全文获取类型
收费全文 | 1194篇 |
免费 | 91篇 |
出版年
2023年 | 11篇 |
2022年 | 19篇 |
2021年 | 35篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 34篇 |
2017年 | 32篇 |
2016年 | 63篇 |
2015年 | 61篇 |
2014年 | 68篇 |
2013年 | 80篇 |
2012年 | 104篇 |
2011年 | 93篇 |
2010年 | 68篇 |
2009年 | 47篇 |
2008年 | 75篇 |
2007年 | 49篇 |
2006年 | 63篇 |
2005年 | 55篇 |
2004年 | 48篇 |
2003年 | 51篇 |
2002年 | 37篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 18篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1968年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有1285条查询结果,搜索用时 31 毫秒
91.
Rocha CS Luz DF Oliveira ML Baracat-Pereira MC Medrano FJ Fontes EP 《Phytochemistry》2007,68(6):802-810
The sucrose binding protein (SBP) belongs to the cupin family of proteins and is structurally related to vicilin-like storage proteins. In this investigation, a SBP isoform (GmSBP2/S64) was expressed in E. coli and large amounts of the protein accumulated in the insoluble fraction as inclusion bodies. The renatured protein was studied by circular dichroism (CD), intrinsic fluorescence, and binding of the hydrophobic probes ANS and Bis-ANS. The estimated content of secondary structure of the renatured protein was consistent with that obtained by theoretical modeling with a large predominance of beta-strand structure (42%) over the alpha-helix (9.9%). The fluorescence emission maximum of 303 nm for SBP2 indicated that the fluorescent tryptophan was completely buried within a highly hydrophobic environment. We also measured the equilibrium dissociation constant (K(d)) of sucrose binding by fluorescence titration using the refolded protein. The low sucrose binding affinity (K(d)=2.79+/-0.22 mM) of the renatured protein was similar to that of the native protein purified from soybean seeds. Collectively, these results indicate that the folded structure of the renatured protein was similar to the native SBP protein. As a member of the bicupin family of proteins, which includes highly stable seed storage proteins, SBP2 was fairly stable at high temperatures. Likewise, it remained folded to a similar extent in the presence or absence of 7.6M urea or 6.7 M GdmHCl. The high stability of the renatured protein may be a reminiscent property of SBP from its evolutionary relatedness to the seed storage proteins. 相似文献
92.
93.
94.
Valdivieso AG Marcucci F Taminelli G Guerrico AG Alvarez S Teiber ML Dankert MA Santa-Coloma TA 《Biochemical and biophysical research communications》2007,356(3):805-809
Cystic fibrosis (CF) is a disease produced by mutations in the CFTR channel. We have previously reported that the CFTR chloride transport activity indirectly regulates the differential expression of several genes, including SRC and MUC1. Here we report that MT-ND4, a mitochondrial gene encoding a subunit of the mitochondrial Complex I (mtCx-I), is also a CFTR-dependent gene. A reduced expression of MT-ND4 was observed in CFDE cells (derived from a CF patient) when compared to CFDE cells ectopically expressing wild-type CFTR. The differential expression of MT-ND4 in CF was confirmed by RT-PCR. In situ hybridizations of deparaffinized human lung tissue slices derived from wt-CFTR or CF patients also showed downregulation of ND4 in CF. In addition, the CFTR chloride transport inhibitors glibenclamide and CFTR(inh)-172 also reduced MT-ND4 expression in CFDE cells ectopically expressing wt CFTR. These results suggest that the CFTR chloride transport activity indirectly up-regulates MT-ND4 expression. 相似文献
95.
Callicott JB Rozzi R Delgado L Monticino M Acevedo M Harcombe P 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2007,362(1478):321-333
The perspective of 'biocomplexity' in the form of 'coupled natural and human systems' represents a resource for the future conservation of biodiversity hotspots in three direct ways: (i) modelling the impact on biodiversity of private land-use decisions and public land-use policies, (ii) indicating how the biocultural history of a biodiversity hotspot may be a resource for its future conservation, and (iii) identifying and deploying the nodes of both the material and psycho-spiritual connectivity between human and natural systems in service to conservation goals. Three biocomplexity case studies of areas notable for their biodiversity, selected for their variability along a latitudinal climate gradient and a human-impact gradient, are developed: the Big Thicket in southeast Texas, the Upper Botanamo River Basin in eastern Venezuela, and the Cape Horn Archipelago at the austral tip of Chile. More deeply, the biocomplexity perspective reveals alternative ways of understanding biodiversity itself, because it directs attention to the human concepts through which biodiversity is perceived and understood. The very meaning of biodiversity is contestable and varies according to the cognitive lenses through which it is perceived. 相似文献
96.
Thomas A. Kursar Catherina C. Caballero-George Todd L. Capson Luis Cubilla-Rios William H. Gerwick Maria V. Heller Alicia Ibañez Roger G. Linington Kerry L. McPhail Eduardo Ortega-Barría Luz I. Romero P. D. Coley 《Biodiversity and Conservation》2007,16(10):2789-2800
The limited international resources for economic aid and conservation can only mitigate poverty and losses of biodiversity.
