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   21794篇
  免费   1594篇
  国内免费   87篇
耳鼻咽喉   185篇
儿科学   730篇
妇产科学   644篇
基础医学   3260篇
口腔科学   478篇
临床医学   2386篇
内科学   4316篇
皮肤病学   642篇
神经病学   2092篇
特种医学   550篇
外国民族医学   2篇
外科学   2227篇
综合类   208篇
一般理论   21篇
预防医学   2339篇
眼科学   358篇
药学   1302篇
中国医学   45篇
肿瘤学   1690篇
  2024年   41篇
  2023年   295篇
  2022年   533篇
  2021年   1006篇
  2020年   615篇
  2019年   811篇
  2018年   869篇
  2017年   663篇
  2016年   743篇
  2015年   767篇
  2014年   947篇
  2013年   1211篇
  2012年   1770篇
  2011年   1826篇
  2010年   947篇
  2009年   823篇
  2008年   1291篇
  2007年   1271篇
  2006年   1103篇
  2005年   1066篇
  2004年   994篇
  2003年   872篇
  2002年   772篇
  2001年   176篇
  2000年   166篇
  1999年   160篇
  1998年   162篇
  1997年   131篇
  1996年   99篇
  1995年   93篇
  1994年   92篇
  1993年   75篇
  1992年   80篇
  1991年   88篇
  1990年   71篇
  1989年   66篇
  1988年   45篇
  1987年   54篇
  1986年   46篇
  1985年   54篇
  1984年   47篇
  1983年   47篇
  1982年   32篇
  1981年   33篇
  1980年   30篇
  1979年   25篇
  1978年   42篇
  1977年   31篇
  1974年   32篇
  1973年   35篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Delaying assessment until emergence from post-traumatic amnesia increases completion rates, but this practice causes variable time delays from the date of injury to testing, which can complicate the interpretation of research findings. In the current study, the performance of 105 head injury survivors on simple tests of language comprehension and attention was used to predict global outcome. It was hypothesized that 1 month performance on these measures would aid in the prediction of Disability Rating Scale (DRS) and Glasgow Outcome Scale (GOS) scores collected at 6 months post injury. Only raw scores on the modified Test of Complex Ideational Material accounted for a significant amount of the variance in DRS scores (4.4%) above that accounted for by age, education, Glasgow Coma Scale score, and pupil response. However, testability at 1 month post injury on all four tests consistently accounted for a larger portion of the variance in DRS scores (10.1-13.2%) and significantly improved prediction of GOS scores. Galveston Orientation and Amnesia Test scores collected at 1 month post injury accounted for substantially less variance in DRS scores (7.7-8.4%). Neuropsychological data, including the testability of patients, collected uniformly at 1 month following injury can contribute to the prediction of global outcome.  相似文献   
73.
Knudson's two-hit hypothesis postulates that genetic alterations in both alleles are required for the inactivation of tumor-suppressor genes. Genetic alterations include small or large deletions and mutations. Over the past years, it has become clear that epigenetic alterations such as DNA methylation are additional mechanisms for gene silencing. Restriction Landmark Genomic Scanning (RLGS) is a two-dimensional gel electrophoresis that assesses the methylation status of thousands of CpG islands. RLGS has been applied successfully to scan cancer genomes for aberrant DNA methylation patterns. So far, the majority of this work was done using NotI as the restriction landmark site. Here, we describe the development of RLGS using AscI as the restriction landmark site for genome-wide scans of cancer genomes. The availability of AscI as a restriction landmark for RLGS allows for scanning almost twice as many CpG islands in the human genome compared with using NotI only. We describe the development of an AscI-EcoRV boundary library that supports the cloning of novel methylated genes. Feasibility of this system is shown in three tumor types, medulloblastomas, lung cancers, and head and neck cancers. We report the cloning of 178 AscI RLGS fragments via two methods by use of this library.  相似文献   
74.
Nuclear matrix attachment regions (MARs) are regulatory DNA sequences that are important for higher-order chromatin organization, long-range enhancer function, and extension of chromatin modifications. Here we characterize a novel cell type-specific MAR-binding protein, SATB2, which binds to the MARs of the endogenous immunoglobulin micro locus in pre-B cells and enhances gene expression. We found that SATB2 differs from the closely related thymocyte-specific protein SATB1 by modifications of two lysines with the small ubiquitive related modifier (SUMO), which are augmented specifically by the SUMO E3 ligase PIAS1. Mutations of the SUMO conjugation sites of SATB2 enhance its activation potential and association with endogenous MARs in vivo, whereas N-terminal fusions with SUMO1 or SUMO3 decrease SATB2-mediated gene activation. Sumoylation is also involved in targeting SATB2 to the nuclear periphery, raising the possibility that this reversible modification of a MAR-binding protein may contribute to the modulation of subnuclear DNA localization.  相似文献   
75.
