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   666篇
  免费   30篇
  国内免费   7篇
化学   425篇
晶体学   12篇
力学   14篇
数学   101篇
物理学   151篇
  2023年   3篇
  2022年   5篇
  2021年   12篇
  2020年   9篇
  2019年   15篇
  2018年   17篇
  2017年   21篇
  2016年   38篇
  2015年   37篇
  2014年   33篇
  2013年   49篇
  2012年   43篇
  2011年   53篇
  2010年   45篇
  2009年   39篇
  2008年   43篇
  2007年   33篇
  2006年   26篇
  2005年   26篇
  2004年   31篇
  2003年   17篇
  2002年   17篇
  2001年   10篇
  2000年   14篇
  1999年   7篇
  1998年   4篇
  1997年   4篇
  1996年   8篇
  1995年   4篇
  1994年   8篇
  1993年   5篇
  1992年   4篇
  1991年   5篇
  1990年   1篇
  1989年   4篇
  1988年   2篇
  1987年   1篇
  1984年   2篇
  1982年   2篇
  1978年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1941年   2篇
排序方式: 共有703条查询结果,搜索用时 171 毫秒
41.
The aim of this study was to develop nanostructured lipid carriers (NLC) for topical delivery of fluticasone propionate (FP) with the aim to further improve the safety profile and decrease the adverse-side effects commonly reported in topical corticotherapy. NLC are colloidal drug-carriers consisting of a blend of a solid lipid and a small amount of liquid lipid since these carriers have proved to be effective in epidermal targeting in particular of glucocorticoids. NLC consisting of glyceryl palmito-stearate, and PEG-containing medium chain triglycerides mixture, stabilised by polysorbate 80 and soybean phosphatidylcholine were prepared. A mean particle size between 380 and 408 nm and entrapment efficacy of 95% were obtained for FP-loaded NLC. The crystallinity and polymorphic phase behaviour of FP-free and FP-loaded NLC were examined by differential scanning calorimetry and wide angle X-ray diffraction. Results revealed a low-crystalline structure and confirmed the incorporation of FP into the particles. The suitability of PEG-containing liquid lipids to form the lipid matrix of NLC was also confirmed.  相似文献   
42.
43.
The Nuclear and Technological Institute (Instituto Tecnológico e Nuclear—ITN) in cooperation with the International Atomic Energy Agency (IAEA) has been conducting a nationwide survey of hydrogen (2H/1H) and oxygen (18O/16O) isotopic composition of monthly precipitation since 1988. This paper focuses on basic features of spatial and temporal distribution of δ18O and δ2H in the precipitation over Continental Portugal derived from ITN database. Phenomenological relationships between stable isotopes composition of precipitation and various climate-related parameters (local air temperature, distance to the Atlantic coast, altitude, amount of precipitation) are established and discussed.  相似文献   
44.
45.
Novel zinc(II) complex compounds of general formula Zn(C6H5COO)2·L2 (where L=caffeine (caf) and urea (u)) were synthesized and characterized by elemental analysis and IR spectroscopy. The thermal behaviour of the complexes was studied during heating in air by thermogravimetry. It was found that the thermal decomposition of the anhydrous Zn(II) benzoate compounds with bioactive ligands was initiated by the release of organic ligands at various temperatures. On further heating of the compounds up to 400°C the thermal degradation of the benzoate anions took place. Zinc oxide was found as the final product of the thermal decomposition of all zinc(II) benzoate complex compounds heated to 600°C. Results of elemental analysis, infrared spectroscopy, mass spectroscopy and thermogravimetry are presented.  相似文献   
46.
A technique was established to study ectomycorrhizal fungi on agar media. Petri dishes, 60 mm in diameter, containing 10 mL of culture medium covered with a cellophane disk were used for easy collection of the mycelium after growth. For analysis of fungal biomass production, a sterilized cellophane sheet was placed on the medium’s surface. Inoculation was achieved by placing a mycelial block onto the center of the cellophane sheet and then incubating at 25°C in the dark. Colony radial growth was measured and biomass dry wt was determined. Fresh mycelia were homogenized with 10 mL of acetate buffer (pH 5.5) for enzyme analysis. A crude extract was obtained by adding all culture medium to 90 mL of distilled water and homogenizing in a Potter. Reducing sugars, enzyme concentration, and pH were determined. Three fungal strains, Suillus collinitus, Pisosithus arrhizus, and Hebeloma cylindrosporum, were grown in different culture media (potato dextrose agar or Pintro’s medium). Parameters measured over time included glucose concentration, phosphatase activity, biomass, and pH.  相似文献   
47.
48.
Physics of the Solid State - In this study, titanium dioxide (TiO2) nanocolloid was synthesized through sol–gel method, and nonlinear optical properties were studied using z-scan method. The...  相似文献   
49.
A procedure for the determination of As, Cd, Cr, Ni, Pb, and V in phytotherapy medicines by inductively coupled plasma–tandem mass spectrometry is reported. The use of tandem mass spectrometry with oxygen into an octopole reaction system at various gas flow rates and the combination of on-mass and mass-shift modes was evaluated. Cadmium, Cr, Ni, and Pb were determined as free atomic ions while As and V were determined as the oxides AsO+ and VO+ in the same run. Samples were prepared by microwave-assisted digestion with dilute nitric acid and hydrogen peroxide. Two plant-certified reference materials (apple leaves and tomato leaves) were used to check the accuracy. For tandem mass spectrometry with 0.5?mL min?1 O2, recoveries in the 85–113% were typically obtained and no statistical differences were observed at the 95% confidence level (t-test) in comparison with the certified values. Using these conditions, the limits of detection for the method were 0.01, 0.0002, 0.008, 0.008, 0.003, and 0.002?µg g?1 for As, Cd, Cr, Ni, Pb, and V, respectively. The procedure was used for the analysis of four phytotherapic drugs and the determined concentrations were up to 0.168?µg g?1 As, 0.03?µg g?1 Cd, 0.82?µg g?1 Cr, 1.18?µg g?1 Ni, 0.52?µg g?1 Pb, and 2.4?µg g?1 V with average precision values of 8% as the relative standard deviation. The found concentrations were compared with limits proposed in official guidelines and, in most cases, the values were below the maximum limits allowed.  相似文献   
50.
This work aimed to immobilize the antibody anti-galectin-3 onto polysiloxane–polyvinyl alcohol (POS-PVA) support, to evaluate its capacity to capture the serum antigen galectin-3 and to quantify by ELISA the antigen levels in sera from patients with prostatic adenocarcinoma (PA) and benign prostatic hyperplasia (BPH) and healthy individuals. Also, for comparative effect, the galectin-3 expression in the prostate tissue through immunohistochemistry was evaluated. The optical density (galectin-3 level) values established for the sera from PA and BPH patients were lower compared with those found for the healthy individuals. Galectin-3 immunohistochemically showed a significant increase and reduction of the cytoplasmatic protein expression in BPH and PA, respectively, compared with the normal prostate. These results showed that POS-PVA disks could be used as solid phase to immobilize serum galectins and in immunoassays procedures for the correspondent IgG anti-galectins detection in human sera.  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