全文获取类型
收费全文 | 8581篇 |
免费 | 1368篇 |
国内免费 | 714篇 |
专业分类
化学 | 5804篇 |
晶体学 | 86篇 |
力学 | 570篇 |
综合类 | 42篇 |
数学 | 1040篇 |
物理学 | 3121篇 |
出版年
2023年 | 162篇 |
2022年 | 197篇 |
2021年 | 259篇 |
2020年 | 376篇 |
2019年 | 313篇 |
2018年 | 274篇 |
2017年 | 255篇 |
2016年 | 417篇 |
2015年 | 413篇 |
2014年 | 465篇 |
2013年 | 605篇 |
2012年 | 796篇 |
2011年 | 773篇 |
2010年 | 547篇 |
2009年 | 502篇 |
2008年 | 567篇 |
2007年 | 433篇 |
2006年 | 471篇 |
2005年 | 346篇 |
2004年 | 274篇 |
2003年 | 235篇 |
2002年 | 184篇 |
2001年 | 152篇 |
2000年 | 170篇 |
1999年 | 184篇 |
1998年 | 170篇 |
1997年 | 140篇 |
1996年 | 134篇 |
1995年 | 117篇 |
1994年 | 101篇 |
1993年 | 83篇 |
1992年 | 83篇 |
1991年 | 80篇 |
1990年 | 44篇 |
1989年 | 45篇 |
1988年 | 44篇 |
1987年 | 36篇 |
1986年 | 28篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 9篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1970年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Ga1-xInxAs(x>0.53)材料是未来长距离低损耗光纤通信的理想光源材料和探测器材料之一.我们采用水平常压MOCVD系统,在InP衬底上成功地生长了Ga1-xInxAs(x>0.53)/InAsyP1-y/Inp异质结材料.其中InAs1-yPy为组份阶梯变化的多层结构.由样品的(400)面X光衍射结果测定了各层组份.由二次离子质谱(SIMS)得到了样品剖面组份变化结果,证明InAs1-yPy层组份为阶梯状变化的.通过对光致发光结果和X光衍射结果比较,可以看到,InAsyP1-y层通过位错和弹性畸变二种方式来释放或积累Ga1-xInxAs与InP间的失配应力,从而减少了Ga1-xInxAs中的失配位错.有效地改善了Ga1-xInxAs的质量.已获得了x高达0.94表面光亮的Ga1-xInxAs/InAs1-yPy/InP异质结材料. 相似文献
42.
Xiangdong Liu Hongwei Liu Kexu Yuan Huiping Du 《International Journal of Infrared and Millimeter Waves》1991,12(9):1023-1034
According to the angular-spectrum method, a radiation beam of an antenna horn in the Fresnal region is decomposed into the plane waves with the fast Fourier transform algorithm and the waves diffracted from a reflection grating are superposed as a diffracted beam. Compared with the reflected beam from the same size mirror, the radiation half width of the diffracted beam from a grating is narrower and its lateral shape is shift. These performances have been experimentally verified at Ka-band by: (1). The relative diffraction efficiencies in the first order with two triangular gratings which is put along propagating direction of a beam produced by a conical lens-horn. (2). H-plane lateral width with power—3dB lapsed of the focus beam from a grating and a mirror in a grating spectrometer for millimeter waves (25–100 GHz). 相似文献
43.
测定了室温下烃类(乙炔、乙烷)烟粒的红外复折射率,并讨论了所获数据在测量烟浓度与烟粒大小分类、计算光谱吸收系数及在特定浓度与温度下评估烟雾辐射率方面的应用。 相似文献
44.
基于RBC模型的动态随机一般均衡的数值解 总被引:1,自引:0,他引:1
以一般均衡为框架,引入随机变量的动态随机一般均衡系统,由于模型的庞大和函数形式的复杂,往往不能给出明确的数值解.本文给出几种操作性强的、有效的寻求一般化模型数值解的方法,并通过介绍模型参数确定的办法,使得理论的模型有了现实的含义. 相似文献
45.
46.
47.
Hongyi Chen Chunguang Du Shiqun Li 《量子光学学报》2006,12(B08):77-78
Recently, research on left-handed materials (LHMs) has attracted considerable attentions. The LHMs are a kind of man-made metameterials which have negative permittivity and negative permeability. These metameterials have many novel properties such as inverse light pressure, and reverse Doppler effect, which lead to many potential applications of LHMs such as superlenses which, in principle, can achieve arbitrary subwavelength resolution. However, though the properties mentioned above are seen to be classical, the quantum phenomena in LHMs have also attracted attentions such as the modified spontaneous emission of atoms in LHME. 相似文献
48.
49.
In this paper the values of the crystalline-electric-field
parameters Anm for R2Fe17 and
R2Fe17H3 (R=Tb,Ho,Er) are evaluated by fitting
calculations to the magnetization curves measured on the single
crystal at several temperatures. The fitted Anm for
R2Fe17 are strikingly different from those for the
corresponding R2Fe17H3. The energy gaps between the
lowest four energy levels for Ho ions in Ho2Fe172 can be
reproduced by using the fitted Anm and exchange field
2μBHex, which estimated from the fit of the
temperature dependence of the spontaneous magnetization combined
with inelastic neutron scattering experiment. 相似文献
50.
Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the material's structure. There appears a relatively large change in structure of the material at about 273K, The anharmonic potential of the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes at around 312 cm^-1 and 464cm^-1 indicate that the latter phonon mode is more anharmonic than the former one. 相似文献