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   1471篇
  免费   19篇
  国内免费   1篇
电工技术   53篇
综合类   3篇
化学工业   285篇
金属工艺   42篇
机械仪表   21篇
建筑科学   11篇
能源动力   64篇
轻工业   84篇
水利工程   6篇
无线电   126篇
一般工业技术   244篇
冶金工业   476篇
原子能技术   23篇
自动化技术   53篇
  2023年   5篇
  2022年   11篇
  2021年   16篇
  2020年   8篇
  2019年   8篇
  2018年   17篇
  2017年   8篇
  2016年   11篇
  2015年   11篇
  2014年   25篇
  2013年   69篇
  2012年   40篇
  2011年   65篇
  2010年   31篇
  2009年   26篇
  2008年   39篇
  2007年   38篇
  2006年   39篇
  2005年   37篇
  2004年   32篇
  2003年   39篇
  2002年   38篇
  2001年   33篇
  2000年   26篇
  1999年   37篇
  1998年   203篇
  1997年   122篇
  1996年   69篇
  1995年   37篇
  1994年   48篇
  1993年   52篇
  1992年   18篇
  1991年   12篇
  1990年   29篇
  1989年   15篇
  1988年   12篇
  1987年   20篇
  1986年   16篇
  1985年   10篇
  1984年   8篇
  1983年   8篇
  1982年   8篇
  1981年   9篇
  1980年   7篇
  1979年   12篇
  1978年   11篇
  1977年   8篇
  1976年   24篇
  1974年   8篇
  1973年   6篇
排序方式: 共有1491条查询结果,搜索用时 0 毫秒
991.
The complete nucleotide sequence of the 957-kb DNA of the human immunoglobulin heavy chain variable (VH) region locus was determined and 43 novel VH segments were identified. The region contains 123 VH segments classifiable into seven different families, of which 79 are pseudogenes. Of the 44 VH segments with an open reading frame, 39 are expressed as heavy chain proteins and 1 as mRNA, while the remaining 4 are not found in immunoglobulin cDNAs. Combinatorial diversity of VH region was calculated to be approximately 6,000. Conservation of the promoter and recombination signal sequences was observed to be higher in functional VH segments than in pseudogenes. Phylogenetic analysis of 114 VH segments clearly showed clustering of the VH segments of each family. However, an independent branch in the tree contained a single VH, V4-44.1P, sharing similar levels of homology to human VH families and to those of other vertebrates. Comparison between different copies of homologous units that appear repeatedly across the locus clearly demonstrates that dynamic DNA reorganization of the locus took place at least eight times between 133 and 10 million years ago. One nonimmunoglobulin gene of unknown function was identified in the intergenic region.  相似文献   
992.
A hospital-based matched case-control study was conducted in order to identify risk factors for the development of bloodstream infections in adult hospitalized patients. Between January 1993 and December 1994, 264 episodes of bloodstream infection were evaluated. Significant variables identified by univariate analysis were included in a multivariate model that showed that central venous catheter [odds ratio (OR), 6.71], poor performance status (OR, 3.40), weight loss (OR, 2.47), hematologic diseases (OR, 2.24), and previous antimicrobial therapy (OR, 2.12) independently influenced the outcome. The knowledge of modifiable risk factors is useful in the development of strategies that may contribute to the prevention of bloodstream infections.  相似文献   
993.
Heparin coated bypass circuits have been reported to improve the biocompatibility of extracorporeal circulation, although it is still insufficient and improvable. Nitric oxide (NO) is known to inhibit platelet activation and inflammatory reactions. In this study, the authors evaluated exogenous NO infusion in enhancing the effect of a heparin coated bypass circuit on the biocompatibility of an extracorporeal circuit, especially in view of the attenuation of the inflammatory response. A miniature closed bypass circuit, including an oxygenator (BioActive surface; Carmeda, Stockholm, Sweden) was primed with fresh human heparinized blood and perfused with a centrifugal pump. Either pure N2 gas (control group: n = 7) or NO gas (NO group [100 ppm in N2]: n = 7) was infused to the oxygenator. NO metabolites (nitrite and nitrate), platelet count, thrombin-antithrombin III complex (TAT), alpha2-plasmin-plasminogen inhibitor complex (PIC), beta-thromboglobulin (beta-TG), platelet factor 4 (PF4), serotonin, complement 3 activation products (C3a), granulocyte elastase, and bradykinin were measured at 0, 30, 60, 120, and 180 min after starting perfusion. At every sampling point, platelet counts were significantly higher, and TAT, beta-TG, and bradykinin were lower in the NO group than in the control group. PF4, C3a, and granulocyte elastase were significantly lower in the NO group at 60, 120, and 180 min. These results suggest that NO gas infusion to the oxygenator enhances the biocompatibility of heparin coated extracorporeal circuits.  相似文献   
994.
