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   425篇
  免费   61篇
  2022年   4篇
  2021年   3篇
  2018年   3篇
  2015年   6篇
  2014年   12篇
  2013年   14篇
  2012年   21篇
  2011年   12篇
  2010年   10篇
  2009年   11篇
  2008年   12篇
  2007年   14篇
  2006年   18篇
  2005年   18篇
  2004年   19篇
  2003年   12篇
  2002年   19篇
  2001年   14篇
  2000年   9篇
  1999年   19篇
  1998年   5篇
  1997年   4篇
  1996年   5篇
  1994年   5篇
  1992年   7篇
  1991年   11篇
  1990年   7篇
  1989年   11篇
  1988年   11篇
  1987年   6篇
  1986年   6篇
  1985年   6篇
  1984年   4篇
  1983年   4篇
  1982年   9篇
  1981年   11篇
  1980年   5篇
  1979年   10篇
  1978年   8篇
  1977年   8篇
  1976年   12篇
  1975年   6篇
  1974年   20篇
  1973年   6篇
  1972年   9篇
  1971年   15篇
  1970年   5篇
  1968年   3篇
  1966年   3篇
  1961年   2篇
排序方式: 共有486条查询结果,搜索用时 15 毫秒
171.
Climate change is predicted to result in changes in the geographic ranges and local prevalence of infectious diseases, either through direct effects on the pathogen, or indirectly through range shifts in vector and reservoir species. To better understand the occurrence of monkeypox virus (MPXV), an emerging Orthopoxvirus in humans, under contemporary and future climate conditions, we used ecological niche modeling techniques in conjunction with climate and remote-sensing variables. We first created spatially explicit probability distributions of its candidate reservoir species in Africa''s Congo Basin. Reservoir species distributions were subsequently used to model current and projected future distributions of human monkeypox (MPX). Results indicate that forest clearing and climate are significant driving factors of the transmission of MPX from wildlife to humans under current climate conditions. Models under contemporary climate conditions performed well, as indicated by high values for the area under the receiver operator curve (AUC), and tests on spatially randomly and non-randomly omitted test data. Future projections were made on IPCC 4th Assessment climate change scenarios for 2050 and 2080, ranging from more conservative to more aggressive, and representing the potential variation within which range shifts can be expected to occur. Future projections showed range shifts into regions where MPX has not been recorded previously. Increased suitability for MPX was predicted in eastern Democratic Republic of Congo. Models developed here are useful for identifying areas where environmental conditions may become more suitable for human MPX; targeting candidate reservoir species for future screening efforts; and prioritizing regions for future MPX surveillance efforts.  相似文献   
172.
173.

Setting

The study was conducted at the National Center for Tuberculosis and Lung Diseases (NCTBLD) in Tbilisi, Georgia.

Objective

To assess the utility of contact investigation for tuberculosis (TB) case detection. We also assessed the prevalence and risk factors for active TB disease and latent TB infection (LTBI) among contacts of active pulmonary TB cases.

Design

A retrospective cohort study was conducted among the contacts of active pulmonary TB cases registered in 2010–2011 at the NCTBLD in Tbilisi, Georgia. Contacts of active TB patients were investigated according to an “invitation model”: they were referred to the NCTBLD by the index case; were queried about clinical symptoms suggestive of active TB disease; tuberculin skin testing and chest radiographs were performed. Demographic, laboratory, and clinical data of TB patients and their contacts were abstracted from existing records up to February 2013.

Results

869 contacts of 396 index cases were enrolled in the study; a median of 2 contacts were referred per index case. Among the 869 contacts, 47 (5.4%) were found to have or developed active TB disease: 30 (63.8%) were diagnosed with TB during the baseline period (co-prevalent cases) and 17 (36.2%) developed active TB disease during the follow-up period (mean follow up of 21 months) (incident TB cases). The incidence rate of active TB disease among contacts was 1126.0 per 100 000 person years (95% CI 655.7–1802.0 per 100,000 person-years). Among the 402 contacts who had a tuberculin skin test (TST) performed, 52.7% (95% CI 47.7–57.7%) had LTBI.

