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   2862篇
  免费   420篇
  国内免费   330篇
化学   1975篇
晶体学   28篇
力学   173篇
综合类   20篇
数学   410篇
物理学   1006篇
  2024年   6篇
  2023年   66篇
  2022年   75篇
  2021年   75篇
  2020年   108篇
  2019年   101篇
  2018年   98篇
  2017年   80篇
  2016年   122篇
  2015年   100篇
  2014年   131篇
  2013年   199篇
  2012年   233篇
  2011年   258篇
  2010年   146篇
  2009年   183篇
  2008年   174篇
  2007年   185篇
  2006年   175篇
  2005年   129篇
  2004年   97篇
  2003年   79篇
  2002年   81篇
  2001年   75篇
  2000年   74篇
  1999年   82篇
  1998年   47篇
  1997年   58篇
  1996年   53篇
  1995年   48篇
  1994年   23篇
  1993年   35篇
  1992年   33篇
  1991年   29篇
  1990年   23篇
  1989年   11篇
  1988年   9篇
  1987年   14篇
  1986年   11篇
  1985年   10篇
  1984年   9篇
  1983年   6篇
  1982年   10篇
  1981年   5篇
  1980年   4篇
  1979年   6篇
  1978年   3篇
  1976年   4篇
  1974年   3篇
  1973年   5篇
排序方式: 共有3612条查询结果,搜索用时 531 毫秒
111.
H2S is considered as the main gas pollutant from livestock farm and activated carbon (AC) is widely used as adsorbent for H2S. This paper focuses on the influence of modification conditions and operation conditions on the H2S adsorption performance on AC samples. The H2S adsorption performance on modified AC (MAC) samples by single and combinatory method has been investigated. It is concluded that the MAC by combinatory method of high-pressure hydrothermal method followed by alkaline solution impregnation method could promote the H2S adsorption performance remarkably. The H2S adsorption performance differs with different operation conditions. Meanwhile the samples of fresh AC and exhausted AC have been characterized using BET, FTIR, TPD and Boehm titration method. The experimental results are confirmed that the characteristics of AC have significant influence on the adsorption ability for H2S.  相似文献   
112.
International Journal of Theoretical Physics - Multi-hop teleportation is of great significance due to long-distance delivery of quantum information and wireless quantum communication networks. In...  相似文献   
113.
A new simple pyrene-substituted acylhydrazone derivative, 4-(3,4-dioctyloxy) phenyl-1-pyrene acylhydrazone (PAH-8), was designed and synthesized. The PAH-8 can form thermo-reversible organogel in DMSO, and shows gelation-induced enhanced fluorescence emission. Xerogel exhibits ribbon-like fibrous aggregates with widths of 0.5-1 μm. The PAH-8 organogel indicates photo-responsive behaviors due to the trans-cis isomerizations of -C=N- bond upon exposure to visible or UV light. Upon visible light irradiation, the partial trans-cis isomerization of the -C=N- bond causes the fiber morphology to disappear, resulting in gel-sol transition, whereas the PAH-8 organogel exhibits few photoisomerizations from trans to cis transition without breakage of the gel state upon UV light irradiation.  相似文献   
114.
115.
