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81.
对微机硬盘常见故障进行了初步分析,包括:硬件电路故障、硬盘读、写故障、硬盘格式化等方面的故障。对上述问题提出了相应的应急维修、恢复办法。 相似文献
82.
Zhenwei Hou Guoyun Tian Hatcher C. Johnson R.W. Yaeger E.K. Konarski M.M. Crane L. 《Electronics Packaging Manufacturing, IEEE Transactions on》2001,24(4):282-292
This paper examines the assembly process for flip chip die with SnAgCu solder bumps and the results of liquid-to-liquid thermal shock testing. The SnAgCu alloy required a thicker dip layer of flux to achieve good wetting compared to the SnPb eutectic alloy. A liquid spray flux yielded more consistent solder wetting with the SnAgCu alloy. With both fluxes, a nitrogen reflow atmosphere was necessary with the SnAgCu alloy. A peak reflow temperature of 246°C was used for the assembly of the SnAgCu thermal shock test vehicles. A lower peak temperature of 235°C did not yield sufficient solder wetting. Liquid-to-liquid thermal shock testing was performed from -40°C to +125°C. The SnPb alloy performed slightly better than the SnAgCu and the dip flux was better that the spray flux. The degree of delamination with the SnAgCu alloy was significantly higher than with the SnPb alloy. Cracks in the underfill between adjacent solder balls were observed. The SnPb alloy extruded into these cracks more readily than the SnAgCu and created electrical shorts 相似文献
83.
Weijie Wu Yuanting Xu Xiaofan Ma Zhiwei Tian Chunmei Zhang Jingquan Han Xiaoshuai Han Shuijian He Gaigai Duan Yiwen Li 《Advanced functional materials》2023,33(36):2302351
The shortage of freshwater resources has become a major obstacle threatening human development, and directly utilizing solar energy by solar evaporators is emerging as a promising method to produce freshwater from the seawater. Compared to many synthetic polymer-based evaporators, cellulose-based evaporators are expected to offer more interesting features benefiting from the renewable feature and abundant reserves of cellulose-contained naturally occurring materials. First, according to the different fabrication methods, cellulose-based solar evaporators can be divided into two types, i.e., top-down utilization (wood-based) and bottom-up assembled (cellulose composite-based), respectively. The different fabrication schemes also bring their own unique advantages, such as the bimodal porous structure of wood-based evaporators and the artificial interconnection microporous network of cellulose composite-based evaporators. Subsequently, this review further summarizes the most recent advances and highlights of those cellulose-based solar evaporators, by focusing on their structural regulation strategies (e.g., drilled channel array, asymmetric wettability structure, delignification, 2D waterway, etc.) and evaporation performance improvements (e.g., salt resistance, high evaporation rate, etc.). Finally, the challenges in this field and potential solutions are also discussed, which are anticipated to provide new opportunities toward the future development of cellulose and other kinds of biomass-based evaporators. 相似文献
84.
85.
激光-MIG复合焊接工艺参数对焊缝形状的影响 总被引:5,自引:0,他引:5
本文以激光-MIG复合焊焊接工艺参数对焊缝形状的影响为出发点,对复合焊进行了初步的研究。实验研究了激光与电弧之间的距离、离焦量、焊接速度、送丝速度、电弧的类型以及激光的倾斜角度等工艺参数对复合焊焊缝的熔深熔宽的影响。实验表明,激光与电弧之间的距离(DL A)对复合焊的熔深影响较大,在DL A为2mm时,熔深达到最大。离焦量主要是通过影响能量密度来影响熔深和熔宽,在离焦量为+2mm时熔深达到最大,不同于单独激光焊负离焦时熔深最大。焊接速度有一个合适的范围,在这个范围内随着焊接速度的增加,熔深熔宽减少。送丝速度对复合焊的焊缝形状影响最大,送丝丝度较小时焊缝形状类似于单独激光焊;送丝速度过大电弧等离子体屏蔽激光,焊缝形状类似于MIG。激光的倾斜角度对复合焊的焊缝熔深熔宽也有一定的影响,当激光的倾斜角度为10oC时,熔深达到最大熔宽最小。 相似文献
86.
移动通信中的智能天线技术 总被引:1,自引:0,他引:1
智能天线技术已经成为移动通信领域中最具吸引力的技术之一,它能够根据所处的电磁环境,智能地调节自身参数,抑制干扰,提高天线增益,增加频谱利用率,从而改善移动通信系统的性能。介绍了智能天线的工作原理,阐述了智能天线常用的算法、数字波束成型技术、对系统性能的改善以及在移动通信系统中的应用,最后对智能天线的未来作了展望。 相似文献
87.
