全文获取类型
收费全文 | 2534篇 |
免费 | 67篇 |
国内免费 | 11篇 |
专业分类
化学 | 1617篇 |
晶体学 | 14篇 |
力学 | 58篇 |
数学 | 340篇 |
物理学 | 583篇 |
出版年
2023年 | 17篇 |
2022年 | 14篇 |
2021年 | 21篇 |
2020年 | 21篇 |
2019年 | 33篇 |
2018年 | 23篇 |
2017年 | 18篇 |
2016年 | 51篇 |
2015年 | 44篇 |
2014年 | 46篇 |
2013年 | 135篇 |
2012年 | 112篇 |
2011年 | 124篇 |
2010年 | 82篇 |
2009年 | 62篇 |
2008年 | 117篇 |
2007年 | 131篇 |
2006年 | 134篇 |
2005年 | 125篇 |
2004年 | 115篇 |
2003年 | 96篇 |
2002年 | 89篇 |
2001年 | 54篇 |
2000年 | 39篇 |
1999年 | 29篇 |
1998年 | 34篇 |
1997年 | 30篇 |
1996年 | 46篇 |
1995年 | 24篇 |
1994年 | 33篇 |
1993年 | 29篇 |
1992年 | 33篇 |
1991年 | 20篇 |
1990年 | 27篇 |
1989年 | 25篇 |
1988年 | 24篇 |
1986年 | 18篇 |
1985年 | 43篇 |
1984年 | 34篇 |
1983年 | 38篇 |
1982年 | 60篇 |
1981年 | 47篇 |
1980年 | 49篇 |
1979年 | 23篇 |
1978年 | 33篇 |
1977年 | 30篇 |
1976年 | 26篇 |
1975年 | 19篇 |
1974年 | 24篇 |
1973年 | 15篇 |
排序方式: 共有2612条查询结果,搜索用时 15 毫秒
81.
The preparation of the η4-4-2,3,5,6-tetramethyl-1,4-benzoquinonecomplex [CO(C5Me5)(C10H12O2)] (I) is reported. Complex I undergoesreversible protonation to yield the 2-6-η-4-hydroxy-1-oxo-2,3,5,6-tetramethylcyclohexadienyl complex [Co(C5Me5)(C10H13O2)BF4 (II) and diprotonation to yield the η6-6-1,4-dihydroxy-2,3,5,6-tetramethylbenzene complex [Co(C5Me5)(C10H14O2)] (BF4)2 (III). Methylation of complex I with MeI/AgPF6 gives the 2---6-η-4-methoxy-1-oxo-2,3,5,6-tetramethylcyclohexadienyl complex [Co(C5Me5)(C11H15O2])PF6 (IV). In trifluoroacetic acid solution complex IV is protonated to form the η6-1-hydroxy-4-methoxy-2,3,5,6-tetramethylbenzene cation [Co(C5Me5)-(C11H16O2)]2+ 相似文献
82.
William J. Orts Geoffrey A. R. Nobes Gregory M. Glenn Gregory M. Gray Syed Imam Bor‐Sen Chiou 《先进技术聚合物》2007,18(8):629-635
Blends of thermoplastic starch with poly(ethylene‐co‐vinyl alcohol) copolymer (EVOH) were melt extruded with water/glycerol as plasticizer and a series of amino acid additives. The biggest factor in end‐use mechanical properties proved to be the relative humidity (RH) during storage. Plasticized starch‐EVOH blends stored at 0 and 50% RH changed significantly over time, with, for example, the tensile strength (TS) of the glycerol‐plasticized blend increasing from 4.7 to 26.3 MPa over 8 weeks when maintained at 0% RH. In contrast, the TS of this same sample stored at 75% RH remained unchanged for 8 weeks. Amino acids provided relatively minor, but significant changes in mechanical properties with time. Based on TS, elongation‐to‐break, and modulus, it may be concluded that β‐alanine, sarcosine, and L ‐proline were more effective than glycerol at maintaining strong flexible blends. Increases in crystallinity and changes in morphology with time, as described by modulated DSC were correlated to these changes in mechanical properties. Published in 2007 by John Wiley & Sons, Ltd. 相似文献
83.