The original Sasol catalytic system for ethylene tetramerization is composed of a Cr source, a PNP ligand, and MAO (methylaluminoxane). The use of expensive MAO in excess has been a critical concern in commercial operation. Many efforts have been made to replace MAO with non‐coordinating anions (e.g., [B(C6F5)4]?); however, most of such attempts were unsuccessful. Herein, an extremely active catalytic system that avoids the use of MAO is presented. The successive addition of two equivalent [H(OEt2)2]+[B(C6F5)4]? and one equivalent CrCl3(THF)3 to (acac)AlEt2 and subsequent treatment with a PNP ligand [CH3(CH2)16]2C(H)N(PPh2)2 ( 1 ) yielded a complex presumably formulated as [ 1 ‐CrAl (acac)Cl3(THF)]2+[B(C6F5)4]?2, which exhibited high activity when combined with iBu3Al (1120 kg/g‐Cr/h; ~4 times that of the original Sasol system composed of Cr (acac)3, iPrN(PPh2)2, and MAO). Via the introduction of bulky trialkylsilyl substituents such as –SiMe3, –Si(nBu)3, or –SiMe2(CH2)7CH3 at the para‐position of phenyl groups in 1 (i.e., by using [CH3(CH2)16]2C(H)N[P(C6H4p‐SiR3)2]2 instead of 1 ), the activities were dramatically improved, i.e., tripled (2960–3340 kg/g‐Cr/h; more than 10 times that of the original Sasol system). The generation of significantly less PE (<0.2 wt%) even at a high temperature is another advantage achieved by the introduction of bulky trialkylsilyl substituents. NMR studies and DFT calculations suggest that increase of the steric bulkiness on the alkyl‐N and P‐aryl moieties restrict the free rotation around (alkyl)N–P (aryl) bonds, which may cause the generation of more robust active species in higher proportion, leading to extremely high activity along with the generation of a smaller amount of PE.  相似文献   
116.
A simple, comprehensive and efficient capillary electrophoresis method using a dual cyclodextrin system was developed for the simultaneous determination of seven isoflavones (3′‐methoxypuerarin, puerarin, 3′‐hydroxypuerarin, ononin, daidzin, daidzein and genistin). Baseline separations of the seven isoflavones were achieved within 11 min with the running buffer consisting of 35 mm sodium tetraborate, 9.0 mm sulfobutylether‐β‐cyclodextrin and 30 mm α‐cyclodextrin at pH 9.34, and peaks were detected at 254 nm. Other separation parameters included the separation voltage for 15 kV and the working temperature for 25°C. Under the optimum conditions, good linearities were obtained with linear correlation coefficients of seven isoflavones of 0.9978–0.9992. The limits of detection and the limits of quantification were 0.7–2.9 and 2.5–9.5 μg/mL, respectively. Excellent precision and accuracy were obtained. The intraday and interday precision ranged from 0.7 to 2.0% and from 0.8 to 1.9%, respectively. The recoveries of seven analytes were from 97.7 to 103.1%. This method was successfully applied to determine the seven analytes in Radix Puerariae and its preparations.  相似文献   
117.
Utilisation of Anagrus nilaparvatae is a promising and effective method for planthoppers manipulation. Twenty-seven components of remote lemongrass (Cymbopogon distans) oil were identified by GC/MS and nine volatiles were selected for behavioural experiments. In this study, we noted that the remote lemongrass oil was attractive to female A. nilaparvatae at concentrations of 0.1 and 1 mg/L. α-Pinene, β-pinene, eucalyptol, carveol and D-carvone attracted female wasps in the dose-dependent bioassays. Blend 1 (a mixture of eucalyptol, D-carvone, carveol, α-pinene, and β-pinene with ratios of remote lemongrass oil volatiles of 625:80:11:5:3) attracted female wasps at 10 mg/L, while blend 2 (a mixture of the same five volatiles at the same loading ratio) attracted them at 0.1 and 1 mg/L. These results suggested that plant essential oils could be attractants for natural enemies to control pests. The ratios of volatiles in the mixtures affect the attractiveness of the synthetic mixtures.  相似文献   
118.
119.
Necessary and sufficient conditions for qualitative properties of infinite dimensional linear programing problems such as solvability, duality, and complementary slackness conditions are studied in this article. As illustrations for the results, we investigate the parametric version of Gale’s example.  相似文献   
120.
This paper presents a Bell-dual-basis-based quantum watermarking protocol composed of three major algorithms: watermark embedding and extracting and the intercepting test. The first two are completed by using the entanglement swapping property of Bell dual basis and the test is accomplished through IBF protocol to guarantee its bottom security. The watermarking protocol is mainly designed for the protection of digital copyright in the existence of classical information. This design finds that the quality of digital contents is not damaged with its zero-watermark attributes when embedding watermarks.  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