全文获取类型
收费全文 | 1806篇 |
免费 | 34篇 |
国内免费 | 4篇 |
专业分类
化学 | 1176篇 |
晶体学 | 11篇 |
力学 | 27篇 |
数学 | 347篇 |
物理学 | 283篇 |
出版年
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 19篇 |
2017年 | 28篇 |
2016年 | 25篇 |
2015年 | 17篇 |
2014年 | 36篇 |
2013年 | 92篇 |
2012年 | 90篇 |
2011年 | 87篇 |
2010年 | 55篇 |
2009年 | 56篇 |
2008年 | 116篇 |
2007年 | 97篇 |
2006年 | 90篇 |
2005年 | 78篇 |
2004年 | 73篇 |
2003年 | 51篇 |
2002年 | 61篇 |
2001年 | 24篇 |
2000年 | 19篇 |
1999年 | 13篇 |
1997年 | 14篇 |
1996年 | 29篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 25篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 31篇 |
1984年 | 35篇 |
1983年 | 22篇 |
1982年 | 41篇 |
1981年 | 29篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 29篇 |
1977年 | 18篇 |
1976年 | 23篇 |
1974年 | 18篇 |
1973年 | 32篇 |
1972年 | 14篇 |
1971年 | 13篇 |
排序方式: 共有1844条查询结果,搜索用时 15 毫秒
21.
22.
Crystals of Ba5Fe5−xPtxClO13 and Ba5Co5−yPtyClO13 were prepared for x=1.31, 1.51, 1.57, 1.59 and y=0, 0.97 and 1.08 in a BaCl2 flux and investigated by X-ray diffraction methods. These compounds adopt a 10H perovskite structure built from the stacking of BaO3 and BaOCl layers in the sequence (BaO3)4(BaOCl) with space group P63/mmc. The cation sites within the trimeric unit of face-sharing octahedra are occupied by Co or Fe and Pt ions, while the tetrahedral sites formed between BaO3 and BaOCl layers are only occupied by Fe or Co. Moreover, oxygen stoichiometry indicates an average oxidation state for Co and Fe higher than +III, indicating the stabilization of Co4+ and Fe4+. 相似文献
23.
24.
Bergen HR Abraham RS Johnson KL Bradwell AR Naylor S 《Biomedical chromatography : BMC》2004,18(3):191-201
Primary systemic amyloidosis (AL) is characterized by the overproduction of immunoglobulin light chain proteins by a monoclonal, terminally differentiated B-lymphocyte or plasma cell clone. The free immunoglobulin light chains are deposited in an abnormal conformation as amyloid in a variety of organs in the body. The mechanism of amyloid formation is not well understood, but appears to be associated with some form of cleavage of the immunoglobulin light chain with subsequent aggregate formation. In an attempt to characterize the structure of amyloid-forming light chain proteins we developed an on-line immunoaffinity purification and subsequent characterization of free kappa and free lambda immunoglobulin light chains by electrospray ionization mass spectrometry. The methodology is totally automated and requires 20 micro L of serum. Mass spectral analysis of Bence Jones proteins under non-denaturing conditions was also utilized to examine the tertiary and quaternary structure of light chain proteins and clearly shows covalent dimer formation of lambda type light chain. This type of on-line assay may prove helpful in elucidating distinguishing features capable of discriminating AL from benign monoclonal gammopathies of undetermined significance as well as diagnosing AL. 相似文献
25.
26.
The reaction of 4, 7-phenanthroline (1) with aqueous transitionmetal complexes [Mn(H2O)6][NO3]2, [Co(H2O)6][NO3]2, [Ni(H2O)6[NO3]2, [Mn(H2O)6][ClO4]2, and [Co(H2O)6][ClO4]2 does not produce coordination complexes between these metal cations and the N-donor ligand as expected. Instead, supramolecular hydrogenbonded networks are formed between the nitrogen donor atoms of 4, 7-phenanthroline and the OH groups of coordinated water molecules: M-O-H...N interactions. This motif of second-sphere coordination for 1 can be exploited as a tool for crystal engineering. As a demonstration of the generality of this new interaction as a supramolecular building block, five X-ray crystal structures are reported that utilise this hydrogen bonding scheme; [Co(H2O)4(NO3)2].(1)2 (2a), [Co(MeCN)2(H2O)4][ClO4]2.(1)2 (2b), [Ni(H2O)4(NO3)2].(1)2 (3a), [Mn(H2O)4(NO3)2].(1)2 (4a), and [Mn(H2O)6][ClO4]2.(1)(4).4H2O (4b). Each network involves complete saturation of the hydrogen-bond donor sets between the aqua complex and 1 using primarily M-O-H...N(1) and M-O-H...O(anion), interactions. Thermogravimteric analysis shows these materials to have stabililities similar to coordination polymers involving metal-ligand bonds; this demonstrates that second-sphere hydrogen bonding has potential for the construction of polymeric metal-containing materials. 相似文献
27.
Steric factors have been shown to be responsible for the anomalous dehydration of 2-phenylindole-3-carboxamide (1) to 2-phenylindole-3-carbonitrile (3) by lithium aluminum hydride. This steric effect was also reflected in the reactions of 2-phenylindole (4) and its derivatives.
Anomale Dehydratisierung von 2-Phenylindol-3-carbonsäureamid zu 2-Phenyl-indol-3-carbonitril mit Lithiumaluminiumhydrid (Kurze Mitteilung)
Zusammenfassung Es wird gezeigt, daß für die anomale Dehydratisierung von 2-Phenylindol-3-carbonsäureamid (1) zum entsprechenden Nitril3 durch Lithiumaluminiumhydrid sterische Faktoren verantwortlich sind. Dieser sterische Effekt zeigt sich auch bei Reaktionen von 2-Phenylindol (4) und seiner Derivate.相似文献
28.
29.
Hubbard AL Davidson GJ Patel RH Wisner JA Loeb SJ 《Chemical communications (Cambridge, England)》2004,(2):138-139
Formation of a [3]catenane containing dibenzo-24-crown ether wheels and a large dipyridiniumethane ring is templated by formation of a host-guest adduct between the [3]catenane and the external crown ether. 相似文献
30.
Raymond J. Abraham Lee Griffiths Philip Loftus 《Journal of computational chemistry》1982,3(3):407-416
Alternative methods of estimating atomic charges in haloalkanes are presented, derived from quantum mechanical and classical treatments. A scheme based on a breakdown of the transmission of charge by polar atoms into one-bond, two-bond, and three-bond additive contributions is given, in which the one-bond effect is proportional to the difference in the electronegativities of the bonded atoms, and the two- and three-bond effects functions of the atomic electronegativity and polarizability. Suitable developments of the basic scheme, including an iterative self-consistent process, give calculated dipole moments for a variety of haloalkanes in good agreement with the observed values. The atomic charges obtained by this scheme are compared with other estimates of these charges. They are similar to those derived from a simple LCAO –MO scheme but differ from those obtained by population analysis of more refined quantum mechanical calculations. 相似文献