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   24362篇
  免费   4691篇
  国内免费   5141篇
化学   18901篇
晶体学   595篇
力学   1397篇
综合类   532篇
数学   2759篇
物理学   10010篇
  2024年   44篇
  2023年   329篇
  2022年   629篇
  2021年   733篇
  2020年   846篇
  2019年   973篇
  2018年   755篇
  2017年   876篇
  2016年   1035篇
  2015年   1210篇
  2014年   1343篇
  2013年   1788篇
  2012年   2201篇
  2011年   2200篇
  2010年   1851篇
  2009年   1861篇
  2008年   2093篇
  2007年   1818篇
  2006年   1814篇
  2005年   1603篇
  2004年   1309篇
  2003年   1020篇
  2002年   1130篇
  2001年   909篇
  2000年   855篇
  1999年   611篇
  1998年   338篇
  1997年   253篇
  1996年   233篇
  1995年   210篇
  1994年   230篇
  1993年   192篇
  1992年   134篇
  1991年   138篇
  1990年   98篇
  1989年   84篇
  1988年   75篇
  1987年   66篇
  1986年   55篇
  1985年   53篇
  1984年   35篇
  1983年   29篇
  1982年   26篇
  1981年   21篇
  1980年   21篇
  1979年   19篇
  1978年   7篇
  1977年   8篇
  1975年   5篇
  1936年   4篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
We describe a new concept for rotaxane synthesis through intramolecular slippage using π‐conjugated molecules as rigid axles linked with organic soluble and flexible permethylated α‐cyclodextrins (PM α‐CDs) as macrocycles. Through hydrophilic–hydrophobic interactions and flipping of PM α‐CDs, successful quantitative conversion into rotaxanes was achieved without covalent bond formation. The rotaxanes had high activation barrier for their de‐threading, so that they were kinetically isolated and derivatized even under conditions unfavorable for maintaining the rotaxane structures. 1H NMR spectroscopy experiments clearly revealed that the restricted motion of the linked macrocycle with the rigid axle made it possible to control the kinetic stability by adjusting the length of the rigid axle in the precursor structure rather than the steric bulkiness of the stopper unit.  相似文献   
992.
Both residual Cesàro alpha-integrability (RCI( α)) and strongly residual Cesàro alpha-integrability (SRCI(α)) are two special kinds of extensions to uniform integrability, and both asymp-totically almost negative association (AANA) and asymptotically quadrant sub-independence (AQSI) are two special kinds of dependence structures. By relating the RCI(α) property as well as the SRCI(α) property with dependence condition AANA or AQSI, we formulate some tail-integrability conditions under which for appropriate α the RCI(α) property yields L1-convergence results and the SRCI(α) property yields strong laws of large numbers, which is the continuation of the corresponding literature.  相似文献   
993.
Stacked organic light-emitting diodes (SOLEDs) with 30-nm nanoparticle (NP) interfacial layers were investigated. Zinc oxide (ZnO) was used as an interfacial layer between two green polymer (GP) layers. SOLEDs with NP interfacial layers had higher device efficiency than did a single-unit device due to the high probability of exciton recombination that originated from the Auger electron-assisted energy up-conversion process. Although the current density and luminance of SOLEDs with ZnO NP interfacial layers were smaller than those of the reference device, the efficiency was doubled because of the big band alignment difference and the large band gap between GP and ZnO NP interfacial layers, which induced more radiative-exciton recombination.  相似文献   
994.
995.
To further explore an efficient modified route for the shift from an antibacterial fluoroquinolone to an antitumor one,mono-Schiff bases 6a-6h related to ciprofloxacin C3 carbonylhydrazone and bis-Schiff bases 4a-4h corresponding to C3/C7 carbonylhydrazone/hydrazone attached on a skeleton of ciprofloquinolone were designed and synthesized,and their in vitro antitumor activity against CHO,HL60,L1210 cells and antibacterial activity against Staphylococcus aureus and Escherichia coli were also reported.  相似文献   
996.
光引发的固态聚合反应一直是令人感兴趣的研究领域.本文综述了固态光聚合的研究进展.着重介绍了双炔类体系,二烯类体系以及(甲基)丙烯酸酯体系的固态光聚合的研究工作以及应用前景.  相似文献   
997.
998.
999.
A rapid and sensitive liquid chromatography tandem mass spectrometry (LC/MS/MS) method was developed and validated using spinasterol as the internal standard (IS) for the simultaneous determination of shionone and epi‐friedelinol in rat plasma. Plasma samples were pretreated using liquid–liquid extraction with ethyl ether. Chromatographic separation was achieved on a C18 column (100 × 2.1 mm, 5 μm) with an isocratic elution consisting of acetonitrile–0.1% formic acid water (75:25, v/v) at a flow rate of 0.30 mL/min. Detection was performed under the selected reaction monitoring scan using an electrospray ionization in the positive ion mode. The mass transitions were as follows: m/z 427.4 → 95.1 for shionone, m/z 411.4 → 205.2 for epi‐friedelinol and m/z 395.3 → 105.2 for IS. All calibration curves exhibited good linearity (r > 0.995) over the concentration range for both components. The intra‐ and inter‐day precisions at three QC and lower limit of quantitation levels were both <10.21% in terms of relative standard deviation, and the accuracy ranged from ?7.13 to 8.02% in terms of relative error. The extraction recoveries of the compounds ranged from 82.07 to 89.81%. The developed method was successfully applied to the pharmacokinetic study of shionone and epi‐friedelinol after oral administration of Aster tataricus extract to rats. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
1000.
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