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991.
Qi Hu Haozhen Hu Xinyi Zhang Kyle Fan Yuning Hong Colin L. Raston Youhong Tang 《Molecules (Basel, Switzerland)》2021,26(14)
Protein folding is important for protein homeostasis/proteostasis in the human body. We have established the ability to manipulate protein unfolding/refolding for β-lactoglobulin using the induced mechanical energy in the thin film microfluidic vortex fluidic device (VFD) with monitoring as such using an aggregation-induced emission luminogen (AIEgen), TPE-MI. When denaturant (guanidine hydrochloride) is present with β-lactoglobulin, the VFD accelerates the denaturation reaction in a controlled way. Conversely, rapid renaturation of the unfolded protein occurs in the VFD in the absence of the denaturant. The novel TPE-MI reacts with exposed cysteine thiol when the protein unfolds, as established with an increase in fluorescence intensity. TPE-MI provides an easy and accurate way to monitor the protein folding, with comparable results established using conventional circular dichroism. The controlled VFD-mediated protein folding coupled with in situ bioprobe AIEgen monitoring is a viable methodology for studying the denaturing of proteins. 相似文献
992.
993.
Garton EM Pixton DA Petersen CA Eady RR Hasnain SS Andrew CR 《Journal of the American Chemical Society》2012,134(3):1461-1463
Cytochromes c' are pentacoordinate heme proteins with sterically hindered distal sites that bind NO and CO but do not form stable complexes with O(2). Removal of distal pocket steric hindrance via a Leu→Ala mutation yields favorable O(2) binding (K(d) ~49 nM) without apparent H-bond stabilization of the Fe-O(2) moiety, as well as an extremely high distal heme-NO affinity (K(d) ~70 fM). The native Leu residue inhibits distal coordination of diatomic ligands by decreasing k(on) as well as increasing k(off). The connection between distal steric constraints, k(off) values, and distal to proximal heme-NO conversion is discussed. 相似文献
994.
Iron(III) meso-tetra(2-carboxyphenyl)porphine chloride (1) was investigated as a soluble electrocatalyst for the oxygen reduction reaction (ORR) in acetonitrile with [H(DMF)(+)]OTf(-). Rotating ring-disk voltammetry, spectroelectrochemistry, and independent reactions with hydrogen peroxide indicate that 1 has very high selectivity for reduction of O(2) to H(2)O, without forming significant amounts of H(2)O(2). Cyclic voltammetric measurements at high substrate/catalyst ratios (high oxygen pressure) allowed the estimation of a turnover frequency (TOF) of 200 s(-1) at -0.4 V vs Cp(2)Fe(+/0). This is, to our knowledge, the first reported TOF for a soluble ORR electrocatalyst under kinetically controlled conditions. The 4-carboxyphenyl isomer of 1, in which the carboxylic acids point away from the iron center, is a much less selective catalyst. This comparison shows that carboxylate groups positioned to act as proton delivery relays can substantially enhance the selectivity of ORR catalysis. 相似文献
995.
Michael Hartmann Burkhard K?mpfer Yury T. Kiselev Vacas K. Magas Eduard Ya. Paryev Andrey Polyanskiy Luis Roca Henry Schade Colin Wilkin 《Hyperfine Interactions》2012,208(1-3):59-63
Information on the properties of the ? meson in the nuclear environment has been derived from its production in proton collisions with C, Cu, Al, and Au nuclear targets. The experiment was carried out with 2.83?GeV protons at the Cooler Synchrotron COSY, with the ? being detected via its K ?+? K ?? decay using the ANKE magnetic spectrometer. The measured dependence of the production cross section on the nuclear mass number has been compared with calculations within three different nuclear models. These suggest a significant broadening of the width of the ? in medium relative to its vacuum value. The ANKE results obtained in the momentum range 0.6?p ? ?1.6?GeV/c are compared with data from photoproduction experiments at slightly higher momenta. 相似文献
996.
The first enantioselective total synthesis of the proposed structure of aldingenin B is reported in 16 steps from known compounds. The stereochemistry at C5 and C6 were established by an asymmetric acetal aldol. Following a ring-closing metathesis, a selective, substrate-controlled hydrogen bond-mediated dihydroxylation provided control of the C2 and C3 stereocenters. Discrepancies in the spectroscopic data of the synthetic and natural material led to the conclusion that the structure of the natural sample was misassigned. 相似文献
997.
Allen FH Groom CR Liebeschuetz JW Bardwell DA Olsson TS Wood PA 《Journal of chemical information and modeling》2012,52(3):857-866
Bioisosterism involving replacement of a carboxylic acid substituent by 1H-tetrazole, yielding deprotonated carboxylate and tetrazolate under physiological conditions, is a well-known synthetic strategy in medicinal chemistry. To improve our overall understanding of bioisosterism, we have used this example to study the geometrical and energetic aspects of the functional group replacement. Specifically, we use crystal structure informatics and high-level ab initio calculations to study the hydrogen bond (H-bond) energy landscapes of the protonated and deprotonated bioisosteric pairs. Each pair exhibits very similar H-bond environments in crystal structures retrieved from the CSD, and the attractive energies of these H-bonds are also very similar. However, by comparison with -COOH and -COO(-), the H-bond environments around 1H-tetrazole and tetrazolate substituents extend further, by about 1.2 ?, from the core of the connected molecule. Analysis of pairs of PDB structures containing ligands which differ only in having a tetrazole or a carboxyl substituent and which are bound to the same protein indicates that the protein binding site must flex sufficiently to form strong H-bonds to either substituent. A survey of DrugBank shows a rather small number of tetrazole-containing drugs in the 'approved' and 'experimental' drug sections of that database. 相似文献
998.
This article reports the structural elucidation of the Alangium alkaloid, tubulosine (1) on the basis of systematic 2D-NMR analyses (DEPT, COSY, TOCSY, NOESY, ROESY, HMQC and HMBC). The data obtained allowed the unambiguous assignment of all proton and carbon signals in 1 for the first time. 相似文献
999.
Coherent diffractive imaging is an optical technique in which the information of an object is encoded in the diffraction intensity using a single-path wave propagation strategy. In recent years, coherent diffractive imaging has attracted much attention in many fields due to its marked advantages, such as robustness to vibration and the suitability for various wavelengths. In this paper, we propose to apply coherent diffractive imaging using multiple wavelengths for optical image encryption. A light wavelength is tuned during the encryption, and a series of diffraction intensity maps (i.e., ciphertexts) is sequentially recorded in the Fresnel domain. During image decryption, an iterative retrieval algorithm is further developed, and cryptosystem security and robustness of the proposed method are also analyzed. Numerical simulation results are presented to demonstrate feasibility and effectiveness of the proposed method. 相似文献
1000.
Casanueva Marenco MJ Fowley C Hyland BW Galindo-Riaño D Sahoo SK Callan JF 《Journal of fluorescence》2012,22(3):795-798
A simple fluorescent sensor 1 has been developed for the recognition of Fe(III) in semi-aqueous solution at pH 7.0. The sensor, containing two Schiff base
type receptors directly connected to naphthalene fluorophores, shows a concentration dependent decrease in emission intensity
upon Fe(III) addition. The sensor was selective for Fe(III) over other metal ions and can measure Fe(III) ion concentration
between 0.05 and 0.12 mM. The binding stoichiometry was established as 1:1 (host: guest) with a binding constant (Logβ) of
4.01. Furthermore, the addition of Fe(III) to a solution of 1 caused a colour change from light yellow to colourless meaning 1 is also capable of detecting Fe(III) by the naked eye. 相似文献