全文获取类型
收费全文 | 2079篇 |
免费 | 182篇 |
国内免费 | 44篇 |
出版年
2023年 | 17篇 |
2022年 | 20篇 |
2021年 | 18篇 |
2020年 | 43篇 |
2019年 | 40篇 |
2018年 | 51篇 |
2017年 | 42篇 |
2016年 | 45篇 |
2015年 | 55篇 |
2014年 | 65篇 |
2013年 | 102篇 |
2012年 | 40篇 |
2011年 | 125篇 |
2010年 | 116篇 |
2009年 | 137篇 |
2008年 | 95篇 |
2007年 | 132篇 |
2006年 | 137篇 |
2005年 | 127篇 |
2004年 | 140篇 |
2003年 | 61篇 |
2002年 | 121篇 |
2001年 | 53篇 |
2000年 | 35篇 |
1999年 | 40篇 |
1998年 | 71篇 |
1997年 | 25篇 |
1996年 | 43篇 |
1995年 | 67篇 |
1994年 | 27篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1976年 | 6篇 |
1973年 | 8篇 |
1972年 | 7篇 |
1971年 | 5篇 |
排序方式: 共有2305条查询结果,搜索用时 484 毫秒
21.
Dr. E. Joan Blanchette-Mackie Thomas Briggs Sidney S. Chernick Robert O. Scow 《Cell and tissue research》1986,244(1):95-105
Summary Cultured mouse (J774.1) macrophages accumulated triacylglycerol, but no cholesteryl ester or cholesterol, when incubated in albumin-poor medium with serum-activated lipid particles containing 84 mol% trioleoylglycerol and 9 mol% cholesteryl oleate. Accumulation of triacylglycerol by cells was associated with hydrolysis of particulate triacylglycerol to fatty acid and glycerol. Both acyl and glyceryl moieties of particulate triacylglycerol were recovered in cellular triacylglycerol with a molar ratio of 3.6. The cells also accumulated fatty acid and monoacylglycerol. Whether acylglycerol was taken up as a single molecular species, such as monoacylglycerol, or as several species can not be determined by the present findings. Macrophages incubated with lipid particles for 24 h had many lipid particles attached to cell surfaces and numerous intracellular lipid droplets. The surface film of attached particles was continuous with the outer leaflet of plasma membrane of the cells. Particles partially depleted of core triacylglycerol and collapsed surface films were found attached to surfaces of macrophages. There was no morphological evidence that lipid particles were taken up intact by cells, through endocytosis or phagocytosis. Macrophages incubated with lipid particles also contained intracellular lamellar structures. They varied in size and shape, and were located in the periphery of cells, sometimes near lipid droplets and endoplasmic reticulum. Only 3% of the lamellar structures were associated with lysosomes, indicating they probably were not of lysosomal origin. Lipid particles attached to cells decreased in size and number, and lamellar structures developed at the surface of particles, or replaced the particles, when glutaraldehyde-fixed specimens were incubated at 25° C, demonstrating lipolytic activity at the surface of macrophages. Our findings suggest that particulate triacylglycerol was hydrolyzed by lipoprotein lipase at the surface of macrophages, and that fatty acid and monoacylglycerol formed by lipolysis were transported directly into the cells to be reesterified. When lipolytic products were taken up faster than they could be utilized, they accumulated as lamellar structures in the cells.Abbreviations MEM
Eagle's alpha modification of minimum essential medium 相似文献
22.
Short- and Long-Term Alterations of Gene Expression in Limbic Structures by Repeated Electroconvulsive-Induced Seizures 总被引:4,自引:2,他引:2
Vincent Leviel Catherine Fayada Bernard Guibert Michel Chaminade Georges Machek Jacques Mallet Nicole Faucon Biguet† 《Journal of neurochemistry》1990,54(3):899-904
Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment. 相似文献
23.
