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971.
Mass analysis in islands of stability with linear quadrupoles with added octopole fields 总被引:1,自引:0,他引:1
Konenkov N Zhao X Xiao Z Douglas DJ 《Journal of the American Society for Mass Spectrometry》2007,18(5):826-834
Mass analysis with linear quadrupole mass filters is possible by forming "islands" in the stability diagram with auxiliary quadrupole excitation. In this work, computer simulations are used to calculate stability boundaries, island positions, and peak shapes and ion transmission for mass analysis with linear quadrupole mass filters that have added octopole fields of about 2 to 4%. Rod sets with exact geometries that have quadrupole and octopole fields only in the potential, and round rod sets, with multipoles up to N = 10 (the twenty pole term) included in the calculations, show the same stability boundaries, island positions, and peak shapes. With the DC voltage applied to the rods so that the Mathieu parameter a < 0, conventional mass analysis is possible without the use of an island. With the DC polarity reversed so that a > 0, the resolution and transmission are poor preventing conventional mass analysis. In principle, mass analysis in an island is possible with operation at either of two tips. Provided the correct island tip is chosen for mass analysis, peak shapes comparable to those with a > 0 and no excitation are possible, both with a > 0 and with a < 0. In the latter case, the use of an island of stability allows mass analysis when the added octopole otherwise prevents conventional mass analysis. 相似文献
972.
Structural characterization of intact proteins is enhanced by prevalent fragmentation pathways rarely observed for peptides 总被引:2,自引:0,他引:2
Jennifer S. Cobb Michael L. Easterling Jeffrey N. Agar 《Journal of the American Society for Mass Spectrometry》2010,21(6):949-959
While collisionally activated dissociation (CAD) pathways for peptides are well characterized, those of intact proteins are
not. We systematically assigned CAD product ions of ubiquitin, myoglobin, and bovine serum albumin generated using high-yield,
in-source fragmentation. Assignment of >98% of hundreds of product ions implies that the fragmentation pathways described
are representative of the major pathways. Protein dissociation mechanisms were found to be modulated by both source declustering
potential and precursor ion charge state. Like peptides, higher charge states of proteins fragmented at lower energies next
to Pro, via mobile protons, while lower charge states fragmented at higher energies after Asp and Glu, via localized protons.
Unlike peptides, however, predominant fragmentation channels of proteins occurred at intermediate charge states via non-canonical
mechanisms and produced extensive internal fragmentation. The non-canonical mechanisms include prominent cleavages C-terminal
to Pro and Asn, and N-terminal to Ile, Leu, and Ser; these cleavages, along with internal fragments, led to a 45% increase
in sequence coverage, improving the specificity of top-down protein identification. Three applications take advantage of the
different mechanisms of protein fragmentation. First, modulation of declustering potential selectively fragments different
charge states, allowing the source region to be used as the first stage of a low-resolution tandem mass spectrometer, facilitating
pseudo-MS3 of product ions with known parent charge states. Second, development and integration of automated modulation of
ion funnel declustering potential allows users access to a particular fragmentation mechanism, yielding facile cleavage on
a liquid chromatography timescale. Third, augmentation of a top-down search engine improved protein characterization. 相似文献
973.
Garrido Frenich A Romero-González R Martínez Vidal JL Martínez Ocaña R Baquero Feria P 《Analytical and bioanalytical chemistry》2011,399(6):2043-2059
This work compares two miniaturised sample preparation methods, solid phase microextraction (SPME) and hollow fiber liquid
phase microextraction (HF-LPME), in combination with gas chromatography coupled to tandem mass spectrometry with a triple
quadrupole analyzer for the determination of 77 pesticides in drinking water. In the case of SPME, extraction temperature
and time were optimized by experimental design, although other parameters, as desorption time, pH, and ionic strength, were
also evaluated. The extraction and desorption solvents [octanol/dihexyl ether (75:25, v/v) and cyclohexane, respectively],
as well as the extraction and desorption time, ionic strength, and pH, were studied for the HF-LPME procedure. Under the optimal
conditions, recoveries (70.2–113.5% for SPME and 70.0–119.5% for HF-LPME), intra-day precision (2.1–19.4% for SPME and 4.3–22.5%
for HF-LPME), inter-day precision (5.2–21.5% for SPME and 8.4–27.3% for HF-LPME), and limits of detection, between 0.1 and
28.8 ng/L for SPME and 0.2 and 47.1 ng/L for HF-LPME and overall uncertainty (9.6–25.2% for SPME and 13.3–27.5% for HF-LPME)
were established for both extraction procedures. Finally, the proposed methods were successfully applied to the analysis of
41 drinking water samples, and similar results were obtained with both extraction approaches. 相似文献
974.
