全文获取类型
收费全文 | 32088篇 |
免费 | 4723篇 |
国内免费 | 3169篇 |
专业分类
化学 | 17998篇 |
晶体学 | 312篇 |
力学 | 1543篇 |
综合类 | 112篇 |
数学 | 2926篇 |
物理学 | 9369篇 |
无线电 | 7720篇 |
出版年
2024年 | 112篇 |
2023年 | 797篇 |
2022年 | 1046篇 |
2021年 | 1280篇 |
2020年 | 1237篇 |
2019年 | 1185篇 |
2018年 | 1014篇 |
2017年 | 930篇 |
2016年 | 1392篇 |
2015年 | 1402篇 |
2014年 | 1654篇 |
2013年 | 2191篇 |
2012年 | 2799篇 |
2011年 | 2791篇 |
2010年 | 1946篇 |
2009年 | 1870篇 |
2008年 | 2069篇 |
2007年 | 1855篇 |
2006年 | 1673篇 |
2005年 | 1535篇 |
2004年 | 1036篇 |
2003年 | 844篇 |
2002年 | 806篇 |
2001年 | 581篇 |
2000年 | 619篇 |
1999年 | 735篇 |
1998年 | 603篇 |
1997年 | 560篇 |
1996年 | 613篇 |
1995年 | 491篇 |
1994年 | 397篇 |
1993年 | 321篇 |
1992年 | 304篇 |
1991年 | 251篇 |
1990年 | 207篇 |
1989年 | 160篇 |
1988年 | 118篇 |
1987年 | 123篇 |
1986年 | 105篇 |
1985年 | 92篇 |
1984年 | 56篇 |
1983年 | 46篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
Shen YH Li SH Li RT Han QB Zhao QS Liang L Sun HD Lu Y Cao P Zheng QT 《Organic letters》2004,6(10):1593-1595
Both coriatone (1). a novel highly oxygenated picrotoxane-type sesquiterpene, and corianlactone (2). with an unprecedented sesquiterpene basic skeleton, named coriane, were isolated from Coriaria nepalensis Wall. The structures of 1 and 2 were determined by analysis of their two-dimensional NMR data, and the structure of 2 was confirmed by X-ray analysis. Compounds 1 and 2 showed no remarkable inhibitory activity toward K(562) cells. They are cytotoxic with IC(50) > 50 microg/mL (cis-platinim: IC(50) = 0.49 microg/mL). 相似文献
262.
Haifang Liu Yuanqiang Sun Zhaohui Li Ran Yang Jie Yang Aaron Albert Aryee Xiaoge Zhang Jia Ge Lingbo Qu Yuehe Lin 《中国化学快报》2019,30(9):1647-1651
Intracellular pH plays a significant role in various biological processes, including cell proliferation, apoptosis, metabolism, enzyme activity and homeostasis. In this work, a novel design strategy for the preparation of pH responsive carbon dots (CDs-pH) for ratiometric intracellular imaging was reported. By using SciFinder database, fluorescent CDs-pH with the required pKa value of 6.84 were rationally designed, which is vital important for precise sensing of intracellular pH. As a result, the synthesized CDs-pH demonstrated robust ability to test pH fluctuations within the physiological range of 5.4-7.4. The CDs-pH was further utilized for fluorescent ratiometric imaging of pH in living HeLa cells, effectively avoided the influence of autofluorescence from native cellular species. Moreover, real-time monitoring of intracellular pH fluctuation under heat shock was successfully realized. This SciFinder-guided design strategy is simple and flexible, which has a great potential to be used for the development of other types of CDs for various applications. 相似文献
263.
264.
265.
Three chelating ion-exchange resins based on macroreticular polyacrylonitrile-divinylbenzene copolymers with thioglycollic acid and cysteine as functional groups have been tested for separation of molybdenum(VI) and tungsten(VI). On a short column of the thioglycollic acid resin, molybdenum(VI) and tungsten(VI) can be selectively sorbed from pH-4.3 acetate buffer and eluted with 2M hydrochloric acid and a mixture of 0.1M sodium hydroxide and 0.1M sodium chloride, respectively, with quantitative recovery even at very low concentrations. Simulated sea-water samples have been analysed. 相似文献
266.
