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   1791670篇
  免费   134805篇
  国内免费   2583篇
耳鼻咽喉   23016篇
儿科学   59790篇
妇产科学   49607篇
基础医学   248740篇
口腔科学   48841篇
临床医学   154142篇
内科学   348066篇
皮肤病学   34937篇
神经病学   147517篇
特种医学   74293篇
外国民族医学   475篇
外科学   276131篇
综合类   42429篇
现状与发展   3篇
一般理论   551篇
预防医学   141790篇
眼科学   39301篇
药学   131754篇
  2篇
中国医学   3601篇
肿瘤学   104072篇
  2018年   37146篇
  2017年   29552篇
  2016年   33721篇
  2015年   16141篇
  2014年   21637篇
  2013年   32496篇
  2012年   49804篇
  2011年   66464篇
  2010年   45322篇
  2009年   37386篇
  2008年   64095篇
  2007年   69550篇
  2006年   46992篇
  2005年   47836篇
  2004年   48728篇
  2003年   48377篇
  2002年   45307篇
  2001年   76163篇
  2000年   79058篇
  1999年   66716篇
  1998年   18079篇
  1997年   16708篇
  1996年   16507篇
  1995年   16222篇
  1994年   15295篇
  1993年   14406篇
  1992年   55557篇
  1991年   53950篇
  1990年   52744篇
  1989年   50959篇
  1988年   47339篇
  1987年   46684篇
  1986年   44388篇
  1985年   42946篇
  1984年   32122篇
  1983年   27646篇
  1982年   16246篇
  1981年   14460篇
  1979年   30573篇
  1978年   21135篇
  1977年   17789篇
  1976年   16773篇
  1975年   17586篇
  1974年   21530篇
  1973年   20691篇
  1972年   18856篇
  1971年   17771篇
  1970年   16323篇
  1969年   15310篇
  1968年   13975篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We report on a child with several café au lait spots in association with a lumbar lipomeningomyelocele as an apparently new association. Cutaneous markers, the identification of which plays a crucial role in the early diagnosis and management of spinal malformations, can accompany occult spinal dysraphism. Herein we report a case of lumbar lipomeningomyelocele associated with an overlying café au lait spot that served as a marker of occult spinal dysraphism. The patient also had segmental café au lait spots on the face, making the association unique.  相似文献   
42.
43.
Magnetic field generated by neuronal activity could alter magnetic resonance imaging (MRI) signals but detection of such signal is under debate. Previous researches proposed that magnitude signal change is below current detectable level, but phase signal change (PSC) may be measurable with current MRI systems. Optimal imaging parameters like echo time, voxel size and external field direction, could increase the probability of detection of this small signal change. We simulate a voxel of cortical column to determine effect of such parameters on PSC signal. We extended a laminar network model for somatosensory cortex to find neuronal current in each segment of pyramidal neurons (PN). 60,000 PNs of simulated network were positioned randomly in a voxel. Biot–savart law applied to calculate neuronal magnetic field and additional phase. The procedure repeated for eleven neuronal arrangements in the voxel. PSC signal variation with the echo time and voxel size was assessed. The simulated results show that PSC signal increases with echo time, especially 100/80 ms after stimulus for gradient echo/spin echo sequence. It can be up to 0.1 mrad for echo time = 175 ms and voxel size = 1.48 × 1.48 × 2.18 mm3. With echo time less than 25 ms after stimulus, it was just acquired effects of physiological noise on PSC signal. The absolute value of the signal increased with decrease of voxel size, but its components had complex variation. External field orthogonal to local surface of cortex maximizes the signal. Expected PSC signal for tactile detection in the somatosensory cortex increase with echo time and have no oscillation.  相似文献   
44.
45.
Bipolar disorder (BD) is a common psychiatric mood disorder affecting more than 1-2% of the general population of different European countries. Unfortunately, there is no objective laboratory-based test to aid BD diagnosis or monitor its progression, and little is known about the molecular basis of BD. Here, we performed a comparative proteomic study to identify differentially expressed plasma proteins in various BD mood states (depressed BD, manic BD, and euthymic BD) relative to healthy controls. A total of 10 euthymic BD, 20 depressed BD, 15 manic BD, and 20 demographically matched healthy control subjects were recruited. Seven high-abundance proteins were immunodepleted in plasma samples from the 4 experimental groups, which were then subjected to proteome-wide expression profiling by two-dimensional electrophoresis and matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight tandem mass spectrometry. Proteomic results were validated by immunoblotting and bioinformatically analyzed using MetaCore. From a total of 32 proteins identified with 1.5-fold changes in expression compared with healthy controls, 16 proteins were perturbed in BD independent of mood state, while 16 proteins were specifically associated with particular BD mood states. Two mood-independent differential proteins, apolipoprotein (Apo) A1 and Apo L1, suggest that BD pathophysiology may be associated with early perturbations in lipid metabolism. Moreover, down-regulation of one mood-dependent protein, carbonic anhydrase 1 (CA-1), suggests it may be involved in the pathophysiology of depressive episodes in BD. Thus, BD pathophysiology may be associated with early perturbations in lipid metabolism that are independent of mood state, while CA-1 may be involved in the pathophysiology of depressive episodes.  相似文献   
46.
47.
48.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  相似文献   
49.
50.
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