Lisette Waits Stephanie Dunkle F. E. Wilkinson P. Moreau Keri Safranski T. Reust Dorothy M. Morré D. J. Morré 《Protoplasma》1990,154(1):8-15
Summary Transfer of radiolabeled lipids from dictyosome-like structures (DLS) from testis tubules of the guinea pig as donor to unlabeled plasma membrane from testis tubules immobilized on nitrocellulose as acceptor was studied in a completely cell-free system. As a general label for lipids of the donor DLS, isolated testis tubules were incubated with [14C]acetate. Time- and temperature-dependent transfer of [14C]acetate labeled constituents was observed in the cellfree system. However, despite the fact that phospholipids and other constituents were highly labeled in the donor fraction, primarily radioactive sterols were transferred to the plasma membrane acceptor vesicles. Transfer at 37°C represented 0.4 to 0.7% of the total radiolabeled cholesterol at 37°C but little or no transfer occurred at 4°C. The sterols transferred exhibited Chromatographic mobilities corresponding to those of cholesterol and lanosterol. Similar results were obtained with [14C]mevalonic acid. In subsequent experiments, cholesterol transfer from DLS to plasma membrane was demonstrated by incubation of DLS with [3H]squalene which was converted into sterol or with [14C]cholesterol. Transfer of sterols required ATP, but not cytosol, and was both time- and temperature-dependent. DLS were more effective than either endoplasmic reticulum or plasma membrane as the donor fraction. The results from the cell-free analysis suggest a possible functional role of the DLS in sterol biogenesis and transfer to the plasma membrane during spermatid development.Abbreviations DLS
dictyosome-like structure(s)
- PBS
phosphatebuffered saline
- HEPES
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- BSA
bovine serum albumin 相似文献
24.
B. Eva Villaroya Luis A. Oro Fernando J. Lahoz Andrew J. Edwards Miguel A. Ciriano Pablo J. Alonso Antonio Tiripicchio Marisa Titipicchio Camellini 《Inorganica chimica acta》1996,250(1-2):241-264
The multiple coordination possibilities of 1,8-naphthyridine-2-one (HOnapy) and 5,7-dimethyl-1,8-napthyridine-2-one (HOMe2napy) ligands allow the synthesis of a variety of tri- di- and mononuclear complexes, showing fluxional behaviour and frequent exchange of the coordinated ML2 fragments. Thus, reactions of [M2(μ-OMe)2(cod)2] (cod = 1,5-cyclooctadiene) with HOnapy and HOMe2napy yield the compounds of the general formula [M(μ-OR2napy) (cod)]n (M = Ir, R = Me (1a, 1b, H (2); M = Rh, R = Me (3a, 3b). They crystallise as inconvertible yellow (a) and purple/orange (b) forms and also show a puzzling behaviour in solution. X-ray diffraction studies on both forms (3a, 3b) and spectroscopic data reveal that the yellow forms are mononuclear complexes whilst the dark-coloured crystals contain dinuclear complexes. In solution, the nuclearity of the complexes depends on the solvent. In addition both types of complexes are fluxional. The mixed-ligand complexes [M2(μ-OMe2napy)2(CO)2(cod)] M = Ir (5), Rh (6) have been isolated and characterised; they are found to be intermediates in the synthesis of the trinuclear complexes [M3(μ3-OMe2napy)2(CO)2(cod)2]+ M = Rh (8), Ir (9). Reactions of [IrCl(CO)2(NH2-p-tolyl] with the complexes [Rh(μ-OR2napy)(diolefin)]n followed by addition of a poor donor anion is a general one-pot synthesis for the hetertrinuclear complexes [Rh2Ir(μ3-OR2napy)2(CO)2(diolefin)2]+ (R=Me, DIOLEFIN = cod (10), tetrafluorobenzo-barrelene (tfbb) (11), 2,5-norbornadiene (nbd) (12); R=H, DIOLEFIN=cod (13)). This synthesis follows a stepwise mechanism from the mononuclear to the trinuclear complexes in which mixed-ligand heterodinuclear complexes are involved as intermediates of the type [(diolefin)Rh(μ-OMe2napy)2Ir(CO)2]. Heteronuclear complexes which possess the core [RhIr2]3+, such as [RhIr2(μ3-OR2napy)2(CO)2(cod)2]BF4 (R=Me (14), H (15)), result from the reaction of 1 or 2 with [Rh(CO)2Sx]+ (S = solvent). The trinuclear complexes undergo two chemically reversible one-electron oxidation processes. The chemical oxidation of 10, 14 and 9 with silver