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   2359篇
  免费   0篇
  国内免费   1篇
化学工业   7篇
金属工艺   1篇
建筑科学   1篇
矿业工程   1篇
水利工程   1篇
石油天然气   1篇
无线电   1篇
一般工业技术   3篇
冶金工业   2344篇
  2013年   1篇
  2010年   1篇
  2006年   1篇
  2003年   3篇
  1999年   70篇
  1998年   654篇
  1997年   386篇
  1996年   292篇
  1995年   128篇
  1994年   113篇
  1993年   165篇
  1992年   19篇
  1991年   33篇
  1990年   31篇
  1989年   36篇
  1988年   24篇
  1987年   30篇
  1986年   34篇
  1985年   32篇
  1983年   4篇
  1982年   14篇
  1981年   26篇
  1980年   22篇
  1978年   7篇
  1977年   69篇
  1976年   156篇
  1975年   3篇
  1974年   1篇
  1965年   1篇
  1964年   1篇
  1959年   1篇
  1955年   2篇
排序方式: 共有2360条查询结果,搜索用时 15 毫秒
81.
An in vivo antitumor screening of extracts of Gomphrena martiana indicated positive activity in the petroleum ether extract, and its further bioactivity-directed fractionation resulted in a lipophilic flavonoid fraction. Upon inoculation of various doses of 5,6,7-trisubstituted flavones on two murine tumor lines, Sarcoma 180 and Ehrlich's carcinoma, a decrease of tumor growth was observed. An in vitro KB cultured cell screen indicated cytotoxicity.  相似文献   
82.
RW Weber 《Canadian Metallurgical Quarterly》1998,80(2):141-5; quiz 146-7
LEARNING OBJECTIVES: The purpose of this review is to introduce the reader to a systematic approach to categorizing pollen types. This will enable the reader to recognize pollen characteristics of the most common botanical sources and determine the relevant contributors to the local aeroallergen burden. DATA SOURCES: Allergenic plant and pollen atlases for pollen characteristics, allergy texts for procedures and overviews, and relevant reviews from the English medical literature (1985 to present). RESULTS: By applying a visual gestalt utilizing grain number, size, shape, surface structures, and internal detail, one is able to identify pollen source to the appropriate botanical taxonomic level. Identification may be possible only to the family or order, but most frequently to the genus, and occasionally to the species. CONCLUSIONS: Outdoor sampling allows the identification of aeroallergen burden in a locale. In conjunction with field work, the relevant sources can be identified as well as time of pollination. This allows the physician to correlate symptoms with exposure and relevant sensitization.  相似文献   
83.
A single-subject experimental design was used to evaluate the effects of center of gravity biofeedback on retraining balance control in a 72-yr.-old male hemiparetic patient. For both assessment and training the subject stood on dual force-plates enclosed on three sides by a visual surround. A 4-wk. training period consisted of subject-initiated shifts in body weight to control movement of a real-time computer display of the subject's center of gravity. A Sensory Organization Test and evaluation of weight distribution indicated that biofeedback retraining positively affected balance control during dynamic conditions and when the ground support moved forward.  相似文献   
84.
Pleuritis or pleural effusion frequently develops in patients with pneumonia or heart failure. Most of these pleural changes regress without intrapleural intervention. The detailed mechanisms of the regression of the pleural changes in humans are not well documented. We studied the parietal pleura of nine patients with lung cancer and two patients with coronary artery disease by scanning electron microscopy (SEM). All patients had neither radiographic nor gross evidence of pleural disease but all had mixed surface alterations by SEM. Focal denudation of mesothelial cells was common. Deeper injuries exposed thick and thin interweaving collagen bundles. Patchy depositions of amorphous or crystallized fibrin covered normal and damaged pleural surfaces, frequently admixed with macrophages, red blood cells, and tissue debris. Reactive mesothelial cells appeared to proliferate over the fibrin. Our findings suggest that subclinical pleural alterations occur often in patients with pulmonary or cardiac diseases and that an intact pleural surface in those patients is restored mainly by the proliferation of reactive mesothelial cells.  相似文献   
85.
86.
