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   11499篇
  免费   796篇
  国内免费   30篇
耳鼻咽喉   81篇
儿科学   364篇
妇产科学   218篇
基础医学   1895篇
口腔科学   261篇
临床医学   1091篇
内科学   2068篇
皮肤病学   336篇
神经病学   1562篇
特种医学   449篇
外科学   948篇
综合类   60篇
一般理论   4篇
预防医学   834篇
眼科学   349篇
药学   768篇
中国医学   16篇
肿瘤学   1021篇
  2024年   18篇
  2023年   111篇
  2022年   172篇
  2021年   287篇
  2020年   225篇
  2019年   257篇
  2018年   307篇
  2017年   276篇
  2016年   379篇
  2015年   402篇
  2014年   495篇
  2013年   649篇
  2012年   918篇
  2011年   929篇
  2010年   530篇
  2009年   522篇
  2008年   829篇
  2007年   799篇
  2006年   748篇
  2005年   721篇
  2004年   616篇
  2003年   576篇
  2002年   532篇
  2001年   92篇
  2000年   77篇
  1999年   89篇
  1998年   112篇
  1997年   107篇
  1996年   87篇
  1995年   69篇
  1994年   47篇
  1993年   43篇
  1992年   37篇
  1991年   31篇
  1990年   14篇
  1989年   11篇
  1988年   17篇
  1987年   13篇
  1986年   27篇
  1985年   16篇
  1984年   12篇
  1983年   13篇
  1982年   11篇
  1981年   10篇
  1980年   8篇
  1979年   11篇
  1978年   12篇
  1977年   5篇
  1976年   8篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
The aim of this prospective randomized study was to determine whether additional doxorubicin chemotherapy improves outcome in patients with hepatocellular carcinoma (HCCA) treated by liver transplantation. Stratification parameters were tumor stage (UICC I-IVa), gender, age 50 years, α-fetoprotein 20 ng/mL, cirrhosis and HbsAg status. For pre-operative chemotherapy doxorubicin (15 mg/m2) was given biweekly, intra-operative chemotherapy was a single dose administered before surgical manipulation. Post-operative chemotherapy from day 10 was as given preoperatively for a total dosage of 300 mg/m2. Outcome parameters were overall survival (OS) and disease-free survival. Of the 75 consecutive patients who received liver transplantation for treatment of HCCA, 62 patients were enrolled. Thirty-four patients were randomized in the chemotherapy group; 28 patients were in the control group and transplanted only. OS rates at 5 years were 38% in the chemotherapy group and 40% in the control group, disease-free survival rates at 5 years 43% and 53%, respectively. Tumor stage and vascular invasion were identified as independent risk factors for recurrence of disease. Doxorubicin chemotherapy did not improve organ survival and disease-free survival in patients undergoing liver transplantation for HCCA.  相似文献   
13.
A partial human cDNA clone for the iron-protein (IP) subunit of succinate dehydrogenase (EC 1.3.99.1) was used in Southern analyses of restriction enzyme digests of genomic human and hamster DNA as well as hamster-human hybrids containing a limited number of human chromosomes. The gene for this protein was mapped to human chromosome 1. Digestion of genomic DNA with several restriction enzymes yielded two fragments detectable on a Southern blot, in contrast to the expectations based on the sequence of the cDNA clone. A preliminary analysis of a genomic clone with most of theIP gene has indicated the presence of several introns containing restriction sites detected by the Southern analysis. This genomic clone was also used for subregional mapping by fluorescence in situ hybridization (FISH) to human metaphase chromosomes. A single locus in the region 1p35-36.1 was identified.  相似文献   
14.
Sexual, reproductive and venereal risk factors for cervical neoplasia were investigated in a population-based case-control study of 586 women with histologically verified, cervical squamous-cell carcinoma in situ, and 59 women with invasive squamous-cell cervical cancer, diagnosed from 1985 to 1986 in Copenhagen. Cases were identified from the computerized Danish Cancer Registry. An age-stratified control group (n=614) was drawn at random from the female population in the study area by means of the Danish Central Population Register. A structured questionnaire was mailed to cases as well as controls. Increasing number of sexual partners exerted a significant effect on the risk both for carcinoma in situ, and invasive cancer, independently of age at first intercourse and other potential confounders. Conversely, the association with early age at first intercourse became statistically insignificant after allowance for other risk factors, although an increasing risk was still observed with decreasing age at sexual debut. Early age at first episode with genital warts was a significant risk factor for carcinoma in situ, perhaps indicating a possible increased susceptibility of the cervix epithelium during adolescence. A history of genital warts was a good predictor of risk for carcinoma in situ, whereas a history of previous gonorrhea was associated with an increased risk for invasive carcinoma. Women with multiple births had a significantly increased adjusted risk, especially for carcinoma in situ, although some association was also observed with invasive cervical cancer. The study supports the hypothesis of cervical neoplasia being a sexually transmitted disease, and that carcinoma in situ and invasive cervical carcinoma, to a high degree, have similar patterns of risk factors.Drs Kjaer, Engholm, and Lynge are with the Danish Cancer Registry. Dr Dahl is with the Department of Surgery, Slagelse Hospital, Denmark. Dr Bock is with the Department of Gynecology, Rigshospitalet, Copenhagen, Denmark. Dr Jensen, formerly with the Danish Cancer Registry, is deceased. Address correspondence to Dr Kjaer, Danish Cancer Registry, Institute of Cancer Epidemiology, Danish Cancer Society, Rosenvengets Hovedvej 35, Box 839, Copenhagen. Denmark. The Danish Cancer Society supported this study through grants.  相似文献   
15.
The study examined predictors of children's prosocial responses to adult negative emotions. An adult displayed anger, sadness and pain during play sessions with 39 preschoolers (mean age = 43 months). Older children responded more prosocially to all three emotions, whereas children with greater emotion knowledge responded more prosocially to the adult's sadness. Children who behaved prosocially in response to peers' negative emotions also were prosocial after the adult's negative emotions, even with effects of age and emotion knowledge held constant. Assertive children responded more prosocially to the adult's anger, even with effects of other variables held constant. Both theoretical and practical implications are discussed.  相似文献   
16.
17.
Background: Inhibition of intestinal peristalsis is a major side effect of drugs used for anesthesia or for analgesia and sedation of patients in the intensive care unit. This in vitro study examined the effect of clonidine and dexmedetomidine on intestinal peristalsis and analyzed some of their mechanisms of action.