Monoclonal antibodies were raised against the surface of epimastigotes and metacylic trypomastigotes of Trypanosoma cruzi, as shown by electron microscopy, agglutination, and immunofluorescence. The antibodies were stage specific but not strain specific. A deleterious effect of the antibodies on T. cruzi culture forms was shown by the drastic reduction of parasite motility and incorporation of nucleic acid precursors. Some fraction of the parasite population, however, was viable and replicated and infected mouse macrophages in culture. The antibodies were found to also mediate complement-induced lysis of culture forms of T. cruzi.  相似文献   
76.
77.
Cell extract-derived differentiation of embryonic stem cells   总被引:1,自引:0,他引:1  
Various means have been used to encourage the differentiation of embryonic stem cells (ESCs) toward specific lineages, including growth factor administration, genetic modification, and coculture with relevant cells/tissues. Cell extract-based reprogramming has recently been used to derive mature cells from nonrelated phenotypes. In this communication, we tested whether this in vitro reprogramming approach can be used to direct ESC differentiation. Permeabilized murine ESCs exposed to extracts of murine type II pneumocytes showed increased expression of surfactant protein C and its corresponding mRNA, reflecting enhanced differentiation of pneumocytes. Subsequent differentiation to a type I phenotype was demonstrated by expression of aquaporin 5. Pneumocyte formation occurred quicker than with growth factor-induced differentiation. Our findings establish that ESCs can be differentiated in vitro using cellular extracts. This model provides a tool for analysis of the key factors involved in the differentiation of ESCs to type II pneumocytes.  相似文献   
78.
Adverse drug reactions and ineffective drug treatment are responsible for a large health care burden. Considerable variability in drug response makes the prediction of the individual reaction difficult. Pharmacogenetics can help to individualize drug treatment in accordance with the genetic make-up of the patient. Drug response is best understood as a complex interplay between pharmacokinetics, pharmacodynamics, and other disease-associated factors. There are a large number of genetic variants in the enzymes of phase I and phase II drug metabolism, in drug transporters, and drug targets, all of which account for differences in drug response. The polymorphisms in the cytochrome P450 enzyme system have been investigated most extensively. Genotype-based dose adjustment which should ensure "bioequivalent" drug concentrations in all patients has been derived from pharmacokinetic parameters, but this approach will have to be verified in prospective studies. Drug transport has recently been recognized as a further crucial determinant in pharmacokinetics. The effect of genetics on disease susceptibility and drug treatment has been studied quite extensively; however, hardly any of this progress is at present reflected in routine health care. The integration of pharmacogenetic factors in clinical trials requires novel considerations for study design and data interpretation. It is to be hoped that the new science bioinformatics will (a) help us identify the contribution of genetics to disease and treatment response and will (b) create data-processing devices which help the physician in the face of the enormously expanding scientific knowledge in selecting the best individually adapted treatment for the patient.  相似文献   
79.
80.
Diabetic neuropathy affects both sensory and autonomic peripheral nerve fibres. Vasoactive intestinal polypeptide (VIP) is present in autonomic fibres which modulate sweat secretion, while calcitonin gene-related peptide (CGRP) is localized to cutaneous sensory fibres. In this study, immunohistochemistry and image analysis were used to assess changes of VIP and CGRP, and of the pan-neuronal marker protein gene-product (PGP)-9.5, in skin biopsies of 18 patients affected by type 1 diabetes (age range 18–46 years) and from seven aged-matched controls. Patients were divided into three groups: group 1 (n=6), with diabetes for 6 months to 3 years; group 2 (n=5), with the disease for 5–10 years; and group 3 (n=7), with diabetes for more than 10 years. VIP immunoreactivity (IR) and PGP-9.5-IR were significantly reduced around sweat glands (P <0.005) in groups 2 and 3. Epidermal CGRP-IR and PGP-9.5-IR were significantly reduced in group 3 (P <0.05). Twenty-eight per cent (5/18) of all patients showed high VIP-IR around sweat glands (>95 per cent confidence limits of controls) and all of these patients had diabetes for less than 3 years. Conversely, 55 per cent (10/18) of patients had low VIP-IR (<5 per cent confidence limit of controls). The latter, compared with the former, showed a significantly longer duration of diabetes (Fisher exact test P=0·002), presence of clinical autonomic neuropathy (Fisher exact test P=0.04), and a reduced sural nerve conduction velocity (Fisher exact test P=0.04). These results suggest that quantitative immunohistochemical analysis of peptide-containing cutaneous nerves allows an objective evaluation of nerve fibre alterations at early stages of diabetes than is currently possible with neurophysiological functional tests.  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