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   2424篇
  免费   133篇
  国内免费   22篇
耳鼻咽喉   13篇
儿科学   160篇
妇产科学   26篇
基础医学   254篇
口腔科学   77篇
临床医学   245篇
内科学   568篇
皮肤病学   86篇
神经病学   65篇
特种医学   473篇
外科学   203篇
综合类   50篇
一般理论   2篇
预防医学   104篇
眼科学   33篇
药学   127篇
中国医学   3篇
肿瘤学   90篇
  2018年   16篇
  2016年   37篇
  2015年   42篇
  2014年   39篇
  2013年   84篇
  2012年   31篇
  2011年   26篇
  2010年   111篇
  2009年   92篇
  2008年   35篇
  2007年   25篇
  2006年   39篇
  2005年   23篇
  2004年   15篇
  2003年   17篇
  2002年   20篇
  2001年   26篇
  2000年   24篇
  1999年   46篇
  1998年   158篇
  1997年   164篇
  1996年   163篇
  1995年   117篇
  1994年   107篇
  1993年   117篇
  1992年   42篇
  1991年   34篇
  1990年   31篇
  1989年   77篇
  1988年   64篇
  1987年   63篇
  1986年   58篇
  1985年   53篇
  1984年   38篇
  1983年   41篇
  1982年   44篇
  1981年   27篇
  1980年   51篇
  1979年   25篇
  1978年   22篇
  1977年   24篇
  1976年   30篇
  1975年   31篇
  1959年   14篇
  1958年   29篇
  1957年   21篇
  1956年   35篇
  1955年   15篇
  1954年   22篇
  1948年   17篇
排序方式: 共有2579条查询结果,搜索用时 671 毫秒
1.
Cancer causes significatlt emotional distress to a considerable majority of patients. Many of these patients typically receive little formal psychological intervention. Support groups, however, have provided one forum from which patients can attempt to gain help and can use to overcome some psychological trauma that accompanies the cancer hagnosis, subsequent treatment and relapse. This article reviews past studies of professionally run cancer support groups as opposed to psychological intervention groups. These studies are considered in light of the proposed benefits and the methodological limitations frequently inherent in such studies.  相似文献   
2.
It has become common practice to rely on fitted estimates ofapparent in vivo metabolic constants (e.g., Vmax and KM) inparameterization of PBPK models. Yet, quantitative estimatesof precision in these fitted parameters are not routinely reported.Such information is needed to assess the reliability of modelpredictions. The purpose of this study was to assess the precisionin estimates of Vmax and KM for chloroform, accounting for boththe statistical uncertainties in parameter estimates from individualdata sets and any additional uncertainty due to differencesin the parameter estimates derived from various experiments.Joint confidence regions for Vmax and KM from each experiment,generated using maximum likelihood techniques, were used toevaluate these questions. Three previously published data setswere considered. Estimates of Vmax and KM obtained from thesedata sets differed more than could be explained as a consequenceof a limited number of observations, measurement error, or stochasticerror. Issues associated with the use of maximum likelihoodtechniques to estimate joint confidence regions, the estimationof metabolic constants from individual experiments within agas uptake study versus the full data set, the degree of overlapin the joint confidence regions for metabolic constants obtainedfrom separate data sets, and the implications for risk assessmentare discussed.  相似文献   
3.
4.
The high-molecular-weight (HMW) protein from the lens is composed mostly of α-crystallin in a highly aggregated state. Bovine HMW protein was carefully separated from α-crystallin by size-exclusion chromatography. α-Crystallin has chaperone-like ability whereby it stabilizes other proteins under conditions of stress (e.g. heat). Comparison of bovine HMW protein and α-crystallin shows that the HMW protein has a markedly reduced chaperone ability compared to α-crystallin. However, in contrast to the results of other workers, we observe no alteration with age in the ability of α-crystallin to act as a chaperone. Using electrospray ionisation mass spectrometry, changes in the phosphorylation of the α-crystallin subunits with age have been quantified. Phosphorylation of α-crystallin occurs early in life but does not alter in proportion after about three years of age. In addition, phosphorylation of the A subunit of α-crystallin has little effect on its chaperone ability. As is found in the artificially prepared HMW complex of α- and γ-crystallin, NMR spectroscopy shows that in the naturally occurring HMW protein, the short C-terminal extension of the αBsubunit has lost its flexibility whereas the αAsubunit extension is still flexible. Post-translational modifications therefore seem to have little effect on the chaperone action of α-crystallin, but alterations in the quaternary structure of α-crystallin via incorporation into the HMW aggregate, lead to major changes in the chaperone ability of the protein. The results are consistent with the notion that one of the contributing factors to cataract formation in the lens is the depletion of α-crystallin with age as it is converted into the HMW protein.  相似文献   
5.
