全文获取类型
收费全文 | 5051篇 |
免费 | 151篇 |
国内免费 | 26篇 |
专业分类
化学 | 4082篇 |
晶体学 | 77篇 |
力学 | 48篇 |
综合类 | 1篇 |
数学 | 256篇 |
物理学 | 764篇 |
出版年
2023年 | 25篇 |
2022年 | 33篇 |
2021年 | 56篇 |
2020年 | 71篇 |
2019年 | 68篇 |
2018年 | 36篇 |
2017年 | 37篇 |
2016年 | 93篇 |
2015年 | 97篇 |
2014年 | 118篇 |
2013年 | 259篇 |
2012年 | 262篇 |
2011年 | 321篇 |
2010年 | 172篇 |
2009年 | 173篇 |
2008年 | 340篇 |
2007年 | 292篇 |
2006年 | 346篇 |
2005年 | 311篇 |
2004年 | 264篇 |
2003年 | 243篇 |
2002年 | 231篇 |
2001年 | 92篇 |
2000年 | 113篇 |
1999年 | 74篇 |
1998年 | 47篇 |
1997年 | 50篇 |
1996年 | 76篇 |
1995年 | 60篇 |
1994年 | 46篇 |
1993年 | 44篇 |
1992年 | 59篇 |
1991年 | 45篇 |
1990年 | 42篇 |
1989年 | 34篇 |
1988年 | 49篇 |
1987年 | 33篇 |
1986年 | 28篇 |
1985年 | 51篇 |
1984年 | 45篇 |
1983年 | 31篇 |
1982年 | 42篇 |
1981年 | 48篇 |
1980年 | 39篇 |
1979年 | 41篇 |
1978年 | 29篇 |
1976年 | 16篇 |
1975年 | 24篇 |
1974年 | 20篇 |
1973年 | 27篇 |
排序方式: 共有5228条查询结果,搜索用时 46 毫秒
91.
T. Takeuchi 《Journal of Radioanalytical and Nuclear Chemistry》1980,59(2):545-569
The proceeding of the IAEA symposium held in 1978 on nuclear activation techniques in the life sciences are reviewed. A total
of 56 papers are reviewed on methodology, analytical quality control, comparisons between neutron activation analysis and
other methods, and applications of activation analysis in biology and medicine (including in-vivo activation analysis) and
in public and environmental health. The materials analysed in the papers are adjusted in connection with the elements determined
and the purposes of the study. Those elements are tabulated together with the analytical methods used for the element determination.
The standard reference materials analysed for the check of the reliability of analysis are also arranged.
Proc. Symp. Nuclear Activation Techniques in the Life Sciences, IAEA, Vienna, 1978. 相似文献
92.
David?I?Fisher Jared?L?Cartwright Hideyoshi?Harashima Hiroyuki?Kamiya Alexander?G?McLennanEmail author 《BMC biochemistry》2004,5(1):7
Background
Nudix hydrolases form a protein family whose function is to hydrolyse intracellular nucleotides and so regulate their levels and eliminate potentially toxic derivatives. The genome of the radioresistant bacterium Deinococcus radiodurans encodes 25 nudix hydrolases, an unexpectedly large number. These may contribute to radioresistance by removing mutagenic oxidised and otherwise damaged nucleotides. Characterisation of these hydrolases is necessary to understand the reason for their presence. Here, we report the cloning and characterisation of the DR0975 gene product, a nudix hydrolase that appears to be unique to this organism. 相似文献93.
Takashima H Mimura N Ohkubo T Yoshida T Tamaoki H Kobayashi Y 《Journal of the American Chemical Society》2004,126(14):4504-4505
Distributed computing has been implemented to the solution structure determination of endothelin-1 to evaluate efficiency of the method for NMR constraint-based structure calculations. A key target of the investigation was determination of the C-terminal folding of the peptide, which had been dispersed in previous studies of NMR, despite its pharmacological significances. With use of tens of thousands of random initial structures to explore the conformational space comprehensively, we determined high-resolution structures with good convergences of C-terminal as well as previously defined N-terminal structures. The previous studies had missed the C-terminal convergence because of initial structure dependencies trapped in localized folding of the N-terminal region, which are strongly constricted by two disulfide bonds. 相似文献
94.
The negative ion mass spectra of chlorine-containing molecules have been measured using a double focusing mass spectrometer with a photographic plate detector. The formulae of the negative ions not previously assigned using an electron multiplier detector have now been assigned. 相似文献
95.
