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   1445篇
  免费   151篇
  国内免费   15篇
耳鼻咽喉   3篇
儿科学   116篇
妇产科学   24篇
基础医学   131篇
口腔科学   41篇
临床医学   212篇
内科学   341篇
皮肤病学   18篇
神经病学   55篇
特种医学   216篇
外科学   121篇
综合类   43篇
预防医学   54篇
眼科学   21篇
药学   84篇
  1篇
中国医学   1篇
肿瘤学   129篇
  2022年   6篇
  2021年   12篇
  2020年   19篇
  2019年   25篇
  2018年   35篇
  2017年   33篇
  2016年   32篇
  2015年   44篇
  2014年   31篇
  2013年   35篇
  2012年   39篇
  2011年   48篇
  2010年   57篇
  2009年   58篇
  2008年   45篇
  2007年   33篇
  2006年   28篇
  2005年   35篇
  2004年   25篇
  2003年   27篇
  2002年   34篇
  2001年   20篇
  2000年   23篇
  1999年   30篇
  1998年   87篇
  1997年   87篇
  1996年   93篇
  1995年   62篇
  1994年   58篇
  1993年   47篇
  1992年   23篇
  1991年   26篇
  1990年   16篇
  1989年   45篇
  1988年   31篇
  1987年   43篇
  1986年   21篇
  1985年   33篇
  1984年   25篇
  1983年   20篇
  1982年   17篇
  1981年   22篇
  1980年   12篇
  1979年   10篇
  1978年   8篇
  1977年   10篇
  1976年   10篇
  1975年   9篇
  1974年   3篇
  1973年   4篇
排序方式: 共有1611条查询结果,搜索用时 0 毫秒
31.
32.

Background

A common hypothesis is that caregiving is deleterious to women’s mental health. International studies continue to emphasize the importance of mental health issues for women. Yet only a few researchers have used population-based surveys to explore the association between caregiving and depressive symptomatology in the context of the community, and even less is known about this aspect of Baby Boomer women in a global context.

Methods

The present study uses eight international surveys covering nineteen nations (N?=?15,100) and uses multilevel logistic models to examine possible linkages between caregiving and the likelihood of depressive symptoms among Baby Boomer women, when taking individual-level and country-level social factors into consideration.

Results

The various analyses found a significant variation in the likelihood of depressive symptoms among these Boomer women across the nations investigated and across both individual-level and country-level characteristics. The significant association of caregiving by women and the likelihood of depressive symptoms is related to their social status in some nations (OR?=?1.30; p?<?0.001). Boomer women living in countries with high rates of female participation in managerial/professional work (OR?=?1.04; p?<?0.05) and living in countries where women are often in vulnerable employment (OR?=?1.01; p?<?0.05) are at greater risk of depressive symptomatology.

