全文获取类型
收费全文 | 3204篇 |
免费 | 200篇 |
国内免费 | 8篇 |
出版年
2022年 | 17篇 |
2021年 | 70篇 |
2020年 | 62篇 |
2019年 | 59篇 |
2018年 | 106篇 |
2017年 | 104篇 |
2016年 | 129篇 |
2015年 | 133篇 |
2014年 | 145篇 |
2013年 | 217篇 |
2012年 | 193篇 |
2011年 | 199篇 |
2010年 | 145篇 |
2009年 | 90篇 |
2008年 | 124篇 |
2007年 | 121篇 |
2006年 | 113篇 |
2005年 | 89篇 |
2004年 | 85篇 |
2003年 | 94篇 |
2002年 | 75篇 |
2001年 | 56篇 |
2000年 | 51篇 |
1999年 | 36篇 |
1998年 | 40篇 |
1997年 | 26篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 27篇 |
1991年 | 35篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 38篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1979年 | 17篇 |
1973年 | 20篇 |
1955年 | 29篇 |
1954年 | 77篇 |
1953年 | 42篇 |
1952年 | 27篇 |
1951年 | 20篇 |
1950年 | 56篇 |
排序方式: 共有3412条查询结果,搜索用时 31 毫秒
61.
Photosynthetic Characteristics of Portulaca grandiflora, a Succulent C(4) Dicot : CELLULAR COMPARTMENTATION OF ENZYMES AND ACID METABOLISM 总被引:4,自引:4,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The succulent, cylindrical leaves of the C4 dicot Portulaca grandiflora possess three distinct green cell types: bundle sheath cells (BSC) in radial arrangement around the vascular bundles; mesophyll cells (MC) in an outer layer adjacent to the BSC; and water storage cells (WSC) in the leaf center. Unlike typical Kranz leaf anatomy, the MC do not surround the bundle sheath tissue but occur only in the area between the bundle sheath and the epidermis. Intercellular localization of photosynthetic enzymes was characterized using protoplasts isolated enzymatically from all three green cell types. 相似文献
62.
Biodegradation of [C]tri-p-cresyl phosphate was studied in a laboratory model sewage treatment system to develop information on the nature of its transformation products. In 24-h experiments, 70 to 80% of tri-p-cresyl phosphate added at the 1-mug/ml level was degraded. The remaining parent compound was associated with the sludge solids. The major metabolite extracted with ethyl ether from the aqueous phase was identified as p-hydroxybenzoic acid by gas chromatography-mass spectrometry. Two unstable ether-extractable metabolites were not identified. The half-life of [C]tri-p-cresyl phosphate was estimated to be 7.5 h. 相似文献
63.
64.
65.
Enzymes of the C4, C3 pathway and photorespiration have beenanalyzed for P. hians and P. milioides, which have chlorenchymatousbundle sheath cells in the leaves. On whole leaf extracts thelevels of PEP carboxylase are relatively low compared to C4species, RuDP carboxylase is typical of C3 species, and enzymesof photorespiratory metabolism appear somewhat intermediatebetween C3 and C4. Substantial levels of PEP carboxylase, RuDPcarboxylase, and photorespiratory enzymes were found in bothmesophyll and bundle sheath cells. Low levels of C4-acid decarboxylatingenzymes may limit the capacity for C4 photosynthesis in P. hiansand P. milioides. The results on enzyme activity and distributionbetween mesophyll and bundle sheath cells are consistent withCO2 fixation via C3 pathway in these two species.
1 This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and bythe University of Wisconsin Research Committee with funds fromthe Wisconsin Alumni Research Foundation; and by the NationalScience Foundation Grant BMS 74-09611. (Received September 16, 1975; ) 相似文献
66.
