首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   924篇
  免费   59篇
  2022年   4篇
  2021年   9篇
  2019年   9篇
  2018年   12篇
  2017年   15篇
  2016年   35篇
  2015年   39篇
  2014年   49篇
  2013年   71篇
  2012年   65篇
  2011年   50篇
  2010年   42篇
  2009年   30篇
  2008年   39篇
  2007年   58篇
  2006年   56篇
  2005年   51篇
  2004年   47篇
  2003年   55篇
  2002年   44篇
  2001年   4篇
  2000年   5篇
  1999年   5篇
  1998年   13篇
  1997年   4篇
  1996年   9篇
  1995年   13篇
  1994年   5篇
  1993年   5篇
  1992年   9篇
  1991年   5篇
  1990年   5篇
  1989年   6篇
  1987年   6篇
  1986年   4篇
  1985年   5篇
  1984年   6篇
  1981年   5篇
  1979年   8篇
  1978年   4篇
  1977年   8篇
  1976年   7篇
  1975年   4篇
  1974年   6篇
  1971年   4篇
  1970年   3篇
  1969年   6篇
  1968年   3篇
  1967年   6篇
  1966年   3篇
排序方式: 共有983条查询结果,搜索用时 15 毫秒
31.
Summary Test releases performed at five symmetrically arranged sites around the loft, at a distance of 78–99 km from it, showed that 1) anosmatic birds transported without alteration of the earth's magnetic field were completely random-oriented, 2) anosmatic birds transported in a container inside which the intensity of the magnetic field was strongly reduced were unable to orientate homewards and mostly departed according to a preferred compass direction, 3) control birds, which could smell, and were transported without alteration of the magnetic field, were homeward oriented and performed better in homing than both experimental groups. The conclusion is that anosmatic birds are unable to detect home direction at unfamiliar sites and that magnetic stimuli perceived during the outward journey are unable to substitute olfactory cues.Abbreviation PCD preferred compass direction Supported by a grant from the Consiglio Nazionale delle Ricerche  相似文献   
32.
Summary In this work the terminal oxidase system of C. lipolytica grown on n-alkanes was identified, and partially purified. Spectral characteristics typical of cytochrome O are obtained, inhibition and photodissociation of CO are reported.  相似文献   
33.
Pseudomonas aeruginosa infection depresses contact sensitivity to oxazolone in mice. To test whether an altered lymphocyte circulation plays a role in this depression51Cr-labeled lymphocytes fromP. aeruginosa-infected and oxazolone-sensitized donors were injected intravenously into infected and sensitized recipients, and the radioactivity uptake of several organs was determine. The controls consisted of normal mice receiving labeled lymphocytes from normal donors. While the radioactivity recovered from the liver, spleen, and mesenteric lymph nodes was similar in the test and the control group, significantly more radioactivity was recovered from the draining lymph nodes of infected and sensitized recipients. The concentration of labeled lymphocytes from sensitized donors in the draining lymph nodes of sensitized recipients was 18% greater than that of the controls but 31% lower than that of infected and sensitized animals receiving cells from infected and sensitized donors.P. aeruginosa infection enhances lymphocyte entrapment within the draining lymph nodes of oxazolone-sensitized mice.  相似文献   
34.
35.
36.
To apply recombinant DNA techniques to the genetic manipulation of cellulolytic ruminal bacteria, a plasmid vector transformation system must be available. The objective of this work was to develop a system for plasmid transformation of Ruminococcus albus. Using high voltage electrotransformation, pSC22 and pCK17 plasmid vectors, derived from lactic acid bacteria plasmids and replicating via single-stranded DNA intermediate, were successfully introduced into three freshly isolated R. albus strains and into R. albus type strain ATCC 27210. The optimization of the electrotransformation condition raised the electroporation efficiency up to 3 x 10(5) transformants per microgram of pSC22 plasmid.  相似文献   
37.
Individuals with Asperger syndrome/High Functioning Autism fail to spontaneously attribute mental states to the self and others, a life-long phenotypic characteristic known as mindblindness. We hypothesized that mindblindness would affect the dynamics of conversational interaction. Using generative models, in particular Gaussian mixture models and observed influence models, conversations were coded as interacting Markov processes, operating on novel speech/silence patterns, termed Steady Conversational Periods (SCPs). SCPs assume that whenever an agent''s process changes state (e.g., from silence to speech), it causes a general transition of the entire conversational process, forcing inter-actant synchronization. SCPs fed into observed influence models, which captured the conversational dynamics of children and adolescents with Asperger syndrome/High Functioning Autism, and age-matched typically developing participants. Analyzing the parameters of the models by means of discriminative classifiers, the dialogs of patients were successfully distinguished from those of control participants. We conclude that meaning-free speech/silence sequences, reflecting inter-actant synchronization, at least partially encode typical and atypical conversational dynamics. This suggests a direct influence of theory of mind abilities onto basic speech initiative behavior.  相似文献   
38.
Summary

Tests on disbudding and their effects on the histogenesis of the wood ring. In this work the effects of hormonic character which appear during the histogenesis of the wood ring have been studied testing disbudding effects on the peach tree.

Some observations on the consequences due to defoliation are also included.

By removal of the buds, the annual ring shows a greater depth and a more marked uniformity of structure, due to an increased frequency of the vascular elements.

By removal of the leaves, the cambial activity is completely inhibited. These results are attributed to the fact that the leaves, according to the more recent hypotheses, produce the substance which stimulates the formation of the wood elements and the differentiation of the newly formed elements.

This inactive substance, produced by the leaf, would exert its action only when the buds, towards which it is directed, transform it into its active form. The removal of the buds would eliminate the centres of diffusion of the inactive substance and also its centres of activation and concentration for the coming rest period, in view of a new vegetative cycle.

As a conseguence the circulation of the inactive substance is more marked, as it is probably activated by the cambium, and its activity lasts longer, producing in the annual ring those characters peculiar to the spring wood, that is of a season in which the circulation of this substance is at its utmost.  相似文献   
39.
40.

Introduction

The diagnostic, predictive and prognostic role of anti-cyclic citrullinated peptide (CCP) antibodies in rheumatoid arthritis (RA) patients is widely accepted. Moreover, detection of these antibodies in subjects presenting with undifferentiated arthritis (UA) is associated with a significant risk to develop the disease. On the other hand, clinical and prognostic significance of evaluating anti-CCP levels in subjects with inflammatory arthritis at disease onset has not been fully clarified. The goal of this prospective study is to analyze the value and prognostic significance of anti-CCP titer quantification in UA subjects.

Methods

Serial anti-CCP assays were measured in 192 consecutive patients presenting with UA lasting less than 12 weeks. Clinical and serological data and arthritis outcome were evaluated every 6 months until two years of follow-up.

Results

Anti-CCP positivity, at both low and high titer, and arthritis of hand joints significantly predicted RA at two years, risk increasing in subjects with high anti-CCP titers at baseline. Moreover, time to RA diagnosis was shorter in patients with high anti-CCP2 titers at enrollment with respect to those with low antibody concentration.

Conclusions

Presence of anti-CCP antibodies, at both low and high concentration, is significantly associated with RA development in subjects with recent onset UA. However, time interval from the onset of the first symptoms to the fulfilment of the classification criteria appears to be directly related to the initial anti-CCP level.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号