全文获取类型
收费全文 | 787篇 |
免费 | 42篇 |
国内免费 | 1篇 |
出版年
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 47篇 |
2014年 | 43篇 |
2013年 | 38篇 |
2012年 | 52篇 |
2011年 | 64篇 |
2010年 | 40篇 |
2009年 | 30篇 |
2008年 | 48篇 |
2007年 | 33篇 |
2006年 | 36篇 |
2005年 | 22篇 |
2004年 | 27篇 |
2003年 | 26篇 |
2002年 | 32篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1970年 | 6篇 |
1968年 | 3篇 |
1967年 | 5篇 |
1966年 | 9篇 |
1965年 | 3篇 |
1962年 | 4篇 |
1959年 | 4篇 |
1957年 | 6篇 |
1956年 | 4篇 |
1955年 | 4篇 |
1954年 | 5篇 |
1951年 | 4篇 |
1940年 | 3篇 |
1937年 | 3篇 |
排序方式: 共有830条查询结果,搜索用时 359 毫秒
101.
Glutathione half-cell reduction potential: A universal stress marker and modulator of programmed cell death? 总被引:2,自引:0,他引:2
The elucidation of factors that contribute to cell viability loss is presently compromised by the lack of a universal measure that quantifies “stress.” We have investigated mechanisms of viability loss in plant seeds to find a reliable marker of stress response. Oxidative damage has previously been correlated with degenerative processes and death, but how exactly this contributes to viability loss is unknown. We show in four species subjected to ageing or desiccation that seed viability decreased by 50% when the half-cell reduction potential of glutathione (EGSSG/2GSH), a major cellular antioxidant and redox buffer, increased to −180 to −160 mV. We then conducted a metaanalysis of data representative of 13 plant and fungal orders to show that plant stress generally becomes lethal when EGSSG/2GSH exceeds −160 mV. We put forward that this change in EGSSG/2GSH is part of the signaling cascade that initiates programmed cell death (PCD), finally causing internucleosomal DNA fragmentation in the final, or execution phase, of PCD. EGSSG/2GSH is therefore a universal marker of plant cell viability and allows us to predict whether a seed will live, germinate, and produce a new plant, or if it will die. 相似文献
102.
Kristof Haneca Ilse Boeren Joris Van Acker Hans Beeckman 《Vegetation History and Archaeobotany》2006,15(2):137-144
Throughout the Middle Ages forests in Flanders (northern Belgium) experienced a dramatic human influence. Forests were logged
for wood supply and converted to arable land. The structure of the remaining forests was altered. This, combined with the
tempering influence of the Atlantic climate, results in conditions that are suboptimal for dendrochronological research. Tree-ring
series of Quercus robur and Q. petraea of timber from medieval archaeological sites are often short, show abrupt growth-rate variations and are complacent. The
question arises whether tree-ring series of this type are potential records of past management and whether they could constitute
the basis of a reference chronology for archaeological dating. During six archaeological excavations in and around the medieval
town of Ypres, cross-sections were collected. The tree-ring series could be dated back to the 12th–14th centuries, using reference
chronologies from surrounding regions. The growth pattern of the short sequences displays a high similarity to tree-ring series
from modern coppice. For the first time, it has been confirmed that dendrochronological analysis in Flanders is possible and
can provide valuable information on medieval forest use and structure. 相似文献
103.
Borrmann CM Grund C Kuhn C Hofmann I Pieperhoff S Franke WW 《European journal of cell biology》2006,85(6):469-485
Using immunofluorescence histochemistry and immunoelectron microscopy on sections through myocardiac tissues of diverse mammalian (human, cow, rat, mouse) and fish species we show that both desmosomal and fascia adhaerens proteins identified by gel electrophoresis and immunoblot occur in the area composita, the by far major type of plaque-bearing junctions of the intercalated disks (IDs) connecting cardiomyocytes. Specifically, we demonstrate that desmoplakin and the other desmosomal proteins occur in these junctions, together with N-cadherin, cadherin-11, alpha- and beta-catenin as well as vinculin, afadin and proteins p120(ctn), ARVCF, p0071, and ZO-1, suggestive of colocalization. We conclude that the predominant type of adhering junction present in IDs is a junction sui generis, termed area composita, that is characterized by an unusually high molecular complexity and an intimate association of molecules of both ensembles, the desmosomal one and the fascia adhaerens category. We discuss possible myocardium-specific, complex-forming interactions between members of the two ensembles and the relevance of our findings for the formation and functioning of the heart and for the understanding of hereditary and other cardiomyopathies. We further propose to use this highly characteristic area composita ensemble of molecules as cardiomyocyte markers for the monitoring of cardiomyogenesis, cardiomyocyte regeneration and possible cardiomyocyte differentiation from mesenchymal stem cells. 相似文献
104.
