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   95134篇
  免费   9064篇
  国内免费   6038篇
电工技术   3120篇
技术理论   1篇
综合类   6001篇
化学工业   22143篇
金属工艺   7527篇
机械仪表   5070篇
建筑科学   3322篇
矿业工程   2402篇
能源动力   2264篇
轻工业   5521篇
水利工程   1335篇
石油天然气   3012篇
武器工业   751篇
无线电   13050篇
一般工业技术   16124篇
冶金工业   3431篇
原子能技术   1209篇
自动化技术   13953篇
  2024年   121篇
  2023年   1717篇
  2022年   1868篇
  2021年   3303篇
  2020年   3037篇
  2019年   2820篇
  2018年   2522篇
  2017年   3080篇
  2016年   3441篇
  2015年   3683篇
  2014年   5163篇
  2013年   5407篇
  2012年   6197篇
  2011年   8035篇
  2010年   6049篇
  2009年   6702篇
  2008年   5819篇
  2007年   6536篇
  2006年   5735篇
  2005年   5088篇
  2004年   4208篇
  2003年   3804篇
  2002年   3156篇
  2001年   2078篇
  2000年   1936篇
  1999年   1574篇
  1998年   1188篇
  1997年   953篇
  1996年   924篇
  1995年   758篇
  1994年   701篇
  1993年   536篇
  1992年   405篇
  1991年   333篇
  1990年   240篇
  1989年   214篇
  1988年   137篇
  1987年   111篇
  1986年   125篇
  1985年   85篇
  1984年   74篇
  1983年   73篇
  1982年   67篇
  1981年   33篇
  1980年   42篇
  1979年   34篇
  1978年   14篇
  1977年   18篇
  1976年   20篇
  1974年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
王鹏  李林  徐建军 《中州煤炭》2020,(9):123-127
在对沁水盆地赵庄矿煤层气开发地质、煤层气生产井资料深入研究的基础上,分析、总结了区内煤层气直井低产原因,并据此提出了区内地面抽采后续开发方向。研究认为:3号煤层气含量偏低、含气饱和度低、临储比低,致使排采阶段气含量可降幅度低,是其低产的宏观表征;3号煤储层不匹配孔级,较差连通性,即微、小孔为主,中孔次之,大孔不发育,微裂隙连通性差,致使扩散缓慢、影响储层改造和抽采效果,是其低产的微观表征;3号煤层远高于顶底板塑性及相近的水平应力,进一步造成改造缝长受限,泄流面积不足。因此,建议区内后续地面抽采方式应以增大泄流面积开发方式为主。  相似文献   
52.
Dense granule proteins (GRAs) are essential components in Toxoplasma gondii, which are suggested to be promising serodiagnostic markers in toxoplasmosis. In this study, we investigated the function of GRA9 in host response and the associated regulatory mechanism, which were unknown. We found that GRA9 interacts with NLR family pyrin domain containing 3 (NLRP3) involved in inflammation by forming the NLRP3 inflammasome. The C-terminal of GRA9 (GRA9C) is essential for GRA9–NLRP3 interaction by disrupting the NLRP3 inflammasome through blocking the binding of apoptotic speck-containing (ASC)-NLRP3. Notably, Q200 of GRA9C is essential for the interaction of NLRP3 and blocking the conjugation of ASC. Recombinant GRA9C (rGRA9C) showed an anti-inflammatory effect and the elimination of bacteria by converting M1 to M2 macrophages. In vivo, rGRA9C increased the anti-inflammatory and bactericidal effects and subsequent anti-septic activity in CLP- and E. coli- or P. aeruginosa-induced sepsis model mice by increasing M2 polarization. Taken together, our findings defined a role of T. gondii GRA9 associated with NLRP3 in host macrophages, suggesting its potential as a new candidate therapeutic agent for sepsis.  相似文献   
53.
《能源学会志》2020,93(1):152-164
The ignition, injection, and micro-explosion characteristics of aviation fuel (RP-3)/ethanol mixed droplets and biodiesel/ethanol mixed droplets at different proportions under high temperature conditions (420 °C) were compared using an experimental setup. A device for measuring small droplet volumes was designed using an infusion set and different types of needles, and a corresponding equation was established. Mixed droplets suspended on high-temperature resistance nichrome wire with a diameter of 0.2 mm were heated by sending them to a position approximately 2 mm from the forklift preheating plug using a moving rail. SLR and high-speed cameras were used to observe the flame structure as well as the injection and micro-explosion of the mixed droplets during combustion, respectively. Expansion, injection, and micro-explosion were observed in the biodiesel/ethanol mixed droplet experiments when the biodiesel content was 60%. Although the micro-explosion of mixed droplets of aviation fuel/ethanol was not observed, expansion and ejection of the droplets were observed. Image Pro-plus software was used to calculate the diameters at different times in the combustion cycle of the droplets. Through this analysis, the occurrence of micro-explosion was described, and a model for the calculation of micro-explosion strength was established.  相似文献   
54.
