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排序方式: 共有1119条查询结果,搜索用时 15 毫秒
81.
Cyclic AMP is sufficient for triggering the exocytic recruitment of aquaporin-2 in renal epithelial cells 总被引:1,自引:0,他引:1
The initial response of renal epithelial cells to the antidiuretic hormone arginine vasopressin (AVP) is an increase in cyclic AMP. By applying immunofluorescence, cell membrane capacitance and transepithelial water flux measurements we show that cAMP alone is sufficient to elicit the antidiuretic cellular response in primary cultured epithelial cells from renal inner medulla, namely the transport of aquaporin-2 (AQP2)-bearing vesicles to, and their subsequent fusion with, the plasma membrane (AQP2 shuttle). The AQP2 shuttle is evoked neither by AVP-independent Ca2+ increases nor by AVP-induced Ca2+ increases. However, clamping cytosolic Ca2+ concentrations below resting levels at 25 nM inhibited exocytosis. Exocytosis was confined to a slow monophasic response, and readily releasable vesicles were missing. Analysis of endocytic capacitance steps revealed that cAMP does not decelerate the retrieval of AQP2 from the plasma membrane. Our data suggest that cAMP initiates an early step, namely the transport of AQP2-bearing vesicles towards the plasma membrane, and do not support a regulatory function for Ca2+ in the AQP2 shuttle. 相似文献
82.
83.
Pankow R Dürkop H Latza U Krause H Kunzendorf U Pohl T Bulfone-Paus S 《Journal of immunology (Baltimore, Md. : 1950)》2000,165(1):263-270
OX40 is a member of the TNF receptor family, expressed on activated T cells. It is the only costimulatory T cell molecule known to be specifically up-regulated in human T cell leukemia virus type-I (HTLV-I)-producing cells. In a T cell line, OX40 surface expression was shown to be induced by HTLV-I Tax alone. To understand molecular mechanisms of OX40 gene regulation and modulation by HTLV-I Tax, we have cloned the human OX40 gene and analyzed its 5'-flanking region. By reporter gene analysis with progressive 5' deletions from nucleotides -1259 to -64, we have defined a 157-bp DNA fragment as a minimal promoter for constitutive expression. In addition, we show that in the OX40+ cell line, Co, Tax is able to further increase OX40 surface expression. Up-regulation of OX40 promoter activity by Tax requires two upstream NF-kappaB sites, which are not active in the constitutive OX40 expression. Their deletion abrogates Tax responsiveness in reporter gene analysis. The site-directed mutagenesis of each NF-kappaB site demonstrates that cooperative NF-kappaB binding is a prerequisite for Tax-directed activity as neither site alone is sufficient for a full Tax responsiveness of the OX40 promoter. Upon Tax expression, both sites bind p65 and c-Rel. These data provide new insight into the direct regulation of OX40 by Tax and add to our understanding of the possible role of the OX40/OX40 ligand system in the proliferation of HTLV-I+ T cells. 相似文献
84.
Kock JL Venter P Smith DP Van Wyk PW Botes PJ Coetzee DJ Pohl CH Botha A Riedel KH Nigam S 《Antonie van Leeuwenhoek》2000,77(4):401-406
Research on the distribution of oxylipins (3-hydroxy fatty acids) in flocculant strains of the yeast Saccharomyces cerevisiae led to the uncovering of a novel ghosting phenomenon observed during assumed lectin-mediated aggregation. We found that intracellular oxylipin-containing osmiophilic layers migrate through yeast cell walls in a ghostlike fashion without visually affecting the cell wall structure or the layers. This migration resulted in the binding of these layers to cell walls of adjacent cells. Consequently, ghosting seems a prerequisite for flocculation to occur. However, ghosting alone may not be sufficient to ensure flocculation. 相似文献
85.
Monitoring gene flow from transgenic sugar beet using cytoplasmic male-sterile bait plants 总被引:10,自引:0,他引:10
One of the most discussed environmental effects associated with the use of transgenic plants is the flow of genes to plants in the environment. The flow of genes may occur through pollen since it is the reproductive system that is designed for gene movement. Pollen-mediated gene escape is hard to control in mating plants. Pollen from a wind pollinator can move over distances of more than 1000 m. To investigate the efficiency of transgenic pollen movement under realistic environmental conditions, the use of bait plants might be an effective tool. In this study, cytoplasmic male-sterile (CMS) sugar beets were tested with regard to their potential for monitoring transgene flow. As the pollen source, transgenic sugar beets were used that express recombinant DNA encoding viral (beet necrotic yellow vein virus) resistance, and antibiotic (kanamycin) and herbicide (glufosinate) tolerance genes. In a field trial, the effectiveness of a hemp (Cannabis sativa) stripe containment strategy was tested by measuring the frequency of pollinated CMS bait plants placed at different distances and directions from a transgenic pollen source. The results demonstrated the ineffectiveness of the containment strategy. Physiological and molecular tests confirmed the escape and production of transgenic offspring more than 200 m behind the hemp containment. Since absolute containment is unlikely to be effective, the CMS-bait plant detection system is a useful tool for other monitoring purposes. 相似文献
86.
