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   47770篇
  免费   4155篇
  国内免费   1796篇
耳鼻咽喉   298篇
儿科学   927篇
妇产科学   2022篇
基础医学   9991篇
口腔科学   1665篇
临床医学   3901篇
内科学   4927篇
皮肤病学   1250篇
神经病学   2757篇
特种医学   1054篇
外国民族医学   20篇
外科学   3149篇
综合类   7220篇
现状与发展   12篇
一般理论   12篇
预防医学   3774篇
眼科学   940篇
药学   5399篇
  22篇
中国医学   1095篇
肿瘤学   3286篇
  2024年   60篇
  2023年   515篇
  2022年   1069篇
  2021年   1557篇
  2020年   1355篇
  2019年   1425篇
  2018年   1393篇
  2017年   1552篇
  2016年   1645篇
  2015年   1607篇
  2014年   2542篇
  2013年   3495篇
  2012年   2465篇
  2011年   2741篇
  2010年   2357篇
  2009年   2155篇
  2008年   2143篇
  2007年   2274篇
  2006年   2161篇
  2005年   1950篇
  2004年   1817篇
  2003年   1624篇
  2002年   1389篇
  2001年   1205篇
  2000年   1043篇
  1999年   929篇
  1998年   906篇
  1997年   857篇
  1996年   804篇
  1995年   765篇
  1994年   664篇
  1993年   618篇
  1992年   555篇
  1991年   500篇
  1990年   374篇
  1989年   376篇
  1988年   332篇
  1987年   243篇
  1986年   222篇
  1985年   396篇
  1984年   331篇
  1983年   230篇
  1982年   256篇
  1981年   206篇
  1980年   159篇
  1979年   106篇
  1978年   107篇
  1977年   66篇
  1976年   66篇
  1975年   34篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
John T. Leith 《The Prostate》1994,24(3):119-124
Because there is extremely limited information on the intrinsic radiosensitivity of human prostatic cancer cells, we have investigated the in vitro radiation response of exponentially growing LNCaP cells. Due to the very poor colony-forming potential of the LNCaP cells, radiation survival was investigated using the dose-dependent (0-6 Gy) changes seen after X-irradiation in the shapes of regrowth curves. Survival was described using both the single-hit, multitarget (SHMT) equation and the linear-quadratic (LQ) equation. The values and 95% confidence limits of the extrapolation number (n), quasi-threshold dose (Dq), and mean lethal dose (Do) in SHMT terminology were respectively: 0.9 (0.7-1.0), 0.0 Gy, and 1.39 (0.11) Gy. The LQ alpha and beta parameters were respectively 6.80 (1.13) and -0.53 (2.89). The X-ray dose response of the LNCaP line is, therefore, purely exponential. The mean survival at the clinically relevant dose of 2 Gy (S2) was 51.2% for the LNCaP line. Comparison of the S2 value for the LNCaP line with previous investigations with other human prostatic cancer cell lines (DU145 and PC-3) indicates a mean S2 value of 47.6%, which suggests that human prostate cancer cells might lie toward the resistant side of the spectrum for various classes of human neoplasms. © 1994 Wiey-Liss, Inc.  相似文献   
82.
Placental growth hormone is the product of the GH-V gene specifically expressed in the syncytiotrophoblast layer of the human placenta. Placental growth hormone differs from pituitary growth hormone by 13 amino acids. It has high somatogenic and low lactogenic activities. Assays by specific monoclonal antibodies reveal that in the maternal circulation from 15 to 20 weeks up to term placental growth hormone gradually replaces pituitary growth hormone, which becomes undetectable. It is secreted by the placenta in a nonpulsatile manner. This continuous secretion appears to have important implications for physiologic adjustment to gestation and especially in the control of maternal insulin-like growth factor-I levels. Placental growth hormone secretion is inhibited by glucose in vitro and in vivo and is significantly decreased in the maternal circulation in pregnancies with intrauterine growth restriction. Placental growth hormone does not appear to have a direct effect on fetal growth because this hormone is not detectable in the fetal circulation. However, the physiologic role might also include a direct influence on placental development through an autocrine or paracrine mechanism, as suggested by the presence of specific growth hormone receptors in this tissue.(Am J Obstet Gynecol 1997;177:1526-34.)  相似文献   
83.
