全文获取类型
收费全文 | 70534篇 |
免费 | 4951篇 |
国内免费 | 2730篇 |
出版年
2024年 | 155篇 |
2023年 | 989篇 |
2022年 | 1412篇 |
2021年 | 1966篇 |
2020年 | 2144篇 |
2019年 | 2766篇 |
2018年 | 2524篇 |
2017年 | 1751篇 |
2016年 | 1760篇 |
2015年 | 2260篇 |
2014年 | 3876篇 |
2013年 | 4616篇 |
2012年 | 2501篇 |
2011年 | 3377篇 |
2010年 | 2565篇 |
2009年 | 3099篇 |
2008年 | 3314篇 |
2007年 | 3312篇 |
2006年 | 3100篇 |
2005年 | 2688篇 |
2004年 | 2424篇 |
2003年 | 2073篇 |
2002年 | 1830篇 |
2001年 | 1345篇 |
2000年 | 1286篇 |
1999年 | 1126篇 |
1998年 | 1082篇 |
1997年 | 1069篇 |
1996年 | 1055篇 |
1995年 | 1099篇 |
1994年 | 1025篇 |
1993年 | 959篇 |
1992年 | 946篇 |
1991年 | 852篇 |
1990年 | 785篇 |
1989年 | 746篇 |
1988年 | 685篇 |
1987年 | 636篇 |
1986年 | 528篇 |
1985年 | 756篇 |
1984年 | 958篇 |
1983年 | 645篇 |
1982年 | 804篇 |
1981年 | 683篇 |
1980年 | 615篇 |
1979年 | 536篇 |
1978年 | 296篇 |
1977年 | 282篇 |
1976年 | 281篇 |
1973年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
Summary Pollen mother cells at early meiotic prophase fromFritillaria lanceolata, F. mutica, Tulbaghia violacea, the lily “Formobel”,Triticum aegilopoides, T. dicoccoides, T. aestivum and synaptic and asynaptic forms ofT. durum were studied in thin sections with the electron microscope (a) in relation to distribution of nuclear pores (b) in respect
of fine structure of the pore complex in those of the first four. The pores were distributed in random clusters during leptotene
to pachytene in all plants, except in the two forms ofT. durum where there were either no pores or so few that they were not detectable. Probably correlated with this, the two membranes
of the nuclear envelope were often widely separated and frequently sacculated. No pores were seen at leptotene in the part
of the envelope to which, in theFritillarias and lily, the nucleolus was adpressed at this time. Evidence supporting a recent model which proposes that annuli are composed
of three rings of eight granular subunits was obtained. These subunits as well as a dense central element, observed in most
pores, were composed of filaments about 3 nm in diameter and evidently protein in character. There was evidence of a continuity
between filaments in the central element and those in the rings of subunits which encircle the pore aperture at both the nuclear
and cytoplasmic sides of the pore. In profiles of pores knobbed filaments were sometimes seen extending laterally from the
pore wall into the perinuclear space at two sides. Questions concerning the role of the annulus are discussed.
The author wish to thank Mr. R. F. Scott for construction to the model. 相似文献
113.
K. Trbacz 《Physiologia plantarum》1992,84(3):448-452
During action potentials triggered by electricity and light, measurements of intra- and extracellular pH in the liverwort Conocephalum conicum L. were carried out by the use of antimony-filled H+ -sensitive microelectrodes. Intracellular pH increased transiently by about 0.05 unit in the course of an action potential, while extracellular pH, measured at the surface of the thallus, remained unchanged. Switching the light off caused a transient increase in intracellular pH by less than 0.1 unit. Turning the light on produced a fast pH decrease by about 0.15 unit followed by a slow increase. When the light was intensive enough, the action potential thus triggered caused a slight increase in intracellular pH superimposed on the phase of a slow pH increment.
The magnitude and time course of the intracellular pH changes seem insufficient for a role as messenger between action potential and the up to 100% increase in the rate of respiration that has been registered in Conocephalum conicum as a consequence of excitation. 相似文献
The magnitude and time course of the intracellular pH changes seem insufficient for a role as messenger between action potential and the up to 100% increase in the rate of respiration that has been registered in Conocephalum conicum as a consequence of excitation. 相似文献
114.