Methods: In isolated segments of the guinea pig small intestine, peristalsis was triggered by a perfusion-induced rise of the intraluminal pressure. The peristaltic pressure threshold to elicit a peristaltic wave was used to quantify drug effects on peristalsis. Vehicle (Tyrode's solution), clonidine (10 nm-100 [mu]m), or dexmedetomidine (0.1-100 nm) were added extraserosally to the organ bath. In other series of experiments, clonidine or dexmedetomidine was administered after pretreatment with yohimbine, prazosin, apamin, naloxone, or vehicle. Clonidine was also tested after blockade of NO synthase with l-NAME and in the presence of the inactive enantiomer d-NAME.

Results: Clonidine and dexmedetomidine concentration-dependently increased peristaltic pressure threshold and inhibited peristalsis (clonidine: EC50 = 19.6 [mu]m; dexmedetomidine: EC50 = 12.0 nm). The inhibition caused by clonidine could be prevented by pretreatment with yohimbine, naloxone, and apamin, but not by prazosin, l-NAME, or d-NAME. Inhibition caused by dexmedetomidine was prevented by yohimbine only.  相似文献   

18.
We have examined the patterns of expression of the major intermediate filament (IF) protein mRNAs during development of the hamster brain. Quantitative northern blotting was used to examine changes in the levels of mRNAs for the low, middle and high molecular weight neurofilament proteins (NF-L, NF-M, NF-H) as well as peripherin, vimentin and glial fibrillary acidic protein (GFAP). Total RNA was isolated from hamster brains at embryonic (E) days 12 and 14 and postnatal (P) days 1, 3, 5, 7, 9, 11, 13, 15, 20, 28 and 60-90 (adult), and probed with specific IF cDNAs. Northern blotting revealed that NF-L and NF-M mRNAs were present at very low levels in embryonic brain and that significant expression of these genes only occurred postnatally when the levels increased dramatically until P28 and then declined again in the adult. Increases in NF-H mRNA levels were somewhat delayed relative to those of NF-L and NF-M. NF-H mRNA was not seen at embryonic stages and was expressed at very low levels prior to P9; after that time the levels increased rapidly until P28 and then declined in the adult. Two of the type III IF genes, peripherin and vimentin, followed a pattern of expression opposite that of the NF genes. Both peripherin and vimentin mRNAs were present in embryonic brain and were expressed at higher levels during early postnatal stages than at later times. The magnitude and rate of reduction in vimentin gene expression in the postnatal interval was much greater than that of peripherin. GFAP mRNA levels were extremely low prior to P9 after which a robust increase occurred, followed by a decline in the adult. We discuss the implication of the dramatic changes in IF isotype expression in brain to the pathways of both neuronal and glial development in vivo.  相似文献   
19.
20.
Summary One hundred thirty-one breast carcinomas with medullary features, registered in the Danish Breast Cancer Cooperative Group from 1977–1982, have been histopathologically reviewed by two senior pathologists and classified as typical medullary carcinoma (TMC), atypical medullary carcinoma (AMC), and non-medullary carcinoma (NMC). Diagnostic criteria were based on those put forward by Ridolfiet al. and Fisheret al. The procedure was repeated with an interval of about one year by both pathologists. The diagnostic interobserver agreement was 72% with a Kappa of 0.55. The intraobserver agreement was 77% and 63% with Kappa values of 0.64 and 0.44, respectively. To see whether the observed inter- and intraobserver variability had any prognostic implications, diagnostic subgroups for both pathologists were analyzed with Kaplan Meier plots for recurrence-free survival (RFS) and with log rank tests. In the first evaluation pathologist 1 segregated a group of TMC with a significantly better RFS than for the NMC group, and pathologist 2 segregated a group of TMC with a corresponding strong trend. These findings could not, however, be reproduced in the second evaluation. The study indicates that the criteria of TMC and AMC as proposed by Ridolfiet al. need to be sharpened and simplified in order to reduce inter-and intraobserver variability. Larger studies with a control group of infiltrating ductal carcinomas are mandatory to elucidate the clinical importance of the diagnoses of Typical and Atypical Medullary Carcinoma of the breast.  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