Hence, developing nations must establish the capacity to resolve their problems. Additionally, policy-makers and donors need
to obtain scientific input on issues such as global change and ecosystem services. We propose that for nations rich in biodiversity,
ecosystem services derived from bioprospecting, or drug discovery, could contribute to economic development. In the case where
unstudied samples are shipped abroad for research, the chances of obtaining royalties are infinitesimally small. Therefore
developing nations will only realize benefits from bioprospecting through in-country research on their own biodiversity. Policy-makers
and donors have failed to appreciate the value of this approach. In order to provide an example of the inherent links between
conservation and sustainable economic development, we initiated a drug discovery effort in Panama that emphasizes local benefit.
As much of the drug discovery process as possible is conducted in Panamanian laboratories, providing jobs dependent on intact
biodiversity and enhancing local research and training. In short, research, plus the spin-offs from research, provide immediate
and long-lasting benefits to Panama. The connection between conservation and development has been highlighted in publicity
about the project in Panama’s urban media. This provides a constructive alternative to the perception the among the urban
populace that economic development inevitably competes with conservation. In summary, our program uses biodiversity to promote
human health as well as to support research capacity, economic development and conservation within Panama. The program provides
an example of the widely recognized but little developed concept of bioprospecting research as an ecosystem service. 相似文献
97.
Preferences for grouping with familiar individuals are shown in many animal species, including the three-spined stickleback (Gasterosteus aculeatus). Shoaling with familiars is advantageous because of more precise anti-predator behaviours or more stable dominance hierarchies. Additionally, associations with familiar individuals facilitate the evolution of altruistic behaviour. Thus, in situations of increased competition one might expect an increased preference for familiar fish. We gave single juvenile sticklebacks of different nutritional state the choice between shoals composed either of familiar or unfamiliar individuals. Satiated fish preferred to shoal with familiar individuals. A comparative analysis of 8 stickleback studies with 15 different tests using familiars showed that all tests gave similar results, i.e. sticklebacks of all age classes preferred to shoal with familiars in a non-sexual context. In contrast, hungry test fish did not prefer to shoal with familiar fish, but even showed a preference for the unfamiliar group. Because sticklebacks use early-life familiarity to recognize kin, the results suggest the avoidance of competition with relatives. To our knowledge, this is the first study showing an impact of nutritional state on social interactions with familiar individuals. 相似文献
98.
99.
Periela da Silva Sousa-Vasconcelos Wellington da Silva Seguins Eduardo de Souza Luz Rosa Teixeira de Pinho 《Memórias do Instituto Oswaldo Cruz》2015,110(6):809-813
Tuberculosis has great public health impact with high rates of mortality and the only
prophylactic measure for it is the Mycobacterium bovisbacillus
Calmette-Guérin (BCG) vaccine. The present study evaluated the release of cytokines
[interleukin (IL)-1, tumour necrosis factor and IL-6] and chemokines [macrophage
inflammatory protein (MIP)-1α and MIP-1β] by THP-1 derived
macrophages infected with BCG vaccine obtained by growing mycobacteria in Viscondessa
de Moraes Institute medium medium (oral) or Sauton medium (intradermic) to compare
the effects of live and heat-killed (HK) mycobacteria. Because BCG has been reported
to lose viability during the lyophilisation process and during storage, we examined
whether exposing BCG to different temperatures also triggers differences in the
expression of some important cytokines and chemokines of the immune response.
Interestingly, we observed that HK mycobacteria stimulated cytokine and chemokine
production in a different pattern from that observed with live mycobacteria. 相似文献
100.
First phylogenetic analysis of the tribe Phyllotini (Rodentia: Sigmodontinae) combining morphological and molecular data 下载免费PDF全文
Luz V. Carrizo Santiago A. Catalano 《Cladistics : the international journal of the Willi Hennig Society》2015,31(6):593-620
Previous phylogenetic analyses of the tribe Phyllotini, one of the largest components of the subfamily Sigmodontinae, have been based on a single source of evidence. In particular, morphological analyses were largely based on craniodental data, almost neglecting the potential phylogenetic information present in the postcranium. Despite the significant advances made in relation to the knowledge of phyllotine phylogeny in recent times, there are several unsolved issues that highlight the importance of a phylogenetic analysis that integrates multiple sources of evidence, including previously considered sources as well as new sources of data. We present here the first combined phylogenetic analysis (morphological and molecular) of phyllotines, which includes the widest taxon and character sampling to date. Our dataset includes 164 morphological characters, of which 83 are postcranial characters, plus 3561 molecular characters, scored for 52 species from 34 genera of Oryzomyalia. In this study 75 postcranial characters not previously considered in this group are thoroughly described, and their utility for solving the relationships within Phyllotini is evaluated by means of different complementary analyses. Phyllotini was retrieved as a monophyletic clade in the combined analysis, with a composition that matches that obtained in most other recent analyses. All genera of phyllotines were monophyletic and show high support values. Abrotrichini, Akodontini and Oryzomyini were also monophyletic. The inclusion of postcranial data appears to be of limited utility to solve the phylogenetic relationships within Phyllotini. 相似文献