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991.
Herringer SN Turnbull MM Landee CP Wikaira JL 《Dalton transactions (Cambridge, England : 2003)》2011,40(16):4242-4252
An isocoordinate family of compounds has been generated with the general formula (2-X-3-methylpyridine)(2)CuX'(2), where X, X' = Cl or Br. While each forms trans-ligand compounds, they vary in copper coordination geometry, canting of the pyridine rings and magnetic behavior. The copper bromide analogues exhibit weak ferromagnetic interactions whereas the copper chloride analogues exhibit antiferromagnetic interactions. Each compound has been characterized by IR, powder X-ray diffraction, single-crystal X-ray diffraction, and temperature dependent magnetic susceptibility. 相似文献
992.
Shen L Johnson TL Clugston S Huang H Butenhof KJ Stanton RV 《Journal of chemical information and modeling》2011,51(8):1957-1965
For oligonucleotide-based therapeutics, a thorough understanding of the thermodynamic properties of duplex formation is critical to developing stable and potent drugs. For unmodified small interfering RNA (siRNA), DNA antisense oligonucleotide (AON) and locked nucleic acid (LNA), DNA/LNA modified oligonucleotides, nearest neighbor (NN) methods can be effectively used to quickly and accurately predict duplex thermodynamic properties such as melting point. Unfortunately, for chemically modified olignonucleotides, there has been no accurate prediction method available. Here we describe the potential of estimating melting temperature (T(m)) for nonstandard oligonucleotides by using the correlation of the experimental T(m) with the calculated duplex binding energy (BE) for oligonucleotides of a given length. This method has been automated into a standardized molecular dynamics (MD) protocol through Pipeline Pilot (PP) using the CHARMm component in Discovery Studio (DS). Results will be presented showing the correlation of the predicted data with experiment for both standard and chemically modified siRNA and AON. 相似文献
993.
Phenytoin (PHT), phenobarbital (PHB), lamotrigine (LTG), and topiramate (TPM) are some of the most widely used antiepileptic
drugs (AEDs). Monitoring of their concentrations in serum is important for the treatment of epilepsy. A reference measurement
procedure (RMP) for certification of PHT, PHB, LTG, and TPM in serum has been developed and critically evaluated. Isotopically
labeled compounds of PHT, PHB, LTG, and TPM are used as internal standards for the four AEDs. The four drugs and their respective
labeled internal standards are simultaneously extracted from serum using solid-phase extraction prior to reversed-phase liquid
chromatography–tandem mass spectrometry (LC-MS/MS). Chromatographic separation was performed using a C18 column. Electrospray ionization (ESI) in the positive ion mode for PHT and LTG, and in the negative ion mode for PHB and
TPM were used. The recovery of AEDs added to serum (accuracy of the extraction method) was evaluated by recovery studies of
measuring the four drugs in spiked samples with known drug levels. The recoveries of the added drugs ranged from 98.6% to
102.0%. The absolute recoveries (extraction efficiencies) of the four drugs with this method ranged from 97% to 100%. Excellent
repeatability was obtained for the four drugs with between-set coefficients of variation (CVs) within 1%. The type B components
estimates are conservatively large and are considerably larger than the type A component. Therefore, we use the usual metrological
expansion factor of 2 to provide an approximate 95% coverage interval. The relative expanded uncertainties for the four AEDs
ranged from 2.3% to 2.4%. This LC-MS/MS RMP for PHT, PHB, LTG, and TPM in serum demonstrating good accuracy and precision
can be used to assess the accuracy of routine methods used in clinical laboratories. 相似文献
994.
Soumitra Choudhary Joseph C. White Whitney L. Stoppel Susan C. Roberts Surita R. Bhatia 《Rheologica Acta》2011,50(1):39-52
We report the preparation and rheological characterization of interpenetrating polymer network (IPN) hydrogels made from alginate
and hydrophobically modified ethyl hydroxyl ethyl cellulose (HMEHEC). To our knowledge, there have been no studies of the
gelation behavior of IPNs. We found that the rheology of these systems can be easily tuned, with the elastic modulus of the
IPN strongly dependent on the relative ratio of HMEHEC to alginate. The sol–gel transition of these systems was found to satisfy
the Winter–Chambon criterion for gelation at various crosslinker densities. From the power law relationship of the dynamic
moduli (G
′ ~G
″ ~ω
n), the exponent n appears to be dependent on both the crosslinker density and relative amount of two polymers. The value of n was found to be ~0.5 for all samples for stoichiometric amounts of crosslinker. The effect of molecular weight of HMEHEC
on the gel point and viscoelastic exponent has also been reported. Alginate seems to dominate the kinetics of the process
but the effect of high molecular weight HMEHEC on the gel point, especially at lower proportion was also evident. 相似文献
995.