Fermentation of a medium containing 5% 2-deoxy-D-glucose and barium carbonate by a strain ofPseudomonas aeruginosa yielded barium 2-deoxy-d-gluconate. The yield was 77% theoretical. The strain in question makes it possible to prepare directly calcium, magnesium, manganese and ferrous salts of 2-deoxy-d-glueonic acid. A treatment of 6% solution of 2-deoxy-d-glucose with commercial glucose oxidase preparation caused also a complete dehydrogenation. 相似文献
67.
Plant desiccation and protein synthesis: an in vitro system from dry and hydrated mosses using endogenous and synthetic messenger ribonucleic Acid
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The conditions and requirements for an in vitro protein synthesizing system from the moss Tortula ruralis are outlined. Using this system the effects of desiccation, achieved quickly or slowly, were studied. Slowly dried moss retained fewer polyribosomes on desiccation but more active ribosomes than rapidly dried moss. Even in the completely desiccated moss the polyribosomes and/or free ribosomes present have retained their synthetic capacities. On rehydration, the slowly dried moss resumed protein synthesis more quickly than moss previously desiccated rapidly. Moss ribosomes are cycloheximide sensitive and chloramphenicol insensitive and thus the major protein synthesis occurs within the cytoplasm on rehydration. Extracted polyribosomes per se can withstand desiccation to a significant extent, suggesting that protection by the cytoplasm might not be necessary. The aquatic moss Hygrohypnum luridum can retain polyribosomal and ribosomal activity during desiccation, but this decreases greatly on rehydration. 相似文献
68.
69.
M. Kučera 《Journal of invertebrate pathology》1980,35(3):304-310
The high molecular fraction of the extract from Metarhizium anisopliae grown on wheat bran contains proteolytic enzymes which are toxic for Galleria mellonella larvae. The complex of proteases was fractionated using precipitation with ammonium sulfate, gel filtration, and electrofocusing. Two components have been found: one with the optimum of activity on hemoglobin at pH 6.5, and the second with the optimum around pH 9. The prevailing protease acting at pH 6.5 was inhibited by phenylmethylsulfonyl fluoride and the inhibition was followed by decrease of toxicity. The molecular weights of the enzymes are 35 × 103 and 71 × 103. 相似文献
70.
Jakub Hofman Radim Ku?era Daniela Cihalova Jiri Klimes Martina Ceckova Frantisek Staud 《PloS one》2013,8(10)
Purine cyclin-dependent kinase inhibitors have been recognized as promising candidates for the treatment of various cancers; nevertheless, data regarding interaction of these substances with drug efflux transporters is still lacking. Recently, we have demonstrated inhibition of breast cancer resistance protein (ABCG2) by olomoucine II and purvalanol A and shown that these compounds are able to synergistically potentiate the antiproliferative effect of mitoxantrone, an ABCG2 substrate. In this follow up study, we investigated whether olomoucine II and purvalanol A are transported by ABCG2 and ABCB1 (P-glycoprotein). Using monolayers of MDCKII cells stably expressing human ABCB1 or ABCG2, we demonstrated that olomoucine II, but not purvalanol A, is a dual substrate of both ABCG2 and ABCB1. We, therefore, assume that pharmacokinetics of olomoucine II will be affected by both ABCB1 and ABCG2 transport proteins, which might potentially result in limited accumulation of the compound in tumor tissues or lead to drug-drug interactions. Pharmacokinetic behavior of purvalanol A, on the other hand, does not seem to be affected by either ABCG2 or ABCB1, theoretically favoring this drug in the potential treatment of efflux transporter-based multidrug resistant tumors. In addition, we observed intensive sulfatation of olomoucine II in MDCKII cell lines with subsequent active efflux of the metabolite out of the cells. Therefore, care should be taken when performing pharmacokinetic studies in MDCKII cells, especially if radiolabeled substrates are used; the generated sulfated conjugate may largely contaminate pharmacokinetic analysis and result in misleading interpretation. With regard to chemical structures of olomoucine II and purvalanol A, our data emphasize that even drugs with remarkable structure similarity may show different pharmacokinetic behavior such as interactions with ABC transporters or biotransformation enzymes. 相似文献