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   450篇
  免费   0篇
综合类   1篇
化学工业   2篇
轻工业   1篇
无线电   4篇
一般工业技术   1篇
冶金工业   439篇
自动化技术   2篇
  2022年   1篇
  2018年   1篇
  2014年   1篇
  2013年   1篇
  2011年   1篇
  2010年   2篇
  2007年   3篇
  2004年   1篇
  2003年   1篇
  1999年   16篇
  1998年   126篇
  1997年   76篇
  1996年   43篇
  1995年   29篇
  1994年   22篇
  1993年   26篇
  1992年   5篇
  1991年   11篇
  1990年   4篇
  1989年   6篇
  1988年   14篇
  1987年   6篇
  1986年   4篇
  1985年   5篇
  1982年   2篇
  1981年   3篇
  1980年   5篇
  1979年   1篇
  1978年   1篇
  1977年   9篇
  1976年   22篇
  1975年   2篇
排序方式: 共有450条查询结果,搜索用时 0 毫秒
81.
82.
This study describes the 'Law Court' technique as applied to City Health Departments in the State of Santa Catarina, in dealing with the issue of obligations on the part of public officials. The project was the first part of a training course for public administrators held in 1997. The article presents the technique's components and results. Some 98% of the 156 participants had a positive opinion of the training course, considering it dynamic/participatory (31%), educational/stimulating reflection (27%), and realistic (24%). The technique fostered the discussion of the main subjects pertaining to the country's Unified Health System (SUS). Although all five juries acquitted the defendants, the issue of ethics was reported by 58% of the participants as the main prerequisite for a public administrator.  相似文献   
83.
Salmonella typhi was isolated from 369 and Salmonella paratyphi A was isolated from 6 of 515 Vietnamese patients with suspected enteric fever. Compared with conventional broth culture of blood, direct plating of the buffy coat had a diagnostic sensitivity of 99.5% (95% confidence interval [CI], 97.1 to 100%). Blood bacterial counts were estimated by the pour plate method. The median S. typhi count in blood was 1 CFU/ml (range, <0.3 to 387 CFU/ml), of which a mean of 63% (95% CI, 58 to 67%) were intracellular. The mean number of bacteria per infected leukocyte was 1.3 (interquartile range [IQR], 0.7 to 2.4) CFU/cell (n = 81). Children (< 15 years old; n = 115) had higher median blood bacterial counts than adults (n = 262): 1.5 (range, <0.3 to 387) versus 0.6 (range, <0.3 to 17.7) CFU/ml (P = 0.008), and patients who excreted S. typhi in feces had higher bacteremias than those who did not: a median of 3 (range, <0.3 to 32) versus 1 (range, <0.3 to 68) CFU/ml (P = 0.02). Blood bacterial counts declined with increasing duration of illness (P = 0.002) and were higher in infections caused by multidrug-resistant S. typhi (1.3 [range, <0.3 to 387] CFU/ml; n = 313) than in infections caused by antibiotic-sensitive S. typhi (0.5 [range, <0.3 to 32] CFU/ml; n = 62) (P = 0.006). In a multivariate analysis this proved to be an independent association, suggesting a relationship between antibiotic resistance and virulence in S. typhi.  相似文献   
84.
Several laboratories have reported that overexpression of the multidrug resistance (MDR) protein is associated with intracellular alkalinization, and several investigators have reported that cells induced to undergo programmed cell death (apoptosis) acidify quite significantly. Because it is difficult to fully explain the resistance to apoptosis-inducing chemotherapeutic drugs that is exhibited by MDR tumor cells solely via altered drug transport alone [Hoffman et al. (1996) J. Gen. Physiol. 108, 295-313], we have investigated whether overexpression of the hu MDR 1 protein alters progression of the apoptotic cascade. LR73 fibroblasts induced to undergo apoptosis either via treatment with the chemotherapeutic drug colchicine or by serum withdrawal exhibit cellular volume changes, intracellular acidification, nuclear condensation, and chromosomal digestion ("ladder formation"), characteristic of apoptosis, in a temporally well-defined pattern. However, multidrug resistant LR73/20E or LR73/27 hu MDR 1 transfectants recently created in our laboratory without selection on chemotherapeutic drug are significantly delayed in the onset of apoptosis as defined by the above criteria, regardless of whether apoptosis is induced by colchicine treatment or by serum withdrawal. Thus, the delay cannot simply be due to the well-known ability of MDR protein overexpression to lower chemotherapeutic drug accumulation in MDR cells. LR73/27V500 "selectants", exhibiting similar levels of MDR protein overexpression but higher multidrug resistance due to selection with the chemotherapeutic drug vincristine, exhibit a slightly longer delay in the progression of apoptosis. Normal apoptotic cascade kinetics are partially restored by pre-treatment of the MDR cells with the MDR protein inhibitor verapamil. Untransfected LR73 cells not expressing MDR protein but elevated in pHi via manipulation of CO2/HCO3- as described [Hoffman et al. (1996) J. Gen. Physiol. 108, 295-313] are inhibited in DNA ladder formation, similar to LR73/hu MDR 1 transfectants. These results uncover an additional mechanism whereby MDR protein overexpression may promote the survival of tumor cells and further support the notion that in some systems intracellular acidification may be either causal or permissive for proper progression of the apoptotic cascade.  相似文献   
85.
