全文获取类型
收费全文 | 15470篇 |
免费 | 1179篇 |
国内免费 | 1205篇 |
专业分类
17854篇 |
出版年
2024年 | 32篇 |
2023年 | 188篇 |
2022年 | 472篇 |
2021年 | 867篇 |
2020年 | 515篇 |
2019年 | 631篇 |
2018年 | 651篇 |
2017年 | 541篇 |
2016年 | 650篇 |
2015年 | 927篇 |
2014年 | 1102篇 |
2013年 | 1240篇 |
2012年 | 1438篇 |
2011年 | 1289篇 |
2010年 | 810篇 |
2009年 | 702篇 |
2008年 | 776篇 |
2007年 | 636篇 |
2006年 | 621篇 |
2005年 | 503篇 |
2004年 | 440篇 |
2003年 | 337篇 |
2002年 | 350篇 |
2001年 | 322篇 |
2000年 | 258篇 |
1999年 | 257篇 |
1998年 | 168篇 |
1997年 | 135篇 |
1996年 | 137篇 |
1995年 | 134篇 |
1994年 | 145篇 |
1993年 | 96篇 |
1992年 | 96篇 |
1991年 | 72篇 |
1990年 | 66篇 |
1989年 | 58篇 |
1988年 | 56篇 |
1987年 | 31篇 |
1986年 | 33篇 |
1985年 | 20篇 |
1984年 | 23篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
I Saboli? L B Shi D Brown D A Ausiello A S Verkman 《Biochimica et biophysica acta》1992,1103(1):137-147
A marked increase in water permeability can be induced in Xenopus oocytes by injection of mRNA from tissues that express water channels, suggesting that the water channel is a protein. In view of this and previous reports which showed that proteinases may interfere with mercurial inhibition of water transport in red blood cells (RBC), we examined the influence of trypsin, chymotrypsin, papain, pronase, subtilisin and thermolysin on water permeability as well as on ATPase activity, H(+)-pump, passive H+ conductance, and Na+/H+ exchange in apical brush-border vesicles (BBMV) and endosomal (EV) vesicles from rat renal cortex. H+ transport was measured by Acridine orange fluorescence quenching and water transport by stopped-flow light scattering. As measured by potential-driven H+ accumulation in BBMV and EV, proteinase treatment had little effect on vesicle integrity. In BBMV, ecto-ATPase activity was inhibited by 15-30%, Na+/H+ exchange by 20-55%, and H+ conductance was unchanged. Osmotic water permeability (Pf) was 570 microns/s and was inhibited 85-90% by 0.6 mM HgCl2; proteinase treatment did not affect Pf or the HgCl2 inhibition. In EV, NEM-sensitive H+ accumulation and ATPase activity were inhibited by greater than 95%. Pf (140 microns/s) and HgCl2 inhibition (75-85%) were not influenced by proteinase treatment. SDS-PAGE showed selective digestion of multiple polypeptides by proteinases. These results confirm the presence of water channels in BBMV and EV and demonstrate selective inhibition of ATPase function and Na+/H+ exchange by proteinase digestion. The lack of effect of proteinases on water transport by mercurials. We conclude that the water channel may be a small integral membrane protein which, unlike the H(+)-ATPase and Na+/H+ exchanger, has no functionally important membrane domains that are sensitive to proteolysis. 相似文献
12.
Transient deformations of leukocytes (WBCs) were studied during their saltation along post-capillary venous endothelium (EC) in mesentery of the rat. During intermittent adhesion of WBCs to EC, prevailing fluid shear stresses, tau wall, resulted in a stepwise loading of the WBC upon attachment with a transient increase in length, L(t), and reduction in height, H(t). Measurements of L(t) and H(t) from frame-by-frame analysis of video recordings were modelled as the simple shear of a standard linear viscoelastic solid to facilitate calculation of the elastic (k1, k2) and viscous (mu) elements with k1 in parallel with serial elements k2 and mu. The magnitude of tau wall was determined from measurements of red cell velocity within the venule. During the spontaneous adhesion of WBCs, a value of cell viscosity (mu) of 45 Poise was determined. Stimulating adhesion by topical application of the chemoattractant FMLP resulted in a 15-fold increase of mu to 668 Poise. Transient deformations during topical application of cytochalesin B to disrupt actin fibers within the WBC, yielded a 40% reduction in k1, compared to an 80% reduction with colchicine which disrupts the microtubule structure. Thus, colchicine treated cells appear to be twice as deformable as cells treated with cytochalesin. During adhesion stimulated by the cytokine Interleukin-1, mu increased 50% without changes in k1 and k2, possibly due to slight activation of the WBC. 相似文献
13.
