全文获取类型
收费全文 | 8862篇 |
免费 | 890篇 |
国内免费 | 727篇 |
专业分类
10479篇 |
出版年
2024年 | 26篇 |
2023年 | 106篇 |
2022年 | 273篇 |
2021年 | 426篇 |
2020年 | 291篇 |
2019年 | 362篇 |
2018年 | 342篇 |
2017年 | 257篇 |
2016年 | 353篇 |
2015年 | 534篇 |
2014年 | 604篇 |
2013年 | 655篇 |
2012年 | 733篇 |
2011年 | 759篇 |
2010年 | 483篇 |
2009年 | 419篇 |
2008年 | 542篇 |
2007年 | 442篇 |
2006年 | 408篇 |
2005年 | 372篇 |
2004年 | 332篇 |
2003年 | 320篇 |
2002年 | 285篇 |
2001年 | 74篇 |
2000年 | 73篇 |
1999年 | 60篇 |
1998年 | 76篇 |
1997年 | 46篇 |
1996年 | 61篇 |
1995年 | 35篇 |
1994年 | 64篇 |
1993年 | 29篇 |
1992年 | 44篇 |
1991年 | 37篇 |
1990年 | 33篇 |
1989年 | 38篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 28篇 |
1985年 | 38篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 31篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1978年 | 21篇 |
1977年 | 16篇 |
1976年 | 25篇 |
1975年 | 16篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
目的:探讨运用腹腔镜诊断子宫内膜异位症,并观察通过手术联合药物治疗子宫内膜异位症的临床疗效.方法:回顾性分析157例子宫内膜异位症患者腹腔镜手术联合药物治疗后的临床资料.结果:不同期别子宫内膜位异症患者术后联合用药后完全缓解率为84.7%,半年复发率为1.9%,半年妊娠率为59.2%.结论:子宫内膜异位症腹腔镜手术后联合用药可有效降低复发率,提高受孕率. 相似文献
112.
113.
Endocytosis leads to the internalisation of both lipids and proteins and their delivery to specific subcellular locations. This involves sorting processes that are not completely understood, but may involve interactions between lipids and proteins as well as pH and calcium gradients. This article discusses the importance of endocytosis in glycosphingolipid (GSL) synthesis as well as the potential roles of GSLs in endocytic membrane transport. Although the accumulation of GSLs in storage diseases clearly disrupts endocytic transport, increasing evidence also supports a role for GSLs in endocytosis in normal cells. 相似文献
114.
对于含有大量多糖如酚、酯、萜等其它二次代谢产物的松科和杉科等针叶植物,要从其组织中提取高质量的基因组DNA一般都比较困难。本文以马尾松(Pinus massoniana)针叶为材料,分别采取了简易提取法、高盐沉淀法、CTAB沉淀法、Ziegenhagen法和QIAGEN公司DNeasy Plant Mini Kits 5种方法提取基因组DNA;并通过琼脂糖凝胶电泳、限制性内切酶处理和RAPD 3种方法对所提取的DNA样品进行检测,将它们在DNA的产量、质量和耗时、耗费等方面的优缺点进行定量总结,以便在实际工作中根据不同的实验目的选取最合适的方法,并根据分子生态学研究工作的实际特点确定了CTAB沉淀法为最佳方法。 相似文献
115.
Alhede M Kragh KN Qvortrup K Allesen-Holm M van Gennip M Christensen LD Jensen PØ Nielsen AK Parsek M Wozniak D Molin S Tolker-Nielsen T Høiby N Givskov M Bjarnsholt T 《PloS one》2011,6(11):e27943
For a chronic infection to be established, bacteria must be able to cope with hostile conditions such as low iron levels, oxidative stress, and clearance by the host defense, as well as antibiotic treatment. It is generally accepted that biofilm formation facilitates tolerance to these adverse conditions. However, microscopic investigations of samples isolated from sites of chronic infections seem to suggest that some bacteria do not need to be attached to surfaces in order to establish chronic infections. In this study we employed scanning electron microscopy, confocal laser scanning microscopy, RT-PCR as well as traditional culturing techniques to study the properties of Pseudomonas aeruginosa aggregates. We found that non-attached aggregates from stationary-phase cultures have comparable growth rates to surface attached biofilms. The growth rate estimations indicated that, independently of age, both aggregates and flow-cell biofilm had the same slow growth rate as a stationary phase shaking cultures. Internal structures of the aggregates matrix components and their capacity to survive otherwise lethal treatments with antibiotics (referred to as tolerance) and resistance to phagocytes were also found to be strikingly similar to flow-cell biofilms. Our data indicate that the tolerance of both biofilms and non-attached aggregates towards antibiotics is reversible by physical disruption. We provide evidence that the antibiotic tolerance is likely to be dependent on both the physiological states of the aggregates and particular matrix components. Bacterial surface-attachment and subsequent biofilm formation are considered hallmarks of the capacity of microbes to cause persistent infections. We have observed non-attached aggregates in the lungs of cystic fibrosis patients; otitis media; soft tissue fillers and non-healing wounds, and we propose that aggregated cells exhibit enhanced survival in the hostile host environment, compared with non-aggregated bacterial populations. 相似文献
116.
