首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   299篇
  免费   20篇
  国内免费   6篇
  2017年   2篇
  2016年   2篇
  2014年   2篇
  2013年   4篇
  2012年   3篇
  2011年   8篇
  2010年   15篇
  2009年   8篇
  2008年   9篇
  2007年   19篇
  2006年   6篇
  2005年   9篇
  2004年   8篇
  2003年   5篇
  2001年   5篇
  2000年   2篇
  1999年   4篇
  1998年   6篇
  1997年   8篇
  1996年   7篇
  1995年   9篇
  1994年   3篇
  1993年   8篇
  1992年   7篇
  1991年   9篇
  1990年   6篇
  1989年   6篇
  1988年   6篇
  1987年   4篇
  1986年   6篇
  1985年   3篇
  1983年   2篇
  1982年   3篇
  1977年   4篇
  1976年   3篇
  1974年   5篇
  1973年   3篇
  1971年   2篇
  1959年   2篇
  1958年   10篇
  1957年   12篇
  1956年   12篇
  1955年   10篇
  1954年   8篇
  1953年   6篇
  1952年   6篇
  1951年   7篇
  1950年   4篇
  1949年   6篇
  1948年   6篇
排序方式: 共有325条查询结果,搜索用时 15 毫秒
81.

Introduction

Male breast cancer (MBC) is a rare, yet potentially aggressive disease. Although literature regarding female breast cancer (FBC) is extensive, little is known about the etiopathogenesis of male breast cancer. Studies from our laboratory show that MBCs have a distinct immunophenotypic profile, suggesting that the etiopathogenesis of MBC is different from FBCs. The aim of this study was to evaluate and correlate the immunohistochemical expression of cell cycle proteins in male breast carcinoma to significant clinico-biological endpoints.

Methods

75 cases of MBC were identified using the records of the Saskatchewan Cancer Agency over 26 years (1970-1996). Cases were reviewed and analyzed for the immunohistochemical expression of PCNA, Ki67, p27, p16, p57, p21, cyclin-D1 and c-myc and correlated to clinico-biological endpoints of tumor size, node status, stage of the disease, and disease free survival (DFS).

Results

Decreased DFS was observed in the majority of tumors that overexpressed PCNA (98%, p = 0.004). The overexpression of PCNA was inversely correlated to the expression of Ki67 which was predominantly negative (78.3%). Cyclin D1 was overexpressed in 83.7% of cases. Cyclin D1 positive tumors were smaller than 2 cm (55.6%, p = 0.005), had a low incidence of lymph node metastasis (38.2%, p = 0.04) and were associated with increased DFS of >150 months (p = 0.04). Overexpression of c-myc (90%) was linked with a higher incidence of node negativity (58.3%, p = 0.006) and increased DFS (p = 0.04). p27 over expression was associated with decreased lymph node metastasis (p = 0.04). P21 and p57 positive tumors were related to decreased DFS (p = 0.04). Though p16 was overexpressed in 76.6%, this did not reach statistical significance with DFS (p = 0.06) or nodal status (p = 0.07).

