全文获取类型
收费全文 | 8515篇 |
免费 | 622篇 |
国内免费 | 5篇 |
出版年
2023年 | 43篇 |
2022年 | 93篇 |
2021年 | 195篇 |
2020年 | 130篇 |
2019年 | 123篇 |
2018年 | 181篇 |
2017年 | 149篇 |
2016年 | 283篇 |
2015年 | 404篇 |
2014年 | 462篇 |
2013年 | 571篇 |
2012年 | 696篇 |
2011年 | 714篇 |
2010年 | 440篇 |
2009年 | 381篇 |
2008年 | 499篇 |
2007年 | 516篇 |
2006年 | 508篇 |
2005年 | 417篇 |
2004年 | 385篇 |
2003年 | 302篇 |
2002年 | 333篇 |
2001年 | 77篇 |
2000年 | 56篇 |
1999年 | 62篇 |
1998年 | 90篇 |
1997年 | 36篇 |
1996年 | 52篇 |
1995年 | 53篇 |
1994年 | 50篇 |
1993年 | 50篇 |
1992年 | 47篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 41篇 |
1988年 | 34篇 |
1987年 | 47篇 |
1986年 | 29篇 |
1985年 | 40篇 |
1984年 | 40篇 |
1983年 | 47篇 |
1982年 | 34篇 |
1981年 | 35篇 |
1980年 | 23篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 35篇 |
1976年 | 20篇 |
1974年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有9142条查询结果,搜索用时 15 毫秒
71.
F1 generace hybrid?Ph. vulgaris L. XPh. coccineus L. je v bílkovinných znacích zhruba intermedierní. V F2 generaci se objevuje ?těpení a r?zné stupně matro- ?i patroklinity. 相似文献
72.
City spore concentrations in the European Economic Community (EEC). VI. Poaceae (Grasses), 1982–1986
Frits Th. M. Spieksma Gennaro D'amato John Mullins Nicole Nolard Reinhard Wachter Eva R. Weeke 《Aerobiologia》1989,5(1):38-43
Summary Airborne grass-pollen concentrations in six cities in the EEC are compared, based on observations from five years, 1982–1986.
Results show that there are quantitative differences both between the monitoring stations and between the years. Very provisionally,
the average seasonal total of the European urban airborne grass-pollen concentration can be put at 4 to 5000 per m3 of air. Also qualitatively, regarding the seasonal fluctuations, there are differences between the stations, and between
the years. Generally, the results confirm that June is the most typical grass-pollen month in northwestern Europe, whereas
in mediterranean Europe May is the more prominent grass-pollen period. There seems to be little coherence between the starting
dates of the grass-pollen season even at relatively nearby stations in northwestern Europe, suggestive for a great influence
of the actual weather situation. 相似文献
73.
The perennial taxa ofCrucianella in Asia form a coherent group, apparently diploid (x = 11) and outbreeding throughout, and should be placed into sect.Roseae. This Irano-Turanian group has its centre of diversity in the mountain systems south of the Caspian Sea and reaches with outposts NE. and E. Anatolia, NE. Iraq, S. Iran and C. Asia. Four species and 13 subspecies (within the polymorphicC. gilanica) are recognized, described (partly as new), and illustrated (Figs. 1–6). Conspectus, keys and distribution maps (Figs. 7 and 8) as well as plesio- and apomorphic character states and data on size of areas are provided (Table 1). There is an obvious correlation between more plesiomorphic taxa with smaller areas in the distribution centre of the group, and more apomorphic taxa with larger areas towards its periphery (Fig. 9). These findings are linked to a working hypothesis on the evolution of the group.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday. 相似文献
74.
15N- and 2H-substituted maleimido-TEMPO spin label ([15N,2H]MTSL) and the fluorescent label 1,5-IAEDANS were used to specifically modify sulfhydryl 1 of myosin to study the orientation of myosin cross-bridges in skeletal muscle fibers. The electron paramagnetic resonance (EPR) spectrum from muscle fibers decorated with labeled myosin subfragment 1 ([15N,2H]MTSL-S1) or the fluorescence polarization spectrum from fibers directly labeled with 1,5-IAEDANS was measured from fibers in various physiological conditions. The EPR spectra from fibers with the fiber axis oriented at 90 degrees to the Zeeman field show a clear spectral shift from the rigor spectrum when the myosin cross-bridge binds MgADP. This shift is attributable to a change in the torsion angle of the spin probe from cross-bridge rotation and is observable due mainly to the improved angular resolution of the substituted probe. The EPR data from [15N,2H]MTSL-S1 decorating fibers are combined with the fluorescence polarization data from the 1,5-IAEDANS-labeled fibers to map the global angular transition of the labeled cross-bridges due to nucleotide binding by an analytical method described in the accompanying paper [Burghardt, T. P., & Ajtai, K. (1992) Biochemistry (preceding paper in this issue)]. We find that the spin and fluorescent probes are quantitatively consistent in the finding that the actin-bound cross-bridge rotates through a large angle upon binding MgADP. We also find that, if the shape of the cross-bridge is described as an ellipsoid with two equivalent minor axes, then cross-bridge rotation takes place mainly about an axis parallel to the major axis of the ellipsoid. This type of rotation may imitate the rotation motion of cross-bridges during force generation. 相似文献
75.
