全文获取类型
收费全文 | 495505篇 |
免费 | 5429篇 |
国内免费 | 1420篇 |
专业分类
化学 | 233898篇 |
晶体学 | 6492篇 |
力学 | 18766篇 |
综合类 | 13篇 |
数学 | 49984篇 |
物理学 | 133221篇 |
无线电 | 59980篇 |
出版年
2021年 | 4130篇 |
2020年 | 4654篇 |
2019年 | 4986篇 |
2018年 | 6401篇 |
2017年 | 6218篇 |
2016年 | 9534篇 |
2015年 | 5887篇 |
2014年 | 9304篇 |
2013年 | 21497篇 |
2012年 | 16460篇 |
2011年 | 20281篇 |
2010年 | 14599篇 |
2009年 | 15185篇 |
2008年 | 19952篇 |
2007年 | 20310篇 |
2006年 | 18997篇 |
2005年 | 17304篇 |
2004年 | 16089篇 |
2003年 | 14386篇 |
2002年 | 14059篇 |
2001年 | 15780篇 |
2000年 | 12394篇 |
1999年 | 10038篇 |
1998年 | 8618篇 |
1997年 | 8284篇 |
1996年 | 7971篇 |
1995年 | 7214篇 |
1994年 | 7103篇 |
1993年 | 6741篇 |
1992年 | 7380篇 |
1991年 | 7475篇 |
1990年 | 7113篇 |
1989年 | 6788篇 |
1988年 | 6617篇 |
1987年 | 6006篇 |
1986年 | 5650篇 |
1985年 | 7192篇 |
1984年 | 7269篇 |
1983年 | 5816篇 |
1982年 | 5810篇 |
1981年 | 5798篇 |
1980年 | 5341篇 |
1979年 | 5659篇 |
1978年 | 5787篇 |
1977年 | 5678篇 |
1976年 | 5568篇 |
1975年 | 5144篇 |
1974年 | 5108篇 |
1973年 | 5118篇 |
1972年 | 3628篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. Schulz 《Microelectronic Engineering》1998,40(3-4):113-130
The classical capacitance-voltage measurement methods and the conductance technique which are frequently used to analyze the SiO2---Si system, are briefly introduced and critically evaluated. These measurement techniques are based on macroscopic device structures, average structure parameters are determined. Transient and random telegraph signal measurements, and charge pumping are now available as new methods to study the SiO2---Si interface in sub-μm device structures. These techniques permit to analyze single, individual traps in the interface. Traps in small devices are isolated. The capture rates are thermally activated by the Coulomb energy. 相似文献
992.
A. M. Stokolos 《Mathematical Notes》1998,64(5):646-657
It is proved that there exists an integrable function on [0, 1]2 whose integral is nondifferentiable in each direction belonging to a set everywhere dense in [0, 2π] but is strongly differentiable.
Translated fromMatematicheskie Zametki, Vol. 64, No. 5, pp. 749–762, November, 1998. 相似文献
993.
The problem of calculating the noise factor of a traveling-wave gyrotron is solved for a model of a thin annular multistart-helical
electron flux taking into account the effect of the quasistatic space-charge field. Plots of the gain and the noise factor
of the traveling-wave gyrotron versus the electrical parameters of the amplifier are obtained.
Zh. Tekh. Fiz. 68, 130–132 (February 1998) 相似文献
994.
V. T. Astrelin A. V. Burdakov V. S. Koidan K. I. Mekler P. I. Mel’nikov V. V. Postupaev M. A. Shcheglov 《Journal of Experimental and Theoretical Physics》1998,86(3):489-500
This paper presents the results of experiments on two-stage heating of a dense plasma by a relativistic electron beam in the
GOL-3 facility. A dense plasma with a length of about a meter and a hydrogen density up to 1017 cm−3 was created in the main plasma, whose density was 1015 cm−3. In the process of interacting with the plasma, the electron beam (1 MeV, 40 kA, 4 μs) imparts its energy to the electrons of the main plasma through collective effects. The heated electrons, as they disperse
along the magnetic field lines, in turn reach the region of dense plasma and impart their energy to it by pairwise collisions.
