全文获取类型
收费全文 | 1670篇 |
免费 | 48篇 |
国内免费 | 9篇 |
专业分类
化学 | 1162篇 |
晶体学 | 14篇 |
力学 | 26篇 |
数学 | 157篇 |
物理学 | 368篇 |
出版年
2023年 | 14篇 |
2022年 | 29篇 |
2021年 | 28篇 |
2020年 | 27篇 |
2019年 | 30篇 |
2018年 | 24篇 |
2017年 | 15篇 |
2016年 | 34篇 |
2015年 | 38篇 |
2014年 | 42篇 |
2013年 | 110篇 |
2012年 | 83篇 |
2011年 | 115篇 |
2010年 | 59篇 |
2009年 | 40篇 |
2008年 | 91篇 |
2007年 | 85篇 |
2006年 | 95篇 |
2005年 | 76篇 |
2004年 | 82篇 |
2003年 | 62篇 |
2002年 | 64篇 |
2001年 | 34篇 |
2000年 | 30篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 17篇 |
1992年 | 29篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1976年 | 16篇 |
1975年 | 10篇 |
1973年 | 11篇 |
排序方式: 共有1727条查询结果,搜索用时 15 毫秒
21.
22.
23.
Alexopoulos T Allen C Anderson EW Balamurali V Banerjee S Beery PD Bhat P Bishop JM Biswas NN Bujak A Carmony DD Carter T Choi Y Cole P DeBonte R DeCarlo V Erwin AR Findeisen C Goshaw AT Gutay LJ Hirsch AS Hojvat C Jennings JR Kenney VP Lindsey CS Loomis C LoSecco JM McMahon T McManus AP Morgan N Nelson K Oh SH Porile NT Reeves D Rimai A Robertson WJ Scharenberg RP Stampke SR Stringfellow BC Thompson M Turkot F Walker WD Wang CH Warchol J Wesson DK Zhan Y 《Physical review D: Particles and fields》1993,48(3):984-997
24.
The molecular mechanics method has been applied to the study of various pathways and transition states for the configurational inversion of 1,1′-binaphthyl. The preferred pathway is found to be one on the anti (“trans”) side involving one point of H?H nonbonded contact in each of two identical transition states, separated by a very shallow minimum. Very satisfactory agreement with available experimental values for the enthalpy of activation is achieved. 相似文献
25.
Shen R Lin CT Bowman EJ Bowman BJ Porco JA 《Journal of the American Chemical Society》2003,125(26):7889-7901
The total synthesis and stereochemical assignment of the potent antitumor macrolide lobatamide C, as well as synthesis of simplified lobatamide analogues, is reported. Cu(I)-mediated enamide formation methodology has been developed to prepare the highly unsaturated enamide side chain of the natural product and analogues. A key fragment coupling employs base-mediated esterification of a beta-hydroxy acid and a salicylate cyanomethyl ester. Three additional stereoisomers of lobatamide C have been prepared using related synthetic routes. The stereochemistry at C8, C11, and C15 of lobatamide C was assigned by comparison of stereoisomers and X-ray analysis of a crystalline derivative. Synthetic lobatamide C, stereoisomers, and simplified analogues have been evaluated for inhibition of bovine chromaffin granule membrane V-ATPase. The salicylate phenol, enamide NH, and ortho-substitution of the salicylate ester have been shown to be important for V-ATPase inhibitory activity. 相似文献
26.
27.
