全文获取类型
收费全文 | 2683篇 |
免费 | 185篇 |
国内免费 | 3篇 |
出版年
2023年 | 8篇 |
2021年 | 31篇 |
2020年 | 17篇 |
2019年 | 31篇 |
2018年 | 32篇 |
2017年 | 28篇 |
2016年 | 55篇 |
2015年 | 100篇 |
2014年 | 92篇 |
2013年 | 148篇 |
2012年 | 211篇 |
2011年 | 201篇 |
2010年 | 125篇 |
2009年 | 105篇 |
2008年 | 152篇 |
2007年 | 193篇 |
2006年 | 160篇 |
2005年 | 144篇 |
2004年 | 158篇 |
2003年 | 167篇 |
2002年 | 145篇 |
2001年 | 21篇 |
2000年 | 11篇 |
1999年 | 26篇 |
1998年 | 28篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 22篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 22篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1969年 | 8篇 |
1968年 | 8篇 |
排序方式: 共有2871条查询结果,搜索用时 125 毫秒
101.
Katalin Nagy István Berhés Tibor Kovács Norbert Kávási János Somlai Tamás Bender 《Radiation and environmental biophysics》2009,48(3):311-315
Radon bath is a well-established modality of balneotherapy for the management of degenerative musculoskeletal disorders. The
present study was conducted to ascertain whether baths of relatively low (80 Bq/l) radon concentration have any influence
on the functioning of the endocrine system. In the study, a non-randomized pilot study, 27 patients with degenerative musculoskeletal
disorders received 30-min radon baths (of 31–32°C temperature and 80 Bq/l average radon concentration) daily, for 15 days.
Twenty-five patients with matching pathologies were subjected to balneotherapy according to the same protocol, using thermal
water with negligible radon content (6 Bq/l). Serum thyroid stimulating hormone, prolactin, cortisol, adrenocorticotropic
hormone, and dehydroepiandrosterone levels were measured before and after a balneotherapy course of 15 sessions. Comparison
of the accumulated data using the Wilcoxon test did not reveal any significant difference between pre- and post-treatment
values or between the two patient groups. It is noted that while the beneficial effects of balneotherapy with radon-containing
water on degenerative disorders is widely known, only few data have been published in the literature on its effect on endocrine
functions. The present study failed to demonstrate any substantial effect of thermal water with relatively low radon content
on the functioning of the endocrine system. 相似文献
102.
Morphology and sedimentology of (clustered) cold-water coral mounds at the south Rockall Trough margins,NE Atlantic Ocean 总被引:1,自引:0,他引:1
Henk de Haas Furu Mienis Norbert Frank Thomas O. Richter Reinhold Steinacher Henko de Stigter Cees van der Land Tjeerd C. E. van Weering 《Facies》2009,55(1):1-26
Cold-water coral mounds on both margins of the Rockall Trough (NE Atlantic Ocean) have a strongly different morphology. Single,
isolated mounds occur on the SE margin and are mainly found on the upper slope between 900 and 650 m water depth, while large
mound clusters are found on the SW margin in water depths between 600 and 1,000 m, in a narrow zone almost parallel to the
slope. Sedimentation rates on the mounds are higher than on the surrounding seabed as a result of baffling of biogenic carbonate
debris and siliciclastic particles by the coral framework covering the mounds. This is confirmed by 210Pb measurements. The individual coral growth rate can be three times higher then the vertical growth rate of the coral cover
(±10 mm year−1) which in turn is more than an order of magnitude higher then the present-day overall mound growth rate (±0.25 mm year−1). The presence of extensive hardgrounds and firmgrounds and the three-dimensional coral framework are considered to be responsible
for the stability of the relatively steep slopes of the mounds. High current velocities in the intramound areas result in
local non-sedimentation and erosion, as is shown by the presence of IRD (ice-rafted debris) lag deposits on the seabed and
moats around some of the mounds. The morphology and sedimentology of cold-water coral-covered (mainly Lophelia pertusa and Madrepora oculata) mounds on the southern Rockall Trough margins (NE Atlantic Ocean) is discussed and a model describing the development of
these mounds is presented. 相似文献
103.
