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   22946篇
  免费   2206篇
  国内免费   1324篇
耳鼻咽喉   200篇
儿科学   291篇
妇产科学   420篇
基础医学   2082篇
口腔科学   447篇
临床医学   3032篇
内科学   2987篇
皮肤病学   266篇
神经病学   1001篇
特种医学   698篇
外国民族医学   8篇
外科学   1520篇
综合类   4708篇
现状与发展   10篇
一般理论   1篇
预防医学   2179篇
眼科学   558篇
药学   2873篇
  19篇
中国医学   1809篇
肿瘤学   1367篇
  2024年   80篇
  2023年   330篇
  2022年   822篇
  2021年   1054篇
  2020年   861篇
  2019年   631篇
  2018年   657篇
  2017年   709篇
  2016年   637篇
  2015年   999篇
  2014年   1265篇
  2013年   1333篇
  2012年   1900篇
  2011年   1991篇
  2010年   1562篇
  2009年   1304篇
  2008年   1553篇
  2007年   1423篇
  2006年   1384篇
  2005年   1156篇
  2004年   836篇
  2003年   732篇
  2002年   684篇
  2001年   522篇
  2000年   422篇
  1999年   315篇
  1998年   182篇
  1997年   188篇
  1996年   139篇
  1995年   139篇
  1994年   102篇
  1993年   67篇
  1992年   89篇
  1991年   78篇
  1990年   62篇
  1989年   53篇
  1988年   47篇
  1987年   35篇
  1986年   35篇
  1985年   17篇
  1984年   11篇
  1983年   7篇
  1982年   7篇
  1981年   7篇
  1977年   5篇
  1973年   4篇
  1972年   4篇
  1956年   3篇
  1955年   6篇
  1954年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
通过对小鼠补体受体Ⅱ型基因(CR2)进行定点突变,然后将野生型和突变型小鼠CR2/1(MCR2/1)及人CR2(hCR2)用电穿孔方法导入小鼠SP2/0进行表达,采用免疫组织化学等方法鉴定阳性细胞系。用EB病毒对转染阳性细胞进行感染,EBER-1杂交结果显示,仅转染hCR2和突变型MCR2(mtMCR2)的SP2/0细胞感染了EB病毒,前者感染EB病毒的阳性率较后者高很多。这为进一步研究EB病毒进入细胞的机制及建立EB病毒相关的鼻咽癌动物模型奠定了良好的基础。  相似文献   
22.
目的:寻找番荔枝科假鹰爪属植物假鹰爪Desmos chinensis抗肿瘤活性成分。方法:采用硅胶柱色谱分离化学成分。根据理化性质及波谱分析等方法鉴定结构。结果:从氯仿萃取物中分离鉴定了7个化合物,分别是unon-al(Ⅰ),黄芩素-7-甲醚(Ⅱ),去甲氧杜鹃花素(Ⅲ),去甲氧杜鹃花素-7-甲醚(Ⅳ),苯甲酸(Ⅴ),β-谷甾醇(Ⅵ)和豆甾醇(Ⅶ)。结论:该种植中鉴定的黄酮类化合物均为β-环未取代,  相似文献   
23.
The poly(l -lactic acid) (PLLA)/carbon nanomaterials composite foams with hierarchical surface microstructural and internal conductive pathways are successfully prepared by a simple crystallization-assisted rapid phase separation (CARPS). The dimension and morphology of carbon nanomaterials can induce different crystallization forms to construct the hierarchical surface microstructure, and they are distributed on the phase interface of solvent and non-solvent to form conductive pathways. It is found that the heterogeneous nucleation of nanomaterials promotes a significant increase in crystallinity, and a stacked granular structure formed on the surface promotes the increase of the water contact angle to 148.7°. Foams with interconnecting pore structures contribute to the formation of 85.3% porosity and 12.33 g g−1 oil absorption. Carbon nanomaterials are distributed on the pore walls of the porous foam, which converts the foam from an insulating material to a conducting polymer. Furthermore, the uniform distribution of nanomaterials significantly affects the thermal stability of the PLLA. In belief, the multifunctional biodegradable foam, prepared by a CARPS method, makes it promising for industrial production and has potential applications in electrical conductivity, oil-water separation, and many other fields.  相似文献   
24.
以对氨基苯磺酸修饰聚乙二醇端头,制备兼具刚性与极性端头的聚合物,考察其制备LB膜与自组装膜的条件,用原子力/摩擦力显微镜表征自组装膜的表面形貌,对其微摩擦性能进行初步的探讨。  相似文献   
25.
评价低温保存板层角膜移植材料的效果。方法将15只人尸角膜分三组保存2年:4℃甘油脱水法,角膜液氮冷冻法,全眼球液氮冷冻法。并做透射电镜观察。结果第一组中,角膜胶原纤维排列紊乱,疏松,缺乏连续性,可见广纤维变性,纤维间可见极低电子密度灶。  相似文献   
26.
