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   175篇
  免费   19篇
  国内免费   4篇
化学   123篇
晶体学   1篇
力学   11篇
数学   30篇
物理学   33篇
  2023年   2篇
  2021年   5篇
  2020年   5篇
  2019年   3篇
  2018年   11篇
  2017年   6篇
  2016年   10篇
  2015年   13篇
  2014年   18篇
  2013年   19篇
  2012年   19篇
  2011年   11篇
  2010年   6篇
  2009年   10篇
  2008年   5篇
  2007年   8篇
  2006年   4篇
  2005年   7篇
  2004年   4篇
  2003年   7篇
  2002年   6篇
  2001年   4篇
  2000年   2篇
  1999年   1篇
  1998年   1篇
  1996年   1篇
  1995年   2篇
  1994年   1篇
  1991年   1篇
  1989年   1篇
  1987年   1篇
  1984年   1篇
  1983年   2篇
  1979年   1篇
排序方式: 共有198条查询结果,搜索用时 24 毫秒
1.
2.
A straightforward method has been developed for the synthesis of 1,2,4‐triazol‐3‐one 3 and 1,2,4‐triazoles 6a , 6b , 6c , 6d starting from N1‐substituted‐N1‐tosylhydrazonates 2 and hydrazine monohydrate. This methodology affords a number of 1,2,4‐triazol‐3‐one 3 and 1,2,4‐triazoles 6a , 6b , 6c , 6d in reasonable yields. The structures of all new compounds were elucidated using infrared, 1H and 13C NMR, high‐resolution mass spectrometry, elemental analysis, and the X‐ray crystallography (for compounds 3 and 6a ). Some of the newly synthesized compounds were screened for their antibacterial activity.  相似文献   
3.
In this paper, we present two general variable neighborhood search (GVNS) based variants for solving the traveling salesman problem with draft limits (TSPDL), a recent extension of the traveling salesman problem. TSPDL arises in the context of maritime transportation. It consists of finding optimal Hamiltonian tour for a given ship which has to visit and deliver products to a set of ports while respecting the draft limit constraints. The proposed methods combine ideas in sequential variable neighborhood descent within GVNS. They are tested on a set of benchmarks from the literature as well as on a new one generated by us. Computational experiments show remarkable efficiency and effectiveness of our new approach. Moreover, new set of benchmarks instances is generated.  相似文献   
4.
Cannabis sativa contains more than 500 constituents, yet the anticancer properties of the vast majority of cannabis compounds remains unknown. We aimed to identify cannabis compounds and their combinations presenting cytotoxicity against bladder urothelial carcinoma (UC), the most common urinary system cancer. An XTT assay was used to determine cytotoxic activity of C. sativa extracts on T24 and HBT-9 cell lines. Extract chemical content was identified by high-performance liquid chromatography (HPLC). Fluorescence-activated cell sorting (FACS) was used to determine apoptosis and cell cycle, using stained F-actin and nuclei. Scratch and transwell assays were used to determine cell migration and invasion, respectively. Gene expression was determined by quantitative Polymerase chain reaction (PCR). The most active decarboxylated extract fraction (F7) of high-cannabidiol (CBD) C. sativa was found to contain cannabichromene (CBC) and Δ9-tetrahydrocannabinol (THC). Synergistic interaction was demonstrated between CBC + THC whereas cannabinoid receptor (CB) type 1 and type 2 inverse agonists reduced cytotoxic activity. Treatments with CBC + THC or CBD led to cell cycle arrest and cell apoptosis. CBC + THC or CBD treatments inhibited cell migration and affected F-actin integrity. Identification of active plant ingredients (API) from cannabis that induce apoptosis and affect cell migration in UC cell lines forms a basis for pre-clinical trials for UC treatment.  相似文献   
5.
6.
7.
8.
We study the asymptotic behavior of the Cramér–von Mises type statistic in the goodness-of-fit hypotheses testing problem for ergodic diffusion processes. The basic (simple) hypothesis is defined by the stochastic differential equation with sign-type trend coefficient and known diffusion coefficient. It is shown that the limit distribution of the proposed test statistic (under hypothesis) is defined by the integral type functional of continuous Gaussian process. We provide the Karhunen–Loève expansion of the corresponding limiting process and show that the eigenfunctions in this expansion are expressed in terms of Bessel functions. This representation for the limit statistic allows us to approximate the threshold.  相似文献   
9.
10.
The interactions between oppositely charged surfactant-polymer systems have been studied using surface tension and conductivity measurements and the dependence of aggregation phenomenon over the polyelectrolyte concentration and chain length of cationic ATAB surfactants, cetyltrimethyl ammonium bromide (CTAB), tetradecyltrimethyl ammonium bromide (TTAB), and dodecyltrimethyl ammonium bromide (DTAB) have been investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolyte at critical aggregation concentration (cac). The cac values of ATAB surfactants in the presence of anionic polyelectrolyte, sodium carboxy methyl cellulose (NaCMC), are considerably lower than their critical micelle concentration (cmc). After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in polyelectrolyte aqueous solution than in pure water. Among the cationic surfactants (i.e., CTAB, TTAB, and DTAB), DTAB was found to have least interaction with NaCMC. Surfactants with longer tail size strongly favor the interaction, indicating the dependence of aggregation phenomenon on the structure, morphology, and tail length of the surfactant.   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