With the aid of a chiral nickel catalyst, enantioselective γ- (and δ-) alkylations of carbonyl compounds can be achieved through the coupling of γ-haloamides with alkylboranes. In addition to primary alkyl nucleophiles, for the first time for an asymmetric cross-coupling of an unactivated alkyl electrophile, an arylmetal, a boronate ester, and a secondary (cyclopropyl) alkylmetal compound are shown to couple with significant enantioselectivity. A mechanistic study indicates that cleavage of the carbon-halogen bond of the electrophile is irreversible under the conditions for asymmetric carbon-carbon bond formation. 相似文献
996.
Keane PM Wojdyla M Doorley GW Watson GW Clark IP Greetham GM Parker AW Towrie M Kelly JM Quinn SJ 《Journal of the American Chemical Society》2011,133(12):4212-4215
The role of N1-substitution in controlling the deactivation processes in photoexcited cytosine derivatives has been explored using picosecond time-resolved IR spectroscopy. The simplest N1-substituted derivative, 1-methylcytosine, exhibits relaxation dynamics similar to the cytosine nucleobase and distinct from the biologically relevant nucleotide and nucleoside analogues, which have longer-lived excited-state intermediates. It is suggested that this is the case because the sugar group either facilitates access to the long-lived (1)n(O)π* state or retards its crossover to the ground state. 相似文献
997.
The combination of microchip electrophoresis with amperometric detection leads to a number of analytical challenges that are associated with isolating the detector from the high voltages used for the separation. While methods such as end-channel alignment and the use of decouplers have been employed, they have limitations. A less common method has been to utilize an electrically isolated potentiostat. This approach allows placement of the working electrode directly in the separation channel without using a decoupler. This paper explores the use of microchip electrophoresis and electrochemical detection with an electrically isolated potentiostat for the separation and in-channel detection of several biologically important anions. The separation employed negative polarity voltages and tetradecyltrimethylammonium bromide (as a buffer modifier) for the separation of nitrite (NO??), glutathione, ascorbic acid, and tyrosine. A half-wave potential shift of approximately negative 500 mV was observed for NO?? and H?O? standards in the in-channel configuration compared to end-channel. Higher separation efficiencies were observed for both NO?? and H?O? with the in-channel detection configuration. The limits of detection were approximately two-fold lower and the sensitivity was approximately two-fold higher for in-channel detection of nitrite when compared to end-channel. The application of this microfluidic device for the separation and detection of biomarkers related to oxidative stress is described. 相似文献
998.
褪黑激素、复合胺及吲哚乙酸等神经递质在高等植物中的发现为理解植物生理的机制提供了新的可能性.建立了一种在线制备方法,将样品粉末化后装填入小柱,利用水、甲酸-水和甲醇-水在线预洗制备后,切换至分析流路,采用梯度洗脱及ESI源LC-MS/MS检测植物中3种神经递质,每个样品的检测时间10 min,较离线方法的分析时间缩短了... 相似文献
999.
Chuangxing Guo Liming DongJoseph Marakovits Susan Kephart 《Tetrahedron letters》2011,52(14):1692-1696
Here we report mild, environmentally-friendly reaction conditions which enable the addition-elimination SNAr reaction between weakly reactive substrates--an aminopyrrolopyrazole template and several substituted pyrimidines. The method was developed during our efforts to synthesize a series of novel P21-activated kinase (PAK) inhibitors. 相似文献
1000.
The application of enhanced fluidity liquid (EFL) mobile phases to improving isocratic chromatographic separation of nucleosides in hydrophilic interaction liquid chromatography (HILIC) mode is described. The EFL mobile phase was created by adding carbon dioxide to a methanol/buffer solution. Previous work has shown that EFL mobile phases typically increase the efficiency and the speed of the separation. Herein, an increase in resolution with the addition of carbon dioxide is also observed. This increase in resolution was achieved through increased selectivity and retention with minimal change in separation efficiency. The addition of CO2 to the mobile phase effectively decreases its polarity, thereby promoting retention in HILIC. Conventional organic solvents of similar nonpolar nature cannot be used to achieve similar results because they are not miscible with methanol and water. The separation of nucleosides with methanol/aqueous buffer/CO2 mobile phases was also compared to that using acetonitrile/buffer mobile phases. A marked decrease in the necessary separation time was noted for methanol/aqueous buffer/CO2 mobile phases compared to acetonitrile/buffer mobile phases. There was also an unusual reversal in the elution order of uridine and adenosine when CO2 was included in the mobile phase. 相似文献