全文获取类型
收费全文 | 4098篇 |
免费 | 139篇 |
国内免费 | 17篇 |
专业分类
化学 | 3355篇 |
晶体学 | 28篇 |
力学 | 31篇 |
数学 | 303篇 |
物理学 | 537篇 |
出版年
2023年 | 17篇 |
2022年 | 33篇 |
2021年 | 39篇 |
2020年 | 47篇 |
2019年 | 60篇 |
2018年 | 38篇 |
2017年 | 39篇 |
2016年 | 76篇 |
2015年 | 80篇 |
2014年 | 89篇 |
2013年 | 211篇 |
2012年 | 214篇 |
2011年 | 261篇 |
2010年 | 151篇 |
2009年 | 156篇 |
2008年 | 277篇 |
2007年 | 277篇 |
2006年 | 227篇 |
2005年 | 236篇 |
2004年 | 175篇 |
2003年 | 172篇 |
2002年 | 139篇 |
2001年 | 88篇 |
2000年 | 92篇 |
1999年 | 66篇 |
1998年 | 59篇 |
1997年 | 67篇 |
1996年 | 63篇 |
1995年 | 39篇 |
1994年 | 38篇 |
1993年 | 51篇 |
1992年 | 35篇 |
1991年 | 31篇 |
1990年 | 32篇 |
1989年 | 28篇 |
1988年 | 28篇 |
1987年 | 38篇 |
1986年 | 20篇 |
1985年 | 52篇 |
1984年 | 52篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 39篇 |
1980年 | 35篇 |
1979年 | 47篇 |
1978年 | 33篇 |
1977年 | 29篇 |
1976年 | 26篇 |
1975年 | 21篇 |
1974年 | 28篇 |
排序方式: 共有4254条查询结果,搜索用时 21 毫秒
211.
Experimental detection of proteolytic activity in a signal peptide peptidase of Arabidopsis thaliana
Hoshi Masako Ohki Yu Ito Keisuke Tomita Taisuke Iwatsubo Takeshi Ishimaru Yoshiro Abe Keiko Asakura Tomiko 《BMC biochemistry》2013,14(1):1-8
Background
The ubiquitin ligase COP1, COnstitutively Photomorphogenic 1, functions in many biological responses in mammalian cells, but its downstream pathway remains unclear.Results
Here, we identified FIP200, a key regulator of mammalian autophagy, as a novel COP1-interacting protein by yeast two-hybrid screening. The interaction was confirmed by a GST-pulldown assay. Split-GFP analysis revealed that interaction between COP1 and FIP200 predominantly occurred in the cytoplasm and was enhanced in cells treated with UV irradiation. Different forms of FIP200 protein were expressed in cultured mammalian cells, and ectopic expression of COP1 reduced one of such forms.Conclusions
These data suggest that COP1 modulates FIP200-associated activities, which may contribute to a variety of cellular functions that COP1 is involved in. 相似文献212.
Hideaki Iizuka Shoko Watanabe Mayuko Koshikawa Yurie Matsumoto Yuki Aoyama Hideaki Ichiba Toshitaka Nabeshima Takeshi Fukushima 《Analytical and bioanalytical chemistry》2013,405(25):8137-8141
It has been reported that repeated phencyclidine (PCP) treatment induces schizophrenia-like behavior in mice. l-Tryptophan (Trp) concentrations in brain tissues of control (n?=?8) and PCP-treated mice (10 mg/kg/day, s.c., 14 days, n?=?10) were determined using high-performance liquid chromatography (HPLC) with fluorescence detection. The HPLC method involved pre-column fluorescence derivatization with (R)-(?)-4-(N,N-dimethylaminosulfonyl)-7-(3-isothiocyanatopyrrolidin-1-yl)-2,1,3-benzoxadiazole (DBD-PyNCS). Eight different parts of the brain, namely, the frontal cortex, nucleus accumbens, striatum, hippocampus, amygdala, thalamus, hypothalamus, and cerebellum, of both groups were investigated. A significant decrease in the l-Trp concentration in the nucleus accumbens (p?=?0.024) and hippocampus (p?=?0.027) was observed in PCP-treated mice, suggesting that alteration of the l-Trp metabolism might occur in these brain parts. 相似文献
213.
Naruyoshi Komiya Takeharu Kageyama Masaya Naito Takeshi Naota 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(5):503-505
rac‐Bis{μ‐trans‐2,2′‐[pentane‐1,5‐diylbis(azanediyl)]ditroponato}dipalladium(II), [Pd2(C19H20N2O2)2], has been synthesized and fully characterized using single‐crystal X‐ray diffraction, 1H NMR, FT–IR and mass spectroscopy. The trans coordination, vaulted structure and anti conformation have been unequivocally established from the X‐ray diffraction studies. This is the first example of a bis(aminotroponato)palladium complex. In the crystalline state, the molecule has twofold symmetry and each molecular unit undergoes intermolecular offset π‐stacking of the tropone rings to afford heterochiral interpenetrating dimers that are aligned in a lamellar manner with a herringbone packing motif. 相似文献
214.
