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   573篇
  免费   38篇
  国内免费   3篇
  2023年   2篇
  2021年   21篇
  2020年   11篇
  2019年   8篇
  2018年   18篇
  2017年   11篇
  2016年   28篇
  2015年   28篇
  2014年   29篇
  2013年   47篇
  2012年   29篇
  2011年   48篇
  2010年   21篇
  2009年   9篇
  2008年   37篇
  2007年   31篇
  2006年   24篇
  2005年   33篇
  2004年   23篇
  2003年   20篇
  2002年   15篇
  2001年   13篇
  2000年   9篇
  1999年   12篇
  1998年   4篇
  1997年   9篇
  1996年   5篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   3篇
  1991年   4篇
  1990年   3篇
  1989年   4篇
  1988年   4篇
  1987年   2篇
  1985年   2篇
  1984年   2篇
  1981年   5篇
  1980年   6篇
  1979年   2篇
  1978年   2篇
  1973年   2篇
  1971年   4篇
  1969年   2篇
  1968年   1篇
  1967年   2篇
  1966年   2篇
  1965年   1篇
  1964年   2篇
排序方式: 共有614条查询结果,搜索用时 171 毫秒
1.
Seed germination inHygrophila auriculata (Schumach.) Haines was found to be under phytochrome control. Exogenous indole-3-acetic acid (IAA) application at concentrations greater than 1×10–6 M inhibited germination in the dark, as well as in the light. Red light-induced radicle growth, prior to radicle protrusion through seed coverings and measured as an angle formed by the radicle with the seed axis, was found to be inhibited by IAA. Delay in application of IAA to red light-irradiated seeds resulted in a gradual increase in percent germination, which probably corresponded to the time-course of Pfr action. It is suggested that exogenously applied IAA probably reimposes dormancy in red light-induced seeds ofHygrophila auriculata.  相似文献   
2.
The purpose of these experiments was to determine the effects of a spontaneously generated inspiration on the size and shape of the left ventricle (LV) in anesthetized supine dogs. We implanted markers in the LV to establish three perpendicular axes and recorded the motion of these markers using biplane cinefluoroscopy at 60 Hz. The primary changes in LV size that accompanied inspiration occurred at end diastole (ED). The largest change in LVED dimension was a 2.46-mm narrowing of the septal-lateral wall dimension, but the apex-base dimension decreased also, by 0.74 mm. The anteroposterior dimension actually widened by 1.07 mm. The septal-lateral narrowing was caused by both a 1.0-mm narrowing of the distance between the septal marker and the apex-base axis, as well as by a 1.4-mm narrowing between the apex-base axis and the lateral wall marker. Narrowing of the septal portion seemed expected because of presumed enhanced right ventricular filling during inspiration. Narrowing of the lateral portion of the LV, while the anteroposterior dimension widened, was surprising because a change in LVEDV shape is implied. Assuming ventricular homogeneity, this change in LVED shape implies that the forces applied to the epicardial surface were not uniform. There must have been a retraction on the anterior and posterior surface that was not experienced by the lateral LV wall. The net effect of these dimensional changes of the LV at end diastole (estimated from the product of the three ED axes) was a 3.5-cm3 reduction in LVED volume.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
3.
The influence of the sulfone drugs, diamino diphenyl sulfone and diamino monophenyl sulfone on the phase transitions and dynamics of dipalmitoyl phosphatidyl choline-H2O/D2O vesicles have been investigated using differential scanning calorimetry and nuclear magnetic resonance. Our results show that diamino diphenyl sulfone interacts quite strongly with the headgroups of dipalmitoyl phosphatidyl choline whereas the diamino monophenyl sulfone-dipalmitoyl phosphatidyl choline interaction is quite weak. This is attributed to the difference in the structure and hydrophobic character of the two drugs.  相似文献   
4.
5.
6.
7.
The swimming behavior of Paramecium is regulated by an excitable membrane that covers the body and cilia of the protozoan. In order to obtain information on the topology and function of ciliary membrane proteins, Paramecia were treated with trypsin, chymotrypsin or pronase and the effects of these proteases were analyzed using electron microscopy, gel electrophoresis of ciliary fractions and behavioral tests. At the concentrations used, trypsin and chymotrypsin had little or no effect on the cells while pronase removed the cell surface coat, visible as fuzzy material covering the cell membrane. The same pronase treatment caused the specific removal of a high molecular weight protein (250 000), as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis. This protein, the ‘immobilization antigen’, constitutes the major protein of the ciliary membrane. Although the immobilization antigen was removed (or markedly decreased), no marked and reproducible difference was observed in the swimming behavior of the treated cells. We also determined the effects of proteases on isolated ciliary fractions to explore the sidedness of ciliary membrane proteins. A set of proteins relatively resistant to protease digestion was identified; they may be intrinsic membrane proteins.  相似文献   
8.