Manabu Tanaka Kaoru Hatta Tomohiko Edura Ken Tsutsui Yasuo Wada Hiroyuki Nishide 《先进技术聚合物》2007,18(11):925-931
The electric conductivity of π‐conjugated and radical‐bearing polymers, i.e., polythiophenes bearing pendant galvinoxyl and phenoxyl radical groups, was measured using a microcomb‐shaped electrode. The electric conductivity was found to be enhanced by the radical content in the polymer. The infrared (IR) and Raman spectroscopies suggested a structural change from an aromatic form to a quinoid one in the polythiophene backbone by the phenoxyl radical generation. The effect of the pendant galvinoxyl radical's unpaired electron on the electric conductivity of the polythiophene was discussed by comparing the conductivity of a radical‐bearing polystyrene and a polythiophene mixed with low‐molecular radical molecules. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
96.
Shin-ichi Hirano Toshinobu Yogo Wataru Sakamoto Seiji Yamada Tomoyuki Nakamura Tomoe Yamammto Hiroyuki Ukai Kouichi Banno Tomoko Nakafuku Yukari Ando 《Journal of Sol-Gel Science and Technology》2003,26(1-3):35-41
Nano sized crystalline particles/polymer hybrids were synthesized form designed metal-organic precursors. The newly developed method is composed of the synthesis of organic matrix by polymerization and the in situ nucleation and growth of crystalline oxide particles in the organic matrix below 100°C. The design of metal-organic precursor modified with polymerizable ligand and the selection of reaction conditions does influence the size and crystallinity of ceramic particles in organic matrix. The nano-sized magnetic particle/polymer hybrid exhibits the interesting feature of superparamagnetism and quantum size effect. The crystalline particles of BaTiO3/, PbTiO3/, and KNbO3/polymer hybrids behave to be dielectric and show the typical electro-rheological behavior. 相似文献
97.
The Pictet-Spengler reaction of tryptamine type 1,2-dihydropyridine 5c derived from the cycloaddition of the sec-nitrodienamine 3c with acetaldehyde afforded the indoloquinolizine derivatives 6 and 7. 相似文献
98.
Tamura O Shiro T Ogasawara M Toyao A Ishibashi H 《The Journal of organic chemistry》2005,70(12):4569-4577
The 4-hydroxy 4-substituted glutamic acid moiety is a common substructure of biologically important natural products such as monatin [(2S,4S)-2], lycoperdic acid (3), and dysiherbaine (4). To develop methodology for syntheses of these natural products, cycloadditions of nitrone 5 with 2-substituted 2-propen-1-ols 6 and 2-substituted acrylates 8 were investigated. Reactions of nitrone 5 with alcohols 6 in the presence of MgBr2OEt2 gave cycloadducts 7 in a highly stereoselective manner, whereas noncatalyzed reactions of 5 with acrylates 8 afforded adducts 9. Using the former reaction, syntheses of monatin [(2S,4S)-2], monatin derivative 18, and lycoperdic acid (3) were accomplished. The C4-epimer of monatin [(2S,4R)-2)] was also synthesized by employing the latter cycloaddition. 相似文献
99.
Yoshio Ueno Yutaka Takeuchi Jinya Koshitani Takatoshi Yoshida 《Journal of heterocyclic chemistry》1981,18(3):645-647
4-Acyl-1,2-dimethyl-3H-phenothiazin-3-ones were prepared by the photochemical reaction of 1,2-dimethyl-3H-phenothiazin-3-one with aldehydes. The structures of the newly prepared compounds were determined by elemental analysis, spectroscopic methods (ir, nmr and ms) and comparison with a sample prepared by an alternate route. 相似文献
100.
Fumiyo Saito Ryo Takeuchi Tomoyuki Kamino Kouji Kuramochi Kengo Sakaguchi Susumu Kobayashi Masashi Tsuda 《Tetrahedron letters》2004,45(43):8069-8071
A total synthesis of the proposed structure of plakevulin A was accomplished. However, the NMR spectral data of the synthetic plakevulin A were not identical of those of the reported compound. We next converted the synthetic plakevulin A into 1-dihydrountenone A. The 1H and 13C NMR spectral data of 1-dihydrountenone A were identical with those of reported plakevulin A except for the peaks derived from levulinic acid. Thus, we repurified sample of the natural product and confirmed that the natural sample contained 1-dihydrountenone A and levulinic acid in the ratio of one to one. We also found that not plakevulin A but 1-dihydountenone A possessed the inhibitory activity against mammalian DNA polymerases α and β. 相似文献