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   49329篇
  免费   6357篇
  国内免费   4753篇
化学   25807篇
晶体学   361篇
力学   2229篇
综合类   241篇
数学   4282篇
物理学   13549篇
无线电   13970篇
  2024年   172篇
  2023年   1148篇
  2022年   1365篇
  2021年   1867篇
  2020年   1789篇
  2019年   1600篇
  2018年   1379篇
  2017年   1330篇
  2016年   1885篇
  2015年   2037篇
  2014年   2482篇
  2013年   3188篇
  2012年   3938篇
  2011年   3860篇
  2010年   2788篇
  2009年   2754篇
  2008年   2973篇
  2007年   2645篇
  2006年   2562篇
  2005年   2253篇
  2004年   1749篇
  2003年   1393篇
  2002年   1246篇
  2001年   1069篇
  2000年   1039篇
  1999年   1175篇
  1998年   1034篇
  1997年   934篇
  1996年   990篇
  1995年   856篇
  1994年   779篇
  1993年   678篇
  1992年   620篇
  1991年   486篇
  1990年   415篇
  1989年   298篇
  1988年   266篇
  1987年   235篇
  1986年   166篇
  1985年   182篇
  1984年   152篇
  1983年   131篇
  1982年   98篇
  1981年   66篇
  1980年   58篇
  1979年   38篇
  1978年   30篇
  1976年   31篇
  1975年   36篇
  1974年   26篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
972.
在多年实践经验基础上,用氧含量X1(质量分数)0.20%~0.38%的四种钽粉,控制钽阳极中残余氧含量X2(质量分数)在0.08%~0.20%间,采用正交设计实验研究了对其漏电流的影响,并建立了漏电流峰值IL和X1、X2间的预示方程,描述了漏电流和钽粉氧含量(X1)、残余氧含量(X2)间的关系。随后,用预示方程讨论了钽中氧和钽阳极中残余氧对其漏电流的影响。  相似文献   
973.
报道了用国产二极管激光端面泵浦自行研制的掺铵铍酸镧(Nd:BEL)晶体得到1.07μm线偏振激光输出的研究结果。分别用非球面透镜成像、加棱镜对扩束、加光纤传输三种方式将泵浦光耦合到增益介质中,由此得到不同的斜效率,并对此作了分析。  相似文献   
974.
介绍一种研究红外吸收光谱的双光束光解方法。用紫外激光300nm解离在C6H12中的Cr(CO)6和用可见激光532nm解离Cr(CO)5.C6H12来研究Cr(CO)5的瞬态红外光谱。  相似文献   
975.
This paper presents a CMOS voltage controlled ring oscillator with temperature compensation for low power time-to-digital converters (TDCs). In order to maintain the oscillation frequency stable, a novel compensation circuit is proposed through adaptively sensing temperature variations. This design has been implemented in TSMC 0.35 μm CMOS standard process with an active area of under 0.039 mm2. Experimental results show that the clock frequency is around 159.0 MHz only with a power consumption of 550 μA. As respective to the room temperature the maximum frequency variation is between ?3.46 and +3.08 % under temperature range of ?40 to 85 °C. The bit error time induced by clock jitter is limited within 4.8 % in the whole clock period, and the differential nonlinearity of the TDC is less than 0.408 LSB.  相似文献   
976.
977.
