全文获取类型
收费全文 | 50766篇 |
免费 | 2649篇 |
国内免费 | 2007篇 |
专业分类
化学 | 28579篇 |
晶体学 | 831篇 |
力学 | 2402篇 |
综合类 | 140篇 |
数学 | 5382篇 |
物理学 | 18088篇 |
出版年
2023年 | 378篇 |
2022年 | 797篇 |
2021年 | 848篇 |
2020年 | 898篇 |
2019年 | 894篇 |
2018年 | 979篇 |
2017年 | 823篇 |
2016年 | 1372篇 |
2015年 | 1054篇 |
2014年 | 1540篇 |
2013年 | 2634篇 |
2012年 | 2737篇 |
2011年 | 3074篇 |
2010年 | 2226篇 |
2009年 | 2090篇 |
2008年 | 2397篇 |
2007年 | 2350篇 |
2006年 | 2151篇 |
2005年 | 1890篇 |
2004年 | 1636篇 |
2003年 | 1444篇 |
2002年 | 1425篇 |
2001年 | 1766篇 |
2000年 | 1258篇 |
1999年 | 1089篇 |
1998年 | 870篇 |
1997年 | 810篇 |
1996年 | 756篇 |
1995年 | 677篇 |
1994年 | 636篇 |
1993年 | 552篇 |
1992年 | 600篇 |
1991年 | 592篇 |
1990年 | 546篇 |
1989年 | 510篇 |
1988年 | 506篇 |
1987年 | 471篇 |
1986年 | 406篇 |
1985年 | 484篇 |
1984年 | 514篇 |
1983年 | 365篇 |
1982年 | 406篇 |
1981年 | 388篇 |
1980年 | 330篇 |
1979年 | 402篇 |
1978年 | 381篇 |
1977年 | 397篇 |
1976年 | 393篇 |
1975年 | 342篇 |
1973年 | 340篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Summary Halogen derivatives of the N-alkylmonoamides and N-alkylimides of maleic and citraconic acid containing the strongly electronegative group CF3 in the alkyl radical, previously unreported in the literature, have been synthesized. 相似文献
82.
83.
Zusammenfassung Der Einfluß von Atmosphäre, Aufheizungsgeschwindigkeit und Spülgasgeschwindigkeit auf die thermische Zersetzung von Alkalibenzolsulfonaten wurde untersucht. Kristallwassergehalt, Dehydratations-temperatur und -wärme, gegebenenfalls die Zusammensetzung, Art, Temperatur und Wärme der Modifikationsänderungen, Schmelzpunkte und Schmelzwärmen der Verbindungen wurden bestimmt. Die Zersetzung verläuft in zwei Abschnitten. In dem ersten Hauptteil entstehen in Inertgasatmosphäre Diphenyloxid, Diphenyl, Diphenylsulfon, Benzol, Phenol, Thiophenol, Diphenylsulfid, Thiantren, Diphenylenoxid und wahrscheinlich Diphenylensulfid, weiterhin Koks, Schwefeldioxid, Natriumsulfit und wenig Natriumsulfat, Natriumsulfid, Acetylen und Wasser. Im zweiten Hauptzersetzungsvorgang entstehen Natriumsulfid und Kohlenoxid. Die Produkte wurden isoliert und analysiert. Dazu wurden Derivatographie, Differentialthermoanalyse, Gaschromatographie, Infrarotspektroskopie, kontinuierliche thermische Titration und chemische Methoden gemeinsam angewandt.
Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965. 相似文献
Summary An investigation was made of the influence of the atmosphere, rate of temperature rise, and velocity of the purging gas on the thermal decomposition of alkali benzene sulfonates. The crystal water content, the dehydration temperature and heat, and if need be the composition, the kind, temperature, and heat of the modification changes, melting points and heats of fusion of the compounds, were determined. The decomposition proceeds in two stages. In the first main stage (in an inert atmosphere) the resulting compounds include diphenyl oxide, diphenyl, diphenylsulfone, benzene, phenol, thiophenol, diphenyl sulfide, thianthrene, diphenylene oxide and probably diphenylene sulfide; also coke, sulfur dioxide, sodium sulfite and a little sodium sulfate, sodium sulfide, acetylene, water. Sodium sulfide and carbon monoxide are formed in the second main decomposition. The products were isolated and analyzed. Furthermore, use was made of derivatography, differential thermal analysis, gas chromatography, infra red spectroscopy, continuous thermal titration, and chemical methods.
