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91.
Delayed fluorescence (DF) excitation spectrometry was examined as a proxy for phytoplankton activity in comparison to pulse-amplitude-modulated (PAM) fluorometry and dissolved oxygen (DO) evolution. During several day–night cycles, the three target variables were monitored simultaneously, together with pH, temperature and photosynthetically active irradiance in an exponentially growing Chlorella population exposed to natural light conditions. It was found that during a diel cycle prompt and DF signals corresponded to each other and were negatively correlated to the light intensity, with maximum values during night and vice versa. The DF signal showed a strong linear relationship with the quantum yield of photosystem II. Our findings thus suggest that, in addition to the continuous monitoring of active chlorophyll of different taxonomical groups, DF excitation spectrometry also carries the potential to continuously monitor the quantum yields and relative electron transport rates in natural phytoplankton assemblages.  相似文献   
92.
The renin-angiotensin system plays an important role in cardiovascular homeostasis by contributing to the regulation of blood volume, blood pressure, and vascular tone. Because AT(1) receptors have been described in the coronary microcirculation, we investigated whether ANG II contributes to the regulation of coronary vascular tone and whether its contribution is altered during exercise. Since the renin-angiotensin system is activated after myocardial infarction, resulting in an increase in circulating ANG II, we also investigated whether the contribution of ANG II to the regulation of vasomotor tone is altered after infarction. Twenty-six chronically instrumented swine were studied at rest and while running on a treadmill at 1-4 km/h. In 13 swine, myocardial infarction was induced by ligation of the left circumflex coronary artery. Blockade of AT(1) receptors (irbesartan, 1 mg/kg iv) had no effect on myocardial O(2) consumption but resulted in an increase in coronary venous O(2) tension and saturation both at rest and during exercise, reflecting coronary vasodilation. Despite increased plasma levels of ANG II after infarction and maintained coronary arteriolar AT(1) receptor levels, the vasodilation evoked by irbesartan was significantly reduced both at rest and during exercise. In conclusion, despite elevated plasma levels, the vasoconstrictor influence of ANG II on the coronary circulation in vivo is reduced after myocardial infarction. This reduction in ANG II-induced coronary vasoconstriction may serve to maintain perfusion of the remodeled myocardium.  相似文献   
93.
Androgen deprivation therapy (ADT) for prostate cancer is now used in earlier disease stages and as adjuvant treatment. Recognizing and reducing the toxicity of this therapy, including worsened lipid levels and cardiovascular disease (CVD) risks, has become an important clinical concern. Oral estrogen therapy induces hypogonadism and mitigates many side effects of ADT, but has a high thrombosis risk. Transdermal estrogen therapy (TDE) has a lower thrombosis risk than oral estrogen and may improve CVD risk compared with ADT. This prospective pilot study of 18 men with androgen-independent prostate cancer receiving ADT measured effects of TDE on lipid and inflammatory CVD risk factors before and after 8 weeks of TDE (estradiol 0.6 mg/day). During treatment, estradiol levels rose 17-fold; total cholesterol, LDL cholesterol, and apolipoprotein B levels decreased. HDL2 cholesterol increased, with no changes in triglyceride or VLDL cholesterol levels. Dense LDL cholesterol decreased and LDL buoyancy increased in association with a decrease in HL activity. Highly sensitive C-reactive protein levels and other inflammatory markers did not worsen. Compared with ADT, short-term TDE therapy of prostate cancer improves lipid levels without deterioration of CVD-associated inflammatory markers and may, on longer-term follow-up, improve CVD and mortality rates.  相似文献   
94.
Ras is a major mediator of PE (phorbol ester) effects in mammalian cells. Various mechanisms for PE activation of Ras have been reported [Downward, Graves, Warne, Rayter and Cantrell (1990) Nature (London) 346, 719-723; Shu, Wu, Mosteller and Broek (2002) Mol. Cell. Biol. 22, 7758-7768; Roose, Mollenauer, Gupta, Stone and Weiss (2005) Mol. Cell. Biol. 25, 4426-4441; Grosse, Roelle, Herrlich, H?hn and Gudermann (2000) J. Biol. Chem. 275, 12251-12260], including pathways that target GAPs (GTPase-activating proteins) for inactivation and those that result in activation of GEFs (guanine nucleotide-exchange factors) Sos (son of sevenless homologue) or RasGRP (RAS guanyl releasing protein). However, a biochemical link between PE and GAP inactivation is missing and GEF stimulation is hard to reconcile with the observation that dominant-negative S17N-Ras does not compromise Ras-dependent ERK (extracellular-signal-regulated kinase) activation by PE. We have addressed this controversy and carried out an in-depth biochemical study of PE-induced Ras activation in COS-7 cells. Using a cell-permeabilization approach to monitor nucleotide exchange on Ras, we demonstrate that PE-induced Ras-GTP accumulation results from GEF stimulation. Nucleotide exchange stimulation by PE is prevented by PKC (protein kinase C) inhibition but not by EGFR [EGF (epidermal growth factor) receptor] blockade, despite the fact that EGFR inhibition aborts basal and PE-induced Shc (Src homology and collagen homology) phosphorylation and Shc-Grb2 (growth-factor-receptor-bound protein 2) association. In fact, EGFR inhibition ablates basal nucleotide exchange on Ras in growth-arrested COS-7 cells. These data disclose the existence of two separate GEF systems that operate independently from each other to accomplish PE-dependent formation of Ras-GTP and to maintain resting Ras-GTP levels respectively. We document that COS-7 cells do not express RasGRP and present evidence that the PE-responsive GEF system may involve PKC-dependent phosphorylation of Sos. More fundamentally, these observations shed new light on enigmatic issues such as the inefficacy of S17N-Ras in blocking PE action or the role of the EGFR in heterologous agonist activation of the Ras/ERK pathway.  相似文献   
95.
Muscular hydrostats, such as tongues, trunks or tentacles, have fewer constraints on their degrees of freedom than musculoskeletal systems, so changes in a structure’s shape may alter the positions and lengths of other components (i.e., induce mechanical reconfiguration). We studied mechanical reconfiguration during rejection and swallowing in the marine mollusk Aplysia californica. During rejection, inedible material is pushed out of an animal’s buccal cavity. The grasper (radula/odontophore) closes on inedible material, and then a posterior muscle, I2, pushes the grasper toward the jaws (protracts it). After the material is released, an anterior muscle complex (the I1/I3/jaw complex) pushes the grasper toward the esophagus (retracts it). During swallowing, the grasper is protracted open, and then retracts closed, pulling in food. Grasper closure changes its shape. Magnetic resonance images show that grasper closure lengthens I2. A kinetic model quantified the changes in the ability of I2 and I1/I3 to exert force as grasper shape changed. Grasper closure increases I2’s ability to protract during rejection, and increases I1/I3’s ability to retract during swallowing. Motor neurons controlling radular closure may therefore affect the behavioral outputs of I2’s and I1/I3’s motor neurons. Thus, motor neurons may modulate the outputs of other motor neurons through mechanical reconfiguration.Valerie A. Novakovic and Gregory P. Sutton contributed equally to the paper.  相似文献   
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98.
Ecological risk actually refers to two separate things. First, risk to the environment as a result of human activity. Contaminated sites are an example. Second, risk to the biota—flora, fauna, and people—as a result of environmental hazards. Geophysical risk arising from natural hazards is an example. Risk is a combination of likelihoods and consequences. This article examines methods used to quantify the consequences. At the general level, such methods are linked to the methods used to quantify the likelihoods and thus to quantify the risks. It is possible to use the existing frameworks of risk management, health risk assessment, and ecological risk analysis to develop a risk management framework that is suitable for ecological risk assessment. The framework consists of the following steps:
  1. Determine concernsby using risk assessment techniques for various scenarios.