Electrode distance between cathode and anode is one of the important parameters for fabricating hydrogenated amorphous silicon (a-Si:H) using plasma-enhanced chemical-vapor-deposition system with parallel plate electrodes. In this work, we have investigated the relationship between electrode distance and stability of a resulting a-Si:H. The stability is improved with decreasing electrode distance. At shorter electrode distance, formation of higher silane-related-reactive species is suppressed by heating effect of gas molecules near the cathode due to a proximity to the heated anode. Using cathode heating method, the stability of a-Si:H is improved even at long electrode distances.  相似文献   
995.
On testing for separable correlations of multivariate time series   总被引:1,自引:0,他引:1  
Abstract.  We propose a test for separability of the correlation structure of a multivariate time series. We construct test statistics based on a spectral density matrix estimated in a nonparametric way and derive their asymptotic properties. We use simulation to check the performance in finite samples.  相似文献   
996.
Chemically vapour-deposited boron nitride (CVD-BN) plates prepared by use of the BCl3-NH3-H2 gas system were investigated as to their stability to moisture. Infrared (IR) spectroscopic measurement, chemical analysis and thermal gravimetric analysis were used in this study. The synthesis conditions of CVD-BN plates have a large influence on their stability to moisture. The stability of CVD-BN plates prepared under a total gas pressure (P tot) of 10 to 60 torr degraded as the deposition temperature (T dep) was lowered. The CVD-BN plates with transparent and isotropic properties, which were prepared at below 1400° C and above 10 torr, showed poor stability to moisture, The CVD-BN plates synthesized under 5 torr had high moisture-resistance, even at aT dep as low as 1400° C. An IR absorption spectral study revealed that the unstable species existing in CVD-BN plans had changed to ammonium borate hydrates by reacting with moisture in the atmosphere. The stability to moisture for CVD-BN plates degraded as the deposition roe was raked, especially for the CVD-BN plates prepared at 1400° C.  相似文献   
997.
Eight components of humic substances were ozonated. Mutagenic activity was found with TA100 with and without S9 mix for all ozonated components. Ozonated products of p-hydroxybenzaldehyde were separated into five fractions by silica gel chromatography and each fraction subjected to mutagenicity assay. Mutagenic activity was found in the chloroform and chloroform-acetone (1:1) fractions. The compounds in these fractions were identified, and aldehydes such as formaldehyde, acetaldehyde, glyoxal, glyoxylic acid and methyl glyoxal were found to be mutagenic. Mutagenic compounds are present in the polar fraction.  相似文献   
998.
A 60-year-old woman was admitted to our hospital with a two month history of dry cough and dyspnea on exertion. A chest roentgenogram revealed diffuse interstitial shadows with a reduction of lower lung volume. Laboratory examinations revealed an increase in CPK and aldolase. There was decreased proximal muscle power, and the findings of a biopsy of the right deltoid were compatible with polymyositis. Myositic symptoms were stable, but the respiratory symptoms worsened, and an open lung biopsy was performed for diagnosis and to determine the best treatment. The histological findings of biopsy materials demonstrated active interstitial pneumonia complicated by cellular interstitial pneumonia, bronchiolitis obliterans organizing pneumonia, usual interstitial pneumonia and lymphoid hyperplasia. The patient responded well to adrenocorticosteroid and immunosuppressive therapy, and is now attending as an out patient. It is well known that PM-DM can be associated with interstitial pneumonia, and this complication is an important prognostic factor clinically. The pathological patterns of interstitial pneumonia in PM-DM may be divided into usual interstitial pneumonia and bronchiolitis obliterans organizing pneumonia. Furthermore, it is well documented that these patterns are concurrent with the response to adrenocorticosteroid and prognostic factors. However, our case of PM-DM, in which various patterns such as rheumatoid arthritis (RA) were pathologically revealed, cannot be considered as having uniform pathological pattern. We consider that pulmonary pathological patterns of PM-DM are very varied, as with RA. It is a very important to evaluate the nature of these patterns and the subsequent clinical course in PM-DM with interstitial pneumonia.  相似文献   
999.
1000.
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