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   74554篇
  免费   8620篇
  国内免费   4492篇
电工技术   6363篇
技术理论   5篇
综合类   5635篇
化学工业   11241篇
金属工艺   4466篇
机械仪表   5001篇
建筑科学   6002篇
矿业工程   2471篇
能源动力   2199篇
轻工业   5534篇
水利工程   1797篇
石油天然气   4171篇
武器工业   856篇
无线电   8996篇
一般工业技术   8348篇
冶金工业   2916篇
原子能技术   766篇
自动化技术   10899篇
  2024年   397篇
  2023年   1772篇
  2022年   3306篇
  2021年   4691篇
  2020年   3377篇
  2019年   2533篇
  2018年   2638篇
  2017年   2888篇
  2016年   2537篇
  2015年   3580篇
  2014年   4226篇
  2013年   4846篇
  2012年   5453篇
  2011年   5697篇
  2010年   4900篇
  2009年   4567篇
  2008年   4534篇
  2007年   4137篇
  2006年   3844篇
  2005年   3366篇
  2004年   2135篇
  2003年   1783篇
  2002年   1762篇
  2001年   1519篇
  2000年   1321篇
  1999年   1287篇
  1998年   890篇
  1997年   743篇
  1996年   668篇
  1995年   556篇
  1994年   455篇
  1993年   292篇
  1992年   240篇
  1991年   165篇
  1990年   136篇
  1989年   100篇
  1988年   73篇
  1987年   60篇
  1986年   55篇
  1985年   28篇
  1984年   14篇
  1983年   9篇
  1982年   15篇
  1981年   14篇
  1980年   19篇
  1979年   14篇
  1978年   2篇
  1959年   8篇
  1953年   1篇
  1951年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
西藏江达县白格村金沙江右岸于2018年10月11日和2018年11月3日先后发生2次大规模滑坡—堰塞湖堵江事件,溃堰洪水对下游拉哇库区不良地质体的稳定性造成不同程度的影响。为保障下游水电站建设安全,对拉哇库区主要不良地质体建立了基于星载InSAR技术、无人机技术和地面传感器实时监测的“天空地”一体化监测预警体系,以多维空间采集技术获取变形信息,通过智能监控平台对信息及时进行处理、分析和可视化呈现,利用平台、短信等方式向相关人员进行分级告警,取得了较好的应用效果。  相似文献   
53.
Loss of β-cell mass and function can lead to insufficient insulin levels and ultimately to hyperglycemia and diabetes mellitus. The mainstream treatment approach involves regulation of insulin levels; however, approaches intended to increase β-cell mass are less developed. Promoting β-cell proliferation with low-molecular-weight inhibitors of dual-specificity tyrosine-regulated kinase 1A (DYRK1A) offers the potential to treat diabetes with oral therapies by restoring β-cell mass, insulin content and glycemic control. GNF4877, a potent dual inhibitor of DYRK1A and glycogen synthase kinase 3β (GSK3β) was previously reported to induce primary human β-cell proliferation in vitro and in vivo. Herein, we describe the lead optimization that lead to the identification of GNF4877 from an aminopyrazine hit identified in a phenotypic high-throughput screening campaign measuring β-cell proliferation.  相似文献   
54.
The appearance of colossal permittivity materials broadened the choice of materials for energy-storage applications. In this work, colossal permittivity in ceramics of TiO2 co-doped with niobium and europium ions ((Eu0.5Nb0.5)xTi1-xO2 ceramics) was reported. A large permittivity (εr ~ 2.01?×?105) and a low dielectric loss (tanδ ~ 0.095) were observed for (Eu0.5Nb0.5)xTi1-xO2 (x?=?1%) ceramics at 1?kHz. Moreover, two significant relaxations were observed in the temperature dependence of dielectric properties for (Eu, Nb) co-doped TiO2 ceramics, which originated from defect dipoles and electron hopping, respectively. The low dielectric loss and high relative permittivity were ascribed to the electron-pinned defect-dipoles and electrons hopping. The (Eu0.5Nb0.5)xTi1-xO2 ceramic with great colossal permittivity is one of the most promising candidates for high-energy density storage applications.  相似文献   
55.
