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991.
Janz JM Ren Y Looby R Kazmi MA Sachdev P Grunbeck A Haggis L Chinnapen D Lin AY Seibert C McMurry T Carlson KE Muir TW Hunt S Sakmar TP 《Journal of the American Chemical Society》2011,133(40):15878-15881
Cell surface heptahelical G protein-coupled receptors (GPCRs) mediate critical cellular signaling pathways and are important pharmaceutical drug targets. (1) In addition to traditional small-molecule approaches, lipopeptide-based GPCR-derived pepducins have emerged as a new class of pharmaceutical agents. (2, 3) To better understand how pepducins interact with targeted receptors, we developed a cell-based photo-cross-linking approach to study the interaction between the pepducin agonist ATI-2341 and its target receptor, chemokine C-X-C-type receptor 4 (CXCR4). A pepducin analogue, ATI-2766, formed a specific UV-light-dependent cross-link to CXCR4 and to mutants with truncations of the N-terminus, the known chemokine docking site. These results demonstrate that CXCR4 is the direct binding target of ATI-2341 and suggest a new mechanism for allosteric modulation of GPCR activity. Adaptation and application of our findings should prove useful in further understanding pepducin modulation of GPCRs as well as enable new experimental approaches to better understand GPCR signal transduction. 相似文献
992.
Wiederkehr AW Motsch M Hogan SD Andrist M Schmutz H Lambillotte B Agner JA Merkt F 《The Journal of chemical physics》2011,135(21):214202
A supersonic beam of metastable neon atoms has been decelerated by exploiting the interaction between the magnetic moment of the atoms and time-dependent inhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91 deceleration solenoids, the atoms were decelerated from an initial velocity of 580 m/s to final velocities as low as 105 m/s, corresponding to a removal of more than 95% of their initial kinetic energy. The phase-space distribution of the cold, decelerated atoms was characterized by time-of-flight and imaging measurements, from which a temperature of 10 mK was obtained in the moving frame of the decelerated sample. In combination with particle-trajectory simulations, these measurements allowed the phase-space acceptance of the decelerator to be quantified. The degree of isotope separation that can be achieved by multistage Zeeman deceleration was also studied by performing experiments with pulse sequences generated for (20)Ne and (22)Ne. 相似文献
993.
Determination of organochlorine pesticide residues in fatty foods: a critical review on the analytical methods and their testing capabilities 总被引:3,自引:0,他引:3
Organochlorine pesticide (OCP) residues in foods have been of concern for several decades. However, the analysis of some of the OCPs and their metabolites or derivatives, such as endrin aldehyde, endrin ketone, nonachlor, etc. in fatty foods (including foods of animal and plant origin), was not commonly included in routine monitoring programme. Recently, the Stockholm Convention introduced nine plus one new persistent organic pollutants (POPs) that included chlordecone and some other OCPs. Is there a method available that can analyze both traditional OCPs, together with their metabolites and derivatives in fatty foods? Furthermore, is there a suitable method that can monitor OCPs and the newly added POPs including chlordecone in fatty foods together in a pot? This review aims to provide some background information to answer these questions. 相似文献
994.
Pillay AE Bassioni G Stephen S Kühn FE 《Journal of the American Society for Mass Spectrometry》2011,22(8):1403-1408
Knowledge of trace metal ‘grains’ in asphaltenes could play a significant role in enhancing refining and processing of crudes
and also in providing useful information on mechanistic and migratory features linked to asphaltenes. These metals originate
directly from interaction of oils with source-rock, mineral matter, and formation water and their accumulation in asphaltene
matrices could vary from oil well to oil well. Suitable asphaltene samples were subjected to high-performance ICP-MS laser
depth profiling (213 nm) to depths of 50 μm at 5 μm intervals. The study was conducted in the absence of standardization and
characteristic intensities originating from the metals of interest were measured. Ten metal profiles were investigated (Na,
Mg, Al, Mn, Fe, Zn, Sr, Pb, V, and Ni). The experimental results showed non-uniform distribution of trace metals and identified
areas where such metals agglomerate. The data suggested that certain chemical and physical conditions within the structure
of asphaltenes are favorable for metal ‘grain’ formation at specific points. The exact mechanism for this behavior is not
clear at this stage, and has considerable scope for future studies, including mathematical modeling simulations of asphaltenes.
We also found that solid asphaltenes could be a useful forerunner of scale formation. 相似文献
995.
Sciuto SV Liu J Konermann L 《Journal of the American Society for Mass Spectrometry》2011,22(10):1679-1689
Electrosprayed multi-protein complexes can be dissociated by collisional activation in the gas phase. Typically, these processes
follow a mechanism whereby a single subunit gets ejected with a disproportionately high amount of charge relative to its mass.
This asymmetric behavior suggests that the departing subunit undergoes some degree of unfolding prior to being separated from
the residual complex. These structural changes occur concomitantly with charge (proton) transfer towards the subunit that
is being unraveled. Charge accumulation takes place up to the point where the subunit loses physical contact with the residual
complex. This work develops a simple electrostatic model for studying the relationship between conformational changes and
charge enrichment during collisional activation. Folded subunits are described as spheres that carry continuum surface charge.
