全文获取类型
收费全文 | 4354篇 |
免费 | 350篇 |
国内免费 | 3篇 |
出版年
2023年 | 28篇 |
2022年 | 61篇 |
2021年 | 125篇 |
2020年 | 72篇 |
2019年 | 97篇 |
2018年 | 96篇 |
2017年 | 92篇 |
2016年 | 167篇 |
2015年 | 227篇 |
2014年 | 236篇 |
2013年 | 328篇 |
2012年 | 346篇 |
2011年 | 346篇 |
2010年 | 217篇 |
2009年 | 164篇 |
2008年 | 275篇 |
2007年 | 254篇 |
2006年 | 255篇 |
2005年 | 199篇 |
2004年 | 191篇 |
2003年 | 147篇 |
2002年 | 129篇 |
2001年 | 53篇 |
2000年 | 43篇 |
1999年 | 35篇 |
1998年 | 40篇 |
1997年 | 29篇 |
1996年 | 14篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 22篇 |
1992年 | 29篇 |
1991年 | 32篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 12篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 13篇 |
1971年 | 11篇 |
1970年 | 13篇 |
排序方式: 共有4707条查询结果,搜索用时 15 毫秒
61.
Walter A. Blank Kenneth J. Elder Wendy P. Gati Alan R. P. Paterson Michael A. Pickard John S. Wilson 《Biotechnology letters》1992,14(8):669-672
Summary Washed cells ofE. coli ATCC 5275, a thymine auxotroph, catalysed formation of 2-chloro-2-deoxyadenosine when incubated with 2-chloroadenosine and a variety of deoxynucleosides. This transdeoxyribosylation reaction was complete after 4 h of shaking at 37°C. The equilibrium reaction mixture favoured product formation when purine rather than pyrimidine deoxyribonucleosides were used as cosubstrates, and when the ratio of deoxysugar donor to 2-chloroadenosine was high. Using deoxyadenosine as cosubstrate, chlorodeoxyadenosine was purified from larger scale reaction mixtures by treatment with Dowex-1 (OH-form) or by high performance liquid chromatography. 相似文献
62.
The hairy root culture of Lippia dulcis Trev., Verbenaceae, was established by transformation with Agrobacterium rhizogenes A4. The transformed roots grew well in Murashige and Skoog medium containing 2% sucrose. The roots turned light green when they were cultured under 16 h/day light. The green hairy roots produced the sweet sesquiterpene hernandulcin (ca. 0.25 mg/g dry wt) together with 20 other mono- and sesquiterpenes, while no terpenes were detected in the nontransformed root cultures. The growth and hernandulcin production in the hairy root cultures were influenced by the addition of auxins to the medium. The addition of a low concentration of chitosan (0.2 – 10.0 mg / l) enhanced the production of hernandulcin 5-fold.Abbreviations Cht
chitosan
- IAA
indole-3-acetic acid
- NAA
1-naphthaleneacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- MS
Murashige and Skoog(1962) 相似文献
63.
Light scattering measurements and scanning electron microscopy show that p-azidobenzylphlorizin (p-AzBPhz) causes changes in the shape and volume of human erythrocytes by at least two, dose-dependent mechanisms: At nominal concentrations above 5 microM, the azide induces cell swelling by either enlarging a pre-existent channel or by creating pores between phase boundaries of the membrane through which salt and water enter, but sucrose remains excluded. However, over the range 0.03 to 0.3 microM, in either isosmotic NaCl or KCl media, when fewer than 1 million molecules of azide are bound per cell, the ligand causes membrane deformations that convert discocytes into cells resembling stage 2 echinocytes. Whereas a cell volume increase of about 10% accompanies these shape changes, (microhematocrit and electronic cell sizing measurements), no net influx of either Na+ or K+ during this stage of swelling was detectable. These cell alterations take place at p-AzBPhz concentrations which concurrently inhibit both chloride and 3-methoxyglucose equilibrium exchange transport. The results may indicate that when the membrane impermeable p-AzBPhz interacts with the anion and/or sugar transporter, some trans-membrane perturbation occurs which alters the cytoskeleton. 相似文献
64.
65.