Conclusions

These findings demonstrate that the depressive consequences of caregiving by women are, to some degree, contingent upon social context and structure. Policies aimed at promoting mental health among female Baby Boomers should therefore be context specific.
  相似文献   
33.
Evidence from animal and human studies suggests that ocular growth is influenced by visual experience. Reduced retinal image quality and imposed optical defocus result in predictable changes in axial eye growth. Higher order aberrations are optical imperfections of the eye that alter retinal image quality despite optimal correction of spherical defocus and astigmatism. Since higher order aberrations reduce retinal image quality and produce variations in optical vergence across the entrance pupil of the eye, they may provide optical signals that contribute to the regulation and modulation of eye growth and refractive error development. The magnitude and type of higher order aberrations vary with age, refractive error, and during near work and accommodation. Furthermore, distinctive changes in higher order aberrations occur with various myopia control treatments, including atropine, near addition spectacle lenses, orthokeratology and soft multifocal and dual-focus contact lenses. Several plausible mechanisms have been proposed by which higher order aberrations may influence axial eye growth, the development of refractive error, and the treatment effect of myopia control interventions. Future studies of higher order aberrations, particularly during childhood, accommodation, and treatment with myopia control interventions are required to further our understanding of their potential role in refractive error development and eye growth.  相似文献   
34.
35.
36.
Plasma levels of plasminogen activator inhibitor type-1 (PAI-1), beta- thromboglobulin (beta TG), and fibrinopeptide A (FPA) were followed over 24 hours in 30 patients treated with alteplase for acute myocardial infarction. Samples were taken at baseline (T Oh), after 90 minutes (under alteplase, no heparin, T 1.5h), after 120 minutes (under alteplase and heparin, T 2h), 30 minutes after thrombolytic therapy (T 3.5h), as well as 12 hours (T 12h) and 24 hours (T 24h) after baseline. PAI-1 antigen levels (55 +/- 9 ng/mL at T Oh, mean +/- SEM) decreased to 35 +/- 5 (T 1.5h) and 40 +/- 6 (T 2h) ng/mL under alteplase, before increasing to 84 +/- 22 (T 3.5h), 130 +/- 30 (T 12h), and 64 +/- 7 (T 24h) ng/mL after therapy, P less than .001. A high baseline PAI-1 activity (18 +/- 3 ng/mL) decreased to 2.0 +/- 0.4 (T 1.5h) and 1.7 +/- 0.2 (T 2h) under alteplase and increased to 32 +/- 5 (T 12h) and 19 +/- 3 (T 24h) ng/mL after therapy (P less than .0001). beta TG levels (339 +/- 105 ng/mL at T Oh) decreased to 203 +/- 48 (T 2h), 154 +/- 51 (T 3.5h), 187 +/- 40 (T 12h), and 142 +/- 32 (T 24h) ng/mL under heparin (P less than .01). FPA levels (34 +/- 9 ng/mL at T Oh) increased to 85 +/- 15 ng/mL under alteplase alone (T 1.5h) and normalized under heparin (11 +/- 4, 6 +/- 2, 4 +/- 2, and 3 +/- 1 ng/mL at T 2h, T 3.5h, T 12h, and T 24h, respectively). A high level of FPA at T 3.5h correlated with reocclusion (33 +/- 12 ng/mL, n = 4 v 2.9 +/- 0.5 ng/mL, n = 21, P less than .005). We conclude that plasma levels of PAI- 1 antigen as well as activity markedly increase after alteplase therapy of acute myocardial infarction. The high activity of PAI-1 and decreasing beta TG levels suggest that platelets do not contribute significantly to this phenomenon. The marked increase of FPA levels under recombinant tissue-type plasminogen activator alone and its normalization under heparin emphasize the important role of concomitant anticoagulation in controlling further intravasal fibrin generation under alteplase.  相似文献   
37.
Gronthos  S; Simmons  PJ 《Blood》1995,85(4):929-940
Factors that regulate the growth and development of primitive bone marrow stromal cell precursors are not well defined. We have examined 25 purified recombinant growth factors for their ability to initiate and support clonogenic growth of fibroblast colony-forming cells (CFU- F) from adult human bone marrow. Assays were performed using bone marrow mononuclear cells (BMMNC) enriched in CFU-F by magnetic- activated cell sorting (MACS) using the monoclonal antibody (MoAb) STRO- 1. A serum-deprived assay was developed to avoid components of fetal calf serum (FCS) that may mask or otherwise modify the response of CFU- F to exogenously added factors. L-ascorbate and the glucocorticoid dexamethasone were found to be essential for CFU-F colony development under serum-deprived conditions. Importantly, clonogenic growth of CFU- F in this culture system was absolutely dependent on an exogenous source of growth factor. Platelet-derived growth factor-BB (PDGF) and epidermal growth factor (EGF) demonstrated the greatest ability to support colony growth. Colony formation was dose-dependent, with half- maximal colony numbers at approximately 0.2 ng/mL for either factor and plateau numbers at concentrations in excess of 1.0 ng/mL. Simultaneous addition of PDGF and EGF had no effect on the number of colonies initiated but resulted in dose-dependent increases in mean colony diameter that were significant (P < or = .05) when compared with the effect of either factor alone or with the size of colonies elicited in control cultures by 20% FCS. Fluorescence-activated cell sorting (FACS) of BMMNC using MoAbs to the alpha chain of the PDGF receptor and to the EGF receptor in combination with the Moab STRO-1 demonstrated constitutive expression of both receptors by greater than 90% on CFU-F. Receptors for insulin-like growth factor-1 (IGF-1) and nerve growth factor (NGF) were also detected on STRO-1+ CFU-F, but in vitro both IGF- 1 and NGF did not support colony growth. This report demonstrates the development of a simple, reproducible, and stringent culture system for the growth and assay of stromal precursors under serum-deprived conditions and represents an important prerequisite for future studies of the role of growth factors in the regulation of stromal cell proliferation, differentiation, and development.  相似文献   
