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   15691篇
  免费   609篇
  国内免费   153篇
化学   8108篇
晶体学   86篇
力学   1331篇
数学   3119篇
物理学   3809篇
  2024年   5篇
  2023年   111篇
  2022年   243篇
  2021年   314篇
  2020年   644篇
  2019年   425篇
  2018年   802篇
  2017年   931篇
  2016年   794篇
  2015年   795篇
  2014年   1233篇
  2013年   1877篇
  2012年   1280篇
  2011年   1168篇
  2010年   1081篇
  2009年   901篇
  2008年   772篇
  2007年   686篇
  2006年   496篇
  2005年   357篇
  2004年   288篇
  2003年   248篇
  2002年   203篇
  2001年   274篇
  2000年   117篇
  1999年   236篇
  1998年   23篇
  1997年   21篇
  1996年   13篇
  1995年   10篇
  1994年   7篇
  1993年   11篇
  1992年   4篇
  1991年   1篇
  1990年   1篇
  1986年   3篇
  1985年   2篇
  1984年   3篇
  1983年   1篇
  1982年   5篇
  1981年   12篇
  1980年   5篇
  1979年   13篇
  1978年   9篇
  1977年   5篇
  1976年   11篇
  1975年   3篇
  1974年   4篇
  1973年   4篇
  1935年   1篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
Journal of Fluorescence - Malachite green (MG) is a dye that has been presented to use as photosensitizers for photodynamic therapy (PDT). Nonlinear absorption coefficient (β) and nonlinear...  相似文献   
2.
In this work, a green technique for preparing TbFeO3/CuO was reported by employing Crataegus and Lantana Camara leaves as fuel and alkalizing agents, respectively. The new sensor based on the perovskite-type nanocomposite was employed as a sensitive and selective platform to detect Pb(II), Zn(II) and Cd(II) simultaneously. TbFeO3/CuO/Carbon paste electrode (CPE) exhibited a large specific surface area and great electrical conductivity, which enhanced electron transport in the electrochemical process considerably. Moreover, square wave anodic stripping voltammetry (SWASV) was used for the investigation of some factors influencing the sensor sensitivity like pH, modifier concentration, as well as accumulation time and potential. Therefore, the low detection limit (LOD) and a wide linear range were obtained at optimum conditions. In this study, a linear range between 0.9 and 110 µg/L for three ions and LOD of 0.48, 0.29 and 0.12 for zinc, cadmium and lead were achieved, respectively. Moreover, TbFeO3/CuO/CPE was employed to detect zinc, cadmium and lead ions simultaneously in the real samples so that the results have shown consistency with a standard inductively coupled plasma (ICP).  相似文献   
3.
4.
  相似文献   
5.
Structural Chemistry - This is an analysis report on the use of density functional theory (DFT) to investigate the potentials of pristine and amino acid–functionalized C4B32 borospherenes in...  相似文献   
6.
7.

One of the main concerns during the COVID-19 pandemic was the protection of healthcare workers against the novel coronavirus. The critical role and vulnerability of healthcare workers during the COVID-19 pandemic leads us to derive a mathematical model to express the spread of coronavirus between the healthcare workers. In the first step, the SECIRH model is introduced, and then the mathematical equations are written. The proposed model includes eight state variables, i.e., Susceptible, Exposed, Carrier, Infected, Hospitalized, ICU admitted, Dead, and finally Recovered. In this model, the vaccination, protective equipment, and recruitment policy are considered as preventive actions. The formal confirmed data provided by the Iranian ministry of health is used to simulate the proposed model. The simulation results revealed that the proposed model has a high degree of consistency with the actual COVID-19 daily statistics. In addition, the roles of vaccination, protective equipment, and recruitment policy for the elimination of coronavirus among the healthcare workers are investigated. The results of this research help the policymakers to adopt the best decisions against the spread of coronavirus among healthcare workers.

  相似文献   
8.
Huang  I-Chiau  Jafari  Raheleh 《Semigroup Forum》2021,103(3):899-915

Numerical semigroup rings are investigated from the relative viewpoint. It is known that algebraic properties such as singularities of a numerical semigroup ring are properties of a flat numerical semigroup algebra. In this paper, we show that arithmetic and set-theoretic properties of a numerical semigroup ring are properties of an equi-gcd numerical semigroup algebra.

  相似文献   
9.
Azaperone, with anti-anxiety and anti-aggressive activities used in veterinary medicine, is a member of the butyrophenone class. It is ordinarily utilized for a wide range of indications, such as sedation, obstetrics, and anesthesia. In this research, an improved synthetic route is presented for azaperone using a phase-transfer catalyst(PTC). In general, it was synthesized as a dopamine antagonist in four steps. The bis(2-chloroethyl) amine intermediate is easily obtained after the conversion of the alcohol groups into the chloride leaving group using thionyl chloride(95% yields). The alkylation of commercially available 2-amino pyridine in the presence of PTC was then carried out, giving 1-(pyridin-2-yl) piperazine with 75% yield. 1-(Pyridin-2-yl) piperazine was finally alkylated using 4-chloro-1-(4-fluorophenyl) butan-1-one to achieve azaperone with 60% yield. The butyrophenone intermediate was obtained via the Friedel-Crafts reaction of fluorobenzene with 4-chlorobutyryl chloride in the presence of AlCl3. High efficiency, gentle reaction conditions, and fast and simple procedure are the advantages of this method. Also, the electrochemical oxidation behaviour of azaperone was investigated using cyclic and differential pulse voltammetry techniques. Cyclic voltammetric studies indicated an irreversible process for azaperone electro-oxidation with a peak potential of 0.78 V in a phosphate buffer solution(pH=7.0) vs. Ag/AgCl(saturated KCl) electrode. The value of the peak current vs. the azaperone concentration was enhanced linearly in the range of 10―70 μmol/L, and the detection limit was found to be 3.33 μmol/L.  相似文献   
10.
In this study, vanadium nanoparticles (VNPs) were green synthesized using Foeniculum vulgare extract. VNPs were characterized using chemical analysis techniques including FT-IR, XRD, FE-SEM, TEM and EDS. The microscopy techniques revealed a spherical morphology for the particles with size less than 50 nm. According to XRD data V2O5 was confirmed for VNPs. Maybe significant anti-human acute leukemia potentials of the synthesized nanoparticles against common human acute leukemia cell lines are linked to their antioxidant activities. MTT assay was used on common acute leukemia cell lines i.e., 32D-FLT3-ITD, MOLT-3 and Jurkat, Clone E6-1 to survey the cytotoxicity and anti-acute leukemia effects of the synthesized nanoparticles. The synthesized nanoparticles had very low cell viability and high anti-acute leukemia activities dose-dependently against 32D-FLT3-ITD, MOLT-3 and Jurkat, Clone E6-1 cell lines without cytotoxicity on the normal cell line (HUVEC). To determine the antioxidant properties of the synthesized nanoparticles, the DPPH test was used in the presence of butylated hydroxytoluene as the positive control. The IC50 of VNPs were 25, 33 and 26 µg/mL against 32D-FLT3-ITD, MOLT-3 and Jurkat, Clone E6-1 cell lines, respectively. The synthesized nanoparticles inhibited half of the DPPH molecules in the concentration of 28 µg/mL.  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