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101.
102.
Identification of overlapping DNA-binding and centromere-targeting domains in the human kinetochore protein CENP-C. 总被引:9,自引:0,他引:9 下载免费PDF全文
C H Yang J Tomkiel H Saitoh D H Johnson W C Earnshaw 《Molecular and cellular biology》1996,16(7):3576-3586
The kinetochore in eukaryotes serves as the chromosomal site of attachment for microtubules of the mitotic spindle and directs the movements necessary for proper chromosome segregation. In mammalian cells, the kinetochore is a highly differentiated trilaminar structure situated at the surface of the centromeric heterochromatin. CENP-C is a basic, DNA-binding protein that localizes to the inner kinetochore plate, the region that abuts the heterochromatin. Microinjection experiments using antibodies specific for CENP-C have demonstrated that this protein is required for the assembly and/or stability of the kinetochore as well as for a timely transition through mitosis. From these observations, it has been suggested that CENP-C is a structural protein that is involved in the organization or the kinetochore. In this report, we wished to identify and map the functional domains of CENP-C. Analysis of CENP-C truncation mutants expressed in vivo demonstrated that CENP-C possesses an autonomous centromere-targeting domain situated at the central region of the CENP-C polypeptide. Similarly, in vitro assays revealed that a region of CENP-C with the ability to bind DNA is also located at the center of the CENP-C molecule, where it overlaps the centromere-targeting domain. 相似文献
103.
We investigated the metabolism and translocation of two gibberellins(GAs), [3H]GA20 and [3H]GA1, which were applied at low concentrationto the cotyledons of Pharbitis nil (cv. Violet). Seedlings weregrown under three different photoperiodic conditions: continuouslight (CL-CL), continous light followed by short day conditions(CL-DT) and long day conditions followed by short day conditions(DT-DT). Translocation of the applied [3H]GAs from cotyledonsto hypocotyls was promoted by DT for all GAs examined. Whilethe conversion of the translocated [3H]GA1 to [3H]GA8 and itsconjugates was rapid in hypocotyl, the conversion of translocated[3H]GA20 to [3H]GA29 was slow. Radioactivity in epicotyls wasdetected much more rapidly on application of [3H]GA20 than of[3H]GA1, [3H]GA8 and [3H]GA29 and their conjugates. The conversionof [3H]GA20 to [3H]GA1 in the epicotyl was more rapid underCL-CL conditions. This result in consistent with the higherlevel of endogenous GA1 existing in epicotyls under CL-DT thanDT-DT conditions. However, when [3H]GA1 was applied to the cotyledon,only small amounts of [3H]GA8 and its conjugates were detectedin the epicotyl regardless of the photoperiodic conditions.This result may suggest that the translocation and metabolismof [3H]GA20 from cotyledons to epicotyl was faster under CL-CLthan DT-DT conditions and may correlate with the increased epicotylelongation of GA20 treated plants under CL-DT than DT-DT conditions. (Received June 28, 1995; Accepted November 2, 1995) 相似文献
104.
Molecular diffusion into horse spleen ferritin: a nitroxide radical spin probe study. 总被引:3,自引:0,他引:3 下载免费PDF全文
Electron paramagnetic resonance spectroscopy and gel permeation chromatography were employed to study the molecular diffusion of a number of small nitroxide spin probes (approximately 7-9 A diameter) into the central cavity of the iron-storage protein ferritin. Charge and polarity of these radicals play a critical role in the diffusion process. The negatively charged radical 4-carboxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-carboxy-TEMPO) does not penetrate the cavity whereas the positively charged 4-amino-TEMPO and 3-(aminomethyl)-proxyl radical and polar 4-hydroxy-TEMPO radical do. Unlike the others, the apolar TEMPO radical does not enter the cavity but instead binds to ferritin, presumably at a hydrophobic region of the protein. The kinetic data indicate that diffusion is not purely passive, the driving force coming not only from the concentration gradient between the inside and outside of the protein but also from charge interactions between the diffusant and the protein. A model for diffusion is derived that describes the observed kinetics. First-order half-lives for diffusion into the protein of 21-26 min are observed, suggesting that reductant molecules with diameters considerably larger than approximately 9 A would probably enter the protein cavity too slowly to mobilize iron efficiently by direct interaction with the mineral core. 相似文献
105.
