全文获取类型
收费全文 | 2206篇 |
免费 | 192篇 |
出版年
2022年 | 29篇 |
2021年 | 62篇 |
2020年 | 41篇 |
2019年 | 37篇 |
2018年 | 35篇 |
2017年 | 36篇 |
2016年 | 49篇 |
2015年 | 105篇 |
2014年 | 99篇 |
2013年 | 106篇 |
2012年 | 127篇 |
2011年 | 150篇 |
2010年 | 87篇 |
2009年 | 75篇 |
2008年 | 94篇 |
2007年 | 133篇 |
2006年 | 94篇 |
2005年 | 85篇 |
2004年 | 77篇 |
2003年 | 83篇 |
2002年 | 69篇 |
2001年 | 32篇 |
2000年 | 24篇 |
1999年 | 16篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 19篇 |
1974年 | 20篇 |
1973年 | 17篇 |
1972年 | 11篇 |
1968年 | 12篇 |
1964年 | 14篇 |
1962年 | 11篇 |
1960年 | 10篇 |
1958年 | 11篇 |
排序方式: 共有2398条查询结果,搜索用时 62 毫秒
51.
Peter Reisinger Heinz Seidel Harald Tschesche Walter P. Hammes 《Archives of microbiology》1980,127(3):187-193
Nisin inhibits murein synthesis with concomitant accumulation of undecaprenyl-pyrophospho-MurNAc(pentapeptide) (lipid intermediate I). This inhibition is caused by the formation of a complex between the antibiotic and lipid intermediate I. Undecaprenyl-pyrophospho-MurNAc(pentapeptide)-GlcNAc (lipid intermediate II) also forms a complex with nisin. However, when murein synthesis is inhibited by nisin, this latter complex is not formed since lipid intermediate II is no longer synthesized.Abbreviations GlcNAc
N-acetylglucosamine
- MurNAc
N-acetylmuramyl
- Pentapeptide
Ala--DGlu-Lys-DAla-DAla
- C55
undecaprenol
Dedicated to Professor Otto Kandler on occasion of his 60th birthday 相似文献
52.
53.
In this paper experimental results on the size, transport and stability of cytoplasmic Balbiani ring RNA and on its appearance in polysomes are presented. Cytoplasmic RNA of salivary gland cells from Chironomus thummi contains two large RNA fractions of about 20×106 dalton and 10×106 dalton in size. These RNA fractions correspond both to Balbiani ring BR 1 RNA and BR 2 RNA and are apparently transported from nucleus into cytoplasm without a significant size reduction. Chase experiments illustrate a great stability of giant cytoplasmic Balbiani ring RNA molecules and exclude the possibility of a precursor-product relationship between these and smaller BR RNA molecules also found in cytoplasm. A part of giant cytoplasmic Balbiani ring RNA molecules is bound to poly(U)-sepharose columns and should, therefore, contain poly(A)-sequences. — Polysomes of salivary gland cells extracted by a gentle lysis procedure and centrifuged through sucrose gradients are characterized by a rather broad sedimentation profile. Polysome sizes up to about 800 S have been detected, but in no case a distinct polysome fraction corresponding in size to Balbiani ring RNA has been observed. Hybridization of polysomal RNA with salivary gland chromosomes in situ resulted in labelling of both Balbiani rings BR 1 and BR 2. 相似文献
54.
Suspension cultures of Perilla ocymoides accumulate caffeic acid, both in free and ester forms, as the only phenylpropanoid end metabolite. Increased levels of growth substances influenced the levels of PAL activity and phenolic accumulation so that cytokinin stimulated, while auxin repressed both parameters. The regulatory role of caffeyl compounds is discussed in relation to their accumulation during the early exponential phase of culture growth. 相似文献
55.
C C Culvenor J A Edgar M V Jago A Qutteridge J E Peterson L W Smith 《Chemico-biological interactions》1976,12(3-4):299-324
62 pyrrolizidine alkaloids and derivatives have been screened for acute and chronic hepato- and pneumotoxicity by the single dose method previously described. This procedure is satisfactory for the compounds of medium to high hepatotoxicity but failed to detect toxicity in certain other compounds of known, low hepatotoxicity. New findings significant in relation to hepatotoxicity are as follows: (i) On a molar basis, diesters of heliotridine and retronecine are about 4 times as toxic as the respective mono-esters and heliotridine esters are 2-4 times as toxic as retronecine esters. (ii) Crotanecine esters are less toxic than retronecine esters, and the 6,9-diester madurensine, 2-4 times less toxic than the 7,9-diester anacrotine (the difference being ascribed to there being only one reactive alkylating centre in the toxic metabolite from madurensine). (iii) Hepatotoxicity was confirmed for 7-angelylheliotridine but not observed for 9-angelyheliotridine and 7- and 9-angelylretronecine. (iv) Other significant compounds failing to induce hepatotoxicity were 9-pivalyl- and 7,9-dipivalyheliotridine, the alpha- and beta-epoxides of monocrotaline, 7-angelyl-1-methylenepyrrolizidine and the methiodides of monocrotaline and senecionine. The following compounds are readily converted by rat liver microsomes in vitro into dehydroheliotridine (or dehydroretronecine): 7- and 9-angelyheliotridine, 7- and 9-angelylretronecine, 7,9-dipivalylheliotridine and otosenine. 7,9-Divalerylheliotridine, the alpha- and beta-epoxides of monocrotaline, and retusamine yield pyrrolic metabolites more slowly. The preparation and characterisation of several alkaloid derivatives are described. Chronic lung lesions were produced by most compounds which gave chronic liver lesions, although a higher dose was required in some instances. This requirement may sometimes mean that chronic lung lesions cannot be induced because of the intervention of acute or peracute deaths. Apart from this factor, structure activity requirements for pneumotoxicity are the same as for hepatotoxicity, consistent with their being both caused by the same toxic metabolites. 相似文献
56.
57.
58.
Raquel Santos Jorge Troy R. Hawkins Edgar G. Hertwich 《The International Journal of Life Cycle Assessment》2012,17(1):9-15
Purpose
The purpose of this study is to provide life cycle inventory data and results for components of electrical grids to the larger community of life cycle assessment practitioners. This article is the first in a series of two, each focusing on different components of power grids. In part 1, the objects under scope are power lines and cables. Systems for overhead, underground, and subsea transmission are modeled here, including HVDC systems used in long-distance transmission. 相似文献59.
60.