全文获取类型
收费全文 | 1433篇 |
免费 | 126篇 |
国内免费 | 49篇 |
出版年
2023年 | 16篇 |
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 34篇 |
2019年 | 25篇 |
2018年 | 29篇 |
2017年 | 27篇 |
2016年 | 48篇 |
2015年 | 54篇 |
2014年 | 82篇 |
2013年 | 91篇 |
2012年 | 66篇 |
2011年 | 68篇 |
2010年 | 57篇 |
2009年 | 62篇 |
2008年 | 72篇 |
2007年 | 50篇 |
2006年 | 73篇 |
2005年 | 71篇 |
2004年 | 76篇 |
2003年 | 42篇 |
2002年 | 44篇 |
2001年 | 34篇 |
2000年 | 34篇 |
1999年 | 35篇 |
1998年 | 41篇 |
1997年 | 29篇 |
1996年 | 38篇 |
1995年 | 31篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 21篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1608条查询结果,搜索用时 15 毫秒
21.
Cecilia Del Casino Yi-Qin Li Alessandra Moscatelli Monica Scali Antonio Tiezzi Mauro Cresti 《Biology of the cell / under the auspices of the European Cell Biology Organization》1993,79(2):125-132
Summary— The distribution of microtubules was investigated in Nicotiana tabacum pollen tubes at different stages of tube growth by immunofluorescence microscopy. Using specific antibodies, the presence of microtubules consisting of different tubulin isoforms was tested. α-, β- and tyrosinated α-tubulin were present within the tube, whereas the acetylated form was lacking. The presence of tubulin subunits in pollen tube extracts was also investigated by immunoblotting analyses. The use of a confocal laser scanning microscope integrated with computer-assisted imaging, allowed a detailed visualization of the microtubule distribution and organization. Cytoplasmic microtubules organized as short bundles with various orientations were detected at the apex of long tubes. 相似文献
22.
Young JH 《Biotechnology and bioengineering》1993,42(1):125-132
Effect of tube diameter on steam-in-place sterilization of dead-ended tubes was studied by examining temperature profiles and rates of kill of Bacillus stearothermophilus spores. Time required for sterilization was determined for 9.4-cm-long tubes with various inside diameters from 0.4 to 1.7 cm. Sterilization time increased with decreasing tube diameter. Experimentally measured kill kinetics in 1.7-cm tubes were in agreement with those predicted if measured temperatures represented saturated steam. A 12-log spore reduction was achieved in 1.7-cm diameter vertical and horizontal tubes in less than 63 minutes. For smaller diameter tubes, entrapped air remained after 2 hours and rates of kill were very dependent on position within the tube, tube diameter, and tube orientation with respect to the gravitational vector. Times to achieve a 1-log drop in spore population in the smaller tubes were as much as 10 times greater than those expected if measured temperatures represented saturated steam. Sterilization was not achieved throughout the 0.4-cm tubes. Recommendations are made for including steam bleeders or using prevaccum cycles for these smaller diameter tubes. (c) 1993 John Wiley & Sons, Inc. 相似文献
23.
Pollen-tube cell walls are unusual in that they are composed almost entirely of callose, a (1,3)--linked glucan with a few 6-linked branches. Regulation of callose synthesis in pollen tubes is under developmental control, and this contrasts with the deposition of callose in the walls of somatic plant cells which generally occurs only in response to wounding or stress. The callose synthase (uridine-diphosphate glucose: 1,3--d-glucan 3--d-glucosyl transferase, EC 2.4.1.34) activities of membrane preparations from cultured pollen tubes and suspension-cultured cells of Nicotiana alata Link et Otto (ornamental tobacco) exhibited different kinetic and regulatory properties. Callose synthesis by membrane preparations from pollen tubes was not stimulated by Ca2+ or other divalent cations, and exhibited Michaelis-Menten kinetics only between 0.25 mM and 6 mM uridine-diphosphate glucose (K
m 1.5–2.5 mM); it was activated by -glucosides and compatible detergents. In contrast, callose synthesis by membrane preparations from suspension-cultured cells was dependent on Ca2+, and in the presence of 2 mM Ca2+ exhibited Michaelis-Menten kinetics above 0.1 mM uridine-diphosphate glucose (K
m 0.45 mM); it also required a -glucoside and low levels of compatible detergent for full activity, but was rapidly inactivated at higher levels of detergent. Callose synthase activity in pollen-tube membranes increased ten fold after treatment of the membranes with trypsin in the presence of detergent, with no changes in cofactor requirements. No increase in callose synthase activity, however, was observed when membranes from suspension-cultured cells were treated with trypsin. The insoluble polymeric product of the pollen-tube enzyme was characterised as a linear (1,3)--d-glucan with no 6-linked glucosyl branches, and the same product was synthesised irrespective of the assay conditions employed.Abbreviations Ara
l-arabinose
- CHAPS
3-[(3-cholamidopropyl)dimethylammonia]-1-propane sulphonic acid
- DAP
diphenylamine-aniline-phosphoric acid stain
- Gal
d-galactose
- Glc
d-glucose
- Man
d-mannose
- Mes
2-(N-morpholino)ethane sulphonic acid
- Rha
d-rhamnose
- Rib
d-ribose
- TFA
trifluoroacetic acid
- UDPGlc
uridine-diphosphate glucose
- Xyl
d-xylose
This research was supported by funds from a Special Research Centre of the Australian Research Council. H.S. was funded by a Melbourne University Postgraduate Scholarship and an Overseas Postgraduate Research Studentship; S.M.R. was supported by a Queen Elizabeth II Research Fellowship. We thank Bruce McGinness and Susan Mau for greenhouse assistance, and Deborah Delmer and Adrienne Clarke for advice and encouragement throughout this project. 相似文献
24.
