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   1647篇
  免费   12篇
  1659篇
  2015年   7篇
  2014年   10篇
  2013年   64篇
  2012年   45篇
  2011年   64篇
  2010年   95篇
  2009年   74篇
  2008年   56篇
  2007年   82篇
  2006年   62篇
  2005年   61篇
  2004年   39篇
  2003年   28篇
  2002年   14篇
  2001年   20篇
  2000年   31篇
  1999年   22篇
  1998年   40篇
  1997年   62篇
  1996年   73篇
  1995年   40篇
  1994年   33篇
  1993年   35篇
  1992年   38篇
  1991年   33篇
  1990年   36篇
  1989年   37篇
  1988年   33篇
  1987年   22篇
  1986年   25篇
  1985年   27篇
  1984年   30篇
  1983年   20篇
  1982年   15篇
  1981年   20篇
  1980年   25篇
  1979年   29篇
  1978年   26篇
  1977年   17篇
  1976年   11篇
  1975年   18篇
  1974年   11篇
  1973年   18篇
  1972年   21篇
  1971年   33篇
  1969年   4篇
  1967年   5篇
  1959年   5篇
  1952年   3篇
  1951年   4篇
排序方式: 共有1659条查询结果,搜索用时 0 毫秒
81.
Phloem transport stops transiently within dicot stems that are cooled rapidly, but the cause remains unknown. Now it is known that (1) rapid cooling depolarizes cell membranes giving a transient increase in cytoplasmic Ca2+, and (2) a rise of free calcium triggers dispersion of forisomes, which then occlude sieve elements (SEs) of fabacean plants. Therefore, we compared the effects of rapid chilling on SE electrophysiology, phloem transport and forisomes in Vicia faba. Forisomes dispersed after rapid cooling with a delay that was longer for slower cooling rates. Phloem transport stopped about 20 s after forisome dispersion, and then transport resumed and forisomes re‐condensed within similar time frames. Transport interruption and forisome dispersion showed parallel behaviour – a cooling rate‐dependent response, transience and desensitization. Chilling induced both a fast and a slow depolarization of SE membranes, the electrical signature suggesting strongly that the cause of forisome dispersion was the transient promotion of SE free calcium. This apparent block of SEs by dispersed forisomes may be assisted by other Ca2+‐dependent sealing proteins that are present in all dicots.  相似文献   
82.
Mentalizing is the process by which we make sense of each other and ourselves, implicitly and explicitly, in terms of subjective states and mental processes. It is a profoundly social construct in the sense that we are attentive to the mental states of those we are with, physically or psychologically. Given the generality of this definition, most mental disorders will inevitably involve some difficulties with mentalization, but it is the application of the concept to the treatment of borderline personality disorder (BPD), a common psychiatric condition with important implications for public health, that has received the most attention. Patients with BPD show reduced capacities to mentalize, which leads to problems with emotional regulation and difficulties in managing impulsivity, especially in the context of interpersonal interactions. Mentalization based treatment (MBT) is a time-limited treatment which structures interventions that promote the further development of mentalizing. It has been tested in research trials and found to be an effective treatment for BPD when delivered by mental health professionals given limited additional training and with moderate levels of supervision. This supports the general utility of MBT in the treatment of BPD within generic mental health services.Borderline personality disorder (BPD) is a complex and serious mental disorder characterized by a pervasive pattern of difficulties with emotion regulation and impulse control, and instability both in relationships and in selfimage 1. It represents a serious public health problem, because it is associated with suicide attempts and self harm, both of which are consistent targets of mental health services. Recurrent suicidal behaviour is reported in 69-80% of patients with BPD, and suicide rates are estimated to be up to 10% 2. BPD is a common condition that is thought to occur globally with a prevalence of 0.2-1.8% in the general population 3. Higher prevalence rates are found in clinical populations. Moran et al 4 found a prevalence rate of 4-6% among primary care attenders, suggesting that people with BPD are more likely to visit their general practitioner. Chanen et al 5 reported a prevalence rate of 11% in adolescent outpatients and 49% in adolescent inpatients. The highest prevalence has been found in people requiring the most intensive level of care, with a rate of 60-80% among patients in forensic services 6-7. The high prevalence and increased suicide rate in patients with BPD make an unassailable argument that effective treatment needs to be developed and that treatment has to be widely available. Whilst a number of treatments for BPD have been shown to be moderately effective in randomized controlled trials, it remains of considerable concern that most of them require extensive training, making them unavailable to most patients. Mentalization based treatment (MBT) was developed with this in mind. It requires relatively little additional training on top of general mental health training, and has been implemented in research studies by community mental health professionals, primarily nurses, with limited training given modest levels of supervision.  相似文献   
83.
