全文获取类型
收费全文 | 3109篇 |
免费 | 224篇 |
专业分类
3333篇 |
出版年
2021年 | 48篇 |
2020年 | 24篇 |
2019年 | 35篇 |
2018年 | 50篇 |
2017年 | 42篇 |
2016年 | 68篇 |
2015年 | 110篇 |
2014年 | 114篇 |
2013年 | 156篇 |
2012年 | 182篇 |
2011年 | 176篇 |
2010年 | 112篇 |
2009年 | 112篇 |
2008年 | 149篇 |
2007年 | 141篇 |
2006年 | 130篇 |
2005年 | 117篇 |
2004年 | 146篇 |
2003年 | 139篇 |
2002年 | 121篇 |
2001年 | 79篇 |
2000年 | 87篇 |
1999年 | 68篇 |
1998年 | 44篇 |
1997年 | 29篇 |
1996年 | 37篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 43篇 |
1992年 | 36篇 |
1991年 | 29篇 |
1990年 | 31篇 |
1989年 | 32篇 |
1988年 | 43篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 27篇 |
1976年 | 27篇 |
1975年 | 18篇 |
1974年 | 32篇 |
1973年 | 19篇 |
1972年 | 22篇 |
1971年 | 16篇 |
排序方式: 共有3333条查询结果,搜索用时 0 毫秒
1.
Y. Paulsson C. Karlsson C.-H. Heldin B. Westermark 《Journal of cellular physiology》1993,157(1):97-103
We have previously found that transforming growth factor-β1 (TGF-β1) inhibits the mitogenic activity of platelet-derived growth factor (PDGF) in cultures of human neonatal fibroblasts in a density-dependent fashion. In the present investigation we determined the effect of TGF-β1 on the PDGF α-receptor, which binds all PDGF isoforms, as well as on the β-receptor, which binds only PDGF-BB with high affinity. We found that the inhibitory effect of TGF-β1 on PDGF-AA-induced mitogenesis was density-dependent; when dense cell cultures were preincubated with TGF-β1, there was an complete inhibition of 3H-thymidine incorporation, whereas the effect was less in sparse cultures. A similar density-dependent effect of TGF-β1 was seen in PDGF-BB treated cells, although less pronounced. The binding of 125I-labeled PDGF-AA and PDGF-BB to the α-receptor was significantly reduced after treatment with TGF-β1 in dense cultures, whereas the sparse cultures were less affected. A decrease of α-receptor mRNA was also seen. The levels of β-receptor protein and mRNA were unaffected. We conclude that the growth inhibitory effect of TGF-β1 is cell density-dependent and involves down-regulation of PDGF α-receptors. © 1993 Wiley-Liss, Inc. 相似文献
2.
3.
J.-. Karlsson 《Journal of neurochemistry》1979,32(2):491-494
Rapidly transported fucose-labelled glycoproteins from the optic system of the rabbit were solubilised with the non-ionic detergent Berol 172. The major labelled components were bound to wheat germ agglutinin or Concanavalin A coupled to Sepharose but not to other lectins or glycoproteins. It was concluded that rapidly transported proteins contain exposed N-acetyl-D-glucosamine 相似文献
4.
The first appearance, the 12-year follow-up, and the autopsy of a patient with a strange soft-tissue tumor in the lower leg region are described. Although it was originally taken for a malignant synovial tumor, its peculiar distribution pattern, together with its histologic picture, confirmed the final diagnosis as an epithelioid sarcoma. 相似文献
5.
Rapid Migration of Inositol Phospholipids with Axonally Transported Substances in the Rabbit Optic Pathway 总被引:3,自引:3,他引:0
Following an intraocular injection of myo-[2-3H]inositol, the axonal transport of labelled water-soluble substances and inositol phospholipids was investigated. Evidence was obtained for a rapid axonal transport of a relatively small amount of labelled inositol phospholipids. In contrast to other axonally transported phospholipids, there was no significant accumulation of labelled, rapidly transported inositol phospholipids in the nerve terminal region at later time intervals following the isotope administration. 相似文献
6.
Ten hypothyroid patients with Hashimoto''s thyroiditis were treated with methimazole 30 mg in addition to thyroxine 0.15 mg daily. Another 10 hypothyroid patients with Hashimoto''s thyroiditis were given thyroxine 0.15 mg alone. After 22 weeks of treatment significant decreases in thyroid microsomal autoantibody titres were observed in both groups (p less than 0.01). There was no difference in the mean change in titre between the two groups. When the patients treated with methimazole were subsequently given thyroxine 0.15 mg alone for a further 22 weeks no additional change in titre was observed. The data suggest that thyroxine, by normalising serum thyroid stimulating hormone concentrations, may reduce the autoantigenic properties of the thyrocytes with a subsequent decrease in autoantibody titres. 相似文献
7.
The imaginal pore plates of Hymenoptera apocrita so far examined embody five or six envelope cells respectively. In early developmental stages, however, supernumerary envelope cells have been found. The results are discussed in the context of cell death as a developmental phenomenon. 相似文献
8.
In soil micromorphology fissures are considered in vertical sections. To get information about the properties of the soil the joint distribution of spatial direction and width of these fissures is of interest. The fissures are mathematically generalized to flat bodies which are defined as stationary weighted surface processes with the weight “thickness”. In a typical point of the surface process suitable, joint parametric distributions of direction and thickness are assumed. The parameters have to be estimated from measurements on vertical sections which are taken from the soil. On these sections only a visible thickness and a visible angle can be observed. The joint distribution of these variables can be expressed by the joint distribution of spatial direction and thickness with the same parameters and in this indirect way the parameters can be estimated. The paper describes how to randomize the vertical section and how to measure the visible variables on the sections. The Chi-Square method is proposed for the parameter estimation. Further it is discussed how to derive good starting values for the numerical procedure. All this is demonstrated in a simulation study using the Bingham-Mardia distribution for the direction and the lognormal distribution for the thickness including a way to correlate the mean thickness and the direction. Finally an application in soil micromorphology is demonstrated for one soil horizon. 相似文献
9.
10.
M Konrad 《The Journal of biological chemistry》1992,267(36):25652-25655
Guanylate kinase catalyzes the reversible transfer of the terminal phosphoryl group of ATP to the acceptor molecule GMP. Detailed analysis of the in vivo function of this enzyme has been limited by the lack of any genetic data. Using oligonucleotides based on amino acid sequence information of the yeast enzyme, the Saccharomyces cerevisiae gene, GUK1, was isolated and characterized. The gene is present in single copy and maps to chromosome IV. Insertional mutagenesis of the GUK1 locus caused recessive lethality, indicating that this enzyme is necessary for vegetative cell growth. Using inducible expression systems, guanylate kinase was produced in large amounts both in S. cerevisiae and in Escherichia coli. 相似文献