunction are discussed briefly.  相似文献   
93.
The mucin MUC1 is overexpressed and aberrantly glycosylated by many epithelial cancer cells manifested by truncated O‐linked saccharides. Although tumor‐associated MUC1 has generated considerable attention because of its potential for the development of a therapeutic cancer vaccine, it has been difficult to design constructs that consistently induce cytotoxic T‐lymphocytes (CTLs) and ADCC‐mediating antibodies specific for the tumor form of MUC1. We have designed, chemically synthesized, and immunologically examined vaccine candidates each composed of a glycopeptide derived from MUC1, a promiscuous Thelper peptide, and a TLR2 (Pam3CysSK4) or TLR9 (CpG‐ODN 1826) agonist. It was found that the Pam3CysSK4‐containing compound elicits more potent antigenic and cellular immune responses, resulting in a therapeutic effect in a mouse model of mammary cancer. It is thus shown, for the first time, that the nature of an inbuilt adjuvant of a tripartite vaccine can significantly impact the quality of immune responses elicited against a tumor‐associated glycopeptide. The unique adjuvant properties of Pam3CysSK4, which can reduce the suppressive function of regulatory T cells and enhance the cytotoxicity of tumor‐specific CTLs, are likely responsible for the superior properties of the vaccine candidate 1 .  相似文献   
94.
BACKGROUND: The etiology of retinal venous occlusion in young patients is not well understood although thrombosis does occur histologically. A search for the risk factors that may lead to thrombosis is highly desirable may contribute to our understanding of the pathogenesis of this complication and may improve our therapeutic strategies. METHODS: We studied 17 patients with retinal venous occlusion. All patients were under 45 years of age (mean 37.8 +/- 7.1). Antiphospholipid antibodies (APAs) and certain hemostatic factors were determined. The results obtained in these patients were compared to those of normal controls. RESULTS: We found APAs in 8 out of 17 patients compared to 5 out of 60 controls (p = 0.0002). In patients with major trunk occlusion, there was a trend for the presence of APAs in those with poor visual acuity at presentation. Deficiencies of the coagulation inhibitor proteins C and S and antithrombin III activities were detected in 6 patients, and reduced levels of Factor XII were found in 4 patients. Levels of hematocrit, erythrocyte sedimentation rate. Fibrinogen, alpha 1-globulin, and alpha 2-globulin were significantly higher in patients compared to the controls (p = 0.019; 0.014; 0.0001; 0.011; 0.047), indicating increased blood viscosity in patients with retinal venous occlusion. CONCLUSION: Prothrombotic changes in the form of APAs and/or deficiencies of coagulation inhibitors and Factor XII may contribute to the etiology of retinal venous occlusion in young adults. Young patients with retinal venous occlusion should be evaluated for these prothrombotic states.  相似文献   
95.
BACKGROUND: Lack of information about the effect of insurance coverage on the demand for and use of smoking-cessation services has prevented widescale adoption of coverage for such services. METHODS: In a longitudinal, natural experiment, we compared the use and cost effectiveness of three forms of coverage with those of a standard form of coverage for smoking-cessation services that included a behavioral program and nicotine-replacement therapy. The study involved seven employers and a total of 90,005 adult enrollees. The standard plan offered 50 percent coverage of the behavioral program and full coverage of nicotine-replacement therapy. The other plans offered 50 percent coverage of both the behavioral program and nicotine-replacement therapy (reduced coverage), full coverage of the behavioral program and 50 percent coverage of nicotine-replacement therapy (flipped coverage), or full coverage of both the behavioral program and nicotine-replacement therapy. RESULTS: Estimated annual rates of use of smoking-cessation services ranged from 2.4 percent (among smokers with reduced coverage) to 10 percent (among those with full coverage). Smoking-cessation rates ranged from 28 percent (among users with full coverage) to 38 percent (among those with standard coverage). The estimated percentage of all smokers who would quit smoking per year as a result of using the services ranged from 0.7 percent (with reduced coverage) to 2.8 percent (with full coverage). The average cost to the health plan per user who quit smoking ranged from $797 (with standard coverage) to $1,171 (with full coverage). The annual cost per smoker ranged from $6 (with reduced coverage) to $33 (with full coverage). The annual cost per enrollee ranged from $0.89 (with reduced coverage) to $4.92 (with full coverage). CONCLUSIONS: Use of smoking-cessation services varies according to the extent of coverage, with the highest rates of use among smokers with full coverage. Although the rate of smoking cessation among the benefit users with full coverage was lower than the rates among users with plans requiring copayments, the effect on the overall prevalence of smoking was greater with full coverage than with the cost-sharing plans.  相似文献   
96.
