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   36119篇
  免费   1953篇
  国内免费   109篇
耳鼻咽喉   438篇
儿科学   2133篇
妇产科学   715篇
基础医学   4654篇
口腔科学   825篇
临床医学   2539篇
内科学   7320篇
皮肤病学   842篇
神经病学   1912篇
特种医学   803篇
外科学   4970篇
综合类   1328篇
一般理论   16篇
预防医学   2113篇
眼科学   1555篇
药学   3528篇
中国医学   274篇
肿瘤学   2216篇
  2023年   242篇
  2022年   694篇
  2021年   1181篇
  2020年   663篇
  2019年   875篇
  2018年   1070篇
  2017年   732篇
  2016年   972篇
  2015年   1009篇
  2014年   1372篇
  2013年   1761篇
  2012年   2421篇
  2011年   2443篇
  2010年   1380篇
  2009年   1237篇
  2008年   1773篇
  2007年   1740篇
  2006年   1757篇
  2005年   1382篇
  2004年   1383篇
  2003年   1175篇
  2002年   1003篇
  2001年   823篇
  2000年   867篇
  1999年   729篇
  1998年   309篇
  1997年   213篇
  1996年   222篇
  1995年   217篇
  1994年   176篇
  1993年   150篇
  1992年   498篇
  1991年   404篇
  1990年   430篇
  1989年   395篇
  1988年   357篇
  1987年   356篇
  1986年   348篇
  1985年   323篇
  1984年   262篇
  1983年   219篇
  1979年   230篇
  1978年   148篇
  1977年   180篇
  1976年   139篇
  1975年   171篇
  1974年   182篇
  1973年   182篇
  1972年   173篇
  1971年   161篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
92.
Between 1995 and 1998, we treated 5 patients with anti-factor VIII antibodies and spontaneous bleeding. All patients had underlying malignant conditions. Initial control of the bleeding episodes and reduction in inhibitor titer was achieved in all patients. Disappearance of factor VIII inhibitor occurred in 3 patients after either resection of the tumor or chemotherapy. Immunosuppression therapy failed to eradicate the antibody in 2 patients with metastatic disease. Antibodies against factor VIII appearing in certain patients may be directly associated with the underlying malignancy, rather than a coincidental finding. Attempts to reduce the titer or eradicate the inhibitor may fail if recognition of the underlying condition is not sought, or an appropriate treatment of cancer is not offered.  相似文献   
93.
Summary 3-Deazaguanine (3-DG), a purine analogue, has unusual antitumor activity against experimental mammary tumor models and a number of other solid tumors. Others have shown that mutant CHO cells deficient in hypoxanthine guanine phosphoribosyl transferase (HGPRTase) or adenine phosphoribosyl transferase (APRTase) are resistant to 3-DG. We developed a L1210 cell line resistant to 3-DG, L1210/3-DG, by subculturing the parent L1210/0 cells in the presence of increasing concentrations of 3-DG. The IC50 was 3.5 M and 620 M for L1210/0 and L1210/3-DG, respectively. Cytotoxicity studies proved the resistance to be stable. Examination of the baseline-specific activity of HGPRTase and APRTase showed that the former was 118-fold lower in L1210/3-DG than in L1210/0, and the latter demonstrated no difference. A 4-h treatment of the cell lines at IC50 doses showed 48% and 23% reductions in IMP dehydrogenase in L1210/0 and L1210/3-DG, respectively. The rate of de novo purine biosynthesis was studied by using [14C]formic acid. Formate flux increased 2-fold in L1210/3DG in concert with the observed deficiency of HGPRTase in the cell line. 3-DG uptake was studied with [14C]-labelled compound. The total radioactivity was 9-fold higher in L1210/0 than in L1210/3-DG at 2 h. Subsequent chromatographic separation of radioactivity showed the 3-DG and 3-deazaguanosine pools of the drug to be equal in both lines. However, 3-DG nucleotide pools at 1 min and 2 h were 2.5-fold and 16-fold lower, respectively, in L1210/3-DG than in L1210/0. 3-DG incorporation studies with radiolabelled drug demonstrated that 3-deazaguanine is incorporated in the acid-insoluble fraction of the cell. These studies conclude that HGPRTase, and not APRTase, is required for the activation of drug. Inhibition of IMP dehydrogenase is partially responsible for antitumor activity of the drug. The incorporation of drug into nucleic acids may be a major mechanism for its antitumor activity. Further studies using a cloned cDNA probe for hypoxanthine guanine phosphoribosyltransferase (HGPRT) demonstrated no change in the DNA arrangements of the L1210/3-DG cell line, and Northern blot analysis showed approximately equal expression of mRNA in both cell lines.Abbreviations used APRTase adenine phosphoribosyltransferase - HGPRTase Hypoxanthine guanine phosphoribosyltransferase - IMPD Inosine mono-phosphate dehydrogenase - PRPP 5-Phosphorylribose-1-pyrophosphate - AOPCP , -Methyleneadenosine 5-diphosphate - NAD Nicotineamide dinucleotide - EDTA Ethylenediamine tetra acetic acid Presented at annual meeting of American Association of Cancer Research in May, 1986Supported in part by Warner-Lambert Company, Ann Arbor, Michigan  相似文献   
94.
