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71.
Lafaye A Junot C Ramounet-Le Gall B Fritsch P Tabet JC Ezan E 《Rapid communications in mass spectrometry : RCM》2003,17(22):2541-2549
This work reports the use of reverse-phase liquid chromatography coupled to electrospray ion trap (QIT) mass spectrometry for the analysis of the metabolome in rat urine. An injection of 20 microL of urine into the chromatographic system is followed by a slow gradient elution and mass spectrometric detection in the scanning mode from m/z 100-1000 in both positive and negative modes. Over a time scale of 90 min, 30 and 20 resolved peaks were observed in the positive and the negative modes, respectively, corresponding to the presence of a few hundred m/z ratios. By using a QIT analyzer, data-dependent tandem mass spectrometry of selected m/z ratios identified several compounds in rat urine and characterized various chemical families, including carboxylic acids, amines, sulfated compounds, glucuronides and glycosides, by the observation of characteristic fragment ions or neutral losses. The method has been applied to the investigation of the chronic toxicity of heavy metals in rat urine. A few tens of m/z ratios, differing in intensity more than threefold from control values, were observed in both positive and negative modes. The time variations for some selected ions suggest that LC/ESI-MS could allow selective characterization of biomarkers in response to specific toxic compounds. 相似文献
72.
A photosensitive precursor (1) to phenylsulfanylcarbene 2 has been synthesized. Laser flash photolysis (308 nm) of 1 and chemical trapping studies of 2 are reported. [structure: see text] 相似文献
73.
Robert E. Linder Hannah Weiler-Feilchenfeld Günter Barth Edward Bunnenberg Carl Djerassi 《Theoretical chemistry accounts》1974,36(2):135-143
CNDO calculations of the MCD spectra of 7- and 9-methyladenine have been carried out in two approximations. A minor modification of the CNDO/S method of Jaffé and coworkers shows an improvement over Jaffé's parameterization with respect to band separations and the signs of the MCDB terms, but is not applicable ton→ π* transitions. 相似文献
74.
Because organotin compounds (OTC) are widely used in many fields of activity, they have become an ubiquitous environmental presence. The presence of organotins in the environment impacts upon food safety, making it important to monitor the levels of organotin pesticides in fruits and vegetables. Nevertheless, only a few studies have been published on organotin speciation in plants. The objective of the present study was to evaluate and optimise a specific procedure based on pressurised solvent extraction (PSE) that is suitable for monitoring organotin content in vegetables. In ASE, solvents are used at elevated temperatures and pressures to increase the rate and efficiency of the extraction process. The results from this procedure were compared to those from the technique usually employed, solid/liquid extraction (SLE) performed in an acidic solvent by mechanical shaking. Three extracting solutions were tested—methanol, ethyl acetate and a mixture of methanol and ethyl acetate—and the mixture was found to give the most quantitative results while preserving the speciation. French bean and lettuce leaves as well as potato tubers were used as the plant materials. These vegetables were considered because they are the vegatables consumed in the most quantities in Europe. The study focuses on trisubstituted OTCs, which are the most toxic tin species. The samples were spiked with four trisubstituted organotins: tributyltin (TBT), triphenyltin (TPhT), tricyclohexyltin (TcHexT) and trioctyltin (TOcT). The influence of the pressure and the temperature of the PSE on the quantitativity of the process and on species preservation was evaluated using the experimental design methodology. The optimised PSE allowed detection limits down to 1–2 ng (Sn) g–1 to be reached. These are higher than those obtained by SLE (0.1–1 ng (Sn) g–1). Although the repeatability is similar for both PSE and SLE (2–12% for triorganotin compounds), this appears to be highly time-dependent in the case of SLE. Comparison with SLE confirms that PSE is an interesting tool for vegetable analysis considering the satisfactory OTC preservation and repeatability obtained for a relatively short extraction duration (only 15 min against 2–12 h for SLE). 相似文献
75.
The magnetic circular dichroism spectra of a number of indole alkaloids show two B-terms of opposite sign in the 250–330 nm wavelength region associated with the 1Lb and 1La electronic transitions, the long wavelength, 1Lb, band being of positive sign, whereas both bands strongly overlap in absorption. Various substituents in different positions of the indole ring cause a red shift of both bands and a broadening of the long wavelength B-term. The sign pattern, howver, remains unchanged in all examples thus far investigated. Dihydroindole and oxindole, on the other hand, exhibit MCD. bands with the opposite sign sequence as compared to the indole chromophore. This observation allows identification of the indole chromophore in alkaloids from the sign pattern of the MCD. bands. 相似文献
76.