Aging biology is intimately associated with dysregulated metabolism, which is one of the hallmarks of aging. Aging‐related pathways such as mTOR and AMPK, which are major targets of anti‐aging interventions including rapamcyin, metformin, and exercise, either directly regulate or intersect with metabolic pathways. In this review, numerous candidate bio‐markers of aging that have emerged using metabolomics are outlined. Metabolomics studies also reveal that not all metabolites are created equally. A set of core “hub” metabolites are emerging as central mediators of aging. The hub metabolites reviewed here are nicotinamide adenine dinucleotide, reduced nicotinamide dinucleotide phosphate, α‐ketoglutarate, and β‐hydroxybutyrate. These “hub” metabolites have signaling and epigenetic roles along with their canonical roles as co‐factors or intermediates of carbon metabolism. Together these hub metabolites suggest a central role of the TCA cycle in signaling and metabolic dysregulation associated with aging.  相似文献   
9.
Breast Cancer (BCa) is the most often diagnosed cancer among women who were in the late 1940’s. Breast cancer growth is largely dependent on the expression of estrogen and progesterone receptor. Breast cancer cells may have one, both, or none of these receptors. The treatment for breast cancer may involve surgery, hormonal therapy (Tamoxifen, an aromatase inhibitor, etc.) and oral chemotherapeutic drugs. The molecular docking technique reported the findings on the potential binding modes of the 2‐(2‐bromo‐3‐nitrophenyl)‐5‐phenyl‐1,3,4‐oxadiazole derivatives with the estrogen receptor (PDB ID: 3ERT). The 1,3,4‐oxadiazole derivatives 4a – 4j have been synthesized and described by spectroscopic method. 2‐(2‐Bromo‐6‐nitrophenyl)‐5‐(4‐bromophenyl)‐1,3,4‐oxadiazole ( 4c ) was reconfirmed by single‐crystal XRD. All the compounds have been tested in combination with generic Imatinib pharmaceutical drug against breast cancer cell lines isolated from Caucasian woman MCF‐7, MDA‐MB‐453 and MCF‐10A non‐cancer cell lines. The compounds with the methoxy (in 4c ) and methyl (in 4j ) substitution were shown to have significant cytotoxicity, with 4c showing dose‐dependent activation and decreased cell viability. The mechanism of action was reported by induced apoptosis and tested by a DNA enzyme inhibitor experiment (ELISA) for Methyl Transferase. Molecular dynamics simulations were made for hit molecule 4c to study the stability and interaction of the protein?ligand complex. The toxicity properties of ADME were calculated for all the compounds. All these results provide essential information for further clinical trials.  相似文献   
10.

This study investigates the effects of dietary Aeromonas veronii V03 supplementation on growth performances, innate immunity, and expression of immune-related genes in lymphoid organs of Cyprinus carpio and resistance to Aeromonas hydrophila infection. Fish were fed for 4 weeks with basal diet (BD; without probiotic), and experiment diet containing different doses of A. veronii V03 at 3.2 × 107 (DI) and 3.5 × 109 (DII) CFU g−1 of diet. At the end of the probiotic feeding trial, fish were challenged with A. hydrophila, and the percentage of survival rates was recorded over 7 days. Results revealed that fish fed with A. veronii V03 demonstrated a significant improvement in growth and enhancement of innate immunity, including respiratory burst, myeloperoxidase, and lysozyme activities, and total immunoglobulin level compared with BD fed to fish. Relatively, expression of cytokines (MyD88, IL-1β1, IL-8, and IL-10) and c- and g-type lysozymes were significantly up- and downregulated in lymphoid organs of fish. Moreover, dietary supplementation of A. veronii V03 exhibited significantly (p < 0.001) higher survival rates of DI (90%) and DII (96.66%) compared with BD (53.33%) fed fish against A. hydrophila infection. These findings help to understand the effects of probiotic A. veronii V03 administrated feed influences on growth and ailment resistance to A. hydrophila infection by regulating innate and systemic immunity in common carp fish.

  相似文献   
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