105.
Ilse C. Van Opzeeland Sofie M. Van Parijs Stephan Frickenhaus Cornelia M. Kreiss Olaf Boebel 《Marine Mammal Science》2012,28(2):E158-E172
Individually stereotyped vocalizations often play an important role in relocation of offspring in gregarious breeders. In phocids, mothers often alternate between foraging at sea and attending their pup. Pup calls are individually distinctive in various phocid species. However, experimental evidence for maternal recognition is rare. In this study, we recorded Weddell seal (Leptonychotes weddellii) pup vocalizations at two whelping patches in Atka Bay, Antarctica, and explored individual vocal variation based on eight vocal parameters. Overall, 58% of calls were correctly classified according to individual. For males (n= 12) and females (n= 9), respectively, nine and seven individuals were correctly identified based on vocal parameters. To investigate whether mothers respond differently to calls of familiar vs. unfamiliar pups, we conducted playback experiments with 21 mothers. Maternal responses did not differ between playbacks of own, familiar, and unfamiliar pup calls. We suggest that Weddell seal pup calls may need to contain only a critical amount of individually distinct information because mothers and pups use a combination of sensory modalities for identification. However, it cannot be excluded that pup developmental factors and differing environmental factors between colonies affect pup acoustic behavior and the role of acoustic cues in the relocation process. 相似文献
106.
JI García-Plazaola R Esteban B Fernández-Marín I Kranner A Porcar-Castell 《Photosynthesis research》2012,113(1-3):89-103
Thermal dissipation of excitation energy is a fundamental photoprotection mechanism in plants. Thermal energy dissipation is frequently estimated using the quenching of the chlorophyll fluorescence signal, termed non-photochemical quenching. Over the last two decades, great progress has been made in the understanding of the mechanism of thermal energy dissipation through the use of a few model plants, mainly Arabidopsis. Nonetheless, an emerging number of studies suggest that this model represents only one strategy among several different solutions for the environmental adjustment of thermal energy dissipation that have evolved among photosynthetic organisms in the course of evolution. In this review, a detailed analysis of three examples highlights the need to use models other than Arabidopsis: first, overwintering evergreens that develop a sustained form of thermal energy dissipation; second, desiccation tolerant plants that induce rapid thermal energy dissipation; and third, understorey plants in which a complementary lutein epoxide cycle modulates thermal energy dissipation. The three examples have in common a shift from a photosynthetically efficient state to a dissipative conformation, a strategy widely distributed among stress-tolerant evergreen perennials. Likewise, they show a distinct operation of the xanthophyll cycle. Expanding the list of model species beyond Arabidopsis will enhance our knowledge of these mechanisms and increase the synergy of the current studies now dispersed over a wide number of species. 相似文献
107.
Nitschke Y Baujat G Botschen U Wittkampf T du Moulin M Stella J Le Merrer M Guest G Lambot K Tazarourte-Pinturier MF Chassaing N Roche O Feenstra I Loechner K Deshpande C Garber SJ Chikarmane R Steinmann B Shahinyan T Martorell L Davies J Smith WE Kahler SG McCulloch M Wraige E Loidi L Höhne W Martin L Hadj-Rabia S Terkeltaub R Rutsch F 《American journal of human genetics》2012,90(1):25-39
Spontaneous pathologic arterial calcifications in childhood can occur in generalized arterial calcification of infancy (GACI) or in pseudoxanthoma elasticum (PXE). GACI is associated with biallelic mutations in ENPP1 in the majority of cases, whereas mutations in ABCC6 are known to cause PXE. However, the genetic basis in subsets of both disease phenotypes remains elusive. We hypothesized that GACI and PXE are in a closely related spectrum of disease. We used a standardized questionnaire to retrospectively evaluate the phenotype of 92 probands with a clinical history of GACI. We obtained the ENPP1 genotype by conventional sequencing. In those patients with less than two disease-causing ENPP1 mutations, we sequenced ABCC6. We observed that three GACI patients who carried biallelic ENPP1 mutations developed typical signs of PXE between 5 and 8 years of age; these signs included angioid streaks and pseudoxanthomatous skin lesions. In 28 patients, no disease-causing ENPP1 mutation was found. In 14 of these patients, we detected pathogenic ABCC6 mutations (biallelic mutations in eight patients, monoallelic mutations in six patients). Thus, ABCC6 mutations account for a significant subset of GACI patients, and ENPP1 mutations can also be associated with PXE lesions in school-aged children. Based on the considerable overlap of genotype and phenotype of GACI and PXE, both entities appear to reflect two ends of a clinical spectrum of ectopic calcification and other organ pathologies, rather than two distinct disorders. ABCC6 and ENPP1 mutations might lead to alterations of the same physiological pathways in tissues beyond the artery. 相似文献
108.