Approximate methods for estimating the pattern of nucleotide substitution and the variation of substitution rates among sites 总被引:13,自引:6,他引:7
We propose two approximate methods (one based on parsimony and one on
pairwise sequence comparison) for estimating the pattern of nucleotide
substitution and a parsimony-based method for estimating the gamma
parameter for variable substitution rates among sites. The matrix of
substitution rates that represents the substitution pattern can be
recovered through its relationship with the observable matrix of site
pattern frequences in pairwise sequence comparisons. In the parsimony
approach, the ancestral sequences reconstructed by the parsimony algorithm
were used, and the two sequences compared are those at the ends of a branch
in the phylogenetic tree. The method for estimating the gamma parameter was
based on a reinterpretation of the numbers of changes at sites inferred by
parsimony. Three data sets were analyzed to examine the utility of the
approximate methods compared with the more reliable likelihood methods. The
new methods for estimating the substitution pattern were found to produce
estimates quite similar to those obtained from the likelihood analyses. The
new method for estimating the gamma parameter was effective in reducing the
bias in conventional parsimony estimates, although it also overestimated
the parameter. The approximate methods are computationally very fast and
appear useful for analyzing large data sets, for which use of the
likelihood method requires excessive computation.
相似文献
106.
107.
通过不同浓度的几种糖类对潜伏侵染在青香蕉果实中的colletotrichum musae和芒果果实中的colletotichum gloeosporioides的菌体的影响进行了测定,结果表明,高浓度淀粉可极显著地提高两种炭疽菌的孢子萌发率,并有利于附着胞和分生孢子的形成。单糖和二糖在较低浓度时有利于孢子萌发和产孢,不利于附着胞形成。未成熟果实的坚硬结构和高淀粉含量为病菌提供了以附着胞形式潜伏侵染在寄主中的条件。 相似文献
108.
Moxidectin, a newly developed endectocide, has previously been demonstrated to have a high efficacy against gastrointestinal nematodes in cattle (Ranjan et al. 1992, Scholl et al. 1992). In a field trial (Yang, Satrija and Nansen, unpublished data) matched groups of 8 first-season Black Pied Friesian heifer calves, 6-8 months of age, were turned out in early May 1992 on a permanent pasture contaminated with trichostrongyles. The groups were grazed separately on comparable plots until they were housed in mid October 1992. Group Β was treated with moxidectin at turnout, and group C was treated at turnout and again 8 weeks after turnout. A third group served as non-treated controls (group A). The results showed that the 2 early season prophylactic treatments (group C) reduced the late season herbage trichostrongyle larval infectivity with 80 to 90%, whereas the reduction accomplished by only 1 treatment at turnout (group B) was much less. Group C excreted significantly lower numbers of strongyle eggs than groups A and B. The non-treated controls showed clinical signs of trichostrongylosis in late September, which coincided with a steep rise in serum pepsinogen levels reaching an average peak level of 3.5 IU tyrosine litre-1. A few animals in group Β showed softening of faeces particularly in the very late season. In contrast, animals receiving 2 moxidectin treatments remained in a clinically good condition throughout the season. 相似文献
109.
110.
应用常规病理、免疫病理及超微病理技术,对33例流行性出血热(EHF)患者皮肤活检标本的病理变化及病毒抗原、免疫复合物进行观察,同时与血清病毒抗原、抗体及循环免疫复合物检出情况进行比较。在23例EHF患者皮肤微血管内皮细胞中检出病毒抗原,部分组织中可同时检出免疫球蛋白及C3,少数组织仅能检出病毒抗原或免疫球蛋白。配对血清小也可检出EHF病毒抗原、抗体及循环免疫复合物。组织及血清免疫复合物形成与血清补体C3水平下降有关,组织内肥大细胞脱颗粒与血清IgE水平升高相关,提示多种变态反应参与了流行性出血热的发病机制。 相似文献