全文获取类型
收费全文 | 1188804篇 |
免费 | 94471篇 |
国内免费 | 98834篇 |
专业分类
1382109篇 |
出版年
2023年 | 8468篇 |
2022年 | 9508篇 |
2021年 | 11000篇 |
2020年 | 9977篇 |
2019年 | 11200篇 |
2018年 | 11558篇 |
2017年 | 8031篇 |
2016年 | 9064篇 |
2015年 | 10336篇 |
2014年 | 13682篇 |
2013年 | 12629篇 |
2012年 | 107810篇 |
2011年 | 121702篇 |
2010年 | 29570篇 |
2009年 | 21961篇 |
2008年 | 102116篇 |
2007年 | 106039篇 |
2006年 | 99385篇 |
2005年 | 94546篇 |
2004年 | 91644篇 |
2003年 | 86936篇 |
2002年 | 77160篇 |
2001年 | 62029篇 |
2000年 | 77383篇 |
1999年 | 32700篇 |
1998年 | 7219篇 |
1997年 | 5470篇 |
1996年 | 4673篇 |
1995年 | 4423篇 |
1994年 | 4593篇 |
1993年 | 3797篇 |
1992年 | 4376篇 |
1991年 | 3869篇 |
1990年 | 3788篇 |
1989年 | 4304篇 |
1988年 | 4273篇 |
1987年 | 3919篇 |
1986年 | 3736篇 |
1985年 | 3573篇 |
1983年 | 3391篇 |
1959年 | 3880篇 |
1958年 | 6827篇 |
1957年 | 6798篇 |
1956年 | 6074篇 |
1955年 | 5733篇 |
1954年 | 5439篇 |
1953年 | 5173篇 |
1952年 | 4656篇 |
1951年 | 4278篇 |
1950年 | 3511篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
内源性阿片样物质(endogenous opiate substance,EOS)在中枢及外周广泛分布,对机体功能产生多方面影响。就其心血管效应而言,休克等应激状态 EOS水平明显升高,可在心血管中枢、交感神经节、交感神经末梢膨体、肾上腺髓质及心血管效应器官等多个环节程度不同地影响交感-肾上腺髓质系统的活性,参与抑制心血管功能。纳洛酮等阿片受体阻断剂可能通过上述环节程度不等地拮抗 EOS 的作用,部分改善休克个体的心血管功能而表现出一定的抗休克效应。 相似文献
932.
1977年以来,通过采用较先进的研究技术,陆续在低等脊椎动物和哺乳动物脊髓中发现了儿茶酚胺能神经元胞体,对其分布和联系进行了研究。脊髓中的儿茶酚胺能神经元可能与多种生理活动的调节有关。 相似文献
933.
934.
A Halobacterium strain, isolated by Ginzburg et al. from the Dead Sea in the late 1960's, often referred to as "Halobacterium marismortui" or "Halobacterium of the Dead Sea" (deposited in the American Type Culture Collection as ATCC 43049) was compared with Halobacterium (Haloarcula) vallismortis ATCC 29715. The strains appeared to be very closely related, as shown by the near identity of their 5S and 16S ribosomal RNA's, and a large number of other common properties. Distinct differences exist, however, in cell morphology, and in their potency to utilize different sugars and other compounds. 相似文献
935.
We have developed a high cell density and high product concentration culture system recycling high molecular weight components. The production of monoclonal antibodies in high concentration was performed by this culture system with mouse human hybridoma H2 and V6 cells in serum-free defined media.The concentration of IgG after 48 days culture of H2 cells in ITES-eRDF reached 2 mg/ml and the purity of IgG in culture fluid was 61%. In addition, high molecular weight components in serum-free media, such as transferrin or BSA, could be reduced to 5% of the original concentration. 相似文献
936.
Primary cultures of rabbit articular chondrocytes have been subcultured within three-dimensional (3D) collagen gels. Under these conditions, the cells remained viable and divided, but with a lower proliferation rate than that observed in control monolayer cultures. Flow cytometric analysis of progression of the cells into the cell cycle has confirmed and extended these findings. Also the cellular volume was decreased in 3D-culture, being in the same range as thein vivo size of cartilage cells. Specific staining for proteoglycans and type II collagen immunolocalization on sections of gels showed the expression of differentiated phenotypes and revealed the accumulation of these matrix components in the immediate surroundings of the cells. The use of Ultroser G (a serum substitute) improved the conditions for 3D- culture of rabbit articular chondrocytes. 相似文献
937.
938.
Mercuric compound toxicity is well documented in animals and man for practically all organs. The recent development of cell culture techniques appeared as a novel fruitful tool in toxicology, especially in renal toxicology. Heavy metal induced renal cell alterations can be evaluated by membrane permeability damages.The present study evaluates mercuric chloride nephrotoxic effect in human kidney epithelial cells by measuring the release of two specific nephrotoxicity marker enzymes, Gamma Glutamyl Transferase (GGT) and Alkaline Phosphatase (ALP) in the culture medium. Cultured kidney epithelial cells were exposed to different HgCl2 concentrations (5, 10, 20, and 50 g). Cultures were examined after 6 and 24 hours exposure. A good correlation between mercury dose and toxic effect, and exposure time and toxic effect was found. Enzymes were significantly released into the culture medium for 5 g and 10 g HgCl2/ml after 6 hours exposure; and after 24 hours exposure, enzymes were released for 5 g/ml only.It appears that the specific tubular enzyme release in the culture medium is a good in vitro test for quantification of specific tubular damage. 相似文献
939.
940.
Twisted ribbons made of polystyrene were used as a packing material for the cultivation of anchorage dependent cells. Normal human fibroblast cells grown on this support in a laboratory scale reactor reached densities of about 5–7×105 cells/ml. The cells adhered strongly to the carrier and no cell detachment was observed upon transfer to serum free medium. The properties of this packing material and its potential use are discussed. 相似文献