Identifying the mechanisms that underlie the assembly of plant communities is critical to the conservation of terrestrial biodiversity. However, it is seldom measured or quantified how much deterministic versus stochastic processes contribute to community assembly in alpine meadows. Here, we measured the decay in community similarity with spatial and environmental distance in the Zoige Plateau. Furthermore, we used redundancy analysis (RDA) to divide the variations in the relative abundance of plant families into four components to assess the effects of environmental and spatial. Species assemblage similarity liner declined with geographical distance (p < .001, R 2 = .6388), and it decreased significantly with increasing distance of total phosphorus (TP), alkali‐hydrolyzable nitrogen (AN), available potassium (AK), nitrate nitrogen (NO3 +–N), and ammonia nitrogen (NH4 +–N). Environmental and spatial variables jointly explained a large proportion (55.2%) of the variation in the relative abundance of plant families. Environmental variables accounted for 13.1% of the total variation, whereas spatial variables accounted for 11.4%, perhaps due to the pronounced abiotic gradients in the alpine areas. Our study highlights the mechanism of plant community assembly in the alpine ecosystem, where environmental filtering plays a more important role than dispersal limitation. In addition, a reasonably controlled abundance of Compositae (the family with the highest niche breadth and large niche overlap value with Gramineae and Cyperaceae) was expected to maintain sustainable development in pastoral production. These results suggest that management measures should be developed with the goal of improving or maintaining suitable local environmental conditions. 相似文献
14.
15.
Xiaojing Meng Lingxiao Yue An Liu Wenjuan Tao Li Shi Wan Zhao Zhongmin Wu Zhi Zhang Liecheng Wang Xulai Zhang Wenjie Zhou 《The Journal of biological chemistry》2022,298(8)
Pain is a multidimensional perception that includes unpleasant somatosensory and affective experiences; however, the underlying neural circuits that mediate different components of pain remain elusive. Although hyperactivity of basolateral amygdala glutamatergic (BLAGlu) neurons is required for the somatosensory and emotional processing of pain, the precise excitatory inputs to BLAGlu neurons and their roles in mediating different aspects of pain are unclear. Here, we identified two discrete glutamatergic neuronal circuits in male mice: a projection from the insular cortex glutamatergic (ICGlu) to BLAGlu neurons, which modulates both the somatosensory and affective components of pain, and a projection from the mediodorsal thalamic nucleus (MDGlu) to BLAGlu neurons, which modulates only the aversive-affective component of pain. Using whole-cell recording and fiber photometry, we found that neurons within the IC→BLA and MD→BLA pathways were activated in mice upon inflammatory pain induced by injection of complete Freund’s adjuvant (CFA) into their paws. Optical inhibition of the ICGlu→BLA pathway increased the nociceptive threshold and induced behavioral place preference in CFA mice. In contrast, optical inhibition of the MDGlu→BLA pathway did not affect the nociceptive threshold but still induced place preference in CFA mice. In normal mice, optical activation of the ICGlu→BLA pathway decreased the nociceptive threshold and induced place aversion, while optical activation of the MDGlu→BLA pathway only evoked aversion. Taken together, our results demonstrate that discrete ICGlu→BLA and MDGlu→BLA pathways are involved in modulating different components of pain, provide insights into its circuit basis, and better our understanding of pain perception. 相似文献
16.