为了提升脑胶质瘤分割精度,提出一种结合注意力机制的3D卷积神经网络算法。输入3个不同尺度的图像块,经过9个卷积层和1个分类层后得到3个不同的分类结果,将分类结果与注意力学习到的权重相乘并逐体素相加得到输出。此外该算法采用了一种混合Dice损失函数与Focal损失函数的超参数损失函数。实验表明,该算法的Dice系数在整体区域、核心区域以及增强区域分别达到了95.31%、80.12%、82.25%。与已有的一种脑胶质瘤分割算法deepmedic相比,整体区域、核心区域以及增强区域的Dice系数分别提升了3%、2%、6%。在脑胶质瘤分割方面,具有重要的临床意义。  相似文献   
55.
针对无线网络链路干扰大、误码率高等特点,以及TCP Westwood算法(TCPW)存在估算带宽时过度依赖包的反馈,缺乏区分传输过程中丢包类型的缺点等问题,提出一种TCPW拥塞控制优化算法--TCPW-F。该算法利用发送速率等构建拥塞因子[F]作为判断丢包类型的依据,同时对判定发生噪声丢包时的拥塞窗口进一步调整,避免噪声丢包引起的窗口下降,提高该情况下窗口的发送效率。仿真结果表明,TCPW-F算法在时延性能方面表现更优,单位时间抖动趋于稳定的速度更快。在同一信道带宽下增大包生成速率,改进算法的实时吞吐量明显高于原算法,具备一定的噪声丢包感知能力,无线网络的TCP传输质量获得较大改善。  相似文献   
56.
This paper introduces two novel nonlinear stochastic attitude estimators developed on the Special Orthogonal Group with the tracking error of the normalized Euclidean distance meeting predefined transient and steady‐state characteristics. The tracking error is confined to initially start within a predetermined large set such that the transient performance is guaranteed to obey dynamically reducing boundaries and decrease smoothly and asymptotically to the origin in probability from almost any initial condition. The proposed estimators produce accurate attitude estimates with remarkable convergence properties using measurements obtained from low‐cost inertial measurement units. The estimators proposed in continuous form are complemented by their discrete versions for the implementation purposes. The simulation results illustrate the effectiveness and robustness of the proposed estimators against uncertain measurements and large initialization error, whether in continuous or discrete form.  相似文献   
57.
Multiplane displays are capable of displaying 3D scenes with correct focus cues by creating multilayer 2D images in the display volume. Hence, such a 3D display technique could effectively address the accommodation‐vergence conflict (AVC) problem, which is prevalent in augmented reality (AR) displays. In this paper, we review the recent progress on multiplane AR displays based on liquid crystals (LCs) for AR applications. The working principle of multiplane AR displays is illustrated, the electro‐optical properties of the tunable LC devices are investigated and display prototypes are demonstrated. Finally, we discuss the prospects and challenges of multiplane AR displays based on LCs.  相似文献   
58.
This article presents a design methodology for linearizing GaN HEMT amplifiers based on splitting a large FET into multiple parallel FETs with same total gate periphery and by biasing them individually. By varying the biases, the magnitude and the phase of the IMD3 components at the output of FET changes. A detailed simulation methodology using commercial microwave CAD software is presented. Simulation results show that by biasing one device in Class AB and other(s) in deep Class AB mode, IMD3 components of parallel FETs can be made out of phase to each other leading to cancellation and improvement in linearity. Three prototype circuits were simulated using (a) a single 5 mm FET (1 × 5 mm), (b) two parallel 2.5 mm FETs (2 × 2.5 mm), and (c) four parallel 1.25 mm FETs (4 × 1.25 mm), for a total gate periphery of 5 mm, over the frequency range of 0.8 to 1.0 GHz. IMD3 improvement up to 20 dBc was achieved with the 4 × 1.25 mm circuit when the FET biases were optimized. Measurement results show improvement in linearity up to 20 dBc for 4 × 1.25 mm circuit. The proposed method improves linearity without a substantial penalty on the power consumption and is straightforward to implement.  相似文献   
59.
60.
Radio-Frequency (RF) energy harvesting must cope with the limited availability and high variability of the energy source. In this paper, the modeling of an RF harvester for ultra low power environments is presented. A mathematical model based on theoretical analysis is developed. The model demonstrates that the maximum transferred power point is located in a three-dimensional space defined by the input capacitance, the output voltage, and the load resistance of the rectifier circuit. Moreover, the mathematical model returns results in substantial agreement with the SPICE simulation results, while guaranteeing a remarkable reduction of the required computation time. Furthermore, the paper reports the implementation of a mixed signal system for the 3-D MPPT, to be embedded in an RF harvester, in a 65 nm CMOS technology. The circuit exhibits a simulated power consumption lower than 100 nW, making this solution suitable for ultra low power harvesting.  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