全文获取类型
收费全文 | 1569篇 |
免费 | 27篇 |
国内免费 | 17篇 |
专业分类
化学 | 1056篇 |
晶体学 | 11篇 |
力学 | 22篇 |
数学 | 308篇 |
物理学 | 216篇 |
出版年
2023年 | 6篇 |
2022年 | 36篇 |
2021年 | 37篇 |
2020年 | 21篇 |
2019年 | 28篇 |
2018年 | 27篇 |
2017年 | 23篇 |
2016年 | 56篇 |
2015年 | 33篇 |
2014年 | 50篇 |
2013年 | 104篇 |
2012年 | 88篇 |
2011年 | 97篇 |
2010年 | 69篇 |
2009年 | 86篇 |
2008年 | 93篇 |
2007年 | 92篇 |
2006年 | 96篇 |
2005年 | 72篇 |
2004年 | 74篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 20篇 |
2000年 | 28篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 18篇 |
1994年 | 8篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 6篇 |
1966年 | 2篇 |
排序方式: 共有1613条查询结果,搜索用时 13 毫秒
991.
Sielicki P Janik H Guzman A Broniszewski M Namieśnik J 《Analytical and bioanalytical chemistry》2011,399(9):3261-3270
The objectives of this work were to develop a means of sampling atmospheric dusts on the premises of an oil refinery for electron
microscopic study to carry out preliminary morphological analyses and to compare these dusts with those collected at sites
beyond the refinery limits. Carbon and collodion membranes were used as a support for collection of dust particles straight
on transmission electron microscopy (TEM) grids. Micrographs of the dust particles were taken at magnifications from ×4,000
to ×80,000 with a Tesla BS500 transmission electron microscope. Four parameters were defined on the basis of the micrographs:
surface area, Feret diameter, circumference, and shape coefficient. The micrographs and literature data were used to classify
the atmospheric dusts into six groups: particles with an irregular shape and rounded edges; particles with an irregular shape
and sharp edges; soot and its aggregates; spherical particles; singly occurring, ultrafine dust particles; and particles not
allocated to any of the previous five groups. The types of dusts found in all the samples were similar, although differences
did exist between the various morphological parameters. Dust particles with the largest Feret diameter were present in sample
3 (mean, 0.739 μm)—these were collected near the refinery's effluent treatment plant. The particles with the smallest diameter
were found in the sample that had been intended to be a reference sample for the remaining results (mean, 0.326 μm). The dust
particles collected in the refinery had larger mean Feret diameters, even 100% larger, than those collected beyond it. Particles
with diameters from 0.1 to 0.2 μm made up the most numerous group in all the samples collected in the refinery. 相似文献
992.
Przemysław Sielicki Helena Janik Agnieszka Guzman Alan Reynolds Jacek Namieśnik 《Central European Journal of Chemistry》2011,9(2):308-313
In years 2006–2010 particulate matter analysis was undertaken for dust samples collected from Gdansk and London area in order
to compare their morphology and composition. Part of those studies was devoted to analysis of particulate matter (PM) bearing
metals. Characterization of the morphology and size of the particles collected onto the filters was performed using a scanning
electron microscope (SEM) and transmission electron microscope (TEM). Both electron microscopes were equipped with energy
dispersive X-ray spectrometers to identify the elemental composition of the particles. On analysis of the X-ray spectra acquired
by both TEM and SEM, the particles were divided into 10 groups as follows: Al-rich, Ba-rich, C-rich, Ca-rich, Cl-rich, Fe-rich,
Mg-rich, Na-rich, S-rich, Si-rich. Speciation of the particles based on the major element and accompanying minor elements
yielded 34 particle types. However, some pairs of elements repeat, for instance: Na-Cl and Cl-Na, Al-S and S-Al, Si-Al and
Al-Si, S-Ca and Ca-S. These are undoubtedly the same types of particles; variation in peak heights of the major and minor
elements is normal in a mixed particle population. 相似文献
993.
994.
995.
996.
The accurate ground‐state potential energy surface of hydrogen peroxide, H2O2, has been determined from ab initio calculations using the coupled‐cluster approach in conjunction with the correlation‐consistent basis sets up to septuple‐zeta quality. Results obtained with the conventional and explicitly correlated coupled‐cluster methods were compared. The core–electron correlation, scalar relativistic, and higher‐order valence–electron correlation effects were taken into account. The adiabatic effects were also discussed. The vibration–rotation energy levels of the H2O2, D2O2, and HOOD isotopologues were predicted, and the experimental vibrational fundamental wavenumbers were reproduced to 1 cm?1 (“spectroscopic”) accuracy. © 2012 Wiley Periodicals, Inc. 相似文献
997.
