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   206篇
  免费   13篇
  219篇
  2021年   2篇
  2019年   2篇
  2016年   3篇
  2015年   8篇
  2013年   14篇
  2012年   9篇
  2011年   8篇
  2010年   4篇
  2009年   9篇
  2008年   6篇
  2007年   17篇
  2006年   9篇
  2005年   9篇
  2004年   6篇
  2003年   7篇
  2002年   8篇
  2001年   9篇
  2000年   9篇
  1999年   6篇
  1998年   3篇
  1997年   6篇
  1996年   8篇
  1995年   4篇
  1994年   2篇
  1993年   2篇
  1991年   2篇
  1989年   2篇
  1988年   2篇
  1986年   1篇
  1984年   4篇
  1983年   4篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1977年   5篇
  1976年   2篇
  1973年   1篇
  1970年   1篇
  1969年   2篇
  1967年   1篇
  1955年   1篇
  1951年   1篇
  1944年   1篇
  1943年   1篇
  1939年   1篇
  1911年   1篇
  1906年   1篇
  1879年   1篇
排序方式: 共有219条查询结果,搜索用时 15 毫秒
1.
OBJECTIVE: To describe how women interpret their experiences of diagnosis and treatment of a cervical abnormality and how healthcare services for such women can be improved. DESIGN: Qualitative study using detailed individual interviews. SETTING: Australian gynaecology clinics. SUBJECTS: 29 Women who had a cervical cytological abnormality and who attended a gynaecologist. MAIN OUTCOME MEASURES: Women''s views on their diagnosis and their information needs. RESULTS: Most women wanted to participate in decisions about their care but found it difficult to get the information they required from doctors because they were confused by what their doctors told them and felt unable to ask questions in the consultation. Medical terms such as wart virus and precancer were difficult to understand. Not being able to see their cervix also made it hard for women to understand what their abnormality meant and what treatment entailed. Most women tried to make sense of their abnormality in the context of their everyday lives. For some women their gynaecological care was not consistent with the way they understood their abnormality. CONCLUSIONS: The inherent power structure of medical practice combined with time pressures often make it difficult for doctors to give the detailed information and reassurance patients need when a diagnosis is distressing or when investigation and treatment are strange and upsetting.  相似文献   
2.
Poly(5-fluoro-2′-deoxyuridylic acid) was synthesized and its properties were compared with those of poly(dT) and poly(dU). It readily complexed with poly(dA). The 1:1 complex melted at about 20°C lower than poly(dA) · poly(dT). A triple-stranded helix, poly(dA)·2 poly(dF5U) was formed only in high salt (2.0 M NaCl).  相似文献   
3.
A THE-1 sequence in intron 7 of the human dystrophin gene has been found to represent a new subfamily of THE-1 elements. The sequence is closely related to the MstII family of repetitive sequences and is more like single-copy sequences found in the galago genome than any other THE-1 sequence previously reported. This new THE-1 sequence has been compared with two other complete THE-1 sequences and three related long-terminal repeat elements that we have previously found in intron 7 of the dystrophin gene, and with members of the same family from elsewhere in the primate genome. Parsimony and deletion analysis show that the cluster of THE-1 sequences in intron 7 of the dystrophin gene has arisen from at least three individual insertion events, rather than from the insertion and duplication of a single progenitor sequence. Correspondence to: G.B. Petersen  相似文献   
4.
5.
The synthesis of a high-molecular-weight, putatively all-syn DNA analogue, poly(8-bromo-2′-deoxyadenylic acid), is described. The syn → anti transition was shown to be both salt and temperature dependent. Conditions were found which favored ‘normal’ Watson-Crick pairing and duplex formation with poly(dT).  相似文献   
6.
Calves were either isolated, spatially but not visually, or group-reared for eight months and then kept together. Rank orders based upon competitive interactions were similar at eight and 20 months. Almost all group-reared animals were higher in rank than all isolation-reared animals. The most frequent nearest neighbour associations were between group-reared animals especially those from the same rearing group. Also frequent at eight months were associations between calves which had been isolated in adjacent pens. Isolation-reared animals associated infrequently with group-reared animals and spent more time alone. Body weight was not correlated with rearing conditions or with behavioural measures. Increase, or decrease, in rank between eight and 20 months was associated with faster, or slower, than average weight gain.  相似文献   
7.
Evolutionarily stable stealing: game theory applied to kleptoparasitism   总被引:4,自引:6,他引:4  
We present an individual-based model of a group of foraginganimals. Individuals can obtain food either by discovering itthemselves or by stealing it from others (kleptoparasitism).Given that challenging another individual for a discovered fooditem costs time (which could otherwise be spent searching foran undiscovered item), attempting to steal from another maynot always be efficient We show that there is generally a uniquestrategy that maximizes uptake rate—always or never challengingothers. For any combination of parameter values, we can identifywhich strategy is appropraite. As a corollary to this, we predictthat small changes in ecolgical conditions can, under some circumstances,cause a dramatic change in the aggressive behavior of individuals.Further, we investigate situations where searching for undiscoveredfood and searching for potential opportunities for stealingare mutually exclusive activities (i.e., success at one canonly be improved at the expense of the other). Using game theory,we are able to find the evolutionarily stable strategy for investmentin these two activities in terms of the ecological parametersof the model.  相似文献   
8.
