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   7426篇
  免费   1103篇
  国内免费   733篇
化学   5391篇
晶体学   60篇
力学   436篇
综合类   24篇
数学   800篇
物理学   2551篇
  2024年   25篇
  2023年   189篇
  2022年   315篇
  2021年   325篇
  2020年   346篇
  2019年   332篇
  2018年   271篇
  2017年   263篇
  2016年   404篇
  2015年   386篇
  2014年   426篇
  2013年   512篇
  2012年   659篇
  2011年   710篇
  2010年   444篇
  2009年   459篇
  2008年   446篇
  2007年   432篇
  2006年   346篇
  2005年   323篇
  2004年   214篇
  2003年   195篇
  2002年   182篇
  2001年   123篇
  2000年   112篇
  1999年   127篇
  1998年   100篇
  1997年   93篇
  1996年   94篇
  1995年   72篇
  1994年   61篇
  1993年   48篇
  1992年   59篇
  1991年   39篇
  1990年   28篇
  1989年   28篇
  1988年   18篇
  1987年   13篇
  1986年   8篇
  1985年   12篇
  1984年   6篇
  1983年   3篇
  1982年   6篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1971年   1篇
  1959年   1篇
  1957年   1篇
排序方式: 共有9262条查询结果,搜索用时 15 毫秒
991.
综述了目前国内外微囊藻毒素检测方面的各种研究方法及成果,对高效液相色谱(HPLC)、液相色谱串联质谱(LC–MS)、气相色谱串联质谱(LC–MS)、毛细管电泳(CE)、薄层色谱(TLC)、生物法和生物化学法等检测方法存在的优缺点进行了评述,并展望了该研究领域的未来发展趋势。  相似文献   
992.
Novel water-compatible molecularly imprinted polymers (MIPs) selective for amiodarone (AD) were designed via a new methodology which relies on screening library of non-imprinted polymers (NIPs). The NIP library consisted of eighteen cross-linked co-polymers synthesized from monomers commonly used in molecular imprinting. The binding capacity of each polymer in the library was analyzed in two different solvents. Binding in water was used to assess non-specific (hydrophobic) interactions and binding in an appropriate organic solvent was used to assess specific interactions. A good correlation was found between the screening tests and modeling of monomer–template interactions performed using computational approach. Additionally, analysis of template–monomer interactions was performed using UV–vis spectroscopy. As the result, 4-vinylpyridine (4-VP) was selected as the best monomer for developing MIP for AD. The 4-VP-based polymers demonstrated imprinting factor equal 3.9. The polymers performance in SPE was evaluated using AD and its structural analogues. The recovery of AD was as high as 96% when extracted from spiked phosphate buffer (pH 4.5) solution and 82.1% from spiked serum samples. The developed MIP shown as a material with specific binding to AD, comparing to its structural analogues, 1-(2-diethylaminoethoxy)-2,6-diiodo-4-nitrobenzene and lidocaine, which shown 9.9% and 25.4% of recovery from the buffer solution, correspondingly. We believe that the screening of NIP library could be proposed as an alternative to commonly used computational and combinatorial approaches.  相似文献   
993.
SnO2/Al2O3 catalyst prepared by sol-gel method showed higher activity than those prepared by impregnation method, and their activity was significantly improved by pre-treatment in the reaction gas. The increased activity is closely related to the agglomeration of SnO2 species and the re-exposure of Al2O3, which was previously covered by dispersed SnO2 species. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
994.
One linear template 13 and one cyclophane template 15, both incorporating two electron rich 1,4‐dialkoxybenzene units and one diamide unit, have been synthesized. By utilizing donor‐acceptor interaction and/or intermolecular hydrogen bonding assembling principles, one novel hetero[3]rotazane 22·4Cl, possessing one neutral and one tetracationic ring components, has been synthesized from 13, through neutral [2]rotaxane 21 as intermediate. With 15 as template, tetracationic [2]catenane 23·4PF6 was assembled by using donor‐acceptor interaction, but no neutral [2]rotaxane could be obtained under the typical conditions of hydrogen bonding assembling principle. The interlocked supramolecular compounds have been characterized and their spectral properties are investigated.  相似文献   
995.
It is well known that porphyrin derivatives play a key role in the primary process of photo-synthesis[1], in which porphyrins directly absorb the sunlight or indirectly acquire excitation en-ergy from light-harvesting antenna system to reach their excited state, and then donate electrons to quinone acceptors to yield a series of charge-separated species. In general, only first singlet ex-cited state of porphyrins is involved in energy transfer process[2]. However, highly excited state (S2 stat…  相似文献   
996.
The phenomenon that metalloporphyrins are coordinated to axial ligands is very common especially in green-plant and photosynthetic bacteria, where such coordination impacts a signifi-cant effect on both the primary charge separation in the reaction center and energy transfer in an-tenna systems[1]. In addition, it plays a key role in photodynamic therapy and medicine synthesis in a sense that some metalloporphyrins have been assembled by coordination bonds to anti-cancer drugs, enhancing the se…  相似文献   
997.
亚甲蓝分光光度法测定水体中的阴离子表面活性剂   总被引:2,自引:0,他引:2  
利用三氯甲烷萃取水体样品中的阴离子表面活性剂,用50mL比色管代替50mL容量瓶对三氯甲烷萃取液进行定容,以亚甲蓝分光光度法进行测定。该方法操作简便,测定阴离子表面活性剂的线性范围为0.150~1.70mg/L,检出限为0.050mg/L,样品加标回收率为89%~98%。  相似文献   
998.
介绍便携式温度计校验仪的工作原理及研制过程。对该仪器的恒温槽体机械结构、制冷器和散热器的设计、恒温槽体温度测量及控制等进行了详细叙述。该仪器提供的温度场稳定、均匀,在-20~100℃范围内可任意设定温度。解决了温度计现场快速校准的问题。  相似文献   
999.
采用Hypersil硅胶柱,在流动相为正己烷-四氢呋喃(体积比90:10),流速为1.0mL/min,检测波长为230nm,柱温为20℃时,速霸螨中克螨特和唑螨酯得到很好分离;克螨特的平均回收率为100%,标准偏差为0.65g/L,相对标准偏差为0.66%;唑螨酯的平均回收率为98%,标准偏差为0.08g/L,相对标准偏差为0.29%;方法简便、快捷、准确。  相似文献   
1000.
研究了碳酸氢铵沉淀法的反应条件对氧化钇粒度的影响,探讨了粒度变化规律。发现在沉淀反应中,晶型碳酸钇铵的形成与否是影响氧化钇粒度的关键因素。在较低的反应温度下,当碳酸氢铵和氯化钇的浓度大于0.25mol·L-1,摩尔比大于5,陈化时间大于60min时得到碳酸钇铵沉淀,经煅烧可获得粒度(D50)大于1μm的氧化钇。当反应物浓度较低、摩尔比小,陈化时间较短时得到无定型碳酸钇沉淀,煅烧沉淀可获得粒度(D50)小于0.5μm的氧化钇。实验证明选择适当的沉淀反应条件,可制备D50在0.3~10μm范围内的不同粒度级别的氧化钇粉体。  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