Pancreatoblastoma or infantile pancreatic carcinoma is a rare pancreatic tumor with distinct acinar and squamoid cell differentiation that generally affects infants and young children. Ultrasound and CT scan may be useful but preoperative diagnosis is often quite difficult. The outcome is generally favourable. A such case of 10 years old boy with an abdominal mass is being presented.  相似文献   
95.
Nie X  Singh RP 《Virus genes》2003,26(1):39-47
A North American (NA) isolate of tobacco veinal necrotic strain of Potato virus Y (PVYN) (N-Jg) and a NA isolate of potato tuber necrotic strain of Potato virus Y (PVYNTN) (Tu 660) were tested for their phenotypes by inoculation to potato plants of three potato cultivars. Upon inoculation with Tu 660, tubers of the cultivars Norchip and Ranger Russet developed potato tuber necrotic ringspot disease (PTNRD) but not the tubers of Russet Burbank. N-Jg failed to induce PTNRD in the tested cultivars. The genomic RNAs of both strains were completely sequenced and analysed. High homology (98% and 99% identity on nucleotide and polyprotein, respectively) was found between Tu 660 and N-Jg. When polyproteins were compared with other isolates, high identity was observed between Tu 660 and an European (Eu) PVYN-605 (98%) and with an Eu-PVYNTN-H (96%). However, when individual mature proteins were compared, much lower identities (86.5–94%) were found between Tu 660 and PVYNTN-H compared to 98–99.5% between Tu 660 and PVYN-605 in the P3, 6K1 and CI regions. Further sequence analysis indicated that the PVYNTN-H is a hybrid molecule of the genomic RNA recombination of PVYO and Eu-PVYN as shown by Glais et al. (Arch Virol 147, 363–378), whereas NA-PVYNTN Tu 660 is free of recombination points. Phylogenetic analysis confirmed this observation, and suggested that, in light of high homology, the Tu 660 might have evolved from NA-PVYN by mutations rather than the genome recombinations. The non-recombinant nature of NA-PVYNTN Tu 660 strongly suggests that the recombinant structure of genome is not a necessary prerequisite for the PTNRD phenotype.  相似文献   
96.
The opioid pentapeptides called enkephalins were originally described as the endogenous ligands for the opioid receptors. Although their precise physiological significance still remains elusive, the enkephalins have been reported to exhibit analgesic, antidepressant, antianxiety and anticonvulsant activities. In addition, enkephalins have also been shown to act as immunomodulator. The first generation of dimeric peptides was derived from enkephalins. Biphalin [(Tyr-D-Ala-Gly-Phe-NH)2] is a bivalent opioid analog containing two tyrosine residues. We have evaluated the immunomodulatory properties of biphalin and its analogs in various in vitro tests. We report that biphalin and one of its analogs [Tyr-D-Ala-Gly-Phe-NH.NH-Phe(p-Cl)-H] stimulate human T cell proliferation, natural killer (NK) cell cytotoxicity in vitro and interleukin-2 (IL-2) production. Biphalin and its analog also released chemokine like factor in the culture supernatant that was responsible for increased chemotaxis of monocytes. Furthermore, these peptides inhibited tumor necrosis factor (TNF-alpha) production in lipopolysaccharide (LPS) stimulated peripheral blood mononuclear cells (PBMC) and nitric oxide (NO) production in mouse macrophage cells, RAW 264.7. Our observations suggest immunomodulatory property of biphalin and its analog.  相似文献   
97.
