全文获取类型
收费全文 | 23727篇 |
免费 | 2023篇 |
国内免费 | 14篇 |
出版年
2023年 | 79篇 |
2021年 | 362篇 |
2020年 | 254篇 |
2019年 | 344篇 |
2018年 | 415篇 |
2017年 | 393篇 |
2016年 | 621篇 |
2015年 | 1038篇 |
2014年 | 1184篇 |
2013年 | 1494篇 |
2012年 | 1682篇 |
2011年 | 1601篇 |
2010年 | 1041篇 |
2009年 | 967篇 |
2008年 | 1288篇 |
2007年 | 1213篇 |
2006年 | 1223篇 |
2005年 | 1183篇 |
2004年 | 1115篇 |
2003年 | 968篇 |
2002年 | 1027篇 |
2001年 | 377篇 |
2000年 | 315篇 |
1999年 | 325篇 |
1998年 | 294篇 |
1997年 | 230篇 |
1996年 | 249篇 |
1995年 | 241篇 |
1994年 | 245篇 |
1993年 | 249篇 |
1992年 | 252篇 |
1991年 | 220篇 |
1990年 | 194篇 |
1989年 | 194篇 |
1988年 | 183篇 |
1987年 | 173篇 |
1986年 | 145篇 |
1985年 | 179篇 |
1984年 | 200篇 |
1983年 | 169篇 |
1982年 | 180篇 |
1981年 | 147篇 |
1980年 | 128篇 |
1979年 | 132篇 |
1978年 | 121篇 |
1977年 | 117篇 |
1976年 | 90篇 |
1975年 | 65篇 |
1974年 | 95篇 |
1973年 | 79篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Jan A. Gossen Wiljo J. F. de Leeuw Aart Verwest Paul H. M. Lohman Jan Vijg 《Mutation research》1991,250(1-2):423-429
To study spontaneous and induced mutagenesis in vivo we recently constructed a series of transgenic mice harboring different numbers of bacteriophage lambda shuttle vectors, provided with a LacZ mutational target gene, integrated in their genome. The transgenic mice enabled analysis of spontaneous and induced mutation frequencies in postmitotic tissues like liver and brain. The obtained data indicated spontaneous mutation frequencies in the order of −5 - 10−6. Here we report a 25–100 times higher spontaneous mutation frequency in liver and brain DNA of mice from strain 35.5, with the lambda-gt10LacZ concatemer integrated on the X-chromosome. These results indicate the presence of a mutational ‘hot spot’ in the mammalian somatic genome in vivo. 相似文献
62.
The spinning apparatus of Uloboridae in relation to the structure and construction of capture threads (Arachnida,Araneida) 总被引:1,自引:0,他引:1
H. M. Peters 《Zoomorphology》1984,104(2):96-104
Summary Besides the two axial fibers and the mass of cribellum fibrils, a third component is present in the capture threads of uloborids. This is a substructure originating from the paracribellum. It probably helps to fasten the axial fibers in their position. The axial fibers are secreted from the two glandulae pseudoflagelliformes whose spigots are situated on the posterior spinnerets. It is hypothesized that the cribellum fibrils become jammed and thus fixed between the axial fibers by periodical abduction and adduction of these spinnerets. 相似文献
63.
Tinoush Moulaei Olga Stuchlik Matthew Reed Weirong Yuan Jan Pohl Wuyuan Lu Lauren Haugh-Krumpe Barry R O'Keefe Alexander Wlodawer 《Protein science : a publication of the Protein Society》2010,19(9):1649-1661
The antiviral lectin scytovirin (SVN) contains a total of five disulfide bonds in two structurally similar domains. Previous reports provided contradictory results on the disulfide pairing in each individual domain, and we have now re‐examined the disulfide topology. N‐terminal sequencing and mass spectrometry were used to analyze proteolytic fragments of native SVN obtained at acidic pH, yielding the assignment as Cys7–Cys55, Cys20–Cys32, Cys26–Cys38, Cys68–Cys80, and Cys74–Cys86. We also analyzed the N‐terminal domain of SVN (SD1, residues 1–48) prepared by expression/oxidative folding of the recombinant protein and by chemical synthesis. The disulfide pairing in the chemically synthesized SD1 was forced into predetermined topologies: SD1A (Cys20–Cys26, Cys32–Cys38) or SD1B (Cys20–Cys32, Cys26–Cys38). The topology of native SVN was found to be in agreement with the SD1B and the one determined for the recombinant SD1 domain. Although the two synthetic forms of SD1 were distinct when subjected to chromatography, their antiviral properties were indistinguishable, having low nM activity against HIV. Tryptic fragments, the “cystine clusters” [Cys20–Cys32/Cys26–Cys38; SD1] and [Cys68–Cys80/Cys74–C‐86; SD2], were found to undergo rapid disulfide interchange at pH 8. This interchange resulted in accumulation of artifactual fragments in alkaline pH digests that are structurally unrelated to the original topology, providing a rational explanation for the differences between the topology reported herein and the one reported earlier (Bokesh et al., Biochemistry 2003;42:2578–2584). Our observations emphasize the fact that proteins such as SVN, with disulfide bonds in close proximity, require considerable precautions when being fragmented for the purpose of disulfide assignment. 相似文献
64.
An individual-based model forDrosophila is formulated, based on competition amongst larvae consuming the same batch of food. The predictions of the model are supported
by data for single speciesDrosophila populations reared in the laboratory. The model is used to build a simple discrete model for the dynamics ofDrosophila populations that are kept over a number of generations. The dynamics of a single species is shown to give either a stable
equilibrium or fluctuations which can be periodic or chaotic. When the dynamics of a species in the absence of the other is
periodic or chaotic, we found coexistence or two alternative states, on neither of which the species can coexist. 相似文献
65.
