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251.
How rapidly does the human mitochondrial genome evolve? 总被引:26,自引:10,他引:16
The results of an empirical nucleotide-sequencing approach indicate that the evolution of the human mitochondrial noncoding D-loop is both more rapid and more complex than is revealed by standard phylogenetic approaches. The nucleotide sequence of the D-loop region of the mitochondrial genome was determined for 45 members of a large matrilineal Leber hereditary optic neuropathy pedigree. Two germ-line mutations have arisen in members of one branch of the family, thereby leading to triplasmic descendants with three mitochondrial genotypes. Segregation toward the homoplasmic state can occur within a single generation in some of these descendants, a result that suggests rapid fixation of mitochondrial mutations as a result of developmental bottlenecking. However, slow segregation was observed in other offspring, and therefore no single or simple pattern of segregation can be generalized from the available data. Evidence for rare mtDNA recombination within the D-loop was obtained for one family member. In addition to these germ-line mutations, a somatic mutation was found in the D-loop of one family member. When this genealogical approach was applied to the nucleotide sequences of mitochondrial coding regions, the results again indicated a very rapid rate of evolution. 相似文献
252.
J. A. Scott J. A. Howell T. C. Arnot K. L. Smith M. Bruska 《Biotechnology Techniques》1996,10(4):287-290
Summary A cross-flow ceramic membrane was coupled to a bioreactor to fulfil the alternate functions of process stream clarifier and primary aerator. At the same air supply rate (delivered as a back-flush), ceramic membranes provided up to 72% greater aeration than a ring-sparger located in the bioreactor. In Biol.ogical treatment of dairy food process waste, the air backflush had the additional benefit of inhibiting membrane fouling, thereby maintaining higher (by about 100%) permeate fluxes. 相似文献
253.
Despite long-term, documented declines in racialized attitudes, racial inequality persists. Scholars have theorized why this dissonance exists but few have empirically demonstrated how views can become more progressive while simultaneously maintaining inequality. The present study uses neighbourhood racial preferences and their influence on racial residential segregation to demonstrate how in a diversifying context residents can become more “accepting” while simultaneously maintaining the racial hierarchy, the opposite of what most of the literature currently assumes. Using data from three distinct sources in the United States, this research finds that U.S. residents are increasingly willing to live amidst diversity yet whites still concentrate in white neighbourhoods. In short, white Americans are more willing to live in diverse neighbourhoods than in the past, but they are not willing to desegregate. We argue this preserves racial inequality. We conclude with a discussion of our findings and their implications for future research and practice. 相似文献
254.
Mouse disabled (mDab1): a Src binding protein implicated in neuronal development. 总被引:16,自引:1,他引:15 下载免费PDF全文
Here, we identify a mouse homolog of the Drosophila Disabled (Dab) protein, mDab1, and show it is an adaptor molecule functioning in neural development. We find that mDab1 is expressed in certain neuronal and hematopoietic cell lines, and is localized to the growing nerves of embryonic mice. During mouse embryogenesis, mDab1 is tyrosine phosphorylated when the nervous system is undergoing dramatic expansion. However, when nerve tracts are established, mDab1 lacks detectable phosphotyrosine. Tyrosine-phosphorylated mDab1 associates with the SH2 domains of Src, Fyn and Abl. An interaction between mDab1 and Src is observed when P19 embryonal carcinoma (EC) cells undergo differentiation into neuronal cell types. mDab1 can also form complexes with cellular phosphotyrosyl proteins through a domain that is related to the phosphotyrosine binding (PTB) domains of the Shc family of adaptor proteins. The mDab1 PTB domain binds to phosphotyrosine-containing proteins of 200, 120 and 40 kDa from extracts of embryonic mouse heads. The properties of mDab1 and genetic analysis of Dab in Drosophila suggest that these molecules function in key signal transduction pathways involved in the formation of neural networks. 相似文献
255.
Susannah M. Walpole Alexia Nicolaou Gareth R. Howell Adam Whittaker David R. Bentley Mark T. Ross John R.W. Yates Dorothy Trump 《Genomics》1997,44(3):300
X-linked retinoschisis (RS) is the leading cause of macular degeneration in young males and has been mapped to Xp22 between DXS418 and DXS999. To facilitate identification of the RS gene, we have constructed a yeast artificial chromosome (YAC) contig across this region comprising 28 YACs and 32 sequence-tagged sites including seven novel end clone markers. To establish the definitive marker order, a PAC contig containing 50 clones was also constructed, and all clones were fingerprinted. The marker order is: Xpter–DXS1317–(AFM205yd12–DXS7175–DXS7992)–60N8T7–DXS1195–DXS7993–DXS7174–60N8-SP6–DXS418–DXS7994–DXS7995–DXS7996–HYAT2–25HA10R–HYAT1–DXS7997–DXS7998–DXS257–434E8R–3542R–DXS6762–DXS7999–DXS6763–434E8L–DXS8000–DXS6760–DXS7176–DXS8001–DXS999–3176R–PHKA2–Xcen. A long-range restriction map was constructed, and the RS region is estimated to be 1300 kb, containing three putative CpG islands. An unstable region was identified between DXS6763 and 434E8L. These data will facilitate positional cloning of RS and other disease genes in Xp22. 相似文献
256.
