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   1110250篇
  免费   82507篇
  国内免费   3061篇
耳鼻咽喉   14210篇
儿科学   38008篇
妇产科学   30395篇
基础医学   160341篇
口腔科学   29825篇
临床医学   101574篇
内科学   217116篇
皮肤病学   24283篇
神经病学   89957篇
特种医学   41897篇
外国民族医学   310篇
外科学   165595篇
综合类   25227篇
现状与发展   1篇
一般理论   533篇
预防医学   87721篇
眼科学   25595篇
药学   79919篇
  4篇
中国医学   2281篇
肿瘤学   61026篇
  2021年   8990篇
  2019年   9469篇
  2018年   13116篇
  2017年   10083篇
  2016年   11500篇
  2015年   13032篇
  2014年   17975篇
  2013年   27113篇
  2012年   36626篇
  2011年   39093篇
  2010年   22990篇
  2009年   21666篇
  2008年   36103篇
  2007年   38253篇
  2006年   38303篇
  2005年   37068篇
  2004年   35905篇
  2003年   34217篇
  2002年   32997篇
  2001年   48025篇
  2000年   48854篇
  1999年   41428篇
  1998年   12508篇
  1997年   11233篇
  1996年   11014篇
  1995年   10644篇
  1994年   9853篇
  1993年   9207篇
  1992年   32879篇
  1991年   32051篇
  1990年   31530篇
  1989年   30361篇
  1988年   27642篇
  1987年   27784篇
  1986年   25846篇
  1985年   25075篇
  1984年   18930篇
  1983年   16013篇
  1982年   9937篇
  1981年   8938篇
  1979年   17206篇
  1978年   12528篇
  1977年   10650篇
  1976年   10010篇
  1975年   10429篇
  1974年   12584篇
  1973年   12098篇
  1972年   11061篇
  1971年   10255篇
  1970年   9494篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Noninvasive localized proton magnetic resonance spectroscopy (MRS) was used for differential diagnosis of a focal brain lesion in a 2.5-year-old girl. The clinical signs were a mild head tilt and neck pain. Magnetic resonance imaging (MRI) revealed a lesion in the right hemisphere of the cerebellum, but its nature remained obscure. In this lesion quantitative determinations of cerebral metabolites by fully relaxed, short-echo-time proton MRS revealed markedly lowered N-acetylaspartate (NAA) and pronounced elevations of choline-containing compounds (Cho) and myo-inositol (Ins), whereas metabolite concentrations in cortical gray matter and white matter were within normal ranges. The metabolite pattern of the lesion indicated loss of vital neuroaxonal tissue (low NAA) and enhanced glial proliferation (high Cho and Ins), which, together with the MRI morphology, suggested a brain tumor. The diagnosis was established by neurosurgical exploration and total extirpation of the tumor. Histology confirmed an astrocytoma (WHO II). After 2 weeks' recovery the child was discharged with no neurological signs.  相似文献   
103.
The role of caffeine or coffee in causing or promoting the incidence of serious disease is equivocal. Two design factors may account for the discrepancies in reported findings on the effects of coffee drinking: (a) imprecision of measurement and (b) confounding variables. A study of 2,714 white U.S. adults disclosed that, of 32 risk factors analyzed by linear and logistic regression, only sex and cigarette smoking were found to be important potential confounders of caffeine and coffee intake. Partial R2 values of the other 30 risk factors were relatively small and were inconsistent for each sex. It is unlikely that any of these factors could explain any of the reported associations between caffeine or coffee consumption and certain diseases. However, certain weak associations with caffeine or coffee intake should be included in the study design when they are known to be risk factors of a disease under investigation. These factors for men are dietary fat intake, vitamin C intake, and body mass index; and for women are vitamin use, alcohol intake, stress, and perceived health status.  相似文献   
104.
The commodity model of social support and features of Nondirective Support may clarify varied results of support interventions for smoking cessation. A commodity model views social support as attractive in and of itself and as an alternative to high-risk choices such as smoking. If such support is easily accessible, a would-be quitter is less likely to choose to smoke. Consistent with the commodity model, social support interventions tend to be effective as long as support remains available, but they lose their effects when support is terminated. From a second approach, Nondirective Support entails accepting recipients' goals, cooperating without taking control, and validating recipients' feelings. In contrast, Directive Support entails taking control and telling recipients what to do and feel. Review of support interventions indicates the value of the continued availability of support suggested by the commodity model and of Nondirective Support's flexibility and responsiveness to the person.  相似文献   
105.
