全文获取类型
收费全文 | 961篇 |
免费 | 161篇 |
国内免费 | 1篇 |
出版年
2021年 | 16篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 28篇 |
2013年 | 33篇 |
2012年 | 45篇 |
2011年 | 41篇 |
2010年 | 28篇 |
2009年 | 25篇 |
2008年 | 36篇 |
2007年 | 38篇 |
2006年 | 28篇 |
2005年 | 31篇 |
2004年 | 35篇 |
2003年 | 30篇 |
2002年 | 27篇 |
2001年 | 35篇 |
2000年 | 30篇 |
1999年 | 23篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 19篇 |
1990年 | 30篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1987年 | 25篇 |
1986年 | 22篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 23篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 19篇 |
1976年 | 11篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1972年 | 7篇 |
1970年 | 9篇 |
1968年 | 6篇 |
排序方式: 共有1123条查询结果,搜索用时 15 毫秒
61.
The two preceding papers of this series suggest that the state of the plasmalemmal lipids affects cell adhesion. Plasmalemmal composition was altered by the experimental incorporation of fatty acids into R1 and R2 positions in the phosphatidyl components of the cell surface. In this paper we report that: (1) If the incorporation is of long chain length fatty acids (saturated) cell adhesion rises. (2) If the incorporation is of unsaturated fatty acids cell adhesion falls as the unsaturation increases. (3) Incorporation has to be extensive to produce a large change in adhesion. (4) Changes in adhesion parallel the plasmalemmal incorporation but do not follow the total cell incorporation. Item (4) argues that it is plasmalemmal and not other membrane lipids that are involved in cell adhesion. Item (3) suggests that bulk membrane properties and not some very specific grouping are involved in the effects of lipids on adhesion. The similar extents of incorporation of the various different fatty acids and the negligible amounts of lysophospholipids in the membranes of cells that have incorporated fatty acids argue that the effects are not due to differential accumulations of these lysolipids when incubations are done with different fatty acids. The changes in adhesion cannot be accounted for by changes in surface charge density since the electrophoretic mobility of the cells is unchanged by these incubations. It is suggested that these effects on adhesion due to changes in plasmalemmal lipids can be explained either in terms of the action of intermembrane van der Waals--London (electrodynamic) forces in cell adhesion or of changes in surface fluidity. These alternatives are discussed. 相似文献
62.
63.
G N Chandler 《BMJ (Clinical research ed.)》1967,4(5581):723-725
64.
X-ray microanalysis of zinc and calcium in ultrathin sections of human sperm cells using the pyroantimonate technique. 总被引:1,自引:0,他引:1
X-ray microanalysis of pyroantimonate-fixed sperm cells indicates the retention of calcium and zinc subcellularly in similar proportions to air dried cells. The ultrastructure is well preserved and is corelated with the analysis. Sodium, potassium and chlorine are all removed during the fixation. CAlcium and zinc are found present intracellularly both in association with and independent of antimonate precipitation. There thus appears to be a varying degree of binding of those elements subcellularly, precipitation occurring where binding is reduced. 相似文献
65.
Jennifer L. Chandler Timothy R. Van Deelen Nathan P. Nibbelink John L. Orrock 《Ecology and evolution》2020,10(14):7145-7156
Because most tree species recruit from seeds, seed predation by small‐mammal granivores may be important for determining plant distribution and regeneration in forests. Despite the importance of seed predation, large‐scale patterns of small‐mammal granivory are often highly variable and thus difficult to predict. We hypothesize distributions of apex predators can create large‐scale variation in the distribution and abundance of mesopredators that consume small mammals, creating predictable areas of high and low granivory. For example, because gray wolf (Canis lupus) territories are characterized by relatively less use by coyotes (C. latrans) and greater use by foxes (Vulpes vulpes, Urocyon cinereoargentus) that consume a greater proportion of small mammals, wolf territories may be areas of reduced small‐mammal granivory. Using large‐scale, multiyear field trials at 22 sites with high‐ and low‐wolf occupancy in northern Wisconsin, we evaluated whether removal of seeds of four tree species was lower in wolf territories. Consistent with the hypothesized consequences of wolf occupancy, seed removal of three species was more than 25% lower in high‐wolf‐occupancy areas across 2 years and small‐mammal abundance was more than 40% lower in high‐wolf areas during one of two study years. These significant results, in conjunction with evidence of seed consumption in situ and the absence of significant habitat differences between high‐ and low‐wolf areas, suggest that top‐down effects of wolves on small‐mammal granivory and seed survival may occur. Understanding how interactions among carnivores create spatial patterns in interactions among lower trophic levels may allow for more accurate predictions of large‐scale patterns in seed survival and forest composition. 相似文献
66.
