全文获取类型
收费全文 | 14887篇 |
免费 | 2170篇 |
国内免费 | 1342篇 |
专业分类
化学 | 10736篇 |
晶体学 | 182篇 |
力学 | 831篇 |
综合类 | 67篇 |
数学 | 1769篇 |
物理学 | 4814篇 |
出版年
2024年 | 50篇 |
2023年 | 323篇 |
2022年 | 561篇 |
2021年 | 593篇 |
2020年 | 674篇 |
2019年 | 580篇 |
2018年 | 507篇 |
2017年 | 441篇 |
2016年 | 699篇 |
2015年 | 729篇 |
2014年 | 753篇 |
2013年 | 1104篇 |
2012年 | 1259篇 |
2011年 | 1256篇 |
2010年 | 827篇 |
2009年 | 831篇 |
2008年 | 975篇 |
2007年 | 833篇 |
2006年 | 743篇 |
2005年 | 705篇 |
2004年 | 515篇 |
2003年 | 423篇 |
2002年 | 409篇 |
2001年 | 324篇 |
2000年 | 292篇 |
1999年 | 294篇 |
1998年 | 196篇 |
1997年 | 155篇 |
1996年 | 197篇 |
1995年 | 166篇 |
1994年 | 138篇 |
1993年 | 124篇 |
1992年 | 104篇 |
1991年 | 86篇 |
1990年 | 91篇 |
1989年 | 68篇 |
1988年 | 64篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 43篇 |
1984年 | 38篇 |
1983年 | 18篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1971年 | 7篇 |
1969年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Two new ent‐abietane diterpenoids, macrophynin E ( 1 ) and macrophynin F ( 2 ), and a known related ent‐abietanoid (?)‐lambertic acid ( 3 ), together with four known ent‐kauranoids, were isolated from the roots and aerial parts of Isodon macrophylla, respectively. The structures of the new compounds were elucidated on the basis of spectroscopic‐data analysis and chemical correlations. 相似文献
103.
A novel histidine-selective method has been developed for the determination of histidine in aqueous solutions by resonance light scattering (RLS) technique. At pH 8.0, the weak RLS intensity of tetraphenylporphyrin manganese (III) chloride [MnTPPCl] was greatly enhanced by the addition of histidine with the maximum peak located at 483 nm. Under the optimum conditions, it was found that the enhanced RLS intensity was in proportion to the concentration of histidine in the range 7.8 × 10−7-2.4 × 10−5 mol l−1. Low detection limit of 9.2 × 10-8 mol l−1 has been achieved. The histidine concentrations in synthetic samples and real samples were determined with satisfactory results. The sensitivity and selectivity of this method are high enough to permit the determination of trace amounts of histidine without any significant interference from high levels of other components such as common anions and especially, other amino acids. 相似文献
104.
Dong Han Kim 《Journal of heterocyclic chemistry》1982,19(1):127-128
Treatment of 10-chloro-5H-benzoxazole[3,2-a]quinolin-5-one (I) with an excess of sodium diethyl malonate at 190° for 3 hours in hexamethylphosphoramide gave, in 38% yield, 9-chloro-8-ethoxy-12-hydroxy-5H-dibenz[c,f]quinolizin-5-one (IV) which, on heating with acetic anhydride, afforded monoacetylated product, V. A possible reaction mechanism for the novel ring expansion reaction is suggested. 相似文献
105.
Chang Xiu Han Ji Li Ren Xue Jiao Tang Bao Gui Zhang 《中国化学快报》2007,18(10):1285-1288
A new ternary Fe-based alloy catalyst FeCuP applied to decompose PH_3 was prepared with low-cost material by chemical reduction deposition method.The properties of it were characterized by XRD,ICP and SEM.Its catalytic activity on the decomposition of PH_3 and the decomposition conditions were studied.FeCuP alloy exhibits high thermal stabilities and high catalytic activity.Using it as catalyst,the decomposition temperature of phosphine decreases from over 800℃to 400-500℃.The decomposition rate of phosphine achieved 100%. 相似文献
106.