Conclusions

A high prevalence of LTBI and active TB disease was found among the contacts of TB cases in Tbilisi, Georgia. Our findings demonstrated that an “invitation” model of contact investigation was an effective method of case detection. Therefore, contact investigation should be scaled up in Georgia.  相似文献   
174.
The effects of doxycycline were examined on articular cartilage glycosaminoglycan (GAG) release and biphasic mechanical properties following two levels of impact loading at 1 and 2 weeks post-injury. Further, treatment for two continuous weeks was compared to treatment for only the 1st week of a 2-week culture period. Following impact at two levels, articular cartilage explants were cultured for 1 or 2 weeks with 0, 50, or 100 microM doxycycline. Histology, GAG release to the media, and creep indentation biomechanical properties were examined. The "High" (2.8 J) impact level had gross surface damage, whereas "Low" (1.1 J) impact was indiscernible from non-impacted controls. GAG staining decreased after High impact, but doxycycline did not visibly affect staining. High impact resulted in decreased aggregate moduli at both 1 and 2 weeks and increased permeability at 2 weeks, but tissue mechanical properties were not affected by doxycycline treatment. At 1 week, High impact resulted in more GAG release compared to non-impacted controls. However, following High impact, 100 microM doxycycline reduced cumulative GAG release at 1 and 2 weeks by 30% and 38%, respectively, compared to no treatment. Interestingly, there was no difference in GAG release comparing 2 weeks continuous treatment with 1 week on, 1 week off. These results support the hypothesis that doxycycline can mitigate GAG release from articular cartilage following impact loads. However, doxycycline was unable to prevent the loss of tissue stiffness observed post-impact, presumably due to initial matrix damage resulting solely from mechanical trauma.  相似文献   
175.
The Fcγ receptor FcRn transports immunoglobulin G (IgG) so as to avoid lysosomal degradation and to carry it bidirectionally across epithelial barriers to affect mucosal immunity. Here, we identify a calmodulin-binding site within the FcRn cytoplasmic tail that affects FcRn trafficking. Calmodulin binding to the FcRn tail is direct, calcium-dependent, reversible, and specific to residues comprising a putative short amphipathic α-helix immediately adjacent to the membrane. FcRn mutants with single residue substitutions in this motif, or FcRn mutants lacking the cytoplasmic tail completely, exhibit a shorter half-life and attenuated transcytosis. Chemical inhibitors of calmodulin phenocopy the mutant FcRn defect in transcytosis. These results suggest a novel mechanism for regulation of IgG transport by calmodulin-dependent sorting of FcRn and its cargo away from a degradative pathway and into a bidirectional transcytotic route.  相似文献   
176.
During spring-summer 2003-2004, the avian community was surveyed for hemosporidian parasites in an oak (Quercus spp.) and madrone (Arbutus spp.) woodland bordering grassland and chaparral habitats at a site in northern California, a geographic location and in habitat types not previously sampled for these parasites. Of 324 birds from 46 species (21 families) sampled (including four species not previously examined for hemosporidians), 126 (39%) were infected with parasites identified as species of one or more of the genera Plasmodium (3% of birds sampled), Haemoproteus (30%), and Leucocytozoon (11%). Species of parasite were identified by morphology in stained blood smears and were consistent with one species of Plasmodium, 11 species of Haemoproteus, and four species of Leucocytozoon. We document the presence of one of the parasite genera in seven new host species and discovered 12 new parasite species-host species associations. Hatching-year birds were found infected with parasites of all three genera. Prevalence of parasites for each genus differed significantly for the entire sample, and prevalence of parasites for the most common genus, Haemoproteus, differed significantly among bird families. Among families with substantial sample sizes, the Vireonidae (63%) and Emberizidae (70%) were most often infected with Haemoproteus spp. No evidence for parasite between-genus interaction, either positive or negative, was found. Overall prevalence of hemosporidians at the northern California sites and predominance of Haemoproteus spp. was similar to that reported in most other surveys for the USA, Canada, and the Caribbean islands.  相似文献   