117.
Dr. Kenjiro Wake Kiyoyuki Motomatsu Chieko Dan Kenji Kaneda 《Cell and tissue research》1988,253(3):563-571
Summary The three-dimensional structure of endothelial cells in the hepatic sinusoids of the rat was studied by application of light- and electron microscopy on Golgi-impregnated specimens. A number of endothelial cells could thus be individually delineated throughout the hepatic lobules. The cytoplasm, showing heavy silver deposits, consists of two distinct areas, a thick and thin portion. The thick portion, issuing from the region of the perikaryon, branches and tapers toward the cell periphery. The thin portion, occupying the remainder of the cytoplasm, consists largely of highly fenestrated sieve plates. Some intralobular variation can be noted; the thick portion of the endothelial cells is well developed in the periportal zone, while the cells in the centrilobular zone are relatively rich in thin portions. In addition, the area of distribution of an individual endothelial cell is larger in the centrilobular sinusoids than in the periportal zone. Some endothelial cells also possess unique cytoplasmic processes projecting into the intercellular space between hepatocytes and connecting the sinusoidal walls of neighboring sinusoids. These processes may anchor the endothelial cells to the hepatic plates. 相似文献
118.
James W. Wallace Kenneth R. Markham David E. Giannasi John T. Mickel Don L. Yopp Luis D. Gomez J. Dan Pittillo Robert Soeder 《American journal of botany》1982,69(3):356-362
A survey for 1,3,6,7-tetrahydroxy-C-glycosylxanthones of representative species within the primitive vascular plants, emphasizing the leptosporangiate ferns, has indicated a limited distribution of these compounds within three leptosporangiate families: Hymenophyllaceae, Aspleniaceae and Marsileaceae. In the Hymenophyllaceae the distribution of these compounds appears to be a useful criterion for segregating species of Mecodium from other species of Hymenophyllum (sensu lato) and suggests that the tubulate vs. the valvate indusial condition may not be an ideal character for separating all species of Hymenophyllum (s.l.) from those of Trichomanes (s.l.). These compounds appear useful for delimiting several species of Elaphoglossum section Pachyglossa and support a relationship among the Aspleniaceae, Athyriaceae, and Elaphoglossaceae. Their presence in Marsilea also raises questions as to the origin of this group of plants. 相似文献
119.
该研究利用硅胶、凝胶、MCI、中压制备色谱(MPLC)和高效液相半制备色谱(semi-HPLC)等方法,对晶帽石斛(Dendrobium crystallinum)进行了化学成分研究。结果表明:提纯、分离共得到10个化合物,经波谱数据分析及与文献数据对照,分别鉴定为石斛酚(1),3,4'-二羟基-5-甲氧基联苄(2),3,4',5-三羟基-3-甲氧基联苄(3),二氢藜芦醇(4),安告佛醇(5),3',5,7-三羟基-4'-甲氧基黄烷酮(6),4',5,7-三羟基-6-甲氧基黄烷酮(7),丁香树脂醇(8),β-谷甾醇(9),β-胡萝卜苷(10)。其中,除化合物2和化合物10以外,其余8个化合物均在该种植物中首次发现。 相似文献
120.
应用单细胞凝胶电泳研究甲醛的发育毒性(简报) 总被引:1,自引:0,他引:1
甲醛(HCHO)属于高挥发性极易溶于水的小分子醛类化合物,是人们日常生活中经常接触的一种空气污染物。甲醛可以引起各种相关疾病,2004年已被世界卫生组织提升为AI类化合物——人类致 相似文献