全文获取类型
收费全文 | 447655篇 |
免费 | 41466篇 |
国内免费 | 1049篇 |
专业分类
490170篇 |
出版年
2018年 | 14499篇 |
2017年 | 13174篇 |
2016年 | 11636篇 |
2015年 | 7058篇 |
2014年 | 7825篇 |
2013年 | 10937篇 |
2012年 | 16050篇 |
2011年 | 24477篇 |
2010年 | 19580篇 |
2009年 | 15321篇 |
2008年 | 20126篇 |
2007年 | 21997篇 |
2006年 | 10977篇 |
2005年 | 10831篇 |
2004年 | 11306篇 |
2003年 | 11060篇 |
2002年 | 10677篇 |
2001年 | 15019篇 |
2000年 | 14854篇 |
1999年 | 12057篇 |
1998年 | 4663篇 |
1997年 | 4589篇 |
1996年 | 4353篇 |
1995年 | 4195篇 |
1994年 | 4191篇 |
1993年 | 4097篇 |
1992年 | 10177篇 |
1991年 | 9742篇 |
1990年 | 9552篇 |
1989年 | 9203篇 |
1988年 | 8670篇 |
1987年 | 8285篇 |
1986年 | 7478篇 |
1985年 | 7663篇 |
1984年 | 6417篇 |
1983年 | 5660篇 |
1982年 | 4583篇 |
1981年 | 4099篇 |
1980年 | 3908篇 |
1979年 | 6362篇 |
1978年 | 4849篇 |
1977年 | 4542篇 |
1976年 | 4238篇 |
1975年 | 4499篇 |
1974年 | 4925篇 |
1973年 | 4970篇 |
1972年 | 4751篇 |
1971年 | 4456篇 |
1970年 | 3600篇 |
1969年 | 3453篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
To ascertain the health risks that may be posed by the land application of sewage sludges, a scheme was devised to determine the types and numbers of pathogenic and potentially pathogenic bacteria present in sludges. A processing treatment was adapted to sludge to give a homogenate which yielded the greatest numbers of viable bacteria. Conventional methods were successful in enumerating Klebsiella, Staphylococcus, gram-negative enteric bacteria, and commonly used indicator organisms. Modifications of conventional methods improved the enumeration of Salmonella, Mycobacterium sp., fluorescent Pseudomonas sp., and Clostridium perfringens. However, Shigella methodology yielded only one isolate. Utilizing the proposed scheme, the population densities of these organisms were estimated in three domestic wastewater sludges. In light of these results, the potential impact of land application of sewage sludges is discussed. 相似文献
992.
993.
We analyzed the pattern of correlations among fitness components, herbivory, and resin characteristics in a natural all-aged
stand of ponderosa pine, to infer the strength and mechanism of natural selection on plant chemistry. Male and female cone
production were monitored yearly for 15 years, and levels of herbivory for 9 years in 165 trees. Resin flow rate and monoterpene
composition were determined for these same trees. Multiple regression of fitness components on resin characteristics showed
significant associations consistent with directional selection for increased resin flow rates and increased proportions of
α- and β-pinene, myrcene and terpinolene. However, negative correlations among monoterpene fractions of the resin constrained
the overall selection. Selective herbivory by aphids approached statistical significance and monoterpenes showed some (non-significant)
effect as deterrents against deer browse. Resin characteristics were not correlated with attack by cone insects or porcupines.
However, the association between resin characteristics and fitness is significantly different from that predicted by the path
coefficients involving herbivores. Therefore the hypothesis that these herbivores mediate selection on the resin is not supported
by the observed pattern of correlations among resin characteristics, herbivory, growth and fecundity. In this population,
most of the association between resin characteristics and fitness appears to be mediated by some other factor independent
of attack by herbivore species present.
Received: 18 March 1996/Accepted: 18 July 1996 相似文献
994.
A double-blind controlled trial in 24 lepromatous leprosy patients in reaction showed that clofazimine (Lamprene) controlled symptoms of erythema nodosum leprosum reaction in lepromatous leprosy better than prednisolone. Clofazimine also appeared to be significantly superior in preventing recurrence once the reaction had been controlled. There was a statistically significant rise in serum albumin among inpatients on clofazimine as compared with patients on prednisolone, but no difference in terms of neurological status, bacterial index, morphological index, and renal functions. Red/black hyperpigmentation was seen among practically all patients on clofazimine. No other side-effects or deleterious systemic effects were observed. 相似文献
995.
Structural polypeptides of three rhinoviruses 总被引:3,自引:0,他引:3
996.
997.
A number of recombinant cell lines which produce human tissue plasminogen activator (tPA) was obtained using different hosts--mouse, rat, hamster, simian and human cell lines. All types of recombinant lines secreted active r-tPA into conditioned medium. A slight difference between molecular weights of secreted variants of r-tPA was mediated by the different mechanisms of protein modification. Treatment of some recombinant cell lines with different substances resulted in increased levels of r-tPA production. 相似文献
998.
Interactions of luciferases isolated from Vibrio fischeri 6 and Escherichia coli JM109(pF3) (bearing cloned V. fischeri luxAB genes) with FMN reductase isolated from E. coli JM109 were studied. FMN reductase formed a stable complex with luciferase, suggesting similar properties of the FMN reductases in the taxonomically close families Vibrionaceae and Enterobacteriaceae. 相似文献
999.
A G Chuchalin V A Babushkina V Ia Arion R D Aspetov T B Sha?khinova 《Biulleten' eksperimental'no? biologii i meditsiny》1984,98(7):76-78
A study was made of the effect of T-activin on the biosynthesis of immune gamma-interferon. It was shown that in 27% of patients with chronic nonspecific pulmonary diseases, production of gamma-interferon by lymphocytes was substantially reduced during exacerbation of inflammatory process in the lungs. It was discovered that T-activin was not an interferon inductor but enhanced its synthesis in patients with a low capacity of producing immune interferon even at small doses of interferon inductor. The preparation does not produce any effect on this process in normal subjects and in patients showing the normal level of gamma-interferon. Thus T-activin can be used for stimulation of interferonogenesis. 相似文献
1000.
N. I. Krikunova M. B. Terenina E. L. Ruchkina T. A. Misharina 《Applied Biochemistry and Microbiology》2006,42(3):335-338
Sorption of aromatic compounds from aqueous solutions by cryotextures and suspensions of native cornstarches was studied by capillary gas chromatography. Acetophenone and benzyl alcohol were not sorbed by cryotropic-cornstarch gel and native-cornstarch suspension. A linear concentration dependence was found for aldehydes. Phenylethyl alcohol was characterized by a nonlinear concentration dependence. The presence of a benzene ring contributed to decreased binding (relative to the level characteristic of aliphatic compounds). The degree of binding depended considerably on the type of functional group in the aromatic compounds. Cryotextures were more potent than granules of native cornstarch in binding aromatic compounds. 相似文献