全文获取类型
收费全文 | 8761篇 |
免费 | 784篇 |
国内免费 | 5篇 |
专业分类
9550篇 |
出版年
2023年 | 30篇 |
2022年 | 117篇 |
2021年 | 171篇 |
2020年 | 88篇 |
2019年 | 137篇 |
2018年 | 165篇 |
2017年 | 144篇 |
2016年 | 272篇 |
2015年 | 425篇 |
2014年 | 497篇 |
2013年 | 605篇 |
2012年 | 687篇 |
2011年 | 643篇 |
2010年 | 430篇 |
2009年 | 406篇 |
2008年 | 515篇 |
2007年 | 516篇 |
2006年 | 524篇 |
2005年 | 529篇 |
2004年 | 500篇 |
2003年 | 416篇 |
2002年 | 405篇 |
2001年 | 100篇 |
2000年 | 66篇 |
1999年 | 88篇 |
1998年 | 136篇 |
1997年 | 75篇 |
1996年 | 62篇 |
1995年 | 60篇 |
1994年 | 61篇 |
1993年 | 63篇 |
1992年 | 56篇 |
1991年 | 42篇 |
1990年 | 65篇 |
1989年 | 40篇 |
1988年 | 39篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 40篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 20篇 |
1980年 | 30篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 17篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有9550条查询结果,搜索用时 15 毫秒
61.
Neural control of the expression of a Ca2+-activated K+ channel involved in the induction of myotonic-like characteristics 总被引:2,自引:0,他引:2
Beatriz U. Ramírez Maria Isabel Behrens Cecilia Vergara 《Cellular and molecular neurobiology》1996,16(1):39-49
Summary 1. Expression of the apamin-sensitive K+ channel (SK+) in rat skeletal muscle is neurally regulated. The regulatory effect of the nerve over the expression of some muscle ion
channels has been attributed to the electrical activity triggered by the nerve and/or to a trophic effect of some molecules
transported from the soma to the axonal endings.
2. SK+ channels apparently are involved in myotonic dystrophy (MD), therefore understanding the factors that regulate their expression
may ultimately have important clinical relevance.
3. To establish if axoplasmic transport is involved in this process, we used two experimental approaches in adult rats: (a)
Both sciatic nerves were severed, leaving a short or a long nerve stump attached to the anterior tibialis (AT). (b) Colchicine
or vinblastine (VBL), two axonal transport blockers of different potencies, was applied on one leg to the sciatic nerve. To
determine whether electrical activity affects the expression of SK+ channels, denervated AT were directly stimulated. The corresponding contralateral muscles were used as controls.
4. With these experimental conditions we measured (a) apamin binding to muscle membranes, (b) muscle contractile characteristics,
and (c) electromyographic activity.
5. In the short- and long-nerve stump experiments, 5 days after denervation125I-apamin binding to AT membranes was 2.0 times higher in the short-stump side. This difference disappeared at longer times.
The delayed expression of SK+ channels in the muscle left with a longer nerve stump can be attributed to the extra axoplasm contained in the longer stump,
which maintains a normally repressive signal for a longer period of time. Ten to 15 days after application of axonal transport
blockers we found that the muscle half-relaxation time increased in the drug-treated side and apamin partially reverted the
prolonged relaxation. Myotonic-like discharges specifically blockable by apamin were always present in the drug-treated leg.125I-Apamin binding, which is undetectable in a microsomal preparation from hind leg control muscles, was increased in the drug-treated
preparations. Apamin binding to denervated and stimulated AT muscles was lower than in the contralateral unstimulated muscles
[3.3±1.0 vs 6.8±0.8 (n=4) fmol/mg protein].
6. Our results demonstrate that electrical activity and axoplasmic transport are involved in the control of expression of
SK+ in rat skeletal muscle. However, the increased expression of this channel induces myotonic-like characteristics that are
reversed by apamin. This myotonic activity could be a model for MD. 相似文献
62.
Xóchttl Castañeda Víctor Ortíz Betania Allen Cecilia García Mauricio Hernández-Avila 《Culture, medicine and psychiatry》1996,20(2):229-247
The central topic of the article is the divided world of female commercial sex workers (FCSW) in Mexico City. Fourteen focus group sessions were conducted with 133 FCSW from varying socio-economic levels and types of work site, as well as seven individual interviews.FCSW live in a constant double bind, as mother and prostitute, and come into daily contact with society's double standard for women. Reactions include justifying sex work as a better paying employment opportunity for women, as a necessary evil, and as a type of social service, while at the same time hiding their profession from their families. FCSW also live out an archetypal female ambivalence, their selves divided between the mother/saint and the traitor/prostitute.This article defines elements which should be taken into account in culturally appropriate programs for prevention of HIV/AIDS transmission, especially the importance which FCSW give to their role as mothers and promotion of the condom as a physical and symbolic barrier between professional and private life. 相似文献
63.
