全文获取类型
收费全文 | 62728篇 |
免费 | 4015篇 |
国内免费 | 7篇 |
专业分类
66750篇 |
出版年
2023年 | 450篇 |
2022年 | 396篇 |
2021年 | 839篇 |
2020年 | 767篇 |
2019年 | 755篇 |
2018年 | 1958篇 |
2017年 | 1824篇 |
2016年 | 2383篇 |
2015年 | 3139篇 |
2014年 | 3107篇 |
2013年 | 4166篇 |
2012年 | 5033篇 |
2011年 | 4497篇 |
2010年 | 2804篇 |
2009年 | 2149篇 |
2008年 | 3500篇 |
2007年 | 3276篇 |
2006年 | 3078篇 |
2005年 | 2638篇 |
2004年 | 2561篇 |
2003年 | 2293篇 |
2002年 | 2112篇 |
2001年 | 1401篇 |
2000年 | 1391篇 |
1999年 | 1067篇 |
1998年 | 469篇 |
1997年 | 330篇 |
1996年 | 345篇 |
1995年 | 318篇 |
1994年 | 254篇 |
1993年 | 239篇 |
1992年 | 544篇 |
1991年 | 453篇 |
1990年 | 407篇 |
1989年 | 401篇 |
1988年 | 395篇 |
1987年 | 354篇 |
1986年 | 336篇 |
1985年 | 342篇 |
1984年 | 341篇 |
1983年 | 235篇 |
1982年 | 213篇 |
1980年 | 172篇 |
1979年 | 209篇 |
1978年 | 203篇 |
1975年 | 195篇 |
1974年 | 213篇 |
1973年 | 219篇 |
1972年 | 183篇 |
1969年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
Paulo FP Pimenta Alessandra S Orfano Ana C Bahia Ana PM Duarte Claudia M Ríos-Velásquez Fabrício F Melo Felipe AC Pessoa Giselle A Oliveira Keillen MM Campos Luis Martínez Villegas Nilton Barnabé Rodrigues Rafael Nacif-Pimenta Rejane C Sim?es Wuelton M Monteiro Rogerio Amino Yara M Traub-Cseko José BP Lima Maria GV Barbosa Marcus VG Lacerda Wanderli P Tadei Nágila FC Secundino 《Memórias do Instituto Oswaldo Cruz》2015,110(1):23-47
In the Americas, areas with a high risk of malaria transmission are mainly located in
the Amazon Forest, which extends across nine countries. One keystone step to
understanding the Plasmodium life cycle in Anopheles species from the Amazon Region
is to obtain experimentally infected mosquito vectors. Several attempts to colonise
Ano- pheles species have been conducted, but with only short-lived success or no
success at all. In this review, we review the literature on malaria transmission from
the perspective of its Amazon vectors. Currently, it is possible to develop
experimental Plasmodium vivax infection of the colonised and field-captured vectors
in laboratories located close to Amazonian endemic areas. We are also reviewing
studies related to the immune response to P. vivax infection of Anopheles aquasalis,
a coastal mosquito species. Finally, we discuss the importance of the modulation of
Plasmodium infection by the vector microbiota and also consider the anopheline
genomes. The establishment of experimental mosquito infections with Plasmodium
falciparum, Plasmodium yoelii and Plasmodium berghei parasites that could provide
interesting models for studying malaria in the Amazonian scenario is important.
Understanding the molecular mechanisms involved in the development of the parasites
in New World vectors is crucial in order to better determine the interaction process
and vectorial competence. 相似文献
934.
