全文获取类型
收费全文 | 3020篇 |
免费 | 327篇 |
出版年
2023年 | 11篇 |
2022年 | 37篇 |
2021年 | 59篇 |
2020年 | 48篇 |
2019年 | 57篇 |
2018年 | 71篇 |
2017年 | 58篇 |
2016年 | 104篇 |
2015年 | 131篇 |
2014年 | 140篇 |
2013年 | 166篇 |
2012年 | 197篇 |
2011年 | 200篇 |
2010年 | 118篇 |
2009年 | 126篇 |
2008年 | 129篇 |
2007年 | 134篇 |
2006年 | 139篇 |
2005年 | 104篇 |
2004年 | 104篇 |
2003年 | 107篇 |
2002年 | 91篇 |
2001年 | 91篇 |
2000年 | 86篇 |
1999年 | 86篇 |
1998年 | 42篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 50篇 |
1991年 | 57篇 |
1990年 | 54篇 |
1989年 | 56篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 36篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 29篇 |
1982年 | 25篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1976年 | 11篇 |
1974年 | 12篇 |
1971年 | 12篇 |
排序方式: 共有3347条查询结果,搜索用时 15 毫秒
991.
Maria Jesus Almela Sonia Lozano Jo?l Lelièvre Gonzalo Colmenarejo José Miguel Coterón Janneth Rodrigues Carolina Gonzalez Esperanza Herreros 《PloS one》2015,10(8)
The discovery of new antimalarials with transmission blocking activity remains a key issue in efforts to control malaria and eventually eradicate the disease. Recently, high-throughput screening (HTS) assays have been successfully applied to Plasmodium falciparum asexual stages to screen millions of compounds, with the identification of thousands of new active molecules, some of which are already in clinical phases. The same approach has now been applied to identify compounds that are active against P. falciparum gametocytes, the parasite stage responsible for transmission. This study reports screening results for the Tres Cantos Antimalarial Set (TCAMS), of approximately 13,533 molecules, against P. falciparum stage V gametocytes. Secondary confirmation and cytotoxicity assays led to the identification of 98 selective molecules with dual activity against gametocytes and asexual stages. Hit compounds were chemically clustered and analyzed for appropriate physicochemical properties. The TCAMS chemical space around the prioritized hits was also studied. A selection of hit compounds was assessed ex vivo in the standard membrane feeding assay and demonstrated complete block in transmission. As a result of this effort, new chemical structures not connected to previously described antimalarials have been identified. This new set of compounds may serve as starting points for future drug discovery programs as well as tool compounds for identifying new modes of action involved in malaria transmission. 相似文献
992.
We introduce a protocol with a reconfigurable filter system to create non-overlapping single loops in the smart power grid for the realization of the Kirchhoff-Law-Johnson-(like)-Noise secure key distribution system. The protocol is valid for one-dimensional radial networks (chain-like power line) which are typical of the electricity distribution network between the utility and the customer. The speed of the protocol (the number of steps needed) versus grid size is analyzed. When properly generalized, such a system has the potential to achieve unconditionally secure key distribution over the smart power grid of arbitrary geometrical dimensions. 相似文献
993.
M. J. Prado M. V. Gonzalez S. Romo M. T. Herrera 《Plant Cell, Tissue and Organ Culture》2007,88(1):1-10
The present work reports on a study of plant regeneration carried out with callus from the leaf blades and petioles of field-grown
male adult kiwifruit plants (Actinidia deliciosa (Chev.) Liang and Ferguson). The cultivars used were ‘Tomuri’ and clone A, a selected male plant grown in north western Spain.
The best shoot induction conditions were obtained in ‘Tomuri’ leaf blades cultured in K(h) medium in the presence of 23 μM
Zeatin and 0.1 μM NAA. Under these conditions, more than 80% of organogenic callus induction was observed, with an average
of 14 new shoots in the second subculture. The initial length of the shoots affected shoot elongation, which was accomplished
by culturing isolated shoots in K(h) medium with half-strength salts, supplemented with 0.4 μM Zeatin and 0.1 μM NAA. A possible
detrimental long-term effect of cytokinins on shoot elongation can account for the results, since elongation was not observed
until 1 month of culture in elongation medium. For rooting, shoots (1 cm in length) were basally immersed in a 5 mM IBA solution
for 15 s, and transferred to half-strength K(h) basal medium. Regenerated plants were acclimated in a sterile peat:perlite
substrate for 10 days, and then transferred to soil. AFLP analysis was accomplished with 15 primer combinations from which
13 showed reproducible and well-resolved bands, producing a total of 1321 fragments from which 1281 were polymorphic (97%).
A dendrogram was constructed using both monomorphic and polymorphic bands, showing genetic variation among field-grown plants
and tissue culture-derived regenerants. 相似文献
994.
995.
996.