Cretaceous Vascoceras and Jurassic Lytoceras show colour markings and etched surfaces representing original organic membranes between the septa. The main difference between the formation of ammonite and Nautilus chambers involved the continuous secretion of a gelatinous cameral liquid to support the ammonite mantle when it moved forward. The gel containing cyclically secreted membranes. here named pseudosepta, resembled the intra-cameral structures of the cuttlebone in Sepia. Pseudoscpta are attached to the shell wall in pseudosutures (Pseudoloben) which are particularly visible in the saddles of the septal suture and tend to mimic them. Their shape suggests reconstruction of posterior mantle shape during translocation. Drag-bands (Schleppstreifen) are spiral markings formed by the overlapping pseudosepta along the axial traces of the foliole folds. The chamber of ammonites was formed by a locally muscular mantle in a tripartite cycle: (1) the mantle initially remained attached to the saddles of the completed septal suture while muscular tissue within the umbilical lobes was contracted and rapidly reattached to the side of the lateral saddles; (2) the whole mantle subsequently crept forward by secreting a gelatinous matrix which contained telescoped membranes, with an adhesive function on pseudolobc flanks; (3) the mantle almost ceased to move within the sites of future lobules, but expanded and crept on before forming the mural and 'gutter' ridges of the septum. □ Ammonites, chamber growth, vascoceratids, LYTOCERAS, Nigeria.  相似文献   
84.
85.
86.
Abstract: We assessed dispersal behavior of 78 radiotagged adult spotted salamanders (Ambystoma maculatum) at a 36-hole golf course in southeastern Connecticut, USA. Lake of Isles Golf Course is atypical of most golf courses in North America because it is much larger (461 ha) than average 18-hole golf courses (54 ha) and deciduous forests accounted for 70% landscape composition on the course. We tracked individuals an average of 164 days as they emigrated from 3 seasonal pools surrounded by golf course fairways and one pool located in contiguous forest (control pool) from March through December 2004. Males and females dispersed similar distances at the control pool, averaging 71 ± 10 m. However, females migrating across the golf course dispersed twice as far (214 ± 25 m) as males on the golf course (102 ± 15 m) and both genders at the control pool. Over 40% the salamanders at the golf course crossed fairways; thus, fairways were not a dispersal barrier to adult spotted salamanders. Previous researchers have suggested establishing a 164-m life zone around breeding ponds to protect pond-breeding amphibian populations. Our results suggest that strategies that protect core upland habitat within 164 m of wetland boundaries would include 82% of adult males and only 50% of adult females. Empirical estimates based on our telemetry study suggest that core terrestrial habitat would have to extend 370 m to protect 95% of adult females, which is much farther than previous estimates.  相似文献   
87.
Responses of cetaceans to anthropogenic noise   总被引:2,自引:0,他引:2  
  • 1 Since the last thorough review of the effects of anthropogenic noise on cetaceans in 1995, a substantial number of research reports has been published and our ability to document response(s), or the lack thereof, has improved. While rigorous measurement of responses remains important, there is an increased need to interpret observed actions in the context of population‐level consequences and acceptable exposure levels. There has been little change in the sources of noise, with the notable addition of noise from wind farms and novel acoustic deterrent and harassment devices (ADDs/AHDs). Overall, the noise sources of primary concern are ships, seismic exploration, sonars of all types and some AHDs.
