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   2436篇
  免费   108篇
  国内免费   4篇
化学   1817篇
晶体学   22篇
力学   51篇
数学   133篇
物理学   525篇
  2023年   21篇
  2022年   18篇
  2021年   50篇
  2020年   50篇
  2019年   56篇
  2018年   50篇
  2017年   62篇
  2016年   84篇
  2015年   71篇
  2014年   107篇
  2013年   178篇
  2012年   209篇
  2011年   237篇
  2010年   122篇
  2009年   92篇
  2008年   171篇
  2007年   146篇
  2006年   140篇
  2005年   132篇
  2004年   99篇
  2003年   93篇
  2002年   55篇
  2001年   39篇
  2000年   17篇
  1999年   10篇
  1998年   7篇
  1997年   16篇
  1996年   9篇
  1995年   9篇
  1994年   6篇
  1992年   5篇
  1991年   8篇
  1990年   5篇
  1989年   6篇
  1988年   8篇
  1987年   5篇
  1986年   7篇
  1985年   6篇
  1984年   8篇
  1983年   5篇
  1982年   9篇
  1981年   10篇
  1980年   11篇
  1979年   10篇
  1978年   9篇
  1977年   19篇
  1976年   10篇
  1974年   7篇
  1973年   6篇
  1962年   4篇
排序方式: 共有2548条查询结果,搜索用时 15 毫秒
1.
Journal of Radioanalytical and Nuclear Chemistry - CaCO3 powder containing C-14, which has a long half-life, is generated from the treatment process of spent activated carbons from the air cleaning...  相似文献   
2.
Organotin complexes of Schiff bases (derived from the condensation of hydrazides with salicylaldehyde derivatives) were prepared and their characterization was done using several spectroscopic techniques like FTIR, NMR (1H, 13C, and 119Sn) and mass spectrometry. The spectroscopic data of the ligands and their corresponding complexes revealed that the Schiff bases chelated to the tin metal in a tridentate manner through –ONO atoms (oxygen atom of the hydroxyl group of the salicylaldehydic derivatives, the nitrogen atom of azomethine group, and the oxygen atom of enolic group present in the carboxylic acid hydrazides). Around tin atom pentacoordinated geometry was exhibited. The synthesized ligands and their complexes have been assessed for their biological potency (antibacterial, antifungal and antioxidant using Ciprofloxacin, Fluconazole and Ascorbic acid as reference compounds) and few of the compounds showed optimistic activity. The ligands having electron withdrawing group attached showed greater antimicrobial activity as compared to the other ligands. The complexes showed the better activity than the ligands. The general trend followed by the complexes was diphenyl ?> ?dibutyl ?> ?dimethyl substituted complexes. Compound 11 was the most active against microbes. The antioxidant activity increased with electron donating group. The phenyl substituted complexes showed better activity as compared to the dibutyl and dimethyl substituted complexes. Compound 20 was the best antioxidant.  相似文献   
3.
Onishi  Yoshito  Seo  Yoshiho  Matsuoka  Masaoki  Serikawa  Shigeru  Tsugane  Ken 《Optical Review》2022,29(5):409-419
Optical Review - Machine vision system has great significance for the automatic inspection to enhance unclear defects. For the purpose of the improvement of the recognition accuracy in the...  相似文献   
4.
Journal of Solid State Electrochemistry - The stress variations during polarization of iron thin film electrode in pH 8.4 borate buffer solution have been measured by a cantilever bending...  相似文献   
5.
Journal of Solid State Electrochemistry - Hierarchical nanostructure materials have attracted significant attention due to their fascinating structural features for the application of...  相似文献   
6.
We consider the random‐cluster model (RCM) on with parameters p∈(0,1) and q ≥ 1. This is a generalization of the standard bond percolation (with edges open independently with probability p) which is biased by a factor q raised to the number of connected components. We study the well‐known Fortuin‐Kasteleyn (FK)‐dynamics on this model where the update at an edge depends on the global geometry of the system unlike the Glauber heat‐bath dynamics for spin systems, and prove that for all small enough p (depending on the dimension) and any q>1, the FK‐dynamics exhibits the cutoff phenomenon at with a window size , where λ is the large n limit of the spectral gap of the process. Our proof extends the information percolation framework of Lubetzky and Sly to the RCM and also relies on the arguments of Blanca and Sinclair who proved a sharp mixing time bound for the planar version. A key aspect of our proof is the analysis of the effect of a sequence of dependent (across time) Bernoulli percolations extracted from the graphical construction of the dynamics, on how information propagates.  相似文献   
7.
Cancer immunotherapy with immune checkpoint inhibitors (ICIs) has revolutionized the treatment of advanced cancers. However, the tumor microenvironment (TME) functions as a formidable barrier that severely impairs the efficacy of ICIs. While the crosstalk between tumor vessels and immune cells determines the nature of anti-tumor immunity, it is skewed toward a destructive cycle in growing tumors. First, the disorganized tumor vessels hinder CD8+ T cell trafficking into the TME, disable effector functions, and even kill T cells. Moreover, VEGF, the key driver of angiogenesis, interferes with the maturation of dendritic cells, thereby suppressing T cell priming, and VEGF also induces TOX-mediated exhaustion of CD8+ T cells. Meanwhile, a variety of innate and adaptive immune cells contribute to the malformation of tumor vessels. Protumoral M2-like macrophages as well as TH2 and Treg cells secrete pro-angiogenic factors that accelerate uncontrolled angiogenesis and promote vascular immaturity. While CD8+ T and CD4+ TH1 cells suppress angiogenesis and induce vascular maturation by secreting IFN-γ, they are unable to infiltrate the TME due to malformed tumor vessels. These findings led to preclinical studies that demonstrated that simultaneous targeting of tumor vessels and immunity is a viable strategy to normalize aberrant vascular-immune crosstalk and potentiate cancer immunotherapy. Furthermore, this combination strategy has been evidently demonstrated through recent pivotal clinical trials, granted approval from FDA, and is now being used in patients with kidney, liver, lung, or uterine cancer. Overall, combining anti-angiogenic therapy and ICI is a valid therapeutic strategy that can enhance cancer immunity and will further expand the landscape of cancer treatment.Subject terms: Cancer immunotherapy, Cancer microenvironment, Tumour angiogenesis, Tumour immunology, Targeted therapies  相似文献   
8.
9.
The milk fat globule-EGF-factor 8 protein (MFG-E8) has been identified in various tissues, where it has an important role in intercellular interactions, cellular migration, and neovascularization. Previous studies showed that MFG-E8 is expressed in different cell types under normal and pathophysiological conditions, but its expression in hematopoietic stem cells (HSCs) during hematopoiesis has not been reported. In the present study, we investigated MFG-E8 expression in multiple hematopoietic tissues at different stages of mouse embryogenesis. Using immunohistochemistry, we showed that MFG-E8 was specifically expressed in CD34+ HSCs at all hematopoietic sites, including the yolk sac, aorta-gonad-mesonephros region, placenta and fetal liver, during embryogenesis. Fluorescence-activated cell sorting and polymerase chain reaction analyses demonstrated that CD34+ cells, purified from the fetal liver, expressed additional HSC markers, c-Kit and Sca-1, and that these CD34+ cells, but not CD34 cells, highly expressed MFG-E8. We also found that MFG-E8 was not expressed in HSCs in adult mouse bone marrow, and that its expression was confined to F4/80+ macrophages. Together, this study demonstrates, for the first time, that MFG-8 is expressed in fetal HSC populations, and that MFG-E8 may have a role in embryonic hematopoiesis.  相似文献   
10.
Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red–orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.  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