177.
The vanilloid receptor represents a promising target for drug development. Building on our previous strategies which have generated potent agonists for VR1, we now describe a series of novel N-(3-acyloxy-2-benzylpropyl)-N'-dihydroxytetrahydrobenzazepine and tetrahydroisoquinoline thiourea analogues, several of which are potent VR1 antagonists. We report here the rationale for the design, the synthesis, and the in vitro characterization of activity in assays for [(3)H]resiniferatoxin binding and (45)Ca influx using heterologously expressed rat VR1.  相似文献   
178.
A modification to a previously described procedure [Gray & del Valle (1970) Biochemistry 9, 2134-2137; Rose, Simona & Offord (1983) Biochem. J. 215, 261-272] for mass-spectral identification of the N-terminal regions of proteins is shown to be useful in cases where the N-terminus is blocked. Three proteins were studied: vesicular-stomatitis-virus N protein, Sendai-virus NP protein, and a rabbit immunoglobulin lambda-light chain. These proteins, found to be blocked at the N-terminus with either the acetyl group or a pyroglutamic acid residue, had all failed to yield to attempted Edman degradation, in one case even after attempted enzymic removal of the pyroglutamic acid residue. The N-terminal regions of all three proteins were sequenced by using the new procedure.  相似文献   
179.
The encapsulation of eggs ofMetaphycus swirskii Annecke &; Mynhardt (Hymenoptera: Encyrtidae) by the pyriform scale,Protopulvinaria pyriformis (Cockerell) (Homoptera: Coccidae), collected in the coastal plain of Israel, was determined during April 1986 to May 1987. The rates of encapsulation were low in November (13.0%) and relatively high in April, May, August and September (32.0–89.0%). The seasonal variations in the encapsulation of eggs ofM. stanleyi Compere and/orM. swirskii byP. pyriformis infesting avocado (Persea americana) and jambolan (Syzygium cumini) were studied at Miqwe Yisra'el (coastal plain) during October 1986 to February 1988. Encapsulation rates were similar in scales infesting either of the two host plants. They were highest during July to August (49.0–75.0%) and lowest during December to February (0.9–10.0%). Encapsulation incidence at Miqwe Yisra'el was correlated with the ambient temperatures (r=0.89). The rate of encapsulation of parasitoid eggs (M. stanleyi and/orM. galbus Annecke) recorded inP. pyriformis sent to Israel from Spain in September 1987 was 42.2%. The high rates of encapsulation ofMetaphycus spp. eggs byP. pyriformis during the summer, may interfere with efficient biological control of the pest.  相似文献   
180.
One-thousand, thirty-eight individuals from Plati, Greece were examined for the following red cell antigens, serum proteins, and red cell enzymes A A1 Ai B H; MNSs Mg Henshaw Nya Mur Vw; CCwcDEeCe; K k Kpa Kpb Jsa Jsb; P1; Lua; Fy1 Fy2; Jka Jkb; Wra; Zt; Vel; Swa; Jensen, Radin, Gerbich, Diego, Gregory, Haptoglobin, Transferrin, Acid phosphatase, Adenylate kinase, Adenosine deaminase, Esterase-D, Glucose-6-phosphate dehydrogenase, Phosphoglucomutase, 6-Phosphogluconate dehydrogenase, Phosphohexose isomerase, Lactate dehydrogenase, Malate dehydrogenase, and Superoxide dismutase. The results are discussed in detail and compared with other Greek and neighbouring populations. Because of the Plati population's long history of residence in the Cappadocian area of Turkey the data have been compared, whenever possible, with results for that region.  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