  • 2 Responses to noise fall into three main categories: behavioural, acoustic and physiological. We reviewed reports of the first two exhaustively, reviewing all peer‐reviewed literature since 1995 with exceptions only for emerging subjects. Furthermore, we fully review only those studies for which received sound characteristics (amplitude and frequency) are reported, because interpreting what elicits responses or lack of responses is impossible without this exposure information. Behavioural responses include changes in surfacing, diving and heading patterns. Acoustic responses include changes in type or timing of vocalizations relative to the noise source. For physiological responses we address the issues of auditory threshold shifts and ‘stress’, albeit in a more limited capacity; a thorough review of physiological consequences is beyond the scope of this paper.
  • 3 Overall, we found significant progress in the documentation of responses of cetaceans to various noise sources. However, we are concerned about the lack of investigation into the potential effects of prevalent noise sources such as commercial sonars, depth finders and fisheries acoustics gear. Furthermore, we were surprised at the number of experiments that failed to report any information about the sound exposure experienced by their experimental subjects. Conducting experiments with cetaceans is challenging and opportunities are limited, so use of the latter should be maximized and include rigorous measurements and or modelling of exposure.
  相似文献   
88.
89.
Abstract The vertical stratification of insect species assemblages inhabiting tropical rainforests is well established but few have examined whether these patterns are reflected in vertical stratification of body size or feeding guilds. We used Malaise and Flight Interception Traps to sample beetle assemblages from five locations, at both canopy and ground zones of a tropical lowland rainforest site near Cape Tribulation, Australia. Beetles from 4 years of sampling were sorted to Family and morphospecies, and allocated to one of five feeding guilds. Within feeding guilds the number of species and individuals, from canopy‐ and ground‐caught traps were compared. The body lengths of species were measure and compared within feeding guilds and families. Herbivores was the dominant guild but was not the majority of all species or individuals. Most beetle species (69%) were less than 5 mm in length and the mean size of canopy‐caught species was greater than that for ground‐caught species. This was probably due to slightly more species of plant feeders (herbivores and xylophages) present in the canopy, which were significantly larger than saprophages, fungivores and predators. Among feeding guilds, there were few overall canopy–ground differences. These results contrast with species composition results presented elsewhere where strong differences between the canopy and the ground were evident. We suggest that our guild groupings may have been too coarse to detect fine‐scale differences and that resource partitioning may have also masked faunal stratification. We propose that fine‐scale differences in resources between the canopy and the ground, together with strong microclimate gradients, are likely to be important in structuring the vertical stratification of insect assemblages at the level of species, but not with respect to functional groups.  相似文献   
90.
Abstract Broadscale habitat use by Eastern Curlews (Numenius madagascariensis) in their non‐breeding range in eastern Australia was assessed using low tide surveys on feeding grounds, where 60 skilled volunteers made repeated counts of the birds on intertidal flats, across 41% (9500 ha) of the intertidal habitat within Moreton Bay, Australia. We analysed 32 defined sections of intertidal flat, of roughly equal area (mostly 200–400 ha), which varied greatly in their curlew density (2–47 birds per 100 ha) and also in substrate and other environmental features. Sites with the least resistant substrates had densities three times those with the most resistant substrates. Of 10 environmental characteristics measured for each site, substrate resistance was the best predictor of curlew density (r2 = 0.45). Characteristics that were poor predictors included distance to the nearest roost, level of human disturbance and distance to urban settlement. For a finer‐scale assessment, microhabitat use and feeding behaviour were recorded during low tide within 12 intertidal flats, which varied in size (23–97 ha), substrate, topography and other features. Across all flats, curlews strongly preferred to feed relatively close (0–50 m) to the low‐water line. They fed on a variety of substrates (including sand, sandy‐mud, mud and seagrass) in broadly similar proportions to their occurrence in the habitat. There was a statistically significant preference for sand, although its magnitude was not strong. These results indicate that curlews select habitat most strongly at a between‐flat rather than within‐flat scale.  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