全文获取类型
收费全文 | 617篇 |
免费 | 118篇 |
专业分类
735篇 |
出版年
2021年 | 6篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 16篇 |
2014年 | 23篇 |
2013年 | 31篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 32篇 |
2006年 | 22篇 |
2005年 | 20篇 |
2004年 | 28篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 21篇 |
2000年 | 23篇 |
1999年 | 13篇 |
1998年 | 21篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1974年 | 7篇 |
1972年 | 8篇 |
1970年 | 4篇 |
1969年 | 5篇 |
1968年 | 3篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1965年 | 4篇 |
1960年 | 3篇 |
1943年 | 3篇 |
排序方式: 共有735条查询结果,搜索用时 0 毫秒
21.
The reelin pathway modulates the structure and function of retinal synaptic circuitry 总被引:8,自引:0,他引:8
The formation of synaptic connections requires the coordination of specific guidance molecules and spontaneous neuronal activity. The visual system has provided a useful model for understanding the role of these cues in shaping the precise connections from the neural retina to the brain. Here, we demonstrate that two essential genes in the Reelin signaling pathway function during the patterning of synaptic connectivity in the retina. Physiological studies of mice deficient in either reelin or disabled-1 reveal an attenuation of rod-driven retinal responses. This defect is associated with a decrease in rod bipolar cell density and an abnormal distribution of processes in the inner plexiform layer. These results imply that, in addition to its essential role during neuronal migration, the Reelin pathway contributes to the formation of neuronal circuits in the central nervous system. 相似文献
22.
Longmuir and co-workers have reported that respiration of certain tissue slices is approximated by Michaelis-Menten kinetics. From this and other experimental findings, Longmuir proposed that a carrier is involved in tissue oxygen transport. Gold developed a deterministic model to examine this hypothesis. This report presents a stochastic model for a fixed site carrier in a more general framework that includes the stochastic counter-part to Gold's deterministic model as a special case. The kinetics of tissue oxygen consumption predicted by the model are examined for various cases. 相似文献
23.
24.
The components that comprise the extracellular matrix (ECM) are integral to normal tissue homeostasis as well as the development and progression of breast tumors. The secretion, construction, and remodeling of the ECM are each regulated by a complex interplay between tumor cells, fibroblasts and macrophages. Transforming growth factor-β (TGF-β) is an essential molecule in regulating the cellular production of ECM molecules and the adhesive interactions of cells with the ECM. Additionally, hypoxic cell signals, initiated by oxygen deprivation, additional metabolic factors or receptor activation, are associated with ECM formation and the progression of breast cancer. Both TGF-β and hypoxic cell signals are implicated in the functional and morphological changes of cancer-associated-fibroblasts and tumor-associated-macrophages. Moreover, the enhanced recruitment of tumor and stromal cells in response to hypoxia-induced chemokines leads to increased ECM deposition and remodeling, increased blood vessel formation, and enhanced tumor migration. Thus, elucidation of the collaborative networks between tumor and stromal cells in response to the combined signals of TGF-β and hypoxia may yield insight into treatment parameters that target both tumor and stromal cells. 相似文献
25.
Allen SJ Curran AR Templer RH Meijberg W Booth PJ 《Journal of molecular biology》2004,342(4):1293-1304
Research into the folding mechanisms of integral membrane proteins lags far behind that of water-soluble proteins, to the extent that the term protein folding is synonymous with water-soluble proteins. Hydrophobic membrane proteins, and particularly those with transmembrane alpha-helical motifs, are frequently considered too difficult to work with. We show that the stored curvature elastic stress of lipid bilayers can be used to guide the design of efficient folding systems for these integral membrane proteins. The curvature elastic stress of synthetic phosphatidylcholine/phosphatidylethanolamine lipid bilayers can be used to control both the rate of folding and the yield of folded protein. The use of a physical bilayer property generalises this approach beyond the particular chemistry of the lipids involved. 相似文献
26.
27.
28.
Accuracy of transrectal ultrasonic diagnosis of fetal gender by identifying and locating the genital tubercle was assessed in 85 horses and 102 dairy heifers and cows. Examinations were made once (horses and cattle) under farm conditions (cattle) on approximately Days 50 to 100. Definite diagnosis was made by removal of fetuses (horses) or after calving or abortion (cattle). In both species and both parities, accuracy was 100% (109 109 totaled over both species) when the certainty level recorded at the time of examination was 95 or 99%. At the lower levels of certainty (65 to 80%, 85 to 90%), the accuracy was 89% (57 64 totaled over both species). A diagnosis was not obtainable in 10 horses (12%) and 5 cattle (5%); this was especially due to inadequate viewing of the fetus when the fetus was beyond Day 64. The time from completion of evacuation of the rectum to diagnosis of gender averaged 1 minute 17 seconds in horses (range, 15 seconds to 3 minutes 55 seconds). The corresponding figure in cattle was 1 minute 53 seconds (range, 16 seconds to 8 minutes 30 seconds). 相似文献
29.
Curran EM Berghaus LJ Vernetti NJ Saporita AJ Lubahn DB Estes DM 《Cellular immunology》2001,214(1):12-20
Natural killer (NK) cells play a crucial role in host defense against pathogens and immune surveillance against cancer. Given that estrogens have been reported to suppress NK cell activity, we sought to elucidate the mechanisms by which estrogen mediates this effect. We demonstrate by immunocytochemical staining with estrogen receptor-alpha (ERalpha)- and estrogen receptor-beta (ERbeta)-specific antibodies that both ERalpha and ERbeta are expressed in murine NK cells. We also compared the ability of high doses of 17beta-estradiol ( approximately 800 pg/ml) to regulate NK cell activity in wild-type and estrogen receptor-alpha-deficient (ERalphaKO) mice. 17beta-estradiol elicited a significant decrease in NK cell activity in both wild-type and ERalphaKO mice (P < 0.001). These data suggest that ERbeta or possibly a novel receptor is involved in mediating estrogen action on NK cell activity and raise the potential for therapeutic modulation of NK cell activity with selective estrogen receptor modulators (SERMS). 相似文献
30.
Khan JA Kudgus RA Szabolcs A Dutta S Wang E Cao S Curran GL Shah V Curley S Mukhopadhyay D Robertson JD Bhattacharya R Mukherjee P 《PloS one》2011,6(6):e20347