Pohl H 《Chronobiology international》2000,17(4):471-488
Circadian pacemakers control both “daytime” activity and nocturnal restlessness of migratory birds, and the daily rhythm of melatonin release from the pineal has been suggested to be involved in the control of migratory activity. To study the phase relations between the two activity components during entrainment and when free running, locomotor activity of bramblings (Fringilla montifringilla) was recorded continuously under a 12:12 “cool light” to “warm light” cycle (CL:WL, ca. 5000 K and ca. 2500 K, respectively) or blue light to red light cycle (BL:RL, maxima at 440 and 650 nm, respectively) at different irradiance ratios. Migratory activity was expressed primarily during the WL or RL phase of the light cycles. Under free-running conditions, the circadian periods τ correlated with the phase relations between day and night (migratory) activity components during preceding entrainment. Bramblings with migratory activity had significantly longer τ at constant light intensity than the same individuals without migratory activity. Birds with migratory activity reentrained faster after a 6h phase shift of the CL:WL cycle than birds without migratory activity. When exogenous melatonin was given in the drinking water (200 μg/mL 1% ethanol or 0.86 mM) to bramblings exposed to 12:12 CL:WL cycles with constant irradiance, the amounts of activity, which were initially higher during the WL phase of the light cycle, were suppressed to similar low levels during both light phases. The systematic changes in the amounts of activity during melatonin treatment were not correlated with consistent changes in entrainment status. The data support the hypothesis that changes in the amplitude and level of the daily melatonin cycle are involved in regulating migratory restlessness, by either allowing or inhibiting nocturnal activity. (Chronobiology International, 17(4), 471-488, 2000) 相似文献
87.
Gerhard Obermeyer Hildegard Klaushofer Marion Nagl Margit Höftberger Friedrich-Wilhelm Bentrup 《Planta》1998,207(2):303-312
Inhibitors of type-2A protein phosphatase (PPase-2A), calyculin A (cal A) and okadaic acid (OA), inhibit pollen grain germination
and growth of pollen tubes of Lilium longiflorum Thunb. at nanomolar concentrations. Half-maximal inhibition of cytoplasmic PPase-2A activity was below 0.1 nM for cal A and
at 0.7 nM for OA. Other protein phosphatase inhibitors (tautomycin, cypermethrin, and dephostatin) were less effective. The
OA- and cal A-sensitive as well as dephostatin-sensitive PPase activity in the cytoplasm did not change during germination
and growth of pollen tubes. Addition of cal A and OA disturbed the direction of pollen tube growth and the distribution of
cytoplasmic organelles and caused cell wall thickenings as observed by light and electron microscopy. Inhibition of PPase-2A
caused multiple effects at the cellular level, cytoskeletal elements being a putative target of PPase-2A activity.
Received: 30 March 1998 / Accepted: 6 July 1998 相似文献
88.
Genotypic differences in acquiring immobile P exist among species or cultivars within one species. We investigated the P-efficiency mechanisms of rapeseed (Brassica napus L.) in low P soil by measuring plant growth, P acquisition and rhizosphere properties. Two genotypes with different P efficiencies were grown in a root-compartment experiment under low P (P15: 15 mg P kg?1) and high P (P100: 100 mg P kg?1) treatments. The P-efficient genotype produced more biomass, and had a high seed yield and high P acquisition efficiency under low P treatment. Under both P treatments, both genotypes decreased inorganic P (Pi) and organic P (Po) fractions in the rhizosphere soil. However there was no decrease in NaHCO3-Po at P100. For the P15 treatment, the concentrations of NaHCO3-Po and NaOH-Po were negatively correlated with soil acid phosphatase activity. The P-efficient genotype 102 differed from the P-inefficient genotype 105 in the following ways. In the rhizosphere the soil pH was lower, acid phosphatase activity was higher, and depletion of P was greater. Further the depletion zones were wider. These results suggested that improving P efficiency based on the character of P efficiency acquisition in P-efficient genotype would be a potential approach for maintaining rapeseed yield potential in soils with low P bioavailability. 相似文献
89.
90.