全文获取类型
收费全文 | 2449篇 |
免费 | 211篇 |
专业分类
2660篇 |
出版年
2023年 | 4篇 |
2022年 | 18篇 |
2021年 | 49篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 32篇 |
2017年 | 35篇 |
2016年 | 76篇 |
2015年 | 116篇 |
2014年 | 130篇 |
2013年 | 144篇 |
2012年 | 218篇 |
2011年 | 205篇 |
2010年 | 151篇 |
2009年 | 131篇 |
2008年 | 141篇 |
2007年 | 156篇 |
2006年 | 136篇 |
2005年 | 123篇 |
2004年 | 147篇 |
2003年 | 124篇 |
2002年 | 128篇 |
2001年 | 30篇 |
2000年 | 20篇 |
1999年 | 31篇 |
1998年 | 39篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 20篇 |
1993年 | 22篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有2660条查询结果,搜索用时 0 毫秒
71.
Tilo Nadler Ulrike StreicherClara Stefen Elke SchwierzChristian Roos 《Der Zoologische Garten (in deutscher Sprache / in German)》2011,80(5):271-286
Ferret-badgers, genus Melogale, are distributed in the Indochinese region, Java, Bali and NE-Borneo. There are currently four species described each having very similar phenotypes. In March 2005, a living ferret-badger of a different phenotype was confiscated by rangers from Cuc Phuong National Park, Vietnam. This individual died and the carcass was not preserved. In January 2006, a newly deceased individual of the same phenotype was found at the Endangered Primate Rescue Center, Cuc Phuong National Park. Due to several different characteristics these individuals vary greatly from the current species. Thus, we describe an additional species, M. cucphuongensis sp. nov. from northern Vietnam, which occurs sympatrically with M. moschata and M. personata, but differs from both species clearly in skull morphology and other features.Based on a 423 bp-long fragment of the mitochondrial cytochrome b gene, M. cucphuongensis sp. nov. is a member of the genus Melogale and represents a sister lineage to a clade consisting of M. personata and M. moschata. 相似文献
72.
73.
Sausbier U Dullin C Missbach-Guentner J Kabagema C Flockerzie K Kuscher GM Stuehmer W Neuhuber W Ruth P Alves F Sausbier M 《PloS one》2011,6(6):e21168
Background
The process of bone resorption by osteoclasts is regulated by Cathepsin K, the lysosomal collagenase responsible for the degradation of the organic bone matrix during bone remodeling. Recently, Cathepsin K was regarded as a potential target for therapeutic intervention of osteoporosis. However, mechanisms leading to osteopenia, which is much more common in young female population and often appears to be the clinical pre-stage of idiopathic osteoporosis, still remain to be elucidated, and molecular targets need to be identified.Methodology/Principal Findings
We found, that in juvenile bone the large conductance, voltage and Ca2+-activated (BK) K+ channel, which links membrane depolarization and local increases in cytosolic calcium to hyperpolarizing K+ outward currents, is exclusively expressed in osteoclasts. In juvenile BK-deficient (BK−/−) female mice, plasma Cathepsin K levels were elevated two-fold when compared to wild-type littermates. This increase was linked to an osteopenic phenotype with reduced bone mineral density in long bones and enhanced porosity of trabecular meshwork in BK−/− vertebrae as demonstrated by high-resolution flat-panel volume computed tomography and micro-CT. However, plasma levels of sRANKL, osteoprotegerin, estrogene, Ca2+ and triiodthyronine as well as osteoclastogenesis were not altered in BK−/− females.Conclusion/Significance
Our findings suggest that the BK channel controls resorptive osteoclast activity by regulating Cathepsin K release. Targeted deletion of BK channel in mice resulted in an osteoclast-autonomous osteopenia, becoming apparent in juvenile females. Thus, the BK−/− mouse-line represents a new model for juvenile osteopenia, and revealed the BK channel as putative new target for therapeutic controlling of osteoclast activity. 相似文献74.