64.
Markus Kurz Karin Schütz Michael Göbel 《Origins of life and evolution of the biosphere》1996,26(3-5):263-264
65.
66.
The nervous system of Tricladida. I. Neuroanatomy ofProcerodes littoralis (Maricola,Procerodidae): An immunocytochemical study 总被引:3,自引:0,他引:3
Maria Reuter Margaretha K. S. Gustafsson Cecilia Sahlgren David W. Halton Aaron G. Maule Chris Shaw 《Invertebrate neuroscience : IN》1995,1(2):113-122
The organization of the nervous system ofProcerodes littoralis (Tricladida, Maricola, Procerodidae) was studied by immunocytochemistry, using antibodies to authentic flatworm neuropeptide
F (NPF) (Moniezia expansa). Compared to earlier investigations of the neuroanatomy of tricladid flatworms, the pattern of NPF immunoreactivity inProcerodes littoralis reveals differences in the following respects: 1. Shape and structure of the brain. 2. Number and composition of longitudinal
nerve cords. 3. Shape of branches of, and transverse connections between, main ventral nerve cords. 4. Composition of the
pharyngeal nervous system. The rich innervation by NPF immunoreactive (IR) fibres and cells of the subepithelial muscle layer,
the pharynx musculature and the musculature of the male copulatory apparatus indicates a neurotransmitter or neuromodulatory
influence on muscular activity. 相似文献
67.
Heidrun Herrmann Christian Müller Ingmar Schmidt Jens Mahnke Lothar Petruschka Karin Hahnke 《Molecular genetics and genomics : MGG》1995,247(2):240-246
The genetic organization of the DNA region encoding the phenol degradation pathway ofPseudomonas putida H has been investigated. This strain can utilize phenol or some of its methylated derivatives as its sole source of carbon and energy. The first step in this process is the conversion of phenol into catechol. Catechol is then further metabolized via themeta-cleavage pathway into TCA cycle intermediates. Genes encoding these enzymes are clustered on the plasmid pPGH1. A region of contiguous DNA spanning about 16 kb contains all of the genetic information necessary for inducible phenol degradation. The analysis of mutants generated by insertion of transposons and cassettes indicates that all of the catabolic genes are contained in a single operon. This codes for a multicomponent phenol hydroxylase andmeta-cleavage pathway enzymes. Catabolic genes are subject to positive control by the gene product(s) of a second locus. 相似文献
68.
The salivary gland secretion in the dipteran Chironomus tentans is composed of approximately 15 different secretory proteins. The most well known of the corresponding genes are the four
closely related Balbiani ring (BR) genes, in which the main part of each approximately 40-kb gene is composed of tandemly
arranged repetitive units. Six of the seven additional secretory protein genes described share structural similarities with
the BR genes and are members of the same BR multigene family. Here we report the identification of a new secretory protein
gene, the spl2 gene, encoding the smallest component of the C. tentans salivary gland secretion. The gene has a corresponding mRNA length of approximately 0.7 kb and codes for a protein with a
calculated molecular weight of 7,619 Da. The sp12 gene was characterized in seven Chironomus species. Based on a comparison of the orthologous gene sequences, we conclude that the sp12 gene has a repetitive structure
consisting of diverged 21-by-long repeats. The repeat structure and the codon composition are similar to the so-called SR
regions of the BR genes and the sp 12 gene may represent a diverged member of the BR multigene family.
Correspondence to: L. Wieslander 相似文献
69.
Effects of Nerve Growth Factor on Glutathione Peroxidase and Catalase in PC 12 Cells 总被引:4,自引:1,他引:3
Deepa Sampath George R. Jackson Karin Werrbach-Perez J. Regino Perez-Polo 《Journal of neurochemistry》1994,62(6):2476-2479
Abstract: Nerve growth factor (NGF) is a member of the neuro- trophin family and is required for the survival and maintenance of peripheral sympathetic and sensory ganglia. In the CNS, NGF regulates cholinergic expression by basal forebrain cholinergic neurons. NGF also stimulates cellular resistance to oxidative stress in the PC12 cell line and protects PC12 cells from the toxic effects of reactive oxygen species. The hypothesis that NGF protection involves changes in antioxidant enzyme expression was tested by measuring its effects on catalase and glutathione per- oxidase (GSH Px) mRNA expression in PC12 cells. NGF increased catalase and GSH Px mRNA levels in PC 12 cells in a time- and dose-dependent manner. There was also a corresponding increase in the enzyme activities of catalase and GSH Px. Thus, NGF can provide cytoprotection to PC12 cells by inducing the free radical scavenging enzymes catalase and GSH Px. 相似文献