38.
Human myelogeneous leukemia cells in liquid culture can be induced to mature along the monocyte/macrophage pathway by a maturation inducer derived from the conditioned medium of activated human T lymphocytes. Serum-free conditioned medium was used for the isolation of the T-cell lymphokine. The maturation inducer was purified approximately equal to 6000-fold by ammonium sulfate precipitation, low-salt elution from DEAE-Sepharose CL-6B, gel filtration on Bio-Gel A-0.5m, and NaDodSO4/PAGE under nonreducing conditions. The molecular weight of the maturation inducer was 36,000-58,000 on NaDodSO4/PAGE. Terminal differentiation associated with inhibition of leukemia cell proliferation and expression of mature cell properties was observed with the isolated maturation inducer, identical to the activity observed with the unfractionated conditioned medium. Cell-cycle analysis revealed that the proportion of replicating S-phase cells was reduced from 40% to 7% after initial interaction of the maturation inducer with cells. The differentiating cells simultaneously acquired monocyte antigen, membrane complement receptors, phagocytic function, and monocyte/macrophage morphology. The maturation-inducing activity is dose-dependent, with more inducer causing the development of more mature cells in a shorter time period. The maturation inducer was shown to be stable after pH 2 treatment, independent of interleukin 2 and colony-stimulating factor, devoid of alpha-, beta-, and gamma-interferon, and not affected by antibody to interferon. The maturation inducer may play a role as a physiological regulator of monocytic and leukemia cell development.  相似文献   
39.
To study the effect of interleukin-1 (IL-1) beta on the proliferation of hematopoietic progenitor cells (HPC) in long-term bone marrow cultures (LTBMC), stromal cell layers were established from normal human bone marrow. Autologous cryopreserved mononuclear phagocyte- and T-lymphocyte-depleted bone marrow cells were reinoculated on the stromal layers in fresh culture medium, with or without the addition of human IL-1 beta (30 U/mL). Once a week, half of the culture supernatant was replaced with fresh culture medium with or without IL-1, and all nonadherent cells were returned to the flasks. At weekly intervals during a period of 5 weeks, one culture was sacrificed to determine the total number of cells and hematopoietic progenitor cells, present in the adherent and the nonadherent cell fractions. In IL-1-stimulated cultures, the number of cells recovered during a period of 5 weeks exceeded the number of cells in unstimulated control cultures by 1.5 times. This difference was attributed to a twofold increase in the number of adherent cells. The number of HPC recovered from IL-1- stimulated cultures was not different from that recovered from controls. The levels of colony-stimulating activity (CSA) in supernatants from IL-1-stimulated cultures were significantly higher than those in supernatants from control cultures. These results indicate that IL-1 enhances the recovery of cells in LTBMC by stimulating the proliferation of HPC with the concurrent release of CSA from stromal cells, without diminishing the number of HPC.  相似文献   
40.
Geraniin has been reported to have numerous biological activities, including antiviral, antihypertensive, antihyperglycaemic, liver protective, antidiabetic, and apoptotic activities. However, the anti‐migration effects of geraniin on oral cancer remain elusive. In this study, we revealed the potential antitumor mechanisms of geraniin through the inhibition of the migration and invasion of human oral cancer cell lines SCC‐9 and SCC‐14. The results of gelatin zymography and Western blot assays revealed that geraniin significantly reduced the activity and expression of matrix metalloproteinase‐2 (MMP‐2) of oral cancer cells in a concentration‐dependent manner. Furthermore, geraniin potently suppressed the phosphorylation of focal adhesion kinase (FAK), Src, and extracellular signal‐regulated kinase (ERK)1/2 but did not affect the phosphorylation of p38 mitogen‐activated protein kinase (MAPK) and c‐Jun N‐terminal kinase 1/2. Moreover, blocking the MAPK/ERK1/2 pathway significantly enhanced the anti‐migration ability of geraniin in oral cancer cells. In conclusion, we demonstrated that geraniin inhibits the motility of SCC‐9 and SCC‐14 cells in vitro through a molecular mechanism that involves the attenuation of MMP‐2 expression and activity mediated by decreased FAK/Src and ERK1/2 pathways.  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