全文获取类型
| 收费全文 | 718篇 |
| 免费 | 200篇 |
| 国内免费 | 229篇 |
专业分类
| 化学 | 479篇 |
| 晶体学 | 21篇 |
| 力学 | 89篇 |
| 综合类 | 52篇 |
| 数学 | 105篇 |
| 物理学 | 401篇 |
出版年
| 2024年 | 9篇 |
| 2023年 | 10篇 |
| 2022年 | 30篇 |
| 2021年 | 25篇 |
| 2020年 | 29篇 |
| 2019年 | 26篇 |
| 2018年 | 24篇 |
| 2017年 | 30篇 |
| 2016年 | 30篇 |
| 2015年 | 27篇 |
| 2014年 | 40篇 |
| 2013年 | 53篇 |
| 2012年 | 58篇 |
| 2011年 | 69篇 |
| 2010年 | 79篇 |
| 2009年 | 62篇 |
| 2008年 | 62篇 |
| 2007年 | 53篇 |
| 2006年 | 59篇 |
| 2005年 | 52篇 |
| 2004年 | 48篇 |
| 2003年 | 38篇 |
| 2002年 | 26篇 |
| 2001年 | 44篇 |
| 2000年 | 41篇 |
| 1999年 | 14篇 |
| 1998年 | 5篇 |
| 1997年 | 10篇 |
| 1996年 | 7篇 |
| 1995年 | 10篇 |
| 1994年 | 11篇 |
| 1993年 | 13篇 |
| 1992年 | 7篇 |
| 1991年 | 6篇 |
| 1990年 | 5篇 |
| 1989年 | 6篇 |
| 1988年 | 7篇 |
| 1987年 | 5篇 |
| 1986年 | 4篇 |
| 1985年 | 3篇 |
| 1983年 | 1篇 |
| 1982年 | 1篇 |
| 1981年 | 2篇 |
| 1979年 | 1篇 |
| 1966年 | 2篇 |
| 1965年 | 1篇 |
| 1959年 | 1篇 |
| 1958年 | 1篇 |
排序方式： 共有1147条查询结果，搜索用时 15 毫秒
41.
高分子电致发光显示器(PLED)是近几年来国际、国内的研究热点,取得了很大的进展,其中高分子化金属配合物是一类很有价值的功能材料。通过甲基丙烯酸甲酯(MMA)、苯乙烯(S)和含有8-羟基喹啉的单体共聚合成模板聚合物,再与氢氧化锂作用,实现了8-羟基喹啉锂配合物的高分子化,获得了一种能够溶解在普通的溶剂中的高相对分子质量的含喹啉锂配合物的发光聚合物,并利用元素分析、1H-NMR、FTIR、UV、PL光谱、DSC、TGA、GPC等方法对其结构和性能作了表征。紫外吸收和光致发光(PL)光谱说明合成共聚物的发光来自于Liq基团,引入的可聚合的链段以及共聚物中的甲基丙烯酸甲酯或苯乙烯链段,并没有影响发光波长的改变。亲核溶剂改变8-羟基喹啉金属配合物分子结构,使共聚物光谱明显红移20nm左右。 相似文献
42.
船用加筋板架爆炸载荷下动态响应数值分析 总被引：15，自引：0，他引：15
针对船用加筋板架复杂结构在爆炸冲击波作用下的动态响应 ,采用商用高动态非线性有限元程序MSC/Dytran ,讨论了大尺寸加强结构板架迎爆承载问题 ,提出了复杂板架结构爆炸冲击波作用下动态响应的有限元计算方法 ,并进行了模型试验。试验结果与计算结果吻合较好 ,验证了应用程序及计算模型参数的稳定性和可靠性。对加筋板架两种承载形式 (大尺寸加强构件迎爆或背爆设置 )在爆炸冲击波作用下的动态响应 (板架中心挠度和塑性分布 )差异的分析研究表明 ,大尺寸骨架 (纵骨和肋骨 )背向爆炸冲击波设置将分散爆炸冲击波的冲击作用、减小板架变形、增强其抵抗爆炸冲击波冲击的能力 ,使结构偏于安全。 相似文献
43.
