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991.
992.
Gabriele Capodaglio Carlo Barbante Clara Turetta Giuseppe Scarponi Paolo Cescon 《Mikrochimica acta》1996,123(1-4):129-136
The problem of contamination during the collection of samples of environmental interest to detect trace metal is discussed. Attention is focused on the leaching of metals from sampling devices used to collect surface and deep seawater. A procedure to test metal release is applied to emphasize the importance of conditioning samplers before use. The procedure for checking the contamination extent and decontamination of firn and ice cores to detect ultratrace elements (particularly Cd and Pb) is presented and applied to some firn cores collected in Antarctica during the 1990–1991 Italian expedition. 相似文献
993.
Summary The collection of low-boiling olefinic aldehydes on 2,4-dinitrophenylhydrazine (DNPH)-coated adsorbents (silica cartridges and glass denuders) is examined. Concurrent formation of two different hydrazones by both acrolein and crotonaldehyde is reported and discussed. Identification and quantitation of these compounds do not represent a problem in HPLC analysis, because of their separation from other C3 and C4 carbonyl derivatives present in airborne sample extracts. 相似文献
994.
Solvent vapors in air may be measured with capillary gas chromatographic columns. By using large diameter columns and sample loops of approximately the same internal diameter, the column may be connected directly to the gas sampling valve. This approach eliminates the use of a splitter or cryogenic trapping and allows low levels to be measured. By operating the column at high velocity, column efficiency is sacrificed for increase in speed. 相似文献
995.
Airborne particulate matter contains numerous organic species, including several polycyclic aromatic hydrocarbons (PAHs) that are known or suspected carcinogens. Existing methods for measuring airborne PAHs are complex and costly, primarily because they are designed to collect both gas-phase and particle-phase PAH constituents. Here, we report an assay for measuring particle-bound PAHs in archived filters from the network of U.S. monitoring stations for particles less than 2.5 microm in diameter (PM2.5), without the need for deploying specialized samplers. PAHs are extracted from Teflon filters with dichloromethane, concentrated, and measured at trace levels using gas chromatography-mass spectrometry. Although PAHs with 3-6 aromatic rings can be assayed, results are only unambiguously accurate for compounds with 5- or 6-rings, due to variable vaporization losses of the more volatile 3- and 4-ring compounds during sampling and/or storage. The method was evaluated for sensitivity, recovery, precision, and agreement of paired air samples, using PM2.5 samplers locally in Chapel Hill, NC. Additionally, three sets of archived samples were analyzed from a study of PM2.5 in the Czech Republic. Levels of some 4-ring and all 5- and 6-ring PAHs in both the local and Czech samples were consistent with published results from investigations employing PAH-specific air samplers. This work strongly suggests that assessment of particle-bound 5- and 6-ring PAHs from archived PM2.5 filters is quantitatively robust. The assay may also be useful for selected 4-ring compounds, notably chrysene and benzo(a)anthracene, if PM2.5 filters are stored under refrigeration. 相似文献
996.
Matschat R Hassler J Traub H Dette A 《Analytical and bioanalytical chemistry》2005,383(7-8):1060-1074
The members of the committee NMP 264 “Chemical analysis of non-oxidic raw and basic materials” of the German Standards Institute
(DIN) have organized two interlaboratory comparisons for multielement determination of trace elements in silicon carbide (SiC)
powders via direct solid sampling methods. One of the interlaboratory comparisons was based on the application of inductively
coupled plasma optical emission spectrometry with electrothermal vaporization (ETV ICP OES), and the other on the application
of optical emission spectrometry with direct current arc (DC arc OES). The interlaboratory comparisons were organized and
performed in the framework of the development of two standards related to “the determination of mass fractions of metallic
impurities in powders and grain sizes of ceramic raw and basic materials” by both methods. SiC powders were used as typical
examples of this category of material. The aim of the interlaboratory comparisons was to determine the repeatability and reproducibility
of both analytical methods to be standardized. This was an important contribution to the practical applicability of both draft
standards. Eight laboratories participated in the interlaboratory comparison with ETV ICP OES and nine in the interlaboratory
comparison with DC arc OES. Ten analytes were investigated by ETV ICP OES and eleven by DC arc OES. Six different SiC powders
were used for the calibration. The mass fractions of their relevant trace elements were determined after wet chemical digestion.
