全文获取类型
收费全文 | 23181篇 |
免费 | 3774篇 |
国内免费 | 3116篇 |
专业分类
化学 | 17376篇 |
晶体学 | 264篇 |
力学 | 1547篇 |
综合类 | 135篇 |
数学 | 2600篇 |
物理学 | 8149篇 |
出版年
2024年 | 68篇 |
2023年 | 402篇 |
2022年 | 745篇 |
2021年 | 761篇 |
2020年 | 824篇 |
2019年 | 840篇 |
2018年 | 729篇 |
2017年 | 700篇 |
2016年 | 1190篇 |
2015年 | 1128篇 |
2014年 | 1356篇 |
2013年 | 1647篇 |
2012年 | 1996篇 |
2011年 | 1986篇 |
2010年 | 1411篇 |
2009年 | 1425篇 |
2008年 | 1597篇 |
2007年 | 1394篇 |
2006年 | 1300篇 |
2005年 | 1172篇 |
2004年 | 929篇 |
2003年 | 841篇 |
2002年 | 978篇 |
2001年 | 795篇 |
2000年 | 530篇 |
1999年 | 490篇 |
1998年 | 383篇 |
1997年 | 315篇 |
1996年 | 330篇 |
1995年 | 310篇 |
1994年 | 244篇 |
1993年 | 179篇 |
1992年 | 179篇 |
1991年 | 183篇 |
1990年 | 150篇 |
1989年 | 114篇 |
1988年 | 100篇 |
1987年 | 77篇 |
1986年 | 60篇 |
1985年 | 54篇 |
1984年 | 39篇 |
1983年 | 33篇 |
1982年 | 20篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1971年 | 4篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Ji-Dong Lou Chun-Ling Gao Li Li Zhi-Gang Fang 《Monatshefte für Chemie / Chemical Monthly》2006,41(10):1071-1074
A new procedure for the selective oxidation of alcohols to the corresponding aldehydes and ketones with potassium permanganate
supported on aluminum silicate at room temperature under solvent-free conditions and shaking is reported. 相似文献
2.
3.
Guofen Yu Yuanci Gao Shenggang Liu Wenxiang Wang Jin Wu 《International Journal of Infrared and Millimeter Waves》2002,23(8):1261-1269
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources. 相似文献
4.
5.
Ching Sum Hui Lillian Sze Man Lam Chun Yin Wai Kin Chan Aleksandra B. Djurii 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1708-1715
Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003 相似文献
6.
7.
Chun‐Yan Hong Ye‐Zi You Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4873-4881
Well‐defined diblock and triblock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) were successfully synthesized through the reversible addition–fragmentation chain transfer polymerization of N‐isopropylacrylamide (NIPAM) with PEO capped with one or two dithiobenzoyl groups as a macrotransfer agent. 1H NMR, Fourier transform infrared, and gel permeation chromatography instruments were used to characterize the block copolymers obtained. The results showed that the diblock and triblock copolymers had well‐defined structures and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.2), and the molecular weight of the PNIPAM block in the diblock and triblock copolymers could be controlled by the initial molar ratio of NIPAM to dithiobenzoate‐terminated PEO and the NIPAM conversion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4873–4881, 2004 相似文献
8.
The gas‐transport properties of poly[2,6‐toluene‐2,2‐bis(3,4‐dicarboxylphenyl)hexafluoropropane diimide] (6FDA‐2,6‐DAT) have been investigated. The sorption behavior of dense 6FDA‐2,6‐DAT membranes is well described by the dual‐mode sorption model and has certain relationships with the critical temperatures of the penetrants. The solubility coefficient decreases with an increase in either the pressure or temperature. The temperature dependence of the diffusivity coefficient increases with an increase in the penetrant size, as the order of the activation energy for the diffusion jump is CH4 > N2 > O2 > CO2. Also, the average diffusion coefficient increases with increasing pressure for all the gases tested. As a combined contribution from sorption and diffusion, permeability decreases with increases in the pressure and the kinetic diameter of the penetrant molecules. Even up to 32.7 atm, no plasticization phenomenon can be observed on flat dense 6FDA‐2,6‐DAT membranes from their permeability–pressure curves. However, just as for other gases, the absolute value of the heat of sorption of CO2 decreases with increasing pressure at a low‐pressure range, but the trend changes when the feed pressure is greater than 10 atm. This implies that CO2‐induced plasticization may occur and reduce the positive enthalpy required to create a site into which a penetrant can be sorbed. Therefore, a better diagnosis of the inherent threshold pressure for the plasticization of a glassy polymer membrane may involve examining the absolute value of the heat of sorption as a function of pressure and identifying the turning point at which the gradient of the absolute value of the heat of sorption against pressure turns from a negative value to a positive one. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 354–364, 2004 相似文献
9.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
10.
DongXiangLI WanGuoHOU ShuPingLI MingTuHAO GaoYongZHANG 《中国化学快报》2004,15(2):224-227
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations. 相似文献