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   1407篇
  免费   72篇
  国内免费   2篇
电工技术   42篇
综合类   1篇
化学工业   435篇
金属工艺   45篇
机械仪表   35篇
建筑科学   19篇
矿业工程   1篇
能源动力   57篇
轻工业   149篇
水利工程   3篇
石油天然气   1篇
无线电   84篇
一般工业技术   280篇
冶金工业   140篇
原子能技术   65篇
自动化技术   124篇
  2023年   28篇
  2022年   53篇
  2021年   74篇
  2020年   39篇
  2019年   40篇
  2018年   58篇
  2017年   45篇
  2016年   60篇
  2015年   53篇
  2014年   37篇
  2013年   90篇
  2012年   77篇
  2011年   97篇
  2010年   55篇
  2009年   55篇
  2008年   76篇
  2007年   51篇
  2006年   28篇
  2005年   36篇
  2004年   23篇
  2003年   33篇
  2002年   27篇
  2001年   12篇
  2000年   21篇
  1999年   21篇
  1998年   55篇
  1997年   30篇
  1996年   25篇
  1995年   9篇
  1994年   17篇
  1993年   25篇
  1992年   13篇
  1991年   11篇
  1990年   5篇
  1989年   5篇
  1988年   10篇
  1987年   10篇
  1986年   11篇
  1985年   10篇
  1984年   5篇
  1983年   6篇
  1982年   6篇
  1981年   10篇
  1980年   3篇
  1979年   3篇
  1978年   4篇
  1976年   6篇
  1974年   2篇
  1973年   3篇
  1970年   2篇
排序方式: 共有1481条查询结果,搜索用时 0 毫秒
101.
Artificial Life and Robotics - The amount of blood under the surface of skin is controlled by the autonomic nervous system and directly influences the facial skin temperature. Classification models...  相似文献   
102.
This paper considers the day‐ahead market with batteries and accumulators to level power generation. First, we model consumers with batteries, generators with batteries, and accumulators, all of whom strive to maximize their own profit. An optimal pricing algorithm based on dual decomposition and the steepest descent method is derived and shown to be stable. Finally, the effectiveness of the algorithm is demonstrated by means of numerical simulations which indicate that it achieves demand–supply balance.  相似文献   
103.
In photoautotrophic cultures of pak-bung hairy roots, strong light irradiation (22 W/m2) increased the content of reactive oxygen species (ROS) in the cells, resulting in chlorophyll (Chl) degradation and DNA injury. The Chl degradation rate, RD, can be used as a parameter to measure the cellular damage caused by photo-induced stress. The presence of the antioxidants ascorbic acid, chlorogenic acid or catechin reduced the RD, while lowering the content of ROS and moderating the DNA injury.  相似文献   
104.
We examined the issue of reliability of InP-based high-electron mobility transistors (HEMTs), focusing on the increase of drain resistance Rd. In investigations of the mechanism of Rd increase, we took note of contaminant incorporation and of the relations between the device lifetime and the strength of the channel electric field. In the fabrication process, reducing contaminants, especially fluorine, significantly suppressed the increase of source and drain resistances. Cross-sectional views of the gate of improved devices, which had a long lifetime, confirmed an almost contaminant-free surface around the gate. In acceleration tests, the most negative impact on drain resistance stability among several bias conditions was found when the current density was high and the channel electric field was large at the same time. The dependence of drain-gate electric field strength E showed that the device lifetimes of HEMTs determined from Rd increase obeyed exp(1/E), which means that impact ionization was the main cause of degradation. We elucidate that the interactions of hot carriers with contaminants around the gate are the main causes of the Rd increase in HEMTs. Suppression of device degradation was achieved by optimizing the fabrication process around the gate. In this way, device lifetime was remarkably enhanced.  相似文献   
105.
Experimental techniques for evaluating the interfacial properties between fiber bundles and the matrix of three-dimensionally reinforced carbon/carbon composites were examined. Specially arranged fiber bundle push-out and pull-out tests were conducted up to 2273 K in vacuum. In these tests, a fiber bundle in the specimens was extruded or pulled out by external compressive or tensile loads. Post-fracture observations revealed that a shear fracture was successfully induced within the carbon matrices at the loaded fiber bundle interface. The interfacial shear strength and initial sliding stress of the fiber bundle monotonically increased with the test temperature. The relief of residual thermal stress and increases in the frictional resistance and anchor effect at the fiber bundle interface were considered to be the major mechanisms that caused the enhancements. An increase in the heat treatment temperature during the processing of the composites resulted in a significant decrease in and .  相似文献   
106.
The structure and rheological properties of binary blends of polycarbonate (PC) and polystyrene (PS) were investigated using various PS samples with different molecular weights, namely PS1k (Mw = 1,000), PS53k (Mw = 53,000), and PS240k (Mw = 240,000). The blends with PS53k and PS240k show phase-separated structures, whereas the blend with PS1k is miscible. The shear viscosity decreases greatly on addition of PS53k and PS240k, especially at high shear rates, which would be a great advantage at processing operations. Because the nonlinear response occurs in the small strain region for multilayered films of PC and PS240k, the origin of the significant viscosity drop for the phase-separated system is interfacial slippage at the phase boundary.  相似文献   
107.
