全文获取类型
收费全文 | 7995篇 |
免费 | 830篇 |
国内免费 | 5篇 |
出版年
2022年 | 59篇 |
2021年 | 67篇 |
2019年 | 58篇 |
2018年 | 80篇 |
2017年 | 58篇 |
2016年 | 139篇 |
2015年 | 218篇 |
2014年 | 263篇 |
2013年 | 350篇 |
2012年 | 439篇 |
2011年 | 410篇 |
2010年 | 305篇 |
2009年 | 281篇 |
2008年 | 463篇 |
2007年 | 466篇 |
2006年 | 409篇 |
2005年 | 424篇 |
2004年 | 434篇 |
2003年 | 449篇 |
2002年 | 375篇 |
2001年 | 142篇 |
2000年 | 109篇 |
1999年 | 120篇 |
1998年 | 121篇 |
1997年 | 79篇 |
1996年 | 91篇 |
1995年 | 76篇 |
1994年 | 95篇 |
1993年 | 92篇 |
1992年 | 100篇 |
1991年 | 84篇 |
1990年 | 85篇 |
1989年 | 80篇 |
1988年 | 71篇 |
1987年 | 77篇 |
1986年 | 90篇 |
1985年 | 99篇 |
1984年 | 97篇 |
1983年 | 87篇 |
1982年 | 89篇 |
1981年 | 79篇 |
1980年 | 76篇 |
1979年 | 82篇 |
1978年 | 65篇 |
1977年 | 65篇 |
1976年 | 56篇 |
1975年 | 52篇 |
1974年 | 67篇 |
1973年 | 52篇 |
1972年 | 46篇 |
排序方式: 共有8830条查询结果,搜索用时 421 毫秒
91.
Richard F. Selden Andre Steinmetz Lee McIntosh Lawrence Bogorad Gerard Burkard Mfika Mubumbila Marcel Kuntz Edwin J. Crouse Jacques H. Weil 《Plant molecular biology》1983,2(3):141-153
A minimum of 37 genes corresponding to tRNAs for 17 different amino acids have been localized on the restriction endonuclease cleavage site map of theZea mays chloroplast DNA molecule. Of these, 14 genes corresponding to tRNAs for 11 amino acids are located in the larger of the two single-copy regions which separate the two inverted copies of the repeat region. One tRNA gene is in the smaller single-copy region. Each copy of the large repeated sequence contains, in addition to the ribosomal RNA genes, 11 tRNA genes corresponding to tRNAs for 8 amino acids. The genes for tRNA2 Ile and tRNAAla map in the ribosomal spacer sequence separating the 16S and 23S ribosomal RNA genes. The three isoaccepting species for the tRNAsLeu and the three for tRNAsSer, as well as the two isoaccepting species for tRNAAsn, tRNAGly, tRNAsIle, tRNAsMet, tRNAsThr, are shown to be encoded at different loci. Two independent methods have been used for the localization of tRNA genes on the physical map of the maize chloroplast DNA molecule: (a) cloned chloroplast DNA fragments were hybridized with radioactively-labelled total 4S RNAs, the hybridized RNAs were then eluted, and identified by two-dimensional polyacrylamide gel electrophoresis, and (b) individual tRNAs were32P-labelledin vitro and hybridized to DNA fragments generated by digestion of maize chloroplast DNA with various restriction endonucleases. 相似文献
92.
Mechanical Method of Inoculating Plates for Antibiotic Sensitivity Testing 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A mechanical method of inoculating culture plates for antibiotic sensitivity testing is described. This method, which involves the use of a modified laboratory centrifuge, is rapid and provides a homogeneous distribution of organisms. 相似文献
93.
Transformation of Murine Cells by Two “Slow Viruses,” Visna Virus and Progressive Pneumonia Virus
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Visna and progressive pneumonia virus (PPV), two antigenically related, non-oncogenic "slow viruses" which have ribonucleic acid (RNA)-dependent deoxyribonucleic acid (DNA) polymerase activity, were examined for their ability to transform cells. Murine cells which had been exposed to either visna or PPV developed foci of altered, spindle-shaped cells 3 to 4 weeks after infection. Visna and PPV transformed lines were established from these cultures. There was no evidence that other oncogenic DNA or RNA viruses were involved in the observed transformation. Visna or PPV could be "rescued" from all transformed lines by co-cultivation with normal sheep testis cells. "Rescued" virus was identified as visna or PPV, and they retained the capacity to transform mouse cells. These experiments may have important implications in the understanding of both viral carcinogenesis and "slow" viral infections. 相似文献
94.