salts gives the mixed-valence trinuclear radicals [Rh2Ir(μ3-OMe2napy)2(CO)2(cod)2]2+ (16), [RhIr2(μ3-OMe2napy)2(CO)2(cod)2]2+ (17) and [Ir3(μ3-OMe2napy)2(CO)2(cod)2]2+ (18), which have been isolated as the perchlorate and tetrafluoroborate salts. The EPR spectrum of 16 indicates that the unpaired electron is essentially in an orbital delocalised on the metals. The molecular structures of the complexes 3a, 3b, 6, 10b and 16a are described. Crystals of 3a are triclinic, P-1, with a = 9.7393(2), b = 14.0148(4), c = 16.0607(4) Å, α = 88.122(3), β = 83.924(3), γ = 87.038(3)°, Z = 4; 3b crystallises in the Pna2i orthorhhombic space group, with a = 16.7541(3), B = 11.7500(8), c = 17.7508(7) Å, Z = 4; complex 6 is packed in the monoclinic space group P2i/c, a = 9.6371(1), b = 11.8054(4), c = 27.2010(9) Å, β = 90.556(4)°, Z = 4; crystals of 10b are monoclinic, P21/n, with a = 17.546(7), b = 13.232(6), c = 17.437(8) Å, β = 106.18(1)°, Z = 4; crystals of 16a are triclinic, P-1, with a = 10.318(4), b = 12.562(6), C = 19.308(8) Å, α = 92.12(8), β = 97.65(9), γ = 90.68(5)°, Z = 2. The five different structures show the coordination versatility of the OMe2napy molecule as ligand, which behaves as a N,N′-chelating (3a), bidentate N,O-donor (3b, 6), or as a tridentate N,N′,O-donor bridging ligand (10b, 16a). 相似文献
25.
The reactions of cadmium halides with the 15-membered macrocyclic crown ethers, 15-crown-5 and benzo-15-crown-5, have been carried out and six new complexes have been isolated and structurally characterized. Metal to ligand stoichiometries of 1:1, 2:1, 3:1 and 3:2 have been observed with a variety of different formulations. Examples of charge separated ion pairs ([(NH4)(benzo-15-crown-5)2]2[Cd2I6]), halogen bridged monomers, dimers or polymers ([Cd(15-crown-5)(OHMe)(μ-Br)CdBr3], [Cd(15-crown-5)(μ-Br)2CdBr(μ-Br)]2(isolated from the same reaction mixture) and [(CdCl2)2CdCl2(15-crown-5)]n), and hydrogen bonded finite chains or polymers ([(Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN and [CdI2(OH2)2(THF)]·benzo-15-crown-5) have been isolated. Three different types of 15-crown-5 coordination modes have been observed in these complexes. In-cavity coordination resulting in pentagonal bipyramidal geometries about Cd2+ was observed in [(CdCl2)2CdCl2(15-crown-5)]n, [Cd(15-crown-5)(OHMe)(μ-Br)CdBr3], and [Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN, [Cd(15-crown-5)(μ-Br)2CdBr(μ-Br)]2 displays out-of-cavity coordination with one etheric donor distorted into an axial position of a distorted pentagonal bipyramid. The third coordination mode is secondary sphere coordination via hydrogen bonding which is observed for [Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN. The good fit of Cd2+ within the cavity of 15-crown-5 results in shorter bonding contacts and a more narrow distribution in Cd---O values (2.273(7)-2.344(6) Å) than observed for cadmium halide complexes of 18-crown-6 (Cd---O = 2.69(1)–2.81(1) Å). 相似文献
26.
Harry Adams Neil A. Bailey Philippe Bertrand Simon R. Collinson David E. Fenton Simon J. Kitchen 《Inorganica chimica acta》1996,250(1-2):139-148
The cyclocondensation of 2,5-diformylthiophene and the amines N,N-bis-(2-aminoethyl)-2-phenylethylamine, N,N-bis-(2aminoethyl)-t-butyl-amine and N,N-bis-(2-aminoethyl)-t-butyl-amine in the presence of silver(I) salts yields homodinuclear bibracchial tetraimine Schiff base macrocyclic complexes. The structures of two such complexes are also reported. The complex Ag2L4(NO3)(PF6) (2) crystallises in the triclinic space group
, No. 2) and has unit-cell dimensions a = 12.834(6), B = 13.183(6), C = 14.588(7) Å, = 64.86(4), β = 79.77(4), γ = 69.44(3)° with Z = 2; there is a monodentate and singly bridging nitrate anion present and the Ag---Ag separation is 4.161 Å. The complex Ag2L4(CH3CN)2(BF4)2·CH3CN (9) crystallises in the triclinic space group
, No. 2) and has unit-cell dimensions a = 9.297(4), B = 12.985(3), C = 21.770(5) Å, = 91.570(10), β = 92.33(3), γ = 97.92(3) ° with Z = 2; there is a strongly bonded acetonitrile molecule coordinated to each silver atom and the Ag---Ag separation is 4.920 Å. 相似文献
27.