An outbreak of nosocomial fungemia due to the unusual yeast, Pichia anomala occurred in the pediatric wards of our hospital over a period of 23 months (April 1996 to February 1998). A total of 379 neonates and children (4.2% admissions) were infected. The probable index case was admitted to the pediatric emergency ward, with subsequent transmission to the premature nursery, pediatric intensive care units, and other children wards. Carriage on the hands of health care personnel was likely to be responsible for dissemination of the fungus. The outbreak could only be controlled after a health education campaign to improve hand-washing practices was instituted and after nystatin-fluconazole prophylaxis to all premature neonates and high-risk infants was introduced. In a case-control study, we identified a lower gestational age, a very low birth weight (<1,500 g), and a longer duration of hospital stay as significant risk factors associated with P. anomala fungemia in premature neonates. We conducted a culture prevalence survey of 50 consecutive premature neonates and found that 28% were colonized with P. anomala at a skin or mucosal site on the date of delivery and that 20% of these neonates subsequently developed P. anomala fungemia. We performed multilocus enzyme electrophoresis on 40 P. anomala outbreak isolates (including patient and health care workers' hand isolates), and the results suggested that these isolates were identical. Our study highlights the importance of P. anomala as an emerging nosocomial fungal pathogen.  相似文献   
98.
The two sampling techniques were studied in 160 randomly selected cases of superficial swellings in various sites of the body. They were sampled by fine needle aspiration (FNA) and by non-aspiration (NA) (a needle without application of aspiration pressure). Cell samples were cytologically assessed and critically evaluated using five objective parameters. Contamination with blood was more in lymphnode, thyroid and liver lesions in aspiration smears than NA smears and values were statistically significant. Similarly when compared for the degree of cellular trauma and cellular degeneration statistically significant better results were obtained by nonaspiration technique for lymphnode lesions. Regarding amount of cellular material obtained by FNA, statistical significant better results were found for breast lesions only. Statistically significant better maintenance of architecture was observed only for thyroid lesions by NA technique. Better average scores were observed by NA technique for lymphnode and thyroid only. Categorizing all the smears obtained by FNA & NA on the basis of their scores according to predetermined criteria, greater number of diagnostically adequate specimens were obtained by FNA than by NA but the number of diagnostically superior specimens obtained by NA technique was found to be more than that by FNA. The difference was found to be statistically significant. However the number of inadequate smears was also more by NA technique than by FNA technique.  相似文献   
99.
Extracts of plants have been widely evaluated for possible antiproliferative and anticarcinogenic properties. The antiproliferative activity of ethanolic extract of Boerhaavia diffusa, a plant used in traditional medicine, was evaluated in several cells. It inhibited T cell mitogen phytohemagglutinin and concanavalin A-stimulated proliferation of human peripheral blood mononuclear cells (PBMC). It also inhibited purified protein derivative antigen-stimulated PBMC proliferation and human mixed lymphocyte culture. In addition, B. diffusa extract inhibited the growth of several cell lines of mouse and human origin, such as mouse macrophage cells (RAW 264.7), human macrophage cells (U937), human monocytic cells (THP-1), mouse fibroblast cells (L929), human embryonic kidney cells (HEK293), mouse liver cells (BNLCL.2), African green monkey kidney cells (COS-1), mouse lymphoma cells (EL-4), human erythroleukemic cells (K562), and human T cells (Jurkat). The present study has demonstrated the antiproliferative potential of ethanolic extract of B. diffusa in vitro.  相似文献   
100.
Studies on pathogenesis of fowl pox: virological study   总被引:1,自引:0,他引:1  
One-month-old WLH chickens were inoculated with a field isolate of fowl pox virus (FPV) by intradermal (i.d.) and intratracheal (i.t.) routes. In intradermally infected chickens, the virus in titrable amounts was first detected in the skin at the inoculation site on day 2 and in lungs on day 4 followed by viraemia on the day 5 post-infection (p.i.). Subsequently the virus was recovered from liver, spleen, kidney and brain, but not from the heart. The chickens infected by i.t. route showed an almost similar outcome with minor differences as the virus was first demonstrated in the lungs on day 2 p.i., viraemia occurred on day 4 p.i. Initiation of pocks at the inoculation site in i.d. infected birds was observed on days 3 to 4 p.i., generalized cutaneous pock lesions appeared from 7 to 8 days p.i.  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