全文获取类型
收费全文 | 21690篇 |
免费 | 999篇 |
国内免费 | 646篇 |
出版年
2024年 | 6篇 |
2023年 | 228篇 |
2022年 | 286篇 |
2021年 | 479篇 |
2020年 | 490篇 |
2019年 | 724篇 |
2018年 | 738篇 |
2017年 | 393篇 |
2016年 | 527篇 |
2015年 | 661篇 |
2014年 | 1368篇 |
2013年 | 1574篇 |
2012年 | 887篇 |
2011年 | 1368篇 |
2010年 | 983篇 |
2009年 | 1086篇 |
2008年 | 1225篇 |
2007年 | 1212篇 |
2006年 | 1130篇 |
2005年 | 992篇 |
2004年 | 893篇 |
2003年 | 740篇 |
2002年 | 715篇 |
2001年 | 445篇 |
2000年 | 391篇 |
1999年 | 386篇 |
1998年 | 386篇 |
1997年 | 308篇 |
1996年 | 279篇 |
1995年 | 323篇 |
1994年 | 291篇 |
1993年 | 234篇 |
1992年 | 193篇 |
1991年 | 171篇 |
1990年 | 149篇 |
1989年 | 129篇 |
1988年 | 112篇 |
1987年 | 109篇 |
1986年 | 80篇 |
1985年 | 92篇 |
1984年 | 116篇 |
1983年 | 98篇 |
1982年 | 92篇 |
1981年 | 71篇 |
1980年 | 66篇 |
1979年 | 44篇 |
1978年 | 25篇 |
1977年 | 15篇 |
1976年 | 7篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Veli Isomaa 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,675(1):9-16
In vitro binding affinities of various progestins to cytosol and nuclear progesterone receptors of rabbit uterus were determined and correlated with the biological potency of these steroids. In addition, cytosol and nuclear progesterone receptor levels were measured after a 5-day administration of different progestins (0.5 mg/kg daily) with variable biologic activites. The receptor levels were compared with the bilological response; the induction of uteroglobin synthesis. Cytosol and nuclear progesterone receptors had identical steroid binding properties (r = 0.98). The correlation between the in vitro binding affinity (cytosol or nuclear) and the in vivo biologic activity of the steroids was good (r = 0.73). After a 5-day treatment with progestins, the nuclear receptor concentration correlated in an inverse manner (r = ?0.84) with the uterine fluid unteroglobin concentration. A similar, but slightly weaker correlation (r = ?0.81) was also found for the cytosol receptor content and uteroglobin secretion. These data indicate that not only nuclear, but also cytosol progesterone receptor levels decrease in the rabbit uterus during chronic hormone action. Decline in the nuclear progesterone receptor content seemed to occur during treatment with all progestational steroids, while onlyi progestins with high biological potency were capable of decreasing the cytosol receptor content. 相似文献
52.
《Cell reports》2020,30(2):308-319.e5
53.
54.
55.
Z. Ouanes I. Ayed-Boussema T. Baati E.E. Creppy H. Bacha 《Mutation Research - Genetic Toxicology and Environmental Mutagenesis》2005,565(2):139-149
The cytogenetic effect of zearalenone (ZEN), a non-steroidal estrogenic mycotoxin, was evaluated in vivo, in mouse bone marrow cells, by assessing the percentage of cells bearing different chromosome aberrations. The studies included different conditions for animal treatment, as follows: (1) single intraperitoneal (ip) injection, (2) repeated ip injections, (3) pre-treatment for 24 h with Vitamin E (Vit E), and (4) pre-treatment for 4 h with 17β-estradiol (17β-Est) or progesterone (Prog). ZEN induced different types of chromosome aberrations, which was concentration-dependent (2–20 mg/kg bw). These doses corresponded to 0.4–4% of the LD50 in the mouse. Interestingly, when the dose of ZEN (40 mg/kg) was fractionated into four equivalent doses (4 × 10 mg/kg bw), into three doses (15 + 10 + 15 mg/kg bw), or into two equivalent doses (2 × 20 mg/kg bw), given every 24 h, the percentage of chromosome aberrations increased significantly. This finding suggests that ZEN proceeds by reversible binding on receptors that could become saturated, and that it damages the chromosomes in a ‘hit and go’ manner. Furthermore, pre-treatment of animals with 17β-estradiol or progesterone significantly decreased the percentage of chromosome aberrations, suggesting that (i) these hormones bind to the same cytoplasmic receptors transported into the nucleus to elicit DNA damage, (ii) they may play a role in preventing chromosome aberrations induced by ZEN. Similarly, Vit E prevented these chromosome aberrations indicating that Vit E, previously reported to prevent most of the toxic effects induced by ZEN, may also bind to the same receptors. 相似文献
56.
