全文获取类型
收费全文 | 250848篇 |
免费 | 2013篇 |
国内免费 | 774篇 |
专业分类
化学 | 145212篇 |
晶体学 | 3458篇 |
力学 | 8973篇 |
综合类 | 7篇 |
数学 | 27532篇 |
物理学 | 68453篇 |
出版年
2020年 | 2144篇 |
2019年 | 2522篇 |
2018年 | 3417篇 |
2017年 | 3307篇 |
2016年 | 4666篇 |
2015年 | 2671篇 |
2014年 | 4217篇 |
2013年 | 10443篇 |
2012年 | 7947篇 |
2011年 | 9758篇 |
2010年 | 6792篇 |
2009年 | 6483篇 |
2008年 | 9316篇 |
2007年 | 9457篇 |
2006年 | 8850篇 |
2005年 | 8166篇 |
2004年 | 7265篇 |
2003年 | 6559篇 |
2002年 | 6389篇 |
2001年 | 6274篇 |
2000年 | 4951篇 |
1999年 | 3691篇 |
1998年 | 3269篇 |
1997年 | 3315篇 |
1996年 | 3180篇 |
1995年 | 2595篇 |
1994年 | 2679篇 |
1993年 | 2699篇 |
1992年 | 2830篇 |
1991年 | 2871篇 |
1990年 | 2756篇 |
1989年 | 2774篇 |
1988年 | 2773篇 |
1987年 | 2768篇 |
1986年 | 2659篇 |
1985年 | 3541篇 |
1984年 | 3728篇 |
1983年 | 2874篇 |
1982年 | 3310篇 |
1981年 | 3145篇 |
1980年 | 3067篇 |
1979年 | 3211篇 |
1978年 | 4058篇 |
1977年 | 3840篇 |
1976年 | 3267篇 |
1975年 | 3037篇 |
1974年 | 2970篇 |
1973年 | 3100篇 |
1972年 | 2104篇 |
1967年 | 2032篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
951.
A. V. Zaikina E. I. Yarmukhamedova Yu. I. Puzin A. A. Fatykhov Yu. B. Monakov 《Polymer Science Series A》2006,48(5):457-461
The specific features of free-radical polymerization of methyl methacrylate in the presence of a new initiating system, benzoyl peroxide-N,N-dimethyl-N-(methylferrocenyl)amine, are studied. Mutual influence of the ferrocene and amino groups on the kinetic parameters of polymerization and on the microstructure of the resulting polymers is revealed. The polymer formed in the presence of this initiating system is shown to have a predominantly syndiotactic structure. 相似文献
952.
Machado AM Wypych F Drechsel SM Nakagaki S 《Journal of colloid and interface science》2002,254(1):158-164
Two samples of montmorillonite (one of Brazilian origin, BNC1 clay, and the other STX-1, supplied by the Clay Mineral Society Repository (University of Missouri, USA) were allowed to react with biomimetic metalloporphyrins of Fe(III) and Mn(III) in cationic form. The compounds were characterized by several techniques, showing that the metalloporphyrins molecules were adsorbed at the surface of the clay platelet crystals. The catalytic activities of the intercalated complexes for the oxidation of alkane were dependent upon the concentration of the porphyrin immobilized in the clay and factors such as the metal ion species in the porphyrins, choice of solvent, and concentration of the iodosylbenzene oxidant. Good selectivity to cyclohexanol instead of cyclohexanone was observed for the catalytic oxidation of cyclohexane by iodosylbenzene. 相似文献
953.
Dynamic behaviour of river colloidal and dissolved organic matter through cross-flow ultrafiltration system 总被引:1,自引:0,他引:1
Through cross-flow filtration (CFF) with a 1-kDa regenerated cellulose Pellicon 2 module, the ultrafiltration characteristics of river organic matter from Longford Stream, UK, were investigated. The concentration of organic carbon (OC) in the retentate in the Longford Stream samples increased substantially with the concentration factor (cf), reaching approximately 40 mg/L at cf 15. The results of dissolved organic carbon (DOC) and colloidal organic carbon (COC) analysis, tracking the isolation of colloids from river waters, show that 2 mg/L of COC was present in those samples and good OC mass balance (77-101%) was achieved. Fluorescence measurements were carried out for the investigation of retentate and permeate behaviour of coloured dissolved organic materials (CDOM). The concentrations of CDOM in both the retentate and permeate increased with increasing cf, although CDOM were significantly more concentrated in the retentate. The permeation model expressing the correlation between log[CDOM] in the permeate and logcf was able to describe the permeation behaviour of CDOM in the river water with regression coefficients (r(2)) of 0.94 and 0.98. Dry weight analysis indicated that the levels of organic colloidal particles were from 49 to 71%, and between 29 and 51% of colloidal particles present were inorganic. COC as a percentage of DOC was found to be 10-16% for Longford Stream samples. 相似文献
954.
