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   1813篇
  免费   72篇
  国内免费   18篇
化学   1147篇
晶体学   32篇
力学   74篇
数学   267篇
物理学   383篇
  2023年   11篇
  2022年   38篇
  2021年   46篇
  2020年   55篇
  2019年   59篇
  2018年   65篇
  2017年   61篇
  2016年   78篇
  2015年   66篇
  2014年   76篇
  2013年   189篇
  2012年   108篇
  2011年   153篇
  2010年   94篇
  2009年   93篇
  2008年   110篇
  2007年   109篇
  2006年   72篇
  2005年   67篇
  2004年   58篇
  2003年   47篇
  2002年   37篇
  2001年   14篇
  2000年   14篇
  1999年   9篇
  1998年   10篇
  1997年   8篇
  1996年   18篇
  1995年   4篇
  1994年   5篇
  1993年   13篇
  1992年   13篇
  1991年   4篇
  1990年   5篇
  1989年   6篇
  1988年   3篇
  1987年   8篇
  1986年   5篇
  1985年   8篇
  1984年   12篇
  1983年   4篇
  1982年   3篇
  1981年   6篇
  1980年   6篇
  1979年   5篇
  1978年   2篇
  1977年   3篇
  1976年   2篇
  1975年   5篇
  1974年   6篇
排序方式: 共有1903条查询结果,搜索用时 531 毫秒
91.
Abstract

A series of imidazole derivatives were synthesized from two-component condensation reaction of phenylgloxal monohydrate with guanylhydrazone. They were characterized by spectroscopic and analytical techniques. The in vitro anticancer evaluation of these compounds was done on human breast cancer (MCF-7) and human liver cancer (HepG2) cell lines using the MTT assay method. Most of the newly synthesized compounds displayed cytotoxic activity against these cancerous cells. In fact, compounds 3a, 3e, and 3?h exhibited more cytotoxic activities than the positive control drugs, fluro-5, and irinocam, against the MCF-7 cell line. Almost all the compounds, except for three, 3b, 3d, and 3f, gave more cytotoxic results than cisplatin. Therefore, these compounds could be considered for further development as anticancer drug candidates.  相似文献   
92.
93.
Four-component, one-pot condensation of dimedon, thiophene-2-carbaldehyde, ammonium acetate, and numerous acetophenones yielded novel 2-aryl-4-thionylquinoline derivatives. The structures were characterized by 1H NMR, 13C NMR, IR, and elemental analysis.  相似文献   
94.
The substituted pyrolidine derivatives with high stereoselectivity were obtained through cycloaddition reaction in the presence of a Lewis acid namely diethylzinc by solvent‐free grinding method.  相似文献   
95.
Terpenoid-like bischalcones (3 and 4) were synthesized from the reaction of α- and β-ionones and benzaldehydes in excellent yields. The Michael addition of 1,3-dicarbonyl compounds to bischalcones (3 and 4) resulted in the formation of cyclohexenones derivatives (10a–d and 14a, b) via regioselective addition of 1,3-dicarbonyls and then cyclization.  相似文献   
96.
A series of chalcone derivatives (3a–k) were prepared via the reaction of cis-bicyclo[3.2.0]hept-2-en-6-one (1) with the respective arylaldehydes (2a–k) and were then characterized by Fourier transform infrared (FT-IR), 1H NMR, 13C NMR, and elemental analyses.  相似文献   
97.
A series of novel 1,2,3,4,6-pentasubstituted-4-hydroxy-cyclohexanes (3a–u) were synthesized from the reaction of aromatic ketones with aromatic aldehydes under mild reaction conditions in good yields. The stereochemistry of the synthesized compounds was established using 1D and 2D-NMR spectra.  相似文献   
98.
This study was carried out to better understand the biokinetics of radiocesium in clams living in sediment. The accumulation and depuration kinetics of 134Cs were investigated in the Manila clam (Ruditapes philippinarum) under controlled laboratory conditions. The concentration factor was found to be 3.0 for 134Cs in the whole body; however, the concentration factor in the soft part of the clams (12) was significantly higher than those in the whole body and shell (0.80). The depuration kinetics of the radionuclide were described by a two-component exponential model for the whole body. The biological half-lives in the fast and slow components were found to be 0.63 and 22.1 days, respectively. The depuration kinetics for 134Cs in the soft parts were described by a single-component exponential model with a resultant the biological half-life of 18.0 days.  相似文献   
99.
In this study, a batch adsorption of Cd(II) ions onto activated carbon (AC) produced from hazelnut husks were investigated. The factors controlling the adsorption process such as initial pH, agitation time, dosage and initial concentration have been examined. The AC was showed a high affinity to Cd(II) ions at pH values between 5.0 and 7.0. The equilibrium time was found to be 300 minutes. Cd(II) adsorption equilibrium was analyzed with both Langmuir and Freundlich isotherm equations and it was found that Langmuir equations fitted well with the experimental data. Maximum Cd(II) adsorption capacity of AC was calculated to be 20.9 mg g?1. Cd(II) adsorption kinetics described well with the pseudo second order model. The activated carbon prepared from hazelnut husks is efficient sorbent material for the removal of Cd(II) ions from aqueous solutions.  相似文献   
100.
The objective of the present investigation was to design a thermodynamically stable and dilutable nanoemulsion formulation of AT-Ca with minimum surfactant concentration that could improve its solubility as well as its oral bioavailability. The composition of optimized nanoemulsion formulation was Sefsol 218 and oleic acid (1:1) 10% w/w, as an oil phase, Tween-20 (19% w/w) as a surfactant, Carbitol (19% w/w) as a cosurfactant and distilled water (52% w/w) as an aqueous phase, containing 10 mg of AT. The optimized formulation showed higher% drug release (99.34%), lower droplet size (42.8 ± 0.42 nm) with low polydispersity index (0.237 ± 0.012), less viscosity (27.51 ± 1.01 cP) and infinite dilution capability. In vitro drug release from the nanoemulsion formulations was highly significant (p < 0.01) as compared to drug suspension.  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