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   1446篇
  免费   26篇
电工技术   1篇
化学工业   115篇
金属工艺   5篇
机械仪表   12篇
建筑科学   4篇
能源动力   14篇
轻工业   109篇
水利工程   5篇
石油天然气   7篇
无线电   46篇
一般工业技术   49篇
冶金工业   1085篇
原子能技术   2篇
自动化技术   18篇
  2024年   3篇
  2022年   12篇
  2021年   23篇
  2020年   13篇
  2019年   20篇
  2018年   28篇
  2017年   11篇
  2016年   11篇
  2015年   9篇
  2014年   20篇
  2013年   38篇
  2012年   19篇
  2011年   28篇
  2010年   19篇
  2009年   22篇
  2008年   16篇
  2007年   11篇
  2006年   12篇
  2005年   10篇
  2004年   11篇
  2003年   7篇
  2002年   5篇
  2001年   3篇
  2000年   2篇
  1999年   35篇
  1998年   325篇
  1997年   217篇
  1996年   119篇
  1995年   54篇
  1994年   64篇
  1993年   64篇
  1992年   17篇
  1991年   8篇
  1990年   17篇
  1989年   12篇
  1988年   20篇
  1987年   19篇
  1986年   8篇
  1985年   11篇
  1984年   3篇
  1983年   2篇
  1981年   3篇
  1980年   12篇
  1978年   5篇
  1977年   26篇
  1976年   72篇
  1973年   1篇
  1972年   1篇
  1965年   1篇
  1929年   1篇
排序方式: 共有1472条查询结果,搜索用时 15 毫秒
71.
72.
Colitis cystica profunda is a benign disease of the colon. Its importance lies in differentiating it from mucus-producing adenocarcinoma. It has rarely been described in the surgical literature. A review of records of patients seen at the Mayo Clinic produced 66 clinical cases of localized colitis cystica profunda, and in 21 patients the diagnosis was confirmed histologically. Follow-up, which was available in all patients, ranged from 2 months to 29 years, with a mean follow-up of more than 8 years. The data suggest that local excision is the preferred initial therapy.  相似文献   
73.
The application of the photo-Fenton process to the treatment of saline wastewater contaminated with hydrocarbons is investigated. Aqueous saline solutions containing raw gasoline were used as a model oil-field-produced water. The dependence on concentrations of the following reagents has been appropriately evaluated: hydrogen peroxide (100-200 mM), iron ions (0.5-1 mM), and sodium chloride (200-2000 ppm). The reactions were monitored by measurement of the absorption spectra and total organic carbon (TOC). Experimental results demonstrate that the photo-Fenton process is feasible for the treatment of wastewaters containing hydrocarbons, even in the presence of high concentrations of salt. The effect of the salt in this process is described through a series of reactions. A simple feedforward neural network model was found to correlate well the observed data for the degradation process.  相似文献   
74.
A comparison of the effects of left stellate ganglion stimulation (SGS) on central and aortic hemodynamics has been made in chloralose-anesthetized mongrel (M), and greyhound (GH) dogs. Measurements of aortic pressure and flow, and left ventricular pressure were made during stimulation of the decentralized left SG at different frequencies from 0 to 20 Hz. The increases in aortic pressure and flow with SGS were larger in the GH, especially for low frequencies of stimulation. Stroke volume was increased with SGS in the GH at all stimulation rates, whereas in the M it was unchanged. A greater decrease in left ventricular end-diastolic pressure with SGS was found in the GH. These results suggest that differences exist in both the intrinsic and extrinsic control of cardiac output in the greyhound dog compared to the mongrel. These differences may be in part responsible for the elevated arterial blood pressure in the greyhound compared to the mongrel.  相似文献   
75.
We report the 14th case of myelolipoma of the adrenal gland. Recommendations for appropriate diagnostic and therapeutic methods are made. Myelolipoma of the adrenal gland is a rare non-functioning tumor composed of lipoid and hematopoietic elements. The most consistent complaint is abdominal pain caused by hemorrhage within the tumor. We identified an association with obesity and hypertension. Ultrasound combined with computed tomography is useful in diagnosis. With expanded use of these studies, myelolipoma will be recognized more frequently. Definitive diagnosis and treatment are accomplished by simple excision; radical surgery is unnecessary.  相似文献   
76.
Reference spectra extracted from spectral libraries can distinguish different water types in images when associated with limnological information. In this study, we compiled available databases into a single spectral library, using field water reflectance spectra and limnological data collected by different researchers and campaigns in the Amazonian region. By using an iterative clustering procedure based on the combination of reflectance and optically active components (OACs), reference spectra representative of the major Amazonian water types were defined from this library. Differences between the resultant limnological classes were also evaluated by paired t-tests at significance level 0.05. Finally, reference spectra were tested for Spectral Angle Mapper (SAM) classification of waters in Hyperion/Earth Observing-One (EO-1) and Medium Resolution Imaging Spectrometer (MERIS)/Environment Satellite (Envisat) images acquired simultaneously as the field campaigns. Results showed highly variable concentrations of OACs due to the complexity of the Amazonian aquatic environments. Ten classes were defined to represent this complexity, broadly grouped into four limnological characteristics: clear waters with low concentrations of OACs (class 1); black waters rich in dissolved organic carbon (DOC) (class 2); waters with large concentrations of inorganic suspended solids (ISSs) (classes 3–7); and waters dominated by chlorophyll-a (chl-a) (classes 8–10). Using the ten reference spectra, SAM classification of the field water curves produced an overall accuracy of 86% with the highest values observed for classes 3, 4, 6 and 7 and the lowest accuracy for classes 1 and 2. The results of paired t-tests confirmed the class differences based on the concentrations of OACs. SAM classification of the Hyperion and MERIS images using ground truth information resulted in overall classification accuracies of 48% and 67%, respectively, with the highest errors associated with specific portions of the scenes that were not adequately represented in the spectral library.  相似文献   
77.
78.
79.
80.
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