全文获取类型
收费全文 | 5504篇 |
免费 | 184篇 |
国内免费 | 26篇 |
专业分类
化学 | 4085篇 |
晶体学 | 15篇 |
力学 | 81篇 |
数学 | 766篇 |
物理学 | 767篇 |
出版年
2021年 | 60篇 |
2020年 | 93篇 |
2019年 | 77篇 |
2018年 | 43篇 |
2017年 | 35篇 |
2016年 | 147篇 |
2015年 | 128篇 |
2014年 | 119篇 |
2013年 | 246篇 |
2012年 | 218篇 |
2011年 | 262篇 |
2010年 | 175篇 |
2009年 | 154篇 |
2008年 | 253篇 |
2007年 | 255篇 |
2006年 | 239篇 |
2005年 | 245篇 |
2004年 | 223篇 |
2003年 | 171篇 |
2002年 | 192篇 |
2001年 | 128篇 |
2000年 | 96篇 |
1999年 | 94篇 |
1998年 | 87篇 |
1997年 | 81篇 |
1996年 | 95篇 |
1995年 | 80篇 |
1994年 | 87篇 |
1993年 | 76篇 |
1992年 | 82篇 |
1991年 | 54篇 |
1990年 | 36篇 |
1989年 | 83篇 |
1988年 | 73篇 |
1987年 | 76篇 |
1986年 | 69篇 |
1985年 | 58篇 |
1984年 | 69篇 |
1983年 | 57篇 |
1982年 | 61篇 |
1981年 | 62篇 |
1980年 | 67篇 |
1979年 | 57篇 |
1978年 | 47篇 |
1977年 | 49篇 |
1976年 | 43篇 |
1975年 | 51篇 |
1974年 | 35篇 |
1973年 | 41篇 |
1970年 | 30篇 |
排序方式: 共有5714条查询结果,搜索用时 125 毫秒
41.
We discuss the gap problem for the sequence m used in our previous Letter (D. H. Mayer, Lett. Math. Phys.
16, 139–143 (1988)). 相似文献
42.
43.
A novel linear trinuclear mu-O-bridging 2-phosphinophenolate nickel(II) complex with fac-tris(P(intersection)O- chelates) in the terminal positions and the three oxygen atoms each facing the central nickel(II) cation was synthesized and structurally characterized by X-ray crystallography. To the best of our knowledge, this is the first example of an octahedral Ni(II) tris(P(intersection)O- chelate). 相似文献
44.
The redox properties of the system Fe(tmphen)3(II/III) (tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline) have been studied in the solvents nitromethane, acetonitrile, propanediol-1,2-carbonate, dimethylformamide, dimethylacetamide, dimethylsulfoxide and of the systems Fe(phen)3(II/III) (phen=1,10-phenanthroline) and Fe(niphen)3(II/III) (niphen=5-nitro-1,10-phenanthroline) in the solvents nitromethane, acetonitrile, propanediol-1,2-carbonate and acetone. The redox potentials of Fe(tmphen)3(II/III) are nearly independent of the solvent suggesting that the system might be used as a reference redox couple similar to the systems ferrocene/ferricinium or bisbiphenylchromium(0/I). In contrast the redox potentials of Fe(niphen)3(II/III) show a significant decrease with increasing donor number of the solvent which can be explained by nucleophilic attack of solvent molecules at the iron. It is shown that such a mechanism is consistent with the known solvent and salt effects on the kinetics of dissociation of ferroin and ferriin type complexes. 相似文献
45.
46.
47.
Nidetzky Bernd Griessler Richard Weinhausel Andreas Haltrich Dietmar Kulbe Klaus D. 《Applied biochemistry and biotechnology》1997,(1):159-172
Some important process properties of α-l,4-D-ghican phosphorylases isolated from the bacteriumCorynebacterium callunae and potato tubers (Solatium tuberosum) were compared. Apart from minor differences in their stability and specificity (represented by the maximum degree of maltodextrin
conversion) and a 10-fold higher affinity of the plant phosphorylase for maltodextrin (K
M of 1.3 g/L at 300 mM of orthophosphate), the performances of both enzymes in a continuous ultrafiltration membrane reactor
were almost identical. Product synthesis was carried out over a time course of 300–400 h in the presence or absence of auxiliary
pullulanase (increasing the accessibility of the glucan substrate for phosphorolytic attack up to 15–20%). The effect of varied
dilution rate and reaction temperature on the resulting productivities was quantitated, and a maximum operational temperature
of 40°C was identified. 相似文献
48.
Riehn C Matylitsky VV Jarzeba W Brutschy B Tarakeshwar P Kim KS 《Journal of the American Chemical Society》2003,125(52):16455-16462
In this paper, we report the use of femtosecond time-resolved degenerate four-wave mixing rotationally resolved spectroscopy to obtain very accurate structural information on the symmetric top cyclohexane. Apart from highlighting the versatility of this method in determining accurate structures of large and complex molecules without dipole moment, the present study also details the comparison of the experimentally determined rotational constant B(0) with that obtained from high-level ab initio calculations. The theoretical calculations, which were carried out at both the second-order M?ller-Plesset (MP2) and coupled-cluster with single, double, and perturbative triple substitutions [CCSD(T)] levels of theory, also take into account vibrational averaging effects. A detailed investigation of the vibrational averaging effects reveals that the corrections emerge from only the six highly symmetric A(1g) modes, a justification of which is provided by an analysis of these modes. 相似文献
49.
A careful deformation density study of tetrafluoroterephthalodinitrile at 98K has been made from X-ray diffraction measurements. Prominent ‘bonding density’ peaks are found at or near the mid-points of the C, C- and C, N-bonds but not for the C, F-bonds, which show only weak density. Similarly weak bonding densities for C, F-bonds are also found for 1, 1, 4, 4-tetrafluorocyclohexane. The possible significance of these results in terms of bonding theory is briefly discussed. 相似文献
50.
The binding of palladium to high-molecular-mass compounds in palladium-treated lettuce is investigated as an example for a biological matrix. The total palladium concentration in lettuce leaves is 10.3 ng/g wet weight. After homogenization, high-molecular-mass compounds (> 10 kDa) are isolated by ultrafiltration. For separation of these palladium species a combination of preparative gel permeation chromatography (GPC) and preparative isotachophoresis (ITP) is used. Palladium is determined in separated fractions by using a highly sensitive total reflection X-ray fluorescence (TXRF) method after preconcentration. After GPC separation, four main fractions of palladium species are collected, each containing palladium in ng quantities (3-10 ng). Two of these fractions are further separated by ITP, yielding at least three main peaks per GPC fraction, each containing palladium in the range of 0.3-3 ng. These palladium containing peaks are characterized by high-performance size exclusion chromatography (HPSEC) and capillary isotachophoresis (cITP) in parallel. HPSEC enables the estimation of the molecular mass of six main palladium peaks, covering a molecular mass range of 69-200 kDa. It is also shown that the estimation of molecular mass after separation is more reliable than the respective estimation directly in the first GPC run. However, cITP reveals that each of the separated peaks is still a mixture of at least five different compounds. 相似文献