S.D. Morley D.E. Jackson M.R. Saunders J.G. Vinter 《Journal of computational chemistry》1992,13(6):693-703
A hybrid conformational search algorithm (DMC) is described that combines a modified form of molecular dynamics with Metropolis Monte Carlo sampling, using the COSMIC(90) force field. Trial configurations are generated by short bursts of high-temperature dynamics in which the initial kinetic energy is focused into single bond rotations or alternatively into “corner-flapping” motions in ring systems. Constant temperature and simulated annealing search protocols have been applied to the conformational analysis of several model hydrocarbons (cyclopentane, cyclohexane, cycloheptane, cyclooctane, cycloheptadecane, decane, and tetradecane), and the performance compared with conventional molecular dynamics and Monte Carlo sampling methods. Optimum Metropolis sampling temperatures have been determined and range from 1000–2000 K for acyclic molecules to 3000 K for cyclic systems. Simulated annealing runs are most successful at locating the global minimum when cooling slowing from these optimum temperatures. 相似文献
955.
Y. E. Kutsovsky A. G. Mariasov Y. I. Aristov V. N. Parmon 《Reaction Kinetics and Catalysis Letters》1990,42(1):19-24
The ESE method was successfully used for investigating the texture of the adsorbents and catalysts. Equations were obtained for the kinetics of ESE signal decay due to dipole-dipole interaction between motionless paramagnetic centers distributed uniformly on the fractal surface of solid.
, . , , .相似文献
956.
Martin B. Hocking David T. Syme David E. Axelson Kirk H. Michaelian 《Journal of polymer science. Part A, Polymer chemistry》1990,28(11):2969-2982
The comonomer required, p-maleimidobenzoic acid (MBA) was first prepared in good yield by refinements of published methods. p-Carboxysuccinanilic acid (CSA), and p-succinimidobenzoic acid (SBA), were also prepared to provide models useful for IR and NMR for spectroscopic assignments of the new copolymers. Polymerization of MBA with acrylamide in glacial acetic acid at 60°C gave copolymers with estimated viscosity average molecular weights of 60,000 to 90,000. Yields and viscosity average molecular weights decreased as the MBA to acrylamide monomer feed ratio was increased. The rate of incorporation of MBA into the copolymer rose from 7 to 23% when the mole ratio in the feed was raised from 5 to 20%. Decreasing the initiator concentration increased molecular weights by less than predicted and reduced the yield of copolymer for any given feed ratio of MBA to acrylamide. In all cases about 30–40% of the MBA units in the purified copolymers were hydrolyzed. A change to dimethyl sulfoxide solvent gave good, and poor yields of copolymer at 5 and 10 mol % MBA, respectively, and no copolymer at 20 mol % MBA. Viscosity average molecular weights of the copolymer products prepared in DMSO were somewhat lower than obtained for the copolymers prepared in acetic acid. Polymerization in a DMSO-water mixture gave a negligible yield of polymeric product. Instead, only hydrolysates of MBA precipitated when the coloured polymerization solutions were added to methanol. 相似文献
957.
Poly(vinyl alcohols) partially allylated have been grafted with sulphonic acid. The influence of experimental parameters (vinyl sulphonic acid concentration, swelling before grafting, photoinitiator concentration, grafting temperature and duration of the irradiation) have been studied in detail. 相似文献
958.
Soltero-Higgin M Carlson EE Phillips JH Kiessling LL 《Journal of the American Chemical Society》2004,126(34):10532-10533
The flavoenzyme uridine 5'-diphosphate (UDP)-galactopyranose mutase (UGM) plays a key role in the cell wall biosynthesis of many pathogens, including Mycobacterium tuberculosis. Using a synthetic fluorescent ligand, we screened 16 000 compounds in a fluorescence polarization assay. Effective inhibitors of UGM were identified. 相似文献
959.
A qualitative classification algorithm for constructing large clusters of aerogel model structures is used. According to this
algorithm, aerogel is classified with polysilicas characterized by a packing of long chains of silicon-oxygen tetrahedra.
A model of the aerogel structure is suggested, according to which aerogel is described as a set of cross-linked chains forming
double or more complex ribbons. This model is in agreement with the conclusions drawn from analysis of the vibration spectra
of its components.
Institute of Surface Chemistry, Ukrainian Academy of Sciences. Russian University of Peoples' Friendship. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 35–38, May–June, 1994.
Translated by O. Kharlamova 相似文献
960.