全文获取类型
收费全文 | 7029篇 |
免费 | 467篇 |
出版年
2023年 | 20篇 |
2022年 | 81篇 |
2021年 | 126篇 |
2020年 | 72篇 |
2019年 | 103篇 |
2018年 | 144篇 |
2017年 | 121篇 |
2016年 | 216篇 |
2015年 | 345篇 |
2014年 | 398篇 |
2013年 | 540篇 |
2012年 | 653篇 |
2011年 | 579篇 |
2010年 | 357篇 |
2009年 | 336篇 |
2008年 | 410篇 |
2007年 | 390篇 |
2006年 | 377篇 |
2005年 | 329篇 |
2004年 | 315篇 |
2003年 | 306篇 |
2002年 | 300篇 |
2001年 | 60篇 |
2000年 | 60篇 |
1999年 | 66篇 |
1998年 | 92篇 |
1997年 | 63篇 |
1996年 | 53篇 |
1995年 | 60篇 |
1994年 | 48篇 |
1993年 | 46篇 |
1992年 | 62篇 |
1991年 | 21篇 |
1990年 | 32篇 |
1989年 | 19篇 |
1988年 | 26篇 |
1987年 | 27篇 |
1986年 | 14篇 |
1985年 | 22篇 |
1984年 | 27篇 |
1983年 | 14篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1978年 | 13篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 8篇 |
排序方式: 共有7496条查询结果,搜索用时 15 毫秒
31.
Carmen Cascales Dan G. Craciunescu Paloma Martín-Sanz María Cascales 《Biological trace element research》1986,11(1):65-73
Enzyme activities and protein content were determined in the cytosolic and mitochondrial fractions of liver homogenates obtained from Rh(III) complex-, thioacetamide- and thioacetamide + Rh(III) complex-treated rats. The Rh(III) complex administered to nonthioacetamide-treated rats produced no significant changes either in the enzymatic activities assayed or in the protein concentration. The Rh(III) complex administered to thioacetamide-treated rats produced significant restoration of the following altered values: cytosolic and mitochondrial aspartate aminotransferase, glutamate dehydrogenase, NADP-isocitrate dehydrogenase, and protein concentration. However, a further increase was produced in the activities of glucose-6-phosphate dehydrogenase and malic enzyme. These increases can be interpreted in terms of an enhancement of the NADPH-dependent detoxifying processes and of nucleic acid synthesis and repair. 相似文献
32.
A B Novikoff H W Spater N Quintana 《The journal of histochemistry and cytochemistry》1983,31(5):656-661
Inosine 5'-diphosphatase (IDPase) activity was demonstrated cytochemically in the endoplasmic reticulum of rat kidney proximal tubule cells in tissue fixed by perfusion with glutaraldehyde--formaldehyde. Incubation for IDPase activity at pH 7.2 was performed with and without 0.5 mM levamisole, a potent inhibitor of alkaline phosphatase (AlkPase) (M Borgers, J Histochem Cytochem 21:812, 1973). Levamisole treatment of sections eliminated all reaction product in the brush border, but did not affect the IDPase activity the endoplasmic reticulum (ER). The ER appears as a basilar-luminal-oriented transcellular structure, suggesting a possible cellular transport route. This study supports and extends earlier observations made by others that suggest a transport role for the ER in these cells. It also emphasizes the value of thick section cytochemistry. 相似文献
33.
A new genus and species of the Protosteliida (Mycetozoa), Ceratiomyxella tahitiensis, was isolated from dead plant material—var. tahitiensis from Tahiti and var. neotropicalis from Brazil and Colombia. The sporocarps have deciduous spores borne singly on slender hollow stalks; zoocysts with anteriorly flagellate planonts are produced. The trophic stage is comprised of uninucleate to plurinucleate amoeboid cells and reticulate plasmodia; the uninucleate cells become flagellate in water. The prespore cells and spores are plurinucleate. Sexuality has not been demonstrated. Var. tahitiensis has globose spores and produces its zoocysts just after spore germination, whereas var. neotropicalis has subglobose spores and forms zoocysts later in the life cycle. The species is thought to show phylogenetic relationships with Ceratiomyxa, which was recently transferred to the Protosteliida by Olive. 相似文献
34.
Three new species of Protostelium (Order Protostelida of the Mycetozoa) are described: P. irregularis, P. zonatura, and P. pyriformis, all with rather wide distribution and occurring on dead attached plant parts, less often in soil and humus. The latter two species differ from the first and from the other two known species, P. mycophaga Olive and Stoianovitch and P. arachisporum Olive, in the endogenous origin of the stalk. P. mycophaga var. crassipes, with vesicular stalk bases, is the third variety of that species to be described. A key to the genus is included. 相似文献
35.