Healable, adhesive, wearable, and soft human‐motion sensors for ultrasensitive human–machine interaction and healthcare monitoring are successfully assembled from conductive and human‐friendly hybrid hydrogels with reliable self‐healing capability and robust self‐adhesiveness. The conductive, healable, and self‐adhesive hybrid network hydrogels are prepared from the delicate conformal coating of conductive functionalized single‐wall carbon nanotube (FSWCNT) networks by dynamic supramolecular cross‐linking among FSWCNT, biocompatible polyvinyl alcohol, and polydopamine. They exhibit fast self‐healing ability (within 2 s), high self‐healing efficiency (99%), and robust adhesiveness, and can be assembled as healable, adhesive, and soft human‐motion sensors with tunable conducting channels of pores for ions and framework for electrons for real time and accurate detection of both large‐scale and tiny human activities (including bending and relaxing of fingers, walking, chewing, and pulse). Furthermore, the soft human‐motion sensors can be enabled to wirelessly monitor the human activities by coupling to a wireless transmitter. Additionally, the in vitro cytotoxicity results suggest that the hydrogels show no cytotoxicity and can facilitate cell attachment and proliferation. Thus, the healable, adhesive, wearable, and soft human‐motion sensors have promising potential in various wearable, wireless, and soft electronics for human–machine interfaces, human activity monitoring, personal healthcare diagnosis, and therapy.  相似文献   
978.
A wearable micro-sensor motion capture system with 16 IMUs and an error-compensatory complementary filter algorithm for real-time motion estimation has been developed to acquire accurate 3D orientation and displacement in real life activities. In the proposed filter algorithm, the gyroscope bias error, orientation error and magnetic disturbance error are estimated and compensated, significantly reducing the orientation estimation error due to sensor noise and drift. Displacement estimation, especially for activities such as jumping, has been the challenge in micro-sensor motion capture. An adaptive gait phase detection algorithm has been developed to accommodate accurate displacement estimation in different types of activities. The performance of this system is benchmarked with respect to the results of VICON optical capture system. The experimental results have demonstrated effectiveness of the system in daily activities tracking, with estimation error 0.16 ±0.06 m for normal walking and 0.13 ±0.11 m for jumping motions.  相似文献   
979.
Due to its significant applications in many relevant fields, light detection in the solar‐blind deep‐ultraviolet (DUV) wavelength region is a subject of great interest for both scientific and industrial communities. The rapid advances in preparing high‐quality ultrawide‐bandgap (UWBG) semiconductors have enabled the realization of various high‐performance DUV photodetectors (DUVPDs) with different geometries, which provide an avenue for circumventing numerous disadvantages in traditional DUV detectors. This article presents a comprehensive review of the applications of inorganic UWBG semiconductors for solar‐blind DUV light detection in the past several decades. Different kinds of DUVPDs, which are based on varied UWBG semiconductors including Ga2O3, MgxZn1?xO, III‐nitride compounds (AlxGa1?xN/AlN and BN), diamond, etc., and operate on different working principles, are introduced and discussed systematically. Some emerging techniques to optimize device performance are addressed as well. Finally, the existing techniques are summarized and future challenges are proposed in order to shed light on development in this critical research field.  相似文献   
980.
The simultaneous and efficient evolution of hydrogen and oxygen with earth‐abundant, highly active, and robust bifunctional electrocatalysts is a significant concern in water splitting. Herein, non‐noble metal‐based Ni–Co–S bifunctional catalysts with tunable stoichiometry and morphology are realized. The engineering of electronic structure and subsequent morphological design synergistically contributes to significantly elevated electrocatalytic performance. Stable overpotentials (η10) of 243 mV (vs reversible hydrogen electrode) for oxygen evolution reaction (OER) and 80 mV for hydrogen evolution reaction (HER), as well as Tafel slopes of 54.9 mV dec?1 for OER and 58.5 mV dec?1 for HER, are demonstrated. In addition, density functional theory calculations are performed to determine the optimal electronic structure via the electron density differences to verify the enhanced OER activity is related to the Co top site on the (110) surface. Moreover, the tandem bifunctional NiCo2S4 exhibit a required voltage of 1.58 V (J = 10 mA cm?2) for simultaneous OER and HER, and no obvious performance decay is observed after 72 h. When integrated with a GaAs solar cell, the resulting photoassisted water splitting electrolyzer shows a certified solar‐to‐hydrogen efficiency of up to 18.01%, further demonstrating the feasibility of engineering protocols and the promising potential of bifunctional NiCo2S4 for large‐scale overall water splitting.  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