全文获取类型
收费全文 | 929篇 |
免费 | 68篇 |
国内免费 | 1篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 29篇 |
2015年 | 32篇 |
2014年 | 32篇 |
2013年 | 33篇 |
2012年 | 74篇 |
2011年 | 59篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 49篇 |
2007年 | 55篇 |
2006年 | 60篇 |
2005年 | 61篇 |
2004年 | 49篇 |
2003年 | 53篇 |
2002年 | 39篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 17篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1975年 | 2篇 |
1971年 | 3篇 |
1965年 | 3篇 |
1963年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有998条查询结果,搜索用时 15 毫秒
81.
82.
Rémy C. Lemoine Ann C. Petersen Lina Setti Jutta Wanner Andreas Jekle Gabrielle Heilek André deRosier Changhua Ji Pamela Berry David Rotstein 《Bioorganic & medicinal chemistry letters》2010,20(2):704-708
Replacement of a secondary amide with an N-acyl or N-sulfonyl gem-disubstituted azacyle in a series of CCR5 antagonists led to the identification of compounds with excellent in vitro HIV antiviral activity and increased intrinsic membrane permeability. 相似文献
83.
84.
Bindschedler LV Tuerck J Maunders M Ruel K Petit-Conil M Danoun S Boudet AM Joseleau JP Bolwell GP 《Phytochemistry》2007,68(21):2635-2648
Extractability and recovery of cellulose from cell walls influences many industrial processes and also the utilisation of biomass for energy purposes. The utility of genetic manipulation of lignin has proven potential for optimising such processes and is also advantageous for the environment. Hemicelluloses, particularly secondary wall xylans, also influence the extractability of cellulose. UDP-glucuronate decarboxylase produces UDP-xylose, the precursor for xylans and the effect of its down-regulation on cell wall structure and cellulose extractability in transgenic tobacco has been investigated. Since there are a number of potential UDP-glucuronate decarboxylase genes, a 490bp sequence of high similarity between members of the family, was chosen for general alteration of the expression of the gene family. Sense and antisense transgenic lines were analysed for enzyme activity using a modified and optimised electrophoretic assay, for enzyme levels by western blotting and for secondary cell wall composition. Some of the down-regulated antisense plants showed high glucose to xylose ratios in xylem walls due to less xylose-containing polymers, while arabinose and uronic acid contents, which could also have been affected by any change in UDP-xylose provision, were unchanged. The overall morphology and stem lignin content of the modified lines remained little changed compared with wild-type. However, there were some changes in vascular organisation and reduction of xylans in the secondary walls was confirmed by immunocytochemistry. Pulping analysis showed a decreased pulp yield and a higher Kappa number in some lines compared with controls, indicating that they were less delignified, although the level of residual alkali was reduced. Such traits probably indicate that lignin was less available for removal in a reduced background of xylans. However, the viscosity was higher in most antisense lines, meaning that the cellulose was less broken-down during the pulping process. This is one of the first studies of a directed manipulation of hemicellulose content on cellulose extractability and shows both positive and negative outcomes. 相似文献
85.
Frerker N Wagner L Wolf R Heiser U Hoffmann T Rahfeld JU Schade J Karl T Naim HY Alfalah M Demuth HU von Hörsten S 《Peptides》2007,28(2):257-268
N-terminal truncation of NPY has important physiological consequences, because the truncated peptides lose their capability to activate the Y1-receptor. The sources of N-terminally truncated NPY and related peptides are unknown and several proline specific peptidases may be involved. First, we therefore provide an overview on the peptidases, belonging to structural and functional homologues of dipeptidyl peptidase 4 (DP4) as well as aminopeptidase P (APP) and thus, represent potential candidates of NPY cleavage in vivo. Second, applying selective inhibitors against DP4, DP8/9 and DP2, respectively, the enzymatic distribution was analyzed in brain extracts from wild type and DP4 deficient F344 rat substrains and human plasma samples in activity studies as well as by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry. Third, co-transfection of Cos-1 cells with Dpp4 and Npy followed by confocal lasermicroscopy illustrated that hNPY-dsRed1-N1 was transported in large dense core vesicles towards the membrane while rDP4-GFP-C1 was transported primarily in different vesicles thereby providing no clear evidence for co-localization of NPY and DP4. Nevertheless, the review and experimental results of activity and mass spectrometry studies support the notion that at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) are potentially involved in NPY cleavage while the serine protease DP4 (CD26) could be the principal peptidase involved in the N-terminal truncation of NPY. However, DP8 and DP9 are also capable of cleaving NPY, whereas no cleavage could be demonstrated for DP2. 相似文献
86.
