全文获取类型
收费全文 | 32961篇 |
免费 | 1098篇 |
国内免费 | 31篇 |
专业分类
化学 | 22443篇 |
晶体学 | 233篇 |
力学 | 635篇 |
数学 | 4730篇 |
物理学 | 6049篇 |
出版年
2023年 | 271篇 |
2022年 | 245篇 |
2021年 | 412篇 |
2020年 | 546篇 |
2019年 | 517篇 |
2018年 | 712篇 |
2017年 | 664篇 |
2016年 | 1280篇 |
2015年 | 1022篇 |
2014年 | 1037篇 |
2013年 | 2130篇 |
2012年 | 2373篇 |
2011年 | 2544篇 |
2010年 | 1446篇 |
2009年 | 1206篇 |
2008年 | 2143篇 |
2007年 | 2102篇 |
2006年 | 1838篇 |
2005年 | 1644篇 |
2004年 | 1357篇 |
2003年 | 1031篇 |
2002年 | 921篇 |
2001年 | 679篇 |
2000年 | 581篇 |
1999年 | 431篇 |
1998年 | 312篇 |
1997年 | 229篇 |
1996年 | 357篇 |
1995年 | 227篇 |
1994年 | 229篇 |
1993年 | 274篇 |
1992年 | 253篇 |
1991年 | 163篇 |
1990年 | 159篇 |
1989年 | 129篇 |
1988年 | 132篇 |
1987年 | 127篇 |
1986年 | 127篇 |
1985年 | 194篇 |
1984年 | 162篇 |
1983年 | 128篇 |
1982年 | 111篇 |
1981年 | 111篇 |
1980年 | 83篇 |
1979年 | 100篇 |
1978年 | 86篇 |
1977年 | 76篇 |
1976年 | 78篇 |
1975年 | 72篇 |
1973年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
R. Usón L.A. Oro D. Carmona M.A. Esteruelas C. Foces-Foces F.H. Cano S. García-Blanco A.Vázquez De Miguel 《Journal of organometallic chemistry》1984,273(1):111-128
A new series of cationic areneiridium(I) complexes of formula [Ir(barrelene)(arene)]+ or [Ir(barrelene)(PhNRPh)]+ (R= Ph or H) have been synthesized from neutral iridium complexes of the type [IrY(barrelene)]x (barrelene = Me3TFB, Y = Cl or OMe (x = 2), Y = acac (x = 1); barrelene = TFB, Y = OMe (x = 2), Y = acac (x = 1)). The crystal structures of [Ir(Me3TFB)(1,4-C6H4Me2)]ClO4 and [Ir(TFB)(PhNPh2)]BF4·CH2Cl2 have been determined by X-ray diffraction. They crystallize in the space groups Pbca and Pna21 respectively with lattice constants of 17.6947(11), 15.8072(10), 16.0019(11) Å and 9.8059(2), 20.8097(9), 14.3367(4) Å. Final R factors were 0.063 and 0.042 for the observed data. Both complexes show a staggered arrangement between the arene and the TFB moieties and deviation from planarity of the coordinated arene ligands. In the second complex the IrC and NC distances, the CNC angle, the type of arene puckering, and the spectroscopic data indicate a distortion of the coordinated arene towards a η5-coordinated iminocyclohexadienyl form. 相似文献
102.
M. García-León C. I. Sánchez-Angulo 《Journal of Radioanalytical and Nuclear Chemistry》1987,115(2):377-388
The analysis of99Tc was carried out in filter, peat and rainwater samples. A solvent extraction technique was used to separate Tc from them, where tributylphosphate was the extracting agent. Radiochemical yield was obtained by using99mTc as an internal tracer. A typical value of 60% was found for it. However, problems encountered in its determination are discussed in the text. Additionally, rainwater samples were analyzed for137Cs. This was adsorbed in ammonium phosphomolibdate. Radiochemical yield was obtained by using134Cs as an internal tracer.Work partially supported under Contract CAICYT No. 2849/83. 相似文献
103.
Martínez-Alvarez R Martín N Seoane C Suárez M Pérez R Rodríguez H Kayali N 《Rapid communications in mass spectrometry : RCM》2001,15(10):758-762
The electrospray ionisation (ESI) in negative mode of the pharmacologically significant 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazin-2-thiones, and their subsequent fragmentations using an ion-trap mass spectrometer, have been investigated. Experiments on sequential product ion fragmentations (MS(n)) were performed in order to elucidate the degradation pathways for these compounds. The data presented show that the fragmentation of the even-electron [M - H](-) ions could proceed through an internal nucleophilic substitution displacement. Decarboxylation and extrusion of carbon disulfide are other fragmentations observed. 相似文献
104.