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
76.
The dynamics of individual endogenous cytokinins within the growth cycle (subculture interval) of an auxin-dependent and cytokinin-independent cell suspension culture ofNicotiana tabacum L. (strain VBI-0) were determined using high performance liquid chromatography and radioimmunoassay. In cells grown at an optimum auxin concentration the transient maxima of N6-(2-isopentenyl)adenine and N6-(2-isopentenyl)-adenosine correlated with the onset of cell division. Cultivation of the cells in a partially auxin-deprived medium resulted in ca. tenfold increase of all endogenous cytokinins. A very distinct maximum of N6-(2-sopentenyl) adenine appeared at the beginning of subculture. This indicates that a lack of auxin induced an accumulation of cytokinins predominantly in the form of the free bases, which are physiologically more active than the corresponding ribosides.Abbreviations iP
N6-(2-isopentenyl)adenine
- [9R]iP
N6-(2-isopentenyl)adenosine
-
t-Z
trans-zeatin
-
t-[9R]Z
trans-zeatin riboside
- IAA
indole-3-acetic acid
- NAA
1-naphthaleneacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- f.w.
fresh weight
- SBI
subculture interval
- C
complete medium
- PAD
partially auxin-deprived medium
- RP-HPLC
reverse phase high performance liquid chromatography
- RIA
radioimmunoassay
- PAL
L-phenylalanine ammonia lyase 相似文献
77.
78.
The Lys residues in the 75-residue Ca2+-binding protein calbindin D9k were reductively methylated with13C-enriched formaldehyde. The possible structural effects resulting from the chemical modification were critically investigated by comparing two-dimensional NMR spectra and the exchange rates of some of the amide protons of the native and the modified protein. Our results show that the protein retains its structure even though 10 Lys out of a total of 75 amino acid residues were modified. In the Ca2+- and apo-forms of the protein, the13C-methylated Lys residues can be detected with high sensitivity and resolution using two-dimensional (1H,13C)-heteronuclear multiple quantum coherence (HMQC) NMR spectroscopy. ThepKa values of the individual Lys residues in Ca2+-calbindin D9k and apo-calbindin D9k were obtained by combiningpH titration experiments and (1H,13C)-HMQC NMR spectroscopy. Each Lys residue in the Ca2+- and apo-forms of calbindin D9k has a uniquepKa value. The LyspKa values in the calcium protein range from 9.3 to 10.9, while those in the apo-protein vary between 9.7 and 10.7. Although apo-calbindin D9k has a very similar structure compared to Ca2+-calbindin D9k, the removal of two Ca2+ ions from the protein leads to an increase of thepKa values of the Lys residues. 相似文献
79.
Mariam Lebbadi Antonio Gálvez Eva Valdivia Manuel Martínez-Blueno Mercedes Maqueda 《Archives of microbiology》1994,162(1-2):98-102
Three antibiotic peptides with amoebolytic activity have been purified from culture supernatants of Bacillus licheniformis M-4 (amoebicins m4-A, m4-B, and m4-C). They were hydrophilic peptides consisting of six different amino acids (Asp, Glu, Ser, Thr, Pro, Tyr). Their molecular weights ranged from 3,000 to 3,200. Purified amoebicins were active against human pathogenic and non-pathogenic strains of Naegleria. They also showed a broad antifungal spectrum, but a narrow antibacterial activity.Abbreviations (TFA)
Trifluoroacetic acid 相似文献
80.
Tova Rahn Martin Ridderstrle Hans Tornqvist Vincent Manganiello Gudrun Fredrikson Per Belfrage Eva Degerman 《FEBS letters》1994,350(2-3):314-318
Incubation of rat adipocytes with wortmannin, a potent and selective phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, completely blocked the antilipolytic action of insulin (IC50≈ 100 nM), the insulin-induced activation and phosphorylation of cGMP-inhibited cAMP phosphodiesterase (cGI-PDE) as well as the activation of the insulin-stimulated cGI-PDE kinase (IC50≈ 10–30 nM). No direct effects of the inhibitor on the insulin-stimulated cGI-PDE kinase, the cGI-PDE and the hormone-sensitive lipase were observed. These data suggest that activation of PI 3-kinase upstream of the insulin-stimulated cGI-PDE kinase in the antilipolytic insulin signalchain has an essential role for insulin-induced cGI-PDE activation/ phosphorylation and anti-lipolysis. 相似文献