This study reports on the synthesis of two fluorescent analogues of thymopentin (TP-5; Arg-Lys-Asp-Val-Tyr). A fluorescein isothiocyanate labeled analogue (FITC-TP-5) and a stilbene isothiocyanate labeled analogue (SITS-TP-5) were extensively purified by ion-exchange and gel filtration chromatography. Characterization of the coupling site through amino acid analysis, dansylation and N-terminal cleavage of the fluorescent amino acid yielded results which indicated that both were mono-labeled analogues derivatized at the N-terminal. These analogues were shown to be TP-5-like in nature by their ability to induce the expression of the Thy 1.2 surface marker on nude mouse prothymocytes in both in vivo and in vitro assays. In addition, these analogues were able to inhibit the specific binding of radiolabeled TP-5 to human lymphocytes. Initial studies describing the interaction of FITC-TP-5 with human lymphocytes are shown.  相似文献   
6.
7.
8.
BACKGROUND: Our aims in the present study were to estimate the influences of pain and urinary symptoms on quality of life, and to determine which of these two variables has the most predictive power with respect to quality of life in young men with chronic prostatitis-like symptoms. METHODS: Chronic prostatitis-like symptoms were measured by the National Institutes of Health-Chronic Prostatitis Symptom Index. Of the 28,841 men aged 20 years who lived in the study community, 18,495 men (a response rate 64.1%) agreed to participate in the study. A total of 1057 men who complained of symptoms indicative of chronic prostatitis were included in the study. The influences of pain and urinary symptoms on quality of life were determined using logistic regression analysis. The receiver operating characteristic (ROC) curve was used to estimate the predictive ability of each of these variables with respect to quality of life. RESULTS: Results from multivariate analysis showed that both pain and urinary symptoms were associated with an increased likelihood of impaired quality of life, although pain contributed more to a reduced quality of life than urinary symptoms. Relative to men who experienced mild pain, men who experienced moderate pain had a 3.9-fold risk of poor quality of life (odds ratio [OR], 3.87; 95% confidence interval [CI], 2.86-5.23; P < 0.001) and those who experienced severe pain had a 15.7-fold risk of reduced quality of life (OR, 15.68; 95% CI, 6.59-37.35; P < 0.001). Moderate urinary symptoms were associated with a 1.4-fold risk of bother (OR, 1.41; 95% CI, 1.01-1.99; P < 0.001) and severe urinary symptoms were associated with 2.4-fold risk (OR, 2.39; 95% CI, 1.37-4.12; P < 0.001), relative to mild urinary symptoms. Comparison of the effects of pain and urinary symptoms showed that pain severity had the most predictive power for bother, quality of life, and quality-of-life impact. The areas under the ROC curves for bother, quality of life, and quality-of-life impact were 71.3%, 69.3% and 72.5%, respectively. CONCLUSION: Urinary symptoms and pain might be associated with an increased likelihood of impaired quality of life in young men with chronic prostatitis-like symptoms. In addition, our findings suggest that pain severity is the most influential variable for determining quality of life in this population.  相似文献   
9.
Measurements of transepithelial electrical resistance (TEER), the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) test and monitoring of poly(ethylene glycol) (PEG) transport have been used to study the effects of the non-ionic surfactants Solulan C24 and Solulan 16, either free in solution or as an integral part of niosome bi-layers, on intestinal epithelial cells from man (Caco-2 cell monolayers). The effects on epithelial integrity and on the transport of the hydrophilic drug metformin depend on the concentration of the surfactants. At concentrations above 1% the effect on TEER of the surfactant in niosomal form and free in solution were equivalent whereas cell viability was preserved to a higher concentration of Solulans when the Solulans were present in the niosomal form. It was concluded that the toxic effect of niosomes arises from free surfactant present in the niosome suspension.  相似文献   
10.
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