Weifeng He Yuan Gao Jing Zhou Yi Shi Dajing Xia Han-Ming Shen 《International journal of biological sciences》2022,18(12):4690
There is increasing amount of evidence indicating the close interplays between the replication cycle of SARS-CoV-2 and the autophagy-lysosome pathway in the host cells. While autophagy machinery is known to either assist or inhibit the viral replication process, the reciprocal effects of the SARS-CoV-2 on the autophagy-lysosome pathway have also been increasingly appreciated. More importantly, despite the disappointing results from the clinical trials of chloroquine and hydroxychloroquine in treatment of COVID-19, there is still ongoing effort in discovering new therapeutics targeting the autophagy-lysosome pathway. In this review, we provide an update-to-date summary of the interplays between the autophagy-lysosome pathway in the host cells and the pathogen SARS-CoV-2 at the molecular level, to highlight the prognostic value of autophagy markers in COVID-19 patients and to discuss the potential of developing novel therapeutic strategies for COVID-19 by targeting the autophagy-lysosome pathway. Thus, understanding the nature of such interactions between SARS-CoV-2 and the autophagy-lysosome pathway in the host cells is expected to provide novel strategies in battling against this global pandemic. 相似文献
17.
Aging is associated with a loss of metabolic homeostasis, with cofactors such as nicotinamide adenine dinucleotide (NAD+) declining over time. The decrease in NAD+ production has been linked to the age‐related loss of circulating extracellular nicotinamide phosphoribosyltransferase (eNAMPT), the rate‐limiting enzyme in the NAD+ biosynthetic pathway. eNAMPT is found almost exclusively in extracellular vesicles (EVs), providing a mechanism for the distribution of the enzyme in different tissues. Currently, the physiological cause for the release of eNAMPT is unknown, and how it may be affected by age and physical exercise. Here, we show that release of small EVs into the bloodstream is stimulated following moderate intensity exercise in humans. Exercise also increased the eNAMPT content in EVs, most prominently in young individuals with higher aerobic fitness. Both mature fit and young unfit individuals exhibited a limited increase in EV‐eNAMPT release following exercise, indicating that this mechanism is related to both the age and physical fitness of a person. Notably, unfit mature individuals were unable to increase the release of eNAMPT in EVs after exercise, suggesting that lower fitness levels and aging attenuate this important signalling mechanism in the body. EVs isolated from exercising humans containing eNAMPT were able to alter the abundance of NAD+ and SIRT1 activity in recipient cells compared to pre‐exercise EVs, indicating a pathway for inter‐tissue signalling promoted through exercise. Our results suggest a mechanism to limit age‐related NAD+ decline, through the systemic delivery of eNAMPT via EVs released during exercise. 相似文献
18.
Zehua Zou Ruixuan Liu Yiwen Wang Yufei Xing Zuowei Shi Kaifu Wang Darning Dong 《Acta biochimica et biophysica Sinica》2021,(3):294-303
The occurrence and progress of osteoporosis(OP)are partially caused by impaired osteoblast differentiation.Interleukin-I receptor antagonist(IL1RN)is an immune ... 相似文献
19.
20.
Yanshu Liu Zhongjie Shi Liyan Gong Richun Cong Xiaohui Yang David J. Eldridge 《Restoration Ecology》2019,27(6):1348-1356
Encroachment of woody plants into grasslands is a global phenomenon that has substantial impacts on pastoral productivity and ecosystem services. Over the past half century, pastoralists and land management agencies have explored various options to control woody plants in order to improve ecosystem services in shrub‐encroached grasslands. We examined the effectiveness of controlling the encroachment of the shrub Caragana microphylla into grassland in Inner Mongolia, China. We cut and removed all of the aboveground biomass from 450 shrubs, predicting that the effectiveness of this technique to control shrubs would depend on shrub morphology. Specifically, we expected that larger shrubs with more biomass would be more difficult to kill by cutting than smaller shrubs. A year after treatment, we found that cutting killed only 11% of the 450 treated shrubs, and of these, three‐quarters of the locations that they occupied reverted to grasses and one‐quarter to bare soil. Shrubs that survived the cutting treatment produced more stems and leaf biomass, and therefore had a greater leaf to stem ratio. Shrubs that died after cutting had a lower crown area and basal area, and less stem biomass than shrubs that resprouted within 12 months of cutting. There were no effects of shrub height on the fate of treated shrubs. Cutting had no effect on understory plant cover or richness, but reproductive plants were taller under shrubs that were not cut. Overall, our study showed that removing aboveground shrub biomass by cutting is an ineffective technique for “restoring” the original grassland community unless shrubs are very small. Strategic targeting of small shrubs would be a more effective technique for controlling the spread of C. microphylla in the long term. 相似文献