Purpose A total of 86 fresh and salt-stored immature human oocytes derived from postmortem ovarian tissue were used for this study.Methods Oocytes were randomly incubated either in synthetic human tubal fluid medium (untreated zonae) or in a chemically defined medium (treated zonae).Results Sperm binding experiments using hemizona assay conditions exhibited a 10-fold increased binding of sperm to treated compared to untreated oocytes (272.7±43 versus 24.3±15 sperm bound, respectively; P<0.0001). pH recordings during incubation showed elevated pH levels of 8.1 compared to pH 7.2 among treated and untreated zonae, respectively. Ultrastructural examination showed a spongy appearance of the surface of treated zonae, whereas untreated zonae appeared compact with smooth surface.Conclusions The marked increase in sperm binding among treated zonae, together with the ultrastructural findings, suggest that the altered zona surface enhances sperm binding. The physiological maturational process of the zona pellucida might be manipulated in vitro, thus increasing sperm binding to the zona.Presented at the IXth World Congress on In Vitro Fertilization and Alternate Assisted Reproduction, April 3–7, 1995. Vienna, Austria.  相似文献   
84.
85.
Dr  N. Sukcharoen  J. Keith 《Andrologia》1996,28(4):203-210
Summary. The present study was carried out to investigate the predictive value of the percentage of sperm motility after 24-h incubation and sperm survival ratio from semen and inseminated sperm suspension using grading of motility by WHO criteria with respect to the fertilization of oocytes in vitro. A total of 789 oocytes from 85 cases were inseminated and the mean fertilization rate obtained was 72.5%. There was no significant correlation between all of the sperm motility results with fertilization rate in vitro. All sperm motility results were not significantly different between the non-fertilizing group and the fertilizing group and also between the group of fertilization rate ≤ 25th percentile (fertilization rate ≤62.5%) and the group of fertilization rate >62.5%. However, the initial percentage of rapid progressive sperm motility and progressive motility in semen and inseminated sperm suspension at 24 h gave significant differences between the group of fertilization ≤ 50th percentile (fertilization rate ≤80%) and the group of fertilization rate >80%. Overall accuracy using these parameters for prediction of fertilization rate >80% was only about 60%. In conclusion, the percentage of sperm motility at 24 h and sperm survival ratio in both semen and inseminated sperm suspension have no practical value in predicting fertilization rate in vitro. Moreover, detailed motility grading cannot improve the predictivity of these sperm motility parameters.  相似文献   
86.
The ability of the human amelanotic melanoma cell line MM-RU to produce experimental metastases and to grow tumors at subcutaneous inoculation sites in 4-week-old nude mice was examined. After i.v. inoculation of 106 cells, all injected mice (n=21) developed consistent numbers of metastatic pulmonary colonies within 32 days. The coefficients of variation for the number of colonies were between 17%–23% in three independent experiments. Survival time after i.v. inoculation was 63 ± 7 days (mean ± SD) (n=20). Within 20 days, subcutaneous inoculation of 5 × 106 cells resulted in tumor growths of 13 ± 3 mm (mean ± SD) at the inoculation sites in all nude mice (n=12). The MM-RU cell line seems to be a simple, fast vehicle for testing the effect of melanoma growth modulators on experimental pulmonary metastases as well as on subcutaneously growing melanoma.  相似文献   
87.
