全文获取类型
收费全文 | 8141篇 |
免费 | 1300篇 |
国内免费 | 386篇 |
专业分类
电工技术 | 4331篇 |
综合类 | 851篇 |
化学工业 | 249篇 |
金属工艺 | 89篇 |
机械仪表 | 586篇 |
建筑科学 | 254篇 |
矿业工程 | 204篇 |
能源动力 | 201篇 |
轻工业 | 79篇 |
水利工程 | 108篇 |
石油天然气 | 147篇 |
武器工业 | 41篇 |
无线电 | 1127篇 |
一般工业技术 | 553篇 |
冶金工业 | 171篇 |
原子能技术 | 53篇 |
自动化技术 | 783篇 |
出版年
2024年 | 22篇 |
2023年 | 93篇 |
2022年 | 179篇 |
2021年 | 213篇 |
2020年 | 233篇 |
2019年 | 214篇 |
2018年 | 194篇 |
2017年 | 346篇 |
2016年 | 351篇 |
2015年 | 398篇 |
2014年 | 528篇 |
2013年 | 512篇 |
2012年 | 651篇 |
2011年 | 698篇 |
2010年 | 573篇 |
2009年 | 584篇 |
2008年 | 576篇 |
2007年 | 658篇 |
2006年 | 554篇 |
2005年 | 426篇 |
2004年 | 363篇 |
2003年 | 279篇 |
2002年 | 227篇 |
2001年 | 220篇 |
2000年 | 174篇 |
1999年 | 113篇 |
1998年 | 73篇 |
1997年 | 67篇 |
1996年 | 72篇 |
1995年 | 54篇 |
1994年 | 45篇 |
1993年 | 26篇 |
1992年 | 28篇 |
1991年 | 18篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有9827条查询结果,搜索用时 15 毫秒
1.
Shannon Lee Scott L. Carnahan Georgiy Akopov Philip Yox Lin-Lin Wang Aaron J. Rossini Kui Wu Kirill Kovnir 《Advanced functional materials》2021,31(16):2010293
Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi4P4 and IrSi3P3 are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and 29Si and 31P magic angle spinning NMR. In agreement with previous report RuSi4P4 crystallizes in NCS space group P1, while IrSi3P3 is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi4P4 and IrSi3P3 to be wide bandgap (Eg) semiconductors, Eg = 1.9 and 1.8 eV, respectively. RuSi4P4 and IrSi3P3 outperform the current state-of-the-art infrared SHG material, AgGaS2, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi4P4 and IrSi3P3 are promising candidates for longer wavelength NLO materials. 相似文献
2.
3.
以某全地域机动车驾驶室为研究对象,建立驾驶室的有限元模型,验证了有限元模型的有效性。以此有限元模型为基础构建驾驶室谐响应模型,进行谐响应分析,发现驾驶室后壁板的振动是引起驾驶室内部噪声的主要原因。研究驾驶室内部噪声特性,分别进行了声学空腔模态分析和声固耦合模态分析,发现声固耦合系统声压分布比较均匀,大部分呈现局部模态,主要原因可能是驾驶室后壁板的振动。通过驾驶员耳旁声压分析发现增加驾驶室后壁板的厚度,可以在一定程度内降低驾驶室内部噪声对驾驶员的影响,为同类驾驶室通过依靠结构改进来改善声场环境提供了案例依据。 相似文献
4.
Daniel Whittaker Andreas Geist Giuseppe Modolo Robin Taylor Mark Sarsfield Andreas Wilden 《溶剂提取与离子交换》2018,36(3):223-256
Over the last decade there has been much interest in the applications of diglycolamide (DGA) ligands for the extraction of the trivalent lanthanide and actinide ions from PUREX high active raffinates or dissolved spent nuclear fuel. Of the DGAs, the N,N,N’,N’-tetraoctyldiglycolamide (TODGA) is the best known and most widely studied. A number of new actinide separation processes have been proposed based on extraction with TODGA. This review covers TODGA-based processes and extraction data, specifically focusing on how phase modifiers have been used to increase metal loading and thus enhance the operating process envelopes. Effects of third phase formation and the organic phase speciation are reviewed in this context. Relevant aspects of the extraction chemistry of important solvents (TODGA-modifier-diluent combinations) are described and their performances demonstrated by a consideration of the published flowsheet tests. It is seen that modifiers are successfully enabling the use of TODGA in actinide separation processes but to date the identification and testing of suitable modifiers has been rather empirical. There is a growing understanding of the fundamental chemistry occurring in the organic phase and how that affects extractant speciation and metal loading capacity but studies are still needed if TODGA-based flowsheets are to become an industrially deployable option for minor actinide (MA) recovery processes. 相似文献
5.
6.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
7.
Based on bibliometric, national and international research output within 2000~2018 of the third generation of semiconductor material SiC and GaN was collected. Analysis and studies were made in the region of time distribution, research forces and research hotspots. The general international development tendency and scientific research level in China were also discussed. Meanwhile, study directions clustering and burst key words detecting were used to discover and explain the inner law of evolutionary in this field, especially in the different research focus of various development stages. This paper could also provide a reference on research and arrangement in further studies. 相似文献
8.
为了降低家具配送成本,提高物流效率,基于第三方物流配送模式,构建了以总行驶距离最短和车辆数最少为最优目标的开放式车辆路径问题(open vehicle routing problem,OVRP)数学模型,并设计了一个改进的两阶段禁忌搜索算法进行求解,第1阶段求解包含所有客户的TSP(traveling salesman problem)路径来作为第2阶段划分OVRP路径的基础.设计了一个随机动态禁忌表,并将"邻域算子编号"和"邻域交换点对"同时作为禁忌对象,避免了过度禁忌的情况.另外,对5个邻域算子进行了测试,表明采用由点交换、分序点插入、点逆序和前点前向插入这4个算子组成的多邻域结构体效果最佳.经算例测试和文献对比,验证了设计算法的有效性,采用第三方物流配送比自营物流配送更节省成本. 相似文献
9.
软启动器作为大型电动机常采用的启停控制装置之一,越来越多地应用到海洋钻井生产过程中。该文从电动机启停特点、软启动器控制方式、接线,并结合海洋钻井平台吊机的设计思路及应用来分析,结合现场相关故障维修实例对软启动器升级改造方案进行了研究。 相似文献
10.