N. Kositzyna M. Antipin K. Lyssenko P. S. Pregosin G. Trabesinger 《Inorganica chimica acta》1996,250(1-2):365-373
A series of cationic allyl complexes of Pd(II) derived from the diterpene carvone
have been synthesised and characterised using the chelating ligands, bipyridine, 1,8-phenanthroline, neocuproin, S,S (-)-Chiraphos and R (+)-Binap as co-ligands. These complexes can be readily converted to new organic products in which one C---H bond of the allyl methyl has been substituted. The structure of a bipyridyl complex as its tetraphenyl borate salt has been determined via X-ray diffraction. 2-D NOESY studies on the Chiraphos and Binap complexes are reported. The Binap, but not the Chiraphos, complex reveals η3-η3η3 isomerisation at ambient temperature. 相似文献
28.
New mixed metal complexes SrCu2(O2CR)3(bdmap)3 (R = CF3 (1a), CH3 (1b)) and a new dinuclear bismuth complex Bi2(O2CCH3)4(bdmap)2(H2O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF2 and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi2O3 at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2J = 34.0(8) cm−1. Crystal data for 1a: C27H51N6O9F9Cu2Sr/THF, monoclinic space group P21/m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) Å3, Z = 2; for 1b: C27H60N6O9Cu2Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) Å3, Z = 8; for 2: C22H48O11N4Bi2, monoclinic space group P21/c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) Å3, Z = 4. 相似文献
29.
The presence of galanin was examined in the cat gut and related autonomic nervous structures using radioimmunoassay (RIA) and high performance liquid chromatography (HPLC). In the gut wall, the concentration of galanin-like immunoreactivity (GAL-LI) was assayed separately in the muscular layers with the nervous plexuses and in the mucosa and ranged from 0.35 to 0.55 pmol/g wet tissue. In the autonomic nervous structures, GAL-LI concentrations ranged from 0.22 (thoracic spinal ganglia) to 0.81 (inferior mesenteric ganglion) pmol/g wet tissue. The presence of galanin was checked by HPLC in the antrum, intestine, and colon. HPLC of extractable material revealed a major peak coeluting with the synthetic porcine peptide and minor earlier peaks representing likely different molecular forms of galanin. Our study strengthens the notion that galanin acts in nervous control of the cat gut functions. 相似文献
30.
James M. Chen Spero Manolatos Paul W. Brandt-Rauf Randall B. Murphy Regina Monaco Matthew R. Pincus 《Journal of Protein Chemistry》1996,15(6):511-518
The three-dimensional structures of theras-p21 protein and its protein inhibitor, rap-1A, have been computed bound to theras-binding domain, RBD (residues 55–131), of theraf-p74 protein, a critical target protein ofras-p21 in theras-induced mitogenic signal transduction pathway. The coordinates of RBD have been reconstructed from the stereoview of an X-ray crystal structure of this domain bound to rap-1A and have been subjected to energy minimization. The energy-minimized structures of bothras- p21 and rap-1A, obtained in previous studies, have been docked against RBD, using the stereo figure of the RBD-rap-1A complex, based on a six-step procedure. The final energy-minimized structure of rap-1A-RBD is identical to the X-ray crystal structure. Comparison of theras-p21- and rap-1A-RBD complexes reveals differences in the structures of effector domains ofras-p21 and rap-1a, including residues 32–47, a domain that directly interacts with RBD, 60–66, 96–110, involved in the interaction ofras-p21 withjun kinase (JNK) andjun protein, and 115–126, involved in the interaction of p21 with JNK. The structure of the RBD remained the same in both complexes with the exception of small deviations in its-2 binding loop (residues 63–71) and residues 89–91, also involved in binding to rap-1A. The results suggest that the binding of these two proteins to RBD may allow them to interact with other cellular target proteins such as JNK andjun. 相似文献