Shizhuo Liu PeiChi Liao Wei Wei Erxun Han Yunkun Wang Huifeng Tian Ruijie Li Jiaqi Pan Chi Zhang Hao Li Yifei Li Zhixin Yao Zhenjiang Li Lina Yang Zhang Zhiyun Li Rong Huang Yunan Gao Junjie Guo Ji Chen Yi Cui Lei Liu 《Advanced functional materials》2023,33(5):2210729
The trivalent outer shell of boron renders this element electron-poor but chemically rich, exhibiting more than one dozen allotropes. Its 2D polymorph has been recently synthesized on metal substrates under ultrahigh vacuum and has attracted intense interest. However, probing its properties ex situ has been challenging due to the quality degradation—surface oxidation—that occurs upon exposure to ambient environments. Herein, this surface chemistry is investigated in regard to the air stability of ultrathin boron flakes on metals prepared by atmospheric-pressure chemical vapor deposition. The characteristic Volmer–Weber growth is recognized by the stacking of polygon-shaped, thin flakes as isolated islands. Significantly, the metal-catalyzed, ultrafast gasification of boron flakes at room temperature, exemplified by the complete, spontaneous vanishment of 200 nm-thick boron islands in 3 h is observed. A two-step mechanism, first oxygen-involved surface oxidation and then subsequent reactions with water forming a highly volatile boric acid layer, is unambiguously revealed by combined surface characterizations. The catalysis by metal substrates, corroborated by theoretical calculations, is attributed as the crucial cause of the unprecedented gasification. The concept of oxygen-free growth is thereby proposed for air-sensitive material growth by introducing in situ oxygen scavengers. These findings significantly expand the fundamental understanding of the surface chemistry of boron and pave the way for the chemical vapor deposition growth of hydrophobic materials. 相似文献
88.
为了满足低成本建设5G广覆盖网络的需求,需要提前研究低频3G、4G网络向5G重耕的最佳方案。在没有进行重耕,因而没有理想的低频5G测试环境的情况下,采用理论分析的手段进行重耕后的覆盖能力估算。以未来L900重耕用于5G广覆盖为例,探讨了链路预算的关键设定、模型选择等问题,并通过多个本地网实际测试数据间接验证估算结果的合理性。所得结论已实际应用于某大运营商对全国900 MHz网络的规划方案,对于指导网络重耕具有重要的借鉴意义,也为面向覆盖和感知的6G网络演进及重耕提供了参考模型。 相似文献
89.
A Supermolecular Photosensitizer with Excellent Anticancer Performance in Photodynamic Therapy 下载免费PDF全文
Ruizheng Liang Rui Tian Lina Ma Lele Zhang Yanli Hu Jian Wang Min Wei Dan Yan David G. Evans Xue Duan 《Advanced functional materials》2014,24(21):3144-3151
A supermolecular photosensitizer with excellent anticancer behavior when used for photodynamic therapy (PDT) is fabricated by the incorporation of zinc phthalocyanines (ZnPc) into the gallery of a layered double hydroxide (LDH). The composite material possesses uniform particle size (hydrodynamic diameter ~120 nm), and the host–guest and guest–guest interactions result in a high dispersion of ZnPc in a monomeric state in the interlayer region of the LDH matrix, with high singlet oxygen production efficiency. In vitro tests performed with HepG2 cells reveal a satisfactory PDT effectiveness of the ZnPc(1.5%)/LDH composite photosensitizer: a cellular damage as high as 85.7% is achieved with a rather low dosage of ZnPc (10 μg/mL). An extraordinarily high specific efficacy is demonstrated (31.59 μg?1 (J/cm2)?1), which is over 185.5% enhancement compared with the previously reported photosensitizers under similar test conditions. Furthermore, an in vivo study of the ZnPc(1.5%)/LDH demonstrates excellent PDT performance with an ultra‐low dose (0.3 mg/kg) and a low optical fluence rate (54 J/cm2). In addition, the ZnPc/LDH photosensitizer displays high stability, good biocompatibility, and low cytotoxicity, which would guarantee its practical application. Therefore, this work provides a facile approach for design and fabrication of inorganic–organic supermolecular materials with greatly enhanced anticancer behavior. 相似文献
90.