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   2412篇
  免费   4篇
  国内免费   2篇
化学   1533篇
晶体学   25篇
力学   74篇
综合类   1篇
数学   277篇
物理学   508篇
  2022年   24篇
  2021年   28篇
  2020年   37篇
  2019年   48篇
  2018年   80篇
  2017年   87篇
  2016年   81篇
  2015年   40篇
  2014年   84篇
  2013年   101篇
  2012年   86篇
  2011年   90篇
  2010年   95篇
  2009年   76篇
  2008年   91篇
  2007年   92篇
  2006年   86篇
  2005年   50篇
  2004年   67篇
  2003年   61篇
  2002年   65篇
  2001年   49篇
  2000年   37篇
  1999年   39篇
  1998年   30篇
  1997年   34篇
  1996年   22篇
  1995年   27篇
  1994年   31篇
  1993年   27篇
  1992年   28篇
  1991年   22篇
  1990年   29篇
  1989年   32篇
  1988年   23篇
  1987年   23篇
  1986年   35篇
  1984年   32篇
  1983年   32篇
  1982年   26篇
  1980年   27篇
  1979年   34篇
  1978年   22篇
  1977年   25篇
  1976年   30篇
  1975年   37篇
  1974年   23篇
  1973年   28篇
  1972年   26篇
  1971年   20篇
排序方式: 共有2418条查询结果,搜索用时 15 毫秒
71.
Derivatives of N-(2-hydroxyethyl)cytisine, N-(2-hydroxypropyl)-, N-(2-hydroxy-2-(1-adamantyl)ethyl)-, and N-(2-hydroxy-2-phenylethyl)cytisine, were synthesized by reduction of N-(2-oxopropyl)-, N-(2-oxo-2-(1-adamantyl)ethyl)-and N-(2-oxo-2-phenylethyl)cytisine with metal hydrides. The antiarrhythmic and analgesic activities of the prepared compounds were investigated. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 157–162, March–April, 2007.  相似文献   
72.
The trimethylsilylation of 5,7-dioxo(4H,6H)-1,3-dithiolo[4,5-d]pyrimidine-2-selone with bis(trimethylsilyl) acetamide enables pyrimido-tetrathiafulvalene derivatives to be prepared in benzene solution and increases the yield of the target compounds compared with the reaction of the unsilylated selone in DMF solution. The intermediate 2,4-bis(trimethyl-silyloxy)pyrimidotetrathisfulvalenes were sensitive to hydrolysis. The previously undescribed [2,4-dioxo(1H,3H)pyrimido]di-(methylthio)tetrathifulvalene has been obtained. The redox properties of the compounds obtained have been investigated by cyclic current-potential measurements.Riga Technical University, Riga LV-1658. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1285–1289, September, 1994. Original article submitted July 25, 1994.  相似文献   
73.
For obtaining 19-hydroxytestosterone from dehydroepiandrosterone a new scheme of synthesis has been developed the key stages of which are the reduction of the 17-keto group to a 17-alcohol, the functionalization of the 19-methyl group via the bromohydrin with the formation of a 6,19-epoxide, the selective hydrolysis of the free -acetoxy group, the conversion of the 3-hydroxy-5-bromo derivative into the 4-3-ketone, and the reductive cleavage of the 6,19-epoxide ring.Institute of Bioorganic Chemistry, Belorussian Academy of Sciences, Minsk. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 672–678, November–December, 1992.  相似文献   
74.
Transmetallation of the dichalcogenide complexes [CpMn(CO)2]2(-X2) (X = S or Se) with M(CO)5(thf) (M = Cr or W) afforded new heterometallic complexes CpMn(CO)2(-Se2)Cr(CO)5, CpMn(CO)2(-Se2)[Cr(CO)5]2, CpMn(CO)2(-X2)[W(CO)5]2 (X = S or Se), and CpMn(CO)2(-Se2)[Cr(CO)5][W(CO)5]. According to the X-ray diffraction data, their molecular structures contain the cyclic MnX2 fragments coordinated by one or two M(CO)5 groups via the X atoms. Study of thermal decomposition of the manganese complexes with different Mn : M : X ratios (M = Cr, W; X = S, Se, Te) by differential scanning calorimetry (DSC) and thermogravimetry demonstrated that this process took place at rather low temperatures (100—400 °C) and was accompanied by complete elimination of the CO groups followed by elimination of the Cp groups. At any metal to chalcogen ratio, the resulting inorganic chalcogenides contained no impurities of metal oxides and carbides.  相似文献   
75.
The dependence of protein kinase and RNA polymerase activities, and also of the synthesis of protein in nuclear chromatin, on the addition of benzylaminopurine and a cytokinin-binding protein to the incubation mixture has been investigated. It has been shown that all three processes are hormone-dependent. It has been found that the activity of protein kinase C is regulated by a cytokinin.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 62 70 71. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 745–749, September–October, 1997.  相似文献   
76.
The effect of solvent polarity and ion pair formation oncis-trans-isomerization of cationic-anionic polymethine dyes and of related simple cationic and anionic dyes is studied by flash photolysis. The change in the rate constant for reversecis-trans- isomerization of photoisomers due to the interaction of a cation with an anion in an ion pair is observed in nonpolar solvents. A drop in the yield of the photoisomers to zero is observed for a number of cationic-anionic dyes in weakly polar and nonpolar solvents which is possibly due to steric hindrances in the photoisomerization process in ion pairs.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 719–724, April, 1993.  相似文献   
77.
Single crystals of triple molybdate of composition 5:1:3 K5Pb0.5Hf1.5(MoO4)6 have been grown and their crystal structure has been solved from X-ray diffraction data (an automated diffractometer X8 APEX, MoK α -radiation, 2173 F(hkl), R = 0.0321). Trigonal unit cell parameters are: a = b = 10.739(2) Å, c = 37.933(9) Å; V = 3789(1) Å3, Z = 6, ρcalc = 4.014 g/cm3, space group \(R\bar 3\). Three-dimensional mixed framework of the structure is formed by two types of MoO4 tetrahedra and Pb and Hf octahedra linking via common O-vertices. Potassium atoms of three types occupy large vacancies in the framework.  相似文献   
78.
Summary Three sesquiterpene hydrocarbons, muurolene-1, muurolene-2, and muurolene-3, have been isolated from the oleoresin ofPinus sibirica R. Mayr.Muurolene-3 is D--muurolene and has the structure (VIII).Khimiya Prirodnykh Soedinenii, Vol. 2, No. 3, pp. 173–176, 1966  相似文献   
79.
Electronic, IR and UV spectroscopy has shown that 2-(N-isatinomethylene)-3(2H)-benzo[b]thiophenone in solution displays photo- and solvatochromism as a result of reversible E Z isomerization, and it readily undergoes alcoholysis of the lactam bond. The resulting aminovinyl ketones exist as mixtures of the thermodynamically stable E- and Z-isomers.For Communication 45, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1217–1220, September, 1989.  相似文献   
80.
Summary 1. The composition of the acid fraction of the oleresin ofPinus pumila (Pall.) Regel. has been studied, and from it has been isolated, in addition to known compounds, the methyl ester of a new labdane acetoxy acid.2. In the hydrocarbon fraction of the oleoresin 11 monoterpenes and 26 sesquiterpenes have been found (and 17 of the latter have been identified).3. The composition of the fraction of neutral oxygen-containing diterpenoids fromP. pumila differs considerably in its diterpenoid components from the corresponding fractions of the oleoresins of botanically related species-P. sibirica andP. koraiensis. Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 299–302, May–June, 1976.  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