全文获取类型
收费全文 | 1073151篇 |
免费 | 83648篇 |
国内免费 | 2769篇 |
专业分类
耳鼻咽喉 | 15119篇 |
儿科学 | 30123篇 |
妇产科学 | 29089篇 |
基础医学 | 150269篇 |
口腔科学 | 29503篇 |
临床医学 | 96947篇 |
内科学 | 208497篇 |
皮肤病学 | 20005篇 |
神经病学 | 91391篇 |
特种医学 | 44347篇 |
外国民族医学 | 184篇 |
外科学 | 169096篇 |
综合类 | 26917篇 |
现状与发展 | 3篇 |
一般理论 | 432篇 |
预防医学 | 82005篇 |
眼科学 | 25583篇 |
药学 | 78584篇 |
1篇 | |
中国医学 | 1881篇 |
肿瘤学 | 59592篇 |
出版年
2021年 | 9804篇 |
2019年 | 9761篇 |
2018年 | 12784篇 |
2017年 | 9818篇 |
2016年 | 10977篇 |
2015年 | 12839篇 |
2014年 | 18607篇 |
2013年 | 26919篇 |
2012年 | 38126篇 |
2011年 | 39834篇 |
2010年 | 22942篇 |
2009年 | 21514篇 |
2008年 | 36875篇 |
2007年 | 39452篇 |
2006年 | 39013篇 |
2005年 | 38507篇 |
2004年 | 37169篇 |
2003年 | 35062篇 |
2002年 | 33739篇 |
2001年 | 37590篇 |
2000年 | 37796篇 |
1999年 | 32708篇 |
1998年 | 11704篇 |
1997年 | 10499篇 |
1996年 | 10161篇 |
1995年 | 9572篇 |
1994年 | 9063篇 |
1992年 | 27551篇 |
1991年 | 26912篇 |
1990年 | 26324篇 |
1989年 | 25347篇 |
1988年 | 23825篇 |
1987年 | 23428篇 |
1986年 | 22315篇 |
1985年 | 21720篇 |
1984年 | 17199篇 |
1983年 | 14711篇 |
1982年 | 9765篇 |
1981年 | 9068篇 |
1979年 | 17156篇 |
1978年 | 12584篇 |
1977年 | 10588篇 |
1976年 | 9710篇 |
1975年 | 10438篇 |
1974年 | 12913篇 |
1973年 | 12374篇 |
1972年 | 11701篇 |
1971年 | 10825篇 |
1970年 | 10316篇 |
1969年 | 9987篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Patrick W. Keeley Mikayla C. Lebo Jordan D. Vieler Jason J. Kim Ace J. St. John Benjamin E. Reese 《The Journal of neuroscience》2021,41(1):103
Amacrine cells of the retina are conspicuously variable in their morphologies, their population demographics, and their ensuing functions. Vesicular glutamate transporter 3 (VGluT3) amacrine cells are a recently characterized type of amacrine cell exhibiting local dendritic autonomy. The present analysis has examined three features of this VGluT3 population, including their density, local distribution, and dendritic spread, to discern the extent to which these are interrelated, using male and female mice. We first demonstrate that Bax-mediated cell death transforms the mosaic of VGluT3 cells from a random distribution into a regular mosaic. We subsequently examine the relationship between cell density and mosaic regularity across recombinant inbred strains of mice, finding that, although both traits vary across the strains, they exhibit minimal covariation. Other genetic determinants must therefore contribute independently to final cell number and to mosaic order. Using a conditional KO approach, we further demonstrate that Bax acts via the bipolar cell population, rather than cell-intrinsically, to control VGluT3 cell number. Finally, we consider the relationship between the dendritic arbors of single VGluT3 cells and the distribution of their homotypic neighbors. Dendritic field area was found to be independent of Voronoi domain area, while dendritic coverage of single cells was not conserved, simply increasing with the size of the dendritic field. Bax-KO retinas exhibited a threefold increase in dendritic coverage. Each cell, however, contributed less dendrites at each depth within the plexus, intermingling their processes with those of neighboring cells to approximate a constant volumetric density, yielding a uniformity in process coverage across the population.SIGNIFICANCE STATEMENT Different types of retinal neuron spread their processes across the surface of the retina to achieve a degree of dendritic coverage that is characteristic of each type. Many of these types achieve a constant coverage by varying their dendritic field area inversely with the local density of like-type neighbors. Here we report a population of retinal amacrine cells that do not develop dendritic arbors in relation to the spatial positioning of such homotypic neighbors; rather, this cell type modulates the extent of its dendritic branching when faced with a variable number of overlapping dendritic fields to approximate a uniformity in dendritic density across the retina. 相似文献
3.
