全文获取类型
收费全文 | 513894篇 |
免费 | 56613篇 |
国内免费 | 200篇 |
专业分类
570707篇 |
出版年
2018年 | 4936篇 |
2016年 | 6697篇 |
2015年 | 8784篇 |
2014年 | 10374篇 |
2013年 | 14433篇 |
2012年 | 15857篇 |
2011年 | 16155篇 |
2010年 | 11394篇 |
2009年 | 10531篇 |
2008年 | 14781篇 |
2007年 | 15207篇 |
2006年 | 14353篇 |
2005年 | 13648篇 |
2004年 | 13631篇 |
2003年 | 12834篇 |
2002年 | 12576篇 |
2001年 | 20948篇 |
2000年 | 20741篇 |
1999年 | 16641篇 |
1998年 | 6168篇 |
1997年 | 6332篇 |
1996年 | 5924篇 |
1995年 | 5548篇 |
1994年 | 5412篇 |
1993年 | 5483篇 |
1992年 | 13794篇 |
1991年 | 13711篇 |
1990年 | 13529篇 |
1989年 | 12938篇 |
1988年 | 12397篇 |
1987年 | 11914篇 |
1986年 | 11059篇 |
1985年 | 10869篇 |
1984年 | 9184篇 |
1983年 | 7969篇 |
1982年 | 6136篇 |
1981年 | 5534篇 |
1980年 | 5312篇 |
1979年 | 8778篇 |
1978年 | 6977篇 |
1977年 | 6435篇 |
1976年 | 6164篇 |
1975年 | 6763篇 |
1974年 | 7525篇 |
1973年 | 7466篇 |
1972年 | 6867篇 |
1971年 | 6230篇 |
1970年 | 5558篇 |
1969年 | 5526篇 |
1968年 | 5242篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
EEG correlates of two main effects of long-term hyperventilation (cyclic breathing similar to rebirthing), namely, psychotic manifestations and sensations in internal organs, are considered. Standard EEGs of 44 subjects were recorded and subsequently treated by multiparametric methods. It was shown that, in the case of psychotic phenomena (hallucinations, visual and auditory images, different scenes, virtual travels, out-of-body experiences, etc.), the changes in the spatial organization of bioelectric potentials as compared with the baseline have different patterns than in the case of sensations in internal organs. The changes are observed in the frontal regions of the cortex: a decrease in spatial synchronization (linear processes) during an increase in spatial disarray (nonlinear processes) of bioelectric potentials and the intensifying of high-frequency β activity. If sensations in internal organs appear, a decrease in the above parameters was observed in the right hemisphere and in posterior cortical areas. The data are discussed from the viewpoint of qualitative specificity of changes in functional states during an altered state of consciousness with manifestations of different psychovisceral phenomena. 相似文献
942.
L. I. Sapunova A. G. Lobanok I. O. Kazakevich E. A. Shlyakhotko A. N. Evtushenkov 《Applied Biochemistry and Microbiology》2006,42(3):246-251
The characteristics of xylose isomerase biosynthesis in the bacteria Arthrobacter nicotianae BIM B-5, Erwinia carotovora subsp atroseptica jn42xylA, and Escherichia coli HB101xylA have been studied. The bacteria produced the enzyme constitutively. Out of the carbon sources studied, D-glucose and D-xylose were most favorable for the biosynthesis of xylose isomerase in E. carotovora subsp. atroseptica, but the least appropriate in terms of the enzyme production efficiency in E. coli. Minimum and maximum levels of xylose isomerase formation in A. nicotianae were noted, respectively, during D-xylose and sucrose utilization. An addition to the D-xylose-containing nutrient medium of 0.1–1.5% D-glucose did not affect the enzyme synthesis in A. nicotianae, but suppressed it in Erwinia carotovora subsp. atroseptica (by 7% at the highest concentration) and Escherichia coli (by 63 and 75% at concentrations of 0.1 and 1.0%, respectively). The enzyme proteins produced by the bacteria exhibited the same substrate specificity and electrophoretic mobility (PAGE) as xylose isomerase A. nicotianae, although insignificant differences in the major physicochemical properties were noted. 相似文献
943.
944.
945.
946.
947.
Werner E.C. Muller Jürgen Conrad Rudolf K. Zahn Renate Steffen Gerhard Uhlenbruck Isabel Miller 《Differentiation; research in biological diversity》1984,26(1-3):30-35
Abstract. The Hexactinellida sponge Aphrocallistes vastus contains a soluble aggregation factor (AF) whose purification has been described in this communication. It is characterized by a S°20.w value of 37 and a buoyant density of 1.45 g/cm3 . The AF is a glycoporteinaceous particle composed of three major protein species; no core structure could be visualized. In the presence of Ca2+ , the AF causes secondary aggregation of single cells. The aggregation process is temperature, pH, and ionic strength independent within a broad range. Evidence is presented indicating that two (or more) AF molecules are required for the establishment of a stable cell: cell interaction. In contrast to the AFs from demosponges, the hexactinellid AF functions species-unspecifically. 相似文献
948.
George O. Poinar Jr. 《Systematic parasitology》1981,2(4):261-266
Summary A new mermithid nematode, Thaumamermis cosgrovei n. gen., n. sp. (Mermithidae: Nematoda) was found parasitizing two terrestrial isopods (Isopoda: Oniscoidea) in California. The hosts, Armadillidium vulgare (Latr.) (a pillbug) and Porcellio scaber (Latr.) (a sowbug) represent the first cases of isopods attacked by mermithid nematodes. The genus Thaumamermis can be distinguished from all previously described mermithids by the extremely dimorphic spicules, one being short and broad and the other long and filiform. It has been discovered that the nematodes are infected with an iridiovirus which commonly destroys the isopod hosts. ac]19800917 相似文献
949.
Five new species of Passiflora subgenera Plectostemma and Tacsonia from Ecuador are described, viz. P. discophora, P. monadelpha, P. subpurpurea, P. hirtiflora and P. sanctaebarbarae . Section Discophora of subg. Plectostemma is proposed. 相似文献
950.
The perirhopalial tissue and swimming muscle of Cyanea were examined with light microscopical and electron microscopical techniques. The perirhopalial tissue is a thin, triangular septum found on the subumbrellar surface of the animal. It separates part of the gastric canal system from the surrounding seawater, and is bound on two sides by radial muscle bands and on the third, the shorter side, by a rhopalium and the margin of the bell. The ectoderm of the perirhopalial tissue is composed of large, somewhat cuboidal, vacuolated, myoepithelial cells. The muscle tails of these cells form a single layer of radial, smooth muscle. Neurons of the “giant fiber nerve net” (GFNN), which form an extensive net over the perirhopalial tissue, lie at the base of the vacuolated portion of the myoepithelial cells. These neurons are visible in living tissue. The morphology of individual GFNN neurons was examined following intracellular injection of the fluorescent dye Lucifer Yellow. The neurons are usually bipolar and free of branches. At the electron microscope level, one usually finds that the GFNN neurons contain large vacuoles. The other characteristic feature of these cells is that they form symmetrical, or nonpolarized, synapses; that is, synaptic vesicles are found on both sides of the synapse. The swimming muscle is striated and composed of myoepithelial cells. Each myoepithelial cell has several muscle tails, and those of adjacent cells are linked to gether by desmosomes. The endoderm of the perirhopalial tissue also was examined. This investigation of the organization and ultrastructure of the perirhopalial tissue and surrounding muscle was undertaken to provide essential background information for an ongoing physiological study of the GFNN neurons and their synapses. 相似文献