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   2724篇
  免费   105篇
  国内免费   37篇
耳鼻咽喉   5篇
儿科学   129篇
妇产科学   79篇
基础医学   366篇
口腔科学   55篇
临床医学   235篇
内科学   549篇
皮肤病学   45篇
神经病学   132篇
特种医学   209篇
外科学   192篇
综合类   193篇
一般理论   3篇
预防医学   171篇
眼科学   43篇
药学   273篇
  2篇
中国医学   26篇
肿瘤学   159篇
  2023年   14篇
  2022年   41篇
  2021年   55篇
  2020年   37篇
  2019年   50篇
  2018年   73篇
  2017年   37篇
  2016年   60篇
  2015年   54篇
  2014年   71篇
  2013年   111篇
  2012年   167篇
  2011年   159篇
  2010年   107篇
  2009年   81篇
  2008年   147篇
  2007年   155篇
  2006年   124篇
  2005年   115篇
  2004年   106篇
  2003年   98篇
  2002年   75篇
  2001年   56篇
  2000年   64篇
  1999年   47篇
  1998年   51篇
  1997年   49篇
  1996年   47篇
  1995年   32篇
  1994年   30篇
  1993年   31篇
  1992年   33篇
  1991年   25篇
  1990年   27篇
  1989年   41篇
  1988年   28篇
  1987年   33篇
  1986年   39篇
  1985年   34篇
  1984年   20篇
  1983年   14篇
  1982年   23篇
  1981年   14篇
  1980年   15篇
  1977年   19篇
  1976年   20篇
  1975年   13篇
  1973年   13篇
  1970年   12篇
  1969年   13篇
排序方式: 共有2866条查询结果,搜索用时 15 毫秒
41.
Hecht  SS; Ronai  ZA; Dolan  L; Desai  D; Amin  S 《Carcinogenesis》1998,19(1):157-160
We compared the tumor-initiating activities toward mouse skin of two structurally related polycyclic aromatic hydrocarbon diol epoxides: racemic anti-1,2,3,4-tetrahydro-5,6-dimethylchrysene-1,2-diol-3,4- epoxide (5,6-diMeCDE) and racemic anti-1,2,3,4-tetrahydro-5- methylchrysene-1,2-diol-3,4-epoxide (5-MeCDE). Tumors induced by these diol epoxides were analysed for mutations in the Ha-ras gene. 5,6- diMeCDE is derived from the non-planar parent compound 5,6- dimethylchrysene, and reacts to approximately equal extents with dA and dG in DNA, whereas 5-MeCDE is derived from a nearly planar parent compound, 5-methylchrysene, and reacts mainly with dG in DNA. 5,6- diMeCDE, at initiating doses of 33, 100 or 400 nmol per mouse, induced 1.2, 2.2 and 6.2 skin tumors per mouse, respectively. It was significantly less tumorigenic than 5-MeCDE which induced 3.1, 7.5 and 9.1 skin tumors per mouse at the same doses. Tumors induced by 5,6- diMeCDE had a large number of CAA-->CTA mutations in codon 61 of the Ha- ras gene: 50, 55 and 75% of the tumors analysed had this mutation at the 33, 100 and 400 nmol doses. No mutations were found in codons 12 and 13 in the tumors induced by 5,6-diMeCDE. In contrast, CAA-->CTA mutations in codon 61 were rarely seen in tumors induced by 5-MeCDE. At the highest dose of 5-MeCDE, 20% of the tumors analysed had mutations at G of codons 12 and 13. The results of this comparative study support the hypothesis that mutations in the Ha-ras gene in mouse skin tumors induced by PAH diol epoxides occur as a result of their direct reaction with the gene. However, pathways other than the commonly observed Ha- ras codon 61 mutations are clearly important in mouse skin tumorigenesis by these diol epoxides.   相似文献   
42.
43.
白首乌化学成分的研究   总被引:4,自引:0,他引:4  
自白首乌主要品种耳叶牛皮消(Cynanchum auriculatum Royle ex Wight)根中首次分得三个已知甾体酯型甙元:告达亭(caudatin),开德甙元(kidjolanin),萝藦甙元(Metaplexigenin)和一种新的二苯酮衍生物(Ⅳ),经光谱分析推定其结构为2,6,2′,5′-四羟基,3-乙酰基,6′-甲基二苯酮,命名白首乌二苯酮。  相似文献   
44.
