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   182489篇
  免费   12503篇
  国内免费   4212篇
耳鼻咽喉   1228篇
儿科学   3937篇
妇产科学   2589篇
基础医学   12363篇
口腔科学   4211篇
临床医学   18990篇
内科学   32265篇
皮肤病学   2708篇
神经病学   12688篇
特种医学   4883篇
外国民族医学   40篇
外科学   19252篇
综合类   22707篇
现状与发展   24篇
一般理论   4篇
预防医学   10511篇
眼科学   2439篇
药学   15744篇
  106篇
中国医学   13699篇
肿瘤学   18816篇
  2024年   381篇
  2023年   3141篇
  2022年   5343篇
  2021年   7998篇
  2020年   7101篇
  2019年   8430篇
  2018年   7439篇
  2017年   7321篇
  2016年   6612篇
  2015年   6195篇
  2014年   11696篇
  2013年   14133篇
  2012年   9504篇
  2011年   10333篇
  2010年   8220篇
  2009年   7640篇
  2008年   7504篇
  2007年   7748篇
  2006年   6764篇
  2005年   5931篇
  2004年   4754篇
  2003年   4310篇
  2002年   3496篇
  2001年   3021篇
  2000年   2513篇
  1999年   1951篇
  1998年   1653篇
  1997年   1396篇
  1996年   1178篇
  1995年   1091篇
  1994年   883篇
  1993年   684篇
  1992年   623篇
  1991年   557篇
  1990年   487篇
  1989年   427篇
  1988年   394篇
  1985年   1732篇
  1984年   2733篇
  1983年   2480篇
  1982年   1901篇
  1981年   1991篇
  1980年   1648篇
  1979年   1452篇
  1978年   1208篇
  1977年   703篇
  1976年   1154篇
  1975年   1004篇
  1974年   831篇
  1973年   792篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
This report describes a new case of chronic myeloid leukemia with an unusual Philadelphia chromosome translocation involving chromosomes No. 4,9, and 22; t(4,9,22) (q31;q34;q11).  相似文献   
972.
A type C RNA virus was isolated from mink lung cell line (American Type Culture Collection No. CCL 64) which had been cocultivated with 5-bromodeoxyuridine (BUDR)-treated mouse spleen cells. The virus has type C RNA virus morphology as demonstrated by electron microscopy. The complement fixation and immunofluorescent tests performed with mouse anti-p30 antisera show a distinctive difference between mink and mouse type C viruses. Complement fixation tests also indicate that mink type C virus is antigenically different from rat, feline leukemia, feline endogenous (RD-114), baboon, and woolly monkey type C viruses. The virus propagates in cells of mouse, rat, cat, sheep, dog, and human origin, but not in bovine (MDBK) or simian (BSC-1) cells. The infection of rabbit (SIRC) cells and cells of virus origin (mink lung) was followed by delayed and low-titer polymerase release in tissue culture media. The virus sediments in sucrose density gradients as a broad band of densities, 1.13–1.17 g/ml, and contains 70 and 4S RNA. The protein profile is similar to that observed in other mammalian type C viruses. The DNA complementary to the poly(A)-containing virion RNA hybridized to a high degree (72%) with the RNA from virus-producing mink lung cells but not with the RNA from mouse cell lines or uninfected mink lung cell line. The nucleotide sequences homologous to mink viral cDNA were found in mink cell DNA from both virus-producing and nonproducing cells, but not in the DNA of mouse, rat, or feline origin. The virus here described therefore represents an endogenous mink type C virus.  相似文献   
973.
974.
Chromosome banding analyses were made on 10 cases of Ph1-positive AML (7 M1 and 3 M2). The standard type Ph1 translocation, t(9q +;22q -), was identified in all of them. Karyotypically normal cells were observed in 6-65% of bone marrow metaphases at the initial cytogenetic examination of 7 patients, whereas the remaining 3 patients had only Ph1-positive cells at diagnosis. Follow-up studies performed in 5 cases indicated that the frequency of karyotypically normal cells increased up to 81-100% when the patients were in remission, whereas it was much reduced in relapse. In 5 cases, there was observed a clone of cells in which the Ph1 translocation was the sole karyotypic abnormality. Various types of other chromosome abnormalities, in addition to the Ph1, were observed in all cases, among which-7 was the most frequent, being found in three cases as a stem line. Other additional changes encountered were + Ph1, del(5), i(17q), - 10, + 18, + X, and various numerical and structural changes including certain secondary translocations that occurred in the Ph1 (22q -) or its partner (9q +). The types and frequencies of these additional changes appeared to be different from those found in the acute phase of CML or in Ph1-positive ALL.  相似文献   
975.
