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   49863篇
  免费   3580篇
  国内免费   20篇
  53463篇
  2024年   53篇
  2023年   188篇
  2022年   592篇
  2021年   956篇
  2020年   592篇
  2019年   732篇
  2018年   1103篇
  2017年   949篇
  2016年   1567篇
  2015年   2455篇
  2014年   2823篇
  2013年   3184篇
  2012年   4158篇
  2011年   3963篇
  2010年   2536篇
  2009年   2328篇
  2008年   3197篇
  2007年   3068篇
  2006年   2681篇
  2005年   2490篇
  2004年   2315篇
  2003年   1972篇
  2002年   1718篇
  2001年   1321篇
  2000年   1247篇
  1999年   1011篇
  1998年   422篇
  1997年   348篇
  1996年   253篇
  1995年   219篇
  1994年   214篇
  1993年   179篇
  1992年   331篇
  1991年   300篇
  1990年   270篇
  1989年   227篇
  1988年   174篇
  1987年   168篇
  1986年   134篇
  1985年   106篇
  1984年   79篇
  1983年   86篇
  1982年   65篇
  1981年   53篇
  1980年   55篇
  1979年   69篇
  1978年   51篇
  1977年   50篇
  1976年   46篇
  1974年   64篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Journal of Industrial Microbiology & Biotechnology - Nocardia spp. are catalase positive, aerobic, and non-motile Gram-positive filamentous bacteria. Many Nocarida spp. have been reported as...  相似文献   
994.
Sleep and Biological Rhythms - Narcoleptics tend to have a low quality of life (QoL). Few studies have compared QoL in narcolepsy against other sleep disorders. The purpose of this study was to...  相似文献   
995.
Toxoplasma gondii causes retinitis and encephalitis. Avoiding targeting by autophagosomes is key for its survival because T. gondii cannot withstand lysosomal degradation. During invasion of host cells, T. gondii triggers epidermal growth factor receptor (EGFR) signalling enabling the parasite to avoid initial autophagic targeting. However, autophagy is a constitutive process indicating that the parasite may also use a strategy operative beyond invasion to maintain blockade of autophagic targeting. Finding that such a strategy exists would be important because it could lead to inhibition of host cell signalling as a novel approach to kill the parasite in previously infected cells and treat toxoplasmosis. We report that T. gondii induced prolonged EGFR autophosphorylation. This effect was mediated by PKCα/PKCβ ? Src because T. gondii caused prolonged activation of these molecules and their knockdown or incubation with inhibitors of PKCα/PKCβ or Src after host cell invasion impaired sustained EGFR autophosphorylation. Addition of EGFR tyrosine kinase inhibitor (TKI) to previously infected cells led to parasite entrapment by LC3 and LAMP‐1 and pathogen killing dependent on the autophagy proteins ULK1 and Beclin 1 as well as lysosomal enzymes. Administration of gefitinib (EGFR TKI) to mice with ocular and cerebral toxoplasmosis resulted in disease control that was dependent on Beclin 1. Thus, T. gondii promotes its survival through sustained EGFR signalling driven by PKCα/β ? Src, and inhibition of EGFR controls pre‐established toxoplasmosis.  相似文献   
996.
Since European settlement, many granivorous birds of northern Australia's savanna landscapes have declined. One such example, the partridge pigeon (Geophaps smithii), has suffered a significant range contraction, disappearing from at least half of its pre‐European range. Multiple factors have been implicated in this decline, including the loss of traditional Aboriginal burning practices, grazing by large exotic herbivores and predation by feral cats (Felis catus). While populations of partridge pigeon on the Tiwi Islands may be particularly important for the long‐term persistence of this species, they too may be at risk of decline. However, as a reliable method to detect this species has not yet been developed and tested, we lack the ability to identify, at an early stage, the species' decline in a given location or region. This severely limits our capacity to make informed management decisions. Here, we demonstrate that the standard camera trapping approach for native mammal monitoring in northern Australia attained an overall probability of detecting partridge pigeon greater than 0.98. We thus provide a robust estimate of partridge pigeon site occupancy (0.30) on Melville Island, the larger of the two main Tiwi Islands. The information presented here for the partridge pigeon represents a critical first step towards the development of optimal monitoring programmes with which to gauge population trajectories, as well as the response to remedial management actions. In the face of ongoing biodiversity loss, such baseline information is vital for management agencies to make informed decisions and should therefore be sought for as many species as possible.  相似文献   
997.
Kim  Ji Yoon  Joo  Gea-Jae 《Limnology》2019,20(1):3-11
Limnology - Maintaining moderate levels of aquatic plant cover in agricultural reservoirs is an important issue because aquatic plant development is closely related to diverse ecosystem functions,...  相似文献   
998.
The purpose of this study is to measure the failure risk of a crown depending on the cusp angle. Three all-ceramic crown models consisting of CH (high incline), CM (middle incline), and CL (low incline) are designed. Stress is applied to the crown with Loading case-1 (top of cusp tip) and Loading case-2 (middle of cusp ridge) with the use of FEA software. In Loading case-1 and case-2, the CH showed the highest Maximum Principal Stress (MPS) while the CL showed the lowest MPS. The cusp angle is an influential factor affecting stress distribution in dental crowns.  相似文献   
999.
Mammalian oocytes lack centrioles but can generate bipolar spindles using several different mechanisms. For example, mouse oocytes have acentriolar microtubule organization centers (MTOCs) that contain many components of the centrosome, and which initiate microtubule polymerization. On the contrary, human oocytes lack MTOCs and the Ran‐mediated mechanisms may be responsible for spindle assembly. Complete knowledge of the different mechanisms of spindle assembly is lacking in various mammalian oocytes. In this study, we demonstrate that both MTOC‐ and Ran‐mediated microtubule nucleation are required for functional meiotic metaphase I spindle generation in porcine oocytes. Acentriolar MTOC components, including Cep192 and pericentrin, were absent in the germinal vesicle and germinal vesicle breakdown stages. However, they start to colocalize to the spindle microtubules, but are absent in the meiotic spindle poles. Knockdown of Cep192 or inhibition of Polo‐like kinase 1 activity impaired the recruitment of Cep192 and pericentrin to the spindles, impaired microtubule assembly, and decreased the polar body extrusion rate. When the RanGTP gradient was perturbed by the expression of dominant negative or constitutively active Ran mutants, severe defects in microtubule nucleation and cytokinesis were observed, and the localization of MTOC materials in the spindles was abolished. These results demonstrate that the stepwise involvement of MTOC‐ and Ran‐mediated microtubule assembly is crucial for the formation of meiotic spindles in porcine oocytes, indicating the diversity of spindle formation mechanisms among mammalian oocytes.  相似文献   
1000.
The lateral resolution of continuous wave (CW) stimulated emission depletion (STED) microscopy is enhanced about 12% by applying annular‐shaped amplitude modulation to the radially polarized excitation beam. A focused annularly filtered radially polarized excitation beam provides a more condensed point spread function (PSF), which contributes to enhance effective STED resolution of CW STED microscopy. Theoretical analysis shows that the FWHM of the effective PSF on the detection plane is smaller than for conventional CW STED. Simulation shows the donut‐shaped PSF of the depletion beam and confocal optics suppress undesired PSF sidelobes. Imaging experiments agree with the simulated resolution improvement.   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