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   1461篇
  免费   96篇
  国内免费   2篇
电工技术   18篇
综合类   2篇
化学工业   428篇
金属工艺   54篇
机械仪表   62篇
建筑科学   28篇
矿业工程   4篇
能源动力   46篇
轻工业   294篇
水利工程   14篇
石油天然气   10篇
无线电   61篇
一般工业技术   297篇
冶金工业   83篇
原子能技术   40篇
自动化技术   118篇
  2024年   5篇
  2023年   22篇
  2022年   67篇
  2021年   83篇
  2020年   52篇
  2019年   77篇
  2018年   61篇
  2017年   60篇
  2016年   64篇
  2015年   51篇
  2014年   77篇
  2013年   96篇
  2012年   106篇
  2011年   103篇
  2010年   94篇
  2009年   90篇
  2008年   67篇
  2007年   68篇
  2006年   39篇
  2005年   26篇
  2004年   24篇
  2003年   24篇
  2002年   25篇
  2001年   19篇
  2000年   17篇
  1999年   16篇
  1998年   27篇
  1997年   21篇
  1996年   18篇
  1995年   17篇
  1994年   10篇
  1993年   4篇
  1992年   3篇
  1991年   6篇
  1990年   3篇
  1989年   3篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1968年   1篇
排序方式: 共有1559条查询结果,搜索用时 14 毫秒
991.
PURPOSE: We present four cases of dissection of the thoracic descending aorta that underwent treatment with an auto expandable dácron-covered stent. METHODS: The stent was deployed through the femoral artery in the hemodynamic laboratory after sedation, local anesthesia in both inguinal areas and systemic heparinization. The catheter with the stent was introduced through a cutdown in the left femoral artery until the area in the thoracic aorta with the previously diagnosed tear. RESULTS: The stent was expanded with immediate occlusion of the false lumen. The whole procedure took 90 minutes and the patients were discharged without complications. CONCLUSION: Stent utilization is an important step to improve treatment results in type B aortic dissection.  相似文献   
992.
In 1987, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) initiated the Agenda for Change, a major revision in the evaluation process for hospitals. An essential component of that change was to shift the emphasis away from standards for individual departments to standards for hospital-wide functions. In recent years, hospital librarians have focused their energy and attention on complying with the standards for the "Management of Information" chapter, specifically the IM.9 section on knowledge-based information. However, the JCAHO has listed the health sciences librarian and library services as having responsibilities in six other chapters within the Comprehensive Accreditation Manual for Hospitals. These chapters can have a major impact on the services of the hospital library for two reasons: (1) they are being read by hospital leaders and other professionals in the organization, and (2) they articulate specific ways to apply knowledge-based information services to the major functions within the hospital. These chapters are "Education"; "Improving Organizational Performance"; "Leadership"; "Management of Human Resources"; "Management of the Environment of Care"; and "Surveillance, Prevention, and Control of Infection." The standards that these chapters promote present specific opportunities for hospital librarians to apply knowledge-based information resources and service to hospital-wide functions. This article reviews these chapters and discusses the standards that relate to knowledge-based information.  相似文献   
993.
OBJECTIVE: To assess ethnic differences in androgenic status related to non insulin-dependent diabetes mellitus (NIDDM) in male and female Melanesians and Europeans of New Caledonia. DESIGN: This is a case-control study nested in a prevalence study for diabetes mellitus in the multiracial population of New Caledonia. SUBJECTS: 186 male subjects were included in the survey (77 Melanesians and 16 Europeans in each case and control group). Each case and control group included 104 female Melanesian subjects (69 premenopausal and 35 postmenopausal). METHODS: Diabetic subjects were matched for age, gender, ethnic group and location, with healthy normoglycaemic subjects. Testosterone levels in men and sex hormone-binding globulin (SHBG) levels in women (measured by radioimmunoassay, RIA) were compared between NIDDM and control subjects in relation to obesity, central adiposity and insulin levels. RESULTS: In both ethnic groups, NIDDM was associated with lower testosterone levels but there was a marked difference among Europeans. Testosterone was negatively associated with the body mass index (BMI) (r= -0.35, P <0.01) and fasting insulin (r= -0.37, P <0.001) in control Melanesians only. In Melanesian women, NIDDM was associated with lower SHBG levels in pre- and postmenopausal women (P <0.001). SHBG mean level was not associated with menopausal status. CONCLUSION: Our results confirm in a Pacific population that NIDDM is associated with low levels of testosterone in men and low levels in SHBG in women. In contrast to white populations, Melanesian women have a more androgenic profile, whatever their menopausal status.  相似文献   
994.