白首乌化学成分的研究   总被引:11,自引:0,他引:11  
自白首乌主要品种耳叶牛皮消(Cynanchum auriculatum Royle ex Wight)根中首次分得三个已知甾体酯型甙元:告达亭(caudatin),开德甙元(kidjolanin),萝藦甙元(Metaplexigenin)和一种新的二苯酮衍生物(Ⅳ),经光谱分析推定其结构为2,6,2′,5′-四羟基,3-乙酰基,6′-甲基二苯酮,命名白首乌二苯酮。  相似文献   
45.
柳枫  廖松生 《药学学报》1989,24(5):372-375
本文用DSC和激光拉曼光谱研究抗癌药物足叶乙甙(4-去甲基表鬼臼毒素-β-D-乙叉吡喃葡萄糖甙,简称VP 16-213)与二棕榈酰磷脂酰胆碱(DPPC)脂质体的作用。VP 16-213分子掺入DPPC脂质体双层中,不但使相转变温度向高温移动,而且吸热峰的半高宽度随VP 16-213浓度增加而变宽。其Raman光谱在频率2850 cm~(-1)处的C-H键对称伸缩振动亦随着药物浓度增加而减弱。这些结果表明VP 16-213分子是定域在脂双层中DPPC分子链的C_1~C_9亚甲基区域,使脂质体的有序性提高而流动性降低。  相似文献   
46.
47.
OBJECTIVE: Glutathione-S-transferases (GSTs) are active in the detoxification of wide variety of endogenous or exogenous carcinogens. We examined the association of the GST gene polymorphism with sporadic bladder cancer patients in Northern India. MATERIAL AND METHODS: The study constituted of 106 bladder cancer cases and 370 age-matched controls. The GSTT1 and GSTM1 null genotypes were identified by multiplex PCR and GSTP1313 A/G by Polymerase Chain Reaction/Restriction Fragment Length Polymorphism method (PCR/RFLP). RESULTS: We observed non-significant association in null alleles of the GSTM1 (p = 0.611, OR = 1.12, 95% CI = 0.72-1.74 and GSTT1 (p = 0.135, OR = 1.45, 95% CI = 0.89-2.37) with risk of bladder cancer. However, the G/G genotype of the GSTP1 gene polymorphism was highly significant when compared to controls (p=0.000, OR = 7.12, 95% CI = 3.14-16.16). The combined analysis of the three risk genotypes demonstrated further increase in the risk of bladder cancer (p = 0.000, OR = 7.29 95% CI = 2.81-18.93). CONCLUSION: Our study demonstrated that GSTP1313 G/G polymorphism is a strong predisposing risk factor for bladder cancer. Combination of three GST genotypes association exhibiting gene-gene interaction further substantiates the increased risk of bladder cancer.  相似文献   
48.
The objectives of this study were to determine the direction and pattern of flow of irrigating solutions inside simulated root canals with different irrigation needles; and to determine whether different needle designs increase the likelihood of irrigating solution passing through the apical foramen. Two types of needles were compared: a standard needle with a bevel and an open end, and a needle with a side opening and closed rounded tip. Observations of irrigant flow within the canals indicated that the side‐venting needle can be dangerous if the needle gauge is small and it reaches the full length of the canal, since this allowed irrigants to flow into the periapical area. With the standard needle, the fluid did not go beyond the tip of the needle when minimal irrigating pressure was employed. As the size of canal increased, the fluid did not extrude beyond the tip of both needles. However, if the needles bound in the canals, then the fluid was forced away from the needle tip, and the pressure applied to the syringe was directly proportional to the distance the fluid flowed away from the needle tip. Both side‐venting and standard needles can be used for irrigation safely and effectively if a dynamic irrigation technique (moving the needle up and down inside the canals while irrigating) is employed.  相似文献   
49.
The novel gadgets are associated constantly at a quick phase for the development of Internet of Things (IoT). Wearable gadgets are another gathering development in those available gadgets. The recent method in gadgets is to coordinate with IoT and idea is implementing the remote sensor systems that convey novel encounters in day by day exercises. Here, I exhibit a regular day to day existence application including a Wireless Sensor Networks (WSN) for gaming situation. By using this, the physical factors of sports person are estimated and directed by wearable gadgets to Wireless Sensor Networks. The end goal to incorporate diverse equipment stages and to present an administration situated semantic middleware arrangement hooked on a solitary request also utilization of Enterprise Service Bus (ESB) is introduced as a scaffold to ensure coordination of the distinctive conditions and interoperability. Through proposed method everyone can procure information by introducing framework to fresh client. Those clients would be able to get to the information through a wide assortment of gadgets (cell phones, tablets, and PCs) and working frameworks (Android, Windows, Linux, iOS, and so on). Finally we introduced one case study of football match for monitoring 11 players and acquiring data’s and to predict the real time situation in football ground.  相似文献   
50.
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