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11.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
12.
Summary We report- the partial characterization of a -glucosidase produced during growth of the thermotolerant yeast, K. marxianus IMB3 on lactose-containing media at 45°C. The enzyme had Km values of 1.1mM and 14.8mM for the substrates p-nitrophenyl--D-glucoside and cellobiose, respectively. The enzyme had a pH optimum of 5.5 and was optimally active at 50°C. It was stable up to 125 hours at 25°C and 35°, with half-lives of 45 hours and 2 hours at 45°C and 50°C, respectively. The enzyme was inhibited to varying degrees in the presence of metal ions and was completely inactivated by Hg2+. Ethanol concentrations [1–10% (v/v)] had little effect on activity. Glucose (20mM) caused inhibition when p-nitrophenyl--D-glucoside was used as substrate, whereas lactose at similar concentrations had no effect. 相似文献
13.
N. Barron R. Marchant L. McHale A. P. McHale 《Applied microbiology and biotechnology》1995,43(3):518-520
The thermotolerant yeast strain, Kluyveromyces marxianus IMB3, was found to be capable of ethanol production during growth at 45°C on media containing milled paper and exogenously
added commercial cellulase. At maximum achievable cellulose concentrations in shake-flask cultures, ethanol production increased
to 6.6 g/l at 45°C, representing an overall level of conversion of 21% of the maximum theoretical yield. Subsequent studies
involving variations in added cellulase concentrations to the batch systems demonstrated that ethanol yields could be increased
to 10 g/l at 45°C, which represented 39% of the maximum theoretical yield. As a result of ethanol production at 45°C in the
systems examined, we suggest that the thermotolerant ethanol-producing yeast strain K. marxianus represents a novel candidate for use in simultaneous saccharification and conversion of the resulting substrates to ethanol.
Received: 9 June 1994/Received revision: 8 August 1994/Accepted: 12 August 1994 相似文献
14.
Summary In order to enhance cellobiose utilization and conversion of substrate to ethanol by the thermotolerant yeast strain, Kluyveromyces marxianus IMB3, the organism was exposed to short, intense electric pulses. When cells were treated with pulses measuring 0.25kV for 10mS, in the presence of cellobiose, ethanol production was found to increase by almost 40% above that found in fermentations containing non-treated cells. When the extracellular culture filtrate was assayed for -glucosidase activity no significant difference in levels was detected between treated and control systems. Increasing the voltage of the pulses resulted in a decrease in ethanol production. 相似文献
15.
Seven residues implicated as acting directly in substrate binding in yeast hexokinase B have been identified in the crystallographic structure by chemical sequencing. The cysteine which is regarded as a residue critically maintaining the active conformation of yeast hexokinase has been selectively labelled and likewise located in the structure. In some parts of the amino acid sequence predicted from the high-resolution electron density map it is found that alignments of chemically sequenced peptides can be made unambiguously; however, the extent of matching to the predicted sequence varies considerably along the chain. 相似文献
16.
Summary Using techniques for enhanced microtubular preservation, including albumin pretreatment (Gray, 1975), occipital cortex of rats was studied electron microscopically at various ages of development. A close structural relationship was seen between microtubules, sacs of SER and the postsynaptic thickening in primordial spines and with the dense plate material of spine apparatuses. Stereoscopic preparations in addition show a more complicated substructure than previously described for the plate. Microtubules may contribute to the formation of the plate of the spine apparatus which in turn is associated with the postsynaptic thickening of the mature spine. Possible functional correlates are discussed.Dr. L.E. Westrum is an affiliate of the CDMRC at the University of Washington and a recipient of a Burroughs-Wellcome (USA) — Wellcome Trust (U.K.) Research Travel Grant. The research was also supported in part by NIH Grants NS 09678, NS 04053 (NINCDS) and DE 04942 (NIDR), DHHS 相似文献
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19.
1. | The relative abundance in Lake Bonney of the trace elements studied was BM>Fe>Cu>Ni>Mo>Co, with more than 90 per cent of each element in the monimolimnion. |
2. | The monimolimnion contains concentrations of B which are probably toxic to phytoplankton, and Cu concentrations which are at least potetially toxic to these organisms. |
3. | Concentrations of B, Cu, and Mn in the mixolimnion occassionally reach potentially toxic concentrations, but there exist mitigating influences such as high calcium levels. |
4. | The relative amounts of trace elements contributed by the Sollas-Lacroix meltstream to the lake were Mn>Fe>Cu>NiCo>B. Except for Co and Mo, the Sollas-Lacroix meltstream did not appear to contribute trace elements in quantities which would explain the weekly changes found in the mixolimnion. |
20.