全文获取类型
收费全文 | 2349篇 |
免费 | 54篇 |
国内免费 | 8篇 |
专业分类
化学 | 1694篇 |
晶体学 | 32篇 |
力学 | 17篇 |
数学 | 109篇 |
物理学 | 559篇 |
出版年
2023年 | 19篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 32篇 |
2019年 | 25篇 |
2018年 | 15篇 |
2016年 | 36篇 |
2015年 | 40篇 |
2014年 | 40篇 |
2013年 | 107篇 |
2012年 | 77篇 |
2011年 | 100篇 |
2010年 | 59篇 |
2009年 | 57篇 |
2008年 | 123篇 |
2007年 | 135篇 |
2006年 | 144篇 |
2005年 | 126篇 |
2004年 | 123篇 |
2003年 | 101篇 |
2002年 | 97篇 |
2001年 | 46篇 |
2000年 | 53篇 |
1999年 | 56篇 |
1998年 | 22篇 |
1997年 | 48篇 |
1996年 | 37篇 |
1995年 | 34篇 |
1994年 | 34篇 |
1993年 | 35篇 |
1992年 | 40篇 |
1991年 | 26篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 25篇 |
1987年 | 28篇 |
1986年 | 25篇 |
1985年 | 32篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 32篇 |
1981年 | 24篇 |
1980年 | 20篇 |
1979年 | 28篇 |
1978年 | 23篇 |
1977年 | 23篇 |
1976年 | 25篇 |
1975年 | 13篇 |
1974年 | 20篇 |
1973年 | 25篇 |
排序方式: 共有2411条查询结果,搜索用时 0 毫秒
41.
W. K. A. Kumuduni Y. Nakata T. Okada M. Maeda 《Applied physics. B, Lasers and optics》1994,58(4):289-294
One-dimensional imaging laser-induced fluorescence spectroscopy has been used for in-situ measurements of spatial distributions of YO molecules produced during the ArF-laser ablation of YBa2 Cu3 O
7–x
in vacuum and oxygen gas environment. The time-integrated angular distribution of particles ejected in vacuum has a cos
n
form, where 11 <n < 13. When oxygen gas was introduced, YO molecules were confined in a smaller volume, and temporal changes of their spatial distribution were interpreted in terms of blast-wave formation. 相似文献
42.
Espy MA Dehnhard D Edwards CM Palarczyk M Langenbrunner JL Davis B Burleson GR Blanchard S Gibbs WR Lail B Nelson B Park BK Zhao Q Cummings WJ Delheij PP Jennings BK Henderson R Häusser O Thiessen D Brash E Jones MK Larson B Brinkmöller B Maeda K Morris CL O'Donnell JM Penttilä S Swenson D Tupa D Bennhold C Kamalov SS 《Physical review letters》1996,76(20):3667-3670
43.
44.
Viscous properties of partially hemolyzed erythrocyte suspensions were studied with a cone-plate viscometer. A Casson plot was successfully applied for analysis of the viscous properties. When the degree of hemolysis was increased, Casson viscosity (
c) of the partially hemolyzed erythrocyte suspensions increased, but the substitution of hemoglobin solution with the same O2-carrying capacity of hemolyzed fraction (containing ghost) reduced the
c remarkably. The yield stress (f
c) of the intact erythrocyte suspension increased with increasing hematocrit, but thef
c of partially hemolyzed erythrocyte suspension was dependent on both hematocrit and the degree of hemolysis. The apparent viscosity (
a) of erythrocyte suspension was drastically increased with the slight hemolysis, and became maximum at a certain degree of hemolysis which was dependent on both total hemoglobin concentration and shear rate. Such influence of hemolysis on the
a was also evident in the mixture of erythrocyte suspension and hemoglobin solution. These results suggest that the hemoglobin molecule plays a certain role in erythrocyte-erythrocyte interaction in their suspension, which modifies the viscosity. 相似文献
45.
46.
Frieder W. Lichtenthaler Jürgen Klotz Katsumi Nakamura 《Tetrahedron: Asymmetry》2003,14(24):3973-3986
The dimethyl esters of the 2,6-anhydro-3-deoxy-hept-2-enaric acids with
-xylo,
-lyxo,
-arabino,
-lyxo- and
-ribo-configuration were synthesized from
-galactose and
-mannose, respectively, and further characterized by their di-O-acetyl and di-O-benzoyl derivatives. Comparison of their physical data with those of Daucus carota derived products revealed (−)-daucic acid to have
-lyxo-configuration 46 rather than the previously assigned
-xylo stereochemistry 1. Dimethyl daucate 43 could be converted by acid-induced ring contraction and dehydration into naturally occurring (+)-osbeckic acid 47, thereby proving its (S)-configuration. Configurational identity in the pyranoid rings of (−)-daucic acid and KDO, together with available biosynthetic evidence on chelidonic acid 4, a leaf closing factor, suggests a joint, KDO 8-P-based pathway for their biosynthesis in plants. 相似文献
47.
Phenols are ethynylated at the ortho position with silylated chloroethyne in the presence of a catalytic amount of GaCl3 and lithium phenoxide. The lithium salt is essential for the catalysis, and addition of 2,6-di(tert-butyl)-4-methylpyridine inhibits desilylation and hydration of the products. The reaction can be applied to various substituted phenols giving the ortho-ethynylated products in high yields, and the turnover numbers based on GaCl3 are between 8 and 10. The reaction mechanism involves addition of in situ formed phenoxygallium to the haloethyne followed by the elimination of GaCl3. 相似文献
48.
Cao B Wakahara T Tsuchiya T Kondo M Maeda Y Aminur Rahman GM Akasaka T Kobayashi K Nagase S Yamamoto K 《Journal of the American Chemical Society》2004,126(30):9164-9165
A new metallofullerene, La2@C78, has been synthesized by DC arc discharge method, isolated by high-performance liquid chromatography, and characterized by laser desorption time-of-flight mass spectrometry, UV-vis-NIR absorption, differential pulse voltammetry, 13C NMR spectroscopy, and theoretical calculations. The La2@C78/CS2 solution is dark violet and presents several characteristic absorption features at 647, 561, 533, and 386 nm, with an onset around 1000 nm. With respect to empty D3-C78, the capability of La2@C78 as an electron acceptor or donor is stronger. Addition of 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disirane to La2@C78 photochemically, as well as thermally, affords bis- and mono-adducts. Theoretical studies and 13C NMR spectroscopic analysis of La2@C78 indicate that it possesses a D3h-C78 cage (78:5). 相似文献
49.
Sinomenine, an alkaloid of the Japanese plant Sinomenium acutum, was converted to the 4-phenylether by the Ullmann reaction in a good yield. The Clemmensen reduction of sinomenine-phenylether and of its derivatives gave (+)-3-methoxy-4-phenoxy-N-methyl-Δx-morphinan.
Hydrogenation and successive sodium-liquid ammonia reduction of (+)-3-methoxy-4-phenoxy-N-methyl-Δx-morphinan gave (+)-3-methoxy-N-methylmorphinan. 相似文献
50.
Juglomycin A has been synthesized in four steps from 5-methoxy-1-naphthol. 相似文献