Various analytical, iterative and rebinning algorithms have been proposed for 3D reconstruction in positron emission tomography. This paper examines execution times of five analytical and rebinning algorithms. Meaningful comparisons are obtained by using similar software modules in all implementations. Reconstruction times are shown to differ by vast amounts: the Favor algorithm of Defrise et al is more than twice as fast as the widely used reprojection algorithm of Kinahan and Rogers; the Fourier rebinning algorithm (Fore) recently developed by Defrise is more than 15 times faster than the reprojection algorithm.  相似文献   
87.
We describe a patient with pauciarticular juvenile rheumatoid arthritis with aortic insufficiency who underwent successful aortic valve replacement with a mechanical prosthetic valve.  相似文献   
88.
OBJECTIVE: We prospectively compared the ability of two techniques--bone scintigraphy with single-photon emission computed tomography (SPECT) of the chest and CT of the chest--to reveal potential osteosarcoma metastases of the lung. SUBJECTS AND METHODS: Our study included 27 patients with osteosarcoma who prospectively underwent both bone scintigraphy with SPECT of the chest and CT of the chest. The imaging results were compared with outcome or pathologic analysis of any lung lesions found. RESULTS: Eight (30%) of the 27 patients had pulmonary metastases. Four of these eight patients had positive results on both CT studies and bone SPECT studies, with additional lesions detected with bone SPECT in two of these four patients. The other four patients with pulmonary metastases had positive results on CT studies, whereas the results of bone SPECT studies remained negative. The results of bone SPECT studies were negative in the 19 patients without pulmonary metastases. CT, however, showed abnormalities in seven (37%) of the 19 patients, which were eventually attributed to benign conditions. CONCLUSION: Negative results on a bone SPECT study of the chest should not be used to exclude the possibility of lung metastases. However, if the results are positive, a bone SPECT study can be used to confirm abnormalities seen on CT scans and may also reveal subtle lesions missed on CT scans.  相似文献   
89.
BACKGROUND: In biological studies of periodontitis, there has been long-standing confusion between the ubiquitous phenomena of inflammation and the essential criterion of attachment loss. This is partly attributable to inadequate methods of clinical measurement, but seems also to be a consequence of an unproven and usually unstated assumption that the same biological processes underlie both inflammation and attachment loss. Developments in unidimensional clinical probing methods have helped in studies of periodontal treatment. However, such methods are intrinsically unsuitable in studies of periodontal diseases, and may have given them a false sense of security. the confusion has been compounded by inappropriate use of statistical techniques in an attempt to solve problems which do not arise from mathematical models but are intrinsic to measurement methods. OBJECTIVE: This paper is a clinician's attempt to state the current difficulties and suggest some ways forward, including the development of three-dimensional measurement, non-invasive probing, and several objectives for biochemical, microbiological and immunological research.  相似文献   
90.
Glutathione (GSH), trypanothione (T(SH)2) and glutathionyl spermidine (GSH-SP) concentrations were determined in the Tulahuén and LQ strains and the DM 28c clone of Trypanosoma cruzi. The concentrations of GSH, T(SH)2 and GSH-SP, expressed as nmol of GSH per g of parasite fresh weight, were 60.1, 397.8 and 103.9, respectively, for the Tulahuén strain. For the DM 28c clone, the values were 113.9, 677.9 and 164.1, respectively, and for the LQ strain they were 199.1, 1100.5 and 55.3, respectively. When the parasites were treated with 10 microM nifurtimox or 50 microM benznidazole for 2 h, the concentrations of all three reduced thiols decreased strongly. The total amount of T(SH)2 decreased by more than 50%. Treatment of the parasites with 5 mM buthionine sulfoximine, an inhibitor of GSH synthesis, for 6 h diminished the concentrations of the reduced thiols by between 27% and 53% with respect to the controls. Cyclohexylamine, an inhibitor of spermidine synthesis, decreased the concentrations of T(SH)2 and GSH-SP but not that of GSH. It is possible to conclude from this study that trypanothione is the most important thiol involved in the detoxication of nifurtimox and benznidazole in T. cruzi and that electrophilic reduced metabolites of both drugs are most probably conjugated with GSH, T(SH)2 and GSH-SP, thus decreasing their concentrations. GSH biosynthesis is an important drug target.  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