全文获取类型
收费全文 | 1136篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 879篇 |
晶体学 | 12篇 |
力学 | 19篇 |
数学 | 19篇 |
物理学 | 231篇 |
出版年
2022年 | 5篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2016年 | 19篇 |
2015年 | 22篇 |
2014年 | 31篇 |
2013年 | 40篇 |
2012年 | 50篇 |
2011年 | 68篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 64篇 |
2007年 | 41篇 |
2006年 | 48篇 |
2005年 | 47篇 |
2004年 | 51篇 |
2003年 | 44篇 |
2002年 | 31篇 |
2001年 | 33篇 |
2000年 | 17篇 |
1999年 | 14篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 23篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 19篇 |
1987年 | 27篇 |
1986年 | 14篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 15篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1978年 | 11篇 |
1977年 | 16篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1974年 | 14篇 |
1973年 | 7篇 |
1971年 | 5篇 |
1968年 | 7篇 |
1967年 | 5篇 |
排序方式: 共有1160条查询结果,搜索用时 0 毫秒
71.
The rotational spectrum of the NiS radical in the X(3)Sigma(-) state was observed by employing a source-modulation microwave spectrometer. The NiS radical was generated in a free space cell by a dc glow discharge in H(2)S diluted with Ar. The nickel atoms were supplied by the sputtering reaction from a nickel cathode. Rotational transitions with J = 11-10 to 25-24 were measured in the region between 135 and 314 GHz. Rotational, centrifugal distortion and several fine-structure constants were determined by a least-squares analysis. Other spectroscopic parameters such as dissociation energy, vibrational wavenumber and equilibrium bond length were also derived from the determined molecular constants. Excitation energies of the lowest (3)Pi and (1)Sigma(+) states were estimated from the fine-structure constants, lambda and gamma. 相似文献
72.
Mitsunori Oda Yosuke Fukuchi Satoshi Ito Nguyen Chung Thanh Shigeyasu Kuroda 《Tetrahedron letters》2007,48(52):9159-9162
Reactions of pyrrolidine with 2 equiv of aldehydes without any catalyst in a pressurized vessel at 140–200 °C yielded 1,3-disubstituted pyrroles. -Branched aldehydes gave fairly good yields of the corresponding products by this method, which provides a facile non-oxidative procedure for synthesizing 1,3-dialkylpyrroles from inexpensive pyrrolidine and aldehydes. 相似文献
73.
Zaima N Goto-Inoue N Hayasaka T Enomoto H Setou M 《Analytical and bioanalytical chemistry》2011,400(7):1865-1871
It has become necessary to assess the authenticity of beef origin because of concerns regarding human health hazards. In this
study, we used a metabolomic approach involving matrix-assisted laser desorption/ionization imaging mass spectrometry to assess
the authenticity of beef origin. Highly accurate data were obtained for samples of extracted lipids from beef of different
origin; the samples were grouped according to their origin. The analysis of extracted lipids in this study ended within 10 min,
suggesting this approach can be used as a simple authenticity assessment before a definitive identification by isotope analysis. 相似文献
74.
Kuroda N Sako A Ohyama K Akiyama S Nakashima K 《Journal of chromatographic science》2005,43(3):116-120
Modified 3-aminopropylsilyl silica stationary phases with 1,8-naphthalic anhydrides [3-(1,8-naphthalimido)propyl (NAIP), 3-(4-amino-1,8-naphthalimido)propyl (4A-NAIP), 3-(3-nitro-1,8-naphthalimido)propyl (3N-NAIP), and 3-(4-nitro-1,8-naphthalimido)propyl modified silyl silica gel (4N-NAIP)] are prepared in a single reaction. Chromatographic properties of these phases are characterized using various solutes including monosubstituted benzenes, alkyl benzenes, and polycyclic aromatic hydrocarbons (PAHs) in high-performance liquid chromatography. Even though the retention in these NAIPs is mainly based on the reversed-phase mode, 3N- and 4N-NAIP show a remarkable recognition toward aromatic hydrocarbons, which is attributed to their strong pi-pi interaction. Furthermore, the recognition ability is according to the molecular planarity and non-linearity of PAHs. Subsequently, 3N- and 4N-NAIP has a distinct selectivity from octadecyl silica and, therefore, will be a valuable alternative for a separation or a solid-phase extraction of aromatic compounds. 相似文献
75.
