全文获取类型
收费全文 | 5700篇 |
免费 | 765篇 |
国内免费 | 1篇 |
出版年
2022年 | 51篇 |
2021年 | 75篇 |
2020年 | 48篇 |
2019年 | 66篇 |
2018年 | 81篇 |
2017年 | 98篇 |
2016年 | 99篇 |
2015年 | 156篇 |
2014年 | 176篇 |
2013年 | 227篇 |
2012年 | 274篇 |
2011年 | 291篇 |
2010年 | 182篇 |
2009年 | 168篇 |
2008年 | 211篇 |
2007年 | 210篇 |
2006年 | 196篇 |
2005年 | 194篇 |
2004年 | 181篇 |
2003年 | 176篇 |
2002年 | 174篇 |
2001年 | 192篇 |
2000年 | 164篇 |
1999年 | 146篇 |
1998年 | 87篇 |
1997年 | 67篇 |
1996年 | 52篇 |
1995年 | 55篇 |
1994年 | 69篇 |
1993年 | 66篇 |
1992年 | 112篇 |
1991年 | 98篇 |
1990年 | 114篇 |
1989年 | 112篇 |
1988年 | 101篇 |
1987年 | 106篇 |
1986年 | 87篇 |
1985年 | 116篇 |
1984年 | 99篇 |
1983年 | 100篇 |
1982年 | 67篇 |
1981年 | 59篇 |
1980年 | 63篇 |
1979年 | 82篇 |
1978年 | 54篇 |
1977年 | 66篇 |
1976年 | 64篇 |
1975年 | 48篇 |
1974年 | 52篇 |
1973年 | 61篇 |
排序方式: 共有6466条查询结果,搜索用时 9 毫秒
941.
R. H. Morgan 《BMJ (Clinical research ed.)》1967,4(5572):171-172
942.
943.
944.
We have developed a sensitive fluorometric assay using bisulfite deaminated (C----U), covalently-closed circular PM2 DNA as the substrate. We describe a reliable way to prepare this substrate without nicking the PM2 DNA. Methods, which depend on toluenization of the cells, are described for reproducibly and quantitatively assaying uracil-DNA glycosylase. The sensitivity is such that only 200 EL4 mouse thymoma cells or 30,000 Escherichia coli cells are needed for each point in a kinetic assay. 相似文献
945.
Uracil-DNA glycosylase in insects. Drosophila and the locust 总被引:3,自引:0,他引:3
It has been reported that Drosophila lacks a uracil-DNA glycosylase but that a direct incising activity on uracil-containing DNA appeared developmentally only in third instar larvae. In contrast we have found by two independent assays, that uracil-DNA glycosylase exists in both Drosophila eggs as well as in third instar larvae. The first assay shows the liberation of [3H] uracil from a d(AT)n polymer randomly substituted with [3H]uracil by its synthesis in the presence of [3H] dUTP. The second fluorometric assay for uracil-DNA glycosylase depends on the unique topological properties of circular DNAs and has the advantage of detecting apyrimidinic/apurinic (AP) endonuclease activity as well. To test one other insect, locust eggs were also assayed for uracil-DNA glycosylase. The amount of uracil-DNA glycosylase correlated well with the amount of DNA in actively replicating cells. 相似文献
946.
W. K. Morgan 《BMJ (Clinical research ed.)》1995,311(7020):1643-1644
947.
Summary The elemental composition of the chloragosomes of the two earthworm species, one with complex highly active Ca-secreting calciferous glands (L. terrestris) and the other with non-secretory glands (A. longa), was determined by the electron probe X-ray microanalysis of unfixed freeze-dried cryosections. The predominant constituents of the chloragosomes of both species were P, Ca, Zn and S, with lesser quantities of K, Cl and Fe. The most striking species differences in chloragosomal chemistry were the higher concentrations (expressed as relative mass fractions) of P(×2.1), Ca(×1.5), and Zn(×2.3) in L. terrestris, and the much higher S(×19.6) in A. longa. These differences were discussed in relation to the general ecophysiology of the two species, and more specifically in relation to heavy metal uptake and binding. 相似文献
948.
949.
The oligodendrocyte-myelin glycoprotein belongs to a distinct family of proteins and contains the HNK-1 carbohydrate 总被引:19,自引:0,他引:19
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The complete primary structure of the human oligodendrocyte-myelin glycoprotein (OMgp), a glycophospholipid-linked membrane protein of oligodendrocytes and central nervous system myelin, has been determined. The deduced amino acid sequence predicts a polypeptide of 433 amino acids which includes a 17-amino acid leader sequence. OMgp consists of four domains: (a) a short cysteine-rich motif at the NH2 terminus; (b) a series of tandem leucine-rich repeats (LRs) present in several other proteins where they may play roles in adhesion; (c) a serine/threonine-rich region that contains probable attachment sites for O-linked carbohydrates; and (d) a hydrophobic COOH-terminal segment that is likely to be cleaved concomitant with the attachment of lipid during biosynthesis of OMgp. OMgp shares the first three of its four domains with the platelet glycoprotein Ib, which is responsible for the initial adhesion of platelets to the exposed subendothelium during hemostasis. Together with glycoprotein Ib and several other proteins, OMgp belongs to a family of proteins that contain both an NH2-terminal cysteine-rich motif and an adjacent series of LRs. In addition, we report that a subpopulation of OMgp molecules contains the HNK-1 carbohydrate, which has been shown to mediate interactions among cells in the central nervous system. 相似文献
950.
S. G. Morgan 《Oecologia》1987,73(3):393-400
Summary Zoeae of some species of estuarine decapods are retained in the estuary throughout development while others are exported into nearshore coastal waters. The horizontal migrations of decapod zoeae to coastal waters may have evolved to reduce the probability of encountering planktivorous fishes which are most abundant in the estuary. If so, then the morphological vulnerability of zoeae to fish predation should be inversely related to the number of predators occurring where they develop. Six species of estuarine decapod zoeae were offered to Menidia menidia and Fundulus heteroclitus. The behavioral interactions were observed to determine the prey's vulnerability to predation, and the mode of operation and relative effectiveness of their defenses. Feeding trials and behavioral observations both demonstrated that M. menidia 6–16 mm long preferred Uca minax and Callinectes sapidus zoeae, which are exported from the estuary, to Rhithropanopeus harrisii, Sesarma reticulatum and Palaemonetes pugio, which are retained within estuaries. Pinnotheres ostreum zoeae develop in the lower estuary and fish demonstrated an intermediate preference for the zoeae. Menidia menidia 20–40 mm long showed similar preferences for R. harrisii S. reticulatum, P. ostreum and U. minax as did small silversides. Large-mouthed demersal fish, Fundulus heteroclitus 6–10 mm long, also preferred U. minax to R. harrisii, but more readily preyed on zoeae than did M. menidia. The exported species of zoeae have shorter spines and smaller bodies than do retained zoeae, except P. ostreum which is small, spineless and passively sinks when attacked by fish. Other retained species of zoeae also have postcontact behavioral defenses which enhance the effectiveness of their morphological defenses. Zoeae do not evade attacks by fishes, but fishes quickly learned to avoid zoeae, which increases the effectiveness of the zoeae's antipredatory adaptations. 相似文献