Zhang Y Burdzinski G Kubicki J Platz MS 《Journal of the American Chemical Society》2008,130(48):16134-16135
Ultrafast laser flash photolysis (lambda(ex) = 270 nm) of phenyldiazirine produces transient infrared absorptions at 2040 and 1582 cm(-1). The first band is assigned to phenyldiazomethane, and the second is assigned to singlet phenylcarbene. This assignment is consistent with DFT calculations. Diazo band integration reveals that photoisomerization from diazirine to diazo occurs within a few picoseconds of the laser pulse. The majority of carbene produced is also formed instantaneously. 相似文献
998.
Dorota Najgebauer-Lejko Agnieszka Pluta-Kubica Jacek Domagaa Katarzyna Turek Iwona Duda Jozef Golian 《Molecules (Basel, Switzerland)》2022,27(24)
This study aimed to assess the effect of milk source and bear garlic addition on the selected properties of soft rennet cheese. Cheeses were produced from cow milk derived from two sources: Polish Red cows (PR) and Polish Holstein-Friesian cows (PHF) with a 0.5% (w/w) addition of bear garlic (Allium ursinum L.) dried leaves. Chemical composition and fatty acid profiles (GC) were determined in fresh cheeses. Fresh and stored for two weeks cheeses were subjected to microbiological studies, i.e., total aerobic bacteria count (TABC); count of Lactococcus sp., yeast and molds; coliforms; analysis of the proteolysis extension by means of o-phthaldialdehyde (OPA) assay and free amino acids content (HPLC); antioxidant capacity as 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and ferric reducing antioxidant power (FRAP); as well as pH and water activity. Cheeses with bear garlic herbs were more prone to proteolysis but this was not accompanied by any effect on the microbial counts, water activity or pH. Cheeses produced from PR milk contained less monounsaturated fatty acids (MUFA) but were richer in n-3 PUFA and had a lower n-6/n-3 FA ratio than cheeses from PHF milk. Bear garlic addition increased DPPH anti-radical power but had less of an effect on the FRAP values. 相似文献
999.
Andrzej Kuczumow Tomasz Blicharski Mieczysaw Gorzelak Jakub Kosiski Agnieszka Lasota Jacek Ggaa Jakub Nowak Maciej Jarzbski Mirosaw Jaboski 《Molecules (Basel, Switzerland)》2022,27(24)
Developments in the field of nanostructures open new ways for designing and manufacturing innovative materials. Here, we focused on new original ways of calculating energy changes during the substitution of foreign ions into the structure of apatites and bioapatites. Using these tools, the energetic costs of ion exchanges were calculated for the exemplary cases known from the literature. It was established that the most costly were ion exchanges of some cations inside apatites and of anions, and the least costly exchanges in tetrad channel positions. Real energy expenses for bioapatites are much smaller in comparison to mineral apatites due to the limited involvement of magnesium and carbonates in the structure of hard tissues. They are of the order of several electron volts per ion. The rigorous dependences of the energy changes and crystallographic cell volumes on the ionic radii of introduced cations were proved. The differentiation of the positioning of foreign ions in locations of Ca(I) and Ca(II) could be calculated in the case of a Ca-Pb reaction in hydroxyapatite. The energetic effects of tooth aging were indicated. The ability of energy change calculation during the ion exchange for isomorphic substances widens the advantages resulting from X-ray diffraction measurements. 相似文献
1000.
Kubicki J Luk HL Zhang Y Vyas S Peng HL Hadad CM Platz MS 《Journal of the American Chemical Society》2012,134(16):7036-7044
The photochemistry of 2-naphthylsulfonyl azide (2-NpSO(2)N(3)) was studied by femtosecond time-resolved infrared (TR-IR) spectroscopy and with quantum chemical calculations. Photolysis of 2-NpSO(2)N(3) with 330 nm light promotes 2-NpSO(2)N(3) to its S(1) state. The S(1) excited state has a prominent azide vibrational band. This is the first direct observation of the S(1) state of a sulfonyl azide, and this vibrational feature allows a mechanistic study of its decay processes. The S(1) state decays to produce the singlet nitrene. Evidence for the formation of the pseudo-Curtius rearrangement product (2-NpNSO(2)) was inconclusive. The singlet sulfonylnitrene (1)(2-NpSO(2)N) is a short-lived species (τ ≈ 700 ± 300 ps in CCl(4)) that decays to the lower-energy and longer-lived triplet nitrene (3)(2-NpSO(2)N). Internal conversion of the S(1) excited state to the ground state S(0) is an efficient deactivation process. Intersystem crossing of the S(1) excited state to the azide triplet state contributes only modestly to deactivation of the S(1) state of 2-NpSO(2)N(3). 相似文献