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   601篇
  免费   26篇
  国内免费   22篇
化学   552篇
力学   2篇
综合类   3篇
物理学   92篇
  2023年   2篇
  2022年   14篇
  2021年   25篇
  2020年   11篇
  2019年   16篇
  2018年   11篇
  2017年   20篇
  2016年   17篇
  2015年   22篇
  2014年   14篇
  2013年   51篇
  2012年   23篇
  2011年   40篇
  2010年   27篇
  2009年   49篇
  2008年   20篇
  2007年   43篇
  2006年   26篇
  2005年   37篇
  2004年   26篇
  2003年   21篇
  2002年   17篇
  2001年   13篇
  2000年   11篇
  1999年   10篇
  1998年   14篇
  1997年   13篇
  1996年   10篇
  1995年   5篇
  1994年   7篇
  1993年   6篇
  1992年   3篇
  1991年   3篇
  1990年   3篇
  1989年   4篇
  1987年   4篇
  1986年   3篇
  1985年   1篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1980年   2篇
排序方式: 共有649条查询结果,搜索用时 15 毫秒
641.
韩国胜  喻祖国  Anh Vo 《中国物理 B》2011,20(10):100504-100504
Apoptosis proteins play an important role in the development and homeostasis of an organism. The elucidation of the subcellular locations and functions of these proteins is helpful for understanding the mechanism of programmed cell death. In this paper, the recurrent quantification analysis, Hilbert-Huang transform methods, the maximum relevance and minimum redundancy method and support vector machine are used to predict the subcellular location of apoptosis proteins. The validation of the jackknife test suggests that the proposed method can improve the prediction accuracy of the subcellular location of apoptosis proteins and its application may be promising in other fields.  相似文献   
642.
We described mathematically the process of peat methanization in a boreal mesotrophic fen. Gaseous and dissolved CH4 and CO2 as well as their δ13C signatures were considered in the dynamic equations for incubation bottles. In accordance with the model, acetate, H2, and CO2 were produced during cellulose hydrolysis and acidogenesis. 13C/12C in CO2 was a key variable reflecting dynamic changes in the rates of cellulose hydrolysis and acidogenesis, acetoclastic and hydrogenotrophic methanogenesis. As CO2 is the substrate in hydrogenotrophic methanogenesis, δ13C–CO2 increased from the start till the dissolved hydrogen concentration became very low. Thereafter, the rate of acetoclastic methanogenesis with the significant current acetate concentration dominated over the rate of hydrogenotrophic methanogenesis leading to the decreasing δ13C–CO2 and the increasing δ13C–CH4. The model was validated by describing the system’s dynamics under strong and weak inhibition of acetoclastic and hydrogenotrophic methanogenesis by methyl fluoride, respectively. During peat methanization at the lowered temperature of 10?°C, the processes of hydrogenotrophic methanogenesis and homoacetogenesis competing for H2 may occur. However, based on dynamics of the carbon isotope signatures, especially on dynamics of δ13C–CO2, the model showed no significant contribution of homoacetogens in peat methanization.  相似文献   
643.
采用超临界戊烷萃取分馏技术,分离了大港减压渣油,得到16个窄馏分和1个萃余残渣,对其组成和结构进行了表征;对超临界萃取分离窄馏分进行了四组分分离,研究了饱和分、芳香分、胶质和沥青质等亚组分的元素组成、相对分子质量分布和平均分子结构。结果表明,由窄馏分得到的四组分(SARA)性质结构差别很大,饱和分的平均分子结构最简单,芳香分的平均相对分子质量最小,胶质中的硫、氮含量最多,从萃余残渣中得到的沥青质相对分子质量分布范围最宽(200~40000)。  相似文献   
644.
