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251.
A G Searle C V Beechey E M Eicher M N Nesbitt L L Washburn 《Cytogenetics and cell genetics》1979,23(4):255-263
The cytologic positions (determined by G-banding) of the breakpoints on mouse chromosome 2 of a series of ten reciprocal translocations were compared with their most probable genetic positions on the linkage map, as determined by studies on recombination with known chromosome 2 (= linkage group V) markers. The most probable proximaldistal orders of the genetic and cytologic breakpoints were found to be the same; i.e., the two sets of breakpoints were colinear. However, there was no close correspondence between these two measures of the distance apart of adjacent breakpoints, since some translocation breaks which were well separated in G-band positions seemed close together in terms of the linkage map, and vice versa. This helps to confirm LYON'S conclusion that in certain mouse chromosomes, including No. 2, the distribution of chiasmata is nonrandom. 相似文献
252.
Phosphorylating electron-transport reactions, using either Photosystem I or Photosystem II, were found to be competent in driving the light-induced increase in rotational hindrance of the spin label Tempamine. The uncoupler gramicidin prevented the change induced by either photosystem while the electron-transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) only prevented the light-induced change associated with Photosystem II. The internal lumen microviscosity is termed ‘η’ and was found to be inversely proportional to the lumen volume. Substances which should compete for Tempamine-binding sites on the thylakoid membrane were found to be largely ineffectual in changing η. These results further support the hypothesis that the magnitude of η is directly related to the proximity of Tempamine to a membrane surface. 相似文献
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255.
Louise M. Streeting Martin L. Dillon Jack Nesbitt Brad Nesbitt Lynn Baker Philip H. Spark Bruce C. Chessman Donald T. McKnight Paul G. McDonald Deborah S. Bower 《Austral ecology》2023,48(8):1571-1587
Introduced red foxes (Vulpes vulpes) are a major predator of freshwater turtle nests in Australia. We evaluated the effectiveness of electric fences, in combination with individual nest protection, for shielding western saw-shelled turtle (Myuchelys bellii: Chelidae) nests from predation by foxes. We compared the numbers of raided and intact turtle nests found in paired fenced treatment and unfenced control areas of streambank. We also individually protected all intact nests found in both area types with wire mesh or a steel cage. The total numbers of nests found in treatment and control areas did not significantly differ from parity, but significantly more intact nests were found in treatment areas and significantly more raided nests in control areas. The fences were occasionally damaged by livestock, wildlife and flooding, rendering them inoperative for varying periods of time until repair. However, foxes raided nests inside the fences on only two occasions, despite these breaks in functionality. Our study demonstrates that electric fences can provide an effective method of protecting entire nesting areas from depredation by foxes. 相似文献
256.
Sterling J. Nesbitt Paul M. Barrett Sarah Werning Christian A. Sidor Alan J. Charig 《Biology letters》2013,9(1)
The rise of dinosaurs was a major event in vertebrate history, but the timing of the origin and early diversification of the group remain poorly constrained. Here, we describe Nyasasaurus parringtoni gen. et sp. nov., which is identified as either the earliest known member of, or the sister–taxon to, Dinosauria. Nyasasaurus possesses a unique combination of dinosaur character states and an elevated growth rate similar to that of definitive early dinosaurs. It demonstrates that the initial dinosaur radiation occurred over a longer timescale than previously thought (possibly 15 Myr earlier), and that dinosaurs and their immediate relatives are better understood as part of a larger Middle Triassic archosauriform radiation. The African provenance of Nyasasaurus supports a southern Pangaean origin for Dinosauria. 相似文献
257.
Avise JC; Shapira JF; Daniel SW; Aquadro CF; Lansman RA 《Molecular biology and evolution》1983,1(1):38-56
We address the problem of the possible significance of biological
speciation to the magnitude and pattern of divergence of asexually
transmitted characters in bisexual species. The empirical data for this
report consist of restriction endonuclease site variability in maternally
transmitted mitochondrial DNA (mtDNA) isolated from 82 samples of
Peromyscus polionotus and P. leucopus collected from major portions of the
respective species' ranges. Data are analyzed together with previously
published information on P. maniculatus, a sibling species to polionotus.
