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   226篇
  免费   24篇
  2022年   3篇
  2021年   7篇
  2019年   2篇
  2017年   2篇
  2016年   2篇
  2015年   12篇
  2014年   10篇
  2013年   19篇
  2012年   16篇
  2011年   7篇
  2010年   8篇
  2009年   12篇
  2008年   7篇
  2007年   2篇
  2006年   4篇
  2005年   3篇
  2004年   2篇
  2003年   9篇
  2002年   4篇
  2001年   6篇
  2000年   3篇
  1999年   9篇
  1998年   3篇
  1996年   4篇
  1995年   4篇
  1994年   2篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   2篇
  1989年   5篇
  1988年   2篇
  1987年   3篇
  1986年   5篇
  1985年   2篇
  1982年   4篇
  1981年   7篇
  1979年   10篇
  1978年   11篇
  1977年   4篇
  1974年   6篇
  1973年   1篇
  1972年   1篇
  1969年   2篇
  1964年   1篇
  1962年   1篇
  1953年   1篇
  1949年   1篇
  1932年   2篇
  1923年   1篇
排序方式: 共有250条查询结果,搜索用时 15 毫秒
51.
The refractive indices, water content, and volume of wet-spun films of Na-hyaluronate have been measured as a function of relative humidity (rh). These data are used with the Lorentz-Lorenz formula to determine the optical polarizabilities of Na-hyaluronate parallel and perpendicular to the helical axis. The analysis reveals a drop in the optical polarizabilities of approximately 20% between 80 and 88% rh, indicating a phase transition.  相似文献   
52.
Molecular evolution of rodent insulins   总被引:1,自引:0,他引:1  
Several trees of amino acid sequences of rodent insulins were derived with the maximum-parsimony procedure. Possible orthologous and paralogous relationships were investigated. Except for a recent gene duplication in the ancestor of rat and mouse, there are no strong arguments for other paralogous relationships. Therefore, a tree in agreement with other biological data is the most reasonable one. According to this tree, the capacity to form zinc-binding hexamers was lost once in the ancestor of the hystricomorph rodents, followed by moderately increased evolutionary rates in the lineages to African porcupine and chinchilla but highly increased rates in at least three independent lines to other taxa of this suborder: guinea pig, cuis, and Octodontoidea (coypu and casiragua).   相似文献   
53.
From 1976 to 1980, 1034 infants with birth weights of 500-2000 g were cared for in the neonatal medical unit; 724 were discharged. Twenty (2.8%) subsequently died and 654 (90.3%) were followed up at a median age of 3 years 3 months. Fifty five (7.6%) survivors had major neurodevelopmental handicaps not attributable to congenital anomalies. Increasing prevalence of major handicap was found with decreasing birth weight and gestation. Children with birth weights of less than 1251 g had a higher incidence of all major disabilities. Handicapped children with a birth weight less than 1251 g were more likely to have blindness, deafness, multiple disabilities, and more severe cerebral palsy. There were 146 (20.2%) children with minor disabilities: neurological impairments (n = 11), borderline results on psychometric testing (n = 18), visual impairments (n = 52), hearing impairments (n = 40), and speech impairments (n = 71). Children weighing less than 1251 g at birth had a higher incidence of minor visual and hearing impairments. In 389 children the mean Griffiths quotient was 101.6 (SD 17.2) (range 50-147), and 158 children had a mean Wechsler preschool and primary intelligence quotient of 101.8 (13.2) (range 56-127): these quotients did not vary with birth weight or gestation but did vary with socioeconomic group, schooling, and family structure. During the study period an improving prognosis in terms of both survival and handicap was observed in children weighing less than 1251 g at birth.  相似文献   
54.
Some social connections are stronger than others. People have not only friends, but also best friends. Social scientists have long recognized this characteristic of social connections and researchers frequently use the term tie strength to refer to this concept. We used online interaction data (specifically, Facebook interactions) to successfully identify real-world strong ties. Ground truth was established by asking users themselves to name their closest friends in real life. We found the frequency of online interaction was diagnostic of strong ties, and interaction frequency was much more useful diagnostically than were attributes of the user or the user’s friends. More private communications (messages) were not necessarily more informative than public communications (comments, wall posts, and other interactions).  相似文献   
55.
Reef-building scleractinian corals widely engage in symbiotic relationships with Symbiodinium dinoflagellates (zooxanthellae), which reside inside cells of the gastrodermis. In most cases, sexually produced larvae acquire their symbionts from the environment in the early developmental stages preceding settlement; however, some scleractinian corals maternally "seed" their oocytes with symbionts, and these symbionts are reported to be restricted to the gastrodermis at the time of its formation (gastrulation). A precise mechanism for how Symbiodinium are translocated to endoderm in these seeded species was previously unknown. In order to examine the process of endoderm formation and Symbiodinium localization during gastrulation, we have examined two species of "robust" clade scleractinians: Fungia scutaria (nonseeded) and Pocillopora meandrina (maternally seeded). We determined that both species, independent of whether or not they are seeded, undergo a "nutritive" stage before gastrulation, wherein lipid-rich cells (F. scutaria) or membrane-bound cellular fragments (P. meandrina) are passed to the blastocoel where they are subsequently taken up by the definitive endoderm. This emergent property of anthozoan development has been co-opted to facilitate the movement of Symbiodinium to the blastocoel (future site of endoderm), in the seeded species, where they are later phagocytosed by the newly formed definitive endoderm. Additionally, both species of robust clade scleractinians examined gastrulate by way of invagination, as do the majority of anthozoans. This invagination differs from the prawn chip-type gastrulation seen in the complex clade corals and provides evidence for a possible linkage between gastrulation type and phylogenetic history.  相似文献   
56.
Two autosomal recessive muscle diseases, limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM), are caused by mutations in the dysferlin gene. These mutations result in poor ability to repair cell membrane damage, which is suggested to be the cause for this disease. However, many patients who share clinical features with MM-type muscular dystrophy do not carry mutations in dysferlin gene. To understand the basis of MM that is not due to mutations in dysferlin gene, we analyzed cells from patients in one such family. In these patients, we found no defects in several potential candidates - annexin A2, caveolin-3, myoferlin and the MMD2 locus on chromosome 10p. Similar to dysferlinopathy, these cells also exhibit membrane repair defects and the severity of the defect correlated with severity of their disease. However, unlike dysferlinopathy, none of the conventional membrane repair pathways are defective in these patient cells. These results add to the existing evidence that cell membrane repair defect may be responsible for MM-type muscular dystrophy and indicate that a previously unsuspected genetic lesion that affects cell membrane repair pathway is responsible for the disease in the non-dysferlin MM patients.  相似文献   
57.
58.
We translocated 120 Agassiz's desert tortoises to 5 sites in Nevada and Utah to evaluate the effects of translocation on tortoise survivorship, reproduction, and habitat use. Translocation sites included several elevations, and extended to sites with vegetation assemblages not typically associated with desert tortoises in order to explore the possibility of moving animals to upper elevation areas. We measured survivorship, reproduction, and movements of translocated and resident animals at each site. Survivorship was not significantly different between translocated and resident animals within and among sites, and survivorship was greater overall during non-drought years. The number of eggs produced by tortoises was similar for translocated and resident females, but differed among sites. Animals translocated to atypical habitat generally moved until they reached vegetation communities more typical of desert tortoise habitat. Even within typical tortoise habitat, tortoises tended to move greater distances in the first year after translocation than did residents, but their movements in the second or third year after translocation were indistinguishable from those of resident tortoises. Our data show that tortoises translocated into typical Mojave desert scrub habitats perform well; however, the large first-year movements of translocated tortoises have important management implications. Projects that employ translocations must consider how much area will be needed to contain translocated tortoises and whether roads need fencing to prevent the loss of animals. © 2012 The Wildlife Society.  相似文献   
59.
60.

