全文获取类型
收费全文 | 16214篇 |
免费 | 1830篇 |
国内免费 | 5篇 |
出版年
2022年 | 62篇 |
2021年 | 320篇 |
2020年 | 206篇 |
2019年 | 260篇 |
2018年 | 319篇 |
2017年 | 272篇 |
2016年 | 461篇 |
2015年 | 829篇 |
2014年 | 827篇 |
2013年 | 952篇 |
2012年 | 1287篇 |
2011年 | 1217篇 |
2010年 | 757篇 |
2009年 | 683篇 |
2008年 | 956篇 |
2007年 | 921篇 |
2006年 | 874篇 |
2005年 | 817篇 |
2004年 | 750篇 |
2003年 | 735篇 |
2002年 | 647篇 |
2001年 | 193篇 |
2000年 | 114篇 |
1999年 | 169篇 |
1998年 | 212篇 |
1997年 | 125篇 |
1996年 | 118篇 |
1995年 | 128篇 |
1994年 | 118篇 |
1993年 | 132篇 |
1992年 | 132篇 |
1991年 | 112篇 |
1990年 | 124篇 |
1989年 | 108篇 |
1988年 | 106篇 |
1987年 | 84篇 |
1986年 | 85篇 |
1985年 | 92篇 |
1984年 | 102篇 |
1983年 | 100篇 |
1982年 | 90篇 |
1981年 | 93篇 |
1980年 | 90篇 |
1979年 | 78篇 |
1978年 | 76篇 |
1977年 | 68篇 |
1976年 | 70篇 |
1975年 | 75篇 |
1974年 | 84篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
Elizabeth Ortiz-Gutiérrez Karla García-Cruz Eugenio Azpeitia Aaron Castillo María de la Paz Sánchez Elena R. álvarez-Buylla 《PLoS computational biology》2015,11(9)
Cell cycle control is fundamental in eukaryotic development. Several modeling efforts have been used to integrate the complex network of interacting molecular components involved in cell cycle dynamics. In this paper, we aimed at recovering the regulatory logic upstream of previously known components of cell cycle control, with the aim of understanding the mechanisms underlying the emergence of the cyclic behavior of such components. We focus on Arabidopsis thaliana, but given that many components of cell cycle regulation are conserved among eukaryotes, when experimental data for this system was not available, we considered experimental results from yeast and animal systems. We are proposing a Boolean gene regulatory network (GRN) that converges into only one robust limit cycle attractor that closely resembles the cyclic behavior of the key cell-cycle molecular components and other regulators considered here. We validate the model by comparing our in silico configurations with data from loss- and gain-of-function mutants, where the endocyclic behavior also was recovered. Additionally, we approximate a continuous model and recovered the temporal periodic expression profiles of the cell-cycle molecular components involved, thus suggesting that the single limit cycle attractor recovered with the Boolean model is not an artifact of its discrete and synchronous nature, but rather an emergent consequence of the inherent characteristics of the regulatory logic proposed here. This dynamical model, hence provides a novel theoretical framework to address cell cycle regulation in plants, and it can also be used to propose novel predictions regarding cell cycle regulation in other eukaryotes. 相似文献
2.
Relationship between growth irradiance and the xanthophyll cycle pool in the diatom Nitzschia palea 总被引:1,自引:0,他引:1
The size and de-epoxidation state of the xanthophyll cycle pool was measured in cultures of Nitzschia palea grown at six fluence rates in continuous light or with a 12 h photoperiod. In both series the size of the pool increased with increasing irradiance. The de-epoxidized form, diatoxanthin, was only present at fluence rates saturating for growth. The portion of diadinoxanthin, which was not readily de-epoxidized in saturating light, was constant and not related to the size of the pool. In the culture grown in a light-dark cycle at 300 μmol photons m-2 s-1 (PAR) increasing de-epoxidation took place in the latter half of the photoperiod, when the rate of photosynthesis was decreasing. A rapid, spectrophotometric method for measuring the extent of de-epoxidation of the xanthophyll cycle pool in a culture of diatoms is described. Upon addition of a small volume of hydrochloric acid to an extract of pigments in 90% acetone, the absorbance at 480 nm is reduced. The size of the reduction is a measure of the state of the xanthophyll cycle pool, since the absorbance of diatoxanthin is reduced by 5%, but the absorbance of diadinoxanthin by 87% due to an epoxide-furanoid rearrangement, which causes the absorption spectrum to be shifted by ca 20 nm towards shorter wavelengths. 相似文献
3.