Maps of restriction sites indicate that all of the variation observed can
be reasonably attributed to base substitutions leading to loss or gain of
particular recognition sites. Magnitude of mtDNA sequence divergence within
polionotus (maximum approximately equal to 2%) is roughly comparable to
that observed within any of five previously identified mtDNA assemblages in
maniculatus. Sequence divergence within leucopus (maximum approximately
equal to 4%) is somewhat greater than that within polionotus. Consideration
of probable evolutionary links among mtDNA restriction site maps allowed
estimation of matriarchal phylogenies within polionotus and leucopus.
Clustering algorithms and qualitative Wagner procedures were used to
generate phenograms and parsimony networks, respectively, for the
between-species comparisons. Three simple graphical models are presented to
illustrate some conceivable relationships of mtDNA differentiation to
speciation. In theoretical case I, each of two reproductively defined
species (A and B) is monophyletic in matriarchal genealogy; the common
female ancestor of either species can either predate or postdate the
speciation. In case II, neither species is monophyletic in matriarchal
genotype. In case III, species B is monophyletic but forms a subclade
within A which is thus paraphyletic with respect to B. The empirical
results for mtDNA in maniculatus and polionotus appear to conform closely
to case III. These theoretical and empirical considerations raise a number
of questions about the general relationship of the speciation process to
the evolution of uniparentally transmitted traits. Some of these
considerations are presented, and it is suggested that the distribution
patterns of mtDNA sequence variation within and among extant species should
be of considerable relevance to the particular demographies of speciation.
相似文献
258.
For studies of alcohol self-administration in a monkey social group, we effectively and humanely enclosed nine Japanese macaques (Macaca fuscata) in an ellipse 32 x 40m, with a 1 m high chain-link fence surmounted by a 3 m curtain of electrically conductive nylon net. High-voltage brief-pulse charges prevent climbing on the net. Materials for this fence cost less than $14.50 per running meter. Weeds and grass grew freely within the ellipse, and seven dead trees interconnected with ropes permitted climbing and swinging. An open, roofed gazebo provided sun and rain shelter, and its single wall blocked the prevailing wind. Mouth activated drinkometer spouts in the corral supplied solutions for voluntary alcohol self-administration. Automatic counters informed an observer of exact doses consumed by each subject. Another observer recorded the frequency of occurrence of various social behaviors. A small kennel run, roofed over with chain-link fencing, connected the corral with a paddock-like, partially heated building, to and from which the monkeys usually had free access. It contained three interconnected chain-link pens. A raceway opening from the pens incorporated a squeeze cage used for weighing animals, drawing blood samples, or administering medications. This unique facility promotes the psychological well-being of research primates, which is being mandated by federal law. 相似文献
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260.
Miguel I. Uyaguari-Diaz Jared R. Slobodan Matthew J. Nesbitt Matthew A. Croxen Judith Isaac-Renton Natalie A. Prystajecky Patrick Tang 《Journal of visualized experiments : JoVE》2015,(98)
Next-generation sequencing of environmental samples can be challenging because of the variable DNA quantity and quality in these samples. High quality DNA libraries are needed for optimal results from next-generation sequencing. Environmental samples such as water may have low quality and quantities of DNA as well as contaminants that co-precipitate with DNA. The mechanical and enzymatic processes involved in extraction and library preparation may further damage the DNA. Gel size selection enables purification and recovery of DNA fragments of a defined size for sequencing applications. Nevertheless, this task is one of the most time-consuming steps in the DNA library preparation workflow. The protocol described here enables complete automation of agarose gel loading, electrophoretic analysis, and recovery of targeted DNA fragments. In this study, we describe a high-throughput approach to prepare high quality DNA libraries from freshwater samples that can be applied also to other environmental samples. We used an indirect approach to concentrate bacterial cells from environmental freshwater samples; DNA was extracted using a commercially available DNA extraction kit, and DNA libraries were prepared using a commercial transposon-based protocol. DNA fragments of 500 to 800 bp were gel size selected using Ranger Technology, an automated electrophoresis workstation. Sequencing of the size-selected DNA libraries demonstrated significant improvements to read length and quality of the sequencing reads. 相似文献