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   3948篇
  免费   346篇
  国内免费   193篇
耳鼻咽喉   6篇
儿科学   11篇
妇产科学   14篇
基础医学   480篇
口腔科学   44篇
临床医学   437篇
内科学   1039篇
皮肤病学   30篇
神经病学   245篇
特种医学   64篇
外科学   257篇
综合类   674篇
预防医学   414篇
眼科学   16篇
药学   394篇
  1篇
中国医学   293篇
肿瘤学   68篇
  2024年   16篇
  2023年   104篇
  2022年   143篇
  2021年   201篇
  2020年   233篇
  2019年   155篇
  2018年   132篇
  2017年   120篇
  2016年   131篇
  2015年   115篇
  2014年   212篇
  2013年   273篇
  2012年   207篇
  2011年   228篇
  2010年   216篇
  2009年   193篇
  2008年   178篇
  2007年   163篇
  2006年   183篇
  2005年   156篇
  2004年   174篇
  2003年   134篇
  2002年   78篇
  2001年   72篇
  2000年   60篇
  1999年   57篇
  1998年   55篇
  1997年   39篇
  1996年   37篇
  1995年   39篇
  1994年   30篇
  1993年   25篇
  1992年   39篇
  1991年   19篇
  1990年   30篇
  1989年   26篇
  1988年   28篇
  1987年   28篇
  1986年   11篇
  1985年   15篇
  1984年   25篇
  1983年   16篇
  1982年   17篇
  1981年   11篇
  1980年   12篇
  1979年   10篇
  1978年   11篇
  1976年   8篇
  1975年   5篇
  1972年   4篇
排序方式: 共有4487条查询结果,搜索用时 15 毫秒
111.
112.
Background: Mesenchymal stem cells (MSCs) were isolated from various sources, including various types of tumors. However choosing an appropriate isolation method is an important step in obtaining cells with optimal quality and yield in companion with economical considerations. The purpose of this study was to isolate more pure MSCs from human breast tumor tissue by a modified explant culture method.

Methods and Materials: The tumor tissues (n = 8) were cut into 1 to 3-mm cube-like pieces (explant). Each explant was placed in a well of 24-well format plates, cultured in Dulbecco’s Modified Eagle’s medium (DMEM), and maintained at 37°C with 5% humidified incubator. Morphological phenotypes of the cells were surveyed by an inverted microscope and wells with rather homogenous fibroblast-like morphology cell were considered as positive and selected for more expansion and characterization.

Results: A total of 185 wells, 63.7% of wells were positive that were chosen for expansion. Flowcytometry analysis demonstrated that isolated cells were positive for CD73, CD44, CD29, CD105, and CD90 but negative for CD11b, CD45, CD34, and HLA?DR. In addition, cells possessed the capability of multipotential differentiation into osteoblasts and adipocytes.  相似文献   
113.
It is well established that social environment, particularly isolation, has a significant impact on social behaviors and neuroendocrine responses. Estrogen receptor alpha (ERα) expression in limbic structures and associated nuclei is related to the display of social behaviors. We hypothesized that the stress of isolation would cause changes in the pattern of ERα expression in the brain. Using a highly social (typically monogamous and biparental) rodent species, the prairie vole (Microtus ochrogaster), we housed juvenile voles with a sibling, stranger or in isolation for either 4 days or 21 days. Housing manipulations began following weaning from parents and group housed siblings. Rodents may be especially sensitive to manipulations of their social environment during this juvenile period. In particular, female prairie voles are induced ovulators, reliant upon exposure to an unrelated male (male urine) to become reproductively active. ERα immunoreactivity was quantified in the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BST), ventromedial nucleus of the hypothalamus (VMH) and medial amygdala (MeA). Significantly fewer ERα immunoreactive (ERα-ir) cells were labeled in the MPOA and BST of females isolated for 21 days compared with stranger housed females. Non-significant differences were shown in the VMH and MeA of females. No differences were found in voles isolated for 4 days. These results suggest that female prairie voles may be more sensitive than males to manipulations of their social environment during the juvenile period.  相似文献   
114.
115.
Multiple cues, across multiple sensory modalities, are involved in mate choice in a wide range of animal taxa. This multiplicity leads to the prediction that, in adaptive radiations, sexual isolation results from divergence in multiple dimensions. However, difficulties in directly measuring preferences and detecting multiple effects limit our ability to empirically assess the number of independent traits contributing to mate choice and sexual isolation. We present an approach to estimate the dimensionality of sexual isolation using mating trials across groups of related populations. We analyze nine radiations: seven in fruit flies (Drosophila) and one each in salamanders (Desmognathus) and cichlid fishes (Pseudotropheus). We find strong evidence that multiple latent traits—linear combinations of phenotypic traits and preferences—are responsible for the patterns of sexual isolation in all nine radiations but that dimensionality has a strong upper limit. Just two latent traits are implicated in the majority of cases. Mapping along latent trait axes tests predictions of sexual-selection models and allows correlation with specific phenotypic traits and functional components of mate choice. We find support for the role of stabilizing natural selection on the sexually selected (male) traits. In the cichlids, latent-trait axes incorporate male-coloration patterns and exhibit convergence as well as divergence among populations. In the salamanders, temporal patterning in sensory modalities and male vs. female preferences are reflected in different latent-trait axes.  相似文献   
116.
