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   1881篇
  免费   308篇
  国内免费   152篇
化学   1294篇
晶体学   25篇
力学   137篇
综合类   12篇
数学   172篇
物理学   701篇
  2023年   33篇
  2022年   42篇
  2021年   64篇
  2020年   70篇
  2019年   54篇
  2018年   70篇
  2017年   66篇
  2016年   92篇
  2015年   109篇
  2014年   116篇
  2013年   151篇
  2012年   183篇
  2011年   196篇
  2010年   112篇
  2009年   123篇
  2008年   125篇
  2007年   120篇
  2006年   100篇
  2005年   75篇
  2004年   40篇
  2003年   33篇
  2002年   34篇
  2001年   31篇
  2000年   34篇
  1999年   30篇
  1998年   25篇
  1997年   24篇
  1996年   32篇
  1995年   15篇
  1994年   18篇
  1993年   12篇
  1992年   7篇
  1991年   15篇
  1990年   24篇
  1989年   16篇
  1988年   11篇
  1987年   11篇
  1986年   7篇
  1985年   2篇
  1981年   2篇
  1979年   1篇
  1976年   2篇
  1957年   1篇
  1942年   1篇
  1941年   1篇
  1936年   4篇
  1930年   2篇
  1929年   1篇
  1927年   1篇
  1923年   1篇
排序方式: 共有2341条查询结果,搜索用时 25 毫秒
31.
Herein, we bring novel insights into a water-soluble conjugated polyelectlyte by deeply studying its properties in cells and observe fl uorescence enhancement of blue emission and turn-on of long-wavelength emission of PFP in HepG2 cells.  相似文献   
32.
With recent advances in understanding the genomic underpinnings and oncogenic drivers of pathogenesis in different subtypes, it is increasingly clear that proper pretreatment diagnostics are essential for the choice of appropriate treatment options for non-small cell lung cancer (NSCLC). Tumor tissue preservation in optimal cutting temperature (OCT) compound is commonly used in the surgical suite. However, proteins recovered from OCT-embedded specimens pose a challenge for LC-MS/MS experiments, due to the large amounts of polymers present in OCT. Here we present a simple workflow for whole proteome analysis of OCT-embedded NSCLC tissue samples, which involves a simple trichloroacetic acid precipitation step. Comparisons of protein recovery between frozen versus OCT-embedded tissue showed excellent consistency with more than 9200 proteins identified. Using an isobaric labeling strategy, we quantified more than 5400 proteins in tumor versus normal OCT-embedded core needle biopsy samples. Gene ontology analysis indicated that a number of proliferative as well as squamous cell carcinoma (SqCC) marker proteins were overexpressed in the tumor, consistent with the patient’s pathology based diagnosis of “poorly differentiated SqCC”. Among the most downregulated proteins in the tumor sample, we noted a number of proteins with potential immunomodulatory functions. Finally, interrogation of the aberrantly expressed proteins using a candidate approach and cross-referencing with publicly available databases led to the identification of potential druggable targets in DNA replication and DNA damage repair pathways. We conclude that our approach allows LC-MS/MS proteomic analyses on OCT-embedded lung cancer specimens, opening the way to bring powerful proteomics into the clinic.
Graphical Abstract ?
  相似文献   
33.
In this paper, N-(2-[18F]fluoropropionyl)-β-glutamic acid 8 ([18F]FP-β-Glu), a new N-substituted 18F-labeled amino acid tracer, was synthesized from the precursor 4 (diethyl 3-(2-bromopropanamido)pentanedioate) via a two-step reaction on the modified FDG synthesizer. The radiochemical yield was 20 ± 5% (n = 10, decay-corrected) from [18F]fluoride within 40 min, the radiochemical purity was 98%. Moreover, microPET studies showed that [18F]FP-β-Glu 8 exhibited rapid tumor uptake and good tumor-to-lung ratio in SPC-A-1 tumor-bearing mice. A high accumulation of radioactivity was found in the kidneys and bladder, which suggested that the tracer was mainly eliminated through the urinary system.  相似文献   
34.