Reduced Activity of Geranylgeranyl Reductase Leads to Loss of Chlorophyll and Tocopherol and to Partially Geranylgeranylated Chlorophyll in Transgenic Tobacco Plants Expressing Antisense RNA for Geranylgeranyl Reductase 总被引:13,自引:1,他引:13 下载免费PDF全文
Ryouichi Tanaka Ulrike Oster Elisabeth Kruse Wolfhart Rüdiger Bernhard Grimm 《Plant physiology》1999,120(3):695-704
The enzyme geranylgeranyl reductase (CHL P) catalyzes the reduction of geranylgeranyl diphosphate to phytyl diphosphate. We identified a tobacco (Nicotiana tabacum) cDNA sequence encoding a 52-kD precursor protein homologous to the Arabidopsis and bacterial CHL P. The effects of deficient CHL P activity on chlorophyll (Chl) and tocopherol contents were studied in transgenic plants expressing antisense CHL P RNA. Transformants with gradually reduced Chl P expression showed a delayed growth rate and a pale or variegated phenotype. Transformants grown in high (500 μmol m−2 s−1; HL) and low (70 μmol photon m−2 s−1; LL) light displayed a similar degree of reduced tocopherol content during leaf development, although growth of wild-type plants in HL conditions led to up to a 2-fold increase in tocopherol content. The total Chl content was more rapidly reduced during HL than LL conditions. Up to 58% of the Chl content was esterified with geranylgeraniol instead of phytol under LL conditions. Our results indicate that CHL P provides phytol for both tocopherol and Chl synthesis. The transformants are a valuable model with which to investigate the adaptation of plants with modified tocopherol levels against deleterious environmental conditions. 相似文献
75.
Dr. Heribert Gras Ulrike Spörhase-Eichmann Michael Hörner Franz Killmann 《Cell and tissue research》1988,251(1):71-79
Summary The anatomical organization of the two dorsal giant fiber systems of the earthworm Lumbricus terrestris is demonstrated in whole mounts and serial-section reconstructions based on backfillings of the ventral nerve cord with cobalt chloride. Both the medial and lateral fiber systems can be labeled selectively over more than ten body segments. They show a characteristic segmental pattern of collaterals with some modification in tail segments and of dorsal plasma protrusions in the unpaired medial giant fiber presumably representing openings in the myelin sheath. We found no multisegmental cobalt transport in other large neurons of the nerve cord. Cobalt passes through the segmentai septa between consecutive axonal elements of the metameric giant fibers and presumably also through commissural contacts between specific collaterals of the lateral giant fibers. Since these sites of contact are known to represent electrical synapses, cobalt coupling may, in L. terrestris, correlate with functional electrotonic coupling.Abbreviations
CL
collateral of lateral giant fiber
-
CM
collateral of medial giant fiber
-
GIN
giant interneuron
-
LGF
lateral giant fiber
-
MGF
medial giant fiber
-
SN
segmental nerve 相似文献
76.
Nilanjan Pal Chowdhury Amr M. Mowafy Julius K. Demmer Vikrant Upadhyay Sebastian Koelzer Elamparithi Jayamani Joerg Kahnt Marco Hornung Ulrike Demmer Ulrich Ermler Wolfgang Buckel 《The Journal of biological chemistry》2014,289(8):5145-5157
Electron bifurcation is a fundamental strategy of energy coupling originally discovered in the Q-cycle of many organisms. Recently a flavin-based electron bifurcation has been detected in anaerobes, first in clostridia and later in acetogens and methanogens. It enables anaerobic bacteria and archaea to reduce the low-potential [4Fe-4S] clusters of ferredoxin, which increases the efficiency of the substrate level and electron transport phosphorylations. Here we characterize the bifurcating electron transferring flavoprotein (EtfAf) and butyryl-CoA dehydrogenase (BcdAf) of Acidaminococcus fermentans, which couple the exergonic reduction of crotonyl-CoA to butyryl-CoA to the endergonic reduction of ferredoxin both with NADH. EtfAf contains one FAD (α-FAD) in subunit α and a second FAD (β-FAD) in subunit β. The distance between the two isoalloxazine rings is 18 Å. The EtfAf-NAD+ complex structure revealed β-FAD as acceptor of the hydride of NADH. The formed β-FADH− is considered as the bifurcating electron donor. As a result of a domain movement, α-FAD is able to approach β-FADH− by about 4 Å and to take up one electron yielding a stable anionic semiquinone, α-FAD⨪, which donates this electron further to Dh-FAD of BcdAf after a second domain movement. The remaining non-stabilized neutral semiquinone, β-FADH•, immediately reduces ferredoxin. Repetition of this process affords a second reduced ferredoxin and Dh-FADH− that converts crotonyl-CoA to butyryl-CoA. 相似文献
77.
