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   227678篇
  免费   3077篇
  国内免费   603篇
化学   118877篇
晶体学   2834篇
力学   9723篇
综合类   5篇
数学   26239篇
物理学   73680篇
  2021年   1923篇
  2020年   2243篇
  2019年   2420篇
  2018年   3299篇
  2017年   3157篇
  2016年   4832篇
  2015年   3156篇
  2014年   4472篇
  2013年   10886篇
  2012年   9195篇
  2011年   10824篇
  2010年   7234篇
  2009年   6900篇
  2008年   9651篇
  2007年   9795篇
  2006年   9203篇
  2005年   8245篇
  2004年   7503篇
  2003年   6447篇
  2002年   6226篇
  2001年   6749篇
  2000年   5102篇
  1999年   3893篇
  1998年   3013篇
  1997年   3042篇
  1996年   2861篇
  1995年   2746篇
  1994年   2592篇
  1993年   2498篇
  1992年   2835篇
  1991年   2736篇
  1990年   2646篇
  1989年   2431篇
  1988年   2488篇
  1987年   2492篇
  1986年   2322篇
  1985年   3067篇
  1984年   3297篇
  1983年   2692篇
  1982年   2849篇
  1981年   2801篇
  1980年   2658篇
  1979年   2772篇
  1978年   2858篇
  1977年   2871篇
  1976年   2933篇
  1975年   2712篇
  1974年   2676篇
  1973年   2830篇
  1972年   1781篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Premchand  V. P.  Balaram  Bipin  Mani  Ajith K.  Narayanan  M. D.  Sajith  A. S. 《Nonlinear dynamics》2022,110(1):573-588
Nonlinear Dynamics - Optimisation procedures for nonlinear vibrating systems are made cumbersome due to the fact that the regimes of periodic response are not known beforehand. Moreover, such...  相似文献   
42.
Advances in Data Analysis and Classification - In the original publication of the article, the line after equation (5) has been published incorrectly  相似文献   
43.
Doklady Physical Chemistry - The rheological behavior of a 1 wt % suspension of highly porous chitosan particles in polydimethylsiloxane in a high electric field has been studied as a function of...  相似文献   
44.
Journal of Structural Chemistry - N-cyanomethylanabasine is prepared with an yield of 70% by the interaction of the alkaloid anabasine with glyconitrile. It is shown that the highest yield of the...  相似文献   
45.
46.
Cedrela genus, a member of the Meliaceae family, presents both chemical characteristics associated with and those that distinguish it from the rest of its members. The presence of triterpenes and limonoids is the characteristic of the Meliaceae family, but the class and type of these chemical constituents are distinctive for each genus. Cedrela includes cycloartane, ursane, oleanane, tirucallane, butyrospermane, and apotirucallane triterpenes, and its limonoids belongs to six class and nine types, known as class Ia-type havanensines, class Ib-type delevoyin, class II-type gedunin, class IIIb-type andirobin, class IIIg-type mexicanolide, class IVa-type evoludone, class Va-type obacunol, class V-type limonin, and class VIII. Each of these structural arrangements includes specific traits, defined by their biosynthetic origin, which can be established by means of structural elucidation techniques, particularly 1H and 13C NMR, which assisted by 2D NMR techniques, allowing to deduce their structures unequivocally. The constant presence of these skeletal arrangements in Cedrela ensures that they are its chemophenetic markers and their recurrence is an important criterion for their identity. This review is a compilation of the occurrence of triterpenes and limonoids in Cedrela genus, detailing their biosynthetic association and collecting and organizing their NMR data, with the purpose of facilitating its location, analysis, and use in the phytochemical study of species from this genus.  相似文献   
47.
Controlling redox activity of judiciously appended redox units on a photo-sensitive molecular core is an effective strategy for visible light energy harvesting and storage. The first example of a photosensitizer - electron donor coordination compound in which the photoinduced electron transfer step is used for light to electrical energy conversion and storage is reported. A photo-responsive Ru-diimine module conjugated with redox-active catechol groups in [Ru(II)(phenanthroline-5,6-diolate)3]4− photosensitizer can mediate photoinduced catechol to dione oxidation in the presence of a sacrificial electron acceptor or at the surface of an electrode. Under potentiostatic condition, visible light triggered current density enhancement confirmed the light harvesting ability of this photosensitizer. Upon implementation in galvanostatic charge-discharge of a Li battery configuration, the storage capacity was found to be increased by 100 %, under 470 nm illumination with output power of 4.0 mW/cm−2. This proof-of-concept molecular system marks an important milestone towards a new generation of molecular photo-rechargeable materials.  相似文献   
48.
Crystallography Reports - A geometrical and topological analysis has been performed, and self-assembly of the crystal structures of intermetallic compounds CsnMk (М = Na, K, Rb, Pt, Au, Hg,...  相似文献   
49.
The Bcl-2 family small molecule inhibitor navitoclax is being clinically evaluated to treat multiple cancers including lymphoid malignancies and small cell lung cancer. A sensitive and reliable method was developed to quantitate navitoclax in human plasma using liquid chromatography with tandem mass spectrometry with which to perform detailed pharmacokinetic studies. Sample preparation involved protein precipitation using acetonitrile. Separation of navitoclax and the internal standard, navitoclax-d8, was achieved with a Waters Acquity UPLC BEH C18 column using isocratic flow over a 3 min total analytical run time. A SCIEX 4500 triple quadrupole mass spectrometer operated in positive electrospray ionization mode was used for the detection of navitoclax. The assay range was 5–5,000 ng/ml and proved to be accurate (89.5–104.9%) and precise (CV ≤ 11%). Long-term frozen plasma stability for navitoclax at −70°C was at least 43 months. The method was applied for the measurement of total plasma concentration of navitoclax in a patient receiving a 250 mg daily oral dose.  相似文献   
50.
Crystallography Reports - The crystal structure and crystallochemical features of a Fe-deficient zirconium-rich analog of eudialyte from the Lovozero alkaline massif (Kola peninsula) have been...  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