全文获取类型
收费全文 | 156332篇 |
免费 | 36818篇 |
国内免费 | 38424篇 |
专业分类
化学 | 104800篇 |
晶体学 | 3754篇 |
力学 | 10535篇 |
综合类 | 2511篇 |
数学 | 21329篇 |
物理学 | 88645篇 |
出版年
2024年 | 627篇 |
2023年 | 1727篇 |
2022年 | 3710篇 |
2021年 | 3759篇 |
2020年 | 3939篇 |
2019年 | 4325篇 |
2018年 | 4075篇 |
2017年 | 5523篇 |
2016年 | 5228篇 |
2015年 | 6391篇 |
2014年 | 7244篇 |
2013年 | 9876篇 |
2012年 | 11000篇 |
2011年 | 12926篇 |
2010年 | 15757篇 |
2009年 | 16259篇 |
2008年 | 11030篇 |
2007年 | 9654篇 |
2006年 | 9000篇 |
2005年 | 8188篇 |
2004年 | 7714篇 |
2003年 | 5955篇 |
2002年 | 5826篇 |
2001年 | 5958篇 |
2000年 | 5339篇 |
1999年 | 4276篇 |
1998年 | 3140篇 |
1997年 | 2729篇 |
1996年 | 2942篇 |
1995年 | 3341篇 |
1994年 | 3363篇 |
1993年 | 3371篇 |
1992年 | 2900篇 |
1991年 | 2448篇 |
1990年 | 2140篇 |
1989年 | 2170篇 |
1988年 | 2083篇 |
1987年 | 1378篇 |
1986年 | 1388篇 |
1985年 | 989篇 |
1984年 | 1097篇 |
1983年 | 465篇 |
1982年 | 963篇 |
1981年 | 814篇 |
1980年 | 833篇 |
1979年 | 633篇 |
1978年 | 563篇 |
1977年 | 652篇 |
1976年 | 1056篇 |
1972年 | 536篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector. 相似文献
52.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous. 相似文献
53.
54.
55.
N. A. Anurova V. A. Blatov G. D. Ilyushin O. A. Blatova A. K. Ivanov-Shitz L. N. Demyanets 《Crystallography Reports》2008,53(6):930-936
A new method was developed for studying voids and channels in crystal structures based on the Voronoi-Dirichlet partition
of crystal space, and 822 structurally characterized ternary compounds Li
p
X
q
O
r
were analyzed for the first time. For these compounds, the dimensionality was determined and the migration patterns of channel
systems capable of providing lithium-ion transport were constructed. The calculated coordinates of lithium atoms in the centers
of the voids are consistent (within 0.4 ?) with the known structural data. Among these compounds, 113 compounds have infinite
channel systems, 60 compounds (18 structural types, STs) have been described earlier in the literature as solid electrolytes,
and 53 compounds (23 STs) can be considered as potential one-, two-, or three-dimensional ionic conductors (13, 3, and 7 STs,
respectively).
Original Russian Text ? N.A. Anurova, V.A. Blatov, G.D. Ilyushin, O.A. Blatova, A.K. Ivanov-Shitz, L.N. Dem’yanets, 2008,
published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 987–993. 相似文献
56.
CONG Fuzhong & LI YongSchool of Mathematics Information Science Shandong Institute of Business Technology Yantai China Office of Mathematics Changchun Flight Academy of the Air Force Changchun China Department of Mathematics Jilin University Changchun China 《中国科学A辑(英文版)》2004,47(5):675-686
An effective stability result for generalized Hamiltonian systems is obtained by applying the simultaneous approximation technique due to Lochak. Among these systems, dimensions of action variables and angle variables might be distinct. 相似文献
57.
58.
59.
Songxin Tan Ram M. Narayanan Sunil K. Shetty 《International Journal of Infrared and Millimeter Waves》2005,26(8):1175-1194
There is growing interest in the use of lidar for remote sensing of vegetation owing to the emergence of reliable and rugged lasers and highly sensitive detectors. Lidar remote sensing has a distinct advantage over conventional techniques in vegetation remote sensing due to its capability for three-dimensional characterization of vegetative targets. The Multiwavelength Airborne Polarimetric Lidar (MAPL) system was developed primarily for vegetation remote sensing applications from an airborne platform of up to 1,000 -m altitude. The lidar system has full waveform capture and polarimetric measurement capability at two wavelengths in the near-infrared (1064 nm) and the green (532 nm) spectral regions. This study presents preliminary ground-based lidar reflectance measurements on a variety of deciduous and coniferous trees under fully foliated conditions with a view towards tree species discrimination. Variations in the reflectance characteristics of selected deciduous trees under unfoliated and fully foliated conditions were also investigated. Our study reveals distinct differences in the reflectance characteristics of various trees. 相似文献
60.
This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated 3-dB modulation bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of conventional electrode structures that are limited by phase velocity mismatch.This work was supported by the U.S. Army Research Office under contract DAAL-03-88-K-0005 and the Texas Advanced Technology Program. 相似文献