全文获取类型
收费全文 | 34197篇 |
免费 | 2879篇 |
国内免费 | 1027篇 |
专业分类
38103篇 |
出版年
2024年 | 89篇 |
2023年 | 485篇 |
2022年 | 710篇 |
2021年 | 1108篇 |
2020年 | 1324篇 |
2019年 | 1677篇 |
2018年 | 1427篇 |
2017年 | 960篇 |
2016年 | 945篇 |
2015年 | 1241篇 |
2014年 | 2029篇 |
2013年 | 2175篇 |
2012年 | 1248篇 |
2011年 | 1669篇 |
2010年 | 1173篇 |
2009年 | 1553篇 |
2008年 | 1659篇 |
2007年 | 1613篇 |
2006年 | 1582篇 |
2005年 | 1366篇 |
2004年 | 1188篇 |
2003年 | 994篇 |
2002年 | 866篇 |
2001年 | 640篇 |
2000年 | 596篇 |
1999年 | 444篇 |
1998年 | 491篇 |
1997年 | 479篇 |
1996年 | 514篇 |
1995年 | 499篇 |
1994年 | 478篇 |
1993年 | 428篇 |
1992年 | 444篇 |
1991年 | 380篇 |
1990年 | 372篇 |
1989年 | 327篇 |
1988年 | 283篇 |
1987年 | 282篇 |
1986年 | 229篇 |
1985年 | 278篇 |
1984年 | 269篇 |
1983年 | 141篇 |
1982年 | 240篇 |
1981年 | 195篇 |
1980年 | 177篇 |
1979年 | 175篇 |
1978年 | 113篇 |
1977年 | 115篇 |
1976年 | 106篇 |
1973年 | 80篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
Lipoproteins in the plasma are the major source of cholesterol obtained by the ovarian theca and granulosa cells for steroidogenesis. In this study, we have identified mRNA expression in bovine theca and granulosa cells of two lipoprotein receptors, low density lipoprotein receptor (LDLr) and very low density lipoprotein receptor (VLDLr) in granulosa cells from small antral follicles through preovulatory follicles and in theca cells from large and medium sized antral follicles. In the corpus luteum (CL) both these receptors were found in the developing and differentiating stages whereas only mRNA for VLDLr was detected in the regression stage. This study also described for the first time, the presence of lipoprotein receptor related protein (LRP8) in granulosa cells from small antral follicles through preovulatory follicles and in theca cells from large and medium sized antral follicles. This may indicate a role of LRP8 in cholesterol delivery to steriodogenic cells. LRP8 was not detected in any of the CL stages. The roles of the LDLr superfamily in lipid transport to ovarian cells and its participation in follicular and CL development and regression is discussed. 相似文献
822.
823.
Summary Glycoproteins rich in mannosyl or glucosyl residues were analyzed in the subcommissural organ (SCO) and the pineal organ of the sheep (Ovis aries). By use of concanavalin A labelled with fluorescein isothiocyanate, fluorescent material was found both in ependymal and hypendymal cells of the SCO. In the pineal organ, either isolated or grouped parenchymal cells showed a marked fluorescence. These cells may correspond to ependymal elements also called interstitial cells or supporting cells. In addition, scarce slender, fluorescent processes were observed in the pineal parenchyma. The techniques of electrophoresis and electrotransfer on nitrocellulose paper have been applied to analyze the glycopeptide content of the SCO and the pineal organ in comparison to cerebellar and cerebral fractions solubilized by use of Triton X 100. Approximately 30 different concanavalin A-reactive glycopeptides were revealed in each fraction. In the SCO extract four glycopeptides (30, 54, 72, 100 kd) might correspond to subunits of the glycoprotein(s) characteristically stored in the ependymal cells of the SCO. In addition, two glycopeptides (32/33, 115 kd) are specific to the pineal organ extract. The possible similarity of the concanavalin A-reactive material in both organs is discussed and a putative secretory activity of the pineal ependymal cells is postulated. 相似文献
824.
825.
826.
Felipe?A.?Cisternas Gladys?Tapia Miguel?Arredondo Denise?Cartier-Ugarte Pamela?Romanque Walter?D.?Sierralta María?T.?Vial Luis?A.?Videla Magdalena?ArayaEmail author 《Biometals》2005,18(5):541-551
Cu is an essential trace element capable of producing toxic effects in animals and man when ingested acutely or chronically
in excess. Although chronic Cu exposure is increasingly recognized as a public health issue, its early effects remain largely
unknown. We approached the significance of a moderate chronic Cu load in young rats to correlate early hepatic histopathological
changes with functional alterations of liver cells. For this purpose, supplementation with 1200 ppm of Cu in rat food for
16 weeks was chosen. In these conditions, Cu load elicited a significant decrease in growth curves. There were mild light
microscopy alterations in Cu-treated rats, although increasing intracellular Cu storage was correlated with longer Cu exposure
both by histological and biochemical measurements. Ultrastructural alterations included lysosomal inclusions as well as mitochondrial
and nuclear changes. Liver perfusion studies revealed higher rates of basal O2 consumption and colloidal carbon-induced O2 uptake in Cu-treated rats, with enhanced carbon-induced O2/carbon uptake ratios and NF-κB DNA binding activity. These changes were time-dependent and returned to control values after
12 or16 weeks. It is concluded that subchronic Cu loading in young rats induces early hepatic morphological changes, with
enhancement in Küpffer cell-dependent respiratory burst activity and NF-κB DNA binding, cellular responses that may prevent
or alleviate the hepatotoxicity of the metal. 相似文献
827.