67.
Carolyn J. Heckman Rachel Chandler Jacqueline D. Kloss Amy Benson Deborah Rooney Teja Munshi Susan D. Darlow Clifford Perlis Sharon L. Manne David W. Oslin 《Journal of visualized experiments : JoVE》2013,(75)
Ultraviolet radiation (UV) therapy is sometimes used as a treatment for various common skin conditions, including psoriasis, acne, and eczema. The dosage of UV light is prescribed according to an individual''s skin sensitivity. Thus, to establish the proper dosage of UV light to administer to a patient, the patient is sometimes screened to determine a minimal erythema dose (MED), which is the amount of UV radiation that will produce minimal erythema (sunburn or redness caused by engorgement of capillaries) of an individual''s skin within a few hours following exposure. This article describes how to conduct minimal erythema dose (MED) testing. There is currently no easy way to determine an appropriate UV dose for clinical or research purposes without conducting formal MED testing, requiring observation hours after testing, or informal trial and error testing with the risks of under- or over-dosing. However, some alternative methods are discussed. 相似文献
68.
Alwin M.D. Wan Emily M. Chandler Maya Madhavan David W. Infanger Christopher K. Ober Delphine Gourdon George G. Malliaras Claudia Fischbach 《Biochimica et Biophysica Acta (BBA)/General Subjects》2013
Background
Changes in fibronectin (Fn) matrix remodeling contribute to mammary tumor angiogenesis and are related to altered behavior of adipogenic stromal cells; yet, the underlying mechanisms remain unclear due in part to a lack of reductionist model systems that allow the inherent complexity of cell-derived extracellular matrices (ECMs) to be deciphered. In particular, breast cancer-associated adipogenic stromal cells not only enhance the composition, quantity, and rigidity of deposited Fn, but also partially unfold these matrices. However, the specific effect of Fn conformation on tumor angiogenesis is undefined.Methods
Decellularized matrices and a conducting polymer device consisting of poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) were used to examine the effect of Fn conformation on the behavior of 3T3-L1 preadipocytes. Changes in cell adhesion and proangiogenic capability were tested via cell counting and by quantification of vascular endothelial growth factor (VEGF) secretion, respectively. Integrin-blocking antibodies were utilized to examine varied integrin specificity as a potential mechanism.Results
Our findings suggest that tumor-associated partial unfolding of Fn decreases adhesion while enhancing VEGF secretion by breast cancer-associated adipogenic precursor cells, and that altered integrin specificity may underlie these changes.Conclusions and general significance
These results not only have important implications for our understanding of tumorigenesis, but also enhance knowledge of cell-ECM interactions that may be harnessed for other applications including advanced tissue engineering approaches. This article is part of a Special Issue entitled Organic Bioelectronics — Novel Applications in Biomedicine. 相似文献69.
70.
Hsan-au Wu Jeremy L. Balsbaugh Hollie Chandler Athena Georgilis Hayley Zullow Jeffrey Shabanowitz Donald F. Hunt Jesus Gil Gordon Peters Emily Bernstein 《The Journal of biological chemistry》2013,288(51):36398-36408
Cbx7 is one of five mammalian orthologs of the Drosophila Polycomb. Cbx7 recognizes methylated lysine residues on the histone H3 tail and contributes to gene silencing in the context of the Polycomb repressive complex 1 (PRC1). However, our knowledge of Cbx7 post-translational modifications remains limited. Through combined biochemical and mass spectrometry approaches, we report a novel phosphorylation site on mouse Cbx7 at residue Thr-118 (Cbx7T118ph), near the highly conserved Polycomb box. The generation of a site-specific antibody to Cbx7T118ph demonstrates that Cbx7 is phosphorylated via MAPK signaling. Furthermore, we find Cbx7T118 phosphorylation in murine mammary carcinoma cells, which can be blocked by MEK inhibitors. Upon EGF stimulation, Cbx7 interacts robustly with other members of PRC1. To test the role of Cbx7T118 phosphorylation in gene silencing, we employed a RAS-induced senescence model system. We demonstrate that Cbx7T118 phosphorylation moderately enhances repression of its target gene p16. In summary, we have identified and characterized a novel MAPK-mediated phosphorylation site on Cbx7 and propose that mitogen signaling to the chromatin template regulates PRC1 function. 相似文献