Background

Internet-based self-management has shown to improve asthma control and asthma related quality of life, but the improvements were only marginally clinically relevant for the group as a whole. We hypothesized that self-management guided by weekly monitoring of asthma control tailors pharmacological therapy to individual needs and improves asthma control for patients with partly controlled or uncontrolled asthma.

Methods

In a 1-year randomised controlled trial involving 200 adults (18-50 years) with mild to moderate persistent asthma we evaluated the adherence with weekly monitoring and effect on asthma control and pharmacological treatment of a self-management algorithm based on the Asthma Control Questionnaire (ACQ). Participants were assigned either to the Internet group (n = 101) that monitored asthma control weekly with the ACQ on the Internet and adjusted treatment using a self-management algorithm supervised by an asthma nurse specialist or to the usual care group (UC) (n = 99). We analysed 3 subgroups: patients with well controlled (ACQ ≤ 0.75), partly controlled (0.75>ACQ ≤ 1.5) or uncontrolled (ACQ>1.5) asthma at baseline.

Results

Overall monitoring adherence was 67% (95% CI, 60% to 74%). Improvements in ACQ score after 12 months were -0.14 (p = 0.23), -0.52 (p < 0.001) and -0.82 (p < 0.001) in the Internet group compared to usual care for patients with well, partly and uncontrolled asthma at baseline, respectively. Daily inhaled corticosteroid dose significantly increased in the Internet group compared to usual care in the first 3 months in patients with uncontrolled asthma (+278 μg, p = 0.001), but not in patients with well or partly controlled asthma. After one year there were no differences in daily inhaled corticosteroid use or long-acting β2-agonists between the Internet group and usual care.

Conclusions

Weekly self-monitoring and subsequent treatment adjustment leads to improved asthma control in patients with partly and uncontrolled asthma at baseline and tailors asthma medication to individual patients'' needs.

Trial registration

Current Controlled Trials ISRCTN79864465  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