Systems’ welfare evaluation, including behavioural testing, is becoming increasingly popular in farm animal assurance schemes. The aims of this study were to investigate whether fairly short-term exposure to gestation housing systems, which varied in physical, environmental and human-input factors, influenced behavioural and physiological measures during a human approach test—often used to identify problems in human–animal interactions. Twenty-four Large White×Landrace gilts were initially subjected to identical human contact and daily husbandry. Forty-two days after service, the gilts were randomly assigned to either an indoor housing system (n=16) or an outdoor housing system (n=8), which differed physically and in the amount of human contact and daily husbandry. The indoor system used an electronic sow feeder (ESF), was more space-limited and thermally-controlled and had human contact centered on cleaning out. The outdoor system was more extensive, had much greater space accessible, was not thermally-controlled and had human contact that centered around feeding. The human approach test was carried out on all gilts 30–44 days after entry to the gestation system. At testing, each individual was fitted with heart rate monitor and then moved into a test arena. After 2 min an unfamiliar human entered the pen and stood motionless for 3 min against one wall and then approached the gilt and touched her snout. Throughout the experimental period, behaviour and sound within the test arena were recorded continuously. During the 2 min familiarisation period, outdoor gilts had lower heart rates (108.2 bpm versus 123.7 bpm, P<0.05) and tended to perform fewer short vocalisations (0.5 calls per min versus 3.4 calls per min, P<0.1). Outdoor-housed gilts also carried out less locomotor behaviour (2.2 sections crossed versus 4.0 sections crossed, P<0.05) and tended to perform fewer short (1.4 calls per min versus 5.0 calls per min, P<0.1) and long vocalisations (0.2 calls per min versus 1.8 calls per min, P<0.1) over the 3 min test period. Outdoor gilts tended to be slower to approach within 0.5 m of the human (69.9 s versus 19.3 s, P<0.1) but they then took less extra time to make physical contact (3.3 s versus 52.7 s, P<0.1). Mean heart rate was significantly lower in outdoor sows over the whole 3 min period (99.5 bpm versus 115.5 bpm, P<0.05). The results demonstrate that short-term exposure to different housing systems did influence behavioural and physiological measures during a standard human approach test and thus, systems differences should be taken into account before making judgements about the human–animal relationship on any commercial farm, based on results of behavioural tests of this type.  相似文献   
9.
Russell  L. K.  Hurd  C. L.  Nelson  W.A.  Falshaw  R.  & Broom  J.E. 《Journal of phycology》2000,36(S3):59-60
Taxonomic discrimination in the genus Pachymenia (Rhodophyta) in New Zealand is based primarily on phenotypic characters of the thallus. The taxonomic problems raised by this classification method are due to highly variable thallus characters such as blade thickness, blade width, degree of thallus branching, and variation in anatomical characters. Delineation of species is further complicated by a lack of adequate knowledge about the responses of phenotype to environmental variation. There are currently three species recognized in this genus that are endemic to New Zealand: a prostrate species P. crassa , and two erect species, P. laciniata and P. lusoria. In this study, two approaches are used to investigate the current delineation of these species. Morphological and anatomical characters of field collected material and herbarium specimens from throughout the species' distributional ranges were quantified. Multivariate analyses were used to identify discrete phenotypic groups. Species relationships were further analyzed by quantifying the variation found within the internal transcribed spacer region (ITS) of the nuclear ribosomal DNA. The results obtained from both approaches will be discussed with regards to possible re-classification of species relationships within this genus. We suggest that the two erect species should be merged, and the currently recognized P. lusoria should be separated into at least two taxonomic groups.  相似文献   
10.
Small biopsy samples are used increasingly to assess the biomarker expression for prognostic information and for monitoring therapeutic responses prior to and during neoadjuvant therapy. The issue of intratumor heterogeneity of expression of biomarkers, however, has raised questions about the validity of the assessment of biomarker expression based on limited tissue samples. We examined immunohistochemically the expression of HER-2neu (p185erbB-2), epidermal growth factor receptor (EGFR), Bcl-2, p53, and proliferating cell nuclear antigen (PCNA) in 30 breast carcinomas using archived, paraffin embedded tissue and determined the extent of intratumor heterogeneity. Each section was divided into four randomly oriented discrete regions, each containing a portion of the infiltrating carcinoma. For each tumor, the entire lesion and four regions were analyzed for the expression of these markers. Scores of both membrane and cytoplasmic staining of HER-2neu and EGFR, scores of cytoplasmic staining of Bcl-2, and scores of nuclear staining of both p53 and PCNA were recorded. The intensity of staining and the proportion of immunostained cells were determined. A semiquantitative immunoscore was calculated by determining the sum of the products of the intensity and corresponding proportion of stained tumor cells. We analyzed both invasive (IDC) and in situ (DCIS) carcinomas. The Wilcoxon signed-rank test was used for paired comparisons between overall and regional immunoscores and between overall and regional percentages of stained cells. Spearman's correlation coefficients were used to assess the level of agreement of overall biomarker expression with each of the regions. Generalized linear models were used to assess overall and pair-wise differences in the absolute values of percent changes between overall and regional expression of biomarkers. For IDCs, there were no statistically significant differences in the expression of the biomarkers in terms of either the percentage of cells staining or the immunoscores when comparing the entire tumor with each region except for the lower EGFR expression of arbitrarily selected region 1 and lower p53 expression of region 1 compared to that of the entire tumor section. For DCIS, there were no statistically significant differences in the expression of the biomarkers between the entire tumor and each region except in PCNA of region 2 compared to that of entire tumor section. Positive correlation of immunoscores was observed between the entire tumor and each region as well as across all four regions for IDC. Similar observations were noted with DCIS except for HER-2neu and PCNA. No statistically significant differences were observed in the absolute values of percent changes of biomarker expression between overall and the four regions for both DCIS and IDC. Therefore, no significant intratumor heterogeneity in the expression of HER-2neu, Bcl-2, and PCNA was observed in IDC. Minor regional variations were observed for EGFR and p53 in IDC. Similarly, no significant regional variation in the expression of markers was observed in DCIS except for PCNA.  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