Unmodified and SiCl4-modified spherical zirconia-supported methylaluminoxane were used as cocatalyst for propylene polymerization as well as ethylene/1-hexene copolymerization in combined with Me2Si(η3-C13H8)(η1-NtBu)TiMe2 (1) at 0 °C. The modification with SiCl4 improved the catalytic activity. The improvement was clearer in ethylene/1-hexene copolymerization than in propylene polymerization. The number average molecular weight (Mn) of polypropylenes increased linearly against the polymerization time regardless the cocatalyst used to give polymers with narrow molecular weight distribution (Mw/Mn < 1.32), indicating the living nature of the catalytic systems. Thus, propagation rate constant (kp) and the number of active centers (C*) were evaluated from Mn and the number of polymer-chains. When the zirconia was modified with SiCl4, the kp value decreased and the C* increased. The latter effect was more significant to enhance the catalytic activity. 相似文献
215.
Reaction of 1-trimethylsilyloxybenzocyclobutene(1) with carbonyl compounds catalyzed by tris(dimethylamino)sulfur (trimethylsilyl)difluoride (TASF) at room temperature gave 1-isochromanol derivatives as corresponding hetero Diels-Alder adducts in good yields. 相似文献
216.
Efficient one-pot synthesis of homoallyl alkyl ethers and dialkyl ethers was performed by the allylation and reduction of ethylene acetals with allyltrimethylsilane and f-butyldimethylsilane, respectively, in the presence of alkoxytrimethylsilane. 相似文献
217.
1,5-Dihydroxynaphthalene and its derivatives can be oxidized by molecular oxygen in the presence of catalytic amounts of salcomine under neutral conditions to afford the corresponding 1,4-naphthoquinones as the major products. 相似文献
218.
Yuki Yanagisawa Takeshi Kageyama Naohisa Wada Masatoshi Tanaka Shin‐ya Ohno 《Photochemistry and photobiology》2013,89(6):1490-1496
The time‐dependent characteristics of firefly bioluminescence initiated by manual injection of adenosine triphosphate (ATP) into buffer solution containing luciferin (Ln), luciferase (Luc) and Mg2+ were measured with a resolution of 10 ms, and compared with those obtained by photolysis of caged ATP. The time course depends on pH; both rise and decay rates decrease when pH is lowered from 7.8 to 6.8. In contrast, the parameter λ in the kinetic formula related to diffusion of ATP is almost independent of pH. The pH dependence of the time course of bioluminescence can be explained by the same pH tendency as the rate of ATP binding at the active site of Luc. The time‐resolved spectra can be decomposed into two Gaussian components with maxima at 2.2 and 2.0 eV. At pH 7.8, the band at 2.2 eV is more intense than that at 2.0 eV for all three concentration conditions. At lower pH, the band at 2.2 eV becomes weaker than that at 2.0 eV. The intensity ratio of the 2.0 and 2.2 eV bands is constant for duration time of 600 s for both injection and photolysis experiments, and the above conclusions are unaffected by the concentration ratio [Ln]/[Luc]. 相似文献
219.
Daisuke Saeki Takeshi Yamada Yasuko In Tetsuya Kajimoto Reiko Tanaka Yota Iizuka Takahisa Nakane Akihito Takano Kazuo Masuda 《Tetrahedron》2013,69(5):1583-1589
Novel 5 lupane-type of triterpenois, i.e., 3β-acetoxy-18α,19α-epoxylupan-21β-ol (1), 18α,19α-epoxy-21β-hydroxylupan-3-one (2), lup-18-ene-3,21-dione (3), lupa-18,21-dien-3β-yl acetate (4), and (17S)-17,18-seco-lup-19(21)-ene-3,18,22-trione (5), named officinatrione, as well as 16 known compounds from the roots of Taraxacum officinale collected in Takatsuki city, Osaka, Japan. Of the above compounds, 5 was the first lupane-type triterpene, of which the D-ring was open to form a nine-membered ring. Compounds 2 and 5 exhibited moderate cytotoxic activities against L1210 cell line (IC50 10.5 and 10.1 μM). 相似文献
220.
Takeshi Kodama Shingo AokiSeiho Kikuchi Tomoki MatsuoYoshimitsu Tachi Keisuke NishikawaYoshiki Morimoto 《Tetrahedron letters》2013
The first concise total synthesis of C2 symmetric (+)-ekeberin D4 (1) that exhibits antiplasmodial activity has been achieved in total nine steps and 27% yield from the known diol 4. The efficient synthetic method features the regio- and diastereoselective epoxidation of 4 and convergent coupling between half fragments 2 and 3 by taking into account the C2 symmetric property. 相似文献