To clarify the effects of microwave roasting on the distribution of tocopherols and FA of phospholipids within soybeans, whole soybeans (Glycine max) were treated by microwave and further evaluted as compared to a raw sample. Tocopherol homologs, measured using HPLC, and phospholipid profiles, quantified with GC, were determined in the seed coat, the embryonic axis, and selections of cotyledons separated from three cultivars. The tocopherols were predominantly detected in the axis, followed by the cotyledons, and then very little in the coat. As much as 25% of the individual tocopherols originally present in the coat were lost at 12 min of roasting, whereas <25% was lost in the cotyledons and the axis after 20 min of roasting. The greatest rate of phospholipid loss (P<0.05) was observed in PE, followed by PC and PI, and their changing patterns were more pronounced in the coat than in the cotyledons or the axis. Thus, tocopherol content and phospholipid profiles change with microwave roasting according to tissue.  相似文献   
108.
DyP-type peroxidases are a family of heme peroxidases named for their ability to degrade persistent anthraquinone dyes. DyP-type peroxidases are subclassified into three classes: classes P, I and V. Based on its genome sequence, Streptomyces avermitilis, eubacteria, has two genes presumed to encode class V DyP-type peroxidases and two class I genes. We have previously shown that ectopically expressed SaDyP2, a member of class V, indeed has the characteristics of a DyP-type peroxidase. In this study, we analyzed SaDyP1, a member of the same class V as SaDyP2. SaDyP1 showed high amino acid sequence identity to SaDyP2, retaining a conserved GXXDG motif and catalytic aspartate. SaDyP1 degraded anthraquinone dyes, which are specific substrates of DyP-type peroxidases but not azo dyes. In addition to such substrate specificity, SaDyP1 showed other features of DyP-type peroxidases, such as low optimal pH. Furthermore, immunoblotting using an anti-SaDyP2 polyclonal antibody revealed that SaDyP1 and/or SaDyP2 is expressed in mycelia of wild-type S. avermitilis.  相似文献   
109.
Background: We investigated and compared the osteogenic potential and bone regeneration capacities of dedifferentiated fat cells (DFAT cells) and adipose-derived stem cells (ASCs). Method: We isolated DFAT cells and ASCs from GFP mice. DFAT cells were established by a new culture method using a mesh culture instead of a ceiling culture. The isolated DFAT cells and ASCs were incubated in osteogenic medium, then alizarin red staining, alkaline phosphatase (ALP) assays, and RT-PCR (for RUNX2, osteopontin, DLX5, osterix, and osteocalcin) were performed to evaluate the osteoblastic differentiation ability of both cell types in vitro. In vivo, the DFAT cells and ASCs were incubated in osteogenic medium for four weeks and seeded on collagen composite scaffolds, then implanted subcutaneously into the backs of mice. We then performed hematoxylin and eosin staining and immunostaining for GFP and osteocalcin. Results: The alizarin red-stained areas in DFAT cells showed weak calcification ability at two weeks, but high calcification ability at three weeks, similar to ASCs. The ALP levels of ASCs increased earlier than in DFAT cells and showed a significant difference (p < 0.05) at 6 and 9 days. The ALP levels of DFATs were higher than those of ASCs after 12 days. The expression levels of osteoblast marker genes (osterix and osteocalcin) of DFAT cells and ASCs were higher after osteogenic differentiation culture. Conclusion: DFAT cells are easily isolated from a small amount of adipose tissue and are readily expanded with high purity; thus, DFAT cells are applicable to many tissue-engineering strategies and cell-based therapies.  相似文献   
110.
Trehangelins are trehalose angelates discovered from endophytic actinomycete Polymorphospora rubra K07‐0510. We identified the trehangelin biosynthetic gene cluster, including genes that encode a glycoside hydrolase‐like protein (thgC), α‐amylase (thgD), 3‐ketoacyl‐ACP synthase III (thgI), 3‐ketoacyl‐ACP reductase (thgK), enoyl‐CoA hydratase (thgH) and acyl transferase (thgJ). Heterologous expression of thgH, thgI, thgJ and thgK confirmed the importance of these genes in the biosynthesis of trehangelin A. Enzymatic activity studies showed that ThgI catalyses the condensation of acetyl‐CoA and methylmalonyl‐CoA to 2‐methylacetoacetyl‐CoA (MAA‐CoA), ThgK catalyses NADPH‐dependent reduction of MAA‐CoA to 3‐hydroxy‐2‐methylbutyryl‐CoA (HMB‐CoA) and ThgH catalyses the dehydration of HMB‐CoA to angelyl‐CoA (AN‐CoA). This is the first report on the elucidation of the enzymatic formation of AN‐CoA.  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