全文获取类型
收费全文 | 1609篇 |
免费 | 90篇 |
国内免费 | 11篇 |
专业分类
化学 | 1209篇 |
晶体学 | 2篇 |
力学 | 30篇 |
综合类 | 2篇 |
数学 | 214篇 |
物理学 | 253篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 36篇 |
2019年 | 50篇 |
2018年 | 23篇 |
2017年 | 21篇 |
2016年 | 43篇 |
2015年 | 52篇 |
2014年 | 64篇 |
2013年 | 85篇 |
2012年 | 147篇 |
2011年 | 179篇 |
2010年 | 73篇 |
2009年 | 47篇 |
2008年 | 119篇 |
2007年 | 112篇 |
2006年 | 112篇 |
2005年 | 104篇 |
2004年 | 70篇 |
2003年 | 68篇 |
2002年 | 44篇 |
2001年 | 21篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有1710条查询结果,搜索用时 520 毫秒
111.
[structure: see text] The recognition of tripeptides by a metal-centered receptor consisting of a rigid backbone region and variable tripeptide arms is described. The studies showed that the receptor was selective for l-Xxx-l-Lys-l-Lys, with Xxx = His, Cys, and Met, giving association constants near 1.0 x 10(6) M(-)(1). Binding enhancement through cooperative interactions of the peptidic arms is demonstrated. 相似文献
112.
We present density functional and quantum Monte Carlo calculations of the stability and optical properties of semiconductor nanomaterials with reconstructed surfaces. We predict the relative stability of silicon nanostructures with reconstructed and unreconstructed surfaces, and we show that surface step geometries unique to highly curved surfaces dramatically reduce the optical gaps and decrease excitonic lifetimes. These predictions provide an explanation of both the variations in the photoluminescence spectra of colloidally synthesized nanoparticles and observed deep gap levels in porous silicon. 相似文献
113.
Cunefare KA Biesel VB Tran J Rye R Graf A Holdhusen M Albanese AM 《The Journal of the Acoustical Society of America》2003,113(2):881-892
Qualification of anechoic chambers is intended to demonstrate that the chamber supports the intended free-field environment within some permissible tolerance bounds. Key qualification issues include the method used to obtain traverse data, the analysis method for the data, and the use of pure tone or broadband noise as the chamber excitation signal. This paper evaluates the relative merits of continuous versus discrete traverses, of fixed versus optimal reference analysis of the traverse data, and of the use of pure tone versus broadband signals. The current practice of using widely space discrete sampling along a traverse is shown to inadequately sample the complexity of the sound field extant with pure tone traverses, but is suitable for broadband traverses. Continuous traverses, with spatial resolution on the order of 15% of the wavelength at the frequency of interest, are shown to be necessary to fully resolve the spatial complexity of pure tone qualifications. The use of an optimal reference method for computing the deviations from inverse square law is shown to significantly improve the apparent performance of the chamber for pure tone qualifications. Finally, the use of broadband noise as the test signal, as compared to pure tone traverses over the same span, is demonstrated to be a marginal indicator of chamber performance. 相似文献
114.
Shi Y Hall C Ciszewski JT Cao C Odom AL 《Chemical communications (Cambridge, England)》2003,(5):586-587
Alkynes are rapidly hydroaminated by primary amines using titanium dipyrrolylmethane derivatives as catalyst. 相似文献
115.
Both hydrophobic and hydrophilic room-temperature ionic liquids can be separated from aqueous solutions with relatively low-pressure gaseous carbon dioxide. 相似文献
116.
Spatial patterning of thin polyacrylamide films bonded to self-assembled monolayers on silica microchannels is described as a means for manipulating cell-adhesion and electroosmotic properties in microchips. Streaming potential measurements indicate that the zeta potential is reduced by at least two orders of magnitude at biological pH, and the adhesion of several kinds of cells is reduced by 80-100%. Results are shown for cover slides and in wet-etched silica microchannels. Because the polyacrylamide film is thin and transparent, this film is consistent with optical manipulation of cells and detection of cell contents. The spatial patterning technique is straightforward and has the potential to aid on-chip analysis of single adherent cells. 相似文献
117.
118.
On the basis of the experimental reports, the mechanism of the second-order susceptibility (2) for the thermal/electric field poling of fused silica is analyzed, and expressions for (2) are detailedly derived and numerically calculated for the first time. By comparison the theoretical value of (2) with the experiment results, we propose that the effective (2) is created via both the interaction of the intense electric field with the third-order susceptibility (3) and the dipole orientation. The theoretical results show that, in the differently applied voltage, the dipole orientation and (3) play different role in the formation of (2). This theory successfully explains some experiment results. 相似文献
119.
In this paper, we classify all optimal linear[n, n/2] codes up to length 12. We show that thereis a unique optimal [10, 5, 5] code up to equivalence. 相似文献
120.
In this paper, new codes of dimension 8 are presented which give improved bounds on the maximum possible minimum distance of ternary linear codes. These codes belong to the class of quasi-twisted (QT) codes, and have been constructed using a stochastic optimization algorithm, tabu search. Twenty three codes are given which improve or establish the bounds for ternary codes. In addition, a table of upper and lower bounds for d
3(n, 8) is presented for n 200. 相似文献