Summary Epidermal growth factor (EGF) has been shown to stimulate DNA synthesis and cell division in normal glia. At least half of malignant human gliomas (MHG) express high levels of the EGF receptor (EGFR), which are above those detected in normal brain. The demonstration that antibodies against the EGFR inhibit the growth of squamous cell carcinoma line A-431, with large numbers of EGFR, in vitro and in vivo raises the possibility that these agents could be used therapeutically against malignant human gliomas either alone or conjugated to other agents. We have measured the growth effects of EGF and an anti-EGFR monoclonal antibody, 528 (Ab-528), on four well-characterized human malignant glioma cell lines, D-263 MG, D-247 MG, U-343 MGa Cl 26, and D-37 MG, with 2.9×104, 1.5×105, 8.6×105 and 1.59×106 EGFRs per cell, respectively. EGF significantly increased cell number in D-263 MG and D-37 MG by 65% and 74%, respectively, had no effect on D-247 MG, and significantly decreased cell number in U-343 MGa Cl 26 by 39%. U-343 MGa Cl 26 growth was inhibited 19% by Ab-528, but Ab-528 had no effect on growth of the other MHG lines. Ab-528 significantly inhibited all EGF-mediated growth effects. These studies demonstrate that, although Ab-528 alone has little antiproliferative activity on MGH, it successfully competes with EGF to reduce the biological effects of EGF-EGFR binding. Therefore, this antibody could potentially be used to target radioisotopes to MHG via the EGFR for diagnosis and therapy.Supported by Grants CA-11898, NS-20023, CA-43722, and the Association for Brain Tumor Research (MHW, PAH)  相似文献   
88.
Verification of inheritance in congenital nystagmus (CN) is only possible through the identification of more than one affected member in a family, since in a single case there are no accurate clinical differentiations between spontaneous and inherited CN. We performed electronystagmographic examinations (ENG) to search for abnormal involuntary eye movements as a sign of heredity in seemingly unaffected members of CN families.ENG registrations were performed under three test conditions: (1) with the subject fixating a target, (2) with the room lights off and (3) with closed eyes.Fifty normally sighted individuals (group (a) underwent the test procedure to provide a baseline of normality. Five CN families (three dominant, two sex-linked recessive) were tested as group (b). The eye movement recordings were analysed in terms of nystagmus intensity (amplitude x frequency of the involuntary saccade). In every one of the five families, abnormalities in seemingly non-affected members could be demonstrated: in four families, fastphase instabilities, in the fifth family a true (CN) (slowphase instability).All certain gene carriers were diagnosed correctly by the ENG.These findings indicate a method for detecting slightly affected members in dominant pedigrees and female gene carriers in sex-linked mode of transmission.  相似文献   
89.
Human slow-wave sleep and the cerebral cortex   总被引:1,自引:1,他引:0  
SUMMARY  Recent hypotheses about the roles of human slow-wave sleep (hSWS—delta EEG activity) are appraised. The possible linkage between hSWS and the functions of the prefrontal cortex (PFC) are explored with respect to normal subjects and to disorders involving PFC deficits.  相似文献   
90.
A distinct subset of rat primary olfactory neurons was identified immunohistochemically by means of a polyclonal antibody against human placental antigen X-P2 (hPAX-P2), an incompletely characterized substance found in all estrogen-biosynthetic organs. The subset of olfactory receptor cells was distributed widely over the olfactory epithelium with some degree of concentration on the dorsocaudal walls of nasal subcavities. The subset formed unique "necklace olfactory glomeruli," which were composed of seven to nine solitary glomeruli located in the caudal end of the olfactory bulb. One of them was located in the "modified glomerular complex" reported to be involved in rat suckling behavior. The projectional patterns of the necklace olfactory system, albeit diffuse, indicated some degree of spatial correspondence between zones of olfactory epithelium and specific glomeruli. Axons emanating from neighboring cells can project to several glomerular loci. From the necklace olfactory system, an average of 150-200 receptor cells were estimated to converge onto a single necklace glomerulus.  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