全文获取类型
收费全文 | 4439篇 |
免费 | 469篇 |
国内免费 | 2篇 |
出版年
2021年 | 34篇 |
2016年 | 38篇 |
2015年 | 76篇 |
2014年 | 85篇 |
2013年 | 128篇 |
2012年 | 160篇 |
2011年 | 174篇 |
2010年 | 131篇 |
2009年 | 108篇 |
2008年 | 154篇 |
2007年 | 163篇 |
2006年 | 157篇 |
2005年 | 170篇 |
2004年 | 179篇 |
2003年 | 188篇 |
2002年 | 203篇 |
2001年 | 43篇 |
2000年 | 35篇 |
1999年 | 69篇 |
1998年 | 60篇 |
1997年 | 47篇 |
1996年 | 42篇 |
1995年 | 38篇 |
1994年 | 43篇 |
1993年 | 50篇 |
1992年 | 41篇 |
1989年 | 40篇 |
1988年 | 41篇 |
1987年 | 36篇 |
1986年 | 35篇 |
1985年 | 64篇 |
1984年 | 76篇 |
1983年 | 67篇 |
1982年 | 127篇 |
1981年 | 116篇 |
1980年 | 96篇 |
1979年 | 69篇 |
1978年 | 66篇 |
1977年 | 58篇 |
1976年 | 77篇 |
1975年 | 54篇 |
1974年 | 54篇 |
1973年 | 59篇 |
1972年 | 42篇 |
1971年 | 44篇 |
1970年 | 47篇 |
1969年 | 37篇 |
1968年 | 37篇 |
1965年 | 34篇 |
1960年 | 38篇 |
排序方式: 共有4910条查询结果,搜索用时 13 毫秒
61.
62.
63.
Sphaerotilus natans required calcium for the production of sheaths and probably requires calcium for growth as well, though at a lower concentration. Neither strontium nor barium substituted for calcium. S. natans grew attached to the culture vessels of the continuous-flow apparatus even when no sheaths were produced. Tentative evidence showed that the requirement for calcium is shared by the manganese-oxidizing species S. discophorus. 相似文献
64.
Growth-promoting Activity of Spent Sulfite Liquor for Sphaerotilus natans Growing in a Continuous-Flow Apparatus 下载免费PDF全文
The calcium in ammonia-base spent sulfite liquor, unlike that in calcium-base spent liquor, is not available for growth of Sphaerotilus natans. It has not been possible to obtain a mixed slime with Sphaerotilus as the dominant organism in a continuous-flow apparatus fed spent sulfite liquor. 相似文献
65.
Dependence of Diaminopurine Utilization on the Mutational Site of Purine Auxotrophy in Bacillus subtilis II. Tracer Experiments 总被引:1,自引:1,他引:0
Tracer experiments were carried out in an attempt to explain why guanineless auxotrophs can use diaminopurine as a guanine replacement but nonexacting purine auxotrophs cannot do so. Cell suspensions of the nonexacting purineless Bacillus subtilis MB-1356 incorporated more radioactivity from diaminopurine-2-14C into nucleic acid than did guanineless B. subtilis MB-1517. The radioactivity in MB-1356 ribonucleic acid (RNA) was distributed in both adenine and guanine nucleotides, thus eliminating the possibility that the deamination of diaminopurine to guanine occurred predominantly on the level of nucleoside di- or triphosphates. Strain MB-1517 incorporated adenine-8-14C into nucleic acids extremely poorly. This correlated with results obtained with cell-free extracts; strain MB-1517 showed much less adenosine monophosphate (AMP) pyrophosphorylase activity than did MB-1356. Likewise, guanineless MB-1517 converted diaminopurine to its nucleotide much more slowly than did the nonexacting purine auxotroph. The results indicated that the lack of growth of nonexacting auxotrophs on diaminopurine alone is due not to an inability to convert the analogue to nucleic acid adenine but to the greater capacity of the nonexacting auxotrophs to convert diaminopurine to its 5′-ribonucleotide. Presumably, this compound, or a coenzyme analogue produced from it, inhibits growth of mutants which cannot make AMP de novo and only when the medium is devoid of adenine. 相似文献
66.
T. G. Amos 《Entomologia Experimentalis et Applicata》1967,10(1):1-6
The humidity reactions of intact and antennaless specimens of Carpophilus dimidiatus and C. hemipterus were studied. The results suggested that the hygroreceptors mediating a response to high humidities are situated on the antennae in both species and those mediating a response to low humidities, in the case of C. dimidiatus, elsewhere on the body.
On transfer from tropical Stored Products Centre, O.D.M., Slough, Bucks 相似文献
Résumé On a étudié la réaction à l'humidité de Carpophilus hemipterus et C. dimidiatus intacts et sans antennes. Les résultats suggèrent que les hygrorécepteurs qui répondent aux humidités élevées se trouvent sur l'antenne dans les deux espèces et ceux qui répondent aux basses humidités sur l'antenne de C. hemipterus et dans une autre partie du corps de C. dimidiatus.
On transfer from tropical Stored Products Centre, O.D.M., Slough, Bucks 相似文献
67.
By gentle sonic treatment, Escherichia coli cells were modified to permit penetration of actinomycin D, adenosine triphosphate, trypsin, ribonuclease, and polyuridylic acid. The behavior of these "soniplasts" as protein-synthesizing particles was investigated. 相似文献
68.
Electrical Properties of the Membranes of the Pleuropneumonia-Like Organism A 5969 总被引:2,自引:0,他引:2 下载免费PDF全文
The electrical properties of the pleuropneumonia-like organism A 5969 have been determined over the frequency range from 0.5 to 250 Mcps. The frequency dependence of the dielectric constant and conductivity of PPLO suspensions is completely consistent with the existence of a membrane. The PPLO has an internal conductance which in part reflects its ionic equilibrium with normal nutrient and macromolecular constituents. But it is fairly independent from variation in external ionic strength. 相似文献
69.
70.
Arthur Leznoff Harold Frank Paul Telner Jacob Rosensweig J. Leonard Brandt 《CMAJ》1964,91(22):1154-1160
Although Montreal is in an endemic area, significant clinical histoplasmosis with systemic manifestations has been, until recently, infrequently diagnosed. However, since the autumn of 1963, 31 cases of clinically significant histoplasmosis have been seen by the authors. These were divided into two groups: (1) patients in whom the diagnosis was established on the basis of histological and/or cultural demonstration of the fungus; (2) patients in whom the diagnosis was based on a positive histoplasmin skin test, a complement fixation antibody titre of 1:32 or greater and compatible clinical and radiological findings. An additional group of 11 patients who presented with erythema multiforme was investigated and a heretofore unrecognized relationship between histoplasmosis and erythema multiforme was established. 相似文献