The stability of Pseudomonas putida F1, a strain harbouring the genes responsible for toluene degradation in the chromosome was evaluated in a bioscrubber under
high toluene loadings and nitrogen limiting conditions at two dilution rates (0.11 and 0.27 h−1). Each experiment was run for 30 days, period long enough for microbial instability to occur considering previously reported
studies carried out with bacterial strains encoding the catabolic genes in the TOL plasmid. At all tested conditions, P. putida F1 exhibited stable performance as shown by the constant values of the specific toluene degradation yield, CO2 produced versus toluene degraded yield, and biomass concentration within each steady state. Benzyl alcohol, a curing agent
causing TOL plasmid deletion in Pseudomonas strains, was present in the cultivation medium as a result of the monooxygenation of toluene by the diooxygenase system of
P. putida F1. However, no mutant population growing at the expense of the extracellular excreted carbon or lysis products was established
in the chemostat as confirmed by the constant dissolved total organic carbon (TOC) concentration and fraction of toluene degrading
cells (approx. 100%). In addition, batch experiments conducted with both lysis substrate and toluene simultaneously confirmed
that P. putida F1 preferentially consumed toluene rather than extracellular excreted carbon. 相似文献
935.
Telomeres in many eukaryotes are maintained by telomerase in whose absence telomere shortening occurs. However, telomerase-deficient
Arabidopsis thaliana mutants (Attert
−/−) show extremely low rates of telomere shortening per plant generation (250–500 bp), which does not correspond to the expected
outcome of replicative telomere shortening resulting from ca. 1,000 meristem cell divisions per seed-to-seed generation. To
investigate the influence of the number of cell divisions per seed-to-seed generation, Attert
−/− mutant plants were propagated from seeds coming either from the lower-most or the upper-most siliques (L- and U-plants) and
the length of their telomeres were followed over several generations. The rate of telomere shortening was faster in U-plants,
than in L-plants, as would be expected from their higher number of cell divisions per generation. However, this trend was
observed only in telomeres whose initial length is relatively high and the differences decreased with progressive general
telomere shortening over generations. But in generation 4, the L-plants frequently show a net telomere elongation, while the
U-plants fail to do so. We propose that this is due to the activation of alternative telomere lengthening (ALT), a process
which is activated in early embryonic development in both U- and L-plants, but is overridden in U-plants due to their higher
number of cell divisions per generation. These data demonstrate what so far has only been speculated, that in the absence
of telomerase, the number of cell divisions within one generation influences the control of telomere lengths. These results
also reveal a fast and efficient activation of ALT mechanism(s) in response to the loss of telomerase activity and imply that
ALT is probably involved also in normal plant development. 相似文献
936.
Guimarães DO Borges WS Kawano CY Ribeiro PH Goldman GH Nomizo A Thiemann OH Oliva G Lopes NP Pupo MT 《FEMS immunology and medical microbiology》2008,52(1):134-144
A total of 39 endophytic fungi have been isolated from Viguiera arenaria and Tithonia diversifolia, both collected in S?o Paulo State, Brazil. The isolates were identified based on their ribosomal DNA sequences. The ethyl acetate (EtOAc) extracts of all endophytic fungi were evaluated for their antimicrobial, antiparasitic and antitumoral activity. Antimicrobial screening was conducted using an agar diffusion assay against three pathogenic microorganisms: Staphylococcus aureus, Escherichia coli and Candida albicans. Antiparasitic activity was determined by enzymatic inhibition of gGAPDH of Trypanosoma cruzi and adenine phosphorybosiltransferase (APRT) of Leishmania tarentolae. Antitumoral activity was tested against human T leukemia cells by the Mosmann colorimetric method. All extracts showed activity in at least one assay: 79.5% of the extracts were cytotoxic against leukemia cells, 5.1% of the extracts were active against S. aureus, 25.6% against E. coli and 64.1% against Candida albicans. Only one extract showed promising results in the inhibition of parasitic enzymes gGAPDH (95.0%) and three were found to inhibit APRT activity. The cytotoxic extract produced by the strain VA1 (Glomerella cingulata) was fractionated and yielded nectriapyrone and tyrosol. Nectriapyrone showed relevant cytotoxic activity against both human T leukemia and melanoma tumor cell lines. 相似文献
937.