The performance of conventional and low-flow nebulizer systems with liquid chromatography in differentiating four arsenic species in urine was evaluated. Two low-flow (DIN and MCN) chamber assemblies and a conventional (CFN) nebulizer-spray chamber assembly were compared in the hyphenation of anion-exchange microbore liquid chromatography with inductively coupled plasma mass spectrometry. Under optimal analytical conditions, the detection limits of the four arsenic species were 0.2-0.6 ng ml(-1) for all the nebulizer systems tested. The chromatographic resolution was best in the case of DIN due to its minimal off-column dead volume and superior transport efficiency. Four arsenic species were determined in the certified reference materials NIST SRM 2670E and 2670N. 相似文献
267.
Chen Xiao-Ming Wu Yu-Luan Tong Ye-Xiang Sun Ziming David N. Hendrickson 《Polyhedron》1997,16(24):1041
A novel tetranuclear terbium(III) complex [Tb4(OH)4(pybet)6(H2O)8][Tb4(OH)4(pybet)6(H2O)7 (NO3)](ClO4)14·6H2O has been synthesized and shown by X-ray crystallography to have a cubane-like Tb4(μ3-OH)4(μ2-carboxylato-O,O′)6 core. The ligand pybet is pyridinoacetate, C5H5+N-CH2CO2−. Magnetic susceptibility data were measured for this Tb4 complex in the range of 2.0–320 K and in fields of 1.0 G to 50.0 kG. It is concluded that either there is very weak antiferromagnetic exchange interaction (J = −0.015 cm−1) or there is a small crystal-field splitting of the 7F6 TbIII ground state. 相似文献
268.
269.
Praic M. Keane Kyra O'Sullivan Fergus E. Poynton Bjrn C. Poulsen Igor V. Sazanovich Michael Towrie Christine J. Cardin Xue-Zhong Sun Michael W. George Thorfinnur Gunnlaugsson Susan J. Quinn John M. Kelly 《Chemical science》2020,11(32):8600
Ruthenium polypyridyl complexes which can sensitise the photo-oxidation of nucleic acids and other biological molecules show potential for photo-therapeutic applications. In this article a combination of transient visible absorption (TrA) and time-resolved infra-red (TRIR) spectroscopy are used to compare the photo-oxidation of guanine by the enantiomers of [Ru(TAP)2(dppz)]2+ in both polymeric {poly(dG-dC), poly(dA-dT) and natural DNA} and small mixed-sequence duplex-forming oligodeoxynucleotides. The products of electron transfer are readily monitored by the appearance of a characteristic TRIR band centred at ca. 1700 cm−1 for the guanine radical cation and a band centered at ca. 515 nm in the TrA for the reduced ruthenium complex. It is found that efficient electron transfer requires that the complex be intercalated at a G-C base-pair containing site. Significantly, changes in the nucleobase vibrations of the TRIR spectra induced by the bound excited state before electron transfer takes place are used to identify preferred intercalation sites in mixed-sequence oligodeoxynucleotides and natural DNA. Interestingly, with natural DNA, while it is found that quenching is inefficient in the picosecond range, a slower electron transfer process occurs, which is not found with the mixed-sequence duplex-forming oligodeoxynucleotides studied.Efficient electron transfer requires the complex to be intercalated at a G-C base-pair. Identification of preferred intercalation sites is achieved by TRIR monitoring of the nucleobase vibrations before electron transfer. 相似文献
270.
Wei Sun 《Tetrahedron letters》2006,47(12):1993-1996
Several salen-ruthenium(II) complexes, which are derived from commercial ligands or simply ethylenediamine, can be successfully applied as catalysts for the olefination of a broad variety of aldehydes. Depending on the electron richness of the applied aldehydes, good to very good olefin yields and high E:Z selectivities are reached at 60 or 80 °C reaction temperature with ethyl diazo acetate being the reaction partner. The reaction rate depends on the electron donor capabilities of the aldehydes. Electron poor aldehydes undergo faster reactions than electron rich aldehydes, but both electron rich and bulky aldehydes can be transformed to corresponding olefins in very good yields and high E-selectivity. 相似文献