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   7993篇
  免费   771篇
  国内免费   35篇
耳鼻咽喉   77篇
儿科学   454篇
妇产科学   152篇
基础医学   1018篇
口腔科学   101篇
临床医学   835篇
内科学   1596篇
皮肤病学   181篇
神经病学   591篇
特种医学   528篇
外科学   1283篇
综合类   217篇
一般理论   2篇
预防医学   599篇
眼科学   148篇
药学   505篇
  2篇
中国医学   6篇
肿瘤学   504篇
  2021年   108篇
  2020年   81篇
  2019年   125篇
  2018年   153篇
  2017年   112篇
  2016年   103篇
  2015年   149篇
  2014年   201篇
  2013年   241篇
  2012年   342篇
  2011年   386篇
  2010年   253篇
  2009年   196篇
  2008年   364篇
  2007年   357篇
  2006年   356篇
  2005年   368篇
  2004年   325篇
  2003年   310篇
  2002年   293篇
  2001年   233篇
  2000年   247篇
  1999年   191篇
  1998年   134篇
  1997年   138篇
  1996年   173篇
  1995年   132篇
  1994年   94篇
  1993年   125篇
  1992年   185篇
  1991年   183篇
  1990年   160篇
  1989年   163篇
  1988年   164篇
  1987年   159篇
  1986年   136篇
  1985年   159篇
  1984年   92篇
  1983年   92篇
  1982年   69篇
  1981年   52篇
  1980年   42篇
  1979年   60篇
  1978年   47篇
  1977年   59篇
  1976年   58篇
  1975年   56篇
  1974年   42篇
  1973年   40篇
  1971年   44篇
排序方式: 共有8799条查询结果,搜索用时 15 毫秒
121.

Purpose

This retrospective study was carried out to evaluate whether increasing the starting dose of FSH stimulation above the standard dose of 150 IU/day in patients with low predicted ovarian reserve can improve IVF outcomes.

Method

A total of 122 women aged less than 36 years in their first cycle of IVF were identified as having likely low ovarian reserve based on a serum AMH measurement below 14 pmol/l. Thirty five women were administered the standard dose of 150 IU/day FSH, while the remaining 87 received a higher starting dose (200–300 IU/day FSH). There were no significant differences in age, BMI, antral follicle count, serum AMH, FSH or aetiology of infertility between the two dose groups.

Results

No significant improvement in oocyte and embryo yield or pregnancy rates was observed following an upward adjustment of FSH starting dose. While increasing the dose of FSH above 150 IU/day did not produce any adverse events such as OHSS, it did consume an extra 1,100 IU of FSH per IVF cycle.

Conclusion

The upward FSH dose adjustment in anticipation of low ovarian reserve can not be advocated as it is both expensive and of no proven clinical value.  相似文献   
122.
The patient's pelvic structures repeatedly shifted out of place. Her physicians found a fix that helped.  相似文献   
123.
124.
The evolutionary history of African hunter-gatherers holds key insights into modern human diversity. Here, we combine ethnographic and genetic data on Central African hunter-gatherers (CAHG) to show that their current distribution and density are explained by ecology rather than by a displacement to marginal habitats due to recent farming expansions, as commonly assumed. We also estimate the range of hunter-gatherer presence across Central Africa over the past 120,000 years using paleoclimatic reconstructions, which were statistically validated by our newly compiled dataset of dated archaeological sites. Finally, we show that genomic estimates of divergence times between CAHG groups match our ecological estimates of periods favoring population splits, and that recoveries of connectivity would have facilitated subsequent gene flow. Our results reveal that CAHG stem from a deep history of partially connected populations. This form of sociality allowed the coexistence of relatively large effective population sizes and local differentiation, with important implications for the evolution of genetic and cultural diversity in Homo sapiens.