Background: The study reviews the anticancer properties of naturalisoflavones which occur in especially high concentration in soybeans. Itconsiders the suitability of soybean products for clinical trials aiming toreduce the progression of breast cancer.Methods: Evidence is reviewed that plant isoflavones such asgenistein show cytostatic activity against human mammary cancer cell linesin vitro and can also suppress carcinogen-induced mammary cancer inyoung and mature rats.Results: Plant isoflavones are converted in the bowel to compoundswith potential antioestrogenic and antioxidative properties. These compoundsshow cytostatic activity for both oestrogen receptor-positive and negativehuman mammary cancer cell lines, and also inhibit growth and progress of therat mammary cancer model. The high content of soybean products in the diet ofAsian women has been postulated as one reason for their relatively low breastcancer incidence.Conclusion: Preclinical studies suggest that soybean products begiven priority for clinical trials in breast cancer protection. A pilot studycould test soy protein supplements as long-term adjuvant dietary treatmentafter primary surgery for early breast cancer, looking for a decrease in therisk of recurrence or of second primary tumours.  相似文献   
106.
107.
The objectives of this study were to investigate (1) changes in consumption of alcohol among pregnant women over a period of 5 years (1984/85–1990), (2) changes of attitudes towards drinking during pregnancy in the general population over the same period of time, and (3) possible connections between (1) and (2). The investigation was designed as a cross-sectional study. Our subjects were two representative samples of pregnant women in Oslo, n = 577 and 425, and two representative samples of the Norwegian population, n = 1004 and 1204. The main outcome measures were a self-completed questionnaire for the pregnant women and a personal interview for the general population sample. There was a significant reduction (50% decrease) in alcohol consumption among the second cohort of pregnant women compared with the first. Furthermore, we found an increase during the 5-year period in the number of persons with a restrictive attitude towards alcohol use during pregnancy. There seems to be a connection between these two phenomena, but with our present state of knowledge it is hard to say anything about the causal relationship between them.  相似文献   
108.
Introduction into fetal rat brain cells of a replication-defective retroviral vector harboring v-Ha-ras and v-gag-myc rapidly causes the induction of highly malignant undifferentiated neuroectodermal tumors following transplantation into the brains of syngeneic hosts [Wiestler, et al. (1992) Cancer Res. 52: 3760–3767]. In the present study, we have investigated the modulating effect of the developmental stage of neural target cells and of the dose of the retroviral vector used in the grafting experiments. Exposure of fetal cells from embryonic day (E)12 or E14 produced a 100% incidence of malignant neuroectodermal tumors which led to the death of recipient animals after a median latency period of 32 days. A 100-fold reduction of the virus dose from 2.062×106 to 2.062×104 focus-forming units/ml resulted in a lower tumor incidence of 25%. Of six neural grafts exposed to v-Ha-ras and v-myc at E16, only one showed evidence of tumorigenesis (low-grade astrocytoma and hemangioma). All other transplants were morphologically normal for observation periods of 26 weeks, indicating a marked loss of transforming activity of ras and myc in more advanced stages of brain development. In retrovirus-exposed donor cells which caused the development of neural tumors in recipient rats, malignant transformation was also evident during culture in vitro, usually after 9–12 days. Oncogene complementation was also studied in the newborn rat brain. After microinjection of the retroviral vector into the brain at postnatal day (P)0, P1 and P3, 5 out of 20 animals (25%) developed a total of seven brain tumors. Histopathologically, three of these neoplasms were malignant neuroectodermal tumors which, in contrast to those induced in fetal brain transplants showed evidence of focal glial and/or neuronal differentiation. In addition, we observed one oligodendroglioma, two hemangiomas and a malignant hemangioendothelioma. These data indicate that neural precursor cells and endothelia of the rat brain represent the major target cells for the complementary action of ras and myc and that the use of target cells from later developmental stages (E16 and postnatal) leads to the induction of both primitive and more differentiated neoplasms.These studies were supported by the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich (Erwin Schrödinger fellowship, JO501-MED), by the Swiss National Science Foundation and by the Cancer League of the Kanton of Zürich  相似文献   
109.
Corpus cavernosography in a patient with erectile dysfunction revealed absence of communication between the 2 cavernous bodies. No similar case was found in a review of 100 consecutive cavernosograms or in the literature. The abnormality may be a source of error in pressure recordings or in intravenous injection of pharmaceutical agents.  相似文献   
110.
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