Margit A Huber Andrea Denk Ralf U Peter Lutz Weber Norbert Kraut Thomas Wirth 《The Journal of biological chemistry》2002,277(2):1268-1275
Tumor necrosis factor (TNF)-alpha-induced phosphorylation of the IkappaB proteins by the IkappaB kinase (IKK) complex containing IKK-2 and subsequent degradation of the IkappaB proteins are prerequisites for NF-kappaB activation, resulting in the stimulation of a variety of pro-inflammatory target genes. The C-C chemokine eotaxin-1 is a potent chemoattractant for eosinophils and Th2 lymphocytes, may play an important role in the pathogenesis of atopic dermatitis, and acts via binding to its receptor CCR3. To investigate the role of NF-kappaB signaling in the regulation of these genes, we stably expressed a transdominant mutant of IkappaBalpha and a constitutively active mutant of IKK-2 in mouse NIH3T3 fibroblasts. The transdominant IkappaBalpha mutant completely inhibited TNF-alpha-mediated induction of both eotaxin-1 and CCR3, whereas expression of constitutively active IKK-2 was sufficient to drive almost full expression of these two genes in the absence of TNF-alpha. Moreover, we observed elevated expression levels of CCR3 and eotaxin-1 protein levels in the skin of IkappaBalpha-deficient mice characterized by a widespread dermatitis. Finally, using dermal fibroblasts derived from IkappaBalpha-deficient mice, we observed elevated basal expression, enhanced inducibility by TNF-alpha, and attenuated down-regulation upon TNF-alpha withdrawal of both CCR3 and eotaxin-1 mRNA levels. These results demonstrate that the IKK-2/IkappaBalpha/NF-kappaB pathway plays a critical role for CCR3 and eotaxin-1 expression in fibroblasts and suggests a critical link to the pathogenesis of atopic dermatitis. 相似文献
104.
Matthias Kraft Markus Tiemann Susanne Riedel Henning Gockel Torsten Kucharzik Reza Parwaresch Wolfram Domschike Norbert Lügering 《Cellular and molecular biology, including cyto-enzymology》2002,48(3):253-263
The interpretation of clonality within H. pylori-associated gastritis and low-grade MALT lymphoma remains controversial. Due to the observation of MALT lymphoma regression after H. pylori eradication, new definitions concerning the border between benign reactive lesions and malignant gastric lymphoma are needed. Gene rearrangements for immunoglobulin heavy-chain in low-grade MALT lymphoma (N= 12) and H. pylori-associated chronic gastritis with lymphatic hyperplasia (N= 13) were analyzed by microdissection and polymerase chain reaction. Furthermore, T cell receptor-gamma chain rearrangements were analyzed by gene scan analysis. In 11 of 12 cases with initial low-grade MALT lymphoma, intraepithelial and subepithelial B cell rearrangements showed a restricted usage of the immunoglobulin heavy-chain 3. In H. pylori-associated chronic gastritis, the intraepithelial B cell compartment showed an oligoclonal the immunoglobulin heavy-chain rearrangement pattern with a predominance of VH3. The subepithelial compartment did not show any restrictive immunoglobulin heavy-chain gene usage. Additionally a mono- to oligoclonal rearrangement pattern of the T cell receptor-y chain was observed in low-grade MALT lymphoma, whereas an oligoclonal pattem was observed in chronic gastritis. Our data provide evidence that low-grade MALT lymphoma may start within the epithelium and subsequently infiltrate the subepithelial compartment. The observation of a mono- to oligoclonal TCR-gamma rearrangement suggests that an antigen selecting process also takes place within reactive T cells. Combining TCR-gamma gene scan analysis with IgH chain rearrangement analysis might help in discriminating between chronic gastritis and initial MALT lymphoma in questionable cases. 相似文献
105.