Wober J Möller F Richter T Unger C Weigt C Jandausch A Zierau O Rettenberger R Kaszkin-Bettag M Vollmer G 《The Journal of steroid biochemistry and molecular biology》2007,107(3-5):191-201
The special extract ERr 731® from the roots of Rheum rhaponticum is the major constituent of Phytoestrol® N which is used for the treatment of climacteric symptoms in menopausal women. However, the molecular mode of action of ERr 731® was unknown. For the first time, ERr 731® and its aglycones trans-rhapontigenin and desoxyrhapontigenin were investigated with regard to the activation of the estrogen receptor- or estrogen receptor-β (ER, ERβ). The related hydroxystilbenes cis-rhapontigenin, resveratrol and piceatannol were studied as comparators. As controls, 17β-estradiol or the selective ER-(propylpyrazoltriol) or ERβ-agonists (diarylpropionitril) were used. Neither in ER-expressing yeast cells, in the ER-responsive Ishikawa cells, nor in human endometrial HEC-1B cells transiently transfected with the ER an activation of ER by ERr 731® or the other single compounds was detected. Furthermore, an antiestrogenic effect was not observed. In contrast in human endometrial HEC-1B cells transiently transfected with the ERβ, 100 ng/ml ERr 731® and the single compounds significantly induced the ERβ-coupled luciferase activity in a range comparable to 10−8 M 17β-estradiol. All effects were abolished with the pure ER antagonist ICI 182780, indicating an ER-specific effect. The ERβ agonistic activity by ERr 731® could be of importance for its clinical use, as central functions relevant to climacteric complaints are proposed to be mediated via ERβ activation. 相似文献
828.
Chemotherapy and zoledronate sensitize solid tumour cells to Vγ9Vδ2 T cell cytotoxicity 总被引:1,自引:0,他引:1
Combinations of cellular immune-based therapies with chemotherapy and other antitumour agents may be of significant clinical
benefit in the treatment of many forms of cancer. Gamma delta (γδ) T cells are of particular interest for use in such combined
therapies due to their potent antitumour cytotoxicity and relative ease of generation in vitro. Here, we demonstrate high
levels of cytotoxicity against solid tumour-derived cell lines with combination treatment utilizing Vγ9Vδ2 T cells, chemotherapeutic
agents and the bisphosphonate, zoledronate. Pre-treatment with low concentrations of chemotherapeutic agents or zoledronate
sensitized tumour cells to rapid killing by Vγ9Vδ2 T cells with levels of cytotoxicity approaching 90%. In addition, zoledronate
enhanced the chemotherapy-induced sensitization of tumour cells to Vγ9Vδ2 T cell cytotoxicity resulting in almost 100% lysis
of tumour targets in some cases. Vγ9Vδ2 T cell cytotoxicity was mediated by perforin following TCR-dependent and isoprenoid-mediated
recognition of tumour cells. Production of IFN-γ by Vγ9Vδ2 T cells was also induced after exposure to sensitized targets.
We conclude that administration of Vγ9Vδ2 T cells at suitable intervals after chemotherapy and zoledronate may substantially
increase antitumour activities in a range of malignancies.
Financial
support and conflicts of interest: This study was supported by grants from Medinet (Japan), and Suncorp Metway and Gallipoli Research Foundation (Australia).
No financial or commercial interests arise from this study. Informed consent: This study was approved by Human Research Ethics Committees of the University of Queensland and Greenslopes Private Hospital
and informed consent was obtained from all subjects. 相似文献
829.
830.
An Inhibitory Role of Nitric Oxide in the Dynamic Regulation of the Blood-Brain Barrier Function 总被引:1,自引:0,他引:1
Yamauchi A Dohgu S Nishioku T Shuto H Naito M Tsuruo T Sawada Y Kataoka Y 《Cellular and molecular neurobiology》2007,27(3):263-270
1. The present study aimed at elucidating the effect of nitric oxide (NO) on blood-brain barrier (BBB) function with mouse
brain capillary endothelial (MBEC4) cells.
2. Histamine (20–100 μM) evoked NO production (1.6–7 μM) in MBEC4 cells in a dose-dependent manner.
3. The permeability coefficient of sodium fluorescein for MBEC4 cells and the cellular accumulation of rhodamine 123 in MBEC4
cells were increased dose-dependently by the addition of NO solutions (14 and 28 μM) every 10 min during a 30-min period.
4. The present study demonstrated that NO increased the permeability and inhibited the P-glycoprotein efflux pump of brain
capillary endothelial cells, suggesting that NO plays an inhibitory role in the dynamic regulation of the BBB function. 相似文献