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   6694篇
  免费   738篇
  国内免费   8篇
耳鼻咽喉   48篇
儿科学   199篇
妇产科学   206篇
基础医学   1135篇
口腔科学   312篇
临床医学   598篇
内科学   1258篇
皮肤病学   67篇
神经病学   739篇
特种医学   166篇
外科学   932篇
综合类   147篇
一般理论   5篇
预防医学   699篇
眼科学   71篇
药学   489篇
肿瘤学   369篇
  2021年   87篇
  2020年   61篇
  2019年   66篇
  2018年   98篇
  2017年   71篇
  2016年   79篇
  2015年   87篇
  2014年   153篇
  2013年   191篇
  2012年   331篇
  2011年   357篇
  2010年   176篇
  2009年   167篇
  2008年   286篇
  2007年   304篇
  2006年   256篇
  2005年   267篇
  2004年   263篇
  2003年   230篇
  2002年   246篇
  2001年   244篇
  2000年   230篇
  1999年   182篇
  1998年   69篇
  1997年   61篇
  1996年   54篇
  1995年   69篇
  1994年   69篇
  1993年   74篇
  1992年   167篇
  1991年   192篇
  1990年   133篇
  1989年   148篇
  1988年   149篇
  1987年   145篇
  1986年   145篇
  1985年   141篇
  1984年   122篇
  1983年   86篇
  1982年   70篇
  1981年   66篇
  1980年   56篇
  1979年   110篇
  1978年   76篇
  1977年   54篇
  1975年   59篇
  1974年   78篇
  1973年   64篇
  1972年   58篇
  1970年   51篇
排序方式: 共有7440条查询结果,搜索用时 16 毫秒
81.
The present study compares 465 singleton live deliveries fromin-vitro fertilization/gamete intra-Fallopian transfer (IVF/GIFT)pregnancies with a large control population to evaluate theincidence of pre-term delivery and small for gestational age(SGA) or very small for gestation age (VSGA) babies resultingfrom IVF/GIFT pregnancies. Overall the incidence of SGA or VSGAfrom an IVF/GIFT pregnancy is higher than from the normal obstetricpopulation (SGA odds ratio 1.76, 95% confidence interval (CI):1.38–2.25 and VSGA odds ratio 1.61, 95% CI: 1.05–2.46)particularly among primiparous women (SGA odds ratio 1.99, 95%CI: 1.25–3.16 and VSGA odds ratio 1.97, 95% CI: 1.49–2.62).After stratifying by the cause of infertility, only women withunexplained infertility had a significantly higher proportionof SGA/VSGA babies. There was a significantly higher incidenceof pre-term deliveries among the young primiparae (odds ratio5.02, 95% CI: 3.09–8.13). Thus the excess risk of deliveringa SGA/VSGA baby and pre-term delivery from an IVF/GIFT pregnancyseems to be largely confined to women with unexplained infertilityand young primiparae.  相似文献   
82.
Bronchial carcinoids and small cell lung cancer (SCLC) are currently recognized as neuroendocrine (NE) neoplasms. However, non-SCLC (NSCLC) may also express NE properties. Paraffin-embedded sections of a comprehensive panel of 113 lung carcinomas were analyzed for the expression of three general markers common to all NE cells, namely, chromogranin A, Leu-7 and neuron-specific enolase (NSE), five specific NE secretory products, and four other tumor markers by immunohistochemistry using the sensitive avidin-biotinylated peroxidase technique. The authors were able to demonstrate the following: (1) most, but not all carcinoids and SCLCs expressed multiple NE markers in a high percentage of tumor cells; (2) up to a half of NSCLC cases contained small subpopulations of cells expressing NE in a high percentage of tumor cells; (2) up to half of NSCLC cases contained small subpopulations of cells expressing NE markers; and (3) occasional NSCLCs showed staining patterns indistinguishable from SCLC. Specifically, 7 of 77 NSCLCs expressed four or more NE markers. NE markers in NSCLCs were more commonly expressed in adenocarcinomas and large cell carcinomas and rarely in squamous cell carcinomas. For comparison, the mean number of NE markers expressed by all cases of NSCLC was 1.5, carcinoids 6.0, and SCLCs 3.8. Individual "marker counts" were not useful in categorizing lung tumors as carcinoids and SCLC versus NSCLC. Instead, 95% of the tumors were correctly classified, applying a statistical model created from staining indices of the three general NE markers (chromogranin A, Leu-7, NSE) and three other tumor markers (carcinoembryonic antigen, keratin, vimentin). Because NSCLCs with NE features might have different clinical characteristics than other NSCLCs, immunohistochemistry provides an effective manner to identify this biologically interesting subset of NSCLCs in routine paraffin sections.  相似文献   
83.