Althoff T Hentschel H Luig J Schütz H Kasch M Kinne RK 《American journal of physiology. Regulatory, integrative and comparative physiology》2007,292(6):R2391-R2399
Studies on membrane vesicles from the kidney of Leucoraja erinacea suggested the sole presence of a sodium-D-glucose cotransporter type 1 involved in renal D-glucose reabsorption. For molecular characterization of this transport system, an mRNA library was screened with primers directed against conserved regions of human sglt1. A cDNA was cloned whose nucleotide and derived amino acid sequence revealed high homology to sodium glucose cotransporter 1 (SGLT1). Xenopus laevis oocytes injected with the respective cRNA showed sodium-dependent high-affinity uptake of D-glucose. Many positions considered functionally essential for sodium glucose cotransporter 1 (SGLT1) are also found in the skate protein. High conservation preferentially in transmembrane helices and small linking loops suggests early appearance and continued preservation of these regions. Larger loops, especially loop 13, which is associated with phlorizin binding, were more variable, as is the interaction with the specific inhibitor in various species. To study the intrarenal distribution of the transporter, a skate SGLT1-specific antibody was generated. In cryosections of skate kidney, various nephron segments could be differentiated by lectin staining. Immunoreaction with the antibody was observed in the proximal tubule segments PIa and PIIa, the early distal tubule, and the collecting tubule. Thus Leucoraja, in contrast to the mammalian kidney, employs only SGLT1 to reabsorb d-glucose in the early, as well as in the late segments of the proximal tubule and probably also in the late distal tubule (LDT). Thereby, it differs also partly from the kidney of the close relative Squalus acanthias, which uses SGLT2 in more distal proximal tubule segments but shows also expression in the later nephron parts. 相似文献
87.
Crop evolution: from genetics to genomics 总被引:1,自引:0,他引:1
The advent of the genomics age has greatly facilitated the study of crop evolution. While full-scale genome sequencing projects are underway for just a handful of crop plants, recent years have witnessed a tremendous increase in the availability of DNA sequence data for virtually all major crops. Such resources have bolstered 'traditional' genetic approaches such as QTL mapping and candidate gene-based association studies. They have also allowed us to undertake genome-wide analyses in which we simultaneously consider the importance of a large and essentially random collection of genes. These sorts of analyses promise a more or less unbiased view of the genetic basis of crop evolution and will probably result in the identification of agronomically important genes that would have otherwise been overlooked. 相似文献
88.
Jutta Stadler Annette Trefflich Roland Brandl Stefan Klotz 《Biodiversity and Conservation》2007,16(3):621-630
Dry grasslands are among the most threatened plant communities of Central Europe. We explore the time scale of spontaneous
regeneration of dry grasslands on abandoned fields in an area of Central Europe, where also ancient grassland communities
occur (Saxony-Anhalt, Germany). On three permanent plots with shallow soils we monitored during 10 years change of species
composition and analysed whether spontaneous succession leads to assemblages similar to the ancient dry grassland communities
in the direct surroundings. We found that dry grassland species are able to invade the permanent plots and during the 10 years
of succession the number of dry grassland species increased. But even after 10 years there was a clear difference between
ancient dry grassland communities and the assemblages on the permanent plots. Our findings suggest two important conclusions:
First, spontaneous succession on abandoned fields is a cheap possibility for the conservation of some dry grassland species,
at least on shallow soils. Second, the time scale of the regeneration process, however, is rather long. Hence, conservation
of remnants of ancient grassland communities needs special attention. 相似文献
89.
90.
The morphology of male genitalia often suggests functions besidessperm transfer that may have evolved under natural or sexualselection. In several species of sexually cannibalistic spiders,males damage their paired genitalia during mating, limitingthem to one copulation per pedipalp. Using a triple-mating experiment,we tested if genital damage in the orb-web spider Argiope bruennichiincreases male fitness either through facilitating his escapefrom an aggressive female or by obstructing the female's inseminationducts against future copulation attempts from other males. Wefound no survival advantage for males damaging their pedipalps;however, copulations into a previously used insemination ductwere significantly shorter when the previous male had left partsof his genitalia inside the insemination duct. Because copulationduration determines paternity in this species, our result suggeststhat male genital damage in A. bruennichi is sexually selected.By breaking off parts of their intromittent organs inside avirgin female, males can reduce sperm competition and therebyincrease their paternity success. 相似文献