全文获取类型
收费全文 | 2418篇 |
免费 | 129篇 |
国内免费 | 12篇 |
专业分类
化学 | 1839篇 |
晶体学 | 11篇 |
力学 | 38篇 |
数学 | 310篇 |
物理学 | 361篇 |
出版年
2023年 | 16篇 |
2021年 | 27篇 |
2020年 | 77篇 |
2019年 | 59篇 |
2018年 | 32篇 |
2017年 | 15篇 |
2016年 | 55篇 |
2015年 | 68篇 |
2014年 | 70篇 |
2013年 | 98篇 |
2012年 | 93篇 |
2011年 | 130篇 |
2010年 | 60篇 |
2009年 | 68篇 |
2008年 | 109篇 |
2007年 | 98篇 |
2006年 | 89篇 |
2005年 | 125篇 |
2004年 | 100篇 |
2003年 | 84篇 |
2002年 | 67篇 |
2001年 | 70篇 |
2000年 | 47篇 |
1999年 | 33篇 |
1998年 | 36篇 |
1997年 | 37篇 |
1996年 | 33篇 |
1995年 | 34篇 |
1994年 | 27篇 |
1993年 | 33篇 |
1992年 | 29篇 |
1991年 | 29篇 |
1990年 | 38篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 29篇 |
1983年 | 15篇 |
1982年 | 17篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 24篇 |
1976年 | 25篇 |
1974年 | 17篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有2559条查询结果,搜索用时 62 毫秒
51.
We present optimal estimates for the asymptotic behavior of
strongly continuous semigroups in terms of growth abscissas of the resolvent function of the generator . In particular we give Ljapunov's classical stability condition a definite form for (infinite dimensional) abstract Cauchy problems: The abscissa of boundedness of equals the growth bound of the classical solutions of .
strongly continuous semigroups in terms of growth abscissas of the resolvent function of the generator . In particular we give Ljapunov's classical stability condition a definite form for (infinite dimensional) abstract Cauchy problems: The abscissa of boundedness of equals the growth bound of the classical solutions of .
52.
53.
The sequence of beta-lithiation and electrophilic substitution of beta-aryl secondary amides is reported. The lithiations occur regioselectively at the beta-position, and the resulting lithiated intermediates can be reacted with a wide range of electrophiles to give substituted products. Reactions of beta-lithiated amides bearing an alpha-substituent provide substituted products with high diastereoselectivity. Electrophilic substitutions of beta-lithiated N-methylamides in the presence of the chiral diamine (-)-sparteine provide highly enantioenriched products. The methodology is used to synthesize enantioenriched beta-aryl beta-substituted amides, acids, and lactones. 相似文献
54.
55.
56.
57.
In den Systemen FeSO3? H2O und NiSO3? H2O konnten folgende Hydrate erhalten werden: α-FeSO3 · 3H2O, γ-FeSO3 · 3H2O, FeSO3 · 2,5 H2O, FeSO3 · 2 H2O, NiSO3 · 6 H2O, NiSO3 · 3 H2O, NiSO3 · 2,5 H2O und NiSO3 · 2 H2O. Die Gitterdaten der folgenden Hydrate wurden anhand von Einkristallmessungen bestimmt: γ-FeSO3 · 3 H2O: a = 965,9(1), b = 557,1(1), c = 944,7(1) pm, Z = 4, FeSO3 · 2 H2O (P21/n): a = 645,6(1), b = 863,1(1), c = 761,2(1) pm, β = 99,84(1)°, Z = 4, NiSO3 · 3 H2O: a = 945,0(1), b = 547,2(1), c = 932,5(1) pm, Z = 4, NiSO3 · 2,5 H2O (P41212): a = b = 935,3(1), c = 1016,6(1) pm, Z = 8, NiSO3 · 2 H2O (P21/n): a = 631,4(1), b = 851,0(1), c = 744,7(1) pm, β = 98,91(1)°, Z = 4. Die IR- und Raman-Spektren sowie das Ergebnis thermoanalytischer Messungen (DTA, DTG, Röntgenheizaufnahmen) werden mitgeteilt. Die bei Sulfiten und Sulfithydraten zweiwertiger Metalle bisher beobachteten Strukturtypen werden diskutiert. Sulfites and Sulfite Hydrates of Iron and Nickel. X-ray, Thermoanalytical, I.R., and Raman Data In the systems FeSO3? H2O and NiSO3? H2O the following hydrates have been found: α-FeSO3 · 3H2O, γ-FeSO3 · 3H2O, FeSO3 · 2,5 H2O, FeSO3 · 2 H2O, NiSO3 · 6 H2O, NiSO3 · 3 H2O, NiSO3 · 2,5 H2O and NiSO3 · 2 H2O. The following crystal data have been determined by single crystal measurements: γ-FeSO3 · 3 H2O: a = 965,9(1), b = 557,1(1), c = 944,7(1) pm, Z = 4, FeSO3 · 2 H2O (P21/n): a = 645,6(1), b = 863,1(1), c = 761,2(1) pm, β = 99,84(1)°, Z = 4, NiSO3 · 3 H2O: a = 945,0(1), b = 547,2(1), c = 932,5(1) pm, Z = 4, NiSO3 · 2,5 H2O (P41212): a = b = 935,3(1), c = 1016,6(1) pm, Z = 8, NiSO3 · 2 H2O (P21/n): a = 631,4(1), b = 851,0(1), c = 744,7(1) pm, β = 98,91(1)°, Z = 4. IR, Raman, and thermoanalytical (DTA, DTG, high temperature X-ray) data are presented. The structure types found for sulfites and sulfite hydrates of bivalent metals are discussed. 相似文献
58.
A method for the analysis of diethylstilbestrol (DES) which is suitable for pharmacokinetic studies has been developed using capillary gas chromatographic (GC) separation and detection with selected-ion mass spectrometry (MS). This technique has been applied to a variety of samples including human plasma samples and extracts of animal tissues including prostate and liver. To investigate the pharmacokinetics of stilphostrol (diethylstilbestrol diphosphate) we have modified the GC-MS method in two ways. One modification involves a dual assay for DES; the first a direct assay, and the second after hydrolysis of a sample with alkaline phosphatase. The difference in these values is the amount of phosphorylated DES present. The other modification separates stilphostrol and DES using a reversed-phase, ion-paired high-performance liquid chromatographic method followed by alkaline phosphatase hydrolysis followed by the GC-MS method. The details of these three methods are described and some representative data are shown. 相似文献
59.
60.