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   11779篇
  免费   1550篇
  国内免费   922篇
化学   6740篇
晶体学   123篇
力学   413篇
综合类   51篇
数学   845篇
物理学   2932篇
无线电   3147篇
  2024年   24篇
  2023年   272篇
  2022年   272篇
  2021年   405篇
  2020年   423篇
  2019年   397篇
  2018年   321篇
  2017年   284篇
  2016年   512篇
  2015年   486篇
  2014年   592篇
  2013年   794篇
  2012年   991篇
  2011年   989篇
  2010年   630篇
  2009年   685篇
  2008年   774篇
  2007年   740篇
  2006年   650篇
  2005年   623篇
  2004年   394篇
  2003年   315篇
  2002年   337篇
  2001年   263篇
  2000年   247篇
  1999年   223篇
  1998年   201篇
  1997年   146篇
  1996年   146篇
  1995年   180篇
  1994年   153篇
  1993年   122篇
  1992年   107篇
  1991年   86篇
  1990年   80篇
  1989年   41篇
  1988年   52篇
  1987年   40篇
  1986年   41篇
  1985年   38篇
  1984年   26篇
  1983年   15篇
  1982年   29篇
  1981年   16篇
  1979年   9篇
  1978年   10篇
  1977年   8篇
  1976年   7篇
  1975年   7篇
  1971年   7篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
新疆野生黑加仑与马林果实的营养成分分析   总被引:2,自引:0,他引:2  
通过对新疆野生黑加仑和野生马林的脂肪油,8种微量元素,17种氨基酸以及维生素C的含量进行测定得出:黑加仑脂肪油含量为17.9%,马林的脂肪油含量为22.3%,其中,黑加仑脂肪油中,r-亚麻酸的含量为19.02%,而马林中,其含量为9.40%,黑加仑中K,Na,Ca,Cu,Zn,Fe的含量比马林中的含量高,而Mn,Mg元素的含量却比马林含量低;马林的维生素C含量为16.22mg/g,黑加仑的含量为108mg/g,黑加仑的氨基酸的总量为1.63%,马林为1.14%。  相似文献   
62.
Using polarized neutron reflectivity (PNR) measurements together with associated simulation, magnetic structures of two Ni80Fe20 (1 1 1)/Ru (0 0 0 1) multilayer samples with Ru thickness of 9 and 21 Å were investigated under various external magnetic fields at room temperature. The results reveal the existence of layer thickness, interface roughness, magnetic moment, interlayer coupling angle and non-collinear coupling. The former three are independent of Ru thickness; while the latter two are strongly dependent of Ru thickness.  相似文献   
63.
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant.  相似文献   
64.
本文利用比较原理以及一种特殊变换研究了一类非线性退化方程的混合问题,得到了这类复杂问题解的渐进性质。  相似文献   
65.
In this work, we present both the theoretical basis as well as supporting experimental measurements for development of a novel mid-infrared thermally stimulated narrow band emitter with a spectral bandwidth of less than 10%. To achieve this, we utilize a metallized-surface 2D photonic crystal of air voids in a silicon background with hexagonal structure symmetry. Our results are based on the generation of discrete surface plasmon (SP) modes in the thin metallized layer residing on the top surface. This yields a series of adequately spaced discrete peaks in the reflection spectrum, dominated by a single sharp feature corresponding to the lowest plasmon order, in an otherwise uniform highly reflective spectrum (>90%) over most of the IR spectrum. This, in turn, gives rise to a sharp absorption feature with a correspondingly narrow thermal emission peak in the emission spectrum. Transfer matrix calculations simulate well both the position and strengths of the absorption peaks. By altering the period of the surface photonic lattice, the SP peak and emissive band can be tuned to the desired wavelength. These devices promise a new class of tunable infrared emitters with high power in a narrow spectral bandwidth. Such narrow band sources are critical to achieving high efficiency gas sensors.  相似文献   
66.
几种常见光源特性的研究   总被引:2,自引:1,他引:1  
本通过大学物理实验中常用光源特性的分析,说明了实验中光源使用的合理性。  相似文献   
67.
A method called visual computing was used to solve angular four-components' proportions and directional vegetation cover fraction for discrete canopies and continuous row-planted plants. It proved effective to predict the angular characteristics on pixel scale. The method could be an alternative way to a classical solution of geometrical optical models. A visual computing method would be effective especially when the canopies' spatial distribution and shapes were irregular and could not be described statistically.  相似文献   
68.
This paper presents a closed-loop optimally controlled force-sensing technology with applications in both micromanipulation and microassembly. The microforce-sensing technology in this paper is based on a cantilevered composite beam structure with embedded piezoelectric polyvinylidene fluoride (PVDF) actuating and sensing layers. In this type of sensor, the application of an external load causes deformation within the PVDF sensing layer. This generates a signal that is fed through a linear quadratic regulator (LQR) optimal servoed controller to the PVDF actuating layer. This in turn generates a balancing force to counteract the externally applied load. As a result, a closed feedback loop is formed, which causes the tip of this highly sensitive sensor to remain in its equilibrium position, even in the presence of dynamically applied external loads. The sensor's stiffness is virtually improved as a result of the equilibrium position whenever the control loop is active, thereby enabling accurate motion control of the sensor tip for fine micromanipulation and microassembly. Furthermore, the applied force can be determined in real time through measurement of the balance force.  相似文献   
69.
脉冲电镀最佳参数之探索和优化   总被引:3,自引:0,他引:3  
本文利用正交实验法对脉冲电镀各控制参数进行试验,对影响分散能力、镀层可靠性及外观质量的各种因素进行探讨,寻找影响外观质量的显著因子并加以控制,同时进一步优化脉冲电镀的工艺参数。  相似文献   
70.
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