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   921篇
  免费   2篇
电工技术   4篇
化学工业   65篇
金属工艺   3篇
机械仪表   10篇
建筑科学   8篇
能源动力   8篇
轻工业   24篇
水利工程   2篇
无线电   33篇
一般工业技术   27篇
冶金工业   694篇
原子能技术   1篇
自动化技术   44篇
  2021年   4篇
  2017年   3篇
  2015年   2篇
  2014年   4篇
  2013年   11篇
  2012年   3篇
  2011年   5篇
  2010年   7篇
  2009年   7篇
  2008年   5篇
  2007年   8篇
  2006年   5篇
  2005年   2篇
  2004年   10篇
  2003年   5篇
  2002年   5篇
  2001年   5篇
  2000年   6篇
  1999年   25篇
  1998年   200篇
  1997年   115篇
  1996年   88篇
  1995年   46篇
  1994年   41篇
  1993年   44篇
  1992年   9篇
  1991年   11篇
  1990年   15篇
  1989年   15篇
  1988年   11篇
  1987年   14篇
  1986年   12篇
  1985年   10篇
  1984年   12篇
  1983年   12篇
  1982年   7篇
  1981年   10篇
  1980年   11篇
  1979年   6篇
  1978年   6篇
  1977年   24篇
  1976年   45篇
  1975年   4篇
  1974年   3篇
  1973年   6篇
  1972年   3篇
  1971年   3篇
  1970年   2篇
  1969年   3篇
  1955年   2篇
排序方式: 共有923条查询结果,搜索用时 15 毫秒
11.
12.
13.
OBJECTIVE: To identify any clinical and pathologic features of treatment modalities that are predictive of outcome in patients with epithelioid sarcoma, a rare slow-growing soft tissue tumor most commonly occurring in the distal extremities of young adults. DESIGN: We reviewed the institutional files for cases of epithelioid sarcoma for the period 1956 to 1991 and analyzed the effect of various factors on survival. MATERIAL AND METHODS: Fifty-five cases of epithelioid sarcoma were found, and the relevant clinical, pathologic, treatment, follow-up, and outcome features were assessed. RESULTS: All tumors were treated initially by operative resection. The recurrence rate progressively decreased with increasing aggressiveness of the initial operation; however, no difference was noted in metastatic rate. Overall, the recurrence rate was 38% and the metastatic rate was 47%. At the end of a mean follow-up of 102 months, 69% of patients had no evidence of disease, 27% had died of the disease, and 4% were alive with disease. Increasing tumor size, necrosis of more than 30%, and vascular invasion correlated significantly with a worse prognosis. CONCLUSION: Epithelioid sarcoma should be considered a malignant neoplasm with a significant potential for aggressive behavior, and close follow-up of affected patients should be maintained for many years. Initial treatment should be aggressive in an attempt to prevent recurrence.  相似文献   
14.
The new M4KDK Diamentor (PTW-Freiburg) for measuring the air-kerma-area product (KAP) and air kerma (AK) simultaneously was evaluated. The special design of the Diamentor chamber influences the variation of the calibration factor with respect to the field size somewhat differently to what is the case with the classic Diamentor. It is therefore recommended that calibration be performed for a larger field size. If the M4KDK Diamentor is calibrated for a field size of 3.8 cm x 3.8 cm (at the chamber), an uncertainty in the AK value of better than 15% for a field size larger than the calibration field, can be expected. The influence of backscattered radiation on the calibration factor is equivalent to that for the classic Diamentor chamber. The variation in response in accordance with tube potential, is also comparable with that of the classic Diamentor. Dramatic changes in response have to be expected if additional filters are introduced in close proximity to the Diamentor chamber.  相似文献   
15.
The specificity of the Escherichia coli RuvC Holliday junction resolvase has been investigated in vitro. RuvC protein cleaves synthetic DNA substrates that model three- or four-stranded recombination intermediates but fails to act upon Y junctions, G/A mismatches, heterologous loop structures, or two-stranded branched junctions. RuvC therefore differs from endonuclease VII of bacteriophage T4 which exhibits broad range specificity. Using related three- and four-stranded synthetic DNA junctions, we show that RuvC cleaves both junctions at the same DNA sequence and requires a region of homology at the junction point. The action of RuvC on three- and four-stranded recombination intermediates made by RecA was also investigated. We found that RuvC fails to resolve three-stranded intermediates in the presence of RecA, although four-stranded intermediates are resolved under the same conditions. However, both three- and four-stranded intermediates are substrates for the nuclease after removal of RecA. We interpret these differences in terms of the contiguity of the RecA nucleoprotein filament which may, under certain conditions, limit access to the Holliday junction resolvase.  相似文献   
16.