Heat shock protein 88 and Aspergillus infection.   总被引:5,自引:0,他引:5       下载免费PDF全文
Immunoblotting was used to dissect the antibody responses in the sera of 50 patients with proven invasive aspergillosis, 28 patients with suspected invasive aspergillosis, 35 patients with allergic bronchopulmonary aspergillosis, and 10 patients with an aspergilloma. This demonstrated the immunodominance of antigenic bands at 88, 84, 51, and 40 kDa. Monoclonal antibodies against the heat shock protein 90 complexes of Candida albicans and the water mold Achlya ambisexualis identified these four antigenic bands as homologous proteins. Similar antigens have been described in humans, mice, Saccharomyces cerevisiae, chickens, and Drosophila species. The antibody against A. ambisexualis has previously been shown to cross-react with antigens belonging to the human heat shock protein 90 complex. Aspergillus heat shock protein 90 was extracted from the sera of patients with invasive aspergillosis by affinity chromatography. This was done with both a rabbit hyperimmune antiserum raised against an extract of Aspergillus fumigatus NCPF 2109 and a monoclonal antibody against the heat shock protein 90 of C. albicans. In vivo expression of the antigen was demonstrated in an aspergilloma surgically removed from a patient. The role of the antigen as an allergen in allergic bronchopulmonary aspergillosis is also discussed.  相似文献   
84.
Oral tonsils: an immunoperoxidase study   总被引:1,自引:0,他引:1  
Tissue morphometry and the distribution of cells containing immunoglobulin (Ig), J chain and secretory component (SC) were studied in eight oral tonsils. Quantitative immunohistochemistry revealed that IgG-containing cells predominated in all lymphoid compartments (follicles, extrafollicular areas and reticular epithelium) and that the IgG:IgA:IgM class ratios of the overall tonsillar immunocyte population were 13:8:2. Cells containing IgD and IgE were rare. IgG immunocytes showed no significant localisation within a given lymphoid compartment, whereas IgA cells were found predominantly in extrafollicular areas, especially adjacent to surface epithelium, and IgM cells were in follicles. J chain was present within IgM and some IgA cells. Tonsillar crypt and surface epithelium was negative for SC, suggesting that these structures are not directly involved in local mucosal immunity.  相似文献   
85.
Summary The BALB/c-3T3 cell transformation assay evaluates the morphologic transforming potential of test chemicals using cultured mammalian cells as targets. The assay is semiquantitative and employs a contact-inhibited clone of cells derived from the original BALB/c-3T3 mouse cell line. Transforming activity, or a focus, is recognized as a dense layer of morphologically altered cells superimposed on a monolayer of the normal cell phenotype. The induction of transforming activity in a standard assay has been reported to correlate well with the carcinogenicity of many test chemicals in rodent bioassay; however, the standard assay does not detect carcinogens of all chemical classes. This report describes an operational protocol for the standard BALB/c-3T3 cell transformation assay. In addition, it provides assay acceptance criteria and a discussion of a method to evaluate transforming activity data.  相似文献   
86.
