全文获取类型
收费全文 | 10189篇 |
免费 | 1033篇 |
国内免费 | 9篇 |
出版年
2022年 | 86篇 |
2021年 | 100篇 |
2019年 | 80篇 |
2018年 | 108篇 |
2017年 | 74篇 |
2016年 | 184篇 |
2015年 | 306篇 |
2014年 | 372篇 |
2013年 | 444篇 |
2012年 | 606篇 |
2011年 | 542篇 |
2010年 | 393篇 |
2009年 | 350篇 |
2008年 | 592篇 |
2007年 | 581篇 |
2006年 | 527篇 |
2005年 | 525篇 |
2004年 | 522篇 |
2003年 | 540篇 |
2002年 | 446篇 |
2001年 | 207篇 |
2000年 | 168篇 |
1999年 | 152篇 |
1998年 | 139篇 |
1997年 | 98篇 |
1996年 | 109篇 |
1995年 | 88篇 |
1994年 | 115篇 |
1993年 | 103篇 |
1992年 | 127篇 |
1991年 | 115篇 |
1990年 | 106篇 |
1989年 | 114篇 |
1988年 | 104篇 |
1987年 | 108篇 |
1986年 | 123篇 |
1985年 | 131篇 |
1984年 | 116篇 |
1983年 | 110篇 |
1982年 | 108篇 |
1981年 | 95篇 |
1980年 | 87篇 |
1979年 | 104篇 |
1978年 | 79篇 |
1977年 | 89篇 |
1976年 | 69篇 |
1975年 | 62篇 |
1974年 | 79篇 |
1973年 | 69篇 |
1972年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
C. R. Ricketts E. J. L. Lowbury J. C. Lawrence M. Hall M. D. Wilkins 《BMJ (Clinical research ed.)》1970,2(5707):444-446
To clarify tthe mechanism by which local application of silver compounds protects burns against infection, an ion-specific electrode was used to measùre the concentration of silver ions in solutions. By this method it was shown that in burn dressings silver ions were reduced to a very low level by precipitation as silver chloride. The antibacterial effect was found to depend on the availability of silver ions from solution in contact with precipitate. Between 10-5 and 10-6 molar silver nitrate solution in water was rapidly bactericidal. The minimal amount of silver nitrate causing inhibition of respiration of skin in tissue culture was about 25 times the minimal concentration of silver nitrate that inhibited growth of Pseudomonas aeruginosa. 相似文献
143.
Lawrence C. Matten 《American journal of botany》1968,55(7):773-782
A new genus from a Middle Devonian locality near Cairo, N. Y., is described. Actinoxylon gen. nov. is based upon pyritic petrifactions. Three orders of branching are present: penultimate branch, ultimate branch, and leaf. The penultimate branch bears spirally arranged ultimate branches and leaves, the leaves apparently replacing the branches in the spiral. The ultimate branches bear opposite to subopposite and decussate leaves. The leaves are non-planated, unwebbed structures which show at least three dichotomies. Each segment of the leaf is terete as are all other axes. Internally the penultimate branch has a six-lobed actinostele with mesarch protoxylem areas, one or two per lobe. Secondary xylem is visible in the oldest parts of several specimens. The xylem has helical-reticulate, reticulate, scalariform and circular-pitted elements. The presumptive areas of phloem are occupied by cells with dark contents. The cortex is composed of a parenchymatous inner region and a sclerenchymatous outer region. The ultimate branch traces are at first three-lobed protosteles, later becoming four-lobed. Several ultimate branch traces also possess secondary xylem while within the cortex of the penultimate branch. The leaf traces are terete strands. Below each forking of a leaf segment there is a corresponding forking of the vascular strand. Actinoxylon is compared with the progymnosperms Actinopodium, Svalbardia, Archaeopteris, Siderella, and Tetraxylopteris. The anatomy of the penultimate branch of Actinoxylon is similar to that of Actinopodium, Archaeopteris macilenta, and Siderella. The ultimate branch traces of Archaeopteris and Actinoxylon are similar. The ultimate branch stele and pattern of trace formation in Actinoxylon is similar to the stelar configuration and trace formation in the r + 2 axes of Tetraxylopteris schmidtii. The unwebbed leaves are similar to those of Archaeopteris fissilis, Svalbardia, and the terminal units of the Aneurophytales. 相似文献
144.
145.
146.
147.
Lysis was induced in seven strains of Clostridium tetani by exposure to mitomycin C. The search for a suitable indicator strain to detect bacteriophage in lysates has, so far, been unsuccessful. Inhibition studies on macromolecular synthesis during induction have shown that deoxyribonucleic acid, ribonucleic acid, and protein syntheses are all involved in the lysis induced by mitomycin C. In experiments comparing toxin and protein content in induced and uninduced cells of C. tetani, the toxin-protein ratio proved to be the same in both systems up to the point of lysis. Several possible hypotheses deduced from these results are discussed. 相似文献
148.
Properties of cyclic 3',5'-nucleotide phosphodiesterase from rat brain 总被引:24,自引:0,他引:24
W Y Cheung 《Biochemistry》1967,6(4):1079-1087
149.
J R Williamson B E Herczeg H S Coles W Y Cheung 《The Journal of biological chemistry》1967,242(21):5119-5124
150.
Summary Since viable intergeneric hybrids between the chicken (Gallus domesticus) and the pheasant (Phasianus colchicus) have been reported, as well as interfamilial hybrids between the chicken and the turkey (Meleagris gallopavo), the chromosome complements of the pheasant and the turkey were compared with that of the chicken. In these three species belonging to the order Galli, the Z-chromosomes appeared to be identical, while the autosomal complements of the pheasant and the turkey differed radically from that of the chicken. It was noted with some surprise that the pheasant of the family Phasianidae and the turkey of the family Meleagridae have very similar chromosome complements, at least so far as gross morphology of somatic metaphase chromosomes is concerned.This work was supported in part by grant C-5138 from the National Cancer Institute, U.S. Public Health Service, and grant C-17601 from the National Science Foundation.The authors gratefully acknowledge the generosity of Rea's Game Birds, Paramount, California, who supplied the pheasant chicks, and the McPherin Hatcheries, Sunnymead, California, who furnished the turkey chicks. The authors also appreciate the editorial assistance of'Patricia A. Ray. 相似文献