Forest nitrogen sinks in large eastern U.S. watersheds: estimates from forest inventory and an ecosystem model 总被引:4,自引:2,他引:2
Goodale Christine L. Lajtha Kate Nadelhoffer Knute J. Boyer Elizabeth W. Jaworski Norbert A. 《Biogeochemistry》2002,(1):239-266
The eastern U.S. receives elevated rates of Ndeposition compared to preindustrial times, yetrelatively little of this N is exported indrainage waters. Net uptake of N into forestbiomass and soils could account for asubstantial portion of the difference between Ndeposition and solution exports. We quantifiedforest N sinks in biomass accumulation andharvest export for 16 large river basins in theeastern U.S. with two separate approaches: (1)using growth data from the USDA ForestService's Forest Inventory and Analysis (FIA)program, and (2) using a model of forestnitrogen cycling (PnET-CN) linked to FIAinformation on forest age-class structure. Themodel was also used to quantify N sinks in soiland dead wood, and nitrate losses below therooting zone. Both methods agreed that netgrowth rates were highest in the relativelyyoung forests on the Schuylkill watershed, andlowest in the cool forests of northern Maine. Across the 16 watersheds, wood export removedan average of 2.7 kg N ha–1 yr–1(range: 1–5 kg N ha–1 yr–1), andstanding stocks increased by 4.0 kg N ha–1yr–1 (–3 to 8 kg N ha–1 yr–1). Together, these sinks for N in woody biomassamounted to a mean of 6.7 kg N ha–1yr–1 (2–9 kg N ha–1 yr–1), or73% (15–115%) of atmospheric N deposition. Modeled rates of net N sinks in dead wood andsoil were small; soils were only a significantnet sink for N during simulations ofreforestation of degraded agricultural sites. Predicted losses of nitrate depended on thecombined effects of N deposition, and bothshort- and long-term effects of disturbance. Linking the model with forest inventoryinformation on age-class structure provided auseful step toward incorporating realisticpatterns of forest disturbance status acrossthe landscape. 相似文献
106.
Anthropogenic nitrogen sources and relationships to riverine nitrogen export in the northeastern U.S.A. 总被引:10,自引:8,他引:2
Boyer Elizabeth W. Goodale Christine L. Jaworski Norbert A. Howarth Robert W. 《Biogeochemistry》2002,(1):137-169
Human activities have greatly altered the nitrogen (N) cycle, accelerating the rate of N fixation in landscapes and delivery of N to water bodies. To examine relationships between anthropogenic N inputs and riverine N export, we constructed budgets describing N inputs and losses for 16 catchments, which encompass a range of climatic variability and are major drainages to the coast of the North Atlantic Ocean along a latitudinal profile from Maine to Virginia. Using data from the early 1990's, we quantified inputs of N to each catchment from atmospheric deposition, application of nitrogenous fertilizers, biological nitrogen fixation, and import of N in agricultural products (food and feed). We compared these inputs with N losses from the system in riverine export.The importance of the relative sources varies widely by catchment and is related to land use. Net atmospheric deposition was the largest N source (>60%) to the forested basins of northern New England (e.g. Penobscot and Kennebec); net import of N in food was the largest source of N to the more populated regions of southern New England (e.g. Charles & Blackstone); and agricultural inputs were the dominant N sources in the Mid-Atlantic region (e.g. Schuylkill & Potomac). Over the combined area of the catchments, net atmospheric deposition was the largest single source input (31%), followed by net imports of N in food and feed (25%), fixation in agricultural lands (24%), fertilizer use (15%), and fixation in forests (5%). The combined effect of fertilizer use, fixation in crop lands, and animal feed imports makes agriculture the largest overall source of N. Riverine export of N is well correlated with N inputs, but it accounts for only a fraction (25%) of the total N inputs. This work provides an understanding of the sources of N in landscapes, and highlights how human activities impact N cycling in the northeast region. 相似文献
107.
108.