Diabetic nephropathy is a frequent cause of end-stage renal failure in patients admitted for renal replacement therapy. PURPOSE: To evaluate the prevalence of DN, as the underline disease, in patients with ESRF. METHODS: 1,303 [male (M) = 767 and female (F) = 536] patients with ESRF who were on a waiting list for cadaver kidney transplant at Nephrology Unit-University Hospital (HC-UNICAMP), from August/90 to June/93--group 1--and 193 (M = 112 and F = 81) patients admitted for renal replacement therapy in a year period (April/92 to March/93), in the city of Campinas, State of S?o Paulo, Brazil, were studied. RESULTS: The prevalence of DN was 10.1% in group 1 and 17.6% in group 2 (x2 = 7.15; p = 0.007), being the third cause of ESRF in both groups, and it was preceded by glomerulonephritis and arterial hypertension. In group 1 the reduction of number of patients with increase in duration of dialysis was significantly greater in patients with diabetic nephropathy (x2 = 30.9; p < 0.001). Among patients with DN 35 (26%) in group 1 and 6 (18%) in group 2 had less than 35 years when they were admitted for renal replacement therapy and are likely to be type 1 (insulin-dependent) diabetic patients. CONCLUSION: In our studied groups DN was a frequent cause of ESRF.  相似文献   
995.
Five elements (Ti, Fe, Co, Er and Au) were implanted in sapphire to fluences between 8×1013 and 5×1017 at/cm2, and energies between 200 and 800 keV. We used Rutherford backscattering to determine the dose and depth of the implanted elements. The data analysis is performed using an artificial neural network (ANN). Here we report a generalisation of previous works where ANNs were successfully applied for specific implantations such as Er in sapphire and Ge in Si. We have now developed a code that it is able to analyse data from implantations of any element with Z between 18 and 83 into sapphire. Although this problem is considerably more complex than single-system ANNs, the ANN developed produced excellent results when applied to experimental data. We discuss the reliability of the ANN and its applicability to the analysis of large batches of implanted samples.  相似文献   
996.
AlN was implanted with 300 keV Eu ions within a wide fluence range from 4 × 1014 to 1.4 × 1017 at/cm2. The damage build-up was investigated by Rutherford Backscattering/Channelling. Sigmoidal shaped damage build-up curves indicate efficient dynamic annealing. A regime with low damage increase for fluences below 1015 at/cm2 is followed by a strong increase for intermediate fluences. For the highest fluences the damage curve rises slowly until a buried amorphous layer is formed. High temperature annealing was performed in nitrogen atmospheres at low pressure (1300 °C, 105 Pa) or at ultra-high pressure (1450 °C, 109 Pa). Implantation damage was found to be extremely stable and annealing only resulted in slight structural recovery. For high fluences out-diffusion of Eu is observed during annealing. Nevertheless, photoluminescence (PL) measurements show intense Eu-related red light emission for all samples with higher PL intensity for the high temperature high pressure annealing.  相似文献   
997.
Plasma facing components in fusion reactor chambers will operate under extreme conditions. Among the processes with implications on the material lifetime are erosion and re-deposition due to plasma interactions.This work will address the behaviour of both JET divertor and outer poloidal limiters (OPL) under plasma irradiation. The limiters comprise about 50 pairs of tiles in a poloidal stack, each of which has a plasma facing surface about 25 mm (poloidal) by 350 mm (toroidal) and is about 50 mm thick. The divertor tiles are located at the bottom of the chamber and withstand high fluxes of radiation and heat. Standard carbon-fibre composite (CFC) tiles coated with a thin layer of W overlaid with a 10 μm layer of C were studied with RBS/PIXE to understand the erosion/re-deposition processes occurring in these regions of the reactor chamber. High resolution surface morphology was assessed through SEM with and without tilting of the sample. The retention of hydrogen isotopes in the tiles were studied combining NRA and ERDA techniques – this is mostly 2H from the fuelling gas, but 3H is also present as a result of 2H–2H fusion reactions, and 1H coming from the atmospheric exposure.  相似文献   
998.
