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   41313篇
  免费   3306篇
  国内免费   3072篇
  2024年   16篇
  2023年   465篇
  2022年   556篇
  2021年   2215篇
  2020年   1460篇
  2019年   1833篇
  2018年   1849篇
  2017年   1266篇
  2016年   1776篇
  2015年   2602篇
  2014年   3064篇
  2013年   3286篇
  2012年   3898篇
  2011年   3411篇
  2010年   2150篇
  2009年   1749篇
  2008年   2121篇
  2007年   1876篇
  2006年   1721篇
  2005年   1413篇
  2004年   1165篇
  2003年   1028篇
  2002年   885篇
  2001年   754篇
  2000年   671篇
  1999年   700篇
  1998年   387篇
  1997年   391篇
  1996年   361篇
  1995年   340篇
  1994年   354篇
  1993年   281篇
  1992年   332篇
  1991年   266篇
  1990年   228篇
  1989年   198篇
  1988年   134篇
  1987年   105篇
  1986年   96篇
  1985年   92篇
  1984年   61篇
  1983年   54篇
  1982年   36篇
  1981年   10篇
  1980年   9篇
  1979年   11篇
  1976年   4篇
  1973年   2篇
  1971年   2篇
  1952年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
To evaluate and compare the effect of raw and processed pyritum on tibial defect healing, 32 male Sprague Dawley rats were randomly divided into four groups. After tibial defect, animals were produced and grouped: sham and control group were orally administrated with distilled water (1 mL/100 g), while treatment groups were given aqueous extracts of raw and processed pyritum (1.5 g/kg) for successive 42 days. Radiographic examination showed that bone defect healing effect of the treatment groups was obviously superior compared to that of the control group. Bone mineral density of whole tibia was increased significantly after treating with pyritum. Inductively coupled plasma-optical emission spectrometry showed that the contents of Ca, P, and Mg in callus significantly increased in the treatment groups comparing with the control. Moreover, serological analysis showed that the concentration of serum phosphorus of the treatment groups significantly increased compared with that of the control group. By in vitro study, we have evaluated the effects of drug-containing serum of raw and processed pyritum on osteoblasts. It was manifested that both the drug-containing sera of raw and processed pyritum significantly increased the mRNA levels of alkaline phosphatase and collagen type I. Protein levels of phosphorylated Smad2/3 also increased. The mRNA levels of osteocalcin and transforming growth factor β (TGF-β) type I and II receptors, as well as the protein levels of TGF-β1 in the processed groups, were higher than those in the control. In summary, both raw and processed pyritum-containing sera exhibited positive effects on osteoblasts, which maybe via the TGF-β1/Smad signaling pathway. Notably, the tibia defect healing effect of pyritum was significantly enhanced after processing.  相似文献   
33.
The objective of this investigation was to find a simple method for the production of phenolic-rich products and sugar derivatives via separation of liquefied lignocellulosic materials. After liquefaction, the liquefied products were separated by addition of a sufficient amount of water. It was found that those hydrophobic phenolics could be largely separated from aqueous solutions. Preparation of polyurethane foams using biopolyol and isocyanate was studied. Water was used as an environmentally friendly blowing agent. The factors influencing the cell structure of foams such as catalyst, dosage of blowing agent, and mass ratio of biopolyol to PEG were studied. The microstructure of synthesized foams was characterized by SEM.  相似文献   
34.
Pallister-Killian syndrome (PKS) is a rare sporadic genetic disorder usually caused by mosaicism of an extra isochromosome of 12p (i(12p)). This retrospective study analysed the prenatal ultrasound manifestations and molecular and cytogenetic results of five PKS foetuses. Samples of amniotic fluid and/or cord blood, skin biopsy and placenta were collected. Conventional karyotyping and single nucleotide polymorphism array (SNP array) were performed on all the amniotic fluid or cord blood samples. Copy number variants sequencing (CNV-seq) and fluorescence in situ hybridization (FISH) were also used for the validation for one foetus. All the five foetuses were from pregnancies with advanced parental age. Two foetuses involved structural abnormalities and one foetus had only soft markers, all of which included increased nuchal translucency. The rest two foetuses had normal ultrasounds in the second trimester, which has rarely been reported before. The karyotype revealed typical i(12p) in four cases and a small supernumerary marker chromosome consisting of 12p and 20p in the remaining one case. The proportion of cells with i(12p) ranged from 0 to 100% in cultural cells, while SNP array results suggested 2−4 copies of 12p. For one foetus, metaphase FISH showed normal results, but the interphase FISH suggested cell lines with two, three and four copies of 12p in the amniotic fluid. Advanced parental age may be an important risk factor for PKS, and there were no typical ultrasound manifestations related to PKS. A combination of karyotype analysis and molecular diagnosis is an effective method for the diagnosis of PKS.  相似文献   
35.
Photosynthesis-irradiance (PI) curves are extensively used in field and laboratory research to evaluate the photon-use efficiency of plants. However, most existing models for PI curves focus on the relationship between the photosynthetic rate (Pn) and photosynthetically active radiation (PAR), and do not take account of the influence of environmental factors on the curve. In the present study, we used a new non-competitive inhibited Michaelis-Menten model (NIMM) to predict the co-variation of Pn, PAR, and the relative pollution index (I). We then evaluated the model with published data and our own experimental data. The results indicate that the Pn of plants decreased with increasing I in the environment and, as predicted, were all fitted well by the NIMM model. Therefore, our model provides a robust basis to evaluate and understand the influence of environmental pollution on plant photosynthesis.  相似文献   
36.
Xian-Hui  Dong  Dong-Xue  Ma  Tian-Ci  Zhang  Xiao-Ping  He  Li-Jun  Xu  Ya-Lei  Liu  Hao  Li  Wei-Juan  Gao 《Neurochemical research》2021,46(5):1068-1080
Neurochemical Research - Alzheimer’s disease (AD) process is characterized classically by two hallmark pathologies: β-amyloid (Aβ) plaque deposition and neurofibrillary tangles of...  相似文献   
37.
38.
Lochbihler  Hans  Ye  Yan  Xu  Yishen 《Plasmonics (Norwell, Mass.)》2018,13(6):2161-2167
Plasmonics - We investigate aluminum nanopatch/nanohole arrays surrounded by a dielectric material on plastic substrates for large area color printing. In this specific arrangement, metallic...  相似文献   
39.
40.
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