105.
In the two-hase water-nitrobenzene extraction system, a method for gradual separation of Cs+, Sr2+ and Ba2+ from the mixture of cations forming stable non-extractable complexes with ethylenediamine-N, N, N,N-tetraacetic acid in the presence of the sodium salt of dicarbollylcobaltate anion {[-(3)-1, 2-B9C2H11]2 Co(III)}– and polyethylene glycol ligand with a mean relative molecular mass of 400 (PEG 400), respectively, was developed. In the first extraction step, Cs+ was extracted into the organic phase while the other cations studied (Ca2+, Sr2+, Ba2+, Zn2+, Co2+, Ce3+) remained in the aqueous phase. In the second extraction step, Sr2+ and Ba2+ were extracted into the nitrobenzene phase. Finally, in the following reextraction step, Sr2+ was transferred into the aqueous phase while Ba2+ remained in the organic phase. 相似文献
106.
A mild and new procedure for the selective cleavage of an alkoxycarbonyl group (Boc, CBz) in N,N-dicarbamoyl-protected amino compounds is described. The method is based on the use of lithium bromide in acetonitrile and is compatible with a large range of other functionalities present in the substrates. Compared with other reported methodologies, the procedure is particularly useful for the Cbz-selective cleavage in N,N-Ts,Cbz-diprotected amines. A rationalization of the selectivity supported by ab initio calculations is also presented. 相似文献
107.
Using two-dimensional electrophoresis we investigated the effect of 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT; induction with 1 mM ALA for 4 h followed by blue light dose of 18 J/cm2) on the protein expression in HL60 leukemia cells. ALA-PDT resulted in extensive qualitative and quantitative changes in the protein pattern of HL60 cell lysates. Of more than 1350 protein spots recognized on the protein maps of ALA-induced cells, seven proteins were enhanced and 17 suppressed following irradiation. Three of these, calreticulin precursor, p58 microsomal protein (ERp57) and protein disulfide isomerase (p55) have been identified by matrix-assisted laser desorption and ionization-mass spectrometry and the pI/molecular weight parameters of the affected proteins were estimated by computer analysis. The findings suggest participation of endoplasmic reticulum Ca(2+)-binding chaperones and/or Ca2+ signaling in ALA-PDT mediated cytotoxicity. 相似文献
108.
Vladimír Kvasnička 《Chemical physics letters》1976,43(2):377-381
A second-quantization representation of the Epstein-Nesbet partitioning of the total electronic hamiltonian is suggested. In this approach, the unperturbed hamiltonian contains not only the one-particle orbital energies but also the Coulomb and corresponding exchange two-particle terms. Such a hamiltonian can advantageously be used in all branches of the many-body diagrammatic perturbation theory for simple and correct inclusion of the diagonal ladder and ring diagrams in all orders of perturbation theory. 相似文献
109.
B. Y. Moreno-Gutiérrez M. T. Olguín 《Journal of Radioanalytical and Nuclear Chemistry》2003,256(2):345-348
The sorption of Hg(II) from aqueous and organo aqueous solutions was investigated by Mexican natural erionite. The mercury chemical species (anionic, cationic or neutral) were determined by high voltage electrophoresis, and the mercury chemical species present in the aqueous media were simulated by a program MEDUSA. The mercury sorption process was monitored during 48 hours. The mercury content was determined by neutron activation analysis. Mixtures of benzene/water[Hg(II)], toluene/water[Hg(II)] and ethanol/water[Hg(II)] were chosen as organo-aqueous media. It was found that both the mercury chemical species and the dielectric constant of solvents play an important role in the mercury sorption by erionite. 相似文献
110.
The fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) was evaluated for the derivatization of tertiary amphetamines prior to liquid chromatographic analysis. Conditions for the derivatization were investigated, including the reaction time, the derivatization reagent concentration and the pH, using N-methylephedrine as a model compound. On the basis of these studies, a method for the quantification of N-methylephedrine is presented. The method involves derivatization with FMOC at ambient temperature and separation of the derivatives formed on a LiChrospher C18, 5 microns, 125 x 4 mm id column using acetonitrile-water gradient elution. The proposed procedure shows good linearity, accuracy and reproducibility in the 1.0-25.0 micrograms mL-1 concentration range. The limit of detection was 0.1 microgram mL-1 and the limit of quantification was 0.5 microgram mL-1. The utility of the assay was demonstrated by determining N-methylephedrine in water and urine samples. 相似文献