An integrative mathematical model was developed to obtain an overall picture of lipid hydroperoxide metabolism in the mitochondrial inner membrane and surrounding matrix environment. The model explicitly considers an aqueous and a membrane phase, integrates a wide set of experimental data, and unsupported assumptions were minimized. The following biochemical processes were considered: the classic reactional scheme of lipid peroxidation; antioxidant and pro-oxidant effects of vitamin E; pro-oxidant effects of iron; action of phospholipase A2, glutathione-dependent peroxidases, glutathione reductase and superoxide dismutase; production of superoxide radicals by the mitochondrial respiratory chain; oxidative damage to proteins and DNA. Steady-state fluxes and concentrations as well as half-lives and mean displacements for the main metabolites were calculated. A picture of lipid hydroperoxide physiological metabolism in mitochondria in vivo showing the main pathways is presented. The main results are: (a) perhydroxyl radical is the main initiation agent of lipid peroxidation (with a flux of 10(-7)MS-1); (b) vitamin E efficiently inhibits lipid peroxidation keeping the amplification (kinetic chain length) of lipid peroxidation at low values (approximately equal to 10); (c) only a very minor fraction of lipid hydroperoxides escapes reduction via glutathione-dependent peroxidases; (d) oxidized glutathione is produced mainly from the reduction of hydrogen peroxide and not from the reduction of lipid hydroperoxides.  相似文献   
999.
A single-extraction method to simultaneously determine aflatoxins (B1, B2, G1, G2), fumonisin B1, and zearalenone in corn meal by ultra performance liquid chromatography tandem mass spectrometry, using a triple quadrupole, was optimized, validated, and applied in an occurrence study. Different extraction solutions were tested, with better performance for methanol/acetonitrile/water (60:20:20, v/v/v). Linearity was observed from 0.25 to 1.50 ng/mL for aflatoxins, from 20 to 120 ng/mL for fumonisin, and from 7.00 to 42.00 ng/mL for zearalenone. Significant matrix effects were shown for all groups. Selectivity was demonstrated, as matrix or spectral interferences were not observed at the predicted retention time window of the target analytes. Average recoveries of 87.57, 93.18, 93.35, 94.20, 78.76, and 95.98% were obtained for aflatoxins (B1, B2, G1, and G2) fumonisin and zearalenone, respectively. A z-score of 0.19 was estimated in a corn certified reference material for fumonisin B1. Maximum relative standard deviation values under repeatability and intermediate precision conditions were determined to be 13.6 and 13.6% for aflatoxins, 3.7 and 6.3% for fumonisin, and 3.5 and 4.0% for zearalenone, respectively. In the occurrence study, 50 samples were analyzed and 44% had measurable levels of fumonisin. Zearalenone was detected in 18%. The proposed method showed considerable advantages, considering environmental impacts, efficiency, and reliability.  相似文献   
1000.
We exploited alternated electrodeposition of Cu, Sn and S to obtain CuxSnySz thin films. These materials are kesterite‐type chalcogenides that have attracted a relevant interest from worldwide researchers as low cost and high conversion efficiency solar cell devices. Films were grown on silver substrate, controlling the growth of the electrodeposited structures at the nanometric level. The obtained films were characterized by diffuse reflectance spectroscopy, voltammetric stripping and atomic force microscopy. Experimental bandgap energies resulted linearly modulated by changes of chemical composition and thickness. On the basis of these results, we candidate electrodeposition as a room temperature method to obtain thin films for solar cell technology with low energy investment and negligible environmental impact. Copyright © 2013 John Wiley & Sons, Ltd.  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