The aim of the survey was to analyse the investment by the Danish Heart Foundation in the cardiovascular research field in the period 1988-1990 and the ensuing research results. One hundred and thirty-nine researchers were allocated a total DDK 24.1 million. Eighty percent of the researchers have concluded their research work and published 362 scientific papers in 131 journals. The total journal impact factor obtained among 270 scientific papers with known journal impact factor was 642. The median journal impact factor was 1.580. Thirty-five percent of the papers were published in journals with journal impact factor greater than three. The productivity, defined as total journal impact factor obtained divided by an estimate of the total amount (DKK 200 million) of economic support received by the researcher from all sources, was estimated to 3.2 Journal Impact Factor/DKK million. A panel of international experts reviewed the outcome of funding by the Danish Heart Foundation, and concluded that the number of publications and their impact factor was adequate in relation to the economic input.  相似文献   
17.
Human immediate hypersensitivity diseases represent the most common example of chronic excessive Th2-like activation in developed nations. While IL-13 shares many functional properties with IL-4, the intensity and regulation of environmental Ag-stimulated IL-13 synthesis by allergic vs nonallergic individuals remain ill defined. Here, we examine the intensity of polyclonally and Ag-stimulated IL-13 production by PBMC of 20 subjects with seasonal allergic rhinitis and 20 healthy controls. Polyclonally driven IL-13 responses did not differ significantly (Mann-Whitney U test, p = 0.68). In contrast, the median CD4-dependent IL-13 response among atopics was markedly stronger than nonatopics in Ag-stimulated primary culture (p = 0.0031) and exhibited a strong correlation with IL-5 (r = 0.76, p = 0.0009), but not IL-4 (r = 0.14, p > 0.05), responses. IL-13 production was unaffected by blocking endogenous IL-4 or IL-5 activity or by addition of rIL-4 or rIL-5. In contrast, it was inhibited by low levels of rIFN-gamma and strongly enhanced upon addition of neutralizing anti-IFN-gamma mAb. Collectively, the data are consistent with a negative regulatory role for endogenous IFN-gamma synthesis in controlling the intensity of systemic IL-13 responses evoked in both atopic and nonatopic populations following exposure to common Ags. They also suggest that the elevated levels of IL-4 and IL-5 characteristic of type 2-dominated responses in vivo are without detectable impact on the maintenance of recall Ag-stimulated IL-13 production.  相似文献   
18.
Violet and purple bacterial pigmentations are uncommon when considering strict aerobes. Here we report discovery of two novel isolates, P102 and P117 from the freshwater Lake Winnipeg, each with violet to deep purple colony colouration. The relationship between pigment production and growth was investigated under different conditions, including a variety of carbon sources, pH, and temperatures. The violet compounds were purified using polar organic solvents, and then structurally characterized via mass spectrometry and nuclear magnetic resonance to be violacein and deoxyviolacein. Strain P117 produced higher concentrations of the darker pigment deoxyviolacein, which resulted in a deeper hue of violet than in cultures of P102. Strain P102, synthesized violacein maximally in liquid rich organic medium at pH 8 and 20 °C, and had 99.3% sequence similarity to the 16S rDNA from Janthinobacterium lividum. Strain P117, related to Massilia violaceinigra sharing 99.2% 16S rDNA sequence similarity, also produced violacein at similar optimal conditions, but developed higher concentrations of pigment at 15 °C. Culture-based methods found that violacein producers composed 0.001% or 0.023% CFU of environmental heterotrophic populations using BG-11 and potato-based media, respectively. Culture-independent high-throughput ribosomal 16S V4 sequencing of environmental DNA was used to detect Gram-negative species known for their production of violacein. Of all bacterial and archaeal sequences present during the fall in littoral waters and sediment of Lake Winnipeg, 5.5% and 6.3%, respectively, belonged to species that have similar pigment, demonstrating the scarcity of violacein producers in this aquatic freshwater system.  相似文献   
19.
As the sensitivity of the new in vitro cancer detection techniques increases, a larger number of "false positive" results can be expected from control populations apparently free from malignant disease at the time of the test. An attempt is made to predict the number of unexplained positives, together with the expected age and sex distribution, using published cancer registration statistics. The predicted numbers are compared with the observed numbers of unexplained positives in two clinical trials of the MEM test.  相似文献   
20.
Cloth Motion Capture   总被引:3,自引:0,他引:3  
  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