全文获取类型
收费全文 | 642篇 |
免费 | 35篇 |
国内免费 | 4篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 7篇 |
2021年 | 31篇 |
2020年 | 15篇 |
2019年 | 25篇 |
2018年 | 32篇 |
2017年 | 16篇 |
2016年 | 37篇 |
2015年 | 30篇 |
2014年 | 31篇 |
2013年 | 47篇 |
2012年 | 53篇 |
2011年 | 64篇 |
2010年 | 36篇 |
2009年 | 31篇 |
2008年 | 37篇 |
2007年 | 29篇 |
2006年 | 29篇 |
2005年 | 25篇 |
2004年 | 35篇 |
2003年 | 23篇 |
2002年 | 13篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
排序方式: 共有681条查询结果,搜索用时 31 毫秒
1.
2.
3.
The opening of the Suez Canal in 1869 caused a migration generally from the Red Sea to the Mediterranean, rarely the opposite
direction, and 63 lessepsian fish species penetrated into the Mediterranean by way of this canal. These species usually spread
northward and most of them can establish wide populations in this area, but some of them can not be successful with respect
to establishment. Thus, it is clearly seen that there are a lot of factors influencing the success of species with respect
to migration, spreading and establishment. So, the lessepsian migration has been formed by the effects of these factors. Lessepsian
species also have the ability to adapt to the ecological conditions of their new environment. Therefore, the influential factors,
their effectiveness and the observed changes in lessepsian species due to the effects of these factors have been discussed
by considering fishes in this paper. 相似文献
4.
5.
6.
【背景】近年来,炎症性肠病患者中艰难梭菌(Clostridium difficile)感染率逐年上升,受到国内外学者广泛关注。我国在该领域的研究起步较晚,但患者数量众多,学习国际上对于炎症性肠病合并艰难梭菌感染的研究,对推动我国在该领域的深入发展具有重要意义。【目的】通过文献计量和可视化分析帮助研究者把握炎症性肠病与艰难梭菌感染相关性研究中的研究主题、方向、热点与前沿。【方法】同时检索Web of Science (WOS)中Science Citation Index Expanded (SCI-E)和CNKI中收录的关于炎症性肠病和艰难梭菌的相关文献,应用CiteSpace 6.2.2r软件进行国家/地区、机构、作者、关键词共现及被引文献、期刊共被引分析,同时进行可视化分析。【结果】经过数据检索和查重,最终可供分析的文献为WOS数据库1 030篇、CNKI数据库80篇。全球范围内,发文最多的国家是美国,主要研究机构有Harvard University、University of California System和Mayo Clinic等,高产作者有Khanna S、Shen B和Ananthakrishnan AN等,高频关键词包括Inflammatory bowel disease、Ulcerative colitis、Clostridium difficile、Clostridium difficile infection和Crohn’s disease等,聚类方向有#0 Diarrhea、#1 Ulcerative colitis、#2 Probiotics、#3 Pouchitis、#4 Gut microbiota、#5 Fecal microbiota transplantation、#6 Depression、#7 Entamoeba histolytica、#8 Pseudomembranous colitis、#9 Clostridium difficile和#10 Clindamycin。国内主要研究机构有南方医科大学和河北医科大学,高产作者有王浦、王斯淇等,高频关键词包括粪菌移植、艰难梭菌、肠道菌群、危险因素和克罗恩病等,聚类方向有#0艰难梭菌、#1益生菌、#2危险因素、#3腹泻和#4粪菌移植。【结论】利用CiteSpace软件对炎症性肠病和艰难梭菌感染相关性研究进行计量及可视化分析可知,该方向仍得到全球各医疗机构及研究者的关注,腹泻及粪菌移植这两个关键词分别代表了WOS数据库和CNKI数据库关于炎症性肠病合并艰难梭菌感染研究的热点。 相似文献
7.
Hélène Hall Sandra Cuellar‐Baena Vladimir Denisov Deniz Kirik 《Journal of neurochemistry》2013,124(3):336-346
Choline acetyltransferase (ChAT) is the key enzyme for acetylcholine (ACh) synthesis and constitutes a reliable marker for the integrity of cholinergic neurons. Cortical ChAT activity is decreased in the brain of patients suffering from Alzheimer's and Parkinson's diseases. The standard method used to measure the activity of ChAT enzyme relies on a very sensitive radiometric assay, but can only be performed on post‐mortem tissue samples. Here, we demonstrate the possibility to monitor ACh synthesis in rat brain homogenates in real time using NMR spectroscopy. First, the experimental conditions of the radiometric assay were carefully adjusted to produce maximum ACh levels. This was important for translating the assay to NMR, which has a low intrinsic sensitivity. We then used 15N‐choline and a pulse sequence designed to filter proton polarization by nitrogen coupling before 1H‐NMR detection. ACh signal was resolved from choline signal and therefore it was possible to monitor ChAT‐mediated ACh synthesis selectively over time. We propose that the present approach using a labeled precursor to monitor the enzymatic synthesis of ACh in rat brain homogenates through real‐time NMR represents a useful tool to detect neurotransmitter synthesis. This method may be adapted to assess the state of the cholinergic system in the brain in vivo in a non‐invasive manner using NMR spectroscopic techniques. 相似文献
8.
Here we report the association of the rs694539 variant of nicotinamide-N-methyltransferase gene with bipolar disorder in a case–control study of 95 bipolar disorder patients and 201 healthy controls (χ2 = 13.382, P = 0.001). With the polymerase chain reaction restriction fragment length polymorphism method we developed we were able to show the association for the first time. This new finding may provide evidence to understand the mechanism of the disease. 相似文献
9.
Nesibe Köse Ünal Akkemik H. Tuncay Güner H. Nüzhet Dalfes Henri D. Grissino-Mayer M. Sinan Özeren Tayfun Kındap 《International journal of biometeorology》2013,57(5):691-701
We developed a high quality reconstruction of May–June precipitation for the interior region of southwestern Turkey using regional tree-ring data calibrated with meteorological data from Burdur. In this study, three new climate sensitive black pine chronologies were built. In addition to new chronologies, four previously published black pine chronologies were used for the reconstruction. Two separate reconstructions were developed. The first reconstruction used all site chronologies over the common interval AD 1813–2004. The second reconstruction used four of the chronologies with a common interval AD 1692–2004. R 2 values of the reconstructions were 0.64 and 0.51 with RE values of 0.63 and 0.51, respectively. During the period AD 1692–1938, 41 dry and 48 wet events were found. Very dry years occurred in AD 1725, 1814, 1851, 1887, 1916, and 1923, while very wet years occurred in AD 1736, 1780, 1788, 1803, and 1892. The longest dry period was 16 years long between 1860 and 1875. We then explored relationships between the reconstructed rainfall patterns and major volcanic eruptions, and discovered that wetter than normal years occurred during or immediately after the years with the largest volcanic eruptions. 相似文献
10.
Sinan Anlaş 《Zoology in the Middle East.》2013,59(2):153-160
Tetartopeus frischi sp. n. from the U?ak Province in western Anatolia, Turkey, is described and illustrated. Additional records of ten species of Tetartopeus are reported from the West Palaearctic region, among them several new country records. An updated key to the Turkish species of Tetartopeus is presented.http://www.zoobank.org/urn:lsid:zoobank.org:pub:8B832717-E48D-444A-9E1A-2946DA1BCA68 相似文献