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   9306篇
  免费   322篇
  国内免费   27篇
化学   6287篇
晶体学   69篇
力学   288篇
综合类   1篇
数学   1244篇
物理学   1766篇
  2023年   75篇
  2022年   65篇
  2021年   267篇
  2020年   201篇
  2019年   201篇
  2018年   198篇
  2017年   176篇
  2016年   383篇
  2015年   321篇
  2014年   328篇
  2013年   587篇
  2012年   689篇
  2011年   704篇
  2010年   500篇
  2009年   447篇
  2008年   625篇
  2007年   576篇
  2006年   472篇
  2005年   422篇
  2004年   338篇
  2003年   309篇
  2002年   220篇
  2001年   170篇
  2000年   137篇
  1999年   87篇
  1998年   85篇
  1997年   68篇
  1996年   79篇
  1995年   68篇
  1994年   65篇
  1993年   60篇
  1992年   67篇
  1991年   59篇
  1990年   47篇
  1989年   35篇
  1988年   39篇
  1987年   32篇
  1986年   31篇
  1985年   60篇
  1984年   45篇
  1983年   27篇
  1982年   26篇
  1981年   24篇
  1980年   39篇
  1979年   21篇
  1978年   27篇
  1976年   23篇
  1975年   19篇
  1974年   15篇
  1973年   20篇
排序方式: 共有9655条查询结果,搜索用时 109 毫秒
1.
2.
A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample.  相似文献   
3.
4.
5.
Annals of Operations Research - The vehicle routing problem is a traditional combinatorial problem with practical relevance for a wide range of industries. In the literature, several specificities...  相似文献   
6.
Journal of Thermal Analysis and Calorimetry - The hot coil slump is a recurrent problem in the manufacturing process of medium and high equivalent carbon steel plates. Even with the success of the...  相似文献   
7.
Journal of Thermal Analysis and Calorimetry - The paper presents the effect of the tabletting pressure and time on the chemical structure and crystallinity of the CuBTC and MIL-53(Al)...  相似文献   
8.
9.
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase.  相似文献   
10.
Administration of β-glucans through various routes, including immersion, dietary inclusion, or injection, have been found to stimulate various facets of immune responses, such as resistance to infections and resistance to environmental stress. β-Glucans used as an immunomodulatory food supplement have been found beneficial in eliciting immunity in commercial aquaculture. Despite extensive research involving more than 3000 published studies, knowledge of the receptors involved in recognition of β-glucans, their downstream signaling, and overall mechanisms of action is still lacking. The aim of this review is to summarize and discuss what is currently known about of the use of β-glucans in fish.  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