全文获取类型
收费全文 | 5606篇 |
免费 | 815篇 |
国内免费 | 731篇 |
出版年
2024年 | 4篇 |
2023年 | 90篇 |
2022年 | 141篇 |
2021年 | 158篇 |
2020年 | 284篇 |
2019年 | 450篇 |
2018年 | 377篇 |
2017年 | 301篇 |
2016年 | 281篇 |
2015年 | 284篇 |
2014年 | 384篇 |
2013年 | 493篇 |
2012年 | 278篇 |
2011年 | 340篇 |
2010年 | 257篇 |
2009年 | 269篇 |
2008年 | 256篇 |
2007年 | 273篇 |
2006年 | 264篇 |
2005年 | 241篇 |
2004年 | 158篇 |
2003年 | 157篇 |
2002年 | 128篇 |
2001年 | 105篇 |
2000年 | 103篇 |
1999年 | 97篇 |
1998年 | 64篇 |
1997年 | 56篇 |
1996年 | 40篇 |
1995年 | 67篇 |
1994年 | 60篇 |
1993年 | 53篇 |
1992年 | 45篇 |
1991年 | 42篇 |
1990年 | 22篇 |
1989年 | 21篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 31篇 |
1985年 | 43篇 |
1984年 | 100篇 |
1983年 | 55篇 |
1982年 | 59篇 |
1981年 | 52篇 |
1980年 | 37篇 |
1979年 | 36篇 |
1978年 | 23篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 9篇 |
排序方式: 共有7152条查询结果,搜索用时 406 毫秒
21.
R Ziegler 《Archives of insect biochemistry and physiology》1990,15(2):111-116
Dose-response curves were measured with synthetic Manduca adipokinetic hormone (AKH) for glycogen phosphorylase activation in larvae and for lipid mobilization in adults. Both responses are known hormonal functions in Manduca sexta. In ligated larvae, full activation of glycogen phosphorylase was achieved with 0.1 pmol and half-maximal activation with 0.03-0.04 pmol. Maximal lipid mobilization in adults required 10 pmol and half-maximal mobilization 0.15 to 0.2 pmol, respectively. An estimate of AKH content of corpora cardiaca from M. sexta was gained by comparing the dose-response curves for synthetic Manduca AKH with curves from gland extracts. Corpora cardiaca extracts were also quantitated by high performance liquid chromatography. According to both estimates corpora cardiaca of adults contain 10-20 pmol AKH per pair, while a pair of larval corpora cardiaca contains 0.7-2 pmol. 相似文献
22.
Data on the physico-chemical properties of proteins from soybean, groundnut, sesame seed, sunflower seed, safflower seed,
mustard seed, rapeseed and cotton seed are fairly extensive. An examination of the available data on high molecular weight
proteins suggests that there are similarities in many of their properties. In this report the similarity in amino acid composition,
size and shape, molecular weight, secondary structure, subunit composition, association-dissociation at high and low pH, stability
towards denaturants, hydrolysis by enzymes and quaternary structure of the high molecular weight proteins is discussed. Based
on these similarities a model has been proposed for the associationdissociation, denaturation and reassociation behaviour
of the high molecular weight proteins of oilseeds. 相似文献
23.
Simultaneous determination of ascorbic acid and dehydroascorbic acid in cultures of C3H/10T1/2 cells
Luminita L. V. Ibric William F. Benedict Andrew R. Peterson 《In vitro cellular & developmental biology. Plant》1988,24(7):669-676
Summary A reproducible method is described for the separation and quantification of ascorbic acid and dehydroascorbic acid by ion-pairing
reverse-phase high performance liquid chromatography and detection by absorbance at 232 nm. Lowest detectable concentrations
with a linear response of detection were 5 nmol for ascorbic acid and 50 nmol for dehydroascorbic acid. This method was applied
to the analysis of C3H/10T1/2 cells and culture medium after influx or efflux experiments and single or multiple treatments
with ascorbic acid. Subsequent measurement of the radioactivity in the eluted fractions increased the detectability of both
ascorbic acid and dehydroascorbic acid to 10 to 20 pmol.
This research was supported by grant CA 09320 and CA 31574 from the National Cancer Institute, Bethesda, MD, and grant BC441
from The American Cancer Society. 相似文献
24.
T. J. Budd C. D. Dolman A. M. Lawson W. Chai J. Saxton F. W. Hemming 《Glycoconjugate journal》1992,9(5):274-278
N-Acetylneuraminic acid (Neu5Ac) andN-glycoloylneuraminic acid (Neu5Gc) are distributed widely in nature. Using a Carbopac PA-1 anion exchange column, we have determined the ratios of Neu5Ac and Neu5Gc in hydrolysates of platelets and their precursors: a rat promegakaryoblastic (RPM) cell line and a human megakaryoblastic leukemia cell line (MEG-01). The ratio of Neu5Gc:Neu5Ac in cultured RPM cells is 16:1, whereas in platelet rich plasma and cultured MEG-01 cells it is 1:38 and 1:28, respectively. The nature of these sialic acids from RPM cells was verified using thin layer chromatography and liquid secondary ion mass spectrometry. The relevance of increased Neu5Gc levels in early stages of development is discussed.Abbreviations Neu5Ac
N-acetylneuraminic acid
- Neu5Gc
N-glycoloylneuraminic acid
- RPM
rat promegakaryoblast
- MEG-01
human megakaryoblastic leukaemia cell line
- PAD
pulsed amperometric detection
- WGA
wheat germ agglutinin
- FCS
foetal calf serum
- PPEADF
phosphatidylethanolamine dipalmitoyl
- LSIMS
liquid secondary ion mass spectrometry
- HPAEC
high performance anion exchange chromatography
- TBA
thiobarbituric acid 相似文献
25.