The densification behaviors of pure B4C and B4C-ZrO2 mixtures were compared during hot pressing. The results showed that in-situ formed ZrB2 effectively enhanced the densification process of B4C-ZrO2 mixtures, more significantly during the intermediate stage. Within the relative density ranging from 0.75 to 0.90, the B4C-15?wt%ZrO2 mixture (B15Z) achieved the maximum densification rate as twice much as that of pure B4C. The stress exponent n>3 indicated plastic deformation was the dominant densification mechanism of B15Z. The viscosities of plastic flow were evaluated using Murray-Rodger-William equation and the viscosity of B15Z was only a quarter of that in pure B4C. The sintering activation energy was calculated to be 305.9?kJ/mol for pure B4C and 197?kJ/mol for B15Z, respectively. It was proposed that the lower viscosity of plastic flow and activation energy accelerated the sliding and propagating motions of plastic flow, by which underlain the enhanced densification behaviors of B4C-ZrO2 mixtures.  相似文献   
56.
Breast cancer is the most frequently diagnosed cancer in women worldwide. The disease and its treatments exert profound effects on an individual’s physical and mental health. There are many factors that impact an individual’s risk of developing breast cancer, their response to treatments, and their risk of recurrence. The community of microorganisms inhabiting the gastrointestinal tract, the gut microbiota, affects human health through metabolic, neural, and endocrine signaling, and immune activity. It is through these mechanisms that the gut microbiota appears to influence breast cancer risk, response to treatment, and recurrence. A disrupted gut microbiota or state of ‘dysbiosis’ can contribute to a biological environment associated with higher risk for cancer development as well as contribute to negative treatment side-effects. Many cancer treatments have been shown to shift the gut microbiota toward dysbiosis; however, the microbiota can also be positively manipulated through diet, prebiotic and probiotic supplementation, and exercise. The objective of this review is to provide an overview of the current understanding of the relationship between the gut microbiota and breast cancer and to highlight potential strategies for modulation of the gut microbiota that could lead to improved clinical outcomes and overall health in this population.  相似文献   
57.
We propose an analytical model to evaluate the lightpath blocking performance for a single ROADM node with intra-node add/drop contention,in which the number of lightpaths that can be added/dropped with the same wavelength is limited by the add/drop contention factor.Different models of traffic load per nodal degree are considered to validate the effectiveness of the analytical model.The simulation results show that the proposed analytical model is effective in predicting the performance for different values of add/drop contention factor C and for variable offered loads at the node.The add/drop contention factor shows an important impact on the lightpath blocking performance and properly raising the contention factor can significantly improve the lightpath blocking performance.When the add/drop contention factor C exceeds a certain level,the performance of a ROADM with intra-node contention is close to that of a contentionless ROADM.  相似文献   
58.
59.
60.
In this work,the ionospheric variability is analyzed by applying the wavelet decomposition technique to the noontime fo F2,F10.7,interplanetary magnetic field(IMF)Bz,Ap,and lower thermospheric temperature at pressure of 10?4 h Pa in 2002.Results show that the variance of periodic oscillations in the ionosphere is largest in the 2–4-day period and declines with the increase of the period.The maximum variance of the periodic oscillations in solar irradiation is in the 16–32-day period.For geomagnetic activities,most of the variance is about equally distributed on intervals of periods shorter than 32 days.Variance distributions of IMF Bz and lower thermospheric temperature are similar to those of the ionosphere.They show the maximum in the 2–4-day period and decline with the increase of the period.By analyzing the distributions of the variances,the potential connections between the ionosphere and the external sources are discussed.  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