76.
Shigeyasu Kuroda Rie KasaiRyo Nagaya Ryuta MiyatakeYoshikazu Horino Naoko MatsumotoMitsunori Oda 《Tetrahedron letters》2011,52(13):1426-1429
3,10-Dipyrrolidinyl-4,9-methanothia[11]annulene reacts with excess dimethyl acetylenedicarboxylate (DMAD) in refluxing toluene to give ring-enlarged 6,11-methanothia[15]annulene. X-ray crystallographic analysis of the product shows two different cis,trans-dienyl parts in the ring system. Product formation possibly involves π-facial selective addition of the enamine with DMAD and torque-selective ring opening of the intermediate cyclobutenes. 相似文献
77.
A flow analysis system involving the on-line configuration of an anion-exchange column has been examined to enrich and determine trace concentrations of zirconium of several ppm to hundred ppm levels in silicate rocks and minerals. About 100 mg of sample is decomposed by fusion with a mixture of boric acid and lithium carbonate and taken up with 1M hydrochloric acid to a total of 100 ml. Depending upon the concentration of zirconium, either a 1- or 4-ml aliquot is introduced into an aqueous carrier stream, merged with sulphuric acid and passed through a small volume anion-exchange column. The enriched zirconium is then back eluted with hydrochloric acid, colour-developed with Arsenazo III, and detected spectrophotometrically at 665 nm. 相似文献
78.
S. Salaymeh S. C. Lee P. K. Kuroda 《Journal of Radioanalytical and Nuclear Chemistry》1987,111(1):147-155
Radiochemical measurements of239,240Pu were carried out for a total of 57 individual rain and snow samples collected at Fayetteville (36 °N, 94 °W), Arkansas, during the period between November 1984 and June 1986. The results indicate that the fallout of plutonium observed during the past three years is due, primarily, to the nuclear debris originating from the 7 February 1983 burn-up of the nuclear-powered Soviet satellite Cosmos-1402.This investigation was supported by the National Science Foundation under Grant ATM 84-07618. 相似文献
79.
Kenji Miyatake Mitsutoshi Jikei Junya Katoh Kimihisa Yamamoto Hiroyuki Nishide Eishun Tsuchida 《先进技术聚合物》1994,5(4):216-220
Poly(2,5-dimethylphenylene sulfide) was prepared by oxidative polymerization of sulfur chloride with p-xylene using 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as an oxidizing agent. The reaction proceeded efficiently under atmospheric pressure and at room temperature. The polymer formed had a high melting temperature and linear structure which was confirmed by spectroscopies. The effects of reaction time, solvent, temperature and oxidizing agent on polymerization are also discussed. 相似文献
80.
Katherine A. Gibney Iva Sovadinova Analette I. Lopez Michael Urban Zachary Ridgway Gregory A. Caputo Kenichi Kuroda 《Macromolecular bioscience》2012,12(9):1279-1289
We report the structure–activity relationship in the antimicrobial activity of linear and branched poly(ethylene imine)s (L‐ and B‐PEIs) with a range of molecular weights (MWs) (500–12 000). Both L‐ and B‐PEIs displayed enhanced activity against Staphylococcus aureus over Escherichia coli. Both B‐ and L‐PEIs did not cause any significant permeabilization of E. coli cytoplasmic membrane. L‐PEIs induced depolarization of S. aureus membrane although B‐PEIs did not. The low MW B‐PEIs caused little or no hemolysis while L‐PEIs are hemolytic. The low MW B‐PEIs are less cytotoxic to human HEp‐2 cells than other PEIs. However, they induced significant cell viability reduction after 24 h incubation. The results presented here highlight the interplay between polymer size and structure on activity.