L-Lactate dehydrogenase (L-LDH, E.C. 1.1.1.27) is encoded by two or three
loci in all vertebrates examined, with the exception of lampreys, which
have a single LDH locus. Biochemical characterizations of LDH proteins have
suggested that a gene duplication early in vertebrate evolution gave rise
to Ldh-A and Ldh-B and that an additional locus, Ldh-C arose in a number of
lineages more recently. Although some phylogenetic studies of LDH protein
sequences have supported this pattern of gene duplication, others have
contradicted it. In particular, a number of studies have suggested that
Ldh-C represents the earliest divergence among vertebrate LDHs and that it
may have diverged from the other loci well before the origin of
vertebrates. Such hypotheses make explicit statements about the
relationship of vertebrate and invertebrate LDHs, but to date, no closely
related invertebrate LDH sequences have been available for comparison. We
have attempted to provide further data on the timing of gene duplications
leading to multiple vertebrate LDHs by determining the cDNA sequence of the
LDH of the tunicate Styela plicata. Phylogenetic analyses of this and other
LDH sequences provide strong support for the duplications giving rise to
multiple vertebrate LDHs having occurred after vertebrates diverged from
tunicates. The timing of these LDH duplications is consistent with data
from a number of other gene families suggesting widespread gene duplication
near the origin of vertebrates. With respect to the relationships among
vertebrate LDHs, our data are not consistent with previous claims that
Ldh-C represented the earliest divergence. However, the precise
relationships among some of the main lineages of vertebrate LDHs were not
resolved in our analyses.
相似文献
257.
During the past six decades, rural women throughout the southeastern state of Oaxaca, Mexico, have comprised a significant percentage (currently the majority) of primary teachers. This article demonstrates that this phenomenon is a result of intertwining socioeconomic factors. It examines why expansion of the education system and economic opportunities may contribute to declining enrollment in teacher training programs even though the career remains a viable, and even desirable, choice for certain rural women. 相似文献
258.
BACKGROUND: Cynomolgus monkeys (Macaca fascicularis) are widely used animal models in biomedical research. However, the phenotypic characteristics of cynomolgus monkey (CM) B cells in peripheral blood (PB) and lymphoid organs are poorly understood. METHODS: FACS analyses of PB-, spleen-, lymph node (LN)-, and bone marrow (BM)-derived B cells were performed. RESULTS: CM peripheral blood B cells have a smaller fraction of CD27(-) (naive) cells ( approximately 40%), as compared to human blood samples ( approximately 70%). Similar to humans, an early activation marker, CD23, is expressed more on CD27(-) CM naive B cells, as compared to CD27(+) B cells. The mean fraction of B cells exhibiting a memory phenotype is similar to that seen in human blood. Unlike humans, CM blood contains a subset of CD20(++)CD80(+)CD21(-)IgM(+/-)CD27(+)CD19(+)FSC(++)BAFF-R(low) B cells that are likely of germinal center origin. Thus, CM blood contains (i) a higher percentage of B cells that express the co-stimulatory molecule CD80, and (ii) a lower fraction of B cells that are CD21(+), as compared to human blood. Due to the relative paucity of information on B-cell subsets in organs of healthy humans, a direct comparison between human and CM lymphoid organ data is limited. The fraction of CD27(+) and CD23(+) B cells appears to be similar, while the fraction of CD80(+) B cells appears to be higher than that seen in human lymphoid organs. CM spleens and to some extent lymph nodes have a distinct subset of CD21(++) cells that are also CD80(+/-)CD23(low)IgM(++)CD27(+/-)FSC(++). This subset is phenotypically similar to the marginal zone B cells present in human spleen and LN samples. We also provide detailed analyses on the fraction of lymphoid organ B cells that express CD21, CD23, CD32, and/or CD80 B-cell markers. CONCLUSIONS: In general, cynomolgus monkey B-cell subsets are similar to those seen in humans, as well as to those seen in other nonhuman primates. However, there are some clear differences between human and cynomolgus monkey B-cell subsets. These findings have direct implications for a variety of in vivo studies in cynomolgus monkeys, ranging from basic research on primate B-cell differentiation to models of infectious diseases and trials of new B-cell targeting therapeutic agents. 相似文献
259.
260.
The activated fibroblast growth factor receptor (FGFR)-1 is phosphorylated on five tyrosine residues outside the catalytic site. Although one such residue, Tyr730, is flanked by potential binding sites for phosphotyrosine-interacting molecules, a physiological role for this region is still controversial. We report that a cell-permeant phosphopeptide mimic of this site, FGFR730(p)Y, inhibits FGF-mediated mitogenesis in cells with no effect on responses stimulated by other growth factors. A similar phosphopeptide corresponding to the phospholipase Cgamma binding site on the receptor had no effect on the mitogenic response. The FGFR730(p)Y peptide did not inhibit phosphorylation of p90/FRS2 or Erk, suggesting that it does not act by inhibiting the Erk-kinase cascade. However, the FGFR730(p)Y peptide bound Shc in a manner requiring both phosphorylated tyrosine and a putative PTB domain binding determinant. These data suggest that the peptide might inhibit mitogenesis by competing with the corresponding site on the FGFR for the ability to bind SHC. 相似文献