全文获取类型
收费全文 | 5179篇 |
免费 | 513篇 |
出版年
2023年 | 34篇 |
2022年 | 103篇 |
2021年 | 187篇 |
2020年 | 72篇 |
2019年 | 119篇 |
2018年 | 128篇 |
2017年 | 111篇 |
2016年 | 208篇 |
2015年 | 284篇 |
2014年 | 273篇 |
2013年 | 316篇 |
2012年 | 431篇 |
2011年 | 373篇 |
2010年 | 206篇 |
2009年 | 195篇 |
2008年 | 256篇 |
2007年 | 254篇 |
2006年 | 218篇 |
2005年 | 209篇 |
2004年 | 217篇 |
2003年 | 171篇 |
2002年 | 182篇 |
2001年 | 65篇 |
2000年 | 84篇 |
1999年 | 54篇 |
1998年 | 50篇 |
1997年 | 28篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 27篇 |
1993年 | 18篇 |
1992年 | 32篇 |
1991年 | 33篇 |
1990年 | 21篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 32篇 |
1986年 | 40篇 |
1985年 | 35篇 |
1984年 | 30篇 |
1983年 | 44篇 |
1982年 | 24篇 |
1981年 | 25篇 |
1980年 | 24篇 |
1979年 | 31篇 |
1978年 | 30篇 |
1977年 | 24篇 |
1976年 | 20篇 |
1974年 | 24篇 |
1971年 | 22篇 |
排序方式: 共有5692条查询结果,搜索用时 62 毫秒
1.
Emma Bricchi Marco Fornaciari Claudia Giannoni Francesca Greco Daniela Fascini Giuseppe Frenguelli Gianfranco Mincigrucci Bruno Romano 《Aerobiologia》1992,8(3):401-406
Summary Gramineae pollination from a pollen monitoring station located in the eastern suburb of Perugia and meteorological correlations are reported. The data refers to the year 1989. Grass pollen peak pollination was from May to July; in this period the influence of relative humidity and of temperature on pollen concentration was very high. Phenological observations, to identify the time of maximum stamen extension in the most common genera in the area, are also reported. During the period of investigation the counts of pollen grains over four-hour periods showed a regular diurnal rhythm with peaks of concentration in the four-hour period 16.00–20.00. Aerosporological data and meteorological data related to four-hour periods were correlated following different criteria. 相似文献
2.
Cultured porcine thoracic aorta endothelial cells were covalently labeled with 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance spectrometry revealed two major binding environments representing strongly and weakly immobilized species. The disorder parameter of weak/strong, determined from the respective peak amplitudes, was irreversibly elevated following incubation of endothelial cells with a superoxide-generating system, indicating increased membrane fluidity. The rate of increase in membrane disorder was dependent upon superoxide generation rates. Incorporation of the spin-label at concentrations less than 250 microM had no effect on cell viability. The cellular proteins reacting with the spin-label were predominantly membrane proteins, characterized by immunoblotting using a rabbit anti-4-maleimido-2,2,6,6-tetramethylpiperidinooxyl IgG, following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophorectic transfer to nitrocellulose. 相似文献
3.
4.
5.
A spontaneous rhythmic motility of the isolated intestine in snail, Chryptomphalus hortensis, has been registered at 30 degrees C with the aid of an electronic transductor and an appropriate amplification. These slow regular movements are affected by ionic composition changes in the suspension medium. Na+, K+ and Ca++ ions prove to be important in this motility, and the addition of Ba++ markedly stimulates it. ACh produces hypermotility from 1.8 X 10(-11) g/ml. Its effect decreases in the presence of atropine and increases in that of pyridostigmine. The intestine is sensitive to 5-HT from 10(-10) g/ml, which stimulates its activity. The effect of histamine is weak. Low concentrations of adrenaline tend to increase the amplitude, whereas concentrations from 10(-5) g/ml onward produce a cease of motility in relaxation. 相似文献
6.
Yiwen Sun Zexuan Zhu Siping Chen Jega Balakrishnan Derek Abbott Anil T. Ahuja Emma Pickwell-MacPherson 《PloS one》2012,7(11)
The GP2 peptide is derived from the Human Epidermal growth factor Receptor 2 (HER2/nue), a marker protein for breast cancer present in saliva. In this paper we study the temperature dependent behavior of hydrated GP2 at terahertz frequencies and find that the peptide undergoes a dynamic transition between 200 and 220 K. By fitting suitable molecular models to the frequency response we determine the molecular processes involved above and below the transition temperature (T
D). In particular, we show that below T
D the dynamic transition is dominated by a simple harmonic vibration with a slow and temperature dependent relaxation time constant and that above T
D, the dynamic behavior is governed by two oscillators, one of which has a fast and temperature independent relaxation time constant and the other of which is a heavily damped oscillator with a slow and temperature dependent time constant. Furthermore a red shifting of the characteristic frequency of the damped oscillator was observed, confirming the presence of a non-harmonic vibration potential. Our measurements and modeling of GP2 highlight the unique capabilities of THz spectroscopy for protein characterization. 相似文献
7.
8.
Nucleotide sequencing of the second Synechocystis 6803 psbG gene, psbG2 shows the predicted polypeptide to be 219 amino acids long. It is less similar to chloroplast psbG genes than is the Synechocystis psbG1 copy. Alignment with seven other psbG protein sequences, including that from the Paramecium mitochondrial genome reveals a central highly conserved region common to each. This is discussed as evidence supporting the proposal that the psbG polypeptide is a NAD(P)H dehydrogenase (complex I) subunit in cyanobacteria, chloroplasts and mitochondria. 相似文献
9.
10.