Carter DL Draper MC Peterson RN Shah DO 《Langmuir : the ACS journal of surfaces and colloids》2005,21(22):10106-10111
At the end of the final spin cycle of the laundry process, the residual moisture content (RMC) of fabric is directly related to the dynamic surface tension of the residual water in the fabric. The LaPlace equation for capillary rise predicts that the capillary rise of solutions in a capillary is proportional to the surface tension at the air-liquid interface. If fabric can be considered to be a large ensemble of capillaries due to interfiber spacing, then the RMC of fabrics will be directly related to the surface tension of residual solution in the fabric. The use of a tailored rinse additive has the potential to decrease the surface tension of solution significantly, thus leading to a decrease in the residual water content of the fabric. It is expected that as the surfactant concentration increases the surface tension decreases. Hence, the RMC of fabrics must decrease with increasing surfactant concentration. However, a peak is observed in the RMC of fabrics before the critical micelle concentration (CMC) is reached. Prior to the CMC, it is proposed that a sudden adsorption of surfactant is occurring on the fabric surface leading to a decrease in bulk monomer concentration. The decrease in free monomer concentration should result in an increase in the equilibrium surface tension of the residual solution leading to a concomitant increase in RMC. Because the dynamic surface tension is measured on a short time scale (on the order of milliseconds), there will be less adsorption of monomer onto the newly created air-liquid interface of the bubbles during the measurement process. This decrease in adsorption should lead to a pronounced increase in the dynamic surface tension. This indeed was observed. The RMC correlates very well with the dynamic surface tension of the residual solution. 相似文献
28.
Steven P. Hopper Michael J. Tremelling Emma W. Goldman 《Journal of organometallic chemistry》1978,156(2):331-340
The heterogeneous gas-solid reaction of trimethylchlorosilane and an equal molar mixture of potassium t-butoxide and sodium methoxide gave exclusively trimethyl-t-butoxysilane. A similar reaction utilizing dimethyldichlorosilane as the vapor phase substrate gave predominant incorporation of butoxide. The heterogeneous reaction of chloromethyldimethylchlorosilane with these two bases was extensively studied. The parameters investigated for the latter system include the dependence of the product distribution on temperature, nitrogen flow rate and the relative hydroxide content of the solid alkoxide base. These studies allow the assessment of the relative reactivities of these bases under the conditions of heterogeneous gas/solid reaction. Under these conditions and with partially hydrolyzed bases a substantial amount of displacement of the chloromethyl group from chloromethyldimethylchlorosilane is observed. The role of hydroxide ion in this reaction is discussed. Convenient syntheses of t-butyl methyl ether and dimethylchloromethoxysilane are reported. 相似文献
29.
Thitivat Suebsaeng Charles A. Wilkie Vern T. Burger Janet Carter Charles Eric Brown 《Journal of polymer science. Part A, Polymer chemistry》1984,22(4):945-957
The solid reaction products from pyrolysis of polyethylene terephthalate in the presence and absence of red phosphorus were characterized by CP/MAS 13C-NMR, FR-IR, and MAS 31P-NMR spectroscopy. Over the temperature range of 300–400°C, polyethylene terephthalate was converted in a sealed vial to a highly crosslinked polymer of terephthalic acid. Pyrolysis in the presence of red phosphorus, which functions as a flame retardant by increasing the amount of char, yielded an intractible polyaromatic phosphate ester. After thermal cleavage of polyethylene terephthalate with formation of free carboxyl and vinyl ester groups, there are two competing reaction pathways. The smaller molecular weight fragments may enter the vapor phase where they undergo further degradation primarily to CO2, CO, and acetaldehyde, as described by others. However, if volatilization of the oligomeric fragments is inhibited, an alternate reaction pathway gives rise to the formation of highly crosslinked char. Red phosphorus decreases the volatility of the oligomeric fragments by converting them to phosphates and thereby enhances char formation. 相似文献
30.
Mokoena Emma M. Datye Abhaya K. Coville Neil J. 《Journal of Sol-Gel Science and Technology》2003,28(3):307-317
DL-tartaric acid was used as a template for the formation of silica nanotubes and spheres by the sol-gel method from tetraethylorthosilicate (TEOS) as silica source. The reactions were carried out in ethanol/water mixtures in the presence of aqueous ammonia, between 0°C and 75°C, using both stirred and non-stirred conditions. TEM and SEM images show that the yield and microstructure of the silica is influenced by the synthetic conditions (temperature, ammonia (aq) concentration, gelation time, solvent mixture). It was observed that the chiral form of the tartaric acid used and the diffusion of TEOS to the template determines the eventual silica structure. 相似文献