The evolutionary history of African hunter-gatherers may hold key insights into patterns and processes behind the evolution of modern human diversity. Recent genomic studies have revealed that these populations represent the oldest and most diverse human genetic lineages and have been genetically differentiated from one another since the origin of humans (13) (SI Appendix, Table S1). Therefore, a first question is whether their current ecological niches were also characteristic of early Homo sapiens populations. However, genetic data alone can neither determine the geographic distribution of hunter-gatherers in the past nor demonstrate a deep history of adaptation of hunter-gatherers to their current environments. In fact, various studies have proposed that farming expansions within the past 5,000 years (in particular by the ancestors of Bantu speakers) would have only recently displaced hunter-gatherers to marginalized regions less favorable to agriculture (such as rainforests and deserts) (47).For example, the central part of Africa, between latitudes 5°N and 5°S currently is inhabited by ∼20 scattered hunter-gatherer ethnic groups (8). These Central African hunter-gatherers (CAHG) form a genetic clade thought to have diverged from other African populations as far back as 120,000 to 200,000 years ago (2, 9). The lack of any major linguistic specificity between them is often implied to reflect extensive contacts with surrounding farmer populations (8, 10), and seen as evidence of recent displacement into marginal forest environments by expanding farming populations. However, anthropologists have remarked on the huge variability in lifestyle, habitat, techniques, and tools between CAHG (11), suggestive of long-term cultural diversification and adaptation to forest environments. Research on the drivers of demography and adaptation of CAHG populations remains extremely limited, which can be partially attributed to the lack of archaeological and osteological data resulting from a rapid disintegration of fossil remains in the rainforest’s acidic soils, in addition to social instability in the region (12). Therefore, we are still left with crucial questions regarding the time depth of occupation of Central Africa by hunter-gatherers, the breadth of the niche exploited by earlier populations in the region, and variations in levels of interconnectivity at different points in time.To address those questions, we first compiled ethnographic data on the distribution of 749 camps from 11 hunter-gatherer groups extending from West to East Central Africa. We used them as inputs for environmental niche models (ENMs) to determine the relative influence of several bioclimatic and ecological factors, as well as the presence of farming populations, on the distribution and abundance of CAHG (13, 14). Then, we used high-resolution paleoclimatic reconstructions and topographic maps to make continuous predictions about where CAHG could have lived over the past 120,000 years and the potential extension of their interaction networks. Next, we compiled all reliably dated archaeological assemblages ascribed to hunter-gatherer groups in the Congo Basin (n = 168) and confirmed the model’s ability to predict the location and date of the sites. We further contextualized genomic estimates of population divergences with changes in population densities and interpopulation connectivity predicted by our model. Last, we complemented these analyses with a detailed assessment of present and historical gene flow between nine CAHG populations (n = 265 individuals), which we used to assess recent interactions between previously diverged CAHG populations, after farming expansions. Our study therefore provides a causal link between past environmental changes and human population dynamics over evolutionary time, by predicting where and when populations across Central Africa could have exchanged genetic and/or cultural information throughout their evolutionary history.  相似文献   
125.
Following a stroke, a patient may present with varying degrees of neurological impairment, depending on the area of the brain which is damaged. Specifically, damage to the left cortical hemisphere may result in aphasia. The characteristic speech in a patient with an aphasia caused by a stroke can be similar to the speech in some patients with schizophrenia or other psychotic disorders. In a new patient without a reliable history who presents with suspected aphasia, it is important to include psychotic disorders as part of the differential diagnosis. Failure to differentiate psychotic disorders from aphasia could result in either a lack of treatment that would improve the patient's thought process, thought content, or language, or in a delayed treatment for a stroke, respectively. While a number of psychotic disorders exist and must be differentiated from one another in accordance with DSM-IV guidelines, speech abnormalities in patients with schizophrenia are well described in the literature. For this reason, schizophrenia is the psychotic disorder of focus in this paper. This case report illustrates a clinical situation where a patient required both a psychiatric and neurological consultation in order to determine the etiology of his language disorder. The purpose of this paper is to emphasize the need to consider both psychiatric disorders and aphasia in patients with unknown histories who present with language abnormalities, and to help the clinician critically examine the patient's speech so that, in conjunction with other clinical data, the correct diagnosis can be made and appropriate treatment initiated.  相似文献   
126.
127.
128.
129.
130.
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