全文获取类型
收费全文 | 2754篇 |
免费 | 237篇 |
国内免费 | 2篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 38篇 |
2021年 | 86篇 |
2020年 | 45篇 |
2019年 | 66篇 |
2018年 | 76篇 |
2017年 | 87篇 |
2016年 | 88篇 |
2015年 | 157篇 |
2014年 | 157篇 |
2013年 | 217篇 |
2012年 | 199篇 |
2011年 | 212篇 |
2010年 | 132篇 |
2009年 | 128篇 |
2008年 | 178篇 |
2007年 | 212篇 |
2006年 | 183篇 |
2005年 | 158篇 |
2004年 | 152篇 |
2003年 | 116篇 |
2002年 | 132篇 |
2001年 | 16篇 |
2000年 | 9篇 |
1999年 | 13篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有2993条查询结果,搜索用时 31 毫秒
81.
Sergey A. Belokobylskij Sara Fadia Ceccarelli Alejandro Zaldívar-Riverón 《法国昆虫学会纪事》2013,49(3-4):394-401
A new genus belonging to the braconid wasp subfamily Doryctinae, Kauriphanes n. gen. (type species K. khalaimi n. sp.), is described from New Zealand. This genus is placed within the doryctine subtribe Caenophanina. The extent of this subtribe is discussed and the phylogenetic relationships of three of its genera were investigated using one mitochondrial and one nuclear DNA sequence markers. Similar to previous studies, the Bayesian analyses performed significantly support a clade with the included members of Caenophanina as a sister group of a clade with the examined species of Spathiini sensu stricto. The placement of the Caenophanini within Doryctini, however, is left pendant to further exhaustive phylogenetic studies. A key to genera and subgenera belonging to Caenophanina is given. 相似文献
82.
Makoto Hibi Takashi Kawashima Pavel M. Sokolov Sergey V. Smirnov Tomohiro Kodera Masakazu Sugiyama Sakayu Shimizu Kenzo Yokozeki Jun Ogawa 《Applied microbiology and biotechnology》2013,97(6):2467-2472
l-Leucine 5-hydroxylase (LdoA) previously found in Nostoc punctiforme PCC 73102 is a novel type of Fe(II)/α-ketoglutarate-dependent dioxygenase. LdoA catalyzed regio- and stereoselective hydroxylation of l-leucine and l-norleucine into (2S,4S)-5-hydroxyleucine and (2S)-5-hydroxynorleucine, respectively. Moreover, LdoA catalyzed sulfoxidation of l-methionine and l-ethionine in the same manner as previously described l-isoleucine 4-hydroxylase. Therefore LdoA should be a promising biocatalyst for effective production of industrially useful amino acids. 相似文献
83.
Genotypic difference in salinity tolerance in quinoa is determined by differential control of xylem Na loading and stomatal density 总被引:2,自引:0,他引:2
Quinoa is regarded as a highly salt tolerant halophyte crop, of great potential for cultivation on saline areas around the world. Fourteen quinoa genotypes of different geographical origin, differing in salinity tolerance, were grown under greenhouse conditions. Salinity treatment started on 10 day old seedlings. Six weeks after the treatment commenced, leaf sap Na and K content and osmolality, stomatal density, chlorophyll fluorescence characteristics, and xylem sap Na and K composition were measured. Responses to salinity differed greatly among the varieties. All cultivars had substantially increased K+ concentrations in the leaf sap, but the most tolerant cultivars had lower xylem Na+ content at the time of sampling. Most tolerant cultivars had lowest leaf sap osmolality. All varieties reduced stomata density when grown under saline conditions. All varieties clustered into two groups (includers and excluders) depending on their strategy of handling Na+ under saline conditions. Under control (non-saline) conditions, a strong positive correlation was observed between salinity tolerance and plants ability to accumulate Na+ in the shoot. Increased leaf sap K+, controlled Na+ loading to the xylem, and reduced stomata density are important physiological traits contributing to genotypic differences in salinity tolerance in quinoa, a halophyte species from Chenopodium family. 相似文献
84.
85.
The formation of textures in DNA films with LiCl, NaCl, KCl, RbCl, and CsCl salts has been studied. The films are prepared by evaporation of water solution with highly polymerized calf thymus DNA and excess salt of specific type. For DNA solution with 10 mM concentration of NaCl, KCl, and RbCl the films with dendritic textures have been obtained, whereas in case of CsCl the textures in the films appear only at 30 mM concentration of excess salt in the initial solution. In the solution with LiCl, the textures in DNA films have not been observed within the whole range of concentration of excess salt under consideration. The analysis of parameters of DNA films with different salts has showed that evaporation of solution leads to crystallization of salt ions on DNA macromolecule and formation of DNA‐salt complexes. Electrostatic energy of the system of crystalline ordered ions and charges of DNA chains has been estimated to study the stability of DNA‐salt complexes. The results obtained for different salts have been showed that the presence of DNA macromolecule enhances crystallization as compared with solution without DNA. The property of excess salt to form the crystalline structures has been found to decrease in the following order: KCl > NaCl > RbCl > CsCl > LiCl. The results of estimation are in good agreement with the experimentally observed dependence of texture formation on excess salt type. © 2013 Wiley Periodicals, Inc. Biopolymers 99: 508–516, 2013. 相似文献
86.