E Matsunaga T Zeugin U M Zanger T Aoyama U A Meyer F J Gonzalez 《The Journal of biological chemistry》1990,265(28):17197-17201
A cDNA coding for an allelic variant of rat IID1, designated IID1v, was isolated that produced a P-450 having a 10-fold lower catalytic activity toward the substrate bufuralol when expressed in COS-1 cells (Matsunaga, E., Zanger, U. M., Hardwick, J. P., Gelboin, H. V., Meyer, U. A., and Gonzalez, F. J. (1989) Biochemistry, 28, 7349-7355). IID1 and IID1v cDNA-deduced proteins differed in sequence by 4 amino acid residues. IID1 has Val, Phe, Arg, and Leu while IID1v has Ile, Leu, Gln, and Phe at amino acid positions 123, 124, 173, and 380, respectively. Chimeric cDNAs between IID1 and IID1v were constructed and expressed in hepatoma cells using vaccinia virus. A chimera having the Phe (IID1v) at amino acid 380, with the remaining 3 variant amino acid residues of IID1, was found to have a 17-fold decrease in Vmax and a 2 to 3-fold decrease in Km for (+)-bufuralol 1'-hydroxylation when compared to a converse chimera having Ile (IID1) in a background of IID1v sequence. Although this enzyme lacked significant bufuralol metabolism, it was able to carry out debrisoquine 4-hydroxylation. In contrast, the chimera having Ile (IID1) at position 380 was lacking in debrisoquine 4-hydroxylation. Type I difference spectra analysis revealed that both forms could bind debrisoquine with similar spectral dissociation constants. These data demonstrate that the single amino acid substitution Ile380----Phe differentially decreases the catalytic activity of IID1 toward bufuralol but not debrisoquine. 相似文献
997.
Dosage dependence of maternal contribution to somatic cell division in Drosophila melanogaster. 总被引:1,自引:0,他引:1
Most mitotic mutants in Drosophila do not lead to lethality in early development despite the highly abnormal chromosome behaviour that they elicit. This has been explained as being the effect of maternally provided wild-type products. We have tested this hypothesis by studying cuticular clones derived from cells in which there has been loss of a marked Y chromosome due to chromosome nondisjunction in individuals homozygous for the mutation abnormal spindle who are progeny of heterozygous mothers. We have found that the size and frequency of these clones are higher than in control flies. Furthermore, by analysing flies whose female parents have different doses of the asp+ gene, we have found that there is a correlation between the amount of maternally contributed asp+ product and the frequency and size of cuticular clones. We have also estimated the time in development when the first mitotic mistakes take place, i.e. the time when maternal products are no longer sufficient to carry out normal cell division. 相似文献
998.
999.
Contrasting demographic history and gene flow patterns of two mangrove species on either side of the Central American Isthmus
下载免费PDF全文
![点击此处可从《Ecology and evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ivania Cerón‐Souza Elena G. Gonzalez Andrea E. Schwarzbach Dayana E. Salas‐Leiva Elsie Rivera‐Ocasio Nelson Toro‐Perea Eldredge Bermingham W. Owen McMillan 《Ecology and evolution》2015,5(16):3486-3499
Comparative phylogeography offers a unique opportunity to understand the interplay between past environmental events and life‐history traits on diversification of unrelated but co‐distributed species. Here, we examined the effects of the quaternary climate fluctuations and palaeomarine currents and present‐day marine currents on the extant patterns of genetic diversity in the two most conspicuous mangrove species of the Neotropics. The black (Avicennia germinans, Avicenniaceae) and the red (Rhizophora mangle, Rhizophoraceae) mangroves have similar geographic ranges but are very distantly related and show striking differences on their life‐history traits. We sampled 18 Atlantic and 26 Pacific locations for A. germinans (N = 292) and R. mangle (N = 422). We performed coalescence simulations using microsatellite diversity to test for evidence of population change associated with quaternary climate fluctuations. In addition, we examined whether patterns of genetic variation were consistent with the directions of major marine (historical and present day) currents in the region. Our demographic analysis was grounded within a phylogeographic framework provided by the sequence analysis of two chloroplasts and one flanking microsatellite region in a subsample of individuals. The two mangrove species shared similar biogeographic histories including: (1) strong genetic breaks between Atlantic and Pacific ocean basins associated with the final closure of the Central American Isthmus (CAI), (2) evidence for simultaneous population declines between the mid‐Pleistocene and early Holocene, (3) asymmetric historical migration with higher gene flow from the Atlantic to the Pacific oceans following the direction of the palaeomarine current, and (4) contemporary gene flow between West Africa and South America following the major Atlantic Ocean currents. Despite the remarkable differences in life‐history traits of mangrove species, which should have had a strong influence on seed dispersal capability and, thus, population connectivity, we found that vicariant events, climate fluctuations and marine currents have shaped the distribution of genetic diversity in strikingly similar ways. 相似文献
1000.