G. Terenghi J. M. Polak L. Probert G. P. McGregor G. L. Ferri M. A. Blank J. M. Butler W. G. Unger Ahu-qi Zhang D. F. Cole S. R. Bloom 《Histochemistry and cell biology》1982,75(3):399-417
Summary VIP- and substance P-like immunoreactivities were found in considerable concentrations (VIP: 17.3±4.8 pmol/g, mean ± SEM; substance P:11.1±1.8 pmol/g) in the uveal portion of the guinea pig eye.d Immunocytochemistry localised these two regulatory peptides to nerve fibres found principally in a plexus in the iris (substance P) and in an extensive network surrounding the blood vessels of the choroid (VIP). A remarkable anatomical demarcation of the two types of peptide-containing nerves was established by the staining of substance P-containing nerves, which stops at the level of the ciliary body. This uveal area is known to be involved in the ocular responses to nociceptive stimuli. At the ultrastructural level, immunoreactivity for both peptides was localised to distinct subpopulations of p-type nerves, distinguishable by the size of their large dense-cored vesicles. Those immunoreactive for VIP were significantly larger (p<0.0005) than those immunoreactive for substance P (95±7 nm and 82±9 nm respectively; mean ± SD). Interruption of the trigeminal pathway produced a remarkable decrease of substance P immunoreactivity in the anterior portion of the uvea (9.1±1.5 pmol/g, mean ± SEM, control; 5.3±1.3 pmol/g, denervated), but not of VIP immunoreactivity in the choroid. Following colchicine treatment, VIP-immunoreactive neuronal cell bodies were localised in the choroid. The separate anatomical localisations and distributions of the two uveal peptides appear to be related to their different origins and functional roles in the response of the eye to noxious stimuli.To whom offprint requests should be sent 相似文献
66.
Regionally Selective Metabolic Effects of Hypoglycemia in Brain 总被引:12,自引:10,他引:2
Robert A. Ratcheson Ann C. Blank James A. Ferrendelli 《Journal of neurochemistry》1981,36(6):1952-1958
Abstract: Regional CNS levels of glucose reserves, glycolytic intermediates, and high-energy phosphate reserves were measured in insulin-treated, hypoglycemic rats and correlated with EEG activity. Intravenous administration of insulin to paralyzed, ventilated animals causes concomitant reduction of blood glucose levels and progressive abnormality and eventual loss of EEG activity. In all regions of brain examined, glucose and glycogen levels decrease until they are essentially depleted, and glucose-6-phosphate and fructose-1,6-biphosphate fall approximately 80%. Pyruvate levels decrease 50% in cerebral cortex and brain stem and a lesser amount in striatum, hippocampus, thalamus, and cerebellum. Lactate levels fall 50–60% in all regions except cerebellum, where no change is observed. ATP and phosphocreatine levels remain normal until the EEG is isoelectric, and then decrease in all regions except cerebellum. These results demonstrate that hypoglycemia does not have a uniform effect on brain glucose and energy metabolism, and cerebellum seems to be relatively protected. 相似文献
67.
68.
R.M. Kostrzewa H. Fukushima A. Morrow P. Cohenour T. Hsi R.E. Lehr C.L. Blank 《Life sciences》1980,27(23):2245-2250
A new synthetic agent R, S-2-amino-1(2-amino-4, 5-dihydroxyphenyl) propane dihydrobromide, also referred to as α-methyl-6-aminodopamine (α-Me-6-ADA), has been found to produce acute (one day) and longer-term (seven day) depletion of norepinephrine (NE) levels in mouse brain and peripheral tissues. A 100 mg/kg dose of α-Me-6-ADA (i.v., free base) produced greater than 85% depletion of NE in the heart and spleen at one day and one week after treatment. Intracranially, α-Me-6-ADA (100 μg i.vtr.) depleted NE in the telencephalon and brain stem by 79% and 21% respectively at seven days. In addition DA was depleted by 45% in the ipsilateral striatum. The α-Me-6-ADA appears to have a relative selectivity for noradrenergic nerves, as an intracranial dose of 10 μg, which decreased NE in mouse whole brain by 52% at one day, failed to alter the DA content. These data suggest that α-Me-6-ADA may be a neurotoxin. 相似文献
69.
70.