In the present study, the removal and immobilization of 137Cs from aqueous waste solutions and a simulated waste was investigated. Two inorganic ion‐exchange complexes: di‐potassium hexacyanocobalt(II)‐ferrate(II), K2CoFe(CN)xH2O (KCFC), and ammonium‐12‐molybdophosphate [(NH4)3PMo12O40·aq] (AMP), were charged separately into porous nylon bags (sorption bags) of 5 µm pore diameter. The first complex (KCFC) was prepared in our laboratory. The second (AMP) was used for comparison. Easy handling and increased potential for reuse characterize the sorption bag technique. The KCFC complex was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA), porosity, infra‐red (IR) and X‐ray powder diffraction (XRD). The chemical and structural investigations revealed that the KCFC complex has adequate ion‐exchange capacity and high affinity for 137Cs. The sorption bag technique showed promising results for the removal of 137Cs from aqueous waste solutions. The KCFC bags showed the highest 137Cs removal (~0.91 g g?1), at pH 8.5; AMP bags gave the highest 137Cs removal (~0.97 g g?1) in 0.1 N HNO3 and 1.5 N HNO3, both with a waste: sorbent ratio of 80 cm3 g?1. Sorption data for both KCFC and AMP revealed a good fit to the Freundlich sorption isotherm. To assess the potential of sorption bags, the used bags were regenerated in different leachants and reused in further sorption investigations. 137Cs recovery from the used sorbents was ~0.46 g g?1 using 6 N HCl as leachant for AMP, compared with ~0.253 g g?1 for KCFC using 6 N NaCl. These results indicated stronger cesium immobilization in the KCFC complex. Copyright © 2003 Society of Chemical Industry  相似文献   
97.
YBCO melt textured samples were studied after Au ion irradiation of two opposite surface layers of the samples and after proton irradiation. The scaling behavior of the pinning force was studied in order to get information about mechanisms responsible for pinning in the studied samples. Correlated disorder introduced bysurface ion irradiation is effective at high reduced temperatures and leads to the occurrence of a kink in the irreversibility line and to the shift of this line toward higher fields and temperatures. Enhancement of critical current density,increasing with temperature and field, was observed. Random disorder due to proton irradiation does not change the irreversibility line and only provides critical current enhancementdecreasing with temperature and field.  相似文献   
98.
An investigation is described in which Nubian goats were given daily oral doses of Piper abyssinica seeds at 0.25; 1 and 5 g/kg body weight. The results of liver and kidney function tests were correlated with the clinical and pathological changes. In goats receiving the plant seed at 5 g/kg body weight/day, death occurred within 5-14 days and the main signs were bloated rumen, diarrhoea, dysponoea and ataxia. Enterohepatonephropathy was accompanied by increases in the activity of serum ALP and GGT, in the concentration of cholesterol, globulin, total lipids and urea and decreases in the level of albumin. Piper seed was toxic but not lethal to goats at doses of 0.25 and 1 g/kg body weight.  相似文献   
99.
A microprocessor-based real time video analysis system has been built and used in conjunction with an oculometer to perform some aspects of eye motion analysis. An outstanding feature of this system is its ability to process data in real time so that information concerning instantaneous eye point of regard is readily available for direct observation.  相似文献   
100.
M.Es.Abdel Moneim 《Wear》1981,66(1):65-75
Constant-feed-rate drilling tests under conditions of dry cutting were performed on three non-ferrous materials, namely free machining brass, aluminium and lead. The tests covered a wide range of cutting speeds. Both thrust forces and torques were affected by the drill diameter and by speed variations. Empirical relationships between the thrust force, the torque and the cutting parameters were derived for the materials used.  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