Equine cytomegalovirus (equine herpesvirus type 2; ECMV) exhibited cultural characteristics typical of the cytomegalovirus group. Ninety-six to one hundred twenty hours were required to reach a maximum titer of 1 × 107 PFU/ml in infected cells, from which no more than 50% of infectious virus produced was released into the supernatant fluid. Only cells of equine or rabbit origin were permissive for virus replication. Ultrastructural investigation of ECMV-infected cells revealed the presence of three types of intranuclear nucleocapsids (empty capsidc, capsidc with a cross-shaped, electron-lucent core, and mature capsidc with an electron-dense core). The mature capsids appeared to acquire their envelope at the nuclear membrane. Infected cells were characterized by nuclei containing marginated chromatin in a large, electron-dense inclusion substance. Viral DNA extracted and purified from virions, nucleocapsids, or infected cells (Hirt fractionation) demonstrated an average density of 1.716 g/cm3 which corresponds to a G+C content of 57.7%. Sedimentation analyses of ECMV DNA in neutral sucrose gradients using phage T4 and equine herpesvirus type 1 (EHV-1) DNA as markers indicated a sedimentation coefficient of approximately 61 S. Sedimentation in alkaline sucrose suggested that the ECMV genome is a non-cross-linked, double-stranded DNA, possibly possessing nonligated areas either within the sugar phosphate backbone of the molecule or within specific alkali-labile regions. Sedimentation analyses of ECMV DNA yielded a molecular weight of approximately 121 × 106 which was confirmed by restriction endonuclease analyses which indicated a value of 126 × 106 Determination of the number, size, and molarity of ECMVDNA fragments generated by digestion with restriction enzymes revealed that ECMV DNA differs markedly in molecular structure from the genome of EHV-1.  相似文献   
976.
Immunologic changes have been reported in the dementing illnesses of mid and late life. The results of two studies of drug-free males meeting research diagnostic criteria for primary neuronal degeneration of the Alzheimer's type suggest that serum IgG levels decrease with the progression of dementia. Serum IgG levels were inversely correlated with duration of illness and the levels of psychiatric symptomatology. Performance on the mini-mental status examination was positively associated with serum IgG concentrations.  相似文献   
977.
目的:了解伴迟发性运动障碍(TD)的慢性精神分裂症患者认知功能的损害情况。方法:以82例伴TD的(TD组)、70例不伴TD的慢性精神分裂症患者(非TD组)为研究对象,两组一般情况相匹配,选用韦氏记忆测验(WMS)、威斯康星卡片分类测验(WCST)及连线测验(TMT)进行认知功能评定。结果:①两组在WMS方面比较无统计学差异。②两组在WCST方面比较,TD组错误应答数、选择错误率、错误思考时间、持续应答数及概念化水平百分数成绩均显著差于非TD组。③两组在TMT方面比较,TD组PartB耗时数显著长于非TD组,而两组PartA耗时数无显著差异。结论:伴TD的慢性精神分裂症病人存在明显的认知功能损害,且可能涉及额叶皮层。  相似文献   
978.
Objectives: To assess the efficacy and tolerability of a new matrix patch delivering 0.05 mg estradiol per day (Estraderm MX 50) in postmenopausal women with moderate to severe postmenopausal symptoms. Methods: A multicenter, double-blin, randomized, between-patient, placebo controlled trial in 109 postmenopausal women was carried out. Patches were applied twice weekly for 12 weeks. Patients were assessed at 4, 8 and 12 weeks of treatment. The primary efficacy variable was change from baseline in mean number of moderate to severe hot flushes (including night sweats) per 24 h during the last 2 weeks of treatment. Other variables included Kupperman Index, local and systemic tolerability. Plasma concentrations of estradiol (E2), estrone (E1) and estrone sulfate (E1S) were determined before and after treatment. Results: Estraderm MX was significantly superior to placebo (P < 0.001) in reducing mean number of moderate to severe hot flushes (including night sweats) per 24 h after 4, 8 and 12 weeks of treatment. The estimate of treatment group differences after 12 weeks was 4.2 hot flushes (95% confidence interval: 2.6–5.5). Estraderm MX also significantly reduced Kupperman Index at all time points compared to placebo (P < 0.001). Estraderm MX induced increases in mean E2, E1 and E1S plasma levels as expected (E2: baseline 2.7 pg/ml, 12 weeks 38.9 pg/ml; E1: baseline 18.8 pg/ml, 12 weeks 41.6 pg/ml; E1S: baseline 235.6 pg/ml, 12 weeks 765.1 pg/ml). Overall rates of adverse experiences were similar for Estraderm MX and placebo. The number of patients reporting skin irritation was low and similar in both groups. Conclusions: Estraderm MX 50, a new matrix patch, offers an effective and well tolerated dosage form for transdermal delivery of 0.05 mg E2 per day.  相似文献   
979.
980.
The property of aerobic glycolysis commonly possessed by malignant cells points to a weakness in oxidative metabolism which has been equated in some tumours with partial uncoupling of oxidative phosphorylation. The suggestions are made, first, that this endogenous defect may account for spontaneous cell death , and, second, that its accentuation would inflict extensive tumour injury upon sensitive neoplasms. Certain drugs not in current use for the treatment of malignant disease are known to be able to interfere selectively with energy metabolism in sensitive tumours to such an extent that widespread necrotisation ensues. The drugs activate an endogenous destructive mechanism that appears to require oxygen. Liminal therapy, the maintenance of continuous destructive pressure on sensitive growths in such a manner that maximal anti-tumour activity in terms of interference with energy production is not achieved at any one time, and under conditions in which the oxygen supply is only partly depleted, is put forward as a possible means of achieving complete and selective tumour destruction .  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