Self-assembled monolayers (SAMs) obtained from 1-(10-acetylsulfanyldecyl)-4-[2-(4-dimethylaminophenyl)vinyl]quinolinium iodide exhibit asymmetric current-voltage (I-V) characteristics. The rectification may be reversibly switched: it is suppressed when the film is exposed to HCl vapor, the intramolecular charge-transfer axis being inhibited by protonation, but restored when exposed to NH(3). The behavior is intrinsic to the donor-(pi-bridge)-acceptor moiety, and ambiguity in the assignment has been excluded by matching the alkyl tails on the substrate and contacting STM tip to locate the chromophore midway between the electrodes: Au-S-C(10)H(21)//D-pi-A-C(10)H(20)-S-Au. Films contacted by gold tips exhibit rectification ratios of ca. 18 at +/-1 V, whereas those contacted by pentanethiolate (Au-S-C(5)H(11))- and decanethiolate (Au-S-C(10)H(21))-coated tips have corresponding ratios of ca. 11 and 5, respectively. The I-V curves are different, but when adjusted for thickness the current versus electric field dependence is indistinguishable. Seven dyes are reported: SAMs with sterically hindered D-pi-A moieties, in which the donor and acceptor are twisted out of plane, exhibit rectification, whereas those that are planar or have a weak donor-acceptor combination do not. 相似文献
84.
Time-consuming fusion and pyrohydrolysis methods for quantifying fluoride and tin in fluoride-doped tin oxide films on glass are replaced by a simple electrolytic reduction for sample preparation. The unusual conductivity of these films enables solutions to be produced in which fluoride can be quantified by ion chromatography. Tin is quantified in the original sample by x-ray fluorescence spectrometry. Electrolytic reduction and the fusion/pyrohydrolysis methods are compared for films with Sn/F ratios of 10–40 (71–183 μg cm?2 tin and 0.54–2.8 μ cm?2 fluoride). The Sn/F ratios and precision are similar for the two methods. The older method only yields the tin/fluoride ratio; the electrolytic method gives results as mass per unit area and requires much less time per sample. 相似文献
85.
Mobilities of H+ and H? in He and in H2, and of H+2 and H+3 in He, are calculated from ion-neutral potentials derived from theory and ion-beam scattering. Agreement with experiment is reasonable except for H? in H2 and H+2 in He, which present unexplained puzzles. 相似文献
86.
87.
T. A. Nichols J. S. Morris V. L. Spate C. J. Tharp C. K. Baskett T. L. Horsman M. M. Mason T. P. Cheng 《Journal of Radioanalytical and Nuclear Chemistry》1998,235(1-2):65-69
A global radionuclide monitoring system is being engineered as part of a multi-technology verification system for the Comprehensive
Nuclear Test Ban Treaty. The system detects airborne radioactive aerosols and gases that can indicate nuclear weapons test
debris. The backbone of the system is a network of 80 remote detection stations that utilize high-volume air sampling and
high-resolution gamma spectrometry to provide in-situ assay and near-real time reporting. These stations are linked to the
International Data Centre, which is a central data processing hub where raw spectral data is automatically processed, analyzed,
and disseminated to the states parties. Measurements are categorized based on spectral content to determine which contain
anomalous anthropogenic radionuclides that require intensive radiochemical analysis at a certified laboratory. The resulting
system has the capability to measure microbecquerel concentrations of radionuclides and provide accessible data products within
minutes of field measurements. During the past year of international operations, the minimum detectable concentrations and
spectroscopy processing statistics were recorded as a function of geographical location and time. The results show that this
system is an effective tool for nuclear test monitoring, as well as other applications such as radiological emergency response,
public health monitoring, and scientific research. 相似文献
88.
David J. Barsky Geoffrey R. Grimmett Charles M. Newman 《Probability Theory and Related Fields》1991,90(1):111-148
Renormalization arguments are developed and applied to independent nearest-neighbor percolation on various subsets of
d
,d2, yielding:
Corollaries of these results include uniqueness of the infinite cluster for such 's and sufficiency of the following for proving continuity of the full-space phase transition: showing that percolation in the full-space at densityp implies percolation in the half-space at thesame density. 相似文献
| Equality of the critical densities,p c (), for a half-space, quarter-space, etc., and (ford>2) equality with the limit of slab critical densities. |
| Continuity of the phase transition for the half-space, quarter-space, etc.; i.e., vanishing of the percolation probability, (p), atp=p c (). |
89.
90.
The rationale for a new class of HMG CoA reductase inhibitors, represented by ,ga-difluoroketones 3 and 4, is described. The syntheses of 3, 4, and their nonfluorinated analogue 5 are presented. 相似文献