目的: 评价准分子激光屈光性角膜切削术治疗放射状角膜切开术后残余近视散光的预测性、稳定性和安全性。方法: 对52 眼 R K 术后残余近视散光患者行再次 P R K 治疗, 并连续随访两年以上。术前残余球镜屈光度- 375±132 D,残余柱镜屈光度- 236±125 D, 最佳矫正视力均≥08。结果: 术后 6 个月球镜屈光度- 032±024 D, 柱镜屈光度- 078±052 D, 裸眼视力≥10 者46 眼 (8846% ), 术后 24 个月球镜屈光度- 037±042 D, 柱镜屈光度- 056±037 D, 裸眼视力≥10 者 42 眼 (8076% )。最佳矫正视力下降 1 行以上者 3 眼 (576% ), 实际球镜矫正度与预期矫正度相差10 D 以内 50 眼 (9015% ), 柱镜相差 10 D以内51 眼 (9807% )。结论: P R K 治疗 R K 术后残余近视散光的两年随访结果表明, 该方法预测性强、稳定性好和安全性高, 特别在矫正残余散光方面, 其结果令人满意。  相似文献   
27.
Z D Lan  L Dai  X L Zhuo  J C Feng  K Xu  C W Chi 《Toxicon》1999,37(5):815-823
Based on the known amino acid sequences of BmK AS and BmK AS-1, the gene specific primers were designed and synthesized for 3' and 5' RACE (Rapid Amplification of cDNA Ends). Their partial cDNA fragments obtained by 3' and 5' RACE were cloned and sequenced, and the full length cDNA sequences of BmK AS and BmK AS-1 were then completed by overlapping their two partial cDNA sequences, respectively. The predicted amino acid sequences both consist of 85 amino acid residues including a putative signal peptide of 19 residues and a mature toxin of 66 residues. They are different in 17 amino acid residues, among them 11 residues in the mature toxin. The predicted amino acid sequences of BmK AS and BmK AS-1 were almost consistent with those determined and revised (personal communication), only different in one and two residues at their COO-terminal parts, respectively. Based on the determined cDNA sequences, and using the total DNAs isolated from the scorpion venom glands as a template, the genomic DNAs of BmK AS and BmK AS-1 were also amplified by PCR and sequenced. It showed that no intron was inserted in their open reading frames, while in the exon of signal peptide sequences of other Na+, K+ and Cl- channel toxins from the same scorpion, an intron is usually found. However, the Northern blot hybridization results indicated that the sizes of their mRNA should be around 800 bp. Their extra sequences around 400 bp which might function as an intron should be located at their 5' untranslated regions.  相似文献   
28.
Correlation analysis of numbers of colony-forming progenitor cells was used as an approach to the quantitation of human pluripotent stem cells. Marrow specimens were obtained from 24 patients with untreated acute myeloblastic leukemia, 22 patients under treatment, and 29 patients with no hematologic malignant disease. Three classes of progenitor cells were assayed: burst-forming units dependent on erythropoietin (BFU-E), colony-forming units dependent on erythropoietin (CFU-E), and granulopoietic progenitors (CFU-C). Significant positive correlations between numbers of BFU-E, CFU-E, and CFU-C were found in all 3 groups of patients. In contrast, no such positive correlations were seen between marrow blasts and any of the classes of colony-forming progenitors. These results were compatible with a shared relationship of the colony-forming progenitors to a pluripotent cell of origin and raised the possibility that the immediate progenitors of the blasts may not be any of the myelopoietic progenitor cells monitored in these studies.  相似文献   
29.
In a study of 331 term pregnancies a four-quadrant technique was used to obtain amniotic fluid index measurements, and the results were compared with the current widely used single-pocket measurement. In contrast to the "2-cm rule," the amniotic fluid index measurements consistently demonstrated higher sensitivity in predicting poor fetal outcome with no decrease in specificity. It was noted that pregnancies with an index of < or = 8 cm showed higher incidences of meconium staining, cesarean delivery for fetal distress, abnormal fetal heart rate monitoring and Apgar scores of < or = 7 or less at one minute.  相似文献   
30.
Objective The study was to explore the safety, firmness and convenience of the fascia around the ischial spine as a new fixation site for the vaginal fornix. Methods Between June 2007 and January 2008, detailed dissections and related measurements of the regions around the ischial spine were performed on 10 Chinese female cadavers (3 unembalmed and 7 embalmed cadavers). At the same time, the sacrospinous ligament,the fascia on the ischial spine, the iliococcygeus fascia as well as the vaginal fornix were exposed and the pull-out strength sequentially tested using a digital push-pull force gauge. Results The fascia on the ischial spine was firm and strong, with a thickness of 3 about mm. No major vessels or nerves were observed on the ischial spine. The greatest pullout strengths of the sacrospinous ligament,the fascia on the ischial spine, the iliococcygeus fascia as well as the vaginal fornix were (102±26),(64±15),(33±8)and(32±6)N, respectively. Conclusion The fascia at 1 cm from anterior lateral ischial spine, free of major vessels and nerves, is safe and strong and could be used as a new site for suspension in vaginal prolapse.  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