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21.
Joan Silk Jenny Short Jeffrey Roberts Jill Kusnitz 《International journal of primatology》1993,14(1):95-104
We describe some of the sources of variation in gestation length among rhesus macaques. the data were obtained from the timed-mating breeding program at the California Regional Primate Research Center (CRPRC). Information about approximately 700 pregnancies that resulted in spontaneous vaginal deliveries of liveborn young is presented. The average length of these pregnancies was 166.5 days. In this population, older females with higher parities had significantly longer pregnancies and significantly heavier infants than other females did. Other factors, including infant sex, month of conception, maternal reproductive history, and paternal identity, had no consistent effect upon gestation length. 相似文献
22.
Andrew F. Feldman Daniel J. Short Gianotti Jianzhi Dong Isabel F. Trigo Guido D. Salvucci Dara Entekhabi 《Global Change Biology》2023,29(1):110-125
Vegetation cover creates competing effects on land surface temperature: it typically cools through enhancing energy dissipation and warms via decreasing surface albedo. Global vegetation has been previously found to overall net cool land surfaces with cooling contributions from temperate and tropical vegetation and warming contributions from boreal vegetation. Recent studies suggest that dryland vegetation across the tropics strongly contributes to this global net cooling feedback. However, observation-based vegetation-temperature interaction studies have been limited in the tropics, especially in their widespread drylands. Theoretical considerations also call into question the ability of dryland vegetation to strongly cool the surface under low water availability. Here, we use satellite observations to investigate how tropical vegetation cover influences the surface energy balance. We find that while increased vegetation cover would impart net cooling feedbacks across the tropics, net vegetal cooling effects are subdued in drylands. Using observations, we determine that dryland plants have less ability to cool the surface due to their cooling pathways being reduced by aridity, overall less efficient dissipation of turbulent energy, and their tendency to strongly increase solar radiation absorption. As a result, while proportional greening across the tropics would create an overall biophysical cooling feedback, dryland tropical vegetation reduces the overall tropical surface cooling magnitude by at least 14%, instead of enhancing cooling as suggested by previous global studies. 相似文献
23.
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
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Co-ordinate changes in enzymes of fatty acid synthesis, activation and esterification in rabbit mammary gland druing pregnancy and lactation.
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1. The activities of fatty acid synthetase, acyl-CoA synthetase, glycerol phosphate acyltransferase and phosphatidate phosphatase were measured in the mammary glands of rabbits from day 16 of pregnancy to day 15 of post partum. 2. There were significant correlations between the increases in activities of these enzymes during this period. This was the case whether the activities were expressed per mg of homogenate protein, per g wet wt. of tissue or per total wet weight of the whole glands. The only exception was the lack of correlation between the activities of fatty acid synthetase and of phosphatidate phosphatase per g wet wt. of tissue. 3. These co-ordinate increases are discussed in relation to the changes which occur in fatty acid metabolism in the mammary gland during pregnancy and lactation. 相似文献
27.
Summary Cells of the scutellum of immature embryos ofSorghum bicolor plated onto an agar medium containing 2,4-D give rise to shoots and embryo-like structures and to some callus. Some of the embryo-like structures later develop into typical sorghum embryos complete with scutellum, coleoptile and coleorhiza. The results of anatomical studies of the development of these secondary growth forms by light and scanning electron microscopy suggest that shoots and embryo-like structures can arise directly from cells of the primary scutellum without an intervening callus phase. In some cases it appears that the scutellum of the secondary embryos arises by folding of the scutellum of the sexual embryo and does not arisede novo. In other cases the structures arise from single cells. No evidence was found to indicate that organized structures arose from proliferating callus cells. The unorganized callus which arises initially is not capable of growth through continuous subculture; it produces a purple-black pigment and rapidly becomes necrotic. The significance of these observations is discussed in relation to present views on morphogenesis in cereal cell cultures and their implications forin vitro cell genetics.Abbreviations used in the text 2,4-D
2,4-dichlorophenoxyacetic acid
- MS
Murashige and Skoog 相似文献
28.
Narcissus mosaic virus: a potexvirus with an encapsidated subgenomic messenger RNA for coat protein 总被引:1,自引:0,他引:1
Narcissus-mosaic-virus RNA is translated into a coat -protein-sized product in wheat-germ cell-free extracts. This protein was shown to be very similar to authentic coat protein by partial proteolysis in SDS/polyacrylamide-gel electrophoresis, and by serology. Fractionation of the RNA revealed a small RNA molecule of approx. 840 nucleotides, which alone coded for the coat protein. This subgenomic RNA was found to be encapsidated in a short virus particle. 相似文献
29.
DNA sequence of the filamentous bacteriophage Pf1 总被引:9,自引:0,他引:9
30.