全文获取类型
收费全文 | 1007篇 |
免费 | 76篇 |
专业分类
1083篇 |
出版年
2022年 | 18篇 |
2021年 | 46篇 |
2020年 | 29篇 |
2019年 | 15篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 27篇 |
2015年 | 36篇 |
2014年 | 48篇 |
2013年 | 56篇 |
2012年 | 70篇 |
2011年 | 72篇 |
2010年 | 38篇 |
2009年 | 34篇 |
2008年 | 50篇 |
2007年 | 53篇 |
2006年 | 36篇 |
2005年 | 36篇 |
2004年 | 37篇 |
2003年 | 29篇 |
2002年 | 18篇 |
2001年 | 25篇 |
2000年 | 29篇 |
1999年 | 27篇 |
1998年 | 12篇 |
1997年 | 20篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1972年 | 7篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1965年 | 4篇 |
1963年 | 3篇 |
排序方式: 共有1083条查询结果,搜索用时 15 毫秒
1.
2.
Mini-mu derivatives carrying plasmid replicons can be used to clone genesin vivo. This method was adopted to generate phasmid clones which were later screened for their ability of restore nitrofurantoin
sensitivity of a nitrofuran-resistant host by eliciting nitroreductase activity. One phasmid-derived clone (pAJ101) resulted
in considerable increase in nitroreductase activity when introduced into a nitrofurantoin-resistant mutant ofEscherichia coli with reduced nitroreductase activity. Subsequently, a 1.8 kb fragment obtained from pAJ101 by partial digestion with 5au3A,
was subcloned into pUC18 to yield pAJ102. The nitroreductase activity attributable to pAJ102 was capable of reducing both
nitrofurantoin and nitrofurazone. The polypeptides encoded by pAJ102 were identified by the minicell method. A large, well-defined
band corresponding to 37 kDa and a smaller, less-defined band corresponding to 35 kDa were detected. Tnl000 mutagenesis was
used to delineate the coding segment of the 1.8 kb insert of pAJ102. A 0.8 kb stretch of DNA was shown to be part of the nitroreductase
gene. The gene was mapped at 19 min on theEscherichia coli linkage map. 相似文献
3.
Nitrofurantoin (NF)-resistant mutants of Escherichia coli were isolated as described previously (18). One of the mutants (SSJ-2) was found to possess NF reductase activity equal to that of its parent (E. coli KL16). Two NF-resistant transductional derivatives, SSJ-2A and SSJ-2B, were isolated using SSJ-2 as the donor. SSJ-2 was found to be a double mutant carrying two mutations, nfnA and nfnB, while SSJ-2A (nfnA) and SSJ-2B (nfnB) carried these mutations individually. Heated extracts from SSJ-2A and SSJ-2B were found to inhibit the reduction of NF by unheated extracts of the NF-sensitive strain E. coli KL16 in vitro. Unheated extracts of these mutants reduced NF poorly relative to E. coli KL16. The poor reduction of NF by unheated extracts of SSJ-2A and SSJ-2B was greatly stimulated by heated extracts of SSJ-2B and SSJ-2A, respectively, and also by heated extracts of E. coli KL16. When heated extracts of SSJ-2A and SSJ-2B were mixed in a particular ratio and added to unheated extracts of E. coli KL16 they lost their inhibitory activity. Two proteins, designated inhibitor A and inhibitor B, have been partially purified from heated extracts of SSJ-2B and SSJ-2A, respectively. Their respective molecular weights, as determined by gel chromatography, were 37,000 and 20,500. The two inhibitors bound nitrofurantoin in vitro, and the NF-binding ability was lost when mixed in the molar ration of 3/1 (B/A). These observations were rationalized in terms of a hypothesis which explains (i) maximal NF reduction in wild-type cells, (ii) maximal NF reduction of nfnA-nfnB- double mutant, and (iii) poor NF reduction in nfnA- or nfnB- single mutants. The possible role of these inhibitors in nitrofurantoin resistance is also discussed. 相似文献
4.
