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   47124篇
  免费   4269篇
  国内免费   68篇
耳鼻咽喉   525篇
儿科学   1443篇
妇产科学   1075篇
基础医学   6065篇
口腔科学   1103篇
临床医学   5421篇
内科学   8972篇
皮肤病学   723篇
神经病学   4914篇
特种医学   2283篇
外国民族医学   4篇
外科学   6382篇
综合类   771篇
一般理论   34篇
预防医学   4433篇
眼科学   1191篇
药学   3194篇
  3篇
中国医学   54篇
肿瘤学   2871篇
  2021年   595篇
  2019年   562篇
  2018年   660篇
  2017年   567篇
  2016年   576篇
  2015年   675篇
  2014年   891篇
  2013年   1436篇
  2012年   1941篇
  2011年   2051篇
  2010年   1173篇
  2009年   1089篇
  2008年   1843篇
  2007年   2073篇
  2006年   1967篇
  2005年   1856篇
  2004年   1808篇
  2003年   1685篇
  2002年   1719篇
  2001年   1542篇
  2000年   1570篇
  1999年   1394篇
  1998年   622篇
  1997年   610篇
  1996年   579篇
  1995年   528篇
  1994年   476篇
  1993年   438篇
  1992年   1171篇
  1991年   1180篇
  1990年   1108篇
  1989年   1127篇
  1988年   939篇
  1987年   1051篇
  1986年   981篇
  1985年   987篇
  1984年   775篇
  1983年   631篇
  1982年   411篇
  1981年   396篇
  1980年   388篇
  1979年   707篇
  1978年   529篇
  1977年   465篇
  1976年   475篇
  1975年   399篇
  1974年   520篇
  1973年   455篇
  1972年   383篇
  1971年   363篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Receptors for IL-2 can be demonstrated on the majority of mouse splenic T cells within 48 h after stimulation with Concanavalin A. We show here that aging leads to a decline in the frequency of cells able to generate detectable levels of IL-2 receptor, as measured by cytofluorimetry using antibodies to the receptor. The age-associated deficit cannot be overcome either by increasing the mitogen dose, or by supplementing the cultures with exogenous IL-2. At least a part of the decline, with age, in T cell-mediated immunity may represent an inability of individual T cells to produce sufficient IL-2 receptor to enable them to reach the IL-2 dependent phases of their first cell cycle.  相似文献   
102.
OBJECTIVE: Inpatients with major depressive illness often have coexistent nonaffective psychiatric and/or medical conditions. The authors' objective is to address the following questions: 1) What is the effect of comorbid illness on the severity of major depression and associated psychosocial factors? 2) How does the course of depression differ for patients with and without concurrent illness? 3) Do patients with compound depression differ in rate of recovery and time to recovery from patients with pure depression? METHOD: The subjects were 78 patients with a DSM-III diagnosis of major depression who were consecutively admitted to an acute care university-affiliated psychiatric hospital; 37 of these patients had major depression only and 41 had major depression compounded by a coexisting axis I, II, or III condition. The patients were studied while hospitalized and for 12 months after hospital discharge. Instruments used included the Modified Hamilton Rating Scale for Depression, the Global Assessment Scale, and the Social Readjustment Rating Scale. RESULTS: Patients with compound depression reported significantly poorer functioning over the 12-month follow-up period and had lower recovery rates than the patients with pure depression. There were no differences in recovery rates between men and women with compound depression, but significantly more men than women with pure depression recovered. CONCLUSIONS: Compound depression is a common clinical occurrence, the course of illness is more difficult for patients with compound depression than for patients with pure depression, and the recovery rate of patients with compound depression is lower than that of patients with pure depression.  相似文献   
103.
Multiple vascular lesions in the brain were identified by angiography in a 45-year-old woman with Von Hippel Lindau disease. One of these lesions was a histologically-proven hemangioblastoma. The occurrence of such lesions in a cerebral hemisphere is exceedingly rare and is usually related to Von Hippel Lindau disease.  相似文献   
104.
105.