Estimates based on experimental data are given for the parameters of the flux of hot plasma electrons, the energy released
in the dense plasma, and the energy balance of the beam-plasma system. The paper discusses the dynamics of the plasma, which
is inhomogeneous in density and temperature, including the appearance of pressure waves.
Zh. éksp. Teor. Fiz. 113, 897–917 (March 1998) 相似文献
995.
996.
997.
The orientational ordering of several liquid crystals containing a difluorosubstituted phenyl ring has been studied through the use of C-13 NMR. The fluorinated phenyl ring of these liquid crystals have Cs symmetry, so three order parameters are required to completely describe the ordering of this ring. All three of these order parameters have been calculated from carbon-fluorine dipolar coupling constants obtained from the carbon-fluorine splittings in the C-13 NMR spectra. Because of the complexity of the fluorine-coupled spectra, variable angle spinning (VAS) was used to resolve the carbon-fluorine splittings. In order to study the orientational ordering over wide ranges of temperature, we have developed an empirical correlation between the order parameter and the value of a carbon-fluorine dipolar coupling constant. This enabled us to study the change in the order parameter with temperature. The results of applying this method to several structurally similar liquid crystals containing the same type of difluorinated phenyl ring are presented. A comparison is made to a similar mono-fluorinated liquid crystal. 相似文献
998.
The influence of humic substances on sorption and methylation processes for inorganic- and organotin species is presented. Four sediment samples from different locations of the Rivers Elbe, Mulde and Spittelwasser, Germany, with different organotin and humic contents were selected to extract the humic and fulvic acids. The various fractions—the original sediment, the humic acid, the fulvic acid and the residual sediment—were analysed for their organotin content. The individual buyltin species show quite different distribution patterns. Monobutyltin is found mostly associated with humic acids. Dibutyltin shows a nonunique behaviour. At low total organotin content, dibutyltin is found bonded to humic and fulvic acids, whereas at high organotin content dibutyltin is distributed more with the residual sediment. Most of the tributyltin remains in the sediment unextracted; only small quantities of it are in the fulvic acid fraction. Tetrabutyltin is only in the humic acid fraction when it binds to humic matter; it mostly remains in the sediment. General observations indicate that ionic butyltin species bind to fulvic acids whereas the non-polar tetrabutyltin is not found in the fulvic acid fractions in any of the samples. The appearance of monomethyl- and dimethyl-tin species in the humic and fulvic acid fractions after the alkaline extraction was surprising. There is a correlation between the humic content of the sample and the formation of methyltin species. Evidence is provided by experiments that humic substances act as methylation agents. 相似文献
999.
Summary A new method of evaluating the Tolman cone angle from X-ray structural data available from the Cambridge Crystallographic Data Base has been developed and a statistical analysis of the cone angles of the phosphines PPh3, PMe2Ph, PMePh2, PMe3, PEt3 and PCy3 (Cy = cyclohexyl) in transition metal complexes has been completed. 相似文献
1000.
Kaneko M. Aratani K. Fukumoto A. Miyaoka S. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1994,82(4):544-553
IRISTER (IRIS Thermal Eclipse Reading) is a remarkable technique for achieving superresolution in optical disks. Two applications of IRISTER are Magnetically induced SuperResolution (MSR) and Premastered optical disk by SuperResolution (PSR). Magnetically induced SuperResolution (MSR) has been realized in magneto-optical disks using exchange-coupled magnetic multilayer films. Two new detection methods have been developed. In the front aperture detection (FAD) method, the heated area in the light spot works as an optical mask so that the signal is read out only from the remaining crescent-shaped area in the spot. In the rear aperture detection (RAD) method, the signal is read out only from the heated area. The cutoff spatial frequency for both types of detection is more than two times higher than that in conventional detection. A high C/N of 42 dB is obtained in the MSR disks by both methods for a mark length of 0.3 μm, which is much shorter than the optical limit. Premastered optical disk by SuperResolution (PSR) has been realized in read-only optical disks using phase-change materials. In the front aperture detection (FAD) method for PSR, the prerecorded signal is read out only from the high reflective crescent-shaped area in the light spot, because the reflectance of the heated area is too low. A C/N of 51 dB for a mark length of 0.3 μm has been obtained for the PSR disk 相似文献