全文获取类型
收费全文 | 31427篇 |
免费 | 1226篇 |
国内免费 | 202篇 |
专业分类
化学 | 21273篇 |
晶体学 | 296篇 |
力学 | 1038篇 |
综合类 | 2篇 |
数学 | 2796篇 |
物理学 | 7450篇 |
出版年
2023年 | 165篇 |
2022年 | 197篇 |
2021年 | 563篇 |
2020年 | 516篇 |
2019年 | 541篇 |
2018年 | 416篇 |
2017年 | 391篇 |
2016年 | 871篇 |
2015年 | 764篇 |
2014年 | 954篇 |
2013年 | 1776篇 |
2012年 | 2248篇 |
2011年 | 2495篇 |
2010年 | 1534篇 |
2009年 | 1339篇 |
2008年 | 2023篇 |
2007年 | 1888篇 |
2006年 | 1785篇 |
2005年 | 1670篇 |
2004年 | 1460篇 |
2003年 | 1164篇 |
2002年 | 1132篇 |
2001年 | 773篇 |
2000年 | 663篇 |
1999年 | 389篇 |
1998年 | 290篇 |
1997年 | 346篇 |
1996年 | 392篇 |
1995年 | 304篇 |
1994年 | 318篇 |
1993年 | 340篇 |
1992年 | 307篇 |
1991年 | 242篇 |
1990年 | 197篇 |
1989年 | 190篇 |
1988年 | 171篇 |
1987年 | 145篇 |
1986年 | 125篇 |
1985年 | 195篇 |
1984年 | 131篇 |
1983年 | 110篇 |
1982年 | 138篇 |
1981年 | 117篇 |
1980年 | 95篇 |
1978年 | 90篇 |
1977年 | 105篇 |
1976年 | 112篇 |
1975年 | 108篇 |
1974年 | 98篇 |
1973年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
32.
Vernon Barger Cheng-Wei Chiang Paul Langacker Hye-Sung Lee 《Physics letters. [Part B]》2004,580(3-4):186-196
We study the effects of an extra U(1)′ gauge boson with flavor changing couplings with fermion mass eigenstates on certain B meson decays that are sensitive to such new physics contributions. In particular, we examine to what extent the current data on Bd→φK and Bd→η′K decays may be explained in such models, concentrating on the example in which the flavor changing couplings are left-chiral. We find that within reasonable ranges of parameters, the Z′ contribution can readily account for the anomaly in SφKS but is not sufficient to explain large branching ratio of Bd→η′K with the same parameter value. SφKS and Sη′KS are seen to be the dominant observables that constrain the extra weak phase in the model. 相似文献
33.
34.
Sungyong Kim Lingxin Chen Sangyeop Lee Gi Hun Seong Jaebum Choo Eun Kyu Lee Chil-Hwan Oh Sanghoon Lee 《Analytical sciences》2007,23(4):401-405
A rapid DNA analysis has been developed based on a fluorescence intensity change of a molecular beacon in a PDMS microfluidic channel. Recently, we reported a new analytical method of DNA hybridization involving a PDMS microfluidic sensor using fluorescence energy transfer (FRET). However, there are some limitations in its application to real DNA samples because the target DNA must be labelled with a suitable fluorescent dye. To resolve this problem, we have developed a new DNA microfluidic sensor using a molecular beacon. By monitoring the change in the restored fluorescence intensity along the channel length, it is possible to rapidly detect any hybridization of the molecular beacon to the target DNA. In this case, the target DNA does not need to be labelled. Our experimental results demonstrate that this microfluidic sensor using a molecular beacon is a promising diagnostic tool for rapid DNA hybridization analysis. 相似文献
35.
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
36.
N. Wright und W. C. Lee 《Fresenius' Journal of Analytical Chemistry》1940,120(1-2):39-40
Ohne Zusammenfassung 相似文献
37.
The transverse momentum spectra for pions observed by WA80 and NA35 collaborations are analysed within a fireball model with collective isentropic expansion and a realistic freeze-out criterion. By varing the initial state of the fireball, an excellent fit to the data is achieved for the whole measured range ofP T . Slight differences in the data for the spectral slopes from central and pheripheral collisions originate in our model from the difference in the size of the fireball and in the number of participating nucleons in central and peripheral collisions. Using additional information from two-pion correlations, we can extrapolate our model back from the freeze-out point (determined from the spectra) to the initial state; we find that an initial energy density of 1.5–2GGeV/fm3 is sufficient to explain the data from central O+Au collisions at 200A GeV. 相似文献
38.
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
39.
Stuart P. RomerilVictor Lee Jack E. Baldwin Timothy D.W. ClaridgeBarbara Odell 《Tetrahedron letters》2003,44(42):7757-7761
The absolute configuration of the marine sponge alkaloid pyrinodemin A is established by organic synthesis. 相似文献
40.