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931.
Duplication and remoulding of tRNA genes during the evolutionary rearrangement of mitochondrial genomes 总被引:8,自引:0,他引:8
During the evolution of sea urchins, a transfer RNA gene lost its tRNA function and became part of a protein-coding gene. This functional loss of a tRNA with specificity for one group of leucine codons (CUN, where N is any base) was accompanied by the gain of a new tRNA with that specificity. The new tRNA gene for CUN codons appears to have evolved by duplication and divergence from a tRNA gene specific for another group of leucine codons (UUR, where R is a purine). These proposals account for (1) the strong sequence resemblance between the modern tRNA genes for CUN and UUR codons in Paracentrotus, (2) the altered location of the CUN gene in mitochondrial DNA of this urchin, and (3) the persistence of a 72-base pair sequence containing a trace of the old CUN gene at its original location. The old CUN gene now codes for an extra 24 amino acids at the amino end of subunit 5 in NADH dehydrogenase. Besides giving clues about the mechanisms by which tRNA genes move during mitochondrial DNA evolution, this finding leads us to propose a pathway relating the arrangements of other genes in mitochondrial DNAs from four animal phyla. 相似文献
932.
933.
Complete nucleotide sequence of an influenza virus haemagglutinin gene from cloned DNA 总被引:69,自引:0,他引:69
A synthetic fowl plague virus (FPV) haemagglutinin gene has been cloned in bacteria and the complete sequence of the RNA gene deduced. It is 1,742 nucleotides long and the mRNA codes for 56.3 amino acids in an uninterrupted sequence. The nature of some of the important domains in the haemagglutinin has been established, and their structure is discussed in relation to their function. Extensive amino acid sequence homologies exist between FPV and human influenza haemagglutinins. 相似文献
934.
M. Orzalesi F. Gloria-Bottini P. Lucarelli N. Lucarini E. Carapella E. Bottini 《Cellular and molecular life sciences : CMLS》1983,39(1):89-91
Summary A discriminant analysis was performed on a set of maternal and neonatal variables to predict at birth the serum bilirubin levels during the neonatal period in infants incompatible with their mothers in the ABO system. The results suggest that the rational and simultaneous utilization of clinical and laboratory parameters allows, a few hours after delivery, a useful classification of these infants in low or high risk for hyperbilirubinemia.This work was supported by grants of NATO, Italian CNR and M.P.I. 相似文献
935.
Unexpected expression of a unique mixed-isotype class II MHC molecule by transfected L-cells 总被引:4,自引:0,他引:4
Class II (Ia) major histocompatibility complex (MHC) molecules are heterodimeric integral membrane proteins composed of non-covalently linked alpha and beta glycoprotein chains. Studies of both normal cells and L-cell transfectants have shown that neither alpha- nor beta-chains are found on the cell surface alone, and that alpha beta dimers are required for membrane expression. In both mouse and man, several distinct non-allelic alpha and beta genes exist. Analysis of Ia molecules by immunoprecipitation and two-dimensional gel electrophoresis has demonstrated apparently selective association of particular pairs of the various alpha- and beta-chains to form the expressed class II isotypes I-A and I-E (mouse) or DQ, DP and DR (human). Because the various alpha- or beta-chains encoded by distinct loci exist in many allelic forms within a species, such specific pairing suggests a special role for isotypically conserved regions of each chain in the association process. In attempting to localize such putative assembly-controlling regions using the technique of DNA-mediated gene transfer, various combinations of murine alpha and beta genes were introduced into L-cells. Here we report the unexpected observation, following transfection, of mixed-isotype (Ad beta Ea/k alpha) molecules on the L-cell membrane and document that the formation of this pair is strongly influenced by allelic polymorphism of the A beta chain. 相似文献
936.
937.
938.
A unique colour and polarization vision system in mantis shrimps 总被引:2,自引:0,他引:2
N J Marshall 《Nature》1988,333(6173):557-560
The apposition compound eyes of mantis shrimps (stomatopods) are divided into three sections, the dorsal and ventral hemispheres and the midband. Many ommatidia of both hemispheres, and all those in the midband, sample the same narrow band in space. The function of the morphologically distinct midband region is not clear, but new evidence suggests that it may be adapted in a unique manner for colour and polarization vision. A series of carotenoid colour filters screen the photopigment and potentially provide a tetrachromatic input for contrast-enhanced vision or true colour vision. The filters are blocks of coloured droplets (red, orange, yellow, purple, pink or blue) within the rhabdoms of two rows of midband ommatidia. The arrangement of tiered microvilli in two other midband rows suggests that they provide a unique form of polarization vision. 相似文献
939.
N. Papanicolaou N. Lefkos M. Safar M. Paris J. Bariety M. Milliez 《Cellular and molecular life sciences : CMLS》1976,32(10):1280-1281
Summary Urinary prostaglandins (PGEs and PGFs), sodium and potassium were measured in 17 essentially hypertensive patients. Significant positive correlations were found between a) PGEs secreted in 24 h and sodium excreted in 24 h, b) the ratio PGEs/UNaV before and PGEs/UNaV after volume expansion and c) the ratio Na/K and urinary PGEs. It was suggested that renal PGEs, potent natriuretic and diuretic substances, play an important homeostatic role in the extracellular fluid regulation, and consequently in long-term control of the arterial blood pressure. 相似文献
940.