本文提出了一种基于改进傅里叶级数的新型数值算法,用于求解任意边界条件下黏弹性夹层板的自由振动特性。该算法利用一阶剪切理论建立面外位移场,采用改进的傅里叶级数拟合位移容许函数,结合Rayleigh-Ritz法计算动能和势能,并利用Hamilton变分原理得到振动特征矩阵方程。计算结果表明,无论是梁式板结构还是各种边界条件下的夹层板结构,该算法得到的自振频率和损耗因子与解析解、2D有限元解、数值计算法和ABAQUS有限元软件等计算结果相比,误差均不超过1%,计算效率提高了10倍,并且克服了传统方法只能求解特定边界下振动问题的局限性。本文建立的方法具有收敛性好、计算效率高和适应性强等特点。 相似文献
44.
制备了基于普鲁士蓝(PB)、石墨烯(GN)、壳聚糖(Chi)的纳米复合物(PB@GN-Chi),并将其修饰在玻碳电极表面制得microRNA电化学传感器。实验发现,GN可有效提高敏感膜的导电性能和比表面积,增强PB在电极表面的稳定性和传感器的重现性。通过戊二醛的交联作用,将氨基化的捕获探针(ssDNA)固载在PB@GN-Chi修饰的电极表面,并用于miR-21的检测。以透射电子显微镜对纳米复合物的形态进行表征,采用循环伏安法、示差脉冲伏安法对传感器的电化学特性进行研究。实验结果表明,该传感器具有良好的稳定性和重现性,在2.8~2.8×104pmol/L浓度范围内,响应电流与miR-21浓度的对数呈线性关系,检出限为0.87pmol/L,可用于miR-21的检测。 相似文献
45.
稀疏矢量阵进行宽带信号处理时,强目标的栅瓣及对称伪峰会干扰弱目标的检测,提出了一种基于理论干扰预测的加权抑制方法。方法利用矢量阵波束形成先获得强目标的波达方向(Direction Of Arrival,DOA)信息以及目标所在方位各频率的幅度谱信息,再利用理论计算公式获得强目标的栅瓣和对称伪峰角度上对应的各频率点的幅度谱强度信息,通过在方位、频率维度加权的方式对强目标的栅瓣和伪峰干扰进行抑制,来改善在强干扰下的弱目标检测能力。方法也适用于多目标情况,对各个目标依次使用,减少多目标时栅瓣和对称伪峰对方位历程的影响,净化了时间方位历程图。对所提方法给出了理论推导过程并进行了仿真和实验验证,实验结果验证可行。结果表明,新方法可以有效地抑制强目标的栅瓣和对称伪峰干扰,提高弱目标的检测能力,此外,净化后的时间方位历程图更利于弱目标检测和目标数量的估计。 相似文献
46.
该文采用非变性电喷雾质谱法(Nativeelectrosprayionizationmassspectrometry,ESI-MS)与分子对接模拟计算(MD)分别研究了1种溴代阻燃剂和2种羟基化代谢物,即3,5,3′,5′四溴4,4′二羟基基二苯砜(TBS)、4羟基2,2′,3,4′,5,5′,6八溴联苯醚(4OH-BDE-187)、6羟基2,2′,3,4,4′,5,5′八溴联苯醚(6OH-BDE-180)与甲状腺素运载蛋白(TTR)的相互作用情况。ESI-MS结果表明,在37℃及生理pH值条件下的醋酸铵缓冲溶液中,TBS与TTR蛋白可形成稳定的化学计量比为1∶1的复合物,4OH-BDE-187、6OH-BDE-180可与TTR蛋白分别形成稳定的化学计量比为1∶1和2∶1的复合物。通过分子对接模拟计算方法推测了上述3种配体与TTR可能的结合模型,发现3种配体与TTR的结合位点位于ASP-74残基附近。研究结果可为进一步了解溴代阻燃剂及其羟基化代谢产物体内的生物过程及毒性机制提供实验基础。 相似文献
47.
