全文获取类型
收费全文 | 1742268篇 |
免费 | 164127篇 |
国内免费 | 1447篇 |
出版年
2021年 | 16969篇 |
2019年 | 16247篇 |
2018年 | 20079篇 |
2017年 | 18884篇 |
2016年 | 29736篇 |
2015年 | 43218篇 |
2014年 | 51407篇 |
2013年 | 77559篇 |
2012年 | 50934篇 |
2011年 | 43317篇 |
2010年 | 49002篇 |
2009年 | 48667篇 |
2008年 | 39358篇 |
2007年 | 39133篇 |
2006年 | 40861篇 |
2005年 | 42051篇 |
2004年 | 40677篇 |
2003年 | 38129篇 |
2002年 | 36088篇 |
2001年 | 57287篇 |
2000年 | 55231篇 |
1999年 | 48413篇 |
1998年 | 26818篇 |
1997年 | 26614篇 |
1996年 | 25666篇 |
1995年 | 25197篇 |
1994年 | 24858篇 |
1993年 | 24125篇 |
1992年 | 41593篇 |
1991年 | 40107篇 |
1990年 | 38453篇 |
1989年 | 38633篇 |
1988年 | 35523篇 |
1987年 | 33756篇 |
1986年 | 31737篇 |
1985年 | 33132篇 |
1984年 | 30365篇 |
1983年 | 26721篇 |
1982年 | 24314篇 |
1981年 | 22993篇 |
1980年 | 21509篇 |
1979年 | 26686篇 |
1978年 | 23315篇 |
1977年 | 21695篇 |
1976年 | 20804篇 |
1975年 | 21444篇 |
1974年 | 22459篇 |
1973年 | 22595篇 |
1972年 | 19771篇 |
1971年 | 17756篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Dora E. Vega-Salas Julio A. San Martino Pedro J.I. Salas Alberto Baldi 《Differentiation; research in biological diversity》1993,54(3):131-141
Abstract. We have previously shown that an integral plasma membrane glycoprotein (AP2) is highly polarized to the apical domain in confluent Madin-Darby canine kidney (MDCK) epithelial cells. However, when the monolayers are prevented from forming intercellular contacts, approximately 60% of the AP2 cellular content is stored in the intracellular vacuolar apical compartment (VAC). In the current work we found that AP2 was present in the non-tumorigenic human mammary epithelial cell line MCF-10A. in the breast carcinoma cell lines MCF-7 and T47D, and in breast ductal carcinomas in vivo. By radioimmunoassay, an intracellular Compartment of AP2 was identified in the mammary cell lines in culture. In MCF-10A, this compartment behaved as in MDCK cells; namely it was observed only when the cells cannot form cell-cell contacts. However, in the carcinoma cell lines MCF-7 and T47D, a significant AP2 intracellular compartment was observed also under conditions permissive for the formation of intercellular contacts. These results were confirmed by immunofluorescence and immunoelectron microscopy experiments that showed VACs in MCF-7 and T47D, even in cells with extensive intercellular contacts. In MCF-7 cells, the addition of serum caused a partial decrease of the AP2 intracellular compartment. The exocytosis of VACs occurred towards the center of multi-cellular groups, forming intercellular lumens, similar to those transiently observed in MDCK cells and to structures described by others during embryo development. Altogether, these results suggest that VAC exocytosis is controlled by cell-cell contact signalling, which may be defective in carcinoma cells. 相似文献
992.
M. U. E. Merz 《Facies》1993,29(1):80-80
The online version of the original article can be found at 相似文献
993.
E. Chiarpotto F. Biasi M. Aragno A. Scavazza O. Danni E. Albano G. Poli 《Cell biochemistry and function》1993,11(1):71-75
The combination of carbon tetrachloride (CCl4) and 1,2-dibromoethane (DBE) in isolated rat hepatocytes led to a significant potentiation of both lipid peroxidation and of plasma membrane damage observed after a single treatment with CCl4. Such a synergistic effect appeared to be related to the CCl4-induced shift of DBE metabolism from the cytosolic conjugation with glutathione towards the microsomal transformation into toxic intermediates. In fact, CCl4 significantly inactivated hepatocyte total GSH-transferase, i.e. the DBE detoxification pathway. Furthermore, while the microsomal metabolism of CCl4 was not affected by the simultaneous presence of DBE, the amount of DBE reactive metabolities covalently bound to hepatocyte protein was significantly enhanced in the presence of CCl4. 相似文献
994.
995.
996.
997.
998.
999.
Amino acid substitutions of human interleukin-6 (IL-6) were performed. Single substitution Met162----Ala and double substitutions Leu159.166----Val resulted in a significant decrease of IL-6 activity in the production of immunoglobulin (Ig) from B-cells. Single substitution Leu166----Val or Leu159----Val gave a slight or no significant decrease in the Ig-induction activity, respectively. The receptor-binding activity of each IL-6 mutant was also examined. It was observed that the decrease of the receptor-binding activity was generally in parallel with that of the Ig-induction activity. We therefore suggest that hydrophobic side-chains existing in Met162, Leu159, and Leu166 are significantly involved in the receptor-binding of IL-6. 相似文献
1000.
In vivo analysis of a new lacZ retrovirus vector suitable for cell lineage marking in avian and other species 总被引:9,自引:0,他引:9
To obtain a replication-defective retrovirus vector well suited for cell lineage marking in early avian embryos, we have constructed and tested a derivative of the avian spleen necrosis virus (SNV) carrying the marker gene lacZ. Consistently high titers of this virus, designated CXL, were produced from retroviral packaging cells with no evidence of contaminating helper virus even after 12 months of continuous culture. CXL expresses lacZ strongly and stably in avian cells and has a host range that extends to other avian and some mammalian species. We show that CXL has the potential to mark a wide variety of chick embryo cell types by infection in ovo. The high titers obtainable with this virus can provide a significant advantage over alternative lacZ vectors, especially in lineage marking of early stage embryos. As an example of this, we show that CXL can be used to mark cells of the precardiac mesoderm in stage 4-5 chick embryos. 相似文献