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   748篇
  免费   3篇
综合类   1篇
化学工业   30篇
金属工艺   2篇
机械仪表   1篇
建筑科学   11篇
能源动力   1篇
轻工业   9篇
无线电   19篇
一般工业技术   18篇
冶金工业   622篇
自动化技术   37篇
  2023年   5篇
  2022年   6篇
  2021年   6篇
  2019年   4篇
  2017年   4篇
  2016年   3篇
  2015年   4篇
  2014年   3篇
  2013年   6篇
  2012年   11篇
  2011年   16篇
  2010年   5篇
  2009年   4篇
  2008年   7篇
  2007年   8篇
  2006年   4篇
  2005年   5篇
  2004年   7篇
  2003年   5篇
  2002年   2篇
  2000年   2篇
  1999年   25篇
  1998年   169篇
  1997年   101篇
  1996年   88篇
  1995年   28篇
  1994年   45篇
  1993年   41篇
  1992年   9篇
  1991年   5篇
  1990年   12篇
  1989年   16篇
  1988年   16篇
  1987年   10篇
  1986年   9篇
  1985年   10篇
  1984年   1篇
  1983年   3篇
  1981年   3篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   9篇
  1976年   17篇
  1975年   3篇
  1974年   1篇
  1972年   1篇
  1971年   3篇
  1969年   1篇
  1968年   1篇
排序方式: 共有751条查询结果,搜索用时 15 毫秒
91.
Growing evidence suggests that posttraumatic stress disorder (PTSD) is associated with poorer health status (e.g., more medical disease, physical symptoms, and sick visits to health care professionals) among veterans who served in Operation Enduring Freedom (OEF) in Afghanistan and Operation Iraqi Freedom (OIF) in Iraq. We investigated whether PTSD, depression, and substance use disorders independently predicted health status over time among OEF/OIF veterans. Information regarding psychiatric and medical conditions and health care utilization was culled for 4,463 OEF/OIF veterans enrolled in Veterans Administration primary care for a period of 6 years. Data were analyzed using multilevel modeling and generalized estimating equations. Results suggest that PTSD, depression, and substance use disorders are independently associated with increased medical disease burden and mental health care utilization but not increased medical health care utilization. The association between PTSD and medical disease burden strengthened over time. These data suggest that OEF/OIF veterans with PTSD may be at risk for increasingly poorer physical health in terms of medical disease burden over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
92.
Posttraumatic stress disorder (PTSD) is common among Veterans Affairs (VA) primary care patients and may be managed via multiple treatment pathways. Using the Behavioral Model of Health Service Use (Anderson, 1995), this retrospective study based on medical chart review examined factors associated with three types of mental health treatment: intervention by a 1) primary care provider (PCP), 2) primary care-mental health integration (PC-MHI) provider, and 3) specialty mental health (SMH) provider. A second goal was to describe PTSD treatment services for patients not receiving SMH by detailing the content of mental health treatment provided by PCPs and PC-MHI providers. Electronic medical record data for a five year time period for 133 Veterans were randomly selected for review from a population 6,637 primary care patients with PTSD. Results indicated that the evaluated needs of participants (i.e., number of unique medical and psychiatric disorders) were associated with Veterans receiving more intensive services (i.e., SMH). PCPs commonly addressed patients' mental health concerns, but patients often declined referrals for mental health treatment. PC-MHI consultations most often focused on medication management and supportive psychotherapy. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
93.
94.
Previous studies have indicated that raingardens are effective at removing petroleum hydrocarbons from stormwater. There are concerns, however, that petroleum hydrocarbons could accumulate in raingarden soil, potentially resulting in liability for the site owner. In this work, 75 soil samples were collected from 58 raingardens and 4 upland (i.e., control) sites in the Minneapolis, Minnesota area, representing a range of raingarden ages and catchment land uses. Total petroleum hydrocarbon (TPH) concentrations in the samples were quantified, as were 16S rRNA genes for Bacteria and two functional genes that encode for enzymes used in the degradation of petroleum hydrocarbons. TPH levels in all of the raingarden soil samples were low (<3 μg/kg) and not significantly different from one another. The TPH concentration in raingarden soil samples was, however, significantly greater (p ≤ 0.002) than TPH levels in upland sites. In addition, the number of copies of Bacteria 16S rRNA genes and functional genes were greater in the raingardens planted with deeply-rooted natives and cultivars than in raingardens containing simply turf grass or mulch (p < 0.036), suggesting that planted raingardens may be better able to assimilate TPH inputs. The ability of microorganisms present in the soil samples to degrade a representative petroleum hydrocarbon (naphthalene) was also investigated in batch experiments. A sub-set of the field sites was selected for re-sampling, and all soil samples tested (n = 8) were able to mineralize naphthalene. In these experiments the initial mineralization rate correlated with the number of copies of Bacteria 16S rRNA genes present.  相似文献   
95.