Edward W. Millhouse Jr. John J. Chiakulas Lawrence E. Scheving 《The Journal of cell biology》1971,48(1):1-14
Beating salamander hearts were maintained in tissue culture for periods ranging from 1 to 6 months. After 1, 3, or 6 months of culture, six hearts, along with six control hearts, were fixed for electron microscopy. In control tissue, the sarcoplasmic reticulum usually demonstrated the normal pattern of paired, linearly arranged membranes, although in some cases, the reticulum showed a variation from these membranes to a series of small vesicles. There was no evidence of a T-system of tubules in any of the material examined. Desmosome-Z band complexes were observed in almost all sections of both control and experimental material. A possible role of these complexes in the excitation-contraction mechanism is discussed. In 3 month cultured material, alterations in normal myofibrillar pattern occurred. Small segments of myofibrils branched from one Z band to join the Z band of an adjacent myofibril, or appeared to be fraying out into the sarcoplasm. In 6 month cultured material, myofibrils were fragmented into short segments from which myofilaments frayed out into the sarcoplasm. This filamentous material may be remnants of myofilaments. Despite the morphological changes in myofibrils, the heart pulsation rate, established at the beginning, was maintained throughout the culture period. It is suggested that the alterations, observed in the experimental material, occurred in elements not essential for heart beat maintenance, or that these alterations have not yet progressed to a critical point of affecting the heart beat. 相似文献
95.
96.
97.
The X-ray mapping procedure of Manney and Mortimer (1964) is the most widely applicable and convenient method for fine structure analysis in yeast, but suffers the disadvantage that suitable X-ray machines or gamma ray sources are very expensive. Although many other recombinogens are known, none gives a linear dose-response like X-rays and few are as convenient or give as reproducible results. Experiments with Saccharomyces cerevisiae reported in this paper show, however, that the near-ultraviolet radiation emitted by fluorescent sunlamps gives linear dose-response relations, as reproducible results as ionizing radiations, and map distances which correlate highly with those obtained by using (60)Co gamma rays. It is suggested that this convenient recombinogen may be a suitable low-cost substitute for ionizing radiations in fine structure mapping. 相似文献
98.
The purpose of this publication as a pedagogical contribution is to illustrate the uniqueness of the method Euler used to determine the unsteady flow of blood in the circulatory system. In his presentation, he accounts for the tapering of the vessels and their elastic behavior. The limitations of this study are based upon the extent of the development of the mathematics of his era. This work may be the first mathematical treatment of circulatory physiology and haemodynamics. Euler perhaps could very well be called the Father of Haemodynamics.The Determination of the Principals of the Motion of Blood through the Arteries.Supported in part by a grant from the American Heart Association (No. 62F4EG).This work was done during the tenure of an Established Investigatorship of the American Heart Association. 相似文献
99.
Lawrence W. Nichol Alexander G. Ogston Donald J. Winzor William H. Sawyer 《The Biochemical journal》1974,143(2):435-443
Theoretical expressions are derived for affinity chromatography of systems comprising an acceptor A with one binding site for attachment to a functional group X on the column matrix and one site for interaction with a small ligand B that specifically affects its elution. From a general relationship covering all possible interactions between A, B and X simpler expressions are derived for affinity systems in which only two equilibria operate. Methods are suggested whereby these simpler systems may be characterized in terms of the two pertinent equilibrium constants and the concentration of matrix-bound constituent. The means by which the theory may be adapted to affinity chromatography of acceptors with multiple binding sites for ligand is also illustrated. Results of partition experiments on the Sephadex G-100-lysozyme-d-glucose system in acetate-chloride buffer (I=0.17m), pH5.4, are used to demonstrate the feasibility of evaluating quantitatively affinity-chromatography interactions. Values of 30m(-1) and 1.2x10(6)m(-1) are obtained for the equilibrium constants for the reactions of lysozyme with glucose and Sephadex respectively, there being only an occasional binding site in the polysaccharide matrix (approximately 1 in 10(5) glucose residues). In a second experimental study the phytohaemagglutinin from Ricinus communis is subjected to frontal chromatography on Sepharose 4B in the presence of different concentrations of d-galactose, the results illustrating some of the difficulties and limitations that are likely to be encountered in quantitative studies of affinity-chromatographic systems. 相似文献
100.
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