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541.
Numata M Yarita T Aoyagi Y Tsuda Y Yamazaki M Takatsu A Ishikawa K Chiba K Okamaoto K 《Analytical and bioanalytical chemistry》2007,387(7):2313-2323
Two marine sediment certified reference materials, NMIJ CRM 7304-a and 7305-a, have been issued by the National Metrology
Institute of Japan in the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) for the determination
of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). The raw materials of the CRMs were collected from
a bay near industrial activity in Japan. Characterization of these CRMs was conducted by NMIJ, where the sediments were analyzed
using multiple analytical methods such as pressurized liquid extraction (PLE), microwave-assisted extraction (MAE), saponification,
Soxhlet extraction, supercritical fluid extraction (SFE), and ultrasonic extraction; the target compounds were determined
by one of the primary methods of measurements, isotope dilution–mass spectrometry (ID-MS). Certified values have been provided
for 14 PCB congeners (PCB numbers 3, 15, 28, 31, 70, 101, 105, 138, 153, 170, 180, 194, 206, 209) and 4 OCPs (γ-HCH, 4,4′-DDT,
4,4′-DDE, 4,4′-DDD) in both CRMs. NMIJ CRM 7304-a has concentrations of the contaminants that are a factor of 2–15 greater
than in CRM 7305-a. Both CRMs have information values for PCB homolog concentrations determined by collaborative analysis
using a Japanese official method for determination of PCBs. The total PCB concentrations in the CRMs are approximately 920
and 86 μg kg−1 dry mass respectively.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
542.
Shakhashiro A Gondin da Fonseca Azeredo AM Sansone U Fajgelj A 《Analytical and bioanalytical chemistry》2007,387(7):2509-2515
The IAEA Reference Materials Group of the Chemistry Unit, Agency’s Laboratories Seibersdorf, has developed and optimized a
procedure for spiking some environmental matrices with gamma-emitting radionuclides. This paper describes the spiking procedure,
homogeneity testing of the spiked material, and assignment of property values and their associated uncertainties for the radionuclides
54Mn, 65Zn, 60Co, 109Cd, 134Cs, 137Cs, 210Pb, and 241Am. This procedure has already been successfully used in an IAEA proficiency test on the determination of 137Cs and 210Pb in spiked soil and has been found to be appropriate for production of soil materials for proficiency testing and internal
quality control samples. The main advantage of this procedure is a low uncertainty arising from heterogeneity, which was found
to be less than 1.2% for all the analytes studied.
相似文献
543.
Point D Davis WC Garcia Alonso JI Monperrus M Christopher SJ Donard OF Becker PR Wise SA 《Analytical and bioanalytical chemistry》2007,389(3):787-798
Two speciated isotope dilution (SID) approaches consisting of a single-spike (SS) method and a double-spike (DS) method including a reaction/transformation model for the correction of inadvertent transformations affecting mercury species were compared in terms of accuracy, method performance, and robustness for the simultaneous determination of methylmercury (MeHg), inorganic mercury (iHg), and total mercury (HgT) concentrations in five biological Standard Reference Materials (SRMs). The SRMs consisted of oyster and mussel tissue materials displaying different mercury species concentration levels and different textural/matrix properties including freeze-dried (FD) materials (SRMs 1566b, 2976, and 2977) and cryogenically prepared and stored fresh-frozen (FF) materials (SRMs 1974a, 1974b). Each sample was spiked with (201)iHg (Oak Ridge National Laboratory, ORNL) and Me(202)Hg (Institute for Reference Materials and Measurements. IRMM-670) solutions and analyzed using alkaline microwave digestion, ethylation, and gas chromatography inductively coupled plasma mass spectrometry (GC/ICP-MS). The results obtained by the SS-SID method suggested that FF and FD materials are not always commutable for the simultaneous determination of iHg, MeHg, and HgT, due to potential transformation reactions resulting probably from the methodology and/or from the textural/matrix properties of the materials. These transformations can occasionally significantly affect mercury species concentration results obtained by SS-SID, depending on the species investigated and the materials considered. The results obtained by the DS-SID method indicated that the two classes of materials were commutable. The simultaneous and corrected concentrations of iHg, MeHg, and HgT obtained by this technique were not found to be statistically different form the certified and reference concentration together with their expanded uncertainty budgets for the five SRMs investigated, exemplifying the robustness, the accuracy, and the improved commutability of this method compared to SS-SID measurements. 相似文献
544.
545.
Dynamic patterns of prices in different markets may motivate (strategic) consumers, who could be monitoring price movements over time, to game vendors. Do past price movements carry information about the probability and magnitude of future price drops?Conducting empirical work in the airline industry on near 1000 US domestic routes, we find that some price-metrics carry information about future price swings: these variables can assist in predicting the likelihood and magnitude of price drops. These price-metrics yield significantly different signals which also vary as the prediction horizon changes. 相似文献
546.