Russell W. Avramenko Elizabeth M. Redman Roy Lewis Thomas A. Yazwinski James D. Wasmuth John S. Gilleard 《PloS one》2015,10(12)
Parasitic helminth infections have a considerable impact on global human health as well as animal welfare and production. Although co-infection with multiple parasite species within a host is common, there is a dearth of tools with which to study the composition of these complex parasite communities. Helminth species vary in their pathogenicity, epidemiology and drug sensitivity and the interactions that occur between co-infecting species and their hosts are poorly understood. We describe the first application of deep amplicon sequencing to study parasitic nematode communities as well as introduce the concept of the gastro-intestinal “nemabiome”. The approach is analogous to 16S rDNA deep sequencing used to explore microbial communities, but utilizes the nematode ITS-2 rDNA locus instead. Gastro-intestinal parasites of cattle were used to develop the concept, as this host has many well-defined gastro-intestinal nematode species that commonly occur as complex co-infections. Further, the availability of pure mono-parasite populations from experimentally infected cattle allowed us to prepare mock parasite communities to determine, and correct for, species representation biases in the sequence data. We demonstrate that, once these biases have been corrected, accurate relative quantitation of gastro-intestinal parasitic nematode communities in cattle fecal samples can be achieved. We have validated the accuracy of the method applied to field-samples by comparing the results of detailed morphological examination of L3 larvae populations with those of the sequencing assay. The results illustrate the insights that can be gained into the species composition of parasite communities, using grazing cattle in the mid-west USA as an example. However, both the technical approach and the concept of the ‘nemabiome’ have a wide range of potential applications in human and veterinary medicine. These include investigations of host-parasite and parasite-parasite interactions during co-infection, parasite epidemiology, parasite ecology and the response of parasite populations to both drug treatments and control programs. 相似文献
4.
The aerial prop roots of the neotropical red mangrove,Rhizophora mangle L., begin growing well above highest high water (HHW) and often extend well below lowest low water (LLW) before rooting in the benthic substratum. In Belize, Central America, prop roots growing below LLW are colonized by diverse assemblages of organisms, including macroalgae, hydrozoans, ascidians, sponges, anemones, hard corals, and isopod crustaceans. Mangroves, root-fouling epibionts, root herbivores, and benthic predators engage in complex interactions that are major determinants of mangrove growth and production. Species richness of root epibionts increases with distance from the mainland and with proximity to the barrier reef. Species richness decreases with variability in water temperature and salinity. Ascidians and sponges transplanted from Lark Cay into the coastal Placencia Lagoon failed to survive, but anemones from Lark Cay survived in Placencia Lagoon. Reciprocal transplants survived off-shore. The gastropod predator,Melongena melongena L., present only in mainland estuaries, reduced local barnacle abundance and epibiont species richness in Placencia Lagoon. Isopod species richness also increases with distance from shore, but the number of roots bored by these species decreases. These isopods can reduce root relative growth rate (RGRroot) by 55%. On off-shore cays, sponges and ascidians ameliorate negative effects of isopods. In mainland estuaries where epibionts are less common, isopod damage to roots is more severe. Experimental studies in mangrove swamps throughout the world would clarify the importance of plant-animal interactions in these widespread tropical ecosystems. 相似文献
5.
6.
A. B. Edmundson D. L. Harris Z.-C. Fan L. W. Guddat B. T. Schley B. L. Hanson G. Tribbick H. M. Geysen 《Proteins》1993,16(3):246-267
An immunoglobulin light chain dimer with a large generic binding cavity was used as a host molecule for designing a series of peptide guest ligands. In a screening procedure peptides coupled to solid supports were systematically tested for binding activity by enzyme linked immunosorbent assays (ELISA). Key members of the binding series were synthesized in milligram quantities and diffused into crystals of the host molecule for X-ray analyses. These peptides were incrementally increased in size and affinity until they nearly filled the cavity. Progressive changes in binding patterns were mapped by comparisons of crystallo-graphically refined structures of 14 peptide–protein complexes at 2.7 Å resolution. These comparisons led to guidelines for ligand design and also suggested ways to modify previously established binding patterns. By manipulating equilibria involving histidine, for example, it was possible to abolish one important intramolecular interaction of the bound ligand and substitute another. These events triggered a change inconformation of the ligand from a compact to an extended form and a comprehensive change in the mode of binding to the protein. In dipeptides of histidine and proline, protonation of both imidazolium nitrogen atoms was used to program anend-to-end reversal of the direction in which the ligand was inserted into the binding cavity. Peptides cocrystallized with proteins produced complexes somewhat different in structure from those in which ligandswere diffused into preexisting crystals. In sucha large and malleable cavity, space utilization was thus different when a ligand was introduced before the imposition of crystal packing restraints. © 1993 Wiley-Liss, Inc. 相似文献
7.
8.
9.