过一硫酸盐催化活化技术因其可产生强氧化性活性氧化物种,可快速氧化降解并矿化有机污染物的优异性能而备受关注.本文成功制备了亚微米级Cu0/Fe3O4复合物,发现其能多相催化过一硫酸盐产生单线态氧降解有机污染物.首先,以CuCl2·2H2O,FeCl2·4H2O和FeCl3·6H2O为铜源和铁源,水合肼为还原剂,采用水热法在180oC反应24 h制备了亚微米级磁性Cu0/Fe3O4复合物.表征结果显示,所制材料为Cu0和Fe3O4的复合物,颗粒大小约为220 nm;单一相Cu0和Fe3O4晶体粒径分别为33.8和106.2 nm,而Cu0/Fe3O4复合物中Cu0和Fe3O4晶体粒径分别减为20.8和31.9 nm.这表明Cu0和Fe3O4复合降低了Cu0和Fe3O4晶体粒径,有利于Cu0和Fe3O4的分散.BET测试结果表明,Cu0/Fe3O4复合物比表面积为4.6 m2/g,与Cu0颗粒的(4.2 m2/g)相当,但远小于Fe3O4的(15.6 m2/g).制备的Cu0/Fe3O4复合物可有效催化过一硫酸盐产生单线态氧降解罗丹明B、亚甲基蓝、金橙II、苯酚和对氯酚.当Cu0/Fe3O4复合物的用量为0.1 g/L,过一硫酸盐浓度为0.5 mmol/L和初始pH为7时,Cu0/Fe3O4复合物可在30 min内完全降解20μmol/L的罗丹明B、亚甲基蓝、金橙II以及0.1 mmol/L的苯酚和对氯酚.对比试验显示,在相同条件下,Cu0和Fe3O4颗粒分别可以降解28%和20%的罗丹明B.这表明Cu0/Fe3O4复合物中的Cu0和Fe3O4晶体在催化过一硫酸盐降解污染物的反应中具有协同作用,这主要来源于Cu0/Fe3O4复合物中Cu0和Fe3O4的晶体粒径变小和更好的分散.采用分光光度法测定了降解反应液中铜和铁离子的溶出量.当Cu0/Fe3O4复合物的用量为0.1 g/L,过一硫酸盐浓度为0.5 mmol/L和初始pH为7时,反应60 min后,降解液中铜和铁离子的浓度分别为0.22和0.1 mg/L,仅占复合物中总铜和总铁量的1.1%和0.2%,表明Cu0/Fe3O4复合物具有较强的化学稳定性.所制Cu0/Fe3O4复合物具有超顺磁性,借助磁场实现快速分离回收,可循环利用五次,表明其优越的催化稳定性.通过加入乙醇和叠氮化钠,考察了Cu0/Fe3O4复合物催化活化过一硫酸盐体系中的活性氧化物种.发现100 mmol/L乙醇的加入对污染物的降解无明显影响,而加入同等量的叠氮化钠可完全抑制污染物的降解,表明Cu0/Fe3O4复合物催化活化过一硫酸盐产生的主要活性氧物种为单线态氧.采用电子顺磁共振谱进一步证实了单线态氧的生成.基于以上研究,Cu0/Fe3O4复合物催化活化过一硫酸盐的机理为Cu0/Fe3O4作为一个电子媒介加速过一硫酸盐和污染物之间的电子转移,从而导致污染物被快速降解.该反应机理不同于常见的金属催化过一硫酸盐产生硫酸根和羟自由基的反应机理.我们推测,电导性优良的Cu0在此催化反应中起着关键性作用.本催化方法可作为一种绿色的氧化技术用于环境污染物的氧化降解处理.  相似文献   
35.
The carbon nanotubes/TiO2 (CNTs/TiO2) composite photocatalysts composed of TiO2 nanoparticles and multiwalled carbon nanotubes (CNTs) were prepared by a facile hydrothermal method. The photocatalysts were characterized by a range of analytical techniques including X-ray powder diffraction, field emission scanning electron microscope, thermal gravimetric analysis and UV–Vis optical absorption spectra, etc. The amount of TiO2 nanoparticles growing on CNTs could be tuned by adjusting the dosage of precursor in the reaction solution. Both the adsorptivity and photocatalytic activities of pure CNTs, pure TiO2, and the CNTs/TiO2 nanocomposites were tested by the removal of methylene blue from water in dark and under a simulated sunlight, respectively. By comparison, the improved photocatalytic activity of the CNTs/TiO2 nanocomposite is mainly due to that the CNTs can disperse the active component of TiO2 nanoparticles, provide a larger the specific surface area, as well as act as an electron sink to accelerate the separation of the photogenerated charges.  相似文献   
36.
In this paper, two susceptible‐infected‐susceptible epidemic models with varying total population size, continuous vaccination, and state‐dependent pulse vaccination are formulated to describe the transmission of infectious diseases, such as diphtheria, measles, rubella, pertussis, and so on. The first model incorporates the proportion of infected individuals in population as monitoring threshold value; we analytically show the existence and orbital asymptotical stability of positive order‐1 periodic solution for this control model. The other model determines control strategy by monitoring the proportion of susceptible individuals in population; we also investigate the existence and global orbital asymptotical stability of the disease‐free periodic solution. Theoretical results imply that the disease dies out in the second case. Finally, using realistic parameter values, we carry out some numerical simulations to illustrate the main theoretical results and the feasibility of state‐dependent pulse control strategy.  相似文献   
37.
38.
Coumarins possesses immeasurable antitumor potential with minimum side effects depending on the substitutions on the basic nucleus, which exhibits great prospects for antitumor drug development. In an attempt to develop novel antitumor candidates, a series of coumarin sulfonamides and amides derivatives were designed and synthetized. The majority of these derivatives showed good cytotoxic activity against MDA-MB-231 and KB cell lines, among which compound 9c was the most potent against MDA-MB-231 cells, with IC50 value of 9.33 μM, comparable to 5-fluorouracil. Further investigation revealed that compound 9c had versatile properties against tumors, including inhibition of cell migration and invasion as well as inducing apoptosis. Reactive oxygen species (ROS) assay and western blotting analysis suggested that compound 9c promoted cancer cell apoptosis by increasing ROS levels and upregulating the expression of caspase-3 in MDA-MB-231 cells. These results indicated that compound 9c could be promising lead compound for further antitumor drug research.  相似文献   
39.
Nie  Weidong  Fan  Wenlin  Jiang  Anqi  Wu  Guanghao  Liu  Houli  Huang  Li-Li  Xie  Hai-Yan 《中国科学:化学(英文版)》2021,64(11):1999-2009
Science China Chemistry - Insufficient tumor tropism, MHC class I molecules (MHC-I) defects of tumor cells, and immunosuppressive tumor micro-environment (TME) seriously imperil the efficacy of...  相似文献   
40.
近年来,具有聚集诱导发光(aggregation-induced emission,AIE)特性的化合物由于在聚集态或固态发光量子效率较高而受到很多关注.含氟的功能化合物,由于氟原子的存在,往往具有独特的结构和物理、化学及生物学性质.根据中心金属和配体的种类,汇总了具有A IE性质的且含有氟代配体的有机金属配合物的研究进展.这些含氟有机金属配合物主要是铱、铂、金配合物,在发光器件、化学传感、细胞成像、数据存储等方面具有潜在应用.还简要讨论了相关研究的发展前景.  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