全文获取类型
收费全文 | 3762篇 |
免费 | 320篇 |
国内免费 | 2篇 |
出版年
2023年 | 23篇 |
2022年 | 16篇 |
2021年 | 60篇 |
2020年 | 52篇 |
2019年 | 59篇 |
2018年 | 64篇 |
2017年 | 82篇 |
2016年 | 121篇 |
2015年 | 174篇 |
2014年 | 217篇 |
2013年 | 246篇 |
2012年 | 321篇 |
2011年 | 285篇 |
2010年 | 211篇 |
2009年 | 163篇 |
2008年 | 219篇 |
2007年 | 242篇 |
2006年 | 193篇 |
2005年 | 192篇 |
2004年 | 172篇 |
2003年 | 149篇 |
2002年 | 172篇 |
2001年 | 44篇 |
2000年 | 44篇 |
1999年 | 48篇 |
1998年 | 44篇 |
1997年 | 31篇 |
1996年 | 36篇 |
1995年 | 29篇 |
1994年 | 30篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 25篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 28篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1974年 | 6篇 |
1973年 | 12篇 |
排序方式: 共有4084条查询结果,搜索用时 15 毫秒
51.
J. Custot Jean-Luc Boucher Sandrine Vadon Catherine Guedes Sylvie Dijols Marcel Delaforge Daniel Mansuy 《Journal of biological inorganic chemistry》1996,1(1):73-82
The effects of various compounds bearing an N-OH group such as N-hydroxy-guanidines, amidoximes, and hydroxylamines, on bovine and rat liver arginases was studied. Some of these compounds
with an l-α-amino acid function at an appropriate distance from the N-OH group acted as strong competitive liver arginase inhibitors,
displaying Ki values between 4 and 150 μM. Two compounds, N
ε-hydroxy-l-lysine and N
ω-hydroxy-d,l-indospicine, which exhibited Ki values of 4 and 20 μM (at pH 7.4), were the most potent inhibitors of arginase described
to date. The distance between the α-amino acid and N-OH functions appeared to be crucial for potent inhibition of arginase,
as N
δ-hydroxy-l-ornithine, which has one -CH2 group less than N
ε-hydroxy-l-lysine, exhibited a 37-fold higher Ki value than N
ε-hydroxy-l-lysine. Based on these results, a model for the interaction of N
ω-hydroxyamino-l-α-amino acids with the arginase active site is proposed. This model involves the binding of the N-OH group of the inhibitors
to the arginase Mn(II) center and suggests that N
ε-hydroxy-l-lysine is a good transition state analog of arginase. 相似文献
52.
Bastiaan L. Slierendregt Nel Otting Marcel Kenter Ronald E. Bontrop 《Immunogenetics》1995,41(1):29-37
Allelic diversity at the major histocompatibility complex class II DP locus of rhesus macaques was studied by sequencing exon 2 of Mamu-DPA1 and -DPB1 genes. The Mamu-DPA1 gene is apparently invariant, whereas the Mamu-DPB1 locus displays polymorphism. Here we report the characterization of 1 Mamu-DPA1 and 13 Mamu-DPB1 alleles which were compared with other available primate Mhc-DPA1 and -DPB1 sequences. As compared with Mhc-DRB and -DQB1, most codons for the contact residues in the antigen binding site of the primate Mhc-DPB1 gene have a relatively low degree of variation in encoding various types of amino acids. In contrast to Mhc-DRB and -DQB, the HLA- and Mamu-DPB1 sequences cluster in a species-specific manner in phylogenetic trees. Mhc-DPB1 polymorphisms, however, are inherited in a transspecies mode of evolution, as is demonstrated by the sharing of lineage members between closely related macaque species. The data demonstrate that the transspecies character of Mhc-DPB1 polymorphism was retained over much shorter periods of time as compared with its sister class II loci, Mhc-DQ and -DR.The nucleotide sequence data reported in this paper have been submitted to the EMBL nucleotide sequence database and have been assigned the accession numbers Z32402–Z32415 相似文献
53.
Swamp gorillas in northern Congo 总被引:3,自引:0,他引:3
54.
Abousalham Abdelkarim; Teissere Marcel; Gardies Anne-Marie; Verger Robert; Noat Georges 《Plant & cell physiology》1995,36(6):989-996
Phospholipase D (phosphatidylcholine phosphatidohydrolase EC3.1.4.4
[EC]
) from soybean (Glycine max L.) suspension-cultured cellwas purified around 1,200-fold to homogeneity by acetone precipitation,Macro-Prep High Q anion exchange, and octyl-Sepharose CL-4Baffinity chromatography. The purified enzyme released 1,600µmol of choline per min per mg of protein. The enzymeis monomeric with a molecular mass of 92 kDa, as estimated bySDS-PAGE. One of the most interesting characteristics of thepurified soybean phospholipase D was the dependence of the pHoptimum on the Ca2+ ion concentration in the assay. With 10mM, 20 mM and 40 mM Ca2+ ions, the optima were at pH 7.5, 6and 5.5, respectively. The specific adsorption of phospholipaseD onto octyl-Sepharose gel suggests that the molecule becomesmore hydrophobic in the presence of Ca2+ ions. The amino acidsequence of the first 18 N-terminal residues of soybean phospholipaseD revealed a high degree of homology with those previously publishedfor cabbage leaf and castor bean endosperm enzymes. Westernblots of the soybean phospholipase D showed an immunoreactivitywith antibodies raised against a synthetic peptide correspondingto the 15 N-terminal aminoacid residues of phospholipase D fromcabbage leaves. (Received March 13, 1995; Accepted May 29, 1995) 相似文献
55.