Sang-Min Jang Christophe E. Redon Bhushan L. Thakur Meriam K. Bahta Mirit I. Aladjem 《Experimental & molecular medicine》2020,52(10):1637
The last decade has revealed new roles for Cullin-RING ubiquitin ligases (CRLs) in a myriad of cellular processes, including cell cycle progression. In addition to CRL1, also named SCF (SKP1-Cullin 1-F box protein), which has been known for decades as an important factor in the regulation of the cell cycle, it is now evident that all eight CRL family members are involved in the intricate cellular pathways driving cell cycle progression. In this review, we summarize the structure of CRLs and their functions in driving the cell cycle. We focus on how CRLs target key proteins for degradation or otherwise alter their functions to control the progression over the various cell cycle phases leading to cell division. We also summarize how CRLs and the anaphase-promoting complex/cyclosome (APC/C) ligase complex closely cooperate to govern efficient cell cycle progression.Subject terms: Drug development, Targeted therapies, Origin firing, Chromatin remodelling, Post-translational modifications 相似文献
77.
Linder DP Rodgers KR Banister J Wyllie GR Ellison MK Scheidt WR 《Journal of the American Chemical Society》2004,126(43):14136-14148
Recent years have seen dramatic growth in our understanding of the biological roles of nitric oxide (NO). Yet, the fundamental underpinnings of its reactivities with transition metal centers in proteins and enzymes, the stabilities of their structures, and the relationships between structure and reactivity remains, to a significant extent, elusive. This is especially true for the so-called ferric heme nitrosyls ([FeNO](6) in the Enemark-Feltham scheme). The Fe-CO and C-O bond strengths in the isoelectronic ferrous carbonyl complexes are widely recognized to be inversely correlated and sensitive to structural, environmental, and electronic factors. On the other hand, the Fe-NO and N-O bonds in [FeNO](6) heme complexes exhibit seemingly inconsistent behavior in response to varying structure and environment. This report contains resonance Raman and density functional theory results that suggest a new model for FeNO bonding in five-coordinate [FeNO](6) complexes. On the basis of resonance Raman and FTIR data, a direct correlation between the nu(Fe)(-)(NO) and nu(N)(-)(O) frequencies of [Fe(OEP)NO](ClO(4)) and [Fe(OEP)NO](ClO(4)).CHCl(3) (two crystal forms of the same complex) has been established. Density functional theory calculations show that the relationship between Fe-NO and N-O bond strengths is responsive to FeNO electron density in three molecular orbitals. The highest energy orbital of the three is sigma-antibonding with respect to the entire FeNO unit. The other two comprise a lower-energy, degenerate, or nearly degenerate pair that is pi-bonding with respect to Fe-NO and pi-antibonding with respect to N-O. The relative sensitivities of the electron density distributions in these orbitals are shown to be consistent with all published indicators of Fe-N-O bond strengths and angles, including the examples reported here. 相似文献
78.
Christophe Thurieau Christel Guyard Serge Simonet Tony J. Verbeuren Jean-Luc Fauchre 《Helvetica chimica acta》1994,77(3):679-684
The synthesis on solid phase of a new derivative of the anticoagulant protein hirudin is described (see Scheme and Fig.1, I ). The henicosapeptide is a bivalent conjugate of the C-terminus of hirudin and of the active-site-binding tetrapeptide D -Phe-Pro-Arg-Pro linked via a tetraglycine spacer. The peptide, for which the name hirufos was coined, incorporates a stable phosphono derivative of L -phenylalanine which, combined with the other structural modifications, leads to a potent anticoagulant agent. Synthesis was readily achieved by the (9H-fluoren-9-yl)-methoxycarbonyl (Fmoc) strategy followed by acidolytic cleavage from the resin and deprotection, including the liberation of the crucial phosphonic group on L -phenylalanine. 相似文献
79.
The stereochemistry of reductive and non reductive Heck cyclisations of 4-substituted-1.4-dihydropyridines is reexamined. The both reactions occur mainly via an anti (from the C4 substituent) 5-exo process without any epimerisation of the C4-H. 相似文献
80.
Iron-catalyzed homo-coupling of simple and functionalized arylmagnesium reagents is described. The reaction is highly chemoselective (CN, COOEt and NO(2) groups are tolerated). The procedure was used to perform intramolecular couplings. This cyclization reaction is the key step of the total synthesis of the N-methylcrinasiadine. 相似文献