Saenko SV French V Brakefield PM Beldade P 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1496):1549-1555
The origin and diversification of evolutionary novelties-lineage-specific traits of new adaptive value-is one of the key issues in evolutionary developmental biology. However, comparative analysis of the genetic and developmental bases of such traits can be difficult when they have no obvious homologue in model organisms. The finding that the evolution of morphological novelties often involves the recruitment of pre-existing genes and/or gene networks offers the potential to overcome this challenge. Knowledge about shared developmental processes obtained from extensive studies in model organisms can then be used to understand the origin and diversification of lineage-specific structures. Here, we illustrate this approach in relation to eyespots on the wings of Bicyclus anynana butterflies. A number of spontaneous mutations isolated in the laboratory affect eyespots, lepidopteran-specific features, and also processes that are shared by most insects. We discuss how eyespot mutants with disturbed embryonic development may help elucidate the genetic pathways involved in eyespot formation, and how venation mutants with altered eyespot patterns might shed light on mechanisms of eyespot development. 相似文献
938.
L Legáth A Naus J Halík 《Journal of hygiene, epidemiology, microbiology, and immunology》1988,32(3):287-297
Studies of aerosol particle deposition in the respiratory tract requires experimental inhalation of artificial model aerosols. The paper formulates some of the most important requirements for the properties of such aerosols. Several suitable fractions were prepared as part of a research project dealing with the use of microporous polymers for diagnostic purposes. 5 fractions of the polymer designated G-gel 60 with the particle size as stated by the manufacturer, ranging from 3 to 7 micron were evaluated using a 16-channel particle dispersity analyzer HIAC/ROYCO MT 3210 with the sensor 1200 and operated by a microprocessor, the equipment being coupled to an APPLE IIe computer. G-gel 60 particles introduced into the aerosol were characterized by the parameters CMAD, MMAD and sg both numerically and graphically. The measurement procedure was found to be very sensitive with respect to all fractions in evaluating the subtile differences between different lot numbers of the aerosol. G-gel 60 fractions characterized both numerically and graphically were compared with the known aerosols from paraffin oil and atmospheric air. The equipment MT 3210 enables prompt determination of the percentages of aerosol particles distribution by size class. The authors conclude that the procedure, both in its numerical and graphical versions, is particularly suitable for the diagnosis of aerosol particles deposition in the respiratory tract, offering a new application for HIAC/ROYCO in the field of medicine. In evaluating atmospheric aerosol in exhaled air, the number of particles was found to be below that in inhaled air, the difference being dependent on the choice of investigation methods. Percentual distribution of deposited particles following one minute ventilation proved to be at its maximum, as regards atmospheric aerosol, in the 0.30-0.50 micron range. The deposition curve was similar to already published curves, being characterized by an S-shaped pattern with maximum deposition in the greater size classes. An analysis of inhaled, exhaled and deposited aerosol suggested that deposited aerosol is more polydisperse and has particles of greater sizes than inhaled aerosol. Investigation of the effect of apnoe on deposition indicated that deposition increased as a function of apnoeic pause. 相似文献
939.
940.
María Isela Gutiérrez 《Photochemical & photobiological sciences》2008,7(4):480-484
Rate constants for the interaction between singlet molecular oxygen [O2(1 delta g)] and the p-quinones 1,4-benzoquinone (BQ), duroquinone (DQ), 9,10-anthraquinone (AQ) and 1,8-dihydroxy-9,10-anthraquinone (OHAQ) are reported for several solvents at room temperature. The solvent effect on the total quenching rate constant (kt) was analysed employing the semiempirical solvatochromic equation proposed by Kamlet and Taft. The higher values of kt (2-7 x 10(7) M(-1) s(-1)) were obtained when the hydrogen-bond donor solvent ability is increased (higher alpha parameter values). The results indicate the importance of specific solvent interactions in governing the rates of the quenching. 相似文献