首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2070篇
  免费   198篇
  国内免费   1篇
  2023年   11篇
  2022年   20篇
  2021年   52篇
  2020年   24篇
  2019年   36篇
  2018年   60篇
  2017年   47篇
  2016年   83篇
  2015年   92篇
  2014年   108篇
  2013年   113篇
  2012年   160篇
  2011年   143篇
  2010年   83篇
  2009年   108篇
  2008年   126篇
  2007年   103篇
  2006年   77篇
  2005年   73篇
  2004年   93篇
  2003年   83篇
  2002年   80篇
  2001年   55篇
  2000年   53篇
  1999年   48篇
  1998年   26篇
  1997年   34篇
  1996年   21篇
  1995年   14篇
  1994年   16篇
  1993年   15篇
  1992年   32篇
  1991年   24篇
  1990年   19篇
  1989年   27篇
  1988年   18篇
  1987年   7篇
  1986年   14篇
  1984年   21篇
  1983年   4篇
  1982年   5篇
  1981年   4篇
  1980年   3篇
  1979年   4篇
  1978年   2篇
  1977年   4篇
  1976年   4篇
  1975年   5篇
  1974年   5篇
  1973年   3篇
排序方式: 共有2269条查询结果,搜索用时 15 毫秒
51.
During insulin stupor in mice, acetylcholine levels in cerebral cortex, cerebellum. brainstem, striatum, and hippocampus were unchanged from control values despite brain glucose concentrations 3-10% of normal, whereas choline levels rose 2.4-3.6-fold in all five CNS regions. Brain acetylcholine and choline levels did not change during recovery following glucose injection. The data suggest that. in hypoglycemic stupor, (1) overall rates of acetylcholine synthesis and degradation remain balanced within each of the CNS regions studied: (2) the biochemical mechanism that elevates brain choline levels is unlikely to be related only to cholinergic synaptic processes: and (3) brain choline levels need not rise for stupor to occur.  相似文献   
52.
1. A procedure was developed for the preparation of plasma membranes from experimental granulation tissue of the rat without the addition of enzymes. The yield is better than 20% and the purification at least tenfold. 2. Values are given for the activities of 5'-nucleotidase, Na-+, k-+-activated Mg-2+dependent adenosine triphosphatase and leucine beta-naphthylamidase, for lipid composition, and for the gel-electrophoretic patterns of proteins and glycoporteins in the membrane preparations. 3. The plasma membranes from the mature granulation tissue contain proportionally more protein in the lipid phase, but the specific activities of 5'-nucleotidase and Na-+,K-+-activated Mg-2+-dependent adenosine triphosphatase are smaller than in the proliferating tissue. Certain differences were repeatedly observed in the gel-electrophoretic patterns of the developmental phases. 4. The plasma membranes from the granulation tissue were compared with those from rat peritoneal macrophages and from embryonic-chick tendon cells.  相似文献   
53.
54.
The Southern Ocean (SO) is among the regions on Earth that are undergoing regionally the fastest environmental changes. The unique ecological features of its marine life make it particularly vulnerable to the multiple effects of climate change. A network of Marine Protected Areas (MPAs) has started to be implemented in the SO to protect marine ecosystems. However, considering future predictions of the Intergovernmental Panel on Climate Change (IPCC), the relevance of current, static, MPAs may be questioned under future scenarios. In this context, the ecoregionalization approach can prove promising in identifying well‐delimited regions of common species composition and environmental settings. These so‐called ecoregions are expected to show similar biotic responses to environmental changes and can be used to define priority areas for the designation of new MPAs and the update of their current delimitation. In the present work, a benthic ecoregionalization of the entire SO is proposed for the first time based on abiotic environmental parameters and the distribution of echinoid fauna, a diversified and common member of Antarctic benthic ecosystems. A novel two‐step approach was developed combining species distribution modeling with Random Forest and Gaussian Mixture modeling from species probabilities to define current ecoregions and predict future ecoregions under IPCC scenarios RCP 4.5 and 8.5. The ecological representativity of current and proposed MPAs of the SO is discussed with regard to the modeled benthic ecoregions. In all, 12 benthic ecoregions were determined under present conditions, they are representative of major biogeographic patterns already described. Our results show that the most dramatic changes can be expected along the Antarctic Peninsula, in East Antarctica and the sub‐Antarctic islands under both IPCC scenarios. Our results advocate for a dynamic definition of MPAs, they also argue for improving the representativity of Antarctic ecoregions in proposed MPAs and support current proposals of Conservation of Antarctic Marine Living Resources for the creation of Antarctic MPAs.  相似文献   
55.