Steffen Franz Mareva Ciatipis Kathrin Pfeifer Birthe Kierdorf Beatrice Sandner Ulrich Bogdahn Armin Blesch Beate Winner Norbert Weidner 《PloS one》2014,9(7)
After spinal cord injury, transected axons fail to regenerate, yet significant, spontaneous functional improvement can be observed over time. Distinct central nervous system regions retain the capacity to generate new neurons and glia from an endogenous pool of progenitor cells and to compensate neural cell loss following certain lesions. The aim of the present study was to investigate whether endogenous cell replacement (neurogenesis or gliogenesis) in the brain (subventricular zone, SVZ; corpus callosum, CC; hippocampus, HC; and motor cortex, MC) or cervical spinal cord might represent a structural correlate for spontaneous locomotor recovery after a thoracic spinal cord injury. Adult Fischer 344 rats received severe contusion injuries (200 kDyn) of the mid-thoracic spinal cord using an Infinite Horizon Impactor. Uninjured rats served as controls. From 4 to 14 days post-injury, both groups received injections of bromodeoxyuridine (BrdU) to label dividing cells. Over the course of six weeks post-injury, spontaneous recovery of locomotor function occurred. Survival of newly generated cells was unaltered in the SVZ, HC, CC, and the MC. Neurogenesis, as determined by identification and quantification of doublecortin immunoreactive neuroblasts or BrdU/neuronal nuclear antigen double positive newly generated neurons, was not present in non-neurogenic regions (MC, CC, and cervical spinal cord) and unaltered in neurogenic regions (dentate gyrus and SVZ) of the brain. The lack of neuronal replacement in the brain and spinal cord after spinal cord injury precludes any relevance for spontaneous recovery of locomotor function. Gliogenesis was increased in the cervical spinal cord remote from the injury site, however, is unlikely to contribute to functional improvement. 相似文献
109.
Jan-Peter Sowa ?zgür Atmaca Alisan Kahraman Martin Schlattjan Marion Lindner Svenja Sydor Norbert Scherbaum Karoline Lackner Guido Gerken Dominik Heider Gavin E. Arteel Yesim Erim Ali Canbay 《PloS one》2014,9(7)
Background & Objective
Currently, a major clinical challenge is to distinguish between chronic liver disease caused by metabolic syndrome (non-alcoholic fatty liver disease, NAFLD) from that caused by long term or excessive alcohol consumption (ALD). The etiology of severe liver disease affects treatment options and priorities for liver transplantation and organ allocation. Thus we compared physiologically similar NAFLD and ALD patients to detect biochemical differences for improved separation of these mechanistically overlapping etiologies.Methods
In a cohort of 31 NAFLD patients with BMI below 30 and a cohort of ALD patient with (ALDC n = 51) or without cirrhosis (ALDNC n = 51) serum transaminases, cell death markers and (adipo-)cytokines were assessed. Groups were compared with One-way ANOVA and Tukey''s correction. Predictive models were built by machine learning techniques.Results
NAFLD, ALDNC or ALDC patients did not differ in demographic parameters. The ratio of alanine aminotransferase/aspartate aminotransferase - common serum parameters for liver damage - was significantly higher in the NAFLD group compared to both ALD groups (each p<0.0001). Adiponectin and tumor necrosis factor(TNF)-alpha were significantly lower in NAFLD than in ALDNC (p<0.05) or ALDC patients (p<0.0001). Significantly higher serum concentrations of cell death markers, hyaluronic acid, adiponectin, and TNF-alpha (each p<0.0001) were found in ALDC compared to ALDNC. Using machine learning techniques we were able to discern NAFLD and ALDNC (up to an AUC of 0.9118±0.0056) or ALDC and ALDNC (up to an AUC of 0.9846±0.0018), respectively.Conclusions
Machine learning techniques relying on ALT/AST ratio, adipokines and cytokines distinguish NAFLD and ALD. In addition, severity of ALD may be non-invasively diagnosed via serum cytokine concentrations. 相似文献110.
Matthias Kott Gunnar Elke Maike Reinicke Supandi Winoto-Morbach Dirk Sch?dler Günther Zick Inéz Frerichs Norbert Weiler Stefan Schütze 《PloS one》2014,9(11)