Renal cell carcinoma is the most lethal cancer of the urological system due to late diagnosis and treatment resistance. Propolis, a beehive product, is a valuable natural source of compounds with bioactivities and may be a beneficial addition to current anticancer treatments. A Portuguese propolis sample, its fractions (n-hexane, ethyl acetate, n-butanol and water) and three subfractions (P1–P3), were tested for their toxicity on A498, 786-O and Caki-2 renal cell carcinoma cell lines and the non-neoplastic HK2 kidney cells. The ethyl acetate fraction showed the strongest toxicity against A498 (IC50 = 0.162 µg mL−1) and 786-O (IC50 = 0.271 µg mL−1) cells. With similar toxicity against 786-O, P1 (IC50 = 3.8 µg mL−1) and P3 (IC50 = 3.1 µg mL−1) exhibited greater effect when combined (IC50 = 2.5 µg mL−1). Results support the potential of propolis and its constituents as promising coadjuvants in renal cell carcinoma treatment.  相似文献   
645.
The conversion of lignocellulosic biomass by pyrolysis or hydrothermal liquefaction gives access to a wide variety of molecules that can be used as fuel or as building blocks in the chemical industry. For such purposes, it is necessary to obtain their detailed chemical composition to adapt the conversion process, including the upgrading steps. Petroleomics has emerged as an integral approach to cover a missing link in the investigation bio-oils and linked products. It relies on ultra-high-resolution mass spectrometry to attempt to unravel the contribution of many compounds in complex samples by a non-targeted approach. The most recent developments in petroleomics partially alter the discriminating nature of the non-targeted analyses. However, a peak referring to one chemical formula possibly hides a forest of isomeric compounds, which may present a large chemical diversity concerning the nature of the chemical functions. This identification of chemical functions is essential in the context of the upgrading of bio-oils. The latest developments dedicated to this analytical challenge will be reviewed and discussed, particularly by integrating ion source features and incorporating new steps in the analytical workflow. The representativeness of the data obtained by the petroleomic approach is still an important issue.  相似文献   
646.
In order to more conveniently simulate and optimize the solubilization of sugarcane bagasse components during formic acid (FA) fractionation, an extended combined severity factor (CSFext) was defined to integrate various operation parameters as a single factor. Two phenomenological models based on Arrhenius and Logistic equations were further used to describe the phenomenological kinetics. Different data-processing methods were compared to fit the severity parameters and model constants. Both Arrhenius-based and Logistic-based models show satisfying fitting results, though the values of Arrhenius-based CSFext (A-CSFext) and Logistic-based CSFext (L-CSFext) were somewhat different under the same fractionation condition. The solubilization of biomass components increased with CSFext, but two distinct stages could be observed with inflection points at A-CSFext of 42 or L-CSFext of 43, corresponding to bulk and residual solubilization stages, respectively. For the enzymatic hydrolysis of cellulosic solids, the highest initial enzymatic glucan conversion (EGC@6h) was obtained at A-CSFext of 39–40 or A-CSFext of 40–41; however, for a long hydrolysis period (72 h), relatively high glucan conversion (EGC@72h) was observed at A-CSFext of 42–43 or A-CSFext of 43–44. Post-treatment for deformylation with a small amount of lime could help to recover the cellulose digestibility.  相似文献   
647.
Crystallization analysis fractionation (Crystaf) is a new technique used to estimate the chemical composition distribution (CCD) of semi-crystalline copolymers. In this study, the effect of chain microstructure and operation parameters on Crystaf profiles was investigated using a series of ethylene/1-hexene copolymers and their blends. The Crystaf profiles were also modeled via stochastic simulation based on the distribution of average ethylene sequence lengths.  相似文献   
648.
649.
采用扫描电子显微镜(SEM)、激光共聚焦显微镜(LSM)和流式细胞仪等技术比较了纳米级和微米级一水草酸钙(COM)对非洲绿猴肾上皮细胞(Vero)的毒性差异。结果显示,尺寸为100 nm和6μm的COM晶体都能引起Vero细胞活力下降、乳酸脱氢酶(LDH)释放量升高、透明质酸(HA)表达量增多、溶酶体完整性降低、线粒体膜电位下降、细胞死亡率升高和细胞周期滞留,表明这些晶体对Vero细胞都有损伤作用且呈现浓度依赖性,但纳米COM的毒性及其在细胞表面的粘附量均大于微米COM晶体。  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