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   158593篇
  免费   15785篇
  国内免费   8006篇
耳鼻咽喉   1266篇
儿科学   2752篇
妇产科学   2712篇
基础医学   39273篇
口腔科学   4882篇
临床医学   12306篇
内科学   21066篇
皮肤病学   3363篇
神经病学   11538篇
特种医学   3257篇
外国民族医学   44篇
外科学   13161篇
综合类   23353篇
现状与发展   44篇
一般理论   14篇
预防医学   6126篇
眼科学   3904篇
药学   15423篇
  38篇
中国医学   4316篇
肿瘤学   13546篇
  2024年   157篇
  2023年   1794篇
  2022年   2458篇
  2021年   4927篇
  2020年   4713篇
  2019年   4478篇
  2018年   4581篇
  2017年   5183篇
  2016年   5731篇
  2015年   6370篇
  2014年   9916篇
  2013年   12445篇
  2012年   9387篇
  2011年   10790篇
  2010年   8968篇
  2009年   8505篇
  2008年   8706篇
  2007年   8886篇
  2006年   8164篇
  2005年   7100篇
  2004年   6103篇
  2003年   5145篇
  2002年   4009篇
  2001年   3420篇
  2000年   2942篇
  1999年   2497篇
  1998年   2365篇
  1997年   2220篇
  1996年   2042篇
  1995年   2014篇
  1994年   1799篇
  1993年   1596篇
  1992年   1347篇
  1991年   1251篇
  1990年   1042篇
  1989年   1013篇
  1988年   885篇
  1987年   749篇
  1986年   666篇
  1985年   1052篇
  1984年   917篇
  1983年   642篇
  1982年   783篇
  1981年   617篇
  1980年   518篇
  1979年   407篇
  1978年   305篇
  1977年   226篇
  1976年   216篇
  1975年   86篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
Using spontaneously established autologous lymphoblastoid B cell lines (LCL), killer cell activities were studied in children with severe infectious mononucleosis (IM), chronic IM, and acute IM, and compared with those in EBV-seropositive normal controls. Natural killer (NK) cell activity of fresh peripheral blood mononuclear cells (PBMC) was normal in acute IM patients, but it was low in four of six patients with severe or chronic IM. Recombinant inter-leukin 2 (rIL-2)-activated PBMC from normal controls showed lymphokine-activated killer (LAK) cell activity against the respective autologous LCL. The levels of LCL lysis by LAK cells were significantly higher in acute IM patients, lower in chronic IM patients, and much lower in severe IM patients. In contrast to the fact that PBMC stimulated in vitro with autologous LCL (IVS cells) from normal controls and acute IM patients showed potent killing of autologous LCL, IVS cells from severe or chronic IM patients showed lower levels of LCL lysis, which were markedly augmented in three patients by rIL-2 addition to the cultures. These killer cell dysfunctions appear to be responsible for the severe or chronic course of EBV infection.  相似文献   
993.
本文报道人精液抑制素的制备及其生物学特性。收集的新鲜人精液经乙醇沉淀和丙酮冲洗,获得的粗提物经Sephadex G100处理,产生具有高活性抑制素hP2组分。应用hP2测定使去势雄性大鼠增高的血清FSH水平降低。其生物特性:hP2的生物活性按单位重量计算为粗提物的10倍以上,包含16种氨基酸,通过SDS-PAGE计算分子量为11,500道尔顿。  相似文献   
994.
该文报道了来自患者自体或同种异体LAK细胞对42例中晚期癌症患者的疗效分析,其中CR2例,PR14例,MR12例,SD11例,PD3例。总有效率为38.10%,绝大多数患者都有不同程度的临床症状改善、生活质量提高、生存期延长、未观察到严重毒副反应。并初步证实体外致敏可增强LAK细胞的抗瘤活性。  相似文献   
995.
PROBLEM : To determine if patients with unexplained recurrent miscarriage have a deficiency of decidual immunosuppressor cells that produce transforming growth factor β type 2, as has been found in mice with abortion due to rejection and/or trophoblast failure. METHODS : Decidual biopsy specimens were taken as near to the placental attachment site as possible under ultrasound guidance from first trimester legal termination (control) patients with recurrent miscarriage and non-viable pregnancy, and from patients with sporadic missed abortion. The tissue was tested for TGFβ-2+ suppressor cells by in situ hybridization, immunohistochemistry, and analysis of supernatants. RESULTS : TGFβ-2-related suppressor molecules similar but not identical to those identified in pregnant mice were released by decidual lymphoid cells. Fifty percent of 14 recurrent miscarriage patients showed a lack of suppressor cells and 59% were subnormal in comparison to 20 controls and 5 sporadic miscarriage patients, where 80–85% of the patients had detectable suppressor cells. CONCLUSIONS : Suppressor cell deficiency is compatible with a role for rejection and/or trophoblast failure in some patients with recurrent miscarriage. Presence of suppressor cells in most patients with missed abortion (4/5) is compatible with an alternative cause of fetal death, similar to findings reported in genetic fetal death mice.  相似文献   
996.
Shi  Gaylor  Cousins  Plevris  Hayes  & Grant 《Artificial organs》1998,22(12):1023-1030
In many bioartificial liver systems currently being designed and evaluated for use in fulminant hepatic failure, direct contact is required between the patient's blood and the liver cells in the device. The efficacy of such devices will be influenced by the interaction of fulminant hepatic failure (FHF) patient serum with the cells. We have found that FHF serum inhibits the growth rate and the synthesis of DNA, RNA, and protein; disturbs glutathione homeostasis; and induces morphological changes in cultured human Hep G2 cells. These interactions should influence the design of bioartificial liver devices based on proliferating cell lines and indicate the requirement to pretreat FHF patient plasma to reduce the toxin load.  相似文献   
997.
急性淋巴细胞白血病的电镜细胞化学诊断   总被引:1,自引:0,他引:1  
  相似文献   
998.
999.
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   
1000.
Glial fibrillary acidic protein (GFAP) is the principal intermediate filament protein found in mature astrocytes. Although the exact function of GFAP is poorly understood, it is presumed to stabilize the astrocyte’s cytoskeleton and help in maintaining cell shape. Previous studies from our laboratory have shown that when astrocytes were cocultured with primary Schwann cells (pSCs), astrocytes became hypertrophied and fibrous with intensely positive GFAP staining and segregated Schwann cells (SCs) into pockets. In order to understand the functional role of GFAP in this already established astrocyte-SC coculture model, we generated GFAP-negative cell lines from a GFAP-positive astrocytoma cell line and cocultured both the cell lines with pSCs. Our studies demonstrate that the GFAP-positive cell line put out processes toward the SCs, whereas the GFAP-negative cells did not form processes and the majority of the cells remained round. The most significant and interesting finding of this study, however, is the formation of elaborate processes by SCs when grown in coculture with the astrocytoma cells, unlike SCs cultured alone, which showed their typical bipolar spindle-shaped morphology. The extent of processes did not seem to be dependent on GFAP, since SCs cultured with both the cell lines formed similar processes. This coculture model may be useful in elucidating the factor(s) responsible for the formation of processes by SCs and can be further help in our understanding of the mechanism of morphological transformation of SCs.  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