All participants followed the analytical requirements described in the draft standards. In the calculation process, three
of the calibration materials were used successively as analytical samples. This was managed in the following manner: the material
that had just been used as the analytical sample was excluded from the calibration, so the five other materials were used
to establish the calibration plot. The results from the interlaboratory comparisons were summarized and used to determine
the repeatability and the reproducibility (expressed as standard deviations) of both methods. The calculation was carried
out according to the related standard. The results are specified and discussed in this paper, as are the optimized analytical
conditions determined and used by the authors of this paper. For both methods, the repeatability relative standard deviations
were <25%, usually ~10%, and the reproducibility relative standard deviations were <35%, usually ~15%. These results were
regarded as satifactory for both methods intended for rapid analysis of materials for which decomposition is difficult and
time-consuming. Also described are some results from an interlaboratory comparison used to certify one of the materials that
had been previously used for validation in both interlaboratory comparisons. Thirty laboratories (from eight countries) participated
in this interlaboratory comparison for certification. As examples, accepted results are shown from laboratories that used
ETV ICP OES or DC arc OES and had performed calibrations by using solutions or oxides, respectively. The certified mass fractions
of the certified reference materials were also compared with the mass fractions determined in the interlaboratory comparisons
performed within the framework of method standardization. Good agreement was found for most of the analytes. 相似文献
997.
High-performance liquid chromatography with mass spectrometric detection was used for the structure elucidation of eighteen primary and secondary amines and ammonia derivatised with naphthylisothiocyanate (NIT). A fragmentation scheme was established using reference compounds and the scheme was applied to real air samples from a tyre repair shop and from the air above a bacterial culture. The sampling was performed using a solid sorbent, XAD-2, impregnated with NIT, and the derivatives were extracted with acetonitrile and analysed with LC-MS/MS. A three-step process was developed for screening and identifying of volatile amines. The first step, selected reaction monitoring; SRM was applied in order to screen the samples for NIT derivatives. In the second step, a precursor ion scan gave the [M+H]+ ion, and in the third step a product ion scan gave the fragments needed for identification. The detection limits varied between 0.12 and 0.25 ng L–1 when screening for unknown derivatised amines. It was possible to separate and identify all the amines with the structural information obtained and the method proved to be general, sensitive and well suited for sampling and analysis of complex environmental samples. 相似文献
998.
A system for purge-and -trap with thermal desorption was developed and optimized to moniotor aroma compounds at ambient temperatures. Canned tomato juice volatiles were used as a model system to develop and evaluate the method. Volatile components were first adsorbed on insert-traps packed with Tenax-TA polymer, then thermally desorbed directly inside a gas chromatograph injector. Volatile matgerials occuring in Very low amounts could be entrained and subsequently chrfomatographed, with sensitivity limited by the purity of the sweep gas. Quantitative measurement of tomato juice volatiles was linear with sample size upn to 100 gram samples. The amount of trapped volatiles was proportional to trapping time; howver, low-and intermediate-boilers broke through the trap after one hour while high-boilers continued to be retained. Apurge gas flow rate of 20ml/min gave optimum results mediate-biolers. Optimum recovery of volatile compounds was obtained with a desorption temperature of 200°c for 5 min. Coefficients of variation from triplicate runs were relatively small. The method showed promise for a simple, sensitive, and reproducibel flavor volatiles collection system for the accurate analysis of tomato compounds. 相似文献
999.
B. A. Sommerville F. M. C. Darling J. P. McCormick J. Waterhouse D. M. Broom 《Chromatographia》1994,39(7-8):469-474
Summary A recirculating system powered by a diaphragm pump which may be readily dismantled for cleaning, is described. The results of operating this system for dynamic headspace sampling in the closed or open mode to load volatiles onto a Tenax trap over a range of temperatures and loading volumes are shown. The system was designed to facilitate the analysis of volatiles in natural products and tested using an equimolar solution of 7 esters of boiling points ranging from 120°C to 299°C. The results showed that compounds in the boiling point range 120–200°C could be loaded onto the trap at 30°C by passing 1–21 of carrier gas through. In order to trap compounds of boiling points approaching 300°C, a temperature of 50–70°C and a loading volume of 2.5–3 1 was necessary. Using the apparatus, human sweat was analysed to show the degree of concentration possible with a natural sample and the variation in the chromatogram profiles of successive trapping from the same sample. Twelve chromatograms from the sweat of two pairs of identical twins were pattern matched to show the high degree of reproducibility possible using this apparatus to trap biological volatiles. 相似文献
1000.