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   1351篇
  免费   44篇
  国内免费   3篇
电工技术   74篇
综合类   3篇
化学工业   371篇
金属工艺   30篇
机械仪表   33篇
建筑科学   27篇
矿业工程   1篇
能源动力   74篇
轻工业   99篇
水利工程   2篇
石油天然气   1篇
无线电   85篇
一般工业技术   257篇
冶金工业   203篇
原子能技术   32篇
自动化技术   106篇
  2023年   7篇
  2022年   21篇
  2021年   31篇
  2020年   9篇
  2019年   13篇
  2018年   28篇
  2017年   26篇
  2016年   31篇
  2015年   28篇
  2014年   19篇
  2013年   69篇
  2012年   42篇
  2011年   66篇
  2010年   46篇
  2009年   65篇
  2008年   57篇
  2007年   64篇
  2006年   52篇
  2005年   40篇
  2004年   40篇
  2003年   34篇
  2002年   27篇
  2001年   25篇
  2000年   37篇
  1999年   30篇
  1998年   70篇
  1997年   46篇
  1996年   43篇
  1995年   19篇
  1994年   29篇
  1993年   26篇
  1992年   19篇
  1991年   14篇
  1990年   18篇
  1989年   21篇
  1988年   21篇
  1987年   17篇
  1986年   6篇
  1985年   15篇
  1984年   15篇
  1983年   8篇
  1982年   9篇
  1981年   6篇
  1980年   11篇
  1979年   12篇
  1978年   10篇
  1977年   11篇
  1976年   16篇
  1975年   9篇
  1973年   11篇
排序方式: 共有1398条查询结果,搜索用时 0 毫秒
981.
A new type of crack arrester concept, named the splice-type crack arrester, was invented and applied to a core–core splice in a foam core sandwich panel in order to suppress interfacial crack growth. An analytical evaluation of this crack arrester including parametric studies was carried out. It was confirmed by finite element (FE) analysis that interfacial crack propagation was suppressed by a decrease in the energy release rate at the crack tip under constant loading owing to the splice-type crack arrester as the crack tip approached the edge of the arrester. Through this study, it was revealed that the leading edge of the splice-type crack arrester, its shape and material, have strong effects on the crack suppression capability.  相似文献   
982.
During the accident that occurred at the Fukushima Daiichi nuclear power plant, a large volume of seawater was introduced as coolant into the storage pools for spent nuclear fuel. If this fuel is reprocessed, some components of seawater will be mixed with the nitric acid solution containing metal ions in the reprocessing process where stainless steels are used as structural material. In this study, we investigated the effect of seawater components in high active liquid waste (HAW) containing nitric acid and metal ions as fission products on the corrosion behavior of SUS316L stainless steel.

Corrosion tests were conducted in surrogate HAW containing artificial seawater (ASW). Intergranular corrosion was observed in the HAW with ASW, where Ru increased the corrosion potential to the transpassive region. An increase in the amount of ASW led to a decrease in the corrosion rate and suppression of intergranular corrosion. Interactions between Ru ions and seawater components, such as chloride ions, were indicated by the results of extended X-ray absorption fine structure spectroscopy and cyclic voltammetry analyses of the solution containing ASW and HAW.  相似文献   

983.
Successive deposition of octa(3-aminopropyl)octasilsesquioxane octahydrochloride and gold nanoparticles coated with carboxylate groups (Au–COO) on glass substrates alternately under mild basic conditions led to systematic buildup of a gold colloidal multilayer. The driving force of the self-assembly was electrostatic interaction between ammonium cations of octa(3-aminopropyl)octasilsesquioxane octahydrochloride and carboxylate anions on Au–COO. A linear increase of surface plasmon resonance of Au–COO with the deposited bilayers indicated the multilayer manipulation was reproducible. Porous nanocomposites were accomplished by precipitation of octa(3-aminopropyl)octasilsesquioxane octahydrochloride modified polystyrene (PS) latex particles and Au–COO followed by removal of the PS particles via tetrahydrofuran (THF) extraction. Porous nanocomposite films were obtained by layer-by-layer (LBL) self-assembly of the octa(3-aminopropyl)octasilsesquioxane octahydrochloride modified PS latex particles and Au–COO followed by removal of the PS particles via THF extraction. Dedicated to Professor Christopher W. Allen for his advances in inorganic ring and polymer chemistry.  相似文献   
984.
Mast cells (MCs) play key roles in IgE-mediated immunoresponses, including in the protection against parasitic infections and the onset and/or symptoms of allergic diseases. IgE-mediated activation induces MCs to release mediators, including histamine and leukotriene, as an early response, and to produce cytokines as a late phase response. Attempts have been made to identify novel antiallergic compounds from natural materials such as Chinese medicines and food ingredients. We herein screened approximately 60 compounds and identified salicylaldehyde, an aromatic aldehyde isolated from plant essential oils, as an inhibitor of the IgE-mediated activation of MCs. A degranulation assay, flow cytometric analyses, and enzyme-linked immunosorbent assays revealed that salicylaldehyde inhibited the IgE-mediated degranulation and cytokine expression of bone-marrow-derived MCs (BMMCs). The salicylaldehyde treatment reduced the surface expression level of FcεRI, the high affinity receptor for IgE, on BMMCs, and suppressed the IgE-induced phosphorylation of tyrosine residues in intercellular proteins, possibly Lyn, Syk, and Fyn, in BMMCs. We also examined the effects of salicylaldehyde in vivo using passive anaphylaxis mouse models and found that salicylaldehyde administration significantly enhanced the recovery of a reduced body temperature due to systemic anaphylaxis and markedly suppressed ear swelling, footpad swelling, and vascular permeability in cutaneous anaphylaxis.  相似文献   
985.