J. Kuligowski 《Talanta》2010,80(5):1771-4862
A new background correction method for the on-line coupling of gradient liquid chromatography and Fourier transform infrared spectrometry has been developed. It is based on the use of a point-to-point matching algorithm that compares the absorption spectra of the sample data set with those of a previously recorded reference data set in order to select an appropriate reference spectrum. The spectral range used for the point-to-point comparison is selected with minimal user-interaction, thus facilitating considerably the application of the whole method. The background correction method has been successfully tested on a chromatographic separation of four nitrophenols running acetonitrile (0.08%, v/v TFA):water (0.08%, v/v TFA) gradients with compositions ranging from 35 to 85% (v/v) acetonitrile, giving accurate results for both, baseline resolved and overlapped peaks. 相似文献
547.
Johan Bjerner Elvar Theodorsson Eivind Hovig Anders Kallner 《Accreditation and quality assurance》2009,14(4):185-192
This study aimed at validating common bootstrap algorithms for reference interval calculation.We simulated 1500 random sets
of 50–120 results originating from eight different statistical distributions. In total, 97.5 percentile reference limits were
estimated from bootstrapping 5000 replicates, with confidence limits obtained by: (a) normal, (b) from standard error, (c)
bootstrap percentile (as in RefVal) (d) BCa, (e) basic, or (f) student methods. Reference interval estimates obtained with
ordinary bootstrapping and confidence intervals by percentile method were accurate for distributions close to normality and
devoid of outliers, but not for log-normal distributions with outliers. Outlier removal and transformation to normality improved
reference interval estimation, and the basic method was superior in such cases. In conclusions, if the neighborhood of the
relevant percentile contains non-normally distributed results, bootstrapping fails. The distribution of bootstrap estimates
should be plotted, and a non-normal distribution should warrant transformation or outlier removal.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
548.
Reference materials have been applied widely to ensure the traceability, comparability and reliability of measurement results.
To achieve this purpose, the quality of reference materials (RMs) themselves is surely an important aspect to be pay attention
to. A quality evaluation system of RMs has been established through the project “The National Sharing Platform of Reference
Materials” in China to give a reliable assessment on the quality of RMs from various sources including the accuracy and comparability
of their property values, which is very useful to promote the appropriate selecting and using of RMs in China. Through the
application of National Metrology Institute calibration and measurement capabilities on the basis of the international mutual
recognition arrangement, it can also provide a powerful supplement to the current activities such as the accreditation of
RM producers in the construction of a global harmonized quality control and assurance system of RMs. 相似文献
549.
Y. Spasova L. Benedik M. Vasile M. Beyermann U. W?tjen S. Pommé 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(1):113-117
In 2007/2008 the Institute for Reference Materials and Measurements (IRMM) organised an interlaboratory comparison (ILC) on
the determination of 226Ra, 228Ra, 234U and 238U activity concentrations in mineral water. This paper describes the determination of the reference values for the activity
concentrations of 234U and 238U by radiochemical separation and α-particle spectrometry performed at two independent laboratories. The experimental uncertainty
of the reference values is discussed in detail. 相似文献
550.
The QuEChERS method developed for 22 organochlorine pesticides (OCPs) and 7-polychlorinated biphenyls (PCBs) in fish tissue involves a simple and efficient freezing technique for removal of lipids. The equipment developed consists of disposable syringes and a freezing block constructed from simple materials found in most laboratories. The freezing block keeps the temperature in the extract at -20.5°C up to 10 min after being exposed to room temperature. After the freezing step 69% of the lipids in tilapia and 61% in salmon are removed. Further reduction of co-extractives up to 96% in tilapia and 87% in salmon can be made by treatment with CaCl(2) and primary secondary amino sorbent (PSA) which removes the fatty acids. Spiking experiments in tilapia at 5 and 50 ng/g and extracted with acetonitrile show recovery range from 70 to 115% for all compounds. In salmon the recoveries are in the range 43-118% for the OCPs and 26-65% for the PCBs. Analysis of a standard reference material shows acceptable results for most of the pesticides but low results for the PCBs. The estimated LOQs were in the range 1-5 ng/g for tilapia and 2-10 ng/g for salmon. The method has been applied to analyse fish samples from Lake Koka in Ethiopia. It was investigated if addition of a less polar water miscible solvent than acetonitrile could increase the recovery of OCPs and PCBs. The results show that a mixture of 75% acetonitrile and 25% tetrahydrofurane (ACN/THF 75/25) clearly enhances the recoveries for most OCPs (47-101%) and PCBs (42-79%) from salmon. The recovery of aldrin increases significantly from 55% to over 80%. The method using ACN/THF 75/25 is applicable to the extraction of OCPs and PCBs from fish tissue having a lipid content of up to about 11% (salmon) with recoveries ≥70% for most of the OCPs and ≥42% for the PCBs. 相似文献