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61.
C O-Yang D J Kertesz A F Kluge P Kuenzler T T Li M M Marx J J Bruno L F Chang 《Prostaglandins》1984,27(6):851-863
Opening of racemic epoxide (3) with (3S)- or (3R)-dimethyl-3-(dimethyl-t-butylsilyloxy)oct-1-ynyl aluminum gave two regioisomers, which were separated chromatographically. The separated regioisomers, themselves mixtures of chromatographically inseparable diastereoisomers, were converted into their dicobalthexacarbonyl complexes, which were easily resolved and isolated by chromatography. The individual diastereoisomers were deprotected to give bicyclo[3.2.0]heptan-3-ones, whose absolute stereochemistry was assigned using circular dichroism. One of these compounds, (1R,2R,3S,5R,3'S)-3-(3'-hydroxyoct-1'-ynyl)-bicyclo[3.2.0]++ +heptan-2-ol-6- oximinoacetic acid (11a) was 4.5 times more potent than PGE1 in inhibiting the ADP-induced aggregation of human platelets. The next most potent compound in this series was the "ent-15-epi" compound (11b), which was 0.034 times the potency of PGE1 in the platelet aggregation assay. 相似文献
62.
Bruno Cavalleri Giancarlo Volpe Giogio Tuan Marisa Berti Francesco Parenti 《Current microbiology》1978,1(5):319-324
Two chlorophenyl-containing antibiotics have been isolated from a strain ofActinoplanes (ATCC 33002). Antibiotic A 15104 Y is a chlorinated phenylpyrrole compound whose structure has been confirmed by chemical
synthesis. Antibiotic A 15104 Z is a chlorophenol derivative for which a structural formula is proposed on the basis of its
physicochemical properties. A 15104 Y shows antimicrobial activity against Gram-positive, Gram-negative, and acid-fast bacteria,
yeasts, fungi, and protozoa, while A 15104 Z possesses a low activity against Gram-positive bacteria andTrichophyton. A 15104 Y has a weak activity in curing experimentally infected mice, at a dose that is one-fifth the LD50 for the same species. This is the first example of a chloropyrrole derivative isolated from an actinomycete. 相似文献
63.
Summary Iodination of proteins and lipoproteins is a widely used in vitro labelling procedure in metabolic, autoradiographic and various other studies. However, all available iodination techniques have involved the possible damage to the proteins by self-irradiation, oxidizing agents, the alkaline milieu or by the introduction of iodine into the molecular structure itself. To evaluate the integrity of iodinated lipoproteins, we observed the electron microscopic appearance of normal and iodinated rabbit very low density lipoproteins (VLDL) by negative staining with phosphotungstic acid. Iodination up to a molar iodine/protein ratio of 2.89 did not result in any change of shape, size or aggregating tendency of the particles. No stacks or disk-like particles like those of various hyperlipoproteinemic states were found. We conclude that electron microscopy is a valuable tool in assessing the morphological appearance of lipoprotein iodination, but it should be complemented by other techniques. 相似文献
64.
Giancarlo Lunazzi Claudio Tiribelli Bruno Gazzin Gianluigi Sottocasa 《生物化学与生物物理学报:生物膜》1982,685(2):117-122
Bilitranslocase, a plasma membrane protein involved in bilirubin and other organic anion uptake by the liver, exhibits a high molecular weight (170 000) when isolated in the presence of deoxycholate. This value is decreased to approx. 100 000 if deoxycholate is not included in the isolation medium. Both preparations can be resolved into two kinds of subunit, α and β, of 37 000 and 35 500, respectively, by reduction with 2-mercaptoethanol and addition of sodium dodecyl sulfate. Under these conditions the two subunits are still capable of high-affinity sulfobromophthalein binding and, despite the presence of the detergent, may be isolated by preparative polyacrylamide gel electrophoresis still associated with the dye. It may be suggested that the physiological subunit composition of bilitranslocase is α2-β. 相似文献
65.
Bruno Samorì Giorgio Lenaz Maurizio Battino Giancarlo Marconi Ida Domini 《The Journal of membrane biology》1992,128(3):193-203
Summary A general approach is developed to interpret linear dichroism (LD) spectra of ubiquinones (Q
n) in host bilayers. Information is reported in terms of guest-host mutual orientation and localization. The overall orientational anisotropy of guest ubiquinone molecules is described by a basic set of limiting orientation/localization modes. Assignments of the UV transitions of the ubiquinone chromophore were obtained by the liquid crystal-linear dichroism technique and molecular orbital (CNDO/S) calculations. The LD spectra of Q
n in the bilayers provided by the lyotropic nematic mesophase exhibited by water solutions of potassium laurate and decanol were interpreted on the basis of the above assignments. The resulting experimental evidence showed a multisite distribution in the host bilayer for the aromatic heads of all the investigated Q
n derivatives except Q0. The orientational distribution suggested by the LD spectra fits the solubilization model recently proposed by G. Lenaz [J. Membrane Biol. (1988) 104:193–209] for ubiquinone in lipid membranes. Within this model Q
n molecules are located in the midplane and their headgroups oscillate transversally across the membrane. Q
0 instead has a single site location, close to the polar bilayer interface. Experimental evidence that the headgroup carbonyls tend to grasp the polar interface of the host bilayer was also obtained. Orientation and location distributions of Q
n guest molecules are therefore likely to result from the tendency of their aromatic heads to grasp the polar heads of the host bilayer and from the concurrent tendency of their chains to settle into the hydrocarbon host interior.abbreviations AA
average absorption
- OD, OD
optical densities for plane polarized radiations parallel () and perpendicular () to the sample optical axis
- OD
OD — OD
- EPR
electron paramagnetic resonance
- LC-LD
liquid crystal-linear dichroism
- LD
linear dichroism
-
LD
r
reduced linear dichroism.
