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991.
Synthesis of a novel superabsorbent hydrogel by copolymerization of acrylamide and cashew gum modified with glycidyl methacrylate 总被引:5,自引:0,他引:5
Marcos R. Guilherme Adriano V. Reis Sulen H. Takahashi Adley F. Rubira Judith P.A. Feitosa Edvani C. Muniz 《Carbohydrate polymers》2005,61(4):464-471
Novel superabsorbent hydrogels were manufactured using chemically modified cashew gum (CGMA) and acrylamide (AAm) as reactants. The route for the synthesis was feasible due to the incorporation of glycidyl methacrylate (GMA) into structure of cashew gum (CG) to form the cashew gum-methacrylated (CGMA), in an appropriate mixture water-DMSO, as solvent, and using TEMED as catalyst. Thereafter, the CGMA was copolymerized with AAm yielding (CGMA-co-AAm) hydrogels. The main characteristics of raw and the modified materials are reported in this paper. 13C NMR, 1H NMR and FTIR spectroscopies confirmed the incorporation of vinyl groups, from GMA, into CG structure. By the spectrophotometry analyses, it was found that, ca. 82% of GMA was incorporated to the CG after 24 h of reaction. The cross-linking of CGMA or co-polymerization of CGMA with acrylamide leads to a hydrogel formation. Their gelation was characterized by FT-IR analysis. Alkaline hydrolysis at 40 °C for 3 and 4.5 h increased the water uptake (WU) capacity. Hydrolyzed CGMA-co-AAm hydrogels present higher values of WU (up to 1500) and may be classified as water superabsorbent material. Applications in agriculture, as soil conditioner, and in biomedical field, as biomaterial (scaffold) are being investigated. 相似文献
992.
993.
994.
Mrc1 and DNA polymerase epsilon function together in linking DNA replication and the S phase checkpoint 总被引:1,自引:0,他引:1
Lou H Komata M Katou Y Guan Z Reis CC Budd M Shirahige K Campbell JL 《Molecular cell》2008,32(1):106-117
Yeast Mrc1, ortholog of metazoan Claspin, is both a central component of normal DNA replication forks and a mediator of the S phase checkpoint. We report that Mrc1 interacts with Pol2, the catalytic subunit of DNA polymerase epsilon, essential for leading-strand DNA replication and for the checkpoint. In unperturbed cells, Mrc1 interacts independently with both the N-terminal and C-terminal halves of Pol2 (Pol2N and Pol2C). Strikingly, phosphorylation of Mrc1 during the S phase checkpoint abolishes Pol2N binding, but not Pol2C interaction. Mrc1 is required to stabilize Pol2 at replication forks stalled in HU. The bimodal Mrc1/Pol2 interaction may be an additional step in regulating the S phase checkpoint response to DNA damage on the leading strand. We propose that Mrc1, which also interacts with the MCMs, may modulate coupling of polymerization and unwinding at the replication fork. 相似文献
995.
Silva MT do Vale A dos Santos NM 《Apoptosis : an international journal on programmed cell death》2008,13(4):463-482
In metazoans apoptosis is a major physiological process of cell elimination during development and in tissue homeostasis and
can be involved in pathological situations. In vitro, apoptosis proceeds through an execution phase during which cell dismantling
is initiated, with or without fragmentation into apoptotic bodies, but with maintenance of a near-to-intact cytoplasmic membrane,
followed by a transition to a necrotic cell elimination traditionally called “secondary necrosis”. Secondary necrosis involves
activation of self-hydrolytic enzymes, and swelling of the cell or of the apoptotic bodies, generalized and irreparable damage
to the cytoplasmic membrane, and culminates with cell disruption. In vivo, under normal conditions, the elimination of apoptosing
cells or apoptotic bodies is by removal through engulfment by scavengers prompted by the exposure of engulfment signals during
the execution phase of apoptosis; if this removal fails progression to secondary necrosis ensues as in the in vitro situation.
In vivo secondary necrosis occurs when massive apoptosis overwhelms the available scavenging capacity, or when the scavenger
mechanism is directly impaired, and may result in leakage of the cell contents with induction of tissue injury and inflammatory
and autoimmune responses. Several disorders where secondary necrosis has been implicated as a pathogenic mechanism will be
reviewed. 相似文献
996.
Holt O Kanno E Bossi G Booth S Daniele T Santoro A Arico M Saegusa C Fukuda M Griffiths GM 《Traffic (Copenhagen, Denmark)》2008,9(4):446-457
Rab27a is required for polarized secretion of lysosomes from cytotoxic T lymphocytes (CTLs) at the immunological synapse. A series of Rab27a-interacting proteins have been identified; however, only Munc13-4 has been found to be expressed in CTL. In this study, we screened for expression of the synaptotagmin-like proteins (Slps): Slp1/JFC1, Slp2-a/exophilin4, Slp3-a, Slp4/granuphilin, Slp5 and rabphilin in CTL. We found that both Slp1 and Slp2-a are expressed in CTL. Isoforms of Slp2-a in CTL showed variation of the linker region but conserved the C2A and C2B and Slp homology (SHD) domains. Both Slp1 and Slp2-a interact with Rab27a in CTL, and Slp2-a, but not Slp1, is rapidly degraded when Rab27a is absent. Slp2-a contains PEST-like sequences within its linker region, which render it susceptible to degradation. Both Slp1 and Slp2-a localize predominantly to the plasma membrane of both human and mouse CTLs, and we show that Slp2-a can focus tightly at the immunological synapse formed with a target cell. Individual knockouts of either Slp2-a or Slp1 fail to impair CTL-mediated killing of targets; however, overexpression of a dominant-negative construct consisting of the SHD of Slp2-a, which is 56% identical to that of Slp1, reduces target cell death, suggesting that both Slp1 and Slp2-a contribute to secretory lysosome exocytosis from CTL. These results suggest that both Slp1 and Slp2-a may form part of a docking complex, capturing secretory lysosomes at the immunological synapse. 相似文献
997.
