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61.
Patrick A. Ryan 《Environmental Biology of Fishes》1986,15(1):47-58
Synopsis An approximately monthly sampling programme in Lake Ellesmere, Canterbury, New Zealand, from January 1974 to April 1976 yielded
487 eels. The stomachs were fixed in 10% neutralised formalin and the contents examined. Preliminary analysis indicated that
the mollusc Potamopyrgus antipodarum, the isopod Austridotea annectens, the mysid Tenagomysis chiltoni, the amphipod Paracalliope fluviatilis, the midge larva Chironomus zealandicus and the teleosts Retropinna retropinna, Galaxias maculatus and Gobiomorphus cotidianus together made up the bulk of the diet. The pre-ingested dry weight (i.e. the reconstructed weight) of the most important
of these prey species was obtained by relating the length of a digestion resistant part to actual dry weight in field collected
specimens. Regression equations for this relationship in each season enabled the reconstructed dry weight of each stomach
item to be calculated. In some instances reconstructed weight was less than the actual digested dry weight of the prey specimen.
In every case the larger value was used. This method is referred to as Combination Dry Weight (CDW) and is believed to be
new. These data, used in conjunction with the energy content of the species concerned, enabled the caloric dietary contribution
of each prey species to be determined. Comparison of relative contribution to eel diet between CDW and energy values calculated
from CDW and bomb calorimetry revealed large differences. Marked variations in diet between ⩽40 cm, 40.1–50 cm, and>50.1 cm
size classes were also shown. Eels ≤40 cm feed primarily on invertebrates and become progressively more piscivorous as they
grow. Eels >50.1 cm are almost entirely piscivorous. Seasonal differences in diet also exist within each size class examined. 相似文献
62.
Confirmation of Occurrence of Hydroxamate Siderophores in Soil by a Novel Escherichia coli Bioassay 总被引:5,自引:3,他引:2 下载免费PDF全文
The occurrence of ferrichrome-type hydroxamate siderophores in soil was confirmed. In the presence of the iron-scavenging chelator ethylenediamine[di(o-hydroxyphenylacetic)acid], soil extract stimulated the growth of an Escherichia coli strain possessing the ferrichrome transport protein (TonA) but did not stimulate growth of a strain lacking this protein (TonA−). The siderophore concentration in a 1:1 (soil-water) extract was estimated to be approximately 78 nM. Specificity of the assay was supported by the absence of significant differential strain responses to ferric citrate, ferric 2,3-dihydroxybenzoate, enterochelin, ferrioxamine B, coprogen, and triacetylfusigen. 相似文献
63.
The effect of grazing on primary productivity and phosphorus cycling in autotrophic streams was studied using the snail Goniobasis clavaeformes. Snails were added to each of three replicate laboratory stream channels, receiving once-through flow of groundwater, in densities of 2.1, 3.0, and 4.2 g ash free dry mass (AFDM)/m2. A fourth channel received no snails and served as an ungrazed control. Presence of snail grazers resulted in a large reduction in aufwuchs biomass, primary productivity, and biotic phosphorus uptake; a modest reduction in fine particulate organic matter (FPOM); and an increase in the fraction of stream particulate organic matter (POM) exported as seston. Although primary production and aufwuchs biomass continued to decline with increasing snail density, phosphorus uptake increased. This increased phosphorus uptake is attributed to abiotic sorption to inorganic surfaces exposed as a result of efficient removal of aufwuchs at high snail densities. Although snail densities were chosen to bracket the density measured in a natural stream, the experimental densities may result in considerably higher grazing pressure on aufwuchs due to the absence of alternate food sources (e.g., coarse particulate organic matter) usually found in natural streams. Presence of snail grazers increased the spiralling length of phosphorus, primarily by reducing aufwuchs biomass and consequently reducing uptake of phosphorus from the water. Presence of snails also increased downstream transport velocity of phosphorus bound to organic particles. These results follow the patterns predicted in a previous theoretical analysis for mildly phosphorus-limited streams. 相似文献
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69.
A fast and sensitive multiple sequence alignment algorithm 总被引:4,自引:0,他引:4
A two-step multiple alignment strategy is presented that allowsrapid alignment of a set of homologous sequences and comparisonof pre-aligned groups of sequences. Examples are given demonstratingthe improvement in the quality of alignments when comparingentire groups instead of single sequences. The modular designof computer programs based on this algorithm allows for storageof aligned sequences and successive alignment of any numberof sequences.
Received on August 23, 1988; accepted on December 6, 1988 相似文献
70.
Preparation and characterization of cell-free protein synthesis systems from oocytes and eggs of Xenopus laevis 总被引:4,自引:0,他引:4
During the maturation of the oocytes of the frog Xenopus laevis, the rate of protein synthesis shows a twofold increase. Studies of the mechanisms involved in this stimulation have been seriously limited by the lack of an active cell-free translation system. We have now prepared such systems from oocytes, progesterone-matured oocytes and eggs of Xenopus laevis by induction of lysis by centrifugation of whole cells. The extracts are highly active in incorporation of labelled amino acids and, in the progesterone-matured and egg extracts, a substantial proportion of this is due to reinitiation on endogenous mRNA, as shown by the use of inhibitors. The increased rate of protein synthesis previously observed in intact oocytes following progesterone-induced maturation is reflected in the relative activities of the extracts. The difference in activity is not due to the presence of a dominant inhibitor of translation in the extracts from unstimulated oocytes. Labelling studies with initiator tRNA ([35S]Met-tRNAf) indicate a higher concentration of 43S preinitiation complexes in the extracts from unstimulated oocytes, suggesting an impairment of initiation of translation at or after the mRNA-binding step. Extracts from both oocytes and progesterone-matured oocytes translated endogenous mRNAs to give products ranging over a wide spectrum of molecular weight. However, significant translation of exogenous (globin) mRNA required the presence of reticulocyte postribosomal supernatant, suggesting that one or more factors required for mRNA recruitment is limiting in these extracts. 相似文献