Wildeman MA Fles R Adham M Mayangsari ID Luirink I Sandberg M Vincent AD Fardizza F Musa Z Armiyanto Middeldorp JM Gerritsen G Suwanto R Tan IB 《PloS one》2012,7(3):e32756
In Indonesia, Nasopharyngeal Carcinoma (NPC) is the most frequent cancer of the head and neck region. At first presentation in the hospital most patients already have advanced NPC. Our previous study showed that general practitioners (GPs) working in Yogyakarta, Indonesia lack the knowledge necessary for early detection of NPC. By providing training on early symptoms of NPC we hope that the diagnosis and referral will occur at an earlier stage. Here we assess the current NPC knowledge levels of GPs in Jakarta, evaluate improvement after training, compare the effectiveness of two training formats, and estimate the loss of recall over a two week period.
Methods
Two Indonesian GPs visited 31 Primary Health Care Centres (PHCCs) and provided a lecture on NPC. The alternative format consisted of a symposium at the Universitas Indonesia, Jakarta, presented by local head and neck surgeons, with all GPs in the region being invited. To evaluate the effect of both formats a questionnaire was conducted before and after.Results
The lecture in the PHCCs was attended by 130 GPs. Sixty-six GPs attended the training in the university hospital and 40 GPs attended both. Pre training the NPC knowledge level was poor with an average of 1.6 symptoms being correctly identified out of a potential maximum of 12, this was increased to 4.9 post training (p<0.0001). GPs attending the PHCC course recorded a greater increase in correct symptoms than those attending the symposium (3.8 vs. 2.8; p = 0.01). After a two week period the knowledge levels had declined slightly from 5.5 correctly identified symptoms to 4.2 (p = 0.25).Conclusion
These results confirm our findings regarding GPs insufficient knowledge of NPC. Lectures in the PHCC and a symposium have both been proven to be effective training tools in the education of GPs. 相似文献109.
van Geel N Speeckaert R Mollet I De Schepper S De Wolf J Tjin EP Luiten RM Lambert J Brochez L 《Pigment cell & melanoma research》2012,25(1):57-65
In this study, we developed an in vivo vitiligo induction model to explore the underlying mechanisms leading to Koebner's phenomenon and to evaluate the efficacy of therapeutic strategies. The model consisted of 12 pigmented test regions on the back of generalized vitiligo patients that were exposed to three Koebner induction methods: cryotherapy, 755 nm laser therapy, and epidermal abrasion. In addition, four cream treatments (pimecrolimus, tacrolimus, steroid and placebo) were randomly applied. Koebnerization was efficiently induced by all three induction methods. In general, cryotherapy was the best method of Koebner induction, followed by 755 nm laser therapy and epidermal abrasion. Reproducible results were obtained, which showed enhanced depigmented surface areas and higher amounts of T lymphocytes in placebo-treated test zones compared to active treated areas. Tacrolimus and local steroids were better inhibitors of Koebner's process (P < 0.05) compared to pimecrolimus. Our in vivo vitiligo induction model is very informative to investigate vitiligo induction and to determine the efficacy of topical treatments in vitiligo. This proof of concept confirms the efficient comparison of head-to-head therapeutic strategies intra-individually in a standardized, specific and better timed way. 相似文献
110.
To evaluate a potential role of Axl, the high-affinity receptor of growth arrest-specific protein 6 (GAS6) in adiposity, murine embryonic fibroblasts (MEF) derived from mice with genetic deficiency of Axl (Axl(-/-)) or wild-type littermates (Axl(+/+)) were differentiated into mature adipocytes. In addition, Axl(-/-) and Axl(+/+) mice were kept on standard fat diet (SFD) or on high-fat diet (HFD) for 15 weeks. Deficiency of Axl in MEF did not affect differentiation, as shown by a similar uptake of Oil Red O and expression of the adipogenic markers aP2 and peroxisome proliferator activator receptor γ (PPARγ) at the end of the differentiation. In the first 7 weeks of HFD feeding, Axl(-/-) mice gained less weight than their wild-type littermates. Weight gain for both genotypes on either SFD of HFD over 15 weeks was, however, not significantly different, resulting in comparable body weights, as well as subcutaneous (s.c.) and gonadal (GON) fat mass. Adipocyte size in the fat tissues was not affected by Axl deficiency. Gene expression analysis indicated that the absence of Axl in vivo may be compensated for by the other TAM family members Mer and Tyro3. Glucose and insulin tolerance tests (ITT) in Axl(-/-) and Axl(+/+) mice did not reveal significant differences in glucose homeostasis. Thus, Axl deficiency had no significant effect on adipogenesis in vitro or in vivo. 相似文献