全文获取类型
收费全文 | 10480篇 |
免费 | 1858篇 |
国内免费 | 968篇 |
专业分类
化学 | 3730篇 |
晶体学 | 128篇 |
力学 | 888篇 |
综合类 | 168篇 |
数学 | 2356篇 |
物理学 | 6036篇 |
出版年
2024年 | 14篇 |
2023年 | 100篇 |
2022年 | 237篇 |
2021年 | 267篇 |
2020年 | 298篇 |
2019年 | 263篇 |
2018年 | 269篇 |
2017年 | 395篇 |
2016年 | 404篇 |
2015年 | 368篇 |
2014年 | 561篇 |
2013年 | 889篇 |
2012年 | 664篇 |
2011年 | 741篇 |
2010年 | 601篇 |
2009年 | 681篇 |
2008年 | 665篇 |
2007年 | 698篇 |
2006年 | 631篇 |
2005年 | 522篇 |
2004年 | 494篇 |
2003年 | 448篇 |
2002年 | 362篇 |
2001年 | 370篇 |
2000年 | 303篇 |
1999年 | 255篇 |
1998年 | 253篇 |
1997年 | 218篇 |
1996年 | 184篇 |
1995年 | 150篇 |
1994年 | 120篇 |
1993年 | 115篇 |
1992年 | 101篇 |
1991年 | 90篇 |
1990年 | 55篇 |
1989年 | 58篇 |
1988年 | 68篇 |
1987年 | 47篇 |
1986年 | 44篇 |
1985年 | 36篇 |
1984年 | 40篇 |
1983年 | 20篇 |
1982年 | 36篇 |
1981年 | 23篇 |
1980年 | 37篇 |
1979年 | 40篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1974年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
61.
一个关于勒让德多项式的积分公式及其简单应用——圆形带电环和电流环的静态电磁势 总被引:1,自引:0,他引:1
给出了一个关于勒让德多项式的积分公式及其证明,用该公式和叠加法方便快捷地导出了圆形带电环和电流环的静态电磁势. 相似文献
62.
In an ADS injector i, there are five superconducting magnets in each cryomodule. Each superconducting magnet contains a solenoid magnet, a horizontal dipole corrector (HDC), and a vertical dipole corrector (VDC). Six current leads will tm required to power the electrical circuits, from room temperature to the 2.1 K liquid helium bath: two leads carry 100 A current for the solenoid magnet while the other four carry 12 A for the HDC and the VDC. This paper presents the principle of current lead optimization, which includes the cooling methods, the choice of material and structure, and the issues for current lead integration. 相似文献
63.
On the basis of the electromagnetic field mode matching theory, the coupling efficiency ratio from spatial light to Bragg fiber is analyzed, which shows that the coupling efficiency ratio is related to the radius of focused facular, the core radius of Bragg fiber and wave number of the core. By optimizing the value of such parameters appropriately, the Bragg fiber coupling efficiency ratio can be improved. It is also important for the analysis of the coupling efficiency of Bragg fiber, which can be applied to the free optical communication system and laser radar system. 相似文献
64.
The band artifact in steady-state free precession can be reduced by synthesizing the multiple images obtained through different phase increments of successive radiofrequency pulses. Even though the complex summation method was reported to be effective in reducing the band artifact, it has the pitfalls of intensity abnormality and sensitivity to the phase abnormality. Two new methods have been developed for more reliable reduction of the band artifact than the complex summation method. One method is to sum the complex images partially and to take the maximum intensity of the partially summed images. The other method is to sum the free induction decay (FID) and primary echo components of the Fourier series that are obtained through Fourier analysis of the complex base images. Both proposed methods were compared with other magnitude (maximum intensity projection, spectrally decomposed synthesis, sum-of-squares, nonlinear averaging) and complex-based (complex summation, magnitude-weighted complex summation) methods experimentally at 3 T for the phantom and volunteer's head imaging. Both proposed methods were confirmed to maintain the advantage of the complex summation in reducing both the dark and bright band artifacts while reducing the intensity abnormality and sensitivity to the phase abnormality from that of the complex summation method over a wide range of flip angles and relaxation times. 相似文献
65.
Current in heterogeneous tunnel junctions is studied in the framework of the parabolic conduction-band model. The developed model of the electron tunneling takes explicitly into account the difference of effective masses between ferromagnetic and insulating layers and between conduction subbands. Calculations for Fe/MgO/Fe-like structures have shown the essential impact of effective mass differences in regions (constituents) of the structure on the tunnel magnetoresistance of the junction. 相似文献
66.
一种新型桥路型HTSFCL的实验研究 总被引:2,自引:0,他引:2
在研究一种新型桥路型高温超导限流器的限流原理的基础上,研制开发了一台三相600V、故障电流峰值100A的实验室样机.本文介绍了该限流器的功率电路、控制器、低温容器和高温超导磁体等部分的结构特点和功能.在三相系统中进行了各种短路故障限流实验,结果表明该限流器有较强的限流能力和重合闸能力,说明新型高温超导限流器的研究对改善电网动态性能和提高电网电能质量有十分重要的意义. 相似文献
67.
Derivation of two point spread functions PSFs suitable for infrared thermograms analysis is illustrated, based on two unique approaches, one based on depth decaying limit and one on diffusion limit. Experimental work using PMMA sample with back drilled holes and pulsed thermographic routine is utilized to show the effectiveness of deconvoluting pixel temperature transient history with suggested PSF’s. Synthetic second time derivative thermograms are utilized for comparison and the signal to noise ratio is used as a figure of merit for quantification. 相似文献
68.
69.
太阳能电池基本特性测定实验 --一个与能源利用有关的综合设计性实验 总被引:7,自引:0,他引:7
“太阳能电池基本特性测定”是与能源利用有关的新的综合性设计实验.本文简述了该实验的原理、实验方法及测量结果,得出了太阳能电池基本参数短路电流Iac,开路电压Uoc与太阳能电池接收到的相对光强度J/Jn的近似函数关系。 相似文献
70.
本文以煤气化(240万吨/年)动力,液体燃料(甲醇,醋酸,醋酐)多联产系统(串联式)为研究对象,分析了循环倍率对系统动力输出、蒸汽、液体燃料产量的影响;确定了可满足具有不同优先级的目标、达到系统动力和蒸汽自平衡的循环倍率、燃气轮机选型等关键单元和系统参数。 相似文献