Accurate stress–strain constitutive properties are essential for understanding the complex deformation and failure mechanisms for materials with highly anisotropic mechanical properties. Among such materials, glass-fiber- and carbon-fiber-reinforced polymer–matrix composites play a critical role in advanced structural designs. The large number of different methods and specimen types currently required to generate three-dimensional allowables for structural design slows down the material characterization. Also, some of the material constitutive properties are never measured due to the prohibitive cost of the specimens needed. This work shows that simple short-beam shear (SBS) specimens are well-suited for measurement of multiple constitutive properties for composite materials and that can enable a major shift toward accurate material characterization. The material characterization is based on the digital image correlation (DIC) full-field deformation measurement. Two key elements show advantage of using DIC in the SBS tests. First, tensile, compressive, and shear stress–strain relations are measured in a single experiment. Second, a counter-intuitive feasibility of closed-form stress and modulus models, normally applicable to long beams, is demonstrated for short-beam specimens. The modulus and stress–strain data are presented for glass/epoxy and carbon/epoxy material systems.  相似文献   
96.
Oh DB  Paige ME  Bomse DS 《Applied optics》1998,37(12):2499-2501
Modulation frequency multiplexing provides a straightforward method, analogous to television or radio broadcasting, for performing simultaneous detection of multiple gases by use of wavelength modulation spectroscopy with diode lasers. When fiber-optic coupled lasers are used, our approach guarantees that all beams transit the same optical path and impinge on the same detector. Each laser is modulated at a different frequency and the detector output is processed by a set of lock-in amplifiers, one for each laser, to measure the absorbance encountered by each laser.  相似文献   
97.
This study provides a scientific basis for interspecies extrapolation of nasal olfactory irritants from rodents to humans. By using a series of short-term in vivo studies, in vitro studies with nasal explants, and computer modeling, regional nasal tissue dose estimates were made and comparisons of tissue doses between species were conducted. To make these comparisons, this study assumes that human and rodent olfactory epithelium have similar susceptibility to the cytotoxic effects of organic acids based on similar histological structure and common mode of action considerations. Interspecies differences in susceptibility to the toxic effects of acidic vapors are therefore assumed to be driven primarily by differences in nasal tissue concentrations that result from regional differences in nasal air flow patterns relative to the species-specific distribution of olfactory epithelium in the nasal cavity. The acute, subchronic, and in vitro studies have demonstrated that the nasal olfactory epithelium is the most sensitive tissue to the effects of inhalation exposure to organic acids and that the sustentacular cells are the most sensitive cell type of this epithelium. A hybrid computational fluid dynamics (CFD) and physiologically based pharmacokinetic (PBPK) dosimetry model was constructed to estimate the regional tissue dose of organic acids in the rodent and human nasal cavity. The CFD-PBPK model simulations indicate that the olfactory epithelium of the human nasal cavity is exposed to two- to threefold lower tissue concentrations of a representative inhaled organic acid vapor, acrylic acid, than the olfactory epithelium of the rodent nasal cavity when the exposure conditions are the same. The magnitude of this difference varies somewhat with the specific exposure scenario that is simulated. The increased olfactory tissue dose in rats relative to humans may be attributed to the large rodent olfactory surface area (greater than 50% of the nasal cavity) and its highly susceptible location (particularly, a projection of olfactory epithelium extending anteriorly in the dorsal meatus region). In contrast, human olfactory epithelium occupies a much smaller surface area (less than 5% of the nasal cavity), and it is in a much less accessible dorsal posterior location. In addition, CFD simulations indicate that human olfactory epithelium is poorly ventilated relative to rodent olfactory epithelium. These studies suggest that the human olfactory epithelium is protected from irritating acidic vapors significantly better than rat olfactory epithelium due to substantive differences in nasal anatomy and nasal air flow. Furthermore, the general structure of the hybrid CFD-PBPK model used for this study appears to be useful for target tissue dosimetry and interspecies dose comparisons for a wide range of inhaled vapors.  相似文献   
98.