The complete larval development (four zoeae and one megalopa) of Clibanarius aequabilis and C. erythropus, reared under laboratory conditions, is described and illustrated. The larval stages of the two northeastern Atlantic Clibanarius species cannot be easily differentiated. Their morphological characters are compared with those of other known Clibanarius larvae. The genus Clibanarius is very homogeneous with respect to larval characters. All Clibanarius zoeae display a broad and blunt rostrum, smooth abdominal segments and an antennal scale without a terminal spine. Beyond
the second zoeal stage, the fourth telson process is present as a fused spine, and the uropods are biramous. In the fourth
larval stage all species display a mandibular palp. The Clibanarius megalopa presents weakly developed or no ocular scales, symmetrical chelipeds, apically curved corneous dactylus in the second
and third pereiopods, and 5–11 setae on the posterior margin of the telson. Apart from the number of zoeal stages, Clibanarius species may be separated, beyond the second zoeal stage, by the telson formula and the morphology of the fourth telson process. 相似文献
998.
Farioli-Vecchioli S Saraulli D Costanzi M Pacioni S Cinà I Aceti M Micheli L Bacci A Cestari V Tirone F 《PLoS biology》2008,6(10):e246
Adult neurogenesis in the dentate gyrus plays a critical role in hippocampus-dependent spatial learning. It remains unknown, however, how new neurons become functionally integrated into spatial circuits and contribute to hippocampus-mediated forms of learning and memory. To investigate these issues, we used a mouse model in which the differentiation of adult-generated dentate gyrus neurons can be anticipated by conditionally expressing the pro-differentiative gene PC3 (Tis21/BTG2) in nestin-positive progenitor cells. In contrast to previous studies that affected the number of newly generated neurons, this strategy selectively changes their timing of differentiation. New, adult-generated dentate gyrus progenitors, in which the PC3 transgene was expressed, showed accelerated differentiation and significantly reduced dendritic arborization and spine density. Functionally, this genetic manipulation specifically affected different hippocampus-dependent learning and memory tasks, including contextual fear conditioning, and selectively reduced synaptic plasticity in the dentate gyrus. Morphological and functional analyses of hippocampal neurons at different stages of differentiation, following transgene activation within defined time-windows, revealed that the new, adult-generated neurons up to 3–4 weeks of age are required not only to acquire new spatial information but also to use previously consolidated memories. Thus, the correct unwinding of these key memory functions, which can be an expression of the ability of adult-generated neurons to link subsequent events in memory circuits, is critically dependent on the correct timing of the initial stages of neuron maturation and connection to existing circuits. 相似文献
999.
Gabriele?Gerardi Antonella?De NinnoEmail author Marco?Prosdocimi Vanni?Ferrari Filippo?Barbaro Sandro?Mazzariol Daniele?Bernardini Getullio?Talpo 《Biomagnetic research and technology》2008,6(1):3
A series of experiments on rats have been performed, to study the effects of long time (50 days) exposure to electromagnetic fields of extremely low frequency (ELF, i.e. less than 100 Hz) and amplitude (non thermal), testing whether the metabolic processes would be affected. The background lies on recent observations on the behaviour of isolated enzymes in vitro exposed to EFL fields. In these experiments, the cyclotron (or Larmor) frequency of the metallic ion has been used to "stimulate" the metalloproteins redox-active site, thus obtaining a clear variation of the enzyme functionality. In this paper we have extended for the first time the check to more complex animal metabolism. The novelty of this approach implies that a large amount of data had to be analyzed since it was not possible, in principle, to select only a few parameters among all the potential effects. Several biochemical parameters have been evaluated by comparing their values during the periods of exposure (field ON) and non exposure (field OFF). The evidence that long term exposure to electromagnetic fields with a well defined frequency may have relevant effects on parameters such as body weight, blood glucose and fatty acid metabolism has been obtained. 相似文献
1000.
Reis AC Gondim MG Moraes GJ Hanna R Schausberger P Lawson-Balagbo LE Barros R 《Neotropical Entomology》2008,37(4):457-462
Aceria guerreronis Keifer can cause severe damage to coconuts in several countries around the world. Rare studies have been conducted to determine the predatory mites associated with A. guerreronis in Brazil. The study evaluated the prevalence of A. guerreronis and associated predators on the bracts and on the surface of the fruits underneath the bracts, for 12 months, on coconut palms grown along the coast of the States of Alagoas, Paraíba and Pernambuco, Northeastern Brazil. Mites of 10 families were found, but by far the most abundant species was A. guerreronis, corresponding to 99.5% of the mites collected. The prevailing species amongst the predators were the Phytoseiidae mites Neoseiulus baraki (Athias-Henriot) and Neoseiulus paspalivorus (De Leon). These are flat mites that have short limbs, characteristics that allow them to invade the main habitat occupied by A. guerreronis. Other predators were found, but in low numbers, due mainly to their difficulty in reaching the fruit areas most inhabited by A. guerreronis. However, these mites could prey on that pest when it leaves its preferred habitat to disperse. No significant correlations were observed between the levels of abiotic factors and the population levels of A. guerreronis or of the phytoseiids associated with it. This probably occurred due to the simultaneous and conflicting effects of those factors on the mites in the field, or to significant differences between the climatic factors measured in the environment and those prevailing in the habitat occupied by A. guerreronis. 相似文献