A 3-methylcholanthrene [(MCA) CAS: 56-49-5]-induced fibrosarcoma cell line and its Friend murine leukemia virus-infected counterpart were assessed for their susceptibility to lysis by so-called "natural" effector cells in a series of 51Cr release assays. Detailed functional and phenotypic analysis of lytic effector cell populations from normal C57BL/6 mouse spleens revealed an identity most closely associated with natural cytotoxic cells. Neither tumor cell line was found to be sensitive to natural killer-mediated lysis. Additionally, virus infection of the MCA-induced fibrosarcoma cell line did not affect susceptibility to natural cell-mediated cytotoxicity.  相似文献   
87.
88.
Archives of Sexual Behavior - Black men who have sex with men (MSM) engaged in sex work (BMSM-SW) experience elevated HIV and sexually transmitted infection (STI) prevalence. Further, BMSM-SW have...  相似文献   
89.
ObjectivesTo inform how the VA should develop and implement network adequacy standards, we convened an expert panel to discuss Community Care Network (CCN) adequacy and how VA might implement network adequacy standards for community care.Data Sources/Study settingData were generated from expert panel ratings and from an audio‐recorded expert panel meeting conducted in Arlington, Virginia, in October 2017.Study DesignWe used a modified Delphi panel process involving one round of expert panel ratings provided by nine experts in network adequacy standards. Expert panel members received a list of network adequacy standard measures used in commercial and government market and were provided a rating form listing a total of 11 measures and characteristics to rate.Data Collection MethodsItems on the rating form were individually discussed during an expert panel meeting between the nine expert panel members and VA Office of Community Care leaders. Attendees addressed discordant views and generated revised or new standards accordingly. Recorded audio data were transcribed to facilitate thematic analysis regarding opportunities and challenges with implementing network adequacy standards in VA Community Care.Principal FindingsThe five highest ranked standards were network directories for Veterans, regular reporting of network adequacy data to VA, maximum wait time/distance standards, minimum ratio of providers to enrolled population, and qualitative assessments of network adequacy. During the expert panel discussion with VA Community Care leaders, opportunities and challenges implementing network adequacy standards were highlighted.ConclusionsOur expert panel shed light on priorities for network adequacy to be implemented under CCN contracts, such as developing comprehensive provider directories for Veterans to use when selecting community providers. Remaining questions focus on whether the VA could reasonably develop and implement network adequacy standards given current Congressional restraints on VA reimbursement to community providers.  相似文献   
90.
Progesterone receptor (PR) variant mRNAs in human endometrium could encode proteins with the potential to alter progesterone action in states of normal and abnormal endometrial development. We have assessed the expression levels of mRNA for the wild-type PR and splice variants of PR mRNA lacking exon 4 (del-4 PR), exon 6 (del-6 PR), exons 4 and 6 (del-4&6 PR), and part of exon 4 (del-p4 PR) or part of exon 6 (del-p6 PR) in the human endometrium throughout menstrual cycle development. Eighty-eight endometrial specimens (47 proliferative, 41 secretory) were collected from patients undergoing hysterectomy for benign gynaecologic causes. Measurements by RT-PCR indicated that mRNAs for wild-type PR, and splice variants del-4 PR, del-6 PR, del-4&6 PR, del-p6 PR, and a novel del-p4 PR were detected in all endometrial specimens throughout the menstrual cycle. Higher levels of wild-type PR and all PR variant mRNAs were found in the early and mid-proliferative endometrial phases than in secretory endometrium. The relative expression of mRNA for all PR variants compared to wild-type PR mRNA, however, did not change through all stages of endometrial development. We, therefore, found no evidence of differential co-expression of the PR variants compared with wild-type PR during normal menstrual development. Future studies will determine if the expression profile of PR variant mRNAs will be different in the endometrium of patients with infertility, recurrent pregnancy loss, or endometrial adenocarcinoma.  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