4.
5.
N. Cody Schaal Raushan A. Salaam Michael Stevens Alex Stubner 《Journal of occupational and environmental hygiene》2019,16(5):329-335
The purpose of this investigation was to characterize noise levels in spaces designated as “effective quiet” areas on a U.S. Navy aircraft carrier. Noise dosimetry samples were collected in 15 designated spaces, representing 15 noise measurements, while at-sea during airwing carrier qualifications. Equivalent sound level (Leq) measurements were collected during flight operations (Leq (flt ops)), non-flight operations (Leq (non-flt ops)), and over 24-hr periods (Leq (24-hr)). These data were compared to the 70 dBA American Conference of Governmental Industrial Hygienists (ACGIH®) Threshold Limit Value (TLV®) for “effective quiet” areas intended for temporary threshold shift recovery when personnel live and work in a potentially noise hazardous environment for periods greater than 24?hr. The monitored areas were selected based on personnel occupancy/use during off-duty time periods. Areas were classified by either (1) leisure areas that included mess (eating areas), gyms, lounges, an internet cafe, and the fantail social area or (2) berthing (sleeping) areas. The Leq measurements in decibels “A” weighted (dBA) were compared to determine significant differences between Leq (flt ops), Leq (non-flt ops), and Leq (24-hr) and were compared between leisure area and berthing area. Measured noise levels according to time period ranged as follows: (1) Leq (24-hr): 70.8–105.4 dBA; (2) Leq (flt ops): 70–101.2 dBA; and (3) Leq (non-flt ops): 39.4–104.6 dBA. All area measurements over the 24-hr period and during flight operations and 46.7% of the areas during the non-flight operation time period exceeded the “effective quiet” 70 dBA ACGIH TLV. Mean Leqs were 15 dBA higher during flight operations compared to non-flight operations in “effective quiet” areas (p?=?0.001). The Leqs in leisure areas were significantly higher than berthing areas by approximately 21 dBA during non-flight operation periods (p?=?0.001). Results suggest noise levels in “effective quiet” areas frequented by aircraft carrier personnel during off-duty hours when at-sea may inhibit auditory recovery from occupational noise exposures that occur on-duty. 相似文献
6.
Madan M. Rehani Emily R. Melick Raza M. Alvi Ruhani Doda Khera Salma Batool-Anwar Tomas G. Neilan Michael Bettmann 《European radiology》2020,30(4):1839-1846
To determine percent of patients without malignancy and ≤ 40 years of age with high cumulative radiation doses through recurrent CT exams and assess imaging appropriateness. From the cohort of patients who received cumulative effective dose (CED) of ≥ 100 mSv over a 5-year period, a sub-set was identified with non-malignant disease. The top 50 clinical indications leading to multiple CTs were determined. Clinical decision support (CDS) system scores were analyzed using a widely adopted standard of 1–3 (red) as “not usually appropriate,” 4–6 (yellow) “may or may not be appropriate,” and 7–9 (green) “usually appropriate.” Clinicians reviewed patient records to assess compliance with appropriate use criteria (AUC). 9.6% of patients in our series were with non-malignant conditions and 1.4% with age ≤ 40 years. CDS scores (rounded) were 2% red, 38% yellow, 27% green, and 33% unscored CTs. Clinical society guidelines for CT exams, wherever available, were followed in 87.5 to 100% of cases. AUCs were not available for several clinical indications as also referral guidelines for serial CT imaging. More than half of CT exams were unrelated to follow-up of a primary chronic disease. We are faced with a situation wherein patients in age ≤ 40 years require or are thought to require many CT exams over the course of a few years but the radiation risk creates concern. There is a fair number of conditions for which AUC are not available. Suggested solutions include development of CT scanners with lesser radiation dose and further development of appropriateness criteria. 相似文献
7.
8.
9.
10.