LIU Shiwei;MEI Haiping;REN Yichong;TAO Zhiwei;Azezigul Abdukirim;ZHANG Junxin;LI Yanling;RAO Ruizhong 《光子学报》2022,51(11):314-325
Compared with interferometry and shadowgraph, Background Oriented Schlieren（BOS） has significant advantages of a large field of view and low cost as a new flow field measurement technology. Developed on the basis of traditional schlieren technology and modern image processing technology, BOS has developed rapidly and has been widely used in a variety of flow field measurements and displays since its invention in 1998, such as combustion field diagnosis, temperature field visualization and density field reconstruction. Consists of a random background, a flow field and an image acquisition and processing system, the device of BOS is simple and can be used in a variety of scenarios, but it also has the limitation of over-reliance on background and algorithms because the core of this technology lies in the use of image processing algorithms, the displacement of pixels are calculated by comparing the original background without the flow field and the disturbing background after passing through the flow field. Furthermore, the pixel offset of the image represents the refractive index gradient of the flow field. In theory, the refractive index can be reconstructed from the gradient with the phase reconstruction algorithm, which is of great significance in the study of flow field structure and fluid characteristics. Firstly, the influence of five different dense optical flow algorithms such as Farneback, Sparsetodense, Deepflow, Pcaflow and Dualtvl1 and the background under different brightness, contrast and correlation on the displacement detection accuracy is analyzed by bilinear interpolation. The research found the following rules： 1） the Farneback algorithm takes the least time and has the best stability as well as the highest accuracy; 2） among the optional parameters of Farneback, the average window size ought to be determined according to the pixel displacement, and the number of iterations should not be too much to avoid time-consuming; 3） the detection accuracy of the optical flow algorithm is negatively correlated with the image correlation, positively correlated with the image contrast, and almost independent of the brightness; 4） under the appropriate algorithm and background, the displacement detection accuracy of the BOS system can be up to 1/400 subpixel. Secondly, after obtaining the pixel offset through the optical flow algorithm, according to the quantitative relationship between the background image displacement and the flow field wavefront gradient, the flow field wavefront can be reconstructed by the Fourier transform method and the iterative method respectively. The Antisymmetric Partial Derivative Integral （ASDI） method is a type of Fourier transform. A least squares error model between the measured slope and the actual slope of the wavefront is constructed firstly, and the integral operation in the space domain is mapped to a linear combination of Fourier primary functions in the frequency domain,and the original gradient matrix is filled and expanded to twice, and then the optimal solution is obtained. The main idea of the Guass-Seidl （GS） iteration method is to generate the current latest refractive index value by iteration, and use the latest value to calculate the next step of the latest parameter, and bring it into the calculation of the refractive index of the surrounding points, and so on until the convergence condition is reached. After numerical simulation, we draw the following conclusions： 1） the ASDI is faster but has lower accuracy, which can be applied to real-time processing; 2） the GS iterative method is slower but more accurate and can be used for post-processing. In practical application, we can choose the appropriate algorithm according to our needs. Finally, a set of high-precision background oriented schlieren flow field detection system was built. In the laboratory, the laser speckle pattern is used as the background, and the temperature pressure gradient is generated by the alcohol lamp combustion as the flow field. After processing the background pictures before and after the alcohol combustion with the algorithm, the obvious fluctuation of the optical path difference above the flame can be clearly seen. In the natural environment, with the forest as the background and the huge sound pressure gradient generated by the gun barrel as the flow field, images were continuously collected, and the propagating sound waves were seen after algorithm processing. The above two experiments prove that under different conditions, the BOS device can achieve both qualitative observation and quantitative measurement. The high-precision background schlieren system is simple in device and mature in the algorithm. In addition to the temperature pressure field and sound pressure field shown in this paper, the refractive index obtained by BOS can also be used for temperature and density calculation of thermal field or density field. The extracted wavefront information also helps to further study the flow field structure, and has a wide range of application prospects in scientific research such as adaptive optics and target detection, as well as in industrial fields such as precision instrument detection, engine performance improvement, aerodynamic shape optimization and so on. 相似文献
48.
为探究晶粒尺寸对硬脆性岩石岩爆的影响,利用真三轴岩爆试验系统,对细中、中粗两种不同晶粒尺寸的含预制圆孔花岗岩开展了岩爆模拟试验。试验结果表明：在相同的加载过程中,细中晶粒花岗岩出现板裂静态脆性破坏,而中粗晶粒花岗岩出现岩爆动力破坏;细中晶粒花岗岩早期声发射活动较弱,大破裂、低主频事件在时空分布上较集中,特征应力较大,而中粗晶粒花岗岩早期声发射活动较活跃,大破裂、低主频事件在时空分布上较离散,特征应力较小,碎屑破碎程度更高。晶粒尺寸对花岗岩的岩爆倾向性具有重要影响,晶粒尺寸较大的硬脆性岩石的岩爆倾向性更强。深部地下岩体工程的岩爆倾向性评价中,除强度和脆性外,晶粒尺寸也是需要考虑的重要因素。 相似文献
49.
50.