全文获取类型
收费全文 | 399301篇 |
免费 | 161282篇 |
国内免费 | 29809篇 |
出版年
2018年 | 5154篇 |
2016年 | 6448篇 |
2015年 | 8936篇 |
2014年 | 9928篇 |
2013年 | 12330篇 |
2012年 | 14423篇 |
2011年 | 14637篇 |
2010年 | 12070篇 |
2009年 | 16122篇 |
2008年 | 13765篇 |
2007年 | 13637篇 |
2006年 | 11900篇 |
2005年 | 11647篇 |
2004年 | 11365篇 |
2003年 | 10776篇 |
2002年 | 10879篇 |
2001年 | 16092篇 |
2000年 | 14057篇 |
1999年 | 16174篇 |
1998年 | 11978篇 |
1997年 | 11976篇 |
1996年 | 11270篇 |
1995年 | 11328篇 |
1994年 | 10703篇 |
1993年 | 10359篇 |
1992年 | 15307篇 |
1991年 | 15040篇 |
1990年 | 15487篇 |
1989年 | 14745篇 |
1988年 | 13697篇 |
1987年 | 12793篇 |
1986年 | 11834篇 |
1985年 | 11494篇 |
1984年 | 9375篇 |
1983年 | 8066篇 |
1982年 | 7273篇 |
1981年 | 6828篇 |
1980年 | 6374篇 |
1979年 | 8920篇 |
1978年 | 7342篇 |
1977年 | 7076篇 |
1976年 | 6709篇 |
1975年 | 6679篇 |
1974年 | 7325篇 |
1973年 | 7189篇 |
1972年 | 7128篇 |
1971年 | 6446篇 |
1970年 | 5712篇 |
1969年 | 5754篇 |
1968年 | 5051篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
181.
Chemical taxonomy of the hinge-ligament proteins of bivalves according to their amino acid compositions. 总被引:1,自引:0,他引:1 下载免费PDF全文
The proteins in the hinge ligaments of molluscan bivalves were subjected to chemotaxonomic studies according to their amino acid compositions. The hinge-ligament protein is a new class of structure proteins, and this is the first attempt to introduce chemical taxonomy into the systematics of bivalves. The hinge-ligament proteins from morphologically close species, namely mactra (superfamily Mactracea) or scallop (family Pectinidae) species, showed high intraspecific homology in their compositions. On the other hand, inconsistent results were obtained with two types of ligament proteins in pearl oyster species (genus Pinctada). The results of our chemotaxonomic analyses were sometimes in good agreement with the morphological classifications and sometimes inconsistent, implying a complicated phylogenetic relationship among the species. 相似文献
182.
183.
David M. Anderson Richard H. Scheller James W. Posakony Linda B. McAllister Steven G. Trabert Clifford Beall Roy J. Britten Eric H. Davidson 《Journal of molecular biology》1981,145(1):5-28
Three repetitive sequence families from the sea urchin genome were studied, each defined by homology with a specific cloned probe one to a few hundred nucleotides long. Recombinant λ-sea urchin DNA libraries were screened with these probes, and individual recombinants were selected that include genomic members of these families. Restriction mapping, gel blot, and kinetic analyses were carried out to determine the organization of each repeat family. Sequence elements belonging to the first of the three repeat families were found to be embedded in longer repeat sequences. These repeat sequences frequently occur in small clusters. Members of the second repeat family are also found in a long repetitive sequence environment, but these repeats usually occur singly in any given region of the DNA. The sequences of the third repeat are only 200 to 300 nucleotides long, and are generally terminated by single copy DNA, though a few examples were found associated with other repeats. These three repeat sequence families constitute sets of homologous sequence elements that relate distant regions of the DNA. 相似文献
184.
185.
We used a polyethylene surface to study the adherence of various urinary pathogens to a representative inert surface. The bacteria were suspended in filter-sterilized urine during this adhesion study, and differential adhesion was clearly demonstrated. Pseudomonas aeruginosa adhered most avidly and formed large microcolonies that were surrounded by an extensive amorphous matrix. Staphylococcus saprophyticus also formed microcolonies on the surface of the plastic droppers. In general, piliated strains of Escherichia coli adhered less avidly than the other organisms, but more avidly than nonpiliated strains; however, one piliated strain of E. coli adhered very poorly and behaved like a nonpiliated strain. 相似文献
186.
187.
188.
189.
A Rauch R A Pfeiffer G Leipold H Singer M Tigges M Hofbeck 《American journal of human genetics》1999,64(2):659-666
190.
Blood smears of both male and female chicken Gallus domesticus were analysed by using the following topochemical methods: a) Periodic acid-Schiff (PAS) for glycogen. b) Mercury-bromophenol blue for protein. c) O-Toluidine for myeloperoxidase. d) Sudan black B for lipid. The PAS reaction revealed glycogen in the cytoplasm of all thrombocytes and in a few heterophils. The presence of proteins was evidenced in all types of cells. However variation in the intensity of staining of protein granules was observed in the fusiform structures of the heterophils. A negative reaction for myeloperoxidase was found in all cells. Although some evidence of myeloperoxidase activity was show in the polymorphonuclears it was not enough to ascertain a positive reaction. Lipids were detected in the cytoplasm of few heterophils, eosinophils and monocytes. 相似文献