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   1214篇
  免费   2篇
  国内免费   1篇
化学工业   5篇
矿业工程   2篇
轻工业   2篇
一般工业技术   11篇
冶金工业   1195篇
自动化技术   2篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2013年   1篇
  2010年   1篇
  2009年   2篇
  2008年   1篇
  2007年   1篇
  2006年   1篇
  2005年   2篇
  2004年   4篇
  2003年   2篇
  1999年   28篇
  1998年   320篇
  1997年   219篇
  1996年   154篇
  1995年   105篇
  1994年   61篇
  1993年   73篇
  1992年   6篇
  1991年   22篇
  1990年   7篇
  1989年   8篇
  1988年   5篇
  1987年   4篇
  1986年   3篇
  1985年   5篇
  1983年   3篇
  1982年   4篇
  1981年   11篇
  1980年   14篇
  1979年   1篇
  1978年   6篇
  1977年   47篇
  1976年   93篇
排序方式: 共有1217条查询结果,搜索用时 31 毫秒
81.
82.
83.
An extensive study of road traffic accident cases occurring within eastern suburban Calcutta during April 1992 to March 1993 was done. Of which 276 fatal cases having minimum medical aids were taken into consideration to avoid erroneous interpretation. Male pedestrians of age group of 50 years and above were mostly involved during the time period of 5 A.M. to 12 Noon. Fatal Accidents mostly occurred during winter and on the broader roads (Highways) and in majority of cases victims were at fault.  相似文献   
84.
Using differential display, we identified an mRNA that is markedly down-regulated in cell line 6A/SB1, derived from a fibrosarcoma formed in an athymic mouse following injection of carcinogen-transformed MSU-1.1 cells. The nontumorigenic parental cell strain, MSU-1.1, expresses high levels of this mRNA. Sequencing of the corresponding cDNA fragment revealed that it corresponded to an expressed sequence tag, which ultimately led to its identification as the fibulin-1D gene. Fibulin-1 is a cysteine-rich, calcium-binding extracellular matrix and plasma protein, which has four isoforms, A-D, derived from alternative splicing. Northern and Western blotting analysis of 16 cell lines established from tumors formed in athymic mice by MSU-1.1-derived cell strains independently transformed in culture showed that 44% exhibited low level or lack of expression of fibulin-1D mRNA and protein. In a similar analysis of 15 malignant cell lines derived from patients, 80% showed low level or no expression. To study the role of fibulin-1D in transformation, we transfected 6A/SB1 cells and a human fibrosarcoma-derived cell line (SHAC) with a fibulin-1D cDNA expression construct. Transfectants displaying high levels of fibulin-1D were isolated and characterized. Elevated expression of fibulin-1D led to reduced ability to form colonies in soft agar and reduced invasive potential as tested in a matrigel in vitro invasion assay. Furthermore, expression of fibulin-1D resulted in a markedly extended latency in tumor formation in athymic mice. These results indicate that low expression of fibulin-1D plays a role in tumor formation and invasion.  相似文献   
85.
Chronic action of different xenobiotics which form a part of condensed hydrogen sulphide-containing gas causes substantial changes in the activity of xenobiotic metabolic enzymes, which is suggestive of the damaged hepatic microsomal monooxygenase system. As the rate of biotransformation becomes higher, there are increases in the activity of microsomal monooxygenases and in the generation of active oxygen forms and hydrogen peroxide, by impairing antiradical and antiperoxide mechanisms. The experimentally used concentration of substances as constituents of condensed gas corresponds to the maximum acceptable air concentration of in the working area of gas-refining plants, but the functional features of the body's detoxifying system--the hepatic monooxygenase system should be taken into account while developing preventive measures of occupational diseases.  相似文献   
86.
The concept of acceptable risk is considered in the context of the system of medical support to space missions. Risk is defined as probability of cosmonaut's health and life deterioration as a result of spaceflight impacts on the human body. Mathematical formulas giving the general characteristic of the relations among risk components, total risk, and human survivability in flight and after its end. The earlier published quantitative recommendations for these parameters are inserted as illustration.  相似文献   
87.
VM Figueredo 《Canadian Metallurgical Quarterly》1997,101(2):165-8, 171-2, 175-6
Alcohol abuse is a substantial public health problem, resulting in staggering financial costs and other burdens. Prolonged alcohol abuse leads to cardiomyopathy in a minority of alcohol abusers, but because alcoholism is so widespread, alcohol is the major cause of nonischemic cardiomyopathy in Western society. In contrast, substantial evidence now suggests that moderate alcohol consumption has cardioprotective effects. It not only reduces the incidence of fatal ischemic heart disease, but it improves outcome in patients who have other risks for coronary events and go on to have myocardial infarctions. Therefore, physicians' recommendations about alcohol consumption should be as individualized as their patients.  相似文献   
88.
