全文获取类型
收费全文 | 1854篇 |
免费 | 77篇 |
国内免费 | 37篇 |
专业分类
化学 | 1103篇 |
晶体学 | 8篇 |
力学 | 22篇 |
综合类 | 12篇 |
数学 | 196篇 |
物理学 | 627篇 |
出版年
2020年 | 37篇 |
2019年 | 21篇 |
2017年 | 19篇 |
2016年 | 32篇 |
2015年 | 45篇 |
2014年 | 25篇 |
2013年 | 43篇 |
2012年 | 81篇 |
2011年 | 89篇 |
2010年 | 45篇 |
2009年 | 50篇 |
2008年 | 73篇 |
2007年 | 78篇 |
2006年 | 68篇 |
2005年 | 48篇 |
2004年 | 52篇 |
2003年 | 36篇 |
2002年 | 37篇 |
2001年 | 56篇 |
2000年 | 53篇 |
1999年 | 49篇 |
1998年 | 24篇 |
1997年 | 33篇 |
1996年 | 19篇 |
1995年 | 26篇 |
1994年 | 43篇 |
1993年 | 39篇 |
1992年 | 36篇 |
1991年 | 27篇 |
1990年 | 30篇 |
1989年 | 23篇 |
1988年 | 28篇 |
1987年 | 37篇 |
1986年 | 29篇 |
1985年 | 34篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 27篇 |
1980年 | 28篇 |
1979年 | 28篇 |
1978年 | 25篇 |
1977年 | 19篇 |
1976年 | 37篇 |
1975年 | 21篇 |
1974年 | 18篇 |
1973年 | 23篇 |
1972年 | 15篇 |
1968年 | 13篇 |
1967年 | 16篇 |
排序方式: 共有1968条查询结果,搜索用时 31 毫秒
41.
Capillary reversed-phase high-performance liquid chromatography (RP-HPLC) utilizing monolithic poly(styrene-divinylbenzene) columns was optimized for the coupling to electrospray ionization mass spectrometry (ESI-MS) by the application of various temperatures and mobile phase additives during peptide and protein analysis. Peak widths at half height improved significantly upon increasing the temperature and ranged from 2.0 to 5.4 s for peptide and protein separations at 70 degrees. Selectivity of peptide elution was significantly modulated by temperature, whereas the effect on proteins was only minor. A comparison of 0.10% formic acid (FA), 0.050% trifluoroacetic acid (TFA), and 0.050% heptafluorobutyric acid (HFBA) as mobile phase additives revealed that highest chromatographic efficiency but poorest mass spectrometric detectabilities were achieved with HFBA. Clusters of HFBA, water, and acetonitrile were observed in the mass spectra at m/z values >500. Although the signal-to-noise ratios for the individual peptides diverged considerably both in the selected ion chromatograms and extracted mass spectra, the average mass spectrometric detectabilities varied only by a factor of less than 1.7 measured with the different additives. Limits of detection for peptides with 500 nl sample volumes injected onto a 60 mm x 0.20 mm monolithic column were in the 0.2-13 fmol range. In the analysis of hydrophobic membrane proteins, HFBA enabled highest separation selectivity at the cost of lower mass spectral quality. The use of 0.050% TFA as mobile phase additive turned out to be the best compromise between chromatographic and mass spectrometric performance in the analysis of peptides and proteins by RP-HPLC-ESI-MS using monolithic separation columns. 相似文献
42.
A total synthesis of the optically active tetrahydroesterastin β -lactam analogue 2 using Miller's hydroxamate approach is described (Scheme 2). Significant modification of published procedures has resulted in a short and facile stereospecific preparation of the N-[(benzyloxycarbonyl)methyl]-β -lactam 17 starting from the readily available D -serine. This material served as intermediate for the preparation of a variety of N-[(benzyloxycarbonyl)methyl]tetrahydroesterastin β-lactam analogues (Scheme 5). 相似文献
43.
44.
Roland Huber 《Geometriae Dedicata》1995,58(3):291-311
We show some topological properties of semianalytic subsets of rigid analytic varieties: curve selection lemma, the closure
of a semianalytic subsetS is semianalytic,
for every quasi-compact morphismf. As an application we show that a morphismf: X Y of rigid analytic varieties is open at a pointx X if and only if SpecO
X,x SpecO
Y,f(x) is surjective. 相似文献
45.
46.
47.
48.
49.
Groundstate absorption, fluorescence, excited-state absorption, and stimulated emission of Pr:YA1O3 were measured in dependence on the polarization. The results reflect the anisotropy of the host lattice. Especially the polarized spectra of the stimulated emission fit very well with the laser data of this material. Seven cw laser transitions in the visible spectral range obtained so far in Pr:YA1O3 with argon-ion laser pumping were identified in the spectra of the stimulated emission. In addition, two infrared cw laser transitions were realized. The best results were achieved for the3
P
03
F
4 laser transition at 746.9 nm with a maximum slope efficiency of 24.6%, a maximum output power of 49.6 mW, and a laser threshold of 25 mW. 相似文献
50.
T. Sandrock T. Danger E. Heumann G. Huber B. H. T. Chai 《Applied physics. B, Lasers and optics》1994,58(2):149-151
We report, to our knowledge for the first time, Continuous Wave (CW) laser emission at room temperature of Pr:LiYF4 (Pr.YLF) at six wavelengths: 522, 545, 607, 639.5, 720 and 907.4 nm. The pump source was an argon-ion laser tuned to a wavelength of = 457.9 nm. The maximum output powers at 522 nm (3Pi 3H5) and 639.5 nm (3P0 3F2) were 144 and 266 mW, respectively. We also observed CW laser action of Pr:GdLiF4 (Pr: GLF) at = 639 nm and of Pr:KYF4 (Pr: KYF) at = 642.5 nm. 相似文献