Résumé On a étudié l'influence de l'atmosphère, de la vitesse d'échauffement et de balayage du gaz, sur la décomposition thermique des benzène-sulfonates alcalins. On a déterminé la teneur en eau de cristallisation, la température et la chaleur de déshydratation, éventuellement la composition, la nature, la température et la chaleur des changements d'état, les points de fusion et les chaleurs de fusion des composés. La décomposition s'effectue en deux temps. Tout d'abord, en atmosphère inerte, il se forme de l'oxyde de diphényle, du diphényle, de la diphénylsulfone, du benzène, du phénol, du thiophénol, du sulfure de diphényle, du thianthrène, de l'oxyde de diphénylène et probablement du sulfure de diphénylène, et aussi du coke, de l'anhydride sulfureux, du sulfite de sodium et, en moins grande quantité, du sulfate de sodium, du sulfure de sodium, de l'acétylène et de l'eau. Dans une deuxième étape de la décomposition principale, du sulfure de sodium et de l'oxyde de carbone prennent naissance. On a isolé et analysé ces produits. Pour cela, on a utilisé simultanément la dérivatographie, l'analyse thermique différentielle, la chromatographie en phase gazeuse, la spectroscopie infrarouge, le titrage thermique en continu et les méthodes chimiques.
Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965. 相似文献
84.
85.
86.
Serber Z Ledwidge R Miller SM Dötsch V 《Journal of the American Chemical Society》2001,123(37):8895-8901
Our recently developed in-cell NMR procedure now enables one to observe protein conformations inside living cells. Optimization of the technique demonstrates that distinguishing the signals produced by a single protein species depends critically on protein overexpression levels and the correlation time in the cytoplasm. Less relevant is the selective incorporation of (15)N. Poorly expressed proteins, insoluble proteins, and proteins that cannot tumble freely due to associations within the cell cannot yet be observed. We show in-cell NMR spectra of bacterial NmerA and human calmodulin and discuss limitations of the technique as well as prospects for future applications. 相似文献
87.
Veliev M. G. Chalabieva A. Z. Shatirova M. I. Akperova E. G. 《Russian Journal of Organic Chemistry》2003,39(6):825-830
Diene condensation of cyclopentadiene with 2-substituted allylacetylenes occurs nonselectively at a double and triple bonds; therewith the dienophile activity grows in parallel with the electron-withdrawing properties of the substituent. Depending on electronic character of functional groups the reaction proceeds as neutral diene synthesis. The relative activity of cyclopentadiene and 1,3-cyclohexadiene in reactions with allylacetylenes is essentially governed by the different distance between the 1,4-reactive sites in these systems. 相似文献
88.
We establish some inequalities connecting natural parameters of a partial order P. For example, if every interval [a,b] contains at most maximal chains, if some antichain has cardinality v, and if there are 1 chains whose union is cofinal and coinitial in P, then the chain decomposition number for P is 1v (Theorem 2.2), and the inequality is sharp in a certain sense (Section 3).This paper was written while the authors were visitors at the Laboratoire d'algèbre ordinale, Département de Mathématiques, Université Claude Bernard, Lyon 1, France.Research supported by NSERC grant # A5198. 相似文献
89.
L. Avanov N. Borodkova Z. NĚmeček A. Omeltchenko J. Šafránková A. Skalski Yu. Yermolaev G. Zastenker 《Czechoslovak Journal of Physics》1987,37(6):759-774
The paper describes the results of investigations of the solar wind ions, carried out on board the high apogee Prognoz 7 and Prognoz 8 Earth's satellites with the aid of an SKS instrument (USSR) and a Monitor instrument (USSR-SSR). Behaviour of proton and that of components on the front of Earth's bow and interplanetary shock waves were compared by means of the energoanalysis and energy-mass analysis techniques. In several long-term periods of observation the solar wind heavy ions — oxygen, silicon and iron were determined. It enabled us to estimate the solar corona chemical composition and electron temperature.Presented at the 5th General Assembly IAGA/IAMAP August 5–17, 1985, Prague, Czechoslovakia. 相似文献
90.
The development of diffusion creep (DC) accompanying superplastic deformation (SPD) of the highly doped nickel alloy ZhS6KP is studied based on an investigation of the redistribution of dispersed intragrain deposits of the phase of Ni3(Al, Ti). Deposit-free zones (DFZ) are formed in the alloy, held at the temperature of SPD and accompanying deformation at the grain boundaries. The contribution of DC to the deformation was determined from a comparative analysis of the width of the DFZ in the deformed and undeformed parts of the samples for different grain sizes and rates of DC taking into account diffusion accommodation. It was established that for the optimum rate of SPD the upper limit of the contribution of DC to deformation for 2-m grains does not exceed 11%. It is concluded, based on the distribution of DFZ, that the effect of DC accompanying SPD is determined by diffusion fluxes, associated with the local concentration of stress accompanying the development of grain-boundary slipping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 40–45, June, 1986.In conclusion, we thank Yu. M. Mishin for a useful discussion of the results. 相似文献