The nucleotide sequences of genes contain information which can potentially be used to understand gene function and thus the biological properties of living organisms. This information can also be used to develop innovative new strategies for chemotherapy employing sequence-specific non-ionic oligonucleoside methylphosphonates. These oligonucleotide analogs, termed Matagen (an acronym for masking tape for gene expression), have the following properties: (1) the negatively charged phosphodiester linkage normally found in nucleic acids is replaced with a non-charged methylphosphonate group which confers increased lipophilicity to the oligomer; (2) the oligomers form stable hydrogen-bonded complexes with complementary nucleic acid sequences and retain the fidelity of Watson-Crick base pairing; (3) the lipophilic oligomers cross the cell membrane and also enter various organs of the body; and (4) the methylphosphonate backbone is inherently resistant to nuclease hydrolysis and thus oligomers are taken up intact from cell culture media and remain stable within the cellular environment. Two general strategies are used to block gene expression by Matagens at the mRNA level in mammalian cells. In the first approach, Matagens complementary to specific sites such as the initiation codon region are used to block translation of mRNA. Thus Matagens specifically inhibit translation of rabbit globin mRNA in cell-free systems and rabbit reticulocytes, and vesicular stomatitis virus protein synthesis, but not cellular protein synthesis, in virus-infected cells. In the second approach, Matagens complementary to splice junctions of precursor mRNAs are used to inhibit splicing. For example, a Matagen complementary to the donor splice junction of simian virus 40 (SV40) large T-antigen mRNA inhibits T-antigen synthesis in SV40-infected cells, and a Matagen complementary to the acceptor splice junction of herpes simplex virus (HSV) immediate early pre-mRNA 4 + 5 inhibits HSV replication in virus-infected cells. Two new types of Matagen, one derivatized with the photoactivatable cross-linking group psoralen and the other derivatized with a hydroxyl radical-producing group, EDTA-Fe(II), have been designed to improve the efficacy of Matagen and to overcome some of the problems inherent in physical binding of Matagens to complementary nucleic acids. The Matagen approach provides a new way to design antiviral and chemotherapeutic agents in a rational manner. It combines nucleic acid chemistry and chemotherapy to form a common basis for drug development as well as to provide fundamental knowledge about organisms and humans.  相似文献   
106.
In order to determine the significance of local oestrogen biosynthesis within the breast, aromatase activity has been measured in adipose tissue from the breasts of women with either benign (n = 36) or malignant breast disease (n = 51). Particulate fractions from all samples possessed aromatase activity, but levels in adipose tissue adjacent to malignant tumours were significantly higher than those in tissue close to benign breast lesions (P less than 0.0001). Elevated aromatase activity in adipose tissue from breast cancer patients may be of importance in view of the central role played by oestrogen in the natural history of breast cancer.  相似文献   
107.
A provisional set of standards of care was derived from a quality assurance strand of a wider research project, which reported the development of evaluation strategies for area integrated mental health services (AIMHS). In contrast to most published standards, they apply to all facets of care in a comprehensive catchment area mental health service, whether clinical or functional, community or hospital based, urban or rural, or managed by the public, private or voluntary sectors. We review briefly existing sets of standards of mental health services and report the process of development of standards of care, each with sub-sets of performance indicators and examples. While the AIMHS standards and a companion quality assurance manual are still undergoing refinement, they offer a guide for mental health professionals to the provision of services, and a checklist to service-users of services that should be available to them at every stage of care in a mental health system.  相似文献   
108.
The lack of a rapid, noninvasive, and accurate method to confirm or rule out prosthetic graft infection continues to constitute a compelling and vexing clinical problem. A host of adjunctive diagnostic techniques has been used in the past, but early promising results subsequently have usually not yielded acceptable sensitivity (reflecting false negatives) and specificity (reflecting false positive) data. White blood cell (WBC) indium 111 scanning has recently been added to this list. The utility and accuracy of 111In WBC scans were assessed by retrospective review of WBC scan results in 70 patients undergoing evaluation for possible prosthetic graft infection over a 7-year period. Operative and autopsy data (mean follow-up, 18 months for survivors with negative scans) were used to confirm the 22 positive, 45 negative, and three equivocal WBC scans. The false positive rate (+/- 70% confidence limits) was 36% +/- 6% (n = 8) among the 22 patients with positive scans (44% +/- 6% [11 of 25] if the three equivocal scans are included as false positive), yielding a specificity of 85% +/- 5% and an overall accuracy rate of 88% +/- 4% (80% +/- 5% and 84% +/- 5%, respectively, if the three equivocal cases are considered as false positive). All three patients with equivocal scans ultimately were judged not to have prosthetic graft infection. As implied by the high accuracy rate, the sensitivity of the test was absolute (100% [14 of 14]); there were no false negative results. (ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
109.
DNase I footprinting and methylation protection studies have been used to analyze the binding of Escherichia coli Trp repressor to the trpR, aroH, and trp operators. The methylation protection assay shows that Trp repressor binds in two successive major grooves of the trpR operator, three successive major grooves of the aroH operator, and four successive major grooves of the trp operator. The simplest model that explains the difference in Trp repressor interaction at the three operators is that the aroH and trp operators are composed of multiple, helically stacked binding sites. When viewed in three dimensions, each site is positioned on a different face of the DNA, and together process up the surface of the DNA helix. Analysis of a deletion derivative of the trp operator supports this model.  相似文献   
110.
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