Identification of the peptides of the crystals of Bacillus thuringiensis var israelensis involved in the mosquito larvicidal activity 总被引:2,自引:0,他引:2
R Sriram H Kamdar K Jayaraman 《Biochemical and biophysical research communications》1985,132(1):19-27
Tryptic digestion of the proteins from the purified crystals of B.thuringiensis var israelensis resulted in the decline of high molecular weight peptides without the loss of mosquito larvicidal activity, measured after immobilization of the digests with DEAE- Sephadex A 50 beads. Amongst the peptides generated (less than 44 kDa), a 21 kDa peptide was immunoreactive to the crystal antiserum. Analysis of the peptides released from spores of the toxic (Cry+) and non-toxic (Cry-) strains has revealed a pattern in which only the 26kDa peptide was missing in the Cry-strain. Sporulation and crystal formation were dissociated by the addition of the antibiotic netropsin, which could also inhibit the crystal assembly, without considerable decrease of the larvicidal activity and retention of the 26kDa peptide. These results implicate the 26kDa peptide in the larvicidal action. 相似文献
5.
6.
7.
S L Monfort S Jayaraman S E Shideler B L Lasley A G Hendrickx 《Journal of medical primatology》1986,15(1):17-26
Investigations were undertaken to determine the applicability of recently reported specific radioimmunoassays for urinary estrone conjugates and progesterone metabolites for monitoring ovarian function in the cynomolgus macaque (Macaca fasciularis) and other macaque species. Mean estrone conjugate measurements appear to accurately reflect the preovulatory estrogen peak in both conceptive (n = 5) and nonconceptive (n = 6) cycles, as well as to indicate early pregnancy through increases which are significantly elevated by Day + 15 (p less than 0.049) post estrone conjugates peak. The mean luteal phase levels of these progesterone metabolites are significantly elevated by Day + 14 (p less than 0.012) in conceptive cycles when compared to the mean values for nonconceptive cycles. 相似文献
8.
The ability of recombinant/purified cytokines to augment delayed-type hypersensitivity (DTH) responses was investigated. Suboptimal doses of haptenized SC were treated in vitro with purified or recombinant derived cytokines and tested for their ability to enhance DTH in vivo. With the use of this protocol, it was shown that both human and mouse rIL-6, as well as mouse rTNF-alpha, potentiated DTH in a dose-dependent manner. In accordance with these data, IL-6/TNF-alpha-containing supernatant from long term nonlymphoid cell lines also possessed the ability to augment DTH. By using the same protocol, we have also identified T cell hybridomas that produce DTH-augmenting activity constitutively. The hybridoma-derived factor, termed the T cell enhancing factor (TCEF), was functionally distinguishable from the defined cytokines IL-1 through IL-6, IFN-gamma, and TNF by bioassay. Furthermore, RNA derived from the hybridoma failed to hybridize with cDNA probes specific for IL-1 to IL-6, IFN-gamma, TNF-alpha, and granulocyte-macrophage CSF. Further characterization of the serum-free conditioned media derived from the hybridoma indicated that the TCEF was a soluble acid labile glycoprotein (Mr greater than 30,000). Finally, we investigated the cellular requirements for DTH augmentation by IL-6, TNF-alpha, and TCEF; all are dependent upon the presence of T cells in the immunizing inoculum. We propose that these cytokines play a critical role in the development of DTH responses in vivo. 相似文献
9.
S. G. Tan J. S. F. Barker O. S. Selvaraj T. K. Mukherjee Y. F. Wong 《Biochemical genetics》1993,31(5-6):223-230
We have developed the methodologies for typing and family studies to establish the modes of inheritance of water buffalo red cell acid phosphatase (Acp), protease inhibitor (Pi), and group-specific component (Gc) on isoelectric focusing and albumin (Alb), red cell -esterase-3 (Est-3), and catalase (Cat) on polyacrylamide gel electrophoresis. Family studies showed that Pi, Gc, Alb, and Cat are coded by autosomal genes with two codominant alleles, while Est-3 is autosomal with two codominant alleles and a recessive null allele and Acp exhibits three codominant alleles.This project was funded by the Australian Centre for International Agricultural Research through Grant PN 8364 and the Malaysian programme for Intensification of Research in Priority Areas through Grant IRPA 1-07-05-057. 相似文献
10.
D. Mayilvahanan G. Annadurai V. Raju M. Chellapandian M. R. V. Krishnan Kunthala Jayaraman 《Bioprocess and biosystems engineering》1996,15(6):323-326
Techniques for possible higher and rapid production of citric acid from the well known industrial medium i.e. molasses has
been reported using Aspergillus niger. This includes optimization of the total reducing sugar (TRS) and nutrients like nitrogen
and phosphorous. The long and unproductive lag periods normally associated with this type of fermentation has been reduced.
These strategies are discussed in detail.
Dr. M. Chellapandian is thankful to the Council of Scientific and Industrial Research, New Delhi, for the award of research
associateship. 相似文献