全文获取类型
收费全文 | 1290篇 |
免费 | 15篇 |
国内免费 | 14篇 |
专业分类
化学 | 969篇 |
晶体学 | 17篇 |
力学 | 12篇 |
数学 | 93篇 |
物理学 | 228篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 18篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 18篇 |
2013年 | 83篇 |
2012年 | 48篇 |
2011年 | 60篇 |
2010年 | 34篇 |
2009年 | 39篇 |
2008年 | 63篇 |
2007年 | 76篇 |
2006年 | 74篇 |
2005年 | 69篇 |
2004年 | 54篇 |
2003年 | 60篇 |
2002年 | 69篇 |
2001年 | 25篇 |
2000年 | 30篇 |
1999年 | 12篇 |
1998年 | 18篇 |
1997年 | 21篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 22篇 |
1993年 | 13篇 |
1992年 | 24篇 |
1991年 | 6篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 20篇 |
1987年 | 6篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 6篇 |
1979年 | 22篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1975年 | 17篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有1319条查询结果,搜索用时 15 毫秒
91.
Kikugawa Y Nagashima A Sakamoto T Miyazawa E Shiiya M 《The Journal of organic chemistry》2003,68(17):6739-6744
N-Phthalimido-N-acylnitrenium ions are generated from N-acylaminophthalimides, a new class of precursors, by treatment with hypervalent iodine compounds (PIFA and HTIB). In HFIP, the nitrenium ions undergo intramolecular electrophilic substitution reactions to afford N-aminonitrogen heterocycles in high yields. In TFEA, spirodienones bearing the 1-azaspiro[4.5]decane skeleton are obtained by treatment of N-phthalimido-3-(4-halogenophenyl)propanamides with HTIB as a result of ipso attack of the intermediate nitrenium ion. Similarly, using PIFA in TFEA, ipso cyclization of unactivated benzenoid compounds occurs to afford spirodiene derivatives. This involves loss of aromaticity despite the absence of other activating substituents on the phenyl group. 相似文献
92.
(--)-Muricatacin, a potent cytotoxic (4R,5R)-5-hydroxyheptadecan-4-olide, has been synthesized through alpha-C--H hydroxyalkylation and alpha'-C--H oxidation of tetrahydrofuran. This study presents a novel method for C--H bond functionalization as a means for preparing gamma-(hydroxyalkyl)-gamma-butyrolactones. 相似文献
93.
94.
Doke T Hayashi T Kikuchi J Sakaguchi T Terasawa K Yoshihira E Nagaoka S Nakano T Takahashi S 《Radiation measurements》2001,33(3):373-387
Dosimetric measurements on the Space Shuttle Missions STS-84, -89 and -91 have been made by the real-time radiation monitoring device III (RRMD-III). Simultaneously, another dosimetry measurement was made by the Dosimetry Telescope (DOSTEL) on STS-84 and by the tissue-equivalent proportional counter (TEPC) on STS-91. First, the RRMD-III instrument is described in detail and its results summarized. Then, the results of DOSTEL and TEPC are compared with those of the RRMD-III. Also, the absorbed doses obtained by TLD (Mg2SiO4) and by RRMD-III on board STS-84 and -91 are compared. 相似文献
95.
96.
Yasuo Kanai 《Proceedings of the American Mathematical Society》1999,127(10):3073-3080
In this paper, we present some relations between generalized distributivity of quotient algebras and Mahlo operations, and show that the distributivity implies some variants of stationary relections.
97.
Experiments have been conducted to investigate an effect of inlet restriction on the thermal-hydraulic stability. A Test
facility used in this study was designed and constructed to have non-dimensional values that are nearly equal to those of
natural circulation BWR. Experimental results showed that driving force of the natural circulation at the stability boundary
was described as a function of heat flux and inlet subcooling independent of inlet restriction. In order to extend experimental
database regarding thermal-hydraulic stability to different inlet restriction, numerical analysis was carried out based on
the homogeneous flow model. Stability maps in reference to the core inlet subcooling and heat flux were presented for various
inlet restrictions using the above-mentioned function. Instability region during the inlet subcooling shifted to the higher
inlet subcooling with increasing inlet restriction and became larger with increasing heat flux.
Received on 17 January 2000 相似文献
98.
Yasuo Iida 《Fresenius' Journal of Analytical Chemistry》1987,328(7):547-552
Summary A new multiwavelength data-analysis method for the determination of multicomponent mixtures, the repetitive spectral subtraction method (RSSM), is proposed. In RSSM, spectral data are obtained at evenly spaced wavelengths in the range of interest, and the analysis of the spectrum is performed as repetitive determination-subtraction cycle. In the determination step, the series of data in the narrow wavelength range is used, which is specified as to include the most characteristic or the largest peak for each component. Assuming a linear background, the target component, which can be a small group of components, is simultaneously determined together with co-existing components. In the next subtraction step, the calculated contribution of the component is subtracted from the spectral data in the whole measured wavelength range, and the component is assigned as determined and is excluded from the following analysis. This determination-subtraction cycle is repeated until all the components are determined.With RSSM, a mixture of many components can be precisely determined by the use of most information contained in the spectrum. The accuracy of determination can be improved by automatic estimation of the background and the gradual decrease of interferences. In order to demonstrate the usefulness of RSSM, the 8 rare earth elements (Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm) in the model mixtures were determined by spectrophotometry, and the results were compared with those of the usual correction factor method and the derivative method. Furthermore, the 8 rare earth elements were determined in ores, monazite and xenotime.
Spektralphotometrische Bestimmung von Seltenen Erden mit Hilfe eines Verfahrens der wiederholten Subtraktion相似文献
99.
The sensor for adenosine-5′-triphosphate (ATP) is based on H+-ATPase immobilized via a polyvinylbutyral resin on a pH-sensitive field effect transistor. A linear relationship was obtained between the initial rate of change of the differential gate output voltage and the logarithm of the ATP concentration over the range 0.2–1.0 mM ATP. The optimum pH was 9.0 at 40°C but pH 7.0 was preferred for routine measurements. Only slight responses were obtained for 1 mM glucose, creatinine or urea. The ATP-sensing system exhibited a response to 1 mM ATP for at least 18 days. 相似文献
100.
S. Suzuki S. Nagaoka I. Koyano K. Tanaka T. Kato 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,4(1):111-119
An apparatus designed for studies of state selected unimolecular and ion-molecule reactions using synchrotron radiation is described. It is installed in the UVSOR storage ring in Okazaki. Threshold electron spectra of some rare gas atoms and diatomic and polyatomic molecules taken with this apparatus are presented and discussed. 相似文献