John S. Adams Mercedes A. Gacad Andrew J. Baker Benjamin Gonzales Robert K. Rude 《American journal of primatology》1985,9(3):219-224
We measured the serum concentration of 25-hydroxyvitamin D3 (25-OH-D3) and 1,25-dihydroxyvitamin D3 (1,25-[OH]2-D3) in 23 different Platyrrhines from four different genera and in 21 Catarrhines from six different genera in residence at the Los Angeles Zoo. The mean (±S.E.) serum concentration of 1,25-(OH)2-D3 was significantly greater in Platyrrhines (810 ± 119 pg/ml) than in Catarrhines (61 ± 5 pg/ml), suggesting that high circulating concentrations of the active vitamin D hormone were a characteristic of New World primates in both the Cebidae and Callitrichidae family. This increase in the serum concentration of 1,25-(OH)2-D3 is probably an adaptational response on the part of Platyrrhini to offset a relative decrease in the concentration of specific receptor for 1,25-(OH)2-D3 in target tissues for the hormone. 相似文献
57.
Pedro J. I. Salas Dora E. Vega-Salas Enrique Rodriguez-Boulan 《The Journal of membrane biology》1987,98(3):223-236
Summary Madin-Darby canine kidney (MDCK) cells kept in suspension culture for 12–15 hr displayed high-affinity binding sites for125I-lathyritic (soluble) collagen (120,000/cell,K
D
=30nm) and preferred collagens types I and IV over laminin or fibronectin as substrates during the first hour of attachment. On the other hand, after 4 hr, attachment to all four substrates was equally efficient. Upon challenge with a collagen substrate, the high-affinity sites were rapidly recruited on it (T1/2=6 min). Their occupancy by soluble collagen triggered the exocytosis of a second large population of low-affinity collagen binding sites that included laminin and seems to be involved in a second cell-attachment mechanism. These results are compatible with a twostep model of MDCK cell attachment to the substrate: first, via high-affinity collagen binding sites, and second, via laminin of cellular origin. 相似文献
58.
Jos C. García‐Borrn Berta L. Snchez‐Laorden Celia Jimnez‐Cervantes 《Pigment cell & melanoma research》2005,18(6):393-410
The melanogenic actions of the melanocortins are mediated by the melanocortin‐1 receptor (MC1R). MC1R is a member of the G‐protein‐coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or α‐melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist‐independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light. 相似文献
59.
Noriya Ohta G. Thompson Burke Panayotis G. Katsoyannis 《Journal of Protein Chemistry》1988,7(1):55-65
As part of our aim to study the conformation of insulin in solution by time-resolved fluorescence spectroscopy, we have synthesized the analogue [19-Tryptophan-A]insulin. In this compound, the tyrosine residue at position 19 of the A-chain of insulin, one of the most strongly conserved residues in insulins from various species, is substituted with the strongly fluorescent tryptophan residue. [19-Tryptophan-A]insulin displays 4.1±1.9% of the potency of natural insulin in binding to the insulin receptor from rat liver plasma membranes, 5.0±2.3% in stimulating lipogenesis in rat adipocytes, and 75.7±4% of the potency of insulin in radioimmunoassay. In connection with our previous work, these data indicate that an aromatic side chain at position A19 of insulin seems necessary but not sufficient for high biological activity. We further conclude that in regard to the immunogenic determinants of insulin, tryptophan in position A19 is an essentially neutral substitution for tyrosine in that position, in sharp contrast to the situation with regard to biological activity. 相似文献
60.