A. A. Serikov 《Journal of biological physics》1991,18(1):65-77
Model equations for the kinetics of the synthesis and decay of molecular aggregates are used to show the high sensitivity of equilibrium concentrations of high-molecular aggregates to external radiation. This phenomenon is used to explain the effects of low-intensity microwave fields on the functioning of biological systems. The experimental results on the influence of SHF-radiation on ferricyanide reduction by erythrocytes are interpreted in detail. 相似文献
26.
High-affinity binding of3H-folate in Triton X-100 solubilized membranes of human liver displayed characteristics, e.g. apparent positive cooperativity, which are typical of specific folate binding. Ultrogel® AcA 44 chromatography of solubilized membranes saturated with3H-folate revealed a major peak of 100 kDa and a minor peak of 25 kDa. The 100 kDa peak could represent a hydrophobic membrane associated molecular form of the protein. This notion was supported by the fact that the two peaks had identical molecular weights as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis with immunoblotting. 相似文献
27.
CO2 and water vapour exchange in four alpine herbs at two altitudes and under varying light and temperature conditions 总被引:1,自引:0,他引:1
CO2 and water vapour exchange rates of four alpine herbs namely: Rheum emodi, R. moorcroftianum, Megacarpaea polyandra and Rumex nepalensis were studied under field conditions at 3600 m (natural habitat) and 550 m altitudes. The effect of light and temperature on CO2 and water vapour exchange was studied in the plants grown at lower altitude. In R. moorcroftianum and R. nepalensis, the average photosynthesis rates were found to be about three times higher at 550 m as compared to that under their natural habitat. However, in M. polyandra, the CO2 exchange rates were two times higher at 3600 m than at 550 m but in R. emodi, there were virtually no differences at the two altitudes. These results indicate the variations in the CO2 exchange rates are species specific. The change in growth altitude does not affect this process uniformly.The transpiration rates in R. emodi and M. polyandra were found to be very high at 3600 m compared to 550 m and are attributed to overall higher stomatal conductance in plants of these species, grown at higher altitude. The mid-day closure of stomata and therefore, restriction of transpirational losses of water were observed in all the species at 550 m altitude. In addition to the effect of temperature and relative humidity, the data also indicate some endogenous rhythmic control of stomatal conductance.The temperature optima for photosynthesis was close to 30°C in M. polyandra and around 20°C in the rest of the three species. High temperature and high light intensity, as well as low temperature and high light intensity, adversely affect the net rate of photosynthesis in these species.Both light compensation point and dark respiration rate increased with increasing temperature.The effect of light was more prominent on photosynthesis than the effect of temperature, however, on transpiration the effect of temperature was more prominent than the effect of light intensity.No definite trends were found in stomatal conductance with respect to light and temperature. Generally, the stomatal conductance was highest at 20°C.The study reveals that all these species can easily be cultivated at relatively lower altitudes. However, proper agronomical methodology will need to be developed for better yields. 相似文献
28.
29.
Addition of calpain II (EC 3.4.22.17) to soluble proteins from 10-day-old rat lens caused an increase in turbidity and production of water-insoluble protein. The insolubilization increased with higher concentrations of both lens protein and calpain II, it could be prevented by the cysteine protease inhibitor E-64; it required at least 0.5 mM Ca2+, it was limited to 6% of the soluble protein present and resulted from precipitation β-crystallin polypeptides. When compared by two-dimensional electrophoresis, the insoluble β-crystallin polypeptides produced by calpain II were similar to insoluble β-crystallin polypeptides found incataractous lenses. Trypsin also caused insolubilization of β-crystallin polypeptides, but these polypeptides were unlike polypeptides produced during cataract formation. These data suggested that the loss of solubility was due to a specific removal of N/or C-terminal extensions from β-crystallin polypeptides by calpain II, and that a similar process may occur in vivo during cataract formation. It is hypothesized that the insoluble protein produced by calpain II causes cataract by increasing light scatter in the lens. 相似文献
30.
Functional mapping of the surface of Escherichia coli ribose-binding protein: mutations that affect chemotaxis and transport. 总被引:3,自引:3,他引:0 下载免费PDF全文
R. A. Binnie H. Zhang S. Mowbray M. A. Hermodson 《Protein science : a publication of the Protein Society》1992,1(12):1642-1651
Ribose-binding protein is a bifunctional soluble receptor found in the periplasm of Escherichia coli. Interaction of liganded binding protein with the ribose high affinity transport complex results in the transfer of ribose across the cytoplasmic membrane. Alternatively, interaction of liganded binding protein with a chemotactic signal transducer, Trg, initiates taxis toward ribose. We have generated a functional map of the surface of ribose-binding protein by creating and analyzing directed mutations of exposed residues. Residues in an area on the cleft side of the molecule including both domains have effects on transport. A portion of the area involved in transport is also essential to chemotactic function. On the opposite face of the protein, mutations in residues near the hinge are shown to affect chemotaxis specifically. 相似文献