Islet transplantation is a promising therapy used to achieve glycometabolic control in a select subgroup of individuals with type I diabetes. However, features that characterize human islet isolation success prior to transplantation are not standardized and lack validation. We conducted a retrospective analysis of 806 isolation records from 14 pancreas‐processing laboratories, considering variables from relevant studies in the last 15 years. The outcome was defined as postpurification islet equivalent count, dichotomized into yields ≥315 000 or ≤220 000. Univariate analysis showed that donor cause of death and use of hormonal medications negatively influenced outcome. Conversely, pancreata from heavier donors and those containing elevated levels of surface fat positively influence outcome, as did heavier pancreata and donors with normal amylase levels. Multivariable logistic regression analysis identified the positive impact on outcome of surgically intact pancreata and donors with normal liver function, and confirmed that younger donors, increased body mass index, shorter cold ischemia times, no administration of fluid/electrolyte medications, absence of organ edema, use of University of Wisconsin preservation solution and a fatty pancreas improves outcome. In conclusion, this multicenter analysis highlights the importance of carefully reviewing all donor, pancreas and processing parameters prior to isolation and transplantation.  相似文献   
117.
Objective: To compare four vancomycin-containing agar media for the isolation of glycopeptide-resistant enterococci (GRE) from clinical fecal specimens: kanamycin-aesculin-azide (KAA) agar; bile-aesculin-polymixin (BAP) agar; aztreonam-amphotericin blood (CBAA) agar; and neomycin blood (CBN) agar.
Methods: Fecal specimens from 125 patients were inoculated onto each medium. Media were examined for enterococci after incubation for up to 48 h. Enterococci were identified to species level, and glycopeptide phenotypes were determined by measuring minimum inhibitory concentrations of vancomycin and teicoplanin.
Results: GRE were isolated from 44/125 samples. Enterococcus faecalis and Enterococcus faecium isolates, expressing glycopeptide resistance of the VanA or VanB phenotypes, were recovered from 27/33 (82%) specimens on BAP medium, 26/33 (79%) on KAA medium, and 21/33 (64%) on CBN and CBAA media. Enterococcus gallinarum and Enterococcus casseliflavus isolates expressing low-level glycopeptide resistance (VanC phenotype) were recovered from 14/15 (93%) specimens on CBAA medium, 7/15 (47%) on KAA and CBN media, and 6/15 (40%) on BAP medium.
Conclusions: The media tested in this study, with the exception of CBN medium, detected at least 75% of patients colonized by GRE. Further development of BAP, CBAA and KAA media is warranted to improve growth and selectivity.  相似文献   
118.
河北省虫媒病毒分离鉴定   总被引:12,自引:0,他引:12  
目的 研究河北省蚊虫携带虫媒病毒情况。方法 在蚊虫孳生地采集标本液氯保存,按照20—30只/组经无菌处理后研磨,研磨液离心后接种C6/36细胞,连续三代观察致细胞病变情况;对细胞病变阳性的分离物,进行血清学和分子生物学鉴定。结果 在河北省涉县两个村共采集蚊虫1310只,分46组进行处理,共获得13株阳性分离物,其中两株分离物经间接免疫荧光检测提示为甲病毒属成员,用甲病毒属特异性引物RT-PCR扩增阳性,经核酸序列测定证实该序列与Getah病毒(AY702913.1)同源性最高(98%),初步鉴定为Getah病毒,其他病毒分离物尚在鉴定。结论 本研究从河北省蚊虫标本中分离到Getah病毒,这是我国内陆地区首次分离到该病毒。  相似文献   
119.
120.
Connecticut River midges in the genus Axarus are constrained to semi-isolated populations associated with submerged clay exposures, and gene flow between populations is restricted. I sampled larval midges from fifteen spatially separated sites in the Connecticut River and determined karyotypes for 3111 larvae in two closely related species. In one of these species, an undescribed species referred to as Axarus species varvestris, 5chromosomal rearrangements were present as polymorphisms. Four of these are paracentric inversions, and the fifth is a terminal insertion or deletion. I used chromosomal rearrangement frequencies to calculate Neis genetic distance measures for all pairwise population comparisons and I constructed a neighbor-joining phenetic tree for the populations using these distances. Genetic distance between populations of A. sp. varvestris increases with geographic separation, and tree structure indicates that restricted gene flow only occurs in a downstream direction. The effect of unidirectional (downstream)gene flow on population genetic structure in riverine midges is described here for the first time. A genetic break is apparent between populations associated with 12 000-year-ol sediments originating in different ancient lakes. The geological break between lakes also coincides with a break in the species composition of the Axarus populations  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