Conclusion

Aberrant cell cycle protein expression supports our view that these are important pathways involved in the etiopathogenesis of MBC. Tumors with overexpression of Cyclin D1 and c-myc had better outcomes, in contrast to tumors with overexpression of p21, p57, and PCNA with significantly worse outcomes. P27 appears to be a predictive marker for lymph nodal status. Such observation strongly suggests that dysregulation of cell cycle proteins may play a unique role in the initiation and progression of disease in male breast cancer. Such findings open up new avenues for the treatment of MBC as a suitable candidate for novel CDK-based anticancer therapies in the future.  相似文献   
82.
Gryphaea arcuata is one of the most studied fossils, but its detailed palaeoecology has been largely neglected. Specimens were collected within a short stratigraphic range (three ammonite zones) in the 'Calcaire à gryphées' of Xeuilley (Lorraine, France) dated Hettangian to Lower Sinemurian. As far as possible, they were sampled from each marly bed of the section. A biometric study and an isotopic analysis are compared in regard to organic matter measurements and palynological data, the results demonstrating a clear relationship between the shape of G. arcuata and environmental parameters. Factors responsible for the various shapes are temperature, oxygen levels on the sea floor and nutrient levels. Two main morphotypes can be related to two kinds of environment. In the first, controlled by a relatively hot and humid climate and tending towards eutrophication, the growth rate of Gryphaea was low, and the shells small, wide and thin. In the second environment, cooler than the first one and closer to the optimal living conditions of G. arcuata, the shell was large, thick and narrow, and exhibited a high growth rate.  相似文献   
83.
6-benzylaminopurine (BAP) delays leaf abscission of soybeanGlycine max (L.) Merr. Abscission of the distal pulvinus ofprimary leaves was induced in 12-d-old seedlings or explantsby removal of the leaf blade. BAP applied to the cut end ofthe pulvinus following leaf blade removal delayed abscission.Discoloration of the pulvinus occurred before abscission commencedand the number of grana in chloroplasts within cortical parenchymacells of the pulvinus decreased over time following leaf bladeremoval. BAP prevented discoloration of pulvinus tissues anda decrease in grana number. Starch grains within amyloplastsof cells of the starch sheath in the pulvinus disappeared followingleaf blade removal, whereas starch accumulated within the abscissionzone prior to abscission. BAP prevented this apparent redistributionof starch and instead promoted an increase in starch withinplastids of cortical parenchyma cells of the pulvinus. Duringthe abscission process, cells within the separation layer enlargedand their nuclei and nucleoli became more evident prior to theirseparation from one another. Cell separation resulted from breakdownof middle lamellae and partial degradation of primary cell walls.Cycloheximide applied directly to the external surface of theabscission zone inhibited abscission in a similar way to theBAP treatment. These results suggest that BAP prevents abscissionby altering patterns of starch distribution in the pulvinusand abscission zone and by inhibiting the synthesis of proteinsthat typically appear de novo in induced abscission zone tissues. Key words: Benzylaminopurine, BAP, Soybean, Pulvinus, Abscission, amyloplast.  相似文献   
84.
Kinetic measurements are employed to reconstruct the steady-state activation of acetylcholine [Ach] receptor channels in electrophorus electroplaques. Neurally evoked postsynaptic currents (PSCs) decay exponentially; at 15 degrees C the rate constant, α, equals 1.2 ms(-1) at 0 mV and decreases e-fold for every 86 mV as the membrane voltage is made more negative. Voltage-jump relaxations have been measured with bath-applied ACh, decamethonium, carbachol, or suberylcholine. We interpret the reciprocal relaxation time 1/τ as the sum of the rate constant α for channel closing and a first-order rate constant for channel opening. Where measureable, the opening rate increases linearly with [agonist] and does not vary with voltage. The voltage sensitivity of small steady-state conductances (e- fold for 86 mV) equals that of the closing rate α, confirming that the opening rate has little or no additional voltage sensitivity. Exposure to α-bungarotoxin irreversibly decreases the agonist-induced conductance but does not affect the relaxation kinetics. Tubocurarine reversibly reduces both the conductance and the opening rate. In the simultaneous presence of two agonist species, voltage-jump relaxations have at least two exponential components. The data are fit by a model in which (a) the channel opens as the receptor binds the second in a sequence of two agonist molecules, with a forward rate constant to 10(7) to 2x10(8) M(-1)s(-1); and (b) the channel then closes as either agonist molecule dissociates, with a voltage-dependent rate constant of 10(2) to 3x10(3)s(-1).  相似文献   
85.
In the first leaf of wheat (Triticum aestivum L. cv. Capelle) the content of soluble protein diminished to about 50% of the initial value between the 7th and the 19th day after sowing. In order to understand proteolysis in the leaves, the activities of several peptidases were measured in extracts from leaves at four different ages. The carboxypeptidase activities increased during the growth of the leaves, and then began to decrease. The activities of the alkaline peptidases increased, while that of the benzoyl-DL-arginine-p-nitroanilide (BAPA) hydrolysing enzyme decreased during the whole period studied. The “naphthylamidase” activities showed first a slow rise, but then leveled off. Two bands with naphthylamidase activity could be detected after disc electrophoresis. All the peptidases studied were present in the leaves at rather high concentrations. This indicates that they all may participate in the hydrolysis of leaf proteins into free amino acids.  相似文献   
86.
Cells ofTetrahymenamay produce autocrine signal molecules with effects on survival and proliferation. Here we have tested the effects of human recombinant and bovine insulin, and the B22–B30 fragment of bovine insulin over a wide range of concentrations (10?5–10?18m ) on cell survival and proliferation in a synthetic nutrient medium. The cells were grown in conical flasks at low initial cell densities (40 and 400cells/ml). Insulin prevented rapid cell death and/or promoted cell proliferation over two separate concentration ranges: down to nanomolar levels and again in the low pico- and femtomolar range. At an initial population density of 400cells/ml the cells multiplied at both concentration intervals. At 40 or fewer organisms/ml the cells multiplied in the high concentration interval, whereas in the low interval they survived for about four times longer than those in the control cultures. B22–B30 added to cultures of 40 initial cells/ml produced a stimulation of cell survival in the low pico- and high femtomolar range. In the presence of hemin (50nm ) cells at 400 initial organisms/ml multiplied at insulin concentrations down to about 3nm and again from 300am to 10pm . In some cases, hemin plus insulin activated cell proliferation between the two concentration intervals as well. At 40cells/ml the cells not only survived but proliferated in the femtomolar range. Cells in cultures supplemented with both hemin and B22–B30 multiplied at the low concentration interval (from about 100fm to 10pm ).  相似文献   
87.
1. Colonisation and population recovery are crucial to species persistence in environmentally variable ecosystems, but are poorly understood processes. After documenting movement rates for several species of stream fish, we predicted that this variable would influence colonisation rates more strongly than local abundance, per cent occupancy, body size and taxonomic family. We also predicted that populations of species with higher movement rates would recover more rapidly than species with lower movement rates and that assemblage structure would change accordingly. 2. To test these predictions, we removed fishes from a headwater and a mainstem creek in southwest Virginia and monitored colonisation over a 2‐year period. Using an information–theoretic approach, we evaluated the relative plausibility of 15 alternative models containing different combinations of our predictor variables. Our best‐supported model contained movement rate and abundance and was 41 times more likely to account for observed patterns in colonisation rates than the next‐best model. Movement rate and abundance were both positively related to colonisation rates and explained 88% of the variation in colonisation rates among species. 3. Population recovery, measured as the per cent of initial abundance restored, was also positively associated with movement rate. One species recovered within 3 months, most recovered within 2 years, but two species still had not recovered after 2 years. Despite high variation in recovery, the removal had only a slight impact on assemblage structure because species that were abundant in pre‐removal samples were also abundant in post‐removal samples. 4. The significance of interspecific variation in colonisation and recovery rates has been underappreciated because of the widely documented recovery of stream fish assemblages following fish kills and small‐scale experimental defaunations. Our results indicate that recovery of the overall assemblage does not imply recovery of each component species. Populations of species that are rare and less mobile will recover more slowly and will be more vulnerable to extinction in systems where chemical spills, hydrological alteration, extreme droughts and other impacts are frequent.  相似文献   
88.
89.
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号