全文获取类型
收费全文 | 43487篇 |
免费 | 3635篇 |
国内免费 | 2063篇 |
专业分类
化学 | 30104篇 |
晶体学 | 436篇 |
力学 | 2087篇 |
综合类 | 136篇 |
数学 | 4351篇 |
物理学 | 12071篇 |
出版年
2023年 | 455篇 |
2022年 | 740篇 |
2021年 | 1011篇 |
2020年 | 1039篇 |
2019年 | 1076篇 |
2018年 | 835篇 |
2017年 | 836篇 |
2016年 | 1447篇 |
2015年 | 1347篇 |
2014年 | 1684篇 |
2013年 | 2603篇 |
2012年 | 3426篇 |
2011年 | 3642篇 |
2010年 | 2321篇 |
2009年 | 2048篇 |
2008年 | 2779篇 |
2007年 | 2573篇 |
2006年 | 2480篇 |
2005年 | 2197篇 |
2004年 | 1848篇 |
2003年 | 1508篇 |
2002年 | 1498篇 |
2001年 | 1125篇 |
2000年 | 913篇 |
1999年 | 692篇 |
1998年 | 539篇 |
1997年 | 556篇 |
1996年 | 627篇 |
1995年 | 489篇 |
1994年 | 474篇 |
1993年 | 433篇 |
1992年 | 430篇 |
1991年 | 374篇 |
1990年 | 280篇 |
1989年 | 261篇 |
1988年 | 215篇 |
1987年 | 186篇 |
1986年 | 172篇 |
1985年 | 227篇 |
1984年 | 166篇 |
1983年 | 139篇 |
1982年 | 154篇 |
1981年 | 119篇 |
1980年 | 108篇 |
1978年 | 104篇 |
1977年 | 110篇 |
1976年 | 117篇 |
1975年 | 119篇 |
1974年 | 95篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Tian-Xi ZhouGuan-Hu Bao Qin-Gao MaGuo-Wei Qin Chu-Tao CheYang Lv Cheng WangQi-Tai Zheng 《Tetrahedron letters》2003,44(1):135-137
Langduin C, a novel dimeric diterpenoid, was isolated from the roots of Euphorbia fischeriana and its structure was established by spectral data and single-crystal X-ray diffraction analysis. 相似文献
62.
Yang Dai Faquan Li Xuewu Cheng Zhiling Jiang Shunsheng Gong 《Optics & Laser Technology》2007,39(7):1374-1379
In Shack–Hartmann wavefront sensor (SHWS), the behavior of the irradiance pattern produced by the micro-lens array is important for an accurate centroid estimation. In this paper, the behavior of a micro-lens array in SHWS is analyzed using Fourier optics, and reveals that in addition to the main, expected spots, secondary spots with smaller intensities also appeared as a result of diffraction by the small dimensions of the micro-lens and interference from the different micro-lenses. This result is confirmed by comparing with a irradiance pattern taken from an actual SHWS. The additional error in centroid estimation caused by these secondary spots is discussed and relationship to the parameters of the micro-lens of SHWS is analyzed. 相似文献
63.
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
64.
N. Wright und W. C. Lee 《Fresenius' Journal of Analytical Chemistry》1940,120(1-2):39-40
Ohne Zusammenfassung 相似文献
65.
Pengbo Jiang Tiexin Cheng Yan Liu Xianghao Cui Yingli Bi Kaiji Zhen 《Reaction Kinetics and Catalysis Letters》2004,82(1):49-56
The novel phase transfer catalysts S-8 [4-(dimethyloctylammonium) propansultan] and DB-X [1,4-bis(triethylmethylammonium)benzene dibromide] were synthesized and employed for high conversion synthesis of dichlorocyclopropane from various olefins.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
66.
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
67.
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
68.
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
69.
Xiao Qi ZHENG Yong Hui WANG Qing Xiang GUO* Li YANG You Cheng LIU Department of Chemistry University of Science Technology of China Hefei National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2003,(8)
As artificial enzymes, the binding constants of cyclodextrins (CDs) and their substrates are expected to be high1. For this purpose, many kinds of bridged cyclodextrin dimers2 whose two cyclodextrins are linked by various spacers have been constructed. It was of interest to make the dimers, whose binding constants would exceed 108dm3/mol3. Up to date, the bridged cyclodextrin dimers have been extensively studied as enzyme models and as molecular receptors4-6. Recently, we synthesized a brid… 相似文献
70.
Aiqing Zhang Xiangdan Li Changwoon Nah Keejun Hwang Myong‐Hoon Lee 《Journal of polymer science. Part A, Polymer chemistry》2003,41(1):22-29
A soluble aromatic polyimide was chloromethylated via a reaction with chloromethyl methyl ether in the presence of tin(IV) chloride to produce a new starting material for the modification of aromatic polyimides. The chemical structure of the resulting polymer was confirmed by 1H NMR and Fourier transform infrared spectroscopy. The maximum number of chloromethyl groups per repeat unit was 1.81. The chloromethylated polyimide was stable up to 250 °C and soluble in both chloroform and tetrahydrofuran. So that its utilization for further modification could be demonstrated, cinnamic acid was reacted with the formed polyimide, and it produced a new photosensitive polyimide with a cinnamoyl side chain. The photosensitivity of the resulting polyimide was investigated with ultraviolet spectroscopic methods. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 22–29, 2003 相似文献