66.
The phylogeny of the fungus gnat family Mycetophilidae (Diptera) is reconstructed with a focus on the species‐rich and taxonomically difficult subfamilies Gnoristinae and Mycomyinae. The multigene phylogenetic analyses are based on five nuclear (18S, 28S, CAD, MCS, ITS2) and four mitochondrial (12S, 16S, COI, CytB) gene markers. The analyses strongly support the monophyly of Mycetophilidae and the subfamilies Manotinae, Sciophilinae, Leiinae, and Mycomyinae, although Gnoristinae is paraphyletic with respect to Mycetophilinae. All the genera and groups of genera included are supported as monophyletic, except for Acomoptera Vockeroth, Boletina Staeger, Dziedzickia Johannsen, Ectrepesthoneura Enderlein, and Neoempheria Osten Sacken. Ancestral character state reconstructions were applied to two morphological features present in Gnoristinae and Mycomyinae (i.e. presence of setae on wing membrane and wing vein R4) in order to assess their evolution. The wing vein R4 appears as an unstable character, spread throughout different clades. A dated phylogeny of the family Mycetophilidae showed that most of the subfamilies of Mycetophilidae originated and diversified during the Cretaceous. The youngest subfamilies, originated in the Paleogene, appear to be Mycomyinae and Mycetophilinae. 相似文献
67.
Thomas Pauli Ruth F. Castillo‐Cajas Paolo Rosa Sandra Kukowka Alexander Berg Eric van den Berghe Felix Fornoff Sebastian Hopfenmüller Manfred Niehuis Ralph S. Peters Michael Staab Franco Strumia Stefan Tischendorf Thomas Schmitt Oliver Niehuis 《Systematic Entomology》2019,44(2):322-335
Cuckoo wasps (Hymenoptera: Chrysididae) are a species‐rich family of obligate brood parasites (i.e. parasitoids and kleptoparasites) whose hosts range from sawflies, wasps and bees, to walking sticks and moths. Their brood parasitic lifestyle has led to the evolution of fascinating adaptations, including chemical mimicry of host odours by some species. Long‐term nomenclatural stability of the higher taxonomic units (e.g. genera, tribes, and subfamilies) in this family and a thorough understanding of the family's evolutionary history critically depend on a robust phylogeny of cuckoo wasps. Here we present the results from phylogenetically analysing ten nuclear‐encoded genes and one mitochondrial gene, all protein‐coding, in a total of 186 different species of cuckoo wasps representing most major cuckoo wasp lineages. The compiled data matrix comprised 4946 coding nucleotide sites and was phylogenetically analysed using classical maximum‐likelihood and Bayesian inference methods. The results of our phylogenetic analyses are mostly consistent with earlier ideas on the phylogenetic relationships of the cuckoo wasps' subfamilies and tribes, but cast doubts on the hitherto hypothesized phylogenetic position of the subfamily Amiseginae. However, the molecular data are not fully conclusive in this respect due to low branch support values at deep nodes. In contrast, our phylogenetic estimates clearly indicate that the current systematics of cuckoo wasps at the genus level is artificial. Several of the currently recognized genera are para‐ or polyphyletic (e.g. Cephaloparnops, Chrysis, Chrysura, Euchroeus, Hedychridium, Praestochrysis, Pseudochrysis, Spintharina, and Spinolia). At the same time, our data support the validity of the genus Colpopyga, previously synonymized with Hedychridium. We discuss possible solutions for how to resolve the current shortcomings in the systematics of cuckoo wasp genera and decided to grant Prospinolia the status of a valid genus (Prospinolia stat.n. ) and transferring Spinolia theresae [du Buysson 1900] from Spinolia to Prospinolia (Prospinolia theresae stat.restit. ). We discuss the implications of our phylogenetic inferences for understanding the evolution of host associations in this group. The results of our study not only shed new light on the evolutionary history of cuckoo wasps, but also set the basis for future phylogenomic investigations on this captivating group of wasps by guiding taxonomic sampling efforts and the design of probes for target DNA enrichment approaches. 相似文献
68.
Jan Batelka Jakub Prokop Hans Pohl Ming Bai Weiwei Zhang Rolf G. Beutel 《Systematic Entomology》2019,44(2):396-407
Extremely miniaturized longipedes insects (body length c. 0.3 mm) embedded in two pieces of Cretaceous amber from Myanmar are described and interpreted. Using inverted fluorescence and light microscopy for detailed analysis of microstructures, the inclusions were identified as primary larvae of the beetle family Ripiphoridae, subfamily Ripidiinae. While the structure of thoracic and abdominal segments including appendages corresponds well with the groundplan known in recent members of Ripidiinae, a curved prosternal ridge with prominent spines (each c. 5 μm), the reduced condition of stemmata and antennae and the lack of sharp mandibles are unique features within the entire family, apparently apomorphies of the longipedes larvae. A sinuate prosternal edge with a dense row of spines (prosternoctenidium) might be homologous with ‘head ctenidia’ in some previously described miniaturized conicocephalate larvae, but further investigation is needed. The morphological differences between the head of longipedes larvae and extant Ripidiinae are interpreted as adaptations to different groups of hosts and life strategies. Palaeoethology of the longipedes larvae is briefly discussed. In addition, the systematic placement of conicocephalate larvae from Canadian, Myanmar and Russian Cretaceous ambers, already interpreted by various authors as primary instars within Coleopterida (assigned to either Strepsiptera or to the coleopteran Tenebrionoidea: Ripiphoridae), is discussed. 相似文献
69.