Eleftheria Palkopoulou Love Dalén Adrian M. Lister Sergey Vartanyan Mikhail Sablin Andrei Sher Veronica Nystr?m Edmark Mikael D. Brandstr?m Mietje Germonpré Ian Barnes Jessica A. Thomas 《Proceedings. Biological sciences / The Royal Society》2013,280(1770)
Ancient DNA analyses have provided enhanced resolution of population histories in many Pleistocene taxa. However, most studies are spatially restricted, making inference of species-level biogeographic histories difficult. Here, we analyse mitochondrial DNA (mtDNA) variation in the woolly mammoth from across its Holarctic range to reconstruct its history over the last 200 thousand years (kyr). We identify a previously undocumented major mtDNA lineage in Europe, which was replaced by another major mtDNA lineage 32–34 kyr before present (BP). Coalescent simulations provide support for demographic expansions at approximately 121 kyr BP, suggesting that the previous interglacial was an important driver for demography and intraspecific genetic divergence. Furthermore, our results suggest an expansion into Eurasia from America around 66 kyr BP, coinciding with the first exposure of the Bering Land Bridge during the Late Pleistocene. Bayesian inference indicates Late Pleistocene demographic stability until 20–15 kyr BP, when a severe population size decline occurred. 相似文献
87.
Mikhail S. Novikov Vladimir T. Valuev-Elliston Denis A. Babkov Maria P. Paramonova Alexander V. Ivanov Sergey A Gavryushov Anastasia L. Khandazhinskaya Sergey N. Kochetkov Christophe Pannecouque Graciela Andrei Robert Snoeck Jan Balzarini Katherine L. Seley-Radtke 《Bioorganic & medicinal chemistry》2013,21(5):1150-1158
A series of phenyloxyethyl and cinnamyl derivatives of substituted uracils were synthesized and found to exhibit potent activity against HIV-RT and HIV replication in cell culture. In general, the cinnamyl derivatives proved superior to the phenyloxyethyl derivatives, however 1-[2-(4-methylphenoxy)ethyl]-3-(3,5-dimethylbenzyl)uracil (19) exhibited the highest activity (EC50 = 0.27 μM) thus confirming that the 3-benzyluracil fragment in the NNRTI structure can be regarded as a functional analogue of the benzophenone pharmacophore typically found in NNRTIs. 相似文献
88.
Irina Venevskaia Sergey Venevsky Chris D. Thomas 《Biodiversity and Conservation》2013,22(6-7):1467-1483
A simple approach is suggested to project potential changes in the diversity of vascular plants. We use the current (recent past) relationship between plant diversity and geographic variation in the climate, as well as elevation range, to project changes in regional species richness (at 100 × 100 km resolution), concentrating on six climate scenarios for 2020, 2050 and 2080. The results show an overall trend towards increased vascular plant species richness. Increases in richness by 2050 and 2080 are expected over approximately three-quarters of the land surface, but decreases are expected in other regions. The magnitudes of richness gains and losses both increase over time, as the level of warming grows. The latitudinal pattern of change suggests that richness increases will be greatest at high latitudes, where plant productivity and diversity are largely limited by temperature. Richness decreases are not projected consistently in any latitudinal band, but are most likely to be observed at 5–40ºN, where declines in precipitation drive most projected decreases in richness. 相似文献
89.
Marina V. Shirmanova Ekaterina O. Serebrovskaya Konstantin A. Lukyanov Ludmila B. Snopova Marina A. Sirotkina Natalia N. Prodanetz Marina L. Bugrova Ekaterina A. Minakova Ilya V. Turchin Vladislav A. Kamensky Sergey A. Lukyanov Elena V. Zagaynova 《Journal of biophotonics》2013,6(3):283-290
KillerRed is known to be a unique red fluorescent protein displaying strong phototoxic properties. Its effectiveness has been shown previously for killing bacterial and cancer cells in vitro. Here, we investigated the photototoxicity of the protein on tumor xenografts in mice. HeLa Kyoto cell line stably expressing KillerRed in mitochondria and in fusion with histone H2B was used. Irradiation of the tumors with 593 nm laser led to photobleaching of KillerRed indicating photosensitization reaction and caused significant destruction of the cells and activation of apoptosis. The portion of the dystrophically changed cells increased from 9.9% to 63.7%, and the cells with apoptosis hallmarks from 6.3% to 14%. The results of this study suggest KillerRed as a potential genetically encoded photosensitizer for photodynamic therapy of cancer. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
90.
G?zde Isik Nancy P. Y. Chung Thijs van Montfort Sergey Menis Katie Matthews William R. Schief John P. Moore Rogier W. Sanders 《PloS one》2013,8(6)
Broadly neutralizing antibodies (bNAbs) that target the HIV-1 envelope glycoproteins (Env) can prevent virus acquisition, but several Env properties limit its ability to induce an antibody response that is of sufficient quantity and quality. The immunogenicity of Env can be increased by fusion to co-stimulatory molecules and here we describe novel soluble Env trimers with embedded interleukin-4 (IL-4) or interleukin-21 (IL-21) domains, designed to activate B cells that recognize Env. In particular, the chimeric EnvIL-21 molecule activated B cells efficiently and induced the differentiation of antibody secreting plasmablast-like cells. We studied whether we could increase the activity of the embedded IL-21 by designing a chimeric IL-21/IL-4 (ChimIL-21/4) molecule and by introducing amino acid substitutions in the receptor binding domain of IL-21 that were predicted to enhance its binding. In addition, we incorporated IL-21 into a cleavable Env trimer and found that insertion of IL-21 did not impair Env cleavage, while Env cleavage did not impair IL-21 activity. These studies should guide the further design of chimeric proteins and EnvIL-21 may prove useful in improving antibody responses against HIV-1. 相似文献