全文获取类型
收费全文 | 2129篇 |
免费 | 119篇 |
国内免费 | 11篇 |
专业分类
化学 | 1638篇 |
晶体学 | 17篇 |
力学 | 29篇 |
数学 | 297篇 |
物理学 | 278篇 |
出版年
2023年 | 21篇 |
2022年 | 21篇 |
2021年 | 26篇 |
2020年 | 77篇 |
2019年 | 57篇 |
2018年 | 31篇 |
2017年 | 16篇 |
2016年 | 46篇 |
2015年 | 67篇 |
2014年 | 64篇 |
2013年 | 95篇 |
2012年 | 84篇 |
2011年 | 118篇 |
2010年 | 50篇 |
2009年 | 63篇 |
2008年 | 102篇 |
2007年 | 86篇 |
2006年 | 77篇 |
2005年 | 100篇 |
2004年 | 100篇 |
2003年 | 66篇 |
2002年 | 58篇 |
2001年 | 54篇 |
2000年 | 37篇 |
1999年 | 32篇 |
1998年 | 34篇 |
1997年 | 34篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 28篇 |
1993年 | 34篇 |
1992年 | 28篇 |
1991年 | 32篇 |
1990年 | 39篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 24篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 19篇 |
1974年 | 17篇 |
1973年 | 15篇 |
排序方式: 共有2259条查询结果,搜索用时 15 毫秒
41.
X-ray, I.R., and Raman Data of Strontium Polysulfides The strontium polysulfides SrS2, SrS3A, and SrS3B were studied in terms of preparation, thermal decomposition, and phase transition. The i.r. and Raman spectra of the strontium polysulfides as well as the normal coordinates of the phonon modes are presented and discussed in comparison with the respective barium compounds. From the spectra it is shown that S32? entities are present in SrS3A as in SrS3B. 相似文献
42.
Mulligan A Lane I Rousseau GB Hecht L Johnston SM Lennon D Kadodwala M 《Chemical communications (Cambridge, England)》2004,(21):2492-2493
Using a novel non-linear optical technique enantiomeric excess within a translationally disordered overlayer on a metal surface has been monitored for the first time. 相似文献
43.
Yiyi Weng Xingxing Ding Joo C. A. Oliveira Xiaobin Xu Nikolaos Kaplaneris Meijie Zhu Hantao Chen Zhuo Chen Lutz Ackermann 《Chemical science》2020,11(34):9290
There is a strong demand for novel native peptide motifs for post-synthetic modifications of peptides without pre-installation and subsequent removal of directing groups. Herein, we report an efficient method for peptide late-stage C(sp3)–H arylations assisted by the unmodified side chain of asparagine (Asn) without any exogenous directing group. Thereby, site-selective arylations of C(sp3)–H bonds at the N-terminus of di-, tri-, and tetrapeptides have been achieved. Likewise, we have constructed a key building block for accessing agouti-related protein (AGRP) active loop analogues in a concise manner.An efficient method for peptide late-stage C(sp3)-H arylations assisted by unmodified side chain of asparagine (Asn) without any exogenous directing group has been reported. 相似文献
44.
E. Burestedt J. Emnéus L. Gorton G. Marko-Varga E. Domínguez F. Ortega A. Narváez H. Irth M. Lutz D. Puig D. Barceló 《Chromatographia》1995,41(3-4):207-215
Summary A fully integrated screening system for phenolic compounds was developed incorporating on-line solid phase extraction, fractionation and biosensor detection. Two different types of biosensors, solid graphite and carbon paste electrodes incorporating the enzyme tyrosinase, were compared and used in the screening system. Interfacing of the solid phase extraction and fractionation with the biosensor detection was given special attention since the biosensors were not compatible with the organic modifier used for desorption of phenols from the solid phase extraction step. The system was validated with conventional analytical techniques. Surface water samples from the Ebro river were spiked with 1,10, and 25g L–1 of catechol, phenol,p-cresol, respectively. Three out of seven samples were spiked and the correct samples were identified, containing phenols equivalent to the spiked concentrations. 相似文献
45.
46.
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 .
47.
48.
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
49.
50.
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