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   1543篇
  免费   46篇
  国内免费   2篇
化学   1136篇
晶体学   19篇
力学   31篇
数学   149篇
物理学   256篇
  2023年   8篇
  2022年   27篇
  2021年   50篇
  2020年   42篇
  2019年   37篇
  2018年   21篇
  2017年   18篇
  2016年   37篇
  2015年   56篇
  2014年   46篇
  2013年   102篇
  2012年   113篇
  2011年   108篇
  2010年   58篇
  2009年   76篇
  2008年   111篇
  2007年   85篇
  2006年   70篇
  2005年   50篇
  2004年   68篇
  2003年   53篇
  2002年   43篇
  2001年   30篇
  2000年   31篇
  1999年   23篇
  1998年   17篇
  1997年   28篇
  1996年   16篇
  1995年   16篇
  1994年   11篇
  1993年   10篇
  1991年   5篇
  1990年   15篇
  1989年   10篇
  1988年   6篇
  1987年   6篇
  1985年   8篇
  1983年   7篇
  1982年   3篇
  1981年   7篇
  1980年   12篇
  1979年   4篇
  1978年   5篇
  1977年   7篇
  1976年   3篇
  1975年   6篇
  1974年   3篇
  1973年   6篇
  1924年   2篇
  1918年   2篇
排序方式: 共有1591条查询结果,搜索用时 218 毫秒
81.
A self-supporting ZSM-5 monolith with a hierarchical porosity was prepared using polyurethane foam (PUF) as a structural template and a hydrothermal synthesis procedure. The synthesized monolith was characterized and investigated towards the adsorption and catalytic oxidation of trichloroethylene (TCE). Adsorption of TCE was studied gravimetrically and oxidation of TCE was studied using a vapor-phase down-flow reactor. Monolithic ZSM-5 displayed good sorption properties and completely oxidized TCE. Conversion levels of 50% and 90% were achieved at reduced temperatures (by ~50 ℃) when compared with the conversion temperatures obtained from the powder counterparts. Besides the activity of the monolith towards TCE adsorption and oxidation, it was stable and enhanced diffusion, thereby reducing pressure drops to a great extent owing to its hierarchical porous nature.  相似文献   
82.
A new family of robust, non-toxic, water-compatible ruthenium(II) vinyl probes allows the rapid, selective and sensitive detection of endogenous carbon monoxide (CO) in live mammalian cells under normoxic and hypoxic conditions. Uniquely, these probes incorporate a viscosity-sensitive BODIPY fluorophore that allows the measurement of microscopic viscosity in live cells via fluorescence lifetime imaging microscopy (FLIM) while also monitoring CO levels. This is the first example of a probe that can simultaneously detect CO alongside small viscosity changes in organelles of live cells.  相似文献   
83.
Petroselinum crispum Mill., Fuss., is a culinary vegetable used as an aromatic herb that garnishes and flavours a great variety of dishes. In the present study, the chemical profiles and bioactivities of leaf samples from 25 cultivars (three types: plain- and curly-leafed and turnip-rooted) from this species were assessed. Seven phenolic compounds were identified in all the varieties, including apigenin and kaempherol derivates. Apigenin-O-pentoside-O-hexoside was the major compound in all the tested parsley types (20, 22 and 13 mg/g of extract, respectively) and responsible for its excellent antioxidant activity, also investigated in this study. Antimicrobial activities were also explored, and the results revealed a good bioactivity against specific tested pathogens, such as bacteria and fungi. In conclusion, the leaves of all the types of P. crispum are a good source of natural bioactive compounds that confer health benefits, and thus, they should be part of a balanced and diversified diet.  相似文献   
84.
Optimized HR-AR-DFB laser structures are proposed foreseeing their use in directly modulated optical communication systems. They present, simultaneously, high single-longitudinal-mode yield, stable single-longitudinal-mode operation, high power efficiency and stable emitted wavelength. Lasers harder to manufacture were previously proposed elsewhere and did not succeed in achieving such high performances. A detailed assessment of the proposed lasers is presented and discussed.  相似文献   
85.
86.
87.
Cobalt compounds supported on 2-, 3-, and 4-aminopyridine-modified silica surfaces, named Sil2Co, Sil3Co, and Sil4Co, respectively, were used to catalyze the decomposition of hydrogen peroxide on ethanolic solutions at 293, 298, and 303 K. The calculated k values (x10(-4) s(-1)) for Sil2Co, Sil3Co, and Sil4Co are 0.65, 1.24, and 4.78 (293 K); 1.23, 1.87, and 6.33 (298 K); and 1.80, 2.80, and 10.30 (303 K), respectively. All obtained results evidence that such decomposition is a first-order reaction. Zinc-, nickel-, and copper-supported compounds were also tested, but exhibited a very low catalytic activity. By using the k values at 298 and 303 K, and employing the equation ln (k1/k2) = E(a)/R(1/T2-1/T1), the activation energy values for the considered reaction were Sil2Co = 57.20, Sil3Co = 60.60, and Sil4Co = 73.10 kJ mol(-1), respectively. The low values calculated for E(a) are in agreement with a free-radical mechanism.  相似文献   
88.
89.
90.
A simple focussing device in the form of a cone has been used to produce a localised flux increase of ultra-cold neutrons.  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