全文获取类型
收费全文 | 27558篇 |
免费 | 1034篇 |
国内免费 | 148篇 |
专业分类
化学 | 19578篇 |
晶体学 | 230篇 |
力学 | 556篇 |
数学 | 3521篇 |
物理学 | 4855篇 |
出版年
2023年 | 180篇 |
2022年 | 232篇 |
2021年 | 373篇 |
2020年 | 500篇 |
2019年 | 484篇 |
2018年 | 333篇 |
2017年 | 284篇 |
2016年 | 747篇 |
2015年 | 641篇 |
2014年 | 767篇 |
2013年 | 1291篇 |
2012年 | 1663篇 |
2011年 | 1830篇 |
2010年 | 1060篇 |
2009年 | 898篇 |
2008年 | 1521篇 |
2007年 | 1458篇 |
2006年 | 1440篇 |
2005年 | 1358篇 |
2004年 | 1176篇 |
2003年 | 891篇 |
2002年 | 934篇 |
2001年 | 480篇 |
2000年 | 415篇 |
1999年 | 412篇 |
1998年 | 394篇 |
1997年 | 372篇 |
1996年 | 372篇 |
1995年 | 325篇 |
1994年 | 356篇 |
1993年 | 325篇 |
1992年 | 286篇 |
1991年 | 223篇 |
1990年 | 241篇 |
1989年 | 217篇 |
1988年 | 215篇 |
1987年 | 202篇 |
1986年 | 190篇 |
1985年 | 301篇 |
1984年 | 292篇 |
1983年 | 205篇 |
1982年 | 226篇 |
1981年 | 197篇 |
1980年 | 200篇 |
1979年 | 194篇 |
1978年 | 218篇 |
1977年 | 205篇 |
1976年 | 157篇 |
1975年 | 160篇 |
1974年 | 176篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
191.
192.
193.
Vieira R Pham-Huu C Keller N Ledoux MJ 《Chemical communications (Cambridge, England)》2002,(9):954-955
Graphite felt supporting 40 nm diameter carbon nanofibers was synthesized and successfully used as a support for a high loaded iridium catalyst (30 wt%) in the decomposition of hydrazine; a strong mechanical resistance and a high thermal conductivity led to a very efficient and stable catalyst as compared to that used industrially, iridium supported on a high surface area alumina. 相似文献
194.
A highly flexible method for direct and quantitative determination of surface Br?nsted acidity of solids in terms of number, type and strength of the acid sites based on quantitative H/D exchange kinetics between the acid solid and gaseous D2O has been developed and applied to materials covering the whole range of acidity. 相似文献
195.
Tucker M. P. Farmer J. D. Keller F. A. Schell D. J. Nguyan Q. A. 《Applied biochemistry and biotechnology》1998,(1):25-35
Single-stage cocurrent dilute acid pretreatments were carried out on yellow poplar (Liriodendron tulipifera) sawdust using an as-installed and short residence time modified pilot-scale Sunds hydrolyzer and a 4-L bench-scale NREL
digester (steam explosion reactor). Pretreatment conditions for the Sunds hydrolyzer, installed in the NREL process development
unit (PDU), which operates at 1 t/d (bone-dry t) feed rate, spanned the temperature range of 160 – 210°C, 0.1 – 1.0% (w/w)
sulfuric acid, and 4-10-min residence times. The batch pretreatments of yellow poplar sawdust in the bench-scale digester
were carried out at 210 and 230°C, 0.26% (w/w) sulfuric acid, and 1-, 3-, and 4-min residence times. The dilute acid prehydrolysis
solubilized more than 90% of the hemicellulose, and increased the enzymatic digestibility of the cellulose that remained in
the solids. Compositional analysis of the pretreated solids and liquors and mass balance data show that the two pretreatment
devices had similar pretreatment performance. 相似文献
196.
Crystal Structure of AgCu3Cu(AsO4)3 and its Structural Relations to AgCo3H2(AsO4)3 and AgZn3H2 (AsO4)3 The compound AgCu3Cu(AsO4)3 was synthesized and investigated by X-rays. It crystallizes in the monoclinic space group C2/c with a = 1 212.7(2), b = 1 249.0(2), c = 727.8(1) pm, β = 117.94(1)°, Z = 4. The structure is closely related to the structures of AgCo3H2(AsO4)3 and AgZn3H2(AsO4)3. Only two hydrogen atoms are replaced by an additional copper atom forming a copper coordination square instead of two hydrogen bridges. The remaining copper atoms are sixfold coordinated with the generally observed Jahn-Teller distortion. Whereas in AgCo3H2(AsO4)3 and AgZn3H2(AsO4)3 silver has a (4+4) coordination, it is in this compound distinctly eightfold coordinated. 相似文献
197.
Understanding the Hofmeister effect in interactions between chaotropic anions and lipid bilayers: molecular dynamics simulations 总被引:1,自引:0,他引:1
A set of all-atom molecular dynamics simulations have been performed to better understand critical phenomena regarding a Hofmeister series of anions and lipid bilayers. The simulations isolate the effect of anion size and show clear differences in the interactions with the dipolar phoshpatidylcholine headgroup. Cl- anions penetrate into the headgroup region of the bilayer, but the simulations confirm theories which predict that larger anions penetrate more deeply, into a more heterogeneous and hydrophobic molecular region. That anion size leads to such differences in partitioning in the bilayer provides atomic-level support to hypotheses inspired by several experimental studies. The ability of larger anions to bury deep within the bilayer is correlated with a less well-structured hydration shell, shedding of which upon penetration incurs a smaller penalty for the larger anions than for Cl-. 相似文献
198.
Thomas C. Amu 《Journal of solution chemistry》1981,10(1):69-78
Interdiffusion coefficient have been measured for 1,1,2,2-tetrabromoethane in 21 organic solvents in order to ascertain the influence of shape, size, viscosity, nature and degree of branching, of the solvent molecules on transport properties. None of the existing correlations for diffusion in binary liquid systems appear to fit all the experimental data. Steric effects due to the solvent molecules are shown to be very important in the interpretation of the diffusion process. 相似文献
199.
200.
Abstract— Oxygen effects on the photocyclization of N-methyldiphenylamine to N-methylcarbazole were investigated in n-hexane, water, and aqueous surfactant solutions by steady state irradiations and flash photolysis measurements. The reaction sequence in micelles was found to involve the same intermediate steps as in homogeneous solutions. In aerated micellar solutions, the quantum yield of N-methylcarbazole is significantly higher than in n-hexane, while the rate constants of the unimolecular reaction steps show no solvent dependence. The bimolecular dehydrogenation of the intermediate 4a, 4b-dihydro-N-methylcarbazole by oxygen is enhanced in aqueous and micellar solutions, whereas the quenching rate of triplet intermediates by oxygen was not affected. The lesuhs are interpreted using a dispersed phase model of micellar solutions. Special 'micellar effects' need not be invoked since the dependence of the quantum yield on the solvent is shown to be due to the difference in the overall oxygen concentration. 相似文献