The adsorption of α1-acid glycoprotein into bilirubin/cholesterol mixed monolayers with various component molar ratios is investigated using surface
pressure-area (π-A) isotherms and (dπ/dA)-A curves. The results showed that the surface area per molecule increased after the adsorption/insertion of glycoprotein molecules
into the monolayers. The compressibility of mixed monolayers increased as a result of hydrogen bonding between bilirubin and
glycoprotein molecules, while the interactions between bilirubin and cholesterol are weakened. The adsorption of glycoprotein
into a monolayer induced changes in molecular surface area depending on the surface pressure and molar fraction of bilirubin.
The transmission electron microscopy of mixed monolayers confirmed the insertion of glycoprotein particles of spherical shape
with an average diameter of about 80 nm into the monolayer.
The text was submitted by the authors in English. 相似文献
107.
Heterobimetallic hexanuclear cyano-bridged complexes, [{Fe(Tp)(CN)3}4{M(MeCN)(H2O)2}(2)].10H2O.2MeCN [M = Ni (1), Co (2), Mn (3); Tp = hydrotris(1-pyrazolyl)borate], have been synthesized in H2O-MeCN solution. Complexes 1-3 are isostructural and hexanuclear with [{Fe(Tp)(CN)3}4{M(MeCN)(H2O)2}2] units linked by hydrogen bonds to form a 2D-structure in the solid state. Complex 1 is a canted antiferromagnet that undergoes a field-induced spin-flop-like transition at approximately 1 T and 2 K. At 4.45 K 1 has a transition to paramagnetic state of noninteracting S = 4 magnetic clusters. However, 2 and 3 show antiferromagnetic intracluster coupling. Facile loss of solvent from 2 alters the local symmetry resulting in changing the intracluster interaction from antiferro- to ferromagnetic. 相似文献
108.
Two novel octanortriterpenoids, micranoic acids A (1) and B (2), along with three known compounds, kadsuric acid (3), 3beta-hydroxy-lanost-9(11),24(25)-dien-26-oic acid (4) and schizandronic acid (5), were isolated from the leaves and stems of Schisandra micrantha. The structures of 1 and 2 were determined by 1D and 2D NMR spectroscopic analysis. Micranoic acids A and B represent a new group of triterpenes in which the entire C-17 side chain has lost. This is the first report of octanortriterpenoids isolated from the family Schisandraceae. 相似文献
109.
A cytotoxic compound from the leaves of Juglans mandshurica 总被引:1,自引:0,他引:1
From Juglans mandshurica leaves, a new quinone compound was isolated through bioassay-guided fractionation. The structure elucidation of the compound was established based on spectroscopic studies, notably of the 2D NMR spectra. The compound exhibited moderate cytotoxic activities against Hela, MCF-7, BGC823 and 3T3-Llcell lines with IC50 ranges from 7.5 to 26.8 μmol/L. 相似文献
110.
Human immunodeficiency virus type 1 (HIV-1) Rev protein is known to regulate the expression of proteins via binding to an RNA site termed the HIV Rev response element (RRE) presumably with a defined shape, mediated mainly by electrostatic interactions. We have developed a quantitative method based on CE-LIF detection for a systematic evaluation of interactions between a truncated RRE (tRRE) RNA and an HIV-1 Rev peptide. Employing a fluorescently labeled HIV-1 Rev protein fragment (RevF) as a probe, buffers were evaluated for the separation and detection as well as for the RNA shape-specific formation of the complex. Selection of an optimal buffer condition allowed us to perform quantitation of the tRRE-RevF complex formation and determine its dissociation constant. In addition, competitive inhibitions of the RNA-peptide interaction by some aminoglycosides were evaluated quantitatively by monitoring the complex peak, resulting in determination of IC(50) values. This sensitive and reliable CE-LIF-based method would be of interest in developing various screening systems for RNA interference in drug discovery. 相似文献