56.
Marcel M. Verbeek Robert M. W. de Waal Janine J. Schipper †William E. Van Nostrand 《Journal of neurochemistry》1997,68(3):1135-1141
Abstract: Amyloid β protein (Aβ) deposition in the cerebral arterial and capillary walls is one of the major characteristics of brains from patients with Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D). Vascular Aβ deposition is accompanied by degeneration of smooth muscle cells and pericytes. In this study we found that Aβ1–40 carrying the "Dutch" mutation (HCHWA-D Aβ1–40 ) as well as wild-type Aβ1–42 induced degeneration of cultured human brain pericytes and human leptomeningeal smooth muscle cells, whereas wild-type Aβ1–40 and HCHWA-D Aβ1–42 were inactive. Cultured brain pericytes appeared to be much more vulnerable to Aβ-induced degeneration than leptomeningeal smooth muscle cells, because in brain pericyte cultures cell viability already decreased after 2 days of exposure to HCHWA-D Aβ1–40 , whereas in leptomeningeal smooth muscle cell cultures cell death was prominent only after 4–5 days. Moreover, leptomeningeal smooth muscle cell cultures were better able to recover than brain pericyte cultures after short-term treatment with HCHWA-D Aβ1–40 . Degeneration of either cell type was preceded by an increased production of cellular amyloid precursor protein. Both cell death and amyloid precursor protein production could be inhibited by the amyloid-binding dye Congo red, suggesting that fibril assembly of Aβ is crucial for initiating its destructive effects. These data imply an important role for Aβ in inducing perivascular cell pathology as observed in the cerebral vasculature of patients with Alzheimer's disease or HCHWA-D. 相似文献
57.
Daniel Duprez Dirk Voet Marc De Buyzere Benny Drieghe Bruno Vyncke Sigrid Mareels Marcel Afschrift Denis L. Clement 《European journal of applied physiology and occupational physiology》1995,71(5):459-463
The splanchnic circulation can make a major contribution to blood flow changes. However, the role of the splanchnic circulation in the reflex adjustments to the blood pressure increase during isometric exercise is not well documented. The central command and the muscle chemoreflex are the two major mechanisms involved in the blood pressure response to isometric exercise. This study aimed to examine the behaviour of the superior mesenteric artery during isometric handgrip (IHG) at 30% maximal voluntary contraction (MVC). The pulsatility index (PI) of the blood velocity waveform of the superior mesenteric artery was taken as the study parameter. A total of ten healthy subjects [mean age, 21.1 (SEM 0.3) years] performed an IHG at 30% MVC for 90 s. At 5 s prior to the end of the exercise, muscle circulation was arrested for 90 s to study the effect of the muscle chemoreflex (post exercise arterial occlusion, PEAO). The IHG at 30% MVC caused a decrease in superior mesenteric artery PI, from 4.84 (SEM 1.57) at control level to 3.90 (SEM 1.07) (P = 0.015). The PI further decreased to 3.17 (SEM 0.70) (P = 0.01) during PEAO. Our results indicated that ergoreceptors may be involved in the superior mesenteric artery vasodilatation during isometric exercise. 相似文献
58.
In starfish, oocytes are released from prophase block by a hormone, which has been identified as 1-methyladenine. The action of 1-methyladenine is indirect in inducing oocyte maturation: it acts on the oocyte surface to produce a cytoplasmic maturation-promoting factor (MPF), the direct trigger of germinal vesicle breakdown (GVBD). Less than 5 min after hormone addition, thus about 10 min before appearance of the cytoplasmic maturation-promoting factor, a factor appears in the germinal vesicle, which triggers the production of cytoplasmic MPF, GVBD, and the subsequent events of meiotic maturation when transferred in the cytoplasm of any fully grown oocyte of the starfishes Marthasterias glacialis and Asterias rubens. Before hormone action, the germinal vesicle also contains a factor capable of inducing meiosis reinitiation in recipient oocytes, but in contrast with nuclear MPF, this factor acts exclusively when transferred in the cytoplasm of a special category of oocytes (the “competent” oocytes). In contrast to other oocytes (the “incompetent” oocytes) the competent oocytes are capable of producing MPF to some extent after enucleation, upon hormonal stimulation. Transfer of either nuclear or cytoplasmic MPF initially produced in hormone-treated maturing oocytes triggers the production of both cytoplasmic and nuclear MPF in non-hormone-treated recipient oocytes of both categories. 相似文献
59.
60.