  2. Identify the consequences by systematically identifying hazards.

  3. Undertake calculations by using relevant models.

  4. Evaluate certainties, uncertainties, and probabilities involved in the calculations of the vulnerability and of the exposure.

  5. Compare with criteriato assess the need for further action.

  6. Determine and act on options to control, mitigate, and adapt to the risk.

  7. Communicatethe results to those who need to know.

  相似文献   
99.
With a view to clarifying the excitatory action of aqueous peat extract (APE) on the spontaneous contractile activity (SCA) of the smooth muscles, in vitro studies were made of the influences of the water-soluble HPLC-fractions of fulvic and ulmic acids separated from peat on smooth-muscle preparations of guinea-pig stomach. The results obtained show that peat contains a large number of water-soluble components, which possess agonistic or partial agonistic actions on the alpha2-adreno- and D2-dopamine receptors. These are chemically stable substances, which retain for months their biological activity unchanged in aqueous solution. The excitatory effect of APE on the SCA of the smooth-muscle preparations was found to be more pronounced than the reactivity of alpha2-adrenoreceptors.  相似文献   
100.
8-Aryl xanthines potent inhibitors of phosphodiesterase 5   总被引:1,自引:0,他引:1  
In clinical studies, several inhibitors of phosphodiesterase 5 (PDE5) have demonstrated utility in the treatment of erectile dysfunction. We describe herein a series of 8-aryl xanthine derivatives which function as potent PDE5 inhibitors with, in many cases, high levels of selectivity versus other PDE isoforms.  相似文献   
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