- MO
molecular orbital
- N
nematic
- NMR
nuclear magnetic resonance
-
S
jj
order parameters of the directions j of the transition moments of the guest chromophore
-
S
ii
order parameters of the orientational axes i of the guest molecule with respect to the magnetic field
-
S
ii
order parameters of the axes i of the guest molecules with respect to the bilayer axis a
-
S
a
order parameters of the host bilayer axis a with respect to the orienting magnetic field
-
j,i
deflection angles between the directions j and the axes i
-
O
i
optical factors of the i axis see Eq. (A4)]
- Qn
ubiquinone whose isoprenoid chain contains n isoprenoid units
Dr. A. Rossi is gratefully acknowledged for the t.e.m. reduction of the spectra. Ubiquinone homologs were kind gifts from Eisai Co., Tokyo, Japan. This work was supported by M.U.R.S.T., and C.N.R. Target Project on Biotechnology and Bioinstrumentation, Rome, Italy. 相似文献
66.
The lambda S lysis gene was cloned into a Saccharomyces cerevisiae expression vector under GAL1 control. Induction with galactose in S. cerevisiae terminated cell growth and prevented colony formation. Several membrane proteins immunoreactive with anti-S antibody accumulated in the membranes, indicating that sodium dodecyl sulfate-resistant oligomers of S are formed, similar to those observed in the membranes of Escherichia coli cells killed by expression of the S gene. These observations suggest that the S gene product functions as a cytotoxic protein in the yeast cytoplasmic membrane as it does in the bacterial membrane. 相似文献
67.
In a search for crystallizing conditions for the ternary complex EF-Tu.GTP.valyl-tRNAval, the influence of various salts on its stability has been examined by measuring the rate of deacylation of the aminoacyl-tRNA in the complex. The most striking result is the general higher stability in solutions of ammonium salts and, in particular, the enhancement of this effect by sulphate and citrate. Thus sodium sulphate and citrate lead to destabilization of the complex, as expected from conventional considerations of adding salt, whereas the corresponding ammonium salts stabilize the complex as shown, for example, by an increase in the half-life of the valyl-tRNAval in the complex from about 20 hours to at least 300 hours in the presence of 1.2 M ammonium sulphate. These results suggest that ammonium sulphate and ammonium citrate might be very suitable precipitants for crystallization studies of the ternary complex. 相似文献
68.
Bruno David 《Geobios》1981,14(6):795-799
Three species of irregular see-urchins form the settlement of a marly level (lower Hauterivian) of the Castellane area. Two of them are strongly smaller than the norm. Their stunting is prouved by ontogenic, mecanical, sedimentological and ecological arguments. The ecological grounds of stunting are discussed. 相似文献
69.
The contribution of the 1–6 N-terminal sequence to the conformational properties of the S-peptide (the 1–20 sequence of ribonuclease A) was assessed by determining in the ribonuclease S′ system the helical content and the binding capability of synthetic [Orn10]-S-peptide analogs, in which lysine1, glutamic2 and threonine3 were progressively deleted, alanine4 and alanine5were alternatively replaced by serine, and alanine6 was substituted by serine or proline. Both the deletion of the three N-terminal residues and the alanine6/proline replacement produces the loss of the helical structure up to lysine7. No or minor effects are found in all other cases. From the comparison of the binding data, the energy for the conformational stabilization of the N-terminal region was calculated to amount to 1.4 kcal/mol. The results are discussed in comparison with the known x-ray data of the enzyme, with some predictive rules of secondary structure which were applied to this region and with the known phylogenetic variance of the residues in this region. 相似文献
70.
In order to determine the influence of amino acid side-chains on α-helix stability, in relation to the protein folding process, the coil-helix transitions of some synthetic [Orn 10]-S-peptide analogues, containing, in position 8, Phe, Tyr, Ile, Ala, cpGly2 and Gly, were investigated by the technique of circular dichroism under two different sets of conditions. First, the transitions of the Speptide analogues in water/trifluoroethanol mixtures were recorded. From the pattern of the transitions and from the ellipticity values in 97% trifluoroethanol, the following increasing order of amino acids as α-helix formers was found: Gly < Tyr ≤ Phe < cpGly < Ala < Ile. This finding indicates that the conformational parameters (Chou & Fasman, 1974) of the residues in position 8 play an important but not exclusive role in α-helix stability, since the hydrophobicity of the side-chain (Nozaki & Tanford, 1971) of residue 8 exerts a strong influence. From the second approach, studying the capability of the S-peptide analogues to bind to S-protein, the following increasing order was found: (Gly, Ala) < Ile < cpGly < Tyr < Phe. This result reveals that the conformational parameters of the residues in position 8 play no role, whereas their hydrophobic character and side-chain interactions with surrounding residues in the S-protein portion are the determining binding factors. This finding explains the reason for the Phe8 invariance in RNAase A during evolution, and furnishes evidence for the relevant role of long-range interactions in the protein folding process. 相似文献