全文获取类型
收费全文 | 23562篇 |
免费 | 3526篇 |
国内免费 | 1588篇 |
专业分类
化学 | 7285篇 |
晶体学 | 77篇 |
力学 | 496篇 |
综合类 | 139篇 |
数学 | 461篇 |
物理学 | 7433篇 |
无线电 | 12785篇 |
出版年
2024年 | 100篇 |
2023年 | 352篇 |
2022年 | 634篇 |
2021年 | 821篇 |
2020年 | 858篇 |
2019年 | 640篇 |
2018年 | 587篇 |
2017年 | 884篇 |
2016年 | 1024篇 |
2015年 | 1155篇 |
2014年 | 1698篇 |
2013年 | 1970篇 |
2012年 | 1823篇 |
2011年 | 1721篇 |
2010年 | 1305篇 |
2009年 | 1469篇 |
2008年 | 1475篇 |
2007年 | 1542篇 |
2006年 | 1286篇 |
2005年 | 1202篇 |
2004年 | 1009篇 |
2003年 | 820篇 |
2002年 | 657篇 |
2001年 | 492篇 |
2000年 | 459篇 |
1999年 | 371篇 |
1998年 | 358篇 |
1997年 | 286篇 |
1996年 | 255篇 |
1995年 | 235篇 |
1994年 | 152篇 |
1993年 | 178篇 |
1992年 | 160篇 |
1991年 | 111篇 |
1990年 | 104篇 |
1989年 | 80篇 |
1988年 | 82篇 |
1987年 | 57篇 |
1986年 | 45篇 |
1985年 | 48篇 |
1984年 | 32篇 |
1983年 | 26篇 |
1982年 | 46篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
71.
72.
Changes in thin zinc-sulfide films under the action of the γ-radiation of Co60 are studied by investigating electroluminescence spectra of terbium embedded in these films as a luminescent probe. It is
shown that changes in the relation of the intensities of bands, a decrease in their halfwidth and the background component,
and simplification of the spectrum are observed in a short-wave region of the Tb radiation spectrum that corresponds to5D3→7Fj transitions. The same modification of the radiation spectrum is characteristic of ZnS films whose crystalline structure is
ordered in the course of thermal annealing at a temperature of 350°C. Based on the analysis of the data obtained it is inferred
that irradiating the ZnS films with small radiation doses of 104–105 rad leads to the ordering of their crystalline structure due to the elimination of one of the types of structural defects.
Institute of Physics of Semiconductors, National Academy of Sciences of Ukraine, 45, Nauka Ave., Kiev-28, 252650. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 338–341, May–June, 1997. 相似文献
73.
一种探测二维电磁目标的新方法 总被引:2,自引:0,他引:2
电磁目标的探测对通信而言有着十分重要的意义。本文描述一种收敛迅速、结果准确、抗强随机噪声的探测二维电磁目标的新方法。首先从体等效原理出发得到一个积分方程组,此方程组可求解散射问题。随后,对此方程组求变分,变形后得到散射场变化与介电参数变化之间关系的矩阵方程,即反演方程。文中列举了几个例子,通过数值实验结果证明本法收敛速度快、反演精度高、适应复杂目标的能力强,能抗强随机噪声干扰 相似文献
74.
A. P. Prishivalko 《Journal of Applied Spectroscopy》1997,64(1):94-100
A method for finding the optimum sizes of pigment particles, their volume concentration, and the paint coating thickness that
provide the covering power and the required coloristic characteristics of reflected light for the minimum flow rate of pigments
is based on using a four-flow approximation of the solution to the equation of radiation transfer in dispersion media and
is extended to coatings of complex composition. The capabilities of the method are demonstrated by examples of coatings of
mixtures of hematite and rutile particles in a binder with n=1.5 for variations of the modal size and the half-width of the
size distribution of the pigment particles.
B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 90–96, January–February, 1997. 相似文献
75.
A highly sensitive method for infrared radiation detection based on thermal resonance in an active bolometer is set forth. An active bolometer is a self-oscillating system consisting of an IR-sensitive cell in a feedback circuit of an adjustable proportional controller. The analysis of an active bolometer autonomous (dark) dynamics reveals that with a generalized gain factor A variation the system evolves from relaxation type towards oscillating and self-oscillating type. When A=Ac, where Ac is a critical value of the generalized gain factor A, the steady state loses stability through self-excited thermal oscillations. The resonance in a system weakly perturbed by IR radiation modulated at self-oscillation frequency q0[1+exp(iωct)] is considered. It is shown that in a small precritical vicinity =(A−Ac)/Ac of the gain factor the amplitude of forced thermal oscillations is proportional to q0/Ac. The D* calculation reveals that the detection power of a passive (A=0) bolometer increases with feedback introduction by a factor of 1/||. The detection powers of feasible versions of an active bolometer are compared. 相似文献
76.
77.
提出利用测量设备与辐射源相对运动速度及测量设备所接收到的辐射功率的估算测量设备到辐射源距离的一种方法。对计算精度进行了分析,通过算例对理论分析进行了检验。 相似文献
78.
79.
利用梯度方向信息的随机Hough变换 总被引:17,自引:0,他引:17
针对随机Hough变换(RHT)在处理复杂图像随机采样造成的大量无效积累提出一种改进的用于直线检测的RHT,较发地解决了无效果累积问题,并使改进后的算法具有计算速度更快,占用内存更少以及检测性能更好等优点。 相似文献
80.
I.IntroductionWhenastructurcvibratcs,itsvibratingsurfacewillmakesurroundingmediummovetogethcrwithit.Ifthernotionissofastthatthcmediumroundthestructureproduccaloca1contractionandcxpansionandthcypropagatefaraway,thesoundradiationisformed.Itispossiblctodcscribeanalytica11ytheradiationfic1dofsimplyandregularlyshapcdsourcessuchaspointsoundsourccs,spherica1soundsourccsandinflnite1engthllnearsoundsourccs,butitisa1mostimpossib1ctosolvetheradiationfiledbyanyanalyt-ica1methodforsourcesofvcrycomplicateds… 相似文献