Mitsuo Matsuda Toshiya Nosaka Masaaki Sato Norio Ohshima 《European journal of applied physiology and occupational physiology》1993,66(2):122-126
To evaluate the effects of exercise on aortic wall elasticity and elastic components, young male rats underwent various exercise regimes for 16 weeks. In the exercised rats, the aortic incremental elastic modulus decreased significantly when under physiological strain. The aortic content of elastin increased significantly and the calcium content of elastin decreased significantly in the exercised group. The accumulated data from the exercised and sedentary groups revealed that the elastin calcium content was related positively to the incremental elastic modulus. We concluded that physical exercise from an early age decreases the calcium deposit in aortic wall elastin and that this effect probably produced in the exercised rats a distensible aorta. 相似文献
25.
26.
Pollen tubes of Nicotiana tabacum and Petunia hybrida show pulsatory growth. Phases of slow growth lasting minutes are interrupted by pulse-like elongations lasting 10–20 seconds involving an increase of growth rate by up to 24-fold. Inhibition of dictyosome activity with brefeldin A or monensin did not result in an inhibition of pulsatory growth but eventually stopped pollen tube elongation. In contrast to this the inhibition of the cytoskeletal elements with cytochalasin D and colchicine caused the pollen tubes to abandon the pulse-like elongations. It was concluded that the activity of the dictyosomes does not have a controlling function in the mechanism of pulsatory growth, even though it is necessary for pollen tube elongation, since cell wall material is provided by secretory vesicles deriving from the Golgi apparatus. In contrast the cytoskeletal elements, actin and microtubules, seem to play an important regulatory role in the pulse-like elongations. In addition, it was observed that during the experiments several pollen tubes burst upon the completion of a pulse-like expansion, indicating on the one hand that the internal turgor is the driving force of the pulse-like expansions. On the other hand, the bursting shows that the pollen tube cell wall is rather weak at the end of a pulse, indicating that at this point of time it is either thinner or less stable than during the slow growth phase or at the beginning of a pulse. 相似文献
27.
毛细管水解及反相高效液相色谱分析蛋白质的氨基酸组成陈平,梁宋平(湖南师范大学生物研究所,长沙410006)氨基酸组成的分析是阐明蛋白质和多肽化学特性的基础,在蛋白质与多肽的氨基酸组成分析中,常采用对水解管反复充氮并抽真空的方法使蛋白质和多肽在隔绝氧气... 相似文献
28.
Summary The monoclonal antibody (MAb) JIM5, marking acidic pectins, was used to localize ultrastructurally pectin molecules in the pollen tube wall ofNicotiana tabacum. Longitudinal sections of LR-White embedded pollen tubes were exposed to antibody treatment; accumulations of pectins were identified by counting the density of the gold particles representing the pectin epitopes along the pollen tube wall. Significant accumulations of gold grains were marked and the distances between them were measured. In many pollen tubes a more or less regular distribution of the accumulations was observed along the tube indicating a periodical deposition of pectin. The distances between the accumulations were 4–6 m. Most of the label was found in the inner part of the outer layer of the bilayered cell wall. These findings correspond to and confirm the earlier observation by our group reporting ring-shaped periodical deposits in pollen tubes after immunofluorescence labelling with the MAb JIM5 under the confocal laser scanning microscope.Abbreviations Ab
antibody
- MAb
monoclonal antibody 相似文献
29.
Effects of heavy metals on pollen tube growth and ultrastructure 总被引:3,自引:0,他引:3
Summary The influence of different concentrations of the heavy metals cadmium (Cd2+), cobalt (Co2+), copper (Cu2+), iron (Fe2+ and Fe3+), mercury (Hg2+), manganese (Mn2+), and zinc (Zn2+), plus aluminium (Al3+) (a toxic metal in polluted areas), on pollen germination and tube growth ofLilium longiflorum was investigated using light microscopy. Effects could be observed with 3 M and 100 M of heavy metal, added as chloride salts to the medium. Cd2+, Cu2+, and Hg2+, showed the greatest toxicity, whereas germination and growth rate was less affected by Mn2+. Affected tubes showed swelling of the tip region. Tubes treated with Cd2+, Co2+, Fe2+, Fe3+, Hg2+, and Mn2+ were also prepared for ultrastructural studies. In all cases, the main effect was abnormal cell wall organization, mostly at the tip, where round, fibrillar aggregates, the shape and size of secretory Golgi vesicles were formed. They built up a loose network which could be up to 10 m thick compared to untreated tubes where the cell wall was composed of thin layers of long fibrils and about 100 nm thick. Cd2+ was the only metal which produced effects at the intracellular level: organelle distribution within the tip region appeared disorganized. A general mechanism of heavy metal action on pollen tube growth is discussed. 相似文献
30.
A. Chandran 《Hydrobiologia》1995,304(3):169-174
The structure and musculature of the mouth tube of the lernaeopodidIsobranchia appendiculata Heegaard is described in detail. Situated on the median eminence, the mouth tube appears to be lodged inside a median longitudinal
groove on the ventral wall of the cephalothorax. The components of the mouth tube, the labrum and the labium are loosely held
together along their lateral edges. The thin, transparent walls of both the labrum and the labium are reinforced by chitinous
rods. The musculature of the mouth tube consists of two pairs ofretractores oris, four pairs ofcompressores labri and two pairs oflevatores labii. The mandibles are operated by a pair of antagonistic muscles, theroto adductor mandibulae androto abductor mandibulae. Like other lernaeopodids,I. appendiculata resorts to a browsing type of feeding. 相似文献