The nitride capacities in CaO-TiO2-TiO1.5 slags, and nitrogen distribution ratio between these slags and liquid Cu (LN = (mass-% N)/[mass-% N]) were measured by a gas-slag-metal equilibration technique, using a Mo crucible in the temperature range of 1823 to 1923 K under controlled partial pressures of oxygen and nitrogen . The values for , (mass-% Ti3+)/(mass-% Ti4+) ratio, and solubility of TiN in CaO-TiO2-TiO1.5 slags were obtained as a function of slag composition (XCaO = 0.24 ~ 0.39) and temperature. Activity coefficients of TiN were evaluated from the values for activity coefficients of Ti in liquid Cu which were calculated from the results of TiN saturation experiments.  相似文献   
986.
A simple and high image quality method for viewpoint image synthesis from multi‐camera images for a stereoscopic 3D display using head tracking is proposed. In this method, slices of images for depth layers are made using approximate depth information, the slices are linearly blended corresponding to the distance between the viewpoint and cameras at each layer, and the layers are overlaid from the perspective of viewpoint. Because the linear blending automatically compensates for depth error because of the visual effects of depth‐fused 3D (DFD), the resulting image is natural to observer's perception. Smooth motion parallax of wide depth range objects induced by viewpoint movement for left‐and‐right and front‐and‐back directions is achieved using multi‐camera images and approximate depth information. Because the calculation algorithm is very simple, it is suitable for real time 3D display applications.  相似文献   
987.
Several studies have documented increased expression of ornithine decarboxylase (ODC) in neoplastic colorectal tissue versus normal-appearing colonic mucosa. The present study was undertaken to determine whether there is an association between the degree of overexpression of ODC in colorectal carcinomas and survival in a series of 74 patients. A high level of tumor ODC expression was found to be significantly associated with greater survival in our patient series. Patients with tumor ODC activities greater than the median and especially in the highest quartile experienced a more favorable outcome than those patients with ODC values below the median or in the lowest quartile (P = 0.03 and 0.02, respectively). The presence of a GTP-activatable isoform of ODC was also significantly associated with a favorable prognosis but only in tumors of the right colon (P = 0.01). There was no association found between ODC activity and tumor grade, tumor size, or patient age, sex, or race. Our results demonstrate that high levels of ODC expression (and presence of a GTP-activatable isoform for right-sided colon tumors) predict a favorable prognosis in human colorectal carcinoma. Knowledge of a patient's ODC status at the time of surgery may be useful in decisions regarding adjuvant therapy. Understanding the mechanism(s) involved should lead to new therapeutic approaches for advanced colorectal carcinoma.  相似文献   
988.
This paper proposes a new QoS framework, called the On-Demand QoS Path framework (ODP). It provides end-to-end QoS guarantees to individual flows with minimal overhead, while keeping the scalability characteristic of DiffServ. ODP exercises per-flow admission control and end-to-end bandwidth reservation at the edge of the network and only differentiates service types in the core of the network. In addition, to adapt to dynamically changing traffic load, ODP monitors the bandwidth utilization of the network and performs dynamic bandwidth reconfiguration in the network core based on the monitored bandwidth utilization. Through extensive simulations, the performance of ODP is investigated and compared with that of IntServ and DiffServ frameworks. The simulation results clearly showed that ODP provides end-to-end QoS guarantees to individual flows, which DiffServ can not provide, with much less overhead than IntServ.  相似文献   
989.
Effects of electrolyte addition on photocatalytic activity of (Ga1−xZnx)(N1−xOx) modified with either Rh2−yCryO3 or RuO2 nanoparticles as cocatalysts for overall water splitting under visible light (λ > 400 nm) are investigated. The cocatalyst Rh2−yCryO3 is confirmed to selectively promote the photoreduction of H+, while RuO2 functions as both H2 evolution sites and as efficient O2 evolution sites. The activity of Rh2−yCryO3-loaded (Ga1−xZnx)(N1−xOx) is found to be suppressed in the presence of Cl, which undergoes oxidation by photogenerated holes in the valence band of (Ga1−xZnx)(N1−xOx). Alkaline- and alkaline earth-metal cations in the reactant solution compensate the negative effect of Cl to a certain extent depending on the metal cation employed. Among the electrolytes examined, the addition of an appropriate amount of NaCl or A2SO4 (A = Li, Na, or K) to the reactant solution without pH control is found to increase activity by up to 75% compared to the case without additives. Direct splitting of seawater to produce H2 and O2 is also demonstrated using Rh2−yCryO3-loaded (Ga1−xZnx)(N1−xOx) catalyst under visible light.  相似文献   
990.
A new method of evaluating the workability of a tube in cold pilgering has been studied on the basis of material deformability and the effects of process conditions. A circumferential compression test of a tube is confirmed to be an effective evaluation method for deformability. The critical reduction in height upon crack initiation in the compression test is also found to be a good measure of material deformability. Systematic cold pilgering tests and the numerical analysis of cold pilgering are conducted. As a result, the ratio of radial strain to circumferential strain during pilgering is a good indicator of process conditions, and a common mechanism of inner fissure formation during pilgering in stainless steel, titanium alloy, and zirconium alloy is proposed. Finally, a suitable expression for workability is obtained by considering material deformability and the effects of pilgering conditions. These findings will assist the selection of appropriate pilgering conditions to prevent the formation of fissures on the inner surface of a tube.  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