全文获取类型
收费全文 | 2702篇 |
免费 | 236篇 |
专业分类
2938篇 |
出版年
2023年 | 10篇 |
2022年 | 22篇 |
2021年 | 48篇 |
2020年 | 26篇 |
2019年 | 42篇 |
2018年 | 47篇 |
2017年 | 41篇 |
2016年 | 60篇 |
2015年 | 108篇 |
2014年 | 118篇 |
2013年 | 169篇 |
2012年 | 221篇 |
2011年 | 213篇 |
2010年 | 125篇 |
2009年 | 98篇 |
2008年 | 196篇 |
2007年 | 206篇 |
2006年 | 175篇 |
2005年 | 175篇 |
2004年 | 157篇 |
2003年 | 145篇 |
2002年 | 129篇 |
2001年 | 28篇 |
2000年 | 17篇 |
1999年 | 32篇 |
1998年 | 40篇 |
1997年 | 29篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1962年 | 3篇 |
排序方式: 共有2938条查询结果,搜索用时 9 毫秒
161.
162.
Colquhoun JA Mexson J Goodfellow M Ward AC Horikoshi K Bull AT 《Antonie van Leeuwenhoek》1998,74(1-3):27-40
A large number of mycolate actinomycetes have been recovered from deep-sea sediments in the NW Pacific Ocean using selective isolation methods. The isolates were putatively assigned to the genus Rhodococcus on the basis of colony characteristics and mycolic acid profiles. The diversity among these isolates and their relationship to type strains of Rhodococcus and other mycolate taxa were assessed by Curie point pyrolysis mass spectrometry (PyMS). Three major (A, C, D) and two minor (B, E) groups were defined by PyMS. Cluster A was a large group of isolates recovered from sediment in the Izu Bonin Trench (2679 m); Cluster C comprised isolates from both the Izu Bonin Trench (6390 and 6499 m) and from the Japan Trench (4418, 6048 and 6455 m). These Cluster C isolates showed close similarity to Dietzia maris and this was subsequently confirmed using molecular methods. Cluster D contained isolates recovered from a sediment taken from a depth of 1168m in Sagami Bay and were identified as members of the terrestrial species Rhodococcus luteus. Clusters B and E had close affinities with members of the genera Gordonia and Mycobacterium. The presence of Thermoactinomyces in certain of the deep-sea sediments studied was indicative of the movement of terrestrial material into the ocean depths.16S ribosomal RNA gene sequence analyses produced excellent definition of most genera of the mycolata, and indicated that the among the deep sea isolates (1) were novel species of Corynebacterium, Gordonia and Mycobacterium, and (2) a Sea of Japan isolate the phylogenetic depth of which suggests the possibility of a new genus. Polyphasic taxonomic analysis revealed considerable diversity among the deep sea rhodococci and evidence for recently diverged species or DNA groups. 相似文献
163.
Joanne Sloan-Lancaster John Presley Jan Ellenberg Tetsuo Yamazaki Jennifer Lippincott-Schwartz Lawrence E. Samelson 《The Journal of cell biology》1998,143(3):613-624
The nonreceptor protein tyrosine kinase ZAP-70 is a critical enzyme required for successful T lymphocyte activation. After antigenic stimulation, ZAP-70 rapidly associates with T cell receptor (TCR) subunits. The kinetics of its translocation to the cell surface, the properties of its specific interaction with the TCRζ chain expressed as a chimeric protein (TTζ and Tζζ), and its mobility in different intracellular compartments were studied in individual live HeLa cells, using ZAP-70 and Tζζ fused to green fluorescent protein (ZAP-70 GFP and Tζζ–GFP, respectively). Time-lapse imaging using confocal microscopy indicated that the activation-induced redistribution of ZAP-70 to the plasma membrane, after a delayed onset, is of long duration. The presence of the TCRζ chain is critical for the redistribution, which is enhanced when an active form of the protein tyrosine kinase Lck is coexpressed. Binding specificity to TTζ was indicated using mutant ZAP-70 GFPs and a truncated ζ chimera. Photobleaching techniques revealed that ZAP-70 GFP has decreased mobility at the plasma membrane, in contrast to its rapid mobility in the cytosol and nucleus. Tζζ– GFP is relatively immobile, while peripherally located ZAP-70 in stimulated cells is less mobile than cytosolic ZAP-70 in unstimulated cells, a phenotype confirmed by determining the respective diffusion constants. Examination of the specific molecular association of signaling proteins using these approaches has provided new insights into the TCRζ–ZAP-70 interaction and will be a powerful tool for continuing studies of lymphocyte activation. 相似文献
164.
165.
cis-Isomers of Cytokinins Predominate
in Chickpea Seeds throughout Their
Development 总被引:2,自引:1,他引:1 下载免费PDF全文
Robert Joseph Neil Emery Laurent Leport Joanne Edith Barton Neil Clifford Turner Craig Anthony Atkins 《Plant physiology》1998,117(4):1515-1523
Trans-isomers of cytokinins (CK) are thought to predominate and have greater biological activity than corresponding cis-isomers in higher plants. However, this study demonstrates a system within which the predominant CK are cis-isomers. CK were measured at four developmental stages in developing chickpea (Cicer arietinum L. cultivar Kaniva) seeds by gas chromatography-mass spectrometry. Concentrations were highest at an early endospermic fluid stage and fell considerably when the cotyledons expanded. The cis-isomers of zeatin nucleotide ([9R-MP]Z), zeatin riboside ([9R]Z), and zeatin (Z) were present in greater concentrations than those of corresponding trans-isomers: (trans)[9R-MP]Z, (trans)[9R]Z, (trans)Z, or dihydrozeatin riboside. Dihydrozeatin, dihydrozeatin nucleotide, and the isopentenyl-type CK concentrations were either low or not detectable. Root xylem exudates also contained predominantly cis-isomers of [9R-MP]Z and [9R]Z. Identities of (cis)[9R]Z and (cis)Z were confirmed by comparison of ion ratios and retention indices, and a full spectrum was obtained for (cis)[9R]Z. Tissues were extracted under conditions that minimized the possibility of RNase hydrolysis of tRNA following tissue disruption, being a significant source of the cis-CK. Since no isomerization of (trans)[2H]CK internal standards occurred, it is unlikely that the cis-CK resulted from enzymic or nonenzymic isomerization during extraction. Although quantities of total CK varied, similar CK profiles were found among three different chickpea cultivars and between adequately watered and water-stressed plants. Developing chickpea seeds will be a useful system for investigating the activity of cis-CK or determining the origin and metabolism of free CK. 相似文献
166.
