全文获取类型
收费全文 | 72987篇 |
免费 | 5214篇 |
国内免费 | 2323篇 |
专业分类
80524篇 |
出版年
2023年 | 993篇 |
2022年 | 1459篇 |
2021年 | 1900篇 |
2020年 | 2208篇 |
2019年 | 2913篇 |
2018年 | 2706篇 |
2017年 | 1862篇 |
2016年 | 1945篇 |
2015年 | 2268篇 |
2014年 | 4236篇 |
2013年 | 5139篇 |
2012年 | 3079篇 |
2011年 | 4205篇 |
2010年 | 3127篇 |
2009年 | 3542篇 |
2008年 | 3880篇 |
2007年 | 3847篇 |
2006年 | 3351篇 |
2005年 | 2995篇 |
2004年 | 2702篇 |
2003年 | 2317篇 |
2002年 | 2103篇 |
2001年 | 1375篇 |
2000年 | 1157篇 |
1999年 | 1223篇 |
1998年 | 1177篇 |
1997年 | 1006篇 |
1996年 | 923篇 |
1995年 | 928篇 |
1994年 | 883篇 |
1993年 | 726篇 |
1992年 | 657篇 |
1991年 | 586篇 |
1990年 | 466篇 |
1989年 | 421篇 |
1988年 | 350篇 |
1987年 | 379篇 |
1986年 | 282篇 |
1985年 | 490篇 |
1984年 | 661篇 |
1983年 | 548篇 |
1982年 | 578篇 |
1981年 | 460篇 |
1980年 | 490篇 |
1979年 | 366篇 |
1978年 | 288篇 |
1977年 | 261篇 |
1976年 | 246篇 |
1975年 | 210篇 |
1974年 | 204篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Enhanced Noradrenergic Neuronal Activity Increases Homovanillic Acid Levels in Cerebrospinal Fluid 总被引:2,自引:2,他引:0
Harry Scheinin 《Journal of neurochemistry》1986,47(3):665-667
Idazoxan, a highly specific and selective alpha 2-adrenoceptor antagonist, caused a dose-dependent increase in the concentration of homovanillic acid (HVA) a metabolite of 3,4-dihydroxyphenylethylamine, in cisternal CSF of freely moving rats. This increase in HVA level could be antagonized by the alpha 2-adrenoceptor agonist medetomidine. The increase was directly proportional to the concurrent elevation in level of 3-methoxy-4-hydroxyphenylglycol, a metabolite of noradrenaline, in the CSF of individual rats and followed a similar time course. It is suggested that the HVA level in CSF may be increased under conditions of enhanced noradrenergic activity and that, in such situations, it reflects noradrenergic rather than dopaminergic neuronal activity. Care should be taken, therefore, when changes in central dopaminergic activity are assessed by measurements of HVA level in CSF. 相似文献
122.
C. Steven McDaniel Taghi Manshouri M. Zouhair Atassi 《Journal of Protein Chemistry》1987,6(5):455-461
A peptide corresponding to residues 26–41 of α-bungarotoxin, and closed by a disulfide bond between two cysteine residues
at the amino and C terminal ends of the peptide, was synthesized and the monomeric form was purified. The peptide, which represents
the exposed part of the long central loop of the toxin molecule, was examined for binding to acetylcholine receptor. The peptide
was shown by radiometric titrations to bind radiolabeled receptor, and radiolabeled peptide was bound by receptor. The specificity
of the binding was confirmed by inhibition with the parent toxin. A synthetic analog of the peptide in which Trp-28 was replaced
by glycine had very little (10%) of the original activity. Succinylation of the amino groups of the peptide resulted in virtually
complete (98%) loss of the binding activity. These results indicate that a shortened loop peptide corresponding to the region
26–41 of α-bungarotoxin exhibits binding activities mimicking those of the parent molecule. In this region, Trp-28, and one
or both of Lys-26 and Lys-38, are essential contact residues in the binding to receptor. 相似文献
123.
James E. Fleming Paula S. Melnikoff Klaus G. Bensch 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,802(2):340-345
Several hundred proteins have been resolved on two-dimensional gels of extracts of [35S]methionine-labeled adult Drosophila melanogaster. 27 of these polypeptides disappear from the gel pattern after feeding the K+ ionophore nonactin. These proteins have been identified as mitochondrial, since the two-dimensional gel pattern of extracts of isolated mitochondria correlates well with the pattern of the proteins missing from that of nonactin-treated flies. Nine new proteins also appear on the two-dimensional gels of the extracts from the nonactin-treated flies. Apparently, these nine proteins are precursors of the mature mitochondrial forms. These particular data support the concept that processing of many of the cytoplasmically synthesized mitochondrial proteins requires a specific membrane potential, and that some of these proteins are modified intramitochondrially. However, using [35S]methionine incorporation techniques, not all labeled polypeptides disappear from mitochondria during such treatment. Feeding similarly radiolabeled flies with chloramphenicol, an inhibitor of mitochondrial protein synthesis, results in the disappearance of only one protein from the gel pattern with the concurrent appearance of a ‘new’ high-molecular-weight polypeptide. Collectively, these data show that a specific group of [35S]methionine-labeled mitochondrial proteins can be identified by selective inhibition of mitochondrial function in whole cell protein maps of adult D. melanogaster. 相似文献
124.
Andrew Leask 《Journal of cell communication and signaling》2010,4(2):109-110
The role of CCN proteins in vivo is only just becoming understood. A prototypical member of the CCN family, CCN3 suppresses proliferation. In a study in press, Shimoyama and colleagues show that mice lacking CCN3 have a hyperproliferative response to vascular injury. These data, along with other recent observations, suggest that CCN3 may represent a novel therapy for hyperproliferative diseases. 相似文献
125.
126.
127.
128.
129.
130.
The effects of a cow's milk diet on receptor activity and histamine metabolism in gastric glands and mucosa isolated from adult rats were examined. The milk diet was associated with (1) a decreased mobilization of H2 receptors by histamine and (2) an increased mobilization of PGE2 (prostaglandin E2) receptors in mucous cells (cytoprotective effect) and parietal cells (antiacid effect). These changes are not observed for the receptors reducing pentagastrin- and histamine-induced gastric acid secretion (pancreatic/enteroglucagons, somatostatin) and stimulating mucus, bicarbonate and pepsin secretions in the rat (secretin). Cimetidine produced a parallel displacement of the histamine dose-response curve, suggesting competitive inhibition between this classical H2 receptor antagonist and histamine in the two experimental groups. Prostaglandins and other components in milk such as EGF (epidermal growth factor) and somatostatin might therefore protect gastric mucosa by a differential control of PGE2 and histamine H2 receptor activity eitherdirectly (PGE2 in milk) orindirectly (inhibition of endogeneous histamine synthesis/release and stimulation of PGE-I synthesis/release). 相似文献