Summary An electron microscopic study has been made of the sympathetic ganglia of a 15 and a 17 week old male human fetus. The fetal sympathetic neurons were densely packed in a scanty connective tissue matrix which also contained blood vessels. The fetal sympathetic neurons had a large, electron-light nucleus with one or two nucleoli, and was of a somewhat mottled appearance due to irregularly dispersed aggregates of fine and coarse granules. The perikaryon usually formed a thin envelope around the nucleus and contained, except for large pigment granules, all intracytoplasmic structures which were also found in mature sympathetic neurons. Adjacent sympathetic cells were either in immediate contact, or slightly separated by a wedge of electron-light satellite expansions, or lined by primitive axons. The satellite cells were in the early state of development. Electron-dense axons either stood side by side with, or were slightly engulfed by light Schwann cell expansions and formed distinct bundles surrounded by a common basement membrane. There was practically no trace of myelin formation or Schwann cell wrapping characteristic for unmyelinated fibers as seen in the adult.This investigation was supported (in whole) by United States Public Health Service Grant NB-01879-05, Institute for Nervous Diseases and Blindness.Grateful acknowledgment is made to Professor Dr. John Lind who madea vailable the fetal material through the Laboratory of Prenatal Growth and Development, Karolinska Institutet, Stockholm, Sweden.The authors wish to thank Docent Dr. Gunnar Bloom who provided the facilities necessary to prepare the fetal material for electron microscopical examination, in his laboratory for Cell Research, Karolinska Institutet, Stockholm, Sweden. 相似文献
36.
The localization of zinc-65 in germinating corn tissues 总被引:1,自引:1,他引:0
37.
Pseudomonas Vaccine I. Preparation and Assay 总被引:3,自引:3,他引:0
38.
Use of Microdialysis for Monitoring Tyrosine Hydroxylase Activity in the Brain of Conscious Rats 总被引:6,自引:5,他引:1
An on-line microdialysis system was developed which monitored the 3,4-dihydroxyphenylalanine (DOPA) formation in the striatum during infusion of a submicromolar concentration of an L-aromatic amino-acid decarboxylase inhibitor (NSD 1015). The absence of DOPA in dialysates of 6-hydroxydopamine-pretreated rats and the disappearance of DOPA after administration of alpha-methyl-p-tyrosine indicated that the dialyzed DOPA was derived from dopaminergic nerve terminals. Next we investigated whether the steady-state DOPA concentration in striatal dialysates could be considered as an index of tyrosine hydroxylase activity. The increase in DOPA output after intraperitoneal administration of haloperidol or gamma-butyrolactone and the decrease in DOPA output after intraperitoneal administration of apomorphine are in excellent agreement with results of postmortem studies, in which a decarboxylase inhibitor was used to measure the activity of tyrosine hydroxylase. The effect of haloperidol on DOPA formation was not visible when a U-shaped cannula (0.80 mm o.d.) was used. Some methodological problems related to microdialysis of the haloperidol-induced increase in DOPA formation are discussed. We concluded that the proposed model is a powerful and reliable in vivo method to monitor tyrosine hydroxylase activity in the brain. The method is of special interest for investigating the effect of compounds which are not able to pass the blood-brain barrier. As an application of the method in the latter situation, we report the effect of infusion the neurotoxin 1-methyl-4-phenylpyridinium ion (10 mmol/L infused over 20 min) on the activity of striatal tyrosine hydroxylase. 相似文献
39.
Gerhard Sandmann M. Luisa Peleato Maria F. Fillat M. Carmen Lázaro Carlos Gómez-Moreno 《Photosynthesis research》1990,26(2):119-125
Iron-dependent formation of ferredoxin and flavodoxin was determined in Anabaena ATCC 29413 and ATCC 29211 by a FPLC procedure. In the first species ferredoxin is replaced by flavodoxin at low iron levels in the vegetative cells only. In the heterocysts from Anabaena ATCC 29151, however, flavodoxin is constitutively formed regardless of the iron supply.Replacement of ferredoxin by flavodoxin had no effect on photosynthetic electron transport, whereas nitrogen fixation was decreased under low iron conditions. As ferredoxin and flavodoxin exhibited the same Km values as electron donors to nitrogenase, an iron-limited synthesis of active nitrogenase was assumed as the reason for inhibited nitrogen fixation. Anabaena ATCC 29211 generally lacks the potential to synthesize flavodoxin. Under iron-starvation conditions, ferredoxin synthesis is limited, with a negative effect on photosynthetic oxygen evolution. 相似文献
40.
Sandra Afione Luciano Debeljuk Adriana Seilicovich Daniel Pisera Mercedes Lasaga María del Carmen Díaz Beatriz Duvilanski 《Peptides》1990,11(6):1065-1068
In the present work we examined the effect of the neutralization of endogenous substance P by the administration of an anti-substance P serum (ASPS) on GABA concentration in the anterior pituitary in hyperprolactinemic conditions induced by 5-hydroxytryptophan or by grafting anterior pituitaries. ASPS reduced the increase in the anterior pituitary GABA concentration induced by hyperprolactinemia. In vitro experiments showed that substance P inhibited K+-evoked GABA efflux from hypothalamic fragments and decreased GABA concentration in the anterior pituitary but ASPS increased it. Our results demonstrate that substance P modifies hypothalamic GABA release and anterior pituitary GABA concentration and suggest that an interaction exists between substance P and GABA. 相似文献