硝基四唑及其高氮化合物* 总被引:6,自引:0,他引:6
硝基四唑及其高氮化合物是指分子中含有5-硝基四唑结构的一类高氮化合物,优越的性能和突出的特点使其成为含能材料领域的研究热点之一,在起爆药、推进剂及其燃速催化剂、高能炸药、气体发生剂等领域有着广泛的应用前景。本文对硝基四唑的结构与热分解机理进行了分析介绍;全面系统地综述评价了硝基四唑及其盐类和配合物类衍生物的合成、性能表征与应用前景。根据其成盐阳离子的不同,硝基四唑盐类主要包括碱金属盐、碱土金属盐、过渡金属盐、胺盐和高氮杂环阳离子盐。根据配位方式的不同,其配合物可分为配阴离子型和配阳离子型。在此基础上,对硝基四唑及其高氮化合物的未来发展及应用提出了展望。 相似文献
975.
We studied cycle time (0.01–10 s with triangular input waves) and poling history (continuous versus fresh poling) dependent electric energy storage and discharge behaviors in poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] films using the electric displacement ― the electric field (D-E) hysteresis loop measurements. Since the permanent dipoles in PVDF are orientational in nature, it is generally considered that both charging and discharging processes should be time and poling history dependent. Intriguingly, our experimental results showed that the charging process depended heavily on the cycle time and the prior poling history, and thus the D-E hysteresis loops had different shapes accordingly. However, the discharged energy density did not change no matter how the D-E loop shape varied due to different measurements. This experimental result could be explained in terms of reversible and irreversible polarizations. The reversible polarization could be charged and discharged fairly quickly (< 5 ms for each process), while the irreversible polarization depended heavily on the poling time and the prior poling history. This study suggests that it is only meaningful to compare the discharged energy density for PVDF and its copolymer films when different cycle times and poling histories are used. 相似文献
976.
Distribution of Heavy Metal Contents and Chemical Fractions in Anaerobically Digested Manure Slurry 总被引:9,自引:0,他引:9
Digested slurry samples from twenty-one large-scale anaerobic digestion plants together with intensive pig and dairy farms
in Jiangsu Province of China were collected and analyzed for total and dissolved concentrations of Zn, Cu and As, as well
as chemical characteristics. The results showed that total concentrations of Zn, Cu and As in digested pig slurries were concentrated
to <10, <5 and 0.02–0.1 mg/l, respectively; while <2 and 10–30, <1, and 0.02–0.1 mg/l, respectively, in digested dairy slurries.
Lowering the dietary supply of these elements to pig and dairy would be the most effective way to control heavy metal contents
in digested manure slurries. Dissolved fractions of Zn, Cu and As accounted for 1–74%, 1–33% and 2–53% of the total concentrations,
respectively, in digested pig slurries; and 18–65%, 12–58% and 3–68% in digested dairy slurries. The chemical fractions of
heavy metals in digested slurries were not only dependent on the total concentrations of heavy metals in raw manures but also
on conditions of digestion and storage. Oxidation pond systems could significantly cripple the total contents of heavy metals
in digested slurries, and the removal effect was better in multi-oxidation-pond systems than that in primary-oxidation-pond
systems. However, the chemical fractions of heavy metals in digested slurries changed in a complicated manner when stored
in oxidation ponds, due to the suspended solid deposition, elements reduction, as well as variations of pH values and oxidation-reduction
potential. 相似文献
977.
分两部分介绍了我国化学物相分析近十余年来研究的新成就。第二部分(下)则对物料物质组成的相态与元素(Fe,I,Mn,Mo,Na,P,Re,S,Sb,Se,Si,Sn,Sr,Ti,U和V等)价态分析、赋存状态分析以及非金属矿物相分析等的研究现状,分别予以简要评述。同时对其存在的问题和进一步研究的方向也进行了讨论。引用文献114篇。 相似文献
978.
In the present study, the acid-base equilibria of N,O-carboxymethy chitosan abbreviated as (NOCC), is investigated. The complex
formation equilibria with the metal ions Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) are investigated potentiometrically. The stability constant values of the binary and ternary complexes formed in solution
were determined and the binding centers of the ligands were assigned. The relationships between the properties of the studied
central metal ions as ionic radius, electronegativity, atomic number, and ionization potential, and the stability constants
of the formed complexes were investigated in an effort to give information about the nature of chemical bonding in complexes
and make possible the calculation of unknown stability constants. Cu(II), Ni(II), and U(VI) complexes with NOCC are isolated as solid complexes and characterized by conventional chemical and physical methods. The
structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies. The ternary copper(II)
complexes involving NOCC and various biologically relevant ligands containing different functional groups, as amino acids
and DNA constituents are investigated. The stability constants of the complexes are determined and the concentration distribution
diagrams of the complexes are evaluated. 相似文献
979.
Sun YX Huang YX Li FL Wang HY Fan C Bao YL Sun LG Ma ZQ Kong J Li YX 《Chemistry Central journal》2012,6(1):2
Background
The virtual screening (VS) of lead compounds using molecular docking and pharmacophore detection is now an important tool in drug discovery. VS tasks typically require a combination of several software tools and a molecular graphics system. Thus, the integration of all the requisite tools in a single operating environment could reduce the complexity of running VS experiments. However, only a few freely available integrated software platforms have been developed. 相似文献980.