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   858篇
  免费   62篇
  国内免费   2篇
  922篇
  2020年   8篇
  2018年   10篇
  2015年   19篇
  2014年   22篇
  2013年   34篇
  2012年   56篇
  2011年   31篇
  2010年   22篇
  2009年   32篇
  2008年   46篇
  2007年   32篇
  2006年   32篇
  2005年   29篇
  2004年   24篇
  2003年   23篇
  2002年   27篇
  2001年   26篇
  2000年   14篇
  1999年   14篇
  1998年   8篇
  1996年   7篇
  1995年   10篇
  1994年   7篇
  1992年   6篇
  1991年   16篇
  1990年   14篇
  1989年   7篇
  1988年   8篇
  1987年   12篇
  1986年   7篇
  1985年   13篇
  1984年   17篇
  1983年   16篇
  1982年   14篇
  1981年   10篇
  1980年   10篇
  1979年   20篇
  1978年   14篇
  1977年   8篇
  1976年   9篇
  1975年   10篇
  1974年   13篇
  1973年   15篇
  1972年   5篇
  1971年   6篇
  1970年   5篇
  1969年   5篇
  1968年   10篇
  1964年   6篇
  1960年   5篇
排序方式: 共有922条查询结果,搜索用时 0 毫秒
811.
Although the traditional “lie detector” test is used frequently in forensic contexts, it has (like most test of deception) some limitations. The concealed knowledge test (CKT) focuses on participants’ recognition of privileged knowledge rather than lying per-se and has been studied extensively using a variety of measures. A “guilty” suspect’s interaction with and memory of crimescene items may vary. Furthermore, memory for crimescene items may diminish over time. The interaction of encoding quality and test delay on CKT efficiency has been previously implied, but not yet demonstrated. We used a response-time based CKT to detect concealed knowledge from shallow and deep study procedures after 10-min, 24-h, and 1-week delays. Results show that more elaborately encoded information afforded higher detection accuracy than poorly encoded items. Although classification accuracy following deep study was unaffected by delay, detection of poorly elaborated information was initially high, but compromised after 1 week. Thus, choosing optimal test items requires considering both test delay and initial encoding level.  相似文献   
812.
This paper studies a class of dynamical systems that model multi-species ecosystems. These systems are ‘resource bounded’ in the sense that species compete to utilize an underlying limiting resource or substrate. This boundedness means that the relevant state space can be reduced to a simplex, with coordinates representing the proportions of substrate utilized by the various species. If the vector field is inward pointing on the boundary of the simplex, the state space is forward invariant under the system flow, a requirement that can be interpreted as the presence of non-zero exogenous recruitment. We consider conditions under which these model systems have a unique interior equilibrium that is globally asymptotically stable. The systems we consider generalize classical multi-species Lotka–Volterra systems, the behaviour of which is characterized by properties of the community (or interaction) matrix. However, the more general systems considered here are not characterized by a single matrix, but rather a family of matrices. We develop a set of ‘explicit conditions’ on the basis of a notion of ‘uniform diagonal dominance’ for such a family of matrices, that allows us to extract a set of sufficient conditions for global asymptotic stability based on properties of a single, derived matrix. Examples of these explicit conditions are discussed.  相似文献   
813.
814.
painless,a Drosophila gene essential for nociception   总被引:11,自引:0,他引:11  
Tracey WD  Wilson RI  Laurent G  Benzer S 《Cell》2003,113(2):261-273
We describe a paradigm for nociception in Drosophila. In response to the touch of a probe heated above 38 degrees C, Drosophila larvae produce a stereotypical rolling behavior, unlike the response to an unheated probe. In a genetic screen for mutants defective in this noxious heat response, we identified the painless gene. Recordings from wild-type larval nerves identified neurons that initiated strong spiking above 38 degrees C, and this activity was absent in the painless mutant. The painless mRNA encodes a protein of the transient receptor potential ion channel family. Painless is required for both thermal and mechanical nociception, but not for sensing light touch. painless is expressed in peripheral neurons that extend multiple branched dendrites beneath the larval epidermis, similar to vertebrate pain receptors. An antibody to Painless binds to localized dendritic structures that we hypothesize are involved in nociceptive signaling.  相似文献   
815.
A large four-generation Chinese family with autosomal dominant optic atrophy (ADOA) was investigated in the present study. Eight of the family members were affected in this pedigree. The affected family members exhibited early-onset and progressive visual impairment, resulting in mild to profound loss of visual acuity. The average age-at-onset was 15.9years. A new heterozygous mutation c.C1198G was identified by sequence analysis of the 12th exon of the OPA1 gene. This mutation resulted in a proline to alanine substitution at codon 400, which was located in an evolutionarily conserved region. This missense mutation in the GTPase domain was supposed to result in a loss of function for the encoded protein and act through a dominant negative effect. No other mutations associated with optic atrophy were found in our present study. The c.C1198G heterozygous mutation in the OPA1 gene may be a novel key pathogenic mutation in this pedigree with ADOA. Furthermore, additional nuclear modifier genes, environmental factors, and psychological factors may also contribute to the phenotypic variability of ADOA in this pedigree.  相似文献   
816.
Incubation of the bovine endothelial cell line, CPAE, with the calcium ionophore (A23187), bradykinin (BK), leukotriene D4 (LTD4) or leukotriene C4 (LTC4) resulted in concentration dependent increases in prostacyclin release measured as 6-ketoprostaglandin F. The kinetics of induction of prostacyclin synthesis differed among the agents studied. Statistically significant increases in prostacyclin were observed one minute after treatment with A23187, at slightly longer times with bradykinin and after approximately three minutes with the leukotrienes. Two other leukotrienes were tested. Both leukotriene B4 and leukotriene E4 (LTE4) were inactive at con- centrations up to 10 μM. The induction of prostacyclin synthesis by LTC4 and LTD4 was inhibited by cycloheximide and actinomycin-D. The effect of BK was inhibited by cycloheximide but not by actinomycin-D. Induction by A23107 was not inhibited by either actinomycin-D or cycloheximide. The results suggest that these agents induced the increases in prostacyclin synthesis by different mechanisms.  相似文献   
817.
818.
819.
820.
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