There is growing international interest in better managing soils to increase soil organic carbon (SOC) content to contribute to climate change mitigation, to enhance resilience to climate change and to underpin food security, through initiatives such as international ‘4p1000’ initiative and the FAO's Global assessment of SOC sequestration potential (GSOCseq) programme. Since SOC content of soils cannot be easily measured, a key barrier to implementing programmes to increase SOC at large scale, is the need for credible and reliable measurement/monitoring, reporting and verification (MRV) platforms, both for national reporting and for emissions trading. Without such platforms, investments could be considered risky. In this paper, we review methods and challenges of measuring SOC change directly in soils, before examining some recent novel developments that show promise for quantifying SOC. We describe how repeat soil surveys are used to estimate changes in SOC over time, and how long‐term experiments and space‐for‐time substitution sites can serve as sources of knowledge and can be used to test models, and as potential benchmark sites in global frameworks to estimate SOC change. We briefly consider models that can be used to simulate and project change in SOC and examine the MRV platforms for SOC change already in use in various countries/regions. In the final section, we bring together the various components described in this review, to describe a new vision for a global framework for MRV of SOC change, to support national and international initiatives seeking to effect change in the way we manage our soils.  相似文献   
56.
57.
Genus Rusa, belonging to the deer family Cervidae is native to the Indo-Malaya Archipelago (IMA). However, detailed information on the Rusa genus in the IMA is limited. This review provides comprehensive information on the Rusa genus in the IMA including, threats and conservation efforts. There are four species of deer in Rusa genus, which is Sambar deer (Rusa unicolor), Javan deer (Rusa timorensis), Visayan spotted deer (Rusa alfredi) and Philippine deer (Rusa marianna). Despite their wide distribution in the South Asian and Southeast Asian regions, they are under serious threats. Some conservation efforts that are being done to protect and conserve them among others are; (1) facilities protection, (2) habitat enrichment programme, (3) Ex-situ conservation, (4) legislations, and (5) captive breeding. Conservation through genetics is also an important step in conserving these species. Recommendations for conservation of the genus are also discussed; 1. maintenance of ecosystem. 2. more effective monitoring system on the existing protected area. 3. ex-situ conservation, and 4. habitat monitoring.  相似文献   
58.
Recent genome‐wide association studies have linked type‐2 diabetes mellitus to a genomic region in chromosome 9p21 near the Ink4/Arf locus, which encodes tumor suppressors that are up‐regulated in a variety of mammalian organs during aging. However, it is unclear whether the susceptibility to type‐2 diabetes is associated with altered expression of the Ink4/Arf locus. In the present study, we investigated the role of Ink4/Arf in age‐dependent alterations of insulin and glucose homeostasis using Super‐Ink4/Arf mice which bear an extra copy of the entire Ink4/Arf locus. We find that, in contrast to age‐matched wild‐type controls, Super‐Ink4/Arf mice do not develop glucose intolerance with aging. Insulin tolerance tests demonstrated increased insulin sensitivity in Super‐Ink4/Arf compared with wild‐type mice, which was accompanied by higher activation of the insulin receptor substrate (IRS)‐PI3K‐AKT pathway in liver, skeletal muscle and heart. Glucose uptake studies in Super‐Ink4/Arf mice showed a tendency toward increased 18F‐fluorodeoxyglucose uptake in skeletal muscle compared with wild‐type mice (= 0.079). Furthermore, a positive correlation between glucose uptake and baseline glucose levels was observed in Super‐Ink4/Arf mice (P < 0.008) but not in wild‐type mice. Our studies reveal a protective role of the Ink4/Arf locus against the development of age‐dependent insulin resistance and glucose intolerance.  相似文献   
59.
Abstract

The experimental FTIR and FT-Raman spectra of 5-chloro-2′-deoxyuridine have been assigned on the basis of normal coordinate analyses, in the light of observed and calculated wavenumbers and isotopic shifts. The results indicate that virtually all normal modes of IDU involve some degree of vibrational coupling between the chlorouracil base and the deoxyribose moiety.  相似文献   
60.