PURPOSE: We investigated the capabilities of chest radiography in the elderly considering that the examination must meet the main clinical indications of this population and that it is necessary in the elderly because the correct clinical assessment is often difficult or impossible. MATERIALS AND METHODS: We reviewed the chest radiographs of 756 consecutive elderly patients admitted to our hospital from September 1 to October 31, 1996. If possible, chest radiographs were performed with the AMBER technique (156 patients, 20.7%); 240 patients (31.7%) underwent conventional radiography and the others frontal projections only (360 patients, 47.6%). T-MAT G RA Kodak high contrast films with Kodak Lanex green transmitting intensifying screens were used in all cases. The AMBER examinations of 48/156 patients with hemodynamic clinical indications were repeated with conventional frontal projections. Radiographic reports were made separately by different radiologists who considered especially the diagnostic accuracy of every examination in determining the venous overload of pulmonary circulation. RESULTS: Hemodynamic studies are the most frequent clinical indication of chest radiography in elderly patients (228/756 patients in our series, 30.2%); moreover, even if careful cardiac and pulmonary circulation studies are very important in these patients, only 52.4% of all radiographs could be made in two orthogonal projections. The blurred appearance of vascular landmarks indicating increased extravascular fluid is better depicted by conventional radiography (59.7% of cases) than by AMBER (40.3%). CONCLUSIONS: We conclude that the reduced pulmonary contrast obtained with the so-called "hard X-ray" technique poorly depicts the blurred appearance of pulmonary vessels in pulmonary venous overload. Moreover, "hard X-ray" techniques can be only sporadically used because elderly patients are often in very critical conditions, which prevents this type of examination.  相似文献   
86.
The simultaneous determination of amino and organic acids in plant tissue extracts using capillary gas chromatography is described. Plant leaves were extracted in 5% (w/v) perchloric acid and neutralized extracts were purified using C18 cartridges. The amino and organic acids in purified extracts were then converted to tert-butyldimethylsilyl (TBDMS) derivatives prior to separation and detection by capillary gas chromatography (GC) with flame ionization detection. Conditions required for optimal derivatization were investigated. Amino and organic acids were readily converted to their TBDMS derivatives using N-methyl-N-tert-butyldimethylsilyltrifluoroacetamide in dimethylformamide solvent 1:6 (v/v) with an average recovery of 90% and a reproducibility of about 5%. The characteristic [M-57] and [M-159] fragment ion of the TBDMS derivatives was confirmed using GC-MS. The proposed method was demonstrated by the determination of amino and organic acids in extracts of Acacia and Eucalyptus leaves, where detection limits were 1-20 ng.  相似文献   
87.
88.
The effect of cholesterol feeding (3 g/day) on bile acid synthesis was examined in 10 New Zealand white rabbits (NZW), 8 Watanabe heterozygous and 10 homozygous rabbits with partial and complete deficiencies of LDL receptors. After 10 days of cholesterol feeding, bile fistulas were constructed and bile acid pool sizes were measured. Cholesterol feeding increased plasma and hepatic cholesterol levels in all rabbit groups. Baseline bile acid pool sizes were smaller (P < 0.01) in heterozygotes (139 +/- 3 mg) and homozygotes (124 +/- 30 mg) than NZW rabbits (254 +/- 44 mg). After feeding cholesterol, bile acid pool sizes doubled with increased cholic acid synthesis in NZW and, to a lesser extent, in Watanabe heterozygous rabbits but not in homozygotes. Baseline cholesterol 7alpha-hydroxylase activity in NZW and heterozygotes declined 69% and 53% (P < 0.001), respectively, after cholesterol feeding. Sterol 27-hydroxylase activity reflecting alternative bile acid synthesis increased 66% (P < 0.01) in NZW and 37% in Watanabe heterozygotes but not in homozygotes after feeding cholesterol. Bile fistula drainage stimulated cholesterol 7alpha-hydroxylase activity but not sterol 27-hydroxylase activity in all three rabbit groups. These results demonstrated that dietary cholesterol increased hepatic sterol 27-hydroxylase activity and alternative bile acid synthesis to expand the bile acid pool and inhibited cholesterol 7alpha-hydroxylase in NZW and in Watanabe heterozygous rabbits but not in homozygotes with absent hepatic LDL receptor function. Thus, in rabbits, sterol 27-hydroxylase is up-regulated by the increased hepatic cholesterol that enters the liver via LDL receptors whereas cholesterol 7alpha-hydroxylase is controlled by the circulating hepatic bile acid flux.  相似文献   
89.
We have investigated the effect of the anticancer compound, camptothecin on Jurkat T-cells, a lymphoblastoid leukemic cell-line. Exposure to low concentrations led to rapid cessation of DNA (more than 95%) and RNA (more than 75%) synthesis. Perturbations to the cell cycle were observed following exposure which caused a significant accumulation of cells within G1 (P = 0.03) with a concomitant decrease in G2/M (P = 0.025). Concentrations below 0.1 microM could inhibit DNA synthesis but not induce apoptosis. Induction of apoptosis was dose dependent and could be detected as early as 3 h post exposure. The apoptotic population appeared to be derived from G1 and S-phase cells but not G2/M, coinciding with the cell cycle compartments in which DNA and RNA polymerases function. However, direct inhibition of DNA polymerase alone was not shown to be associated the induction of apoptosis or with a decrease in susceptibility to camptothecin-induced cell death. The effects of camptothecin on Jurkat T-cells and the potential mechanisms involved are discussed in the context of observations made in other transformed cell lines.  相似文献   
90.
To address ST use effectively, awareness needs to be raised regarding its harmful affects and addictive nature. Clinicians can and should take a leadership role in the control of ST by addressing ST use with patients. The recommendations provide clinicians with practical tools and strategies for intervention with ST users and potential users. Although many of these strategies require training and time, it should be emphasized that even minimal intervention can be effective in combating ST use.  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