The prognosis for a patient who has survived an acute myocardial infarction depends on three general prognostic factors: (1) residual left ventricular function, (2) remaining viable myocardium at risk (residual ischemia), and (3) presence of substrate for the development of malignant arrhythmias. Multiple clinical and historical factors predict the presence of one or more of these prognostic indicators. Electrocardiographic exercise treadmill testing needs to be done in all patients with uncomplicated infarctions. Guidelines of the American College of Cardiology/American Heart Association Task Force are recommended for risk stratification in most patients after acute myocardial infarction.  相似文献   
89.
Na(+)-glucose transport and transepithelial permeability were investigated during symptomatic acute cryptosporidiosis in newborn rats. The infection resulted in a significant (P < 0.01) decrease in the ileal short-circuit current and a nonsignificant fall in the transepithelial potential difference and conductance. In glucose-stimulated conditions, the rise in ileal short-circuit current and transepithelial permeability were significantly lower in Cryptosporidium parvum-infected rats than in controls (delta Isc = 3.24 +/- 1.21 microA.cm-2 vs delta Isc = 5.09 +/- 2.23 microA.cm-2 in infected and control animals, respectively; P < 0.001; delta PD = -0.35 +/- 0.13 mV vs delta PD = -0.44 +/- 0.14 mV for infected and control animals, respectively; P < 0.01). Electrical parameters were not affected by addition of the cyclooxygenase inhibitor indomethacin in either Cryptosporidium-infected newborn rats or controls. Horseradish peroxidase and mannitol flux studies demonstrated a significant decrease (P < 0.05) in transepithelial molecular permeability in infected enterocyte rats, HRP flux = 380, range 68-5570 ng.cm-2, and mannitol flux = 1.06, range, 0.34-1.44%.cm-2.min-1, compared with controls rats, HRP flux = 4446 range, 1121-124,363 ng.cm-2, and mannitol flux = 1.99, range, 0.57-5.09%.cm-2.min-1; P < 0.05. These effects could originate from C. parvum-induced alteration of intracellular trafficking of pinocytosis vesicles and therefore account for the decrease in permeability to solute and macromolecules, together with impaired transcellular nutrient transport, in suckling rats.  相似文献   
90.
OBJECTIVE: The goal was to assess the safety of magnetic resonance imaging (MRI) with implanted neurostimulators, in an in vitro and in vivo study. METHODS: Two different implantable pulse generators (IPGs) (ITREL II and 3; Medtronic, Minneapolis, MN) and different leads (separately and connected to an IPG) were tested in three different MRI scanners (0.2, 0.25, and 1.5 T). Measurements of the induced voltages (using an external oscilloscope) and the induced heat (using an infrared camera) were performed in an in vitro study. Finally, 38 patients with implanted neurostimulator systems (leads and IPGs) underwent MRI in 50 examinations, with continuous monitoring by a physician with uninterrupted visual and vocal contact with the patient. Twenty-five patients were studied prospectively, with documented printouts of the parameter settings before and after MRI. RESULTS: An induced voltage of 2.4 to 5.5 V was measured in the experimental configuration with a lead connected to an IPG. The voltage was higher with the leads alone, compared with the leads connected to the IPG, and was dependent on the MRI scanner, the sequences, and the type of lead. No heat induction was observed in any part of the hardware. No change of pulse shape or change of IPG parameters was observed during MRI. No adverse effects occurred in patients with chronically implanted deep brain leads connected to an IPG. CONCLUSION: MRI can be safely performed in patients with implanted neurostimulation systems with the tested deep brain leads connected to an IPG (ITREL II and 3), with running parameters. No heat induction was detected, and the experimentally measured induced voltage did not seem to harm the patients. Only the reed switch of the IPGs was activated; the other parameters remained unchanged. Further investigations must be performed to study the local electrical effects in larger plate electrodes; these effects might cause slight discomfort. There is no danger with any type of electrode during MRI examinations if the electrodes lie outside the region of interest. These observations are restricted to the tested devices. A conscientious estimation of the risks and benefits of MRI for patients with implanted devices is recommended. If the type of device is not known to the examiner, MRI should still be considered to be contraindicated.  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