For some foodstuffs, determination of the mycotoxin ochratoxin A (OTA) requires time consuming clean up by means of solid
phase extraction (SPE). Therefore a system for automated SPE was tested for cleaning up roasted coffee as a possible way of
shortening preparation time. Validation of the method in accordance to the so called “Concept '98” led to a LOD of 0.2 μg/kg
and a recovery rate of 92%. By using the described procedure with samples of roasted coffee the OTA contents varied between
the LOD and 3.4 μg/kg. This method was also used to determine ochratoxin A in liquorice roots, ginger and valerian.
Presented at the 26th Mykotoxin Workshop in Herrsching, Germany, May 17–19, 2004 相似文献
115.
《Current biology : CB》2020,30(5):827-839.e4
- Download : Download high-res image (204KB)
- Download : Download full-size image
116.
Origin of bombesin-like peptides in human fetal lung 总被引:2,自引:0,他引:2
Four different forms of bombesin-like immunoreactive peaks were detected in extracts of human fetal lung by the use of reversed-phase high performance liquid chromatography (HPLC). Peaks I, II, III and IV, (increasing retention time), were eluted using a 14-38% of acetonitrile gradient containing 0.1% trifluoroacetic acid (TFA). Peak II was the major material found in the extract of human fetal lung obtained at 16-20 weeks gestation. None of the four compounds contained in the eluted peaks had the same retention time as amphibian bombesin or porcine gastrin releasing peptide (GRP). On reversed-phase HPLC using two different solvent systems TFA or heptafluorobutyric acid (HFBA) as a hydrophobic counter ion, and in gel filtration chromatography, the chromatographic behavior of the main peak (peak II) was the same as that of the carboxyl terminal fragments of GRP, GRP18-27 or GRP19-27. This suggested that the peptide(s) in peak II resembled in composition the carboxy terminal 9 or 10 amino acids of porcine GRP. Following tryptic digestion the material in peak IV was converted to the more polar compound present in peak II. Two other peptide peaks were eluted close to peak II and these were presumed to be a modification of this main peak. One of the possible biosynthetic steps in the formation of bombesin-like peptides in human fetal lung could be a tryptic conversion of a less polar peptide to a more polar form (peak IV to II). 相似文献
117.
Energy calculations have been carried out on high-symmetry cuboctahedral Ni-Al nanoalloy clusters, of varying composition, with the interatomic interactions modelled by the Gupta many-body potential. Relaxations of cuboctahedral fragments cut from the bulk lattice of Ni3Al, with 13-561 atoms, were undertaken, as were relaxations of high symmetry clusters with 55 and 147 atoms. The lowest energy isomers were found to be dominated by three factors: the tendency toward mixing due to the favourable energy of mixing, ΔmixE; the size difference between nickel and aluminium; and the higher cohesive and surface energy of nickel compared to aluminium. The latter two factors favour Al-segregation to the surface. The most stable Ni:Al composition approaches 3:1 for larger clusters. 相似文献
118.
The imaginal pore plates of Hymenoptera apocrita so far examined embody five or six envelope cells respectively. In early developmental stages, however, supernumerary envelope cells have been found. The results are discussed in the context of cell death as a developmental phenomenon. 相似文献
119.
120.
The effects of two glycosylated whey hydrolysates (GWH-Gal A and GWH-Gal B) on glutathione (GSH) and related antioxidant enzymes in SGC-7901 cells were evaluated. Two whey glycosylated hydrolysates promoted an increase in reduced glutathione (GSH) in normal SGC-7901 cells. GSH, glutathione peroxidase (GPx), γ-glutamine cysteine synthetaase (γ-GCS), and catalase (CAT) at 1.0 and 2.0 mg/mL in normal SGC-7901 cells were higher in the GWH-Gal A group than in the GWH-Gal B group (P < 0.05). Compared with GWH-Gal B, GWH-Gal A more strongly inhibited decreases in intracellular GSH, GPx, γ-GCS, CAT, and superoxide dismutase (SOD) in H2O2-induced SGC-7901 cells. Compared with GWH-Gal B, GWH-Gal A at 1.0 and 2.0 mg/mL effectively inhibited increases in lactate dehydrogenase (LDH) and malondialdehyde (MDA) in H2O2-induced SGC-7901 cells (P < 0.05). Therefore, GSH content and related antioxidant enzyme activity levels (GPx, γ-GCS, CAT, SOD) in both normal and H2O2-induced SGC-7901 cells were considerably stronger in the GWH-Gal A group than in the GWH-Gal B group. 相似文献