全文获取类型
收费全文 | 233659篇 |
免费 | 3653篇 |
国内免费 | 630篇 |
专业分类
化学 | 130371篇 |
晶体学 | 3450篇 |
力学 | 8694篇 |
综合类 | 5篇 |
数学 | 25622篇 |
物理学 | 69800篇 |
出版年
2018年 | 1785篇 |
2017年 | 1703篇 |
2016年 | 3398篇 |
2015年 | 2646篇 |
2014年 | 3445篇 |
2013年 | 9965篇 |
2012年 | 7085篇 |
2011年 | 8767篇 |
2010年 | 5547篇 |
2009年 | 5313篇 |
2008年 | 8008篇 |
2007年 | 8113篇 |
2006年 | 7686篇 |
2005年 | 6945篇 |
2004年 | 6160篇 |
2003年 | 5439篇 |
2002年 | 5238篇 |
2001年 | 6476篇 |
2000年 | 5024篇 |
1999年 | 3952篇 |
1998年 | 3120篇 |
1997年 | 3170篇 |
1996年 | 3226篇 |
1995年 | 2970篇 |
1994年 | 2890篇 |
1993年 | 2861篇 |
1992年 | 3258篇 |
1991年 | 3008篇 |
1990年 | 2975篇 |
1989年 | 2953篇 |
1988年 | 2882篇 |
1987年 | 2906篇 |
1986年 | 2716篇 |
1985年 | 3713篇 |
1984年 | 3738篇 |
1983年 | 3094篇 |
1982年 | 3302篇 |
1981年 | 3240篇 |
1980年 | 3146篇 |
1979年 | 3232篇 |
1978年 | 3514篇 |
1977年 | 3317篇 |
1976年 | 3191篇 |
1975年 | 3042篇 |
1974年 | 2986篇 |
1973年 | 2989篇 |
1972年 | 1890篇 |
1968年 | 2065篇 |
1967年 | 2274篇 |
1966年 | 2066篇 |
排序方式: 共有10000条查询结果,搜索用时 42 毫秒
991.
992.
Solubility of carbon dioxide in aqueous solutions of sodium chloride: Experimental results and correlation 总被引:2,自引:0,他引:2
The solubility of carbon dioxide in aqueous solutions of sodium chloride was measured in the temperature range from 40 to 160°C, up to 6 mol-kg salt solutions and total pressures up to 10 MPa. Pitzer's(1) equations as well as the Chen and Evans(2) model were used to correlate the new data. Results are reported and compared to literature data and correlations. 相似文献
993.
Lead(II) alkanoates with even chain lengths from octanoate to octadecanoate have been investigated by Raman spectroscopy. In the low frequency region, transverse and longitudinal acoustical modes (TAM, LAM) have been assigned. It was shown that LAM-1 is the vibration of the double chain with the node of the vibration in the Pb2+ layer. A fully extended conformation of the chains in the low temperature phase was confirmed. The frequencies and intensities of the LAMs as compared with those of the alkanes and the fatty acids led to an estimate of the force constant and polarizability of the Pb2+ -COO- bond relative to the C-C bond. The defects at the chain ends were investigated in the ρ(CH3) and v(CC) region. For the intermediate (CM) phase, both the Pb2+ layer distance reduction and the chain length independent enthalpy contributions can be attributed mainly to defects at the chain ends. 相似文献
994.
D.G. Seapy S.S.H. Al-Mahmoodi N.M.M. Al-Belushi F.A.M. Al-Mjeni 《Journal of photochemistry and photobiology. A, Chemistry》1994,80(1-3):241-249
The relatives photoreactives of bridged-ring systems 1, 3, 5-X and 6-X (X ≡ Cl or Br) have been studied at 254 nm in acetic acid. The formation of photosolvolysis product was rationalized in terms of photoinduced intramolecular electron transfer (ET) processes. The relative ease of ET in these donor—bridge—acceptor model system was analyzed in terms of known ET variables including free-energy changes, orientation effects and ridigity effects. The observed relative photoreactivities agreed better with the calculated free-energy changes when relative rigidities of the electron acceptor termini were evaluated. In general, the more rigid system were more photoreactive. 相似文献
995.
A series of unsaturated polyesters based on phthalic anhydride (PHA), maleic anhydride (MA), ethylene glycol (EG), diethylene glycol (DG), triethylene glycol (TG), propylene glycol (PG), styrene (Sty) and acrylonitrile (AN) were prepared. The molecular weights of the prepared polyesters were determined by end-group analysis. The effect of the structure of the resin on its curing behavior has been investigated. On the basis of the experimental study, the following were concluded: (1) The maximum curing temperature (Tmax) is related to the molecular weight of the glycol incorporated in these castings. In this context the Tmax was found to decrease with increasing the molecular weight. Meanwhile the time to peak temperature tmax was increasing. (2) The higher the percentage of AN in the crosslinking monomer system, the slower a resin cures. (3) The values of Tmax were found to be influenced to a large extent by the percentage of AN. 相似文献
996.
997.
Reduced charge montmorillonites (RCM) were prepared by the thermal treatment of lithiumsaturated montmorillonite. Samples prepared by mild thermal treatment with lithium contained more water sorbed than the original montmorrilonite. When RCMs were prepared, part of the lithium cations reacted with hydroxyl groups in the octahedral sheet and released protons, which reacted with the structure. Acid treatment probably enhanced the surface area. which was reflected in the amount of water sorbed. Deprotonation of hydroxyl groups was proved by the measurements of the ignition loss. The heating of lithium saturated montmorillonite at higher temperatures brough about the collapse of the interlayers and a decrease in the amount of water sorbed. 相似文献
998.
E. K. Merabet H. K. Yuen W. A. Grote K. L. Deppermann 《Journal of Thermal Analysis and Calorimetry》1994,42(5):895-906
A new sensitive isothermal titration microcalorimeter using polyvinylidene difluoride (PVDF) as detector has been developed. Heat pulses of less than 0.4 μJ can be detected and the baseline noise level (p-p) is 40 nW. The calorimeter is constructed with one reaction cell (0.7 ml) insulated by several radiation shields inside a vacuum chamber. The performance of the instrument was examined by measuring the heat of protonation of Tris with HCl. The enthalpy of reaction was found to be ?49±1 kJ·mol?1, in good agreement with the reported value of ?47.5 kJ·mol?1. 相似文献
999.
J. -M. Douillard H. Malandrini T. Zoungrana F. Clauss S. Partyka 《Journal of Thermal Analysis and Calorimetry》1994,41(6):1205-1210
It is possible to estimate surface tension of high-energy solids combining the immersion microcalorimetry thermodynamics and Van Oss' model. In this study we have applied this method on talc and talc-chlorite samples in order to obtain thermodynamic values which permit to understand surface properties useful in the industrial applications of these solids. Some talcite samples are preferentially used in specific industrial applications because they are less hydrophobic or more lamellar. This method seems to be reliable to classify the solids and predict some properties. 相似文献
1000.
Z. Szeglowski H. Bruchertseifer V. B. Brudanin G. V. Buklanov O. Constantinescu Dinh Thi Lien V. P. Domanov L. I. Guseva M. Hussonnois G. S. Tikhomirova I. Zvara Yu. Ts. Oganessian 《Journal of Radioanalytical and Nuclear Chemistry》1994,186(4):353-359
The short-lived isotopes of W and their descendants have been isolated from the products of the bombardment of144Sm with24Mg by a fast continuous ion-exchange method, using HF solution media. The feasibility of this method for isolation of element 106 is discussed. 相似文献