The unfolded chain is envisioned as random coil bead string. Simulations are guided by the principle that the system will
adopt the charge configuration with the lowest potential energy for any backbone conformation. A finite-difference gradient
algorithm is used to determine the charge on each subunit throughout the dissociation process. Both dimeric and tetrameric
protein complexes are investigated. The model reproduces the occurrence of asymmetric charge partitioning for dissociation
events that are preceded by subunit unfolding. Quantitative comparisons of experimental MS/MS data with model predictions
yield estimates of the structural changes that occur during collisional activation. Our findings suggest that subunit separation
can occur over a wide range of scission point structures that correspond to different degrees of unfolding. 相似文献
996.
Syed SU Sreekumar J Gibson JR Taylor S 《Journal of the American Society for Mass Spectrometry》2011,22(8):1381-1387
We report here a study using a quadrupole mass spectrometer (QMS) in which a static magnetic field is applied transversely
to the body of the mass filter operating in stability zone 3. Significant improvement in QMS performance was obtained under
certain magnetic field conditions, and these have been explained in terms of our theoretical model. The theoretical approach
assumed in the model is that the QMS contains hyperbolic rods as electrodes and that the magnetic field acts over the full
length of the mass filter assembly. Our latest analysis also predicts for what values of operating parameters an enhancement
of the quadrupole resolution is achieved when a transverse magnetic field is applied. The model predicts instrument resolution
R > 5000 for Ar with a 100 mm long mass filter and R > 3500 for a HT and D2 mixture with a 200 mm long mass filter via application of a transverse magnetic field. 相似文献
997.
Amundson LM Owen BC Gallardo VA Habicht SC Fu M Shea RC Mossman AB Kenttämaa HI 《Journal of the American Society for Mass Spectrometry》2011,22(4):670-682
Positive-mode atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS
n
) was tested for the differentiation of regioisomeric aromatic ketocarboxylic acids. Each analyte forms exclusively an abundant
protonated molecule upon ionization via positive-mode APCI in a commercial linear quadrupole ion trap (LQIT) mass spectrometer.
Energy-resolved collision-activated dissociation (CAD) experiments carried out on the protonated analytes revealed fragmentation
patterns that varied based on the location of the functional groups. Unambiguous differentiation between the regioisomers
was achieved in each case by observing different fragmentation patterns, different relative abundances of ion-molecule reaction
products, or different relative abundances of fragment ions formed at different collision energies. The mechanisms of some
of the reactions were examined by H/D exchange reactions and molecular orbital calculations. 相似文献
998.
Castro-Perez J Roddy TP Nibbering NM Shah V McLaren DG Previs S Attygalle AB Herath K Chen Z Wang SP Mitnaul L Hubbard BK Vreeken RJ Johns DG Hankemeier T 《Journal of the American Society for Mass Spectrometry》2011,22(9):1552-1567
A high content molecular fragmentation for the analysis of phosphatidylcholines (PC) was achieved utilizing a two-stage [trap (first generation fragmentation) and transfer (second generation fragmentation)] collision-induced dissociation (CID) in combination with travelling-wave ion mobility spectrometry (TWIMS). The novel aspects of this work reside in the fact that a TWIMS arrangement was used to obtain a high level structural information including location of fatty acyl substituents and double bonds for PCs in plasma, and the presence of alkali metal adduct ions such as [M?+?Li]+ was not required to obtain double bond positions. Elemental compositions for fragment ions were confirmed by accurate mass measurements. A very specific first generation fragment ion m/z 577 (M-phosphoryl choline) from the PC [16:0/18:1 (9Z)] was produced, which by further CID generated acylium ions containing either the fatty acyl 16:0 (C15H31CO+, m/z 239) or 18:1 (9Z) (C17H33CO+, m/z 265) substituent. Subsequent water loss from these acylium ions was key in producing hydrocarbon fragment ions mainly from the α-proximal position of the carbonyl group such as the hydrocarbon ion m/z 67 (+H2C-HC?=?CH-CH?=?CH2). Formation of these ions was of important significance for determining double bonds in the fatty acyl chains. In addition to this, and with the aid of 13C labeled lyso-phosphatidylcholine (LPC) 18:1 (9Z) in the ω-position (methyl) TAP fragmentation produced the ion at m/z 57. And was proven to be derived from the α-proximal (carboxylate) or distant ω-position (methyl) in the LPC. 相似文献
999.
Two analytical procedures used to determine total, soluble, and insoluble solids in tomato paste were evaluated. The microwave oven (MO) method was compared to the vacuum oven (VO) method. The VO method is tedious and measured the three solids fractions in the paste directly, while the MO method measured the total solids directly but used an equation to calculate the water-soluble and -insoluble solids. The MO method was faster and less labor-intensive, and yielded small but statistically significant higher values for total and insoluble solids and lower statistically significant values for soluble solids. 相似文献
1000.
Firefly luciferase-catalyzed light emission from D-luciferin is widely used as a reporter of gene expression and enzymatic activity both in vitro and in vivo. Despite the power of bioluminescence for imaging and drug discovery, light emission from firefly luciferase is fundamentally limited by the physical properties of the D-luciferin substrate. We and others have synthesized aminoluciferin analogs that exhibit light emission at longer wavelengths than D-luciferin and have increased affinity for luciferase. However, although these substrates can emit an intense initial burst of light that approaches that of D-luciferin, this is followed by much lower levels of sustained light output. Here we describe the creation of mutant luciferases that yield improved sustained light emission with aminoluciferins in both lysed and live mammalian cells, allowing the use of aminoluciferins for cell-based bioluminescence experiments. 相似文献