全文获取类型
收费全文 | 39875篇 |
免费 | 823篇 |
国内免费 | 381篇 |
专业分类
化学 | 20349篇 |
晶体学 | 690篇 |
力学 | 1771篇 |
综合类 | 24篇 |
数学 | 4070篇 |
物理学 | 14175篇 |
出版年
2022年 | 370篇 |
2021年 | 419篇 |
2020年 | 405篇 |
2019年 | 401篇 |
2018年 | 584篇 |
2017年 | 501篇 |
2016年 | 832篇 |
2015年 | 509篇 |
2014年 | 859篇 |
2013年 | 1806篇 |
2012年 | 1785篇 |
2011年 | 2137篇 |
2010年 | 1549篇 |
2009年 | 1506篇 |
2008年 | 1756篇 |
2007年 | 1694篇 |
2006年 | 1559篇 |
2005年 | 1356篇 |
2004年 | 1269篇 |
2003年 | 1127篇 |
2002年 | 1051篇 |
2001年 | 1438篇 |
2000年 | 1035篇 |
1999年 | 865篇 |
1998年 | 654篇 |
1997年 | 639篇 |
1996年 | 570篇 |
1995年 | 516篇 |
1994年 | 484篇 |
1993年 | 426篇 |
1992年 | 488篇 |
1991年 | 486篇 |
1990年 | 483篇 |
1989年 | 437篇 |
1988年 | 459篇 |
1987年 | 443篇 |
1986年 | 387篇 |
1985年 | 457篇 |
1984年 | 491篇 |
1983年 | 355篇 |
1982年 | 398篇 |
1981年 | 382篇 |
1980年 | 332篇 |
1979年 | 413篇 |
1978年 | 385篇 |
1977年 | 397篇 |
1976年 | 399篇 |
1975年 | 347篇 |
1974年 | 327篇 |
1973年 | 340篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The redox behaviour of adsorbed species of 2,4,6-tri(2-pyridyl)-1,3-5-triazine (TPTZ) at the surface of a mercury electrode was examined using cycling voltammetry. Based on the adsorption and accumulation of TPTZ at the charged mercury surface cathodic adsorptive stripping voltammetry (CSV) is applied for the trace determination of TPTZ using a differential pulse (DP) technique. Experimental and operational parameters for the quantitative analysis of TPTZ are optimized and the detection limit was found to be 3×10–9 mol/l. The effect of some interferences, e.g. organic compounds, cations and anions, are investigated. 相似文献
942.
离子注入修饰电极检测硝基苯 总被引:9,自引:0,他引:9
离子注入是一种新技术,可按人们的意愿和需要,将不同的离子注入不同的基本电极表面,制成具有催化活性强,稳定性高,重现性好等特点的修饰电极。作者研究了离子注入钴和注入镍的玻碳电极在0.1mol/LHAc-NaAc缓冲溶液中硝基苯的行为及测定。 相似文献
943.
Epiphytic lichens have long been considered to be reliable bioindicators of air pollution. In the present study only one lichen species, Hypogymnia physodes (L.) Nyl., was chosen; this species is very often used for biomonitoring in Europe. Total mercury and methylmercury were determined in lichens taken from various polluted and unpolluted locations in Slovenia, including a mercury mining area around Idrija. Additionally, total gaseous mercury in air was also determined at several sampling points. 相似文献
944.
Z. G. Aliev A. M. Sipyagin V. G. Kartsev L. O. Atovmyan 《Russian Chemical Bulletin》1986,35(1):120-124
Conclusions Under the conditions of the acidic cyclization reaction of homologous 3- and 4-[(4-chlorophenyl)sulfamoyl]-1-diazoalkan-2-ones, the formation of the five-membered heterocycle, a pyrrolidin-3-one derivative, is more convenient than the formation of the four-membered heterocycle- an azetidin-3-one derivative. These results are in agreement with the differences in conformations of diazoalkane molecules in the crystalline state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 134–138, January, 1986. 相似文献
945.
946.
Chen T Barton SC Binyamin G Gao Z Zhang Y Kim HH Heller A 《Journal of the American Chemical Society》2001,123(35):8630-8631
947.
Commercial poly(ethylene terephthalate) (PET) was treated at R. H.>80% and room temperature for a set time. The glass transition
temperature (Tg) decreases with the time of exposure to high humidity. The decrease in Tg is a result of plasticization. Our
data indicate that the Tg of dry PET of 76-78°C may decrease to as low a temperature as 65-67°C when it is wet. Induced crystallization
of PET in the presence of water reduces the cold crystallization temperature (Tc). The structure of water-induced crystals
is imperfect and can be improved in perfection by annealing.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
948.
The linear sweep polarographic wave of the uranium-Xylidyl Blue I complex in ethylenediamine-1,10-phenanthroline-hydrochloric acid medium has been studied. The complex, corresponding to UO(2)(XBI)(2-)(2) with log beta' = 9.09 (by polarography), 8.81 (by spectrophotometry), is strongly adsorbed on the surface of the mercury electrode. The polarographic wave is attributed to the reduction of Xylidyl Blue I in the complex. The method is very sensitive with a detection limit of 3 x 10(-8)M. The wave height is proportional to the concentration of uranium over the range 8 x 10(-8)-7 x 10(-6)M. Solvent extraction is used to separate possible interferences. The recommended procedure has been applied to the determination of trace amounts of uranium in ores. 相似文献
949.
950.
Stoltz C Ramesha K Sirchio SA Gönen ZS Eichhorn BW Salamanca-Riba L Gopalakrishnan J 《Journal of the American Chemical Society》2003,125(14):4285-4292
Anion metathesis reactions between ZrNCl and A(2)S (A = Na, K, Rb) in the solid state follow three different pathways depending on reaction temperature and reactant stoichiometry: (1) the reaction of ZrNCl with A(2)S in the 2:1 stoichiometry at 800 degrees C/72 h/in vacuo yields alpha-Zr(2)N(2)S with the expected layered structure of La(2)O(2)S. Above 850 degrees C, alpha-Zr(2)N(2)S (P3 macro m1; a = 3.605(1) A, c = 6.421(3) A) neatly transforms to beta-Zr(2)N(2)S (P6(3)/mmc: a = 3.602(1) A, c = 12.817(1) A). The structures of the alpha- and beta-forms are related by an a/2 shift of successive Zr(2)N(2) layers. (2) The same reaction at low temperatures (300-400 degrees C) yields ACl intercalated phases of the formula A(x)Zr(2)N(2)SCl(x) (0 < x < approximately 0.15), where alkali ions are inserted between the S/Cl.S/Cl van der Waals gap of a ZrNCl-type structure. The S and Cl ions are disordered and the c lattice parameters are alkali dependent (R3 macro m, a approximately 3.6 A, c approximately 28.4 (Na), 28.9 (K), and 30.5 A (Rb). A(x)Zr(2)N(2)SCl(x) phases are hygroscopic and reversibly absorb water to give monohydrates. (3) Reaction of ZrNCl with excess A(2)S at 400-1000 degrees C gives A(2)S intercalated phases of the formula A(2)(x)Zr(2)N(2)S(1+)(x) (0 < x < 0.5), where the alkali ions reside between the S.S van der Waals gap of a ZrNCl type structure (R3 macro m, a approximately 3.64 A, c approximately 29.48 A). Structural characterization of the new phases and implications of the results are described. 相似文献