BACKGROUND: Combination chemotherapy consisting of methotrexate, doxorubicin, cyclophosphamide, vincristine, prednisolone, and bleomycin (MACOP-B) has been frequently used for the treatment of non-Hodgkin's lymphoma. This randomized study was undertaken to assess the efficacy and toxicity of this regimen when either doxorubicin or epirubicin was used as the anthracycline drug. METHODS: Between April 1989 and December 1993, 211 previously untreated patients with intermediate grade and high grade non-Hodgkin's lymphoma were randomized to receive either doxorubicin (n=106) or epirubicin (n=105) with the MACOP-B regimen. These patients were followed through December 1996. Numerous clinical features predictive of response and survival were analyzed. Cardiac and noncardiac toxicity in the two treatment arms were compared. RESULTS: The median age of the patients was 48 years. Complete remission was experienced by 122 patients (58.3%); 62 patients (58.5%) achieved complete remission in the doxorubicin arm and 60 (58.1%) in the epirubicin arm. Response rates, time to treatment failure, relapse data, and overall survival were comparable between the two arms. Morbidity due to mucositis, vomiting, peripheral neuropathy, and cardiotoxicity were also comparable. The overall mortality was 10%. Mortality due to neutropenic sepsis was considerably higher among patients who received epirubicin (10 patients) than among those who received doxorubicin (5 patients). Cardiac evaluation revealed no difference in toxicity between the two arms. CONCLUSIONS: Epirubicin was as effective as doxorubicin in terms of patients' responses to therapy. There was no difference in cardiotoxicity between the two treatment arms. However, in this study, the mortality due to neutropenic sepsis was significantly higher among patients treated with epirubicin.  相似文献   
99.
KT Bogen 《Canadian Metallurgical Quarterly》1998,17(12):691-6; discussion 701-4, 708-18
A mechanistically based cytodynamic two-stage (CD2) cancer model was shown recently to predict both ecologic US county data and underground-miner data on lung-cancer mortality (LCM) vs radon concentration, indicating biological plausibility of the apparent negative dose-response relation exhibited by the ecologic data. To further investigate this hypothesis, the CD2 model was fitted to combine age-specific LCM data vs estimated radon-exposure in white females of age 40+ years in 2821 US counties during 1950-1954 using new estimates of county-specific mean residential radon exposure, and in five cohorts of underground nonsmoking miners. The negative association of radon levels and corresponding county-level LCM rates apparent in women dying in 1950-1954 (11% of whom never smoked) was also apparent in women of age 60+ years (5% of whom never smoked). The CD2 fit obtained to the combined residential and occupational data was found to predict the combined data using biologically plausible parameter values, and also to predict inverse dose-rate effects exhibited in nonsmoking miner data to which the CD2 model was not fit. These results are consistent with the hypothesis that residential radon exposure has a nonlinear U-shaped relation to LCM risk, and that current linear extrapolation models substantially overestimate such risk.  相似文献   
100.
BACKGROUND: This study investigated the assignment of preference values to health states which may follow head and neck cancer (HNC) treatment. Preference values for these health states were provided by HNC patients, HNC health-care providers, and a group of college students representing individuals with little knowledge of HNC. METHODS: A time trade-off technique was used by participants to assign preference values to four health states in the domains of appearance, eating, speech, breathing, pain, and work/social functioning. RESULTS: Patients' and health-care professionals' rank-ordered preference value scores for health states in appearance, breathing, eating, and speech were not significantly different (p < .05). These two groups differed significantly in ranking four of the eight pain and work/social functioning health states. Patients and students differed significantly in ranking 21 of the 24 health states (p < .05). CONCLUSIONS: Health-care professionals and patients had very similar perspectives regarding health states in the HNC-specific domains, indicating that these professionals appear to be a legitimate proxy for patients' attitudes in these domains. Healthcare professionals placed a significantly greater value on avoiding both pain and social confinement than did patients. Students, representing individuals naive regarding HNC, differed from patients and health-care professionals in their rankings of these health-state outcomes.  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