Biogenesis and function of the lipidic structures of pollen grains 总被引:31,自引:0,他引:31
Pollen grains contain several lipidic structures, which play a key role in their development as male gametophytes. The elaborate
extracellular pollen wall, the exine, is largely formed from acyl lipid and phenylpropanoid precursors, which together form
the exceptionally stable biopolymer sporopollenin. An additional extracellular lipidic matrix, the pollen coat, which is particularly
prominent in entomophilous plants, covers the interstices of the exine and has many important functions in pollen dispersal
and pollen-stigma recognition. The sporopollenin and pollen coat precursors are both synthesised in the tapetum under the
control of the sporophytic genome, but at different stages of development. Pollen grains also contain two major intracellular
lipidic structures, namely storage oil bodies and an extensive membrane network. These intracellular lipids are synthesised
in the vegetative cell of the pollen grain under the control of the gametophytic genome. Over the past few years there has
been significant progress in elucidating the composition, biogenesis and function of these important pollen structures. The
purpose of this review is to describe these recent advances within the historical context of research into pollen development.
Received: 1 November 1997 / Revision accepted: 3 February 1998 相似文献
167.
dCAPS, a simple technique for the genetic analysis of single nucleotide polymorphisms: experimental applications in Arabidopsis thaliana genetics 总被引:19,自引:9,他引:10
Michael M. Neff Joseph D. Neff Joanne Chory Alan E. Pepper 《The Plant journal : for cell and molecular biology》1998,14(3):387-392
PCR-based detection of single nucleotide polymorphisms is a powerful tool for the plant geneticist. Cleaved amplified polymorphic sequence analysis is the most widely used approach for the detection of single nucleotide polymorphisms. However, this technique is limited to mutations which create or disrupt a restriction enzyme recognition site. This paper presents a modification of this technique where mismatches in a PCR primer are used to create a polymorphism based on the target mutation. This technique is useful for following known mutations in segregating populations and genetic mapping of isolated DNAs used for positional based cloning of new genes. In addition, a computer program has been developed that facilitates the design of these PCR primers. 相似文献
168.
Brennan J Dillon P O'Kennedy R 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2003,786(1-2):327-342
We have generated a single chain antigen binding protein (scFv) recognising morphine. Variable regions of heavy (V(H)) and light (V(L)) chain antibody genes isolated from a murine immune repertoire were connected via a glycine-serine linker and cloned into the expression vector pAK 400. The scFv was produced in Escherichia coli JM83 yielding a functional protein of approximately M(r) 30000. Immunoaffinity chromatography using M3G-BSA-Sepharose column proved most effective for scFv purification. Purity was monitored by SDS-PAGE and Western blotting and the scFv characterised using ELISA and BIAcore. The scFv was capable of specifically binding free morphine in solution and was applicable to real sample analysis in saliva. In order to express a bivalent "minibody" the scFv gene was recloned into a vector containing a gene encoding a helix for dimerisation. The scFv was expressed as a protein of M(r) 75000 and retained its antibody binding capabilities. Cloning the scFv gene into a vector containing the bacterial alkaline phosphatase gene produced a bifunctional molecule, which retained the binding activity of the parental scFv along with the enzymatic activity of alkaline phosphatase. 相似文献
169.
Anne Mercier Joanne Bertaux Jérôme Lesobre Kevin Gravouil Julien Verdon Christine Imbert 《Biofouling》2016,32(3):287-299
Electromagnetic field (EMF) treatment has proven to be effective against mineral scaling in water systems. Therefore, it should be assessed for the treatment of other deposits such as biofilms. In this study, a commercial device producing low-frequency EMF (1–10 kHz) was applied to a reactor fed with natural water for 45 days. The treatment promoted the concentration of microorganisms in suspension and limited the amount of sessile microorganisms in the biofilm, as determined by the measurement of total DNA, qPCR and microscopy. The structure of the bacterial community was assessed by t-RFLP and pyrosequencing analysis. The results showed that EMF treatment affected both planktonic and sessile community composition. EMFs were responsible for a shift in classes of Proteobacteria during development of the biofilm. It may be speculated that the EMF treatment affected particle solubility and/or microorganism hydration. This study indicated that EMFs modulated biofilm formation in natural water. 相似文献
170.
Parker MF Barten DM Bergstrom CP Bronson JJ Corsa JA Deshpande MS Felsenstein KM Guss VL Hansel SB Johnson G Keavy DJ Lau WY Mock J Prasad CV Polson CT Sloan CP Smith DW Wallace OB Wang HH Williams A Zheng M 《Bioorganic & medicinal chemistry letters》2007,17(16):4432-4436
A series of N-alkylbenzenesulfonamides were developed from a high throughput screening hit. Classic and parallel synthesis strategies were employed to produce compounds with good in vitro and in vivo gamma-secretase activity. 相似文献