Programmed cell death is an event displayed by many different organisms along the evolutionary scale. In plants, programmed cell death is necessary for development and the hypersensitive response to stress or pathogenic infection. A common feature in programmed cell death across organisms is the translocation of cytochrome c from mitochondria to the cytosol. To better understand the role of cytochrome c in the onset of programmed cell death in plants, a proteomic approach was developed based on affinity chromatography and using Arabidopsis thaliana cytochrome c as bait. Using this approach, ten putative new cytochrome c partners were identified. Of these putative partners and as indicated by bimolecular fluorescence complementation, nine of them bind the heme protein in plant protoplasts and human cells as a heterologous system. The in vitro interaction between cytochrome c and such soluble cytochrome c-targets was further corroborated using surface plasmon resonance. Taken together, the results obtained in the study indicate that Arabidopsis thaliana cytochrome c interacts with several distinct proteins involved in protein folding, translational regulation, cell death, oxidative stress, DNA damage, energetic metabolism, and mRNA metabolism. Interestingly, some of these novel Arabidopsis thaliana cytochrome c-targets are closely related to those for Homo sapiens cytochrome c (Martínez-Fábregas et al., unpublished). These results indicate that the evolutionarily well-conserved cytosolic cytochrome c, appearing in organisms from plants to mammals, interacts with a wide range of targets on programmed cell death. The data have been deposited to the ProteomeXchange with identifier PXD000280.Programmed cell death (PCD)1 is a fundamental event for the development of multicellular organisms and the homeostasis of their tissues. It is an evolutionarily conserved mechanism present in organisms ranging from yeast to mammals (13).In mammals, cytochrome c (Cc) and dATP bind to apoptosis protease-activating factor-1 (Apaf-1) in the cytoplasm, a process leading to the formation of the Apaf-1/caspase-9 complex known as apoptosome. This apoptosome subsequently activates caspases-3 and -7 (4, 5). In other organisms, such as Caenorhabditis elegans or Drosophila melanogaster, however, Cc is not essential for the assembly and activation of the apoptosome (6) despite the presence of proteins homologous to Apaf-1—cell death abnormality-4 (CED-4) in C. elegans and Drosophila Apaf-1-related killer (Dark) in D. melanogaster—which have been found to be essential for caspase cascade activation. Furthermore, other organisms such as Arabidopsis thaliana lack Apaf-1 (7). In fact, only highly distant caspase homologues (metacaspases) (8, 9), serine proteases (saspases) (10), phytaspases (11) and VEIDases (1214) with caspase-like activity have been detected in plants; however, their targets remain veiled and whether they are activated by Cc remains unclear.Intriguingly, the release of Cc from mitochondria into the cytoplasm during the onset of PCD is an evolutionarily conserved event found in organisms ranging from yeast (15) and plants (16) to flies (17), and mammals (18). However, understanding of the roles of this phenomenon in different species can be said to be uneven at best. In fact, the release of Cc from mitochondria has thus far been considered a random event in all organisms, save mammals. Thus, the participation of Cc in the onset and progression of PCD needs to be further elucidated.Even in the case of mammals, the role(s) of Cc in the cytoplasm during PCD remain(s) controversial. Recently, new putative functions of Cc, going beyond the already-established apoptosome assembly process, have been proposed in the nucleus (19, 20) and the endoplasmic reticulum (2123). Neither these newly proposed functions nor other arising functions, such as oxidative stress (24), are as yet fully understood. This current state of affairs demands deeper exploration of the additional roles played by Cc in nonmammalian species.In this study, putative novel Cc-partners involved in plant PCD were identified. For this identification, a proteomic approach was employed based on affinity chromatography and using Cc as bait. The Cc-interacting proteins were identified using nano-liquid chromatography tandem mass spectrometry (NanoLC-MS/MS). These Cc-partners were then further confirmed in vivo through bimolecular fluorescence complementation (BiFC) in A. thaliana protoplasts and human HEK293T cells, as a heterologous system. Finally, the Cc-GLY2, Cc-NRP1 and Cc-TCL interactions were corroborated in vitro using surface plasmon resonance (SPR).These results indicate that Cc is able to interact with targets in the plant cell cytoplasm during PCD. Moreover, they provide new ways of understanding why Cc release is an evolutionarily well-conserved event, and allow us to propose Cc as a signaling messenger, which somehow controls different essential events during PCD.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号