Blanca Arango-Gonzalez Dragana Trifunovi? Ayse Sahaboglu Katharina Kranz Stylianos Michalakis Pietro Farinelli Susanne Koch Fred Koch Sandra Cottet Ulrike Janssen-Bienhold Karin Dedek Martin Biel Eberhart Zrenner Thomas Euler Per Ekstr?m Marius Ueffing Fran?ois Paquet-Durand 《PloS one》2014,9(11)
Cell death in neurodegenerative diseases is often thought to be governed by apoptosis; however, an increasing body of evidence suggests the involvement of alternative cell death mechanisms in neuronal degeneration. We studied retinal neurodegeneration using 10 different animal models, covering all major groups of hereditary human blindness (rd1, rd2, rd10, Cngb1 KO, Rho KO, S334ter, P23H, Cnga3 KO, cpfl1, Rpe65 KO), by investigating metabolic processes relevant for different forms of cell death. We show that apoptosis plays only a minor role in the inherited forms of retinal neurodegeneration studied, where instead, a non-apoptotic degenerative mechanism common to all mutants is of major importance. Hallmark features of this pathway are activation of histone deacetylase, poly-ADP-ribose-polymerase, and calpain, as well as accumulation of cyclic guanosine monophosphate and poly-ADP-ribose. Our work thus demonstrates the prevalence of alternative cell death mechanisms in inherited retinal degeneration and provides a rational basis for the design of mutation-independent treatments. 相似文献
78.
79.
René H?hn Ulrike Kottler Tunde Peto Maria Blettner Thomas Münzel Stefan Blankenberg Karl J. Lackner Manfred Beutel Philipp S. Wild Norbert Pfeiffer 《PloS one》2015,10(3)
Purpose
This paper describes the study design, methodology, cohort profile and self-reported diseases in the ophthalmological branch of the Gutenberg Health Study (GHS).Methods
The GHS is an ongoing, prospective, interdisciplinary, single-center, population-based cohort study in Germany. The main goals of the ophthalmological section are to assess the prevalence and incidence of ocular diseases and to explore risk factors, genetic determinants and associations with systemic diseases and conditions. The eye examination at baseline included a medical history, self-reported eye diseases, visual acuity, refractive errors, intraocular pressure, visual field, pachymetry, keratometry, fundus photography and tear sampling. The 5-year follow-up visit additionally encompassed optical coherence tomography, anterior segment imaging and optical biometry. The general examination included anthropometry; blood pressure measurement; carotid artery ultrasound; electrocardiogram; echocardiography; spirometry; cognitive tests; questionnaires; assessment of mental conditions; and DNA, RNA, blood and urine sampling.Results
Of 15,010 participants (aged 35-74 years at the time of inclusion), ocular data are available for 14,700 subjects (97.9%). The mean visual acuity (standard deviation), mean spherical equivalent, median decimal visual acuity, and mean intraocular pressure were 0.08 (0.17) logMar, -0.42 (2.43) diopters, 0.9 and 14.24 (2.79) mm Hg, respectively. The frequencies of self-reported strabismus, glaucoma, surgery for retinal detachment and retinal vascular occlusions were 2.7%, 2.3%, 0.2% and 0.4%, respectively.Conclusions
The GHS is the most extensive dataset of ophthalmic diseases and conditions and their risk factors in Germany and one of the largest cohorts worldwide. This dataset will provide new insight in the epidemiology of ophthalmic diseases and related medical specialties. 相似文献80.
Sascha Knauf Ulrike Barnett Peter Maciej Matthias Klapproth Ibrahima Ndao Sieghard Frischmann Julia Fischer Dietmar Zinner Hsi Liu 《PloS one》2015,10(11)
The bacterium Treponema pallidum is known to cause syphilis (ssp. pallidum), yaws (ssp. pertenue), and endemic syphilis (ssp. endemicum) in humans. Nonhuman primates have also been reported to be infected with the bacterium with equally versatile clinical manifestations, from severe skin ulcerations to asymptomatic. At present all simian strains are closely related to human yaws-causing strains, an important consideration for yaws eradication. We tested clinically healthy Guinea baboons (Papio papio) at Parc National Niokolo Koba in south eastern Senegal for the presence of anti-T. pallidum antibodies. Since T. pallidum infection in this species was identified 50 years ago, and there has been no attempt to treat non-human primates for infection, it was hypothesized that a large number of West African baboons are still infected with simian strains of the yaws-bacterium. All animals were without clinical signs of treponematoses, but 18 of 20 (90%) baboons tested positive for antibodies against T. pallidum based on treponemal tests. Yet, Guinea baboons seem to develop no clinical symptoms, though it must be assumed that infection is chronic or comparable to the latent stage in human yaws infection. The non-active character is supported by the low anti-T. pallidum serum titers in Guinea baboons (median = 1:2,560) versus serum titers that are found in genital-ulcerated olive baboons with active infection in Tanzania (range of medians among the groups of initial, moderate, and severe infected animals = 1:15,360 to 1:2.097e+7). Our findings provide evidence for simian infection with T. pallidum in wild Senegalese baboons. Potentially, Guinea baboons in West Africa serve as a natural reservoir for human infection, as the West African simian strain has been shown to cause sustainable yaws infection when inoculated into humans. The present study pinpoints an area where further research is needed to support the currently on-going second WHO led yaws eradication campaign with its goal to eradicate yaws by 2020. 相似文献