全文获取类型
收费全文 | 5161篇 |
免费 | 1445篇 |
国内免费 | 459篇 |
专业分类
化学 | 2111篇 |
晶体学 | 121篇 |
力学 | 327篇 |
综合类 | 100篇 |
数学 | 357篇 |
物理学 | 4049篇 |
出版年
2024年 | 11篇 |
2023年 | 67篇 |
2022年 | 145篇 |
2021年 | 174篇 |
2020年 | 184篇 |
2019年 | 191篇 |
2018年 | 212篇 |
2017年 | 295篇 |
2016年 | 300篇 |
2015年 | 294篇 |
2014年 | 385篇 |
2013年 | 459篇 |
2012年 | 368篇 |
2011年 | 433篇 |
2010年 | 313篇 |
2009年 | 356篇 |
2008年 | 338篇 |
2007年 | 314篇 |
2006年 | 273篇 |
2005年 | 253篇 |
2004年 | 236篇 |
2003年 | 233篇 |
2002年 | 199篇 |
2001年 | 167篇 |
2000年 | 144篇 |
1999年 | 125篇 |
1998年 | 102篇 |
1997年 | 79篇 |
1996年 | 75篇 |
1995年 | 52篇 |
1994年 | 47篇 |
1993年 | 30篇 |
1992年 | 30篇 |
1991年 | 24篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1973年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有7065条查询结果,搜索用时 578 毫秒
21.
I.IntroductionThepcrformanccsofAcousto-optic(AO)dcviccareoftenlimitcdbythepropertiesofAOmcdiawhenitisusedinAOsigna1processingsystems.Thespectrumanalyzersandcorre1ationreceivers,forinstancc,areexpcctcdtoimprovcthereso1utionanddynamicrangcwhilereducingtheproccssorvolume.Rccent1y,ancwclassofmateria1s,themercurousha1ides,promiscstocontributeimportantsolutionstosuchnccdsandisrefincdtopractica1uti1izations.Themecurousha1ideweconsidcrinthispapcrismecurouschloride(Hg,C1,).Thesing1ecrystalofHg,Cl… 相似文献
22.
新型X射线靶设计为:由SiO2和TiO2组成具有12个周期的一维光子晶体,在它的中间嵌入光靶材料层作为缺陷层,SiO2,TiO2和光靶层的光学厚度分别为λ4、λ4和λ2,λ为抽运激光波长.与普通平板光靶相比,当抽运光垂直照射到这种光靶时,靶层内部的光强将提高2个数量级,所以抽运激光的阈值强度将降低2个数量级,这有利于X射线激光的小型化.在同样的抽运激光照射下,X射线激光的强度将提高4个数量级,转换效率也将提高约4个数量级.由于平均电离度随抽运激光强度的提高而提高,所以采用这种光靶有利于使X射线激光向短波长推进.
关键词:
X射线激光
光子晶体
光波局域 相似文献
23.
为提高CCD摄像机的成像质量,同时使镜头结构紧凑、小型化,在大视场光学镜头的设计中,引入标准二次曲面和偶次非球面。根据初级像差理论,分析了非球面的位置、初始结构参数的求解规律。通过理论计算和ZEMAX光学设计软件的优化,给出工作波长为0.4~0.7μm、全视场角为80°,相对孔径为1∶1.5的镜头设计实例。该镜头由7块镜片组成,包括一个标准二次曲面和两个8次方非球面;在40lp/mm空间频率处的MTF值超过0.85,全视场畸变小于3%,像质优良 相似文献
24.
This paper describes the performance and simulation of a compact integrated optical processor for the real-time reconstruction of two-dimensional images in airborne stripmap synthetic aperture radar applications. The functional behavior of the processor is explained in some detail. The design criteria are briefly given. The simulation step allowed the main processor characteristics and properties to be identified. A number of comparisons were obtained in airborne SAR mission scenarios between the predictions of the optical device and those achieved by the modern electronic digital approach, based on the wavefront reconstruction method by matched filtering. 相似文献
25.
Tunable properties of light propagation in photonic crystal fibers filled with liquid crystals, called photonic liquid crystal
fibers (PLCFs) are presented. The propagation properties of PLCFs strongly depend on contrast between refractive indices of
the solid core (pure silica glass) and liquid crystals (LCs) filing the holes of the fiber. Due to relatively strong thermo-optical
effect, we can change the refractive index of the LC by changing its temperature. Numerical analysis of light propagation
in PLCF, based on two simulation methods, such as finite difference (FD) and multipole method (MM) is presented. The numerical
results obtained are in good agreement with our earlier experimental results presented elsewhere [1]. 相似文献
26.
The signals of a single-pulse echo (SE) generated on nonresonant excitation of an inhomogeneously broadened two-level system by a radio-frequency pulse (RFP), against the background of which a magnetic video pulse (MVP) of certain length has been switched on, have been described analytically. It is established that under the conditions of such excitation several SE signals are formed whose generation moments are determined by the duration and amplitudes of the RFP and MVP. The amplitudes of some of these signals depend on the Rabi frequency according to a quadratic law, and the amplitudes of others depend on this frequency according to a biquadratic law. It has been established that the mechanism underlying the appearance of these signals is associated with zero beats arising as a result of superposition of the magnetization fluctuations at variable frequencies and at a frequency of detuning from resonance. It is shown that in the limiting case, where the RFP duration considerably exceeds the duration of the MVP or is comparable with it, the number of SE signals decreases to two. Theoretical results on the formation of SE and the dependence of the amplitude of these signals on the MVP amplitude agree with the experimental data on NMR pulsed signals in ferromagnetic materials. 相似文献
27.
28.
本文用准平衡模型分析讨论了线性电压扫描下MIS器件的I/V瞬态.文中除了给出一般的处理方法以外,还给出了几种不同电压扫描率下I/Y特性的计算结果,并与已往的模型作了比较. 相似文献
29.
在利用Harris两参数公式研究Bohr-Mottelson转动谱公式参数之间的关系的基础上,改用Harris三参数公式,并由此提出了Bohr-Mottelson转动谱公式参数之间的新关系式,进而用I(I+1)四参数展开式计算了A~60,80,130,140,150,190区超形变偶偶核的基带和锕系和稀土区正常形变核基带,讨论了参数之间的关系,发现新关系式与实验较好地符合. 相似文献
30.
Gap length (GL) of reading head is one of the most critical parameters for high-density magnetic recording systems. A novel method is proposed for quantitative evaluation of the GL fluctuation among a batch of magneto-resistive/giant magneto-resistive heads with same structure design. The method works at head-gimbal assembly level and the evaluation can be done with any read/write analysis equipment. The testing process is based on harmonic analysis of the readback signal. The testing system consists of a selected reference head and sample heads for evaluation. A GL variation function is introduced for the evaluation of GL deviation between the reference head and sample head. This method proved to be easy for implementation and results suggest that variation of GL is considerable and has obvious effect on recording performance in high recording density systems. 相似文献