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   26599篇
  免费   2789篇
  国内免费   3534篇
化学   20644篇
晶体学   413篇
力学   937篇
综合类   202篇
数学   3352篇
物理学   7374篇
  2024年   25篇
  2023年   238篇
  2022年   386篇
  2021年   798篇
  2020年   713篇
  2019年   687篇
  2018年   642篇
  2017年   647篇
  2016年   1076篇
  2015年   1063篇
  2014年   1288篇
  2013年   2085篇
  2012年   2157篇
  2011年   2379篇
  2010年   1614篇
  2009年   1793篇
  2008年   1891篇
  2007年   1780篇
  2006年   1574篇
  2005年   1469篇
  2004年   1601篇
  2003年   1172篇
  2002年   1087篇
  2001年   717篇
  2000年   581篇
  1999年   437篇
  1998年   328篇
  1997年   294篇
  1996年   304篇
  1995年   232篇
  1994年   179篇
  1993年   204篇
  1992年   162篇
  1991年   115篇
  1990年   122篇
  1989年   79篇
  1988年   89篇
  1987年   72篇
  1986年   78篇
  1985年   103篇
  1984年   95篇
  1983年   71篇
  1982年   64篇
  1981年   60篇
  1980年   55篇
  1979年   37篇
  1978年   28篇
  1977年   35篇
  1976年   27篇
  1974年   28篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
As photosensitizer for solar cell, a new ruthenium (Ⅱ) complex with four ester groups had been synthesized, in which a phenol substituted by {[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)amino]methyl} is covalently linked to ruthenium (Ⅱ) tris-bipyridine. The structures of the new compounds were confirmed by NMR and ESI-MS spectra. The electrochemical and photochemical properties were also studied.  相似文献   
62.
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported.  相似文献   
63.
The first hyperpolarizabilities of a series of novel azulenic-barbituric acid chromophores have been studied by using 12 excitation wavelengths, ranging from 900 to 1907 nm. The dispersion relation of the first hyperpolarizabilities of chromophores holds the same tendency as the experimental results. In addition, the static first hyperpolarizability β0 of molecules was calculated by means of the Sum-Over-States (SOS) expression and the two-level formula respectively. The results show that these molecules possess large static first hyperpolarizabilities and the, β0 value increases as the donor or acceptor strength enhances; the distorted degree of molecules has also an important influence on the β0 value.  相似文献   
64.
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity.  相似文献   
65.
In this paper, two classes of closely related multilinear singular and fractional integrals,which include the commutators as special cases, are studied and their boundedness on Herz type spaces is discussed. In fact, it is proved that these operators are actually not bounded in certain extreme cases.  相似文献   
66.
A partnership in a cooperative game is a coalition that possesses an internal structure and, simultaneously, behaves as an individual member. Forming partnerships leads to a modification of the original game which differs from the quotient game that arises when one or more coalitions are actually formed. In this paper, the Shapley value is used to discuss the convenience to form either coalitions or partnerships. To this end, the difference between the additive Shapley value of the partnership in the partnership game and the Shapley alliance value of the coalition, and also between the corresponding value of the internal and external players, are analysed. Simple games are especially considered. Research partially supported by Grant BFM 2003-01314 of the Science and Technology Spanish Ministry and the European Regional Development Fund.  相似文献   
67.
铁基添加剂增强细水雾灭火性能的实验研究   总被引:7,自引:0,他引:7  
采用实验模拟的方法,研究了添加氯化亚铁的细水雾在不同添加剂浓度、不同喷头压力下,熄灭不同性质的液体池火的性能。实验结果表明:添加有氯化亚铁的细水雾,其灭火性能发生了显著变化。存在一个最佳的灭火浓度,其对应的灭火时间最短,耗水量最少,灭火效率最高。细水雾喷头的工作压力和燃料的性质也对细水雾的灭火性能有影响:工作压力越大,细水雾的平均灭火时间越短。在相同的实验条件下,细水雾扑灭煤油池火的时间要短于扑灭酒精池火的时间。  相似文献   
68.
A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N2O and SiH4, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiO x films by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase.  相似文献   
69.